Clavicle

• Clavicle is the only long bone in the body that lies horizontally.
• It is doubly curved and its rounded medial end articulates with the manubrium of the sternum forming the sternoclavicular joint.
• At its flattened lateral end it articulates with the acromion of the scapula to form the acromioclavicular joint.
• It serves as a strut between the scapula and the sternum.
• Protects the neurovascular bundle that supplies the upper limb.
• The acromial end has a rough inferior surface that bears the trapezoid line and the conoid tubercle for attachment of the respective ligaments.
• It is the first bone to ossify in the body (5 weeks of gestation) and last to fuse (medial epiphysis fuses at 25 years).

Attachments to the clavicle

1. Superior surface:
   • Deltoid muscle
   • Trapezius muscle
2. Inferior surface
   • Subclavius muscle
   • Conoid ligament
   • Trapezoid ligament
3. Anterior border
   • Pectoralis major muscle
4. Posterior border
   • Sternocleidomastoid muscle
   • Sternohyoid muscle
   • Trapezius muscle
5. Lateral End
   • Acromioclavicular Ligaments
6. Medial End
   • Sternoclavicular Ligaments

1. Scapula is a wide, flat bone lying on the thoracic wall from 2nd to 7th rib
2.  It provides attachment for various groups of muscles.
3. The scapular glenoid provides articulation for the shoulder joint and is retroverted by about 5-7 degrees.
4. The processes of scapula include:
• Scapular spine
• Coracoid
• Acromion

Supra-scapular notch:

• The Suprascapular notch is present at the superior aspect of scapula and contains the suprascapular nerve and the suprascapular artery.
• It is covered by the superior transverse scapular ligament, which separates the artery from nerve with the artery going over the ligament (water flows over the bridge).

Spinoglenoid notch:

• The suprascapular artery and the nerve lie in the spinogelnoid notch covered by the inferior transverse scapular ligament.
• A ganglion arising from the posterior labrum in the notch can cause compression of suprascapular nerve resulting in atrophy and weakness of the infraspinatus muscle.

Coraco-acromial arch:

The coraco-acromial ligament extends between the coracoid process and the acromion forming the coraco-acromial arch.

Figure 1. Scapula. The suprascapular nerve and vessel in the supra-scapular and spinoglenoid notch.

• The shoulder is a ball and socket joint
• It is made by articulation of the humeral head and glenoid of scapula.
• It provides the greatest range of movement than any other joint in the body.
•  Shoulder is the least stable joint in body.

Stability of shoulder joint:

Static and dynamic stabilizers stabilize shoulder joint.

1. Static stabilizers:

• Articular anatomy: Retroversion of the humeral head and relative anteversion of the glenoid.
• Glenoid labrum
• Articular cartilage: thicker at periphery than center increasing joint conformity
• Negative intra-articular pressure
• Joint capsule
• Ligaments

2. Dynamic stabilizers:

• Rotator cuff muscles
• Biceps tendon and superior labrum
• Scapulothoracic motion

Important Ligaments of the shoulder joint:

1.Glenoid labrum

• The laburm is a fibro-cartilaginous rim attached around the margin of the glenoid
•  It deepens the glenoid cavity and thus helps in improving shoulder stability.
• At the superior margin it gives origin to the long head of biceps tendon.

2.Glenohumeral ligaments (GHL)

• Superior GHL: Is the superior most of the ligaments and prevents anterior and inferior glide of humeral head over the glenoid. It is tightest in the adducted position of shoulder.
• Middle GHL: prevents anterior glide of humerus on glenoid and is tightest in the externally rotated position.
• Inferior GHL: Most important of three ligaments. It has anterior and posterior parts, which are taut in abducted, and externally and internally rotated positions respectively.

3.Coracohumeral ligament:

• Arises from the lateral border of the coracoid process and passes obliquely downward and laterally to the front of the greater tuberosity of the humerus, blending with the tendon of the supraspinatus muscle.

4.Transverse humeral ligament:

• Runs from the lesser to the greater tuberosity of the humeral head and converts the intertubercular groove into a canal where long head of biceps tendon runs.

The sternoclavicular joint (SCJ) is formed by articulation of medial clavicle with manubrium sterni. It is a double gliding joint with an articular disc, which allows approximately 30 degrees of movement with shoulder elevation.

1. Ligaments stabilizing SCJ

a. Capsule

b. Anterior and Posterior Sternoclavicular ligaments

c. Interclavicular ligament

d. Costoclavicular ligament

Figure 2. Sternoclavicular joint and its ligaments

The acromioclavicular joint (ACJ) is formed by articulation of lateral end of clavicle with the acromion. It also consists of a fibrocartilaginous disc and allows gliding movement.

1. Ligaments stabilizing ACJ

a. Capsule

b. Acromioclavicular (superior and inferior) ligaments

c. Coracoclavicular ligaments

• Trapezoid (anterolateral)

• Conoid (posteromedial)

The acromioclavicular ligaments provide anteroposterior stability and coracoclavicular ligaments provide superoinferior stability.

Figure 3. Acromioclavicular joint and its ligaments

1. The scapulothoracic joint is not a true joint.
2. It provides motion between the scapula and rib cage.
3. For every 2 degrees of glenohumeral joint movement there is 1 degree of scapulothoracic joint movement.
4. The muscles, which mediate scapulothoracic joint rotation(Figure 4 ),are
   • serratus anterior (anterolateral movement of inferior angle of scapula) and
   • trapezius (superior and medial pull on spine of scapula)
5. Scapulothoracic joint motion is important for:
   • Enhancing glenohumeral joint stability.
   • Elevating the acromion and preventing impingement.

Maintaining an effective working length of the scapulohumeral muscles.

Figure 4. Scapular muscles involved in rotation

There are three important spaces of the shoulder that allow passage of important neurovascular structures. The spaces are

1. Quadrangular Space:

1. Contents: 
   • Axillary nerve
   • Posterior humeral circumflex vessels
2. Boundaries:
   • Medial: long head of triceps
   • Lateral: humeral shaft
   • Superior: teres minor
   • Inferior: teres major

2. Triangular Space

1. Contents: 
   • Circumflex scapular vessels
2. Boundaries:
   • Inferior: teres major
   • Lateral:long head of triceps
   • Superior: lower border of teres minor

3. Triangular Interval

1. Contents: 
   • Radial nerve
   • Profunda brachii vessels
2. Boundaries:
3. Superior: teres major
4. Lateral: lateral head of the triceps or the humerus
5. Medial: long head of the triceps

Also called the antecubital fossa, the cubital fossa is a triangular area located on the anterior aspect of elbow.

Boundaries

1. Superior (proximal) boundary: Imaginary line joining the medial and lateral epicondyles of humerus
2. Medial (ulnar) boundary: Lateral border of Pronator Teres
3. Lateral (radial) boundary: Medial border of Brachioradialis
4. Apex: Junction of the lateral and medial boundaries
5. Floor: Brachialis and Supinator
6. Roof: Skin and soft tissues

Contents: Lateral to Medial

1. Radial nerve, between brachioradialis and brachialis muscles
2. Biceps brachii tendon
3. Brachial artery
4. Median nerve
5. Veins, median cubital vein, cephalic vein, and basilic vein

The elbow joint is formed by articulation between the humerus in upper arm and radius and ulna in forearm.

There are 3 joints within the elbow surrounded by elbow capsule:

1. Ulnohumeral joint
2. Radiocapitellar joint
3. Proximal radioulnar joint

Important Ligaments of Elbow joint:

Radial Collateral Ligament complex (Figure 6)

1. Radial collateral ligament proper
   • Runs from the lateral epicondyle to the annular ligament deep to the common extensor tendon
2. Lateral ulnar collateral ligament (LUCL)
   • Runs from the lateral epicondyle to the supinator crest on the ulna. It is the chief stabilizer of elbow against varus stress.
3. Annular ligament
   • Runs from the posterior to the anterior margins of radial notch on the ulna and encircles the head of radius
4. Accessory lateral collateral/accessory annular ligament
• Runs from the inferior margin of the annular ligament to the supinator crest.

It is the chief stabilizer of elbow joint against valgus stress. The ulnar collateral ligament is triangular in shape. Its apex is attached to the medial epicondyle of humerus and its base to the ulna. The ligament has thick anterior and posterior bands.

1. The anterior band:
   • Directed obliquely forward, is attached above by its apex to the front part of the medial epicondyle of the humerus and below, by its broad base, to the medial margin of the coronoid process of the ulna (sublime tubercle).
2. The posterior band:
   • Shaped like a fan, is attached above by its apex to the lower and posterior part of the medial epicondyle and below to the medial margin of the olecranon.
3. The transverse/oblique portion:
   • Joins the anterior and posterior portions (also called ligament of Cooper)

Figure 7. Elbow Medial Ligaments. Medial ligament complex of elbow

The PRUJ is formed by the articulation of radial head with radial notch on proximal ulna.

Important Ligaments stabilizing PRUJ are:

1. Annular ligament:
   • Runs from the posterior to the anterior margins of radial notch on the ulna and encircles the head of radius.
2. Quadrate ligament:
   • A fibrous band from the inferior border of the radial notch on the ulna to the neck of the radius.
3. Oblique cord: 
   • Runs from the lateral side of the ulnar tuberosity at the base of the coronoid process to the radius a little below the radial tuberosity.

Figure 8. Proximal radio ulnar joint. The PRUJ and its ligaments.

1. Radioulnar ligaments (RUL):
   • Palmar and
   • Dorsal radioulnar ligaments

The RUL’s are the principal stabilizers of the distal radioulnar joint (DRUJ).

The PRUJ, DRUJ and the interosseous membrane coordinate the pronation and supination movements of forearm.

The wrist joint (also known as the radiocarpal joint) is a synovial joint between the distal radius and the proximal carpal row (except pisiform).

Wrist joint Ligaments:

The ligaments of wrist joint can be divided into extrinsic and intrinsic ligaments.

1. Extrinsic Ligaments:

The extrinsic ligaments bridge the carpal bones to the radius and ulna or metacarpals.

They include volar (stronger)(Figure 9) and dorsal ligaments(figure 10).

Volar radio-carpal ligaments

1. Radial collateral ligament:

Runs from the tip of the radial styloid to the radial side of the scaphoid and some fibres extend to the lateral side of the trapezium.

It limits ulnar deviation at the wrist.

2. Radioscaphocapitate ligament:

The radioscaphocapitate ligament (RSC) passes beneath the waist of the scaphoid, and inserts onto the capitate, creating a sling to support the scaphoid.

3.Long radiolunate ligament
4.Short radiolunate ligament
5.Radioscapholunate ligament

The radioscapholunate ligament (RSL / ligament of Testut) is not considered a true ligament, because it is composed of vascular and neural elements and no ligamentous tissue.

The space of Poirier represents an area of weakness between the long radiolunate and radioscaphocapitate ligaments at the level of the midcarpal joint. In lunate dislocations, the lunate escapes into this space.

Volar ulno-carpal ligaments

1. Ulnotriquetral ligament
2. Ulnolunate ligament
3. Ulnocapitate ligament

The ulnolunate an ulnocapitate ligaments prevent dorsal migration of the distal ulna.

Dorsal Ligaments

1. Radiotriquetral
2. Dorsal intercarpal (DIC)
3. Radiolunate
4. Radioscaphoi

Intrinsic ligaments:

Originate and insert on carpal bones

1.Scapholunate interosseous ligament

The scapholunate ligament is an intra-articular ligament binding the scaphoid and lunate together. It is divided into three areas, dorsal, proximal and palmar, with the dorsal segment being the strongest part. It is the main stabilizer of the scaphoid.

2.Lunotriquetral Interosseous ligament

In contrast to the scapholunate ligament, the lunotriquetral ligament is more prominent on the palmar side.

3.Trapeziotrapezoid ligament
4.Capitotrapezoid ligament
5.Capitohamate ligament

The TFCC is formed by the:

1. Triangular fibrocartilage (TFC)

2. Ulnocarpal ligaments (volar ulnolunate and ulnotriquetral ligaments)

3. Meniscal homologue

4. Extensor Carpi Ulnaris (ECU) sheath

• TFCC is a main stabilizer of the radioulnar joint.
• The TFC is an articular discus that lies on the pole of the distal ulna.
• It has a triangular shape and a biconcave body; the periphery is thicker than its center. The central portion of the TFC is thin and consists of chondroid fibrocartilage to bear compressive load.
• The central area is often so thin that it is translucent and in some cases it is even absent ---it has no blood supply.
• The peripheral portion of the TFC is well vascularized.
• This discus is attached by thick tissue to the base of the ulnar styloid and by thinner tissue to the edge of the radius just proximal to the radiocarpal articular surface.

1. The dorsal digital expansion / dorsal hood is the special connective attachment by which the extensor tendons insert into the phalanges.
2. Distal to the MCP joint, the extensor digitorum tendon flattens to form extensor expansions. The extensor expansion (hood or dorsal expansion) is a triangular, tendinous expansion that wraps around the dorsum and sides of the metacarpals and proximal phalanx.
3. The expansion then divides into three parts which progress further as two lateral slips on either side and a central slip in middle.
4. The lateral slips join the deep head of the interosseous and lumbrical muscles to become the conjoined lateral band. The two lateral bands converge and join over the middle phalanx and go on to insert on the base of the dorsum of the distal phalanx and extend the DIPJ.
5. The central slip inserts into the base of the dorsum of middle phalanx and extends the PIPJ.
6. The retinacular ligaments help to retain and position common extensor mechanism during PIP and DIP flexion.
7. Transverse retinacular ligament arises from the flexor tendon sheath and inserts onto the lateral border of the conjoined lateral bands. It prevent excessive dorsal translation of lateral bands.
8. Oblique band (oblique retinacular ligament of Landsmeer) links the motion of DIPJ to PIPJ. It arises from the flexor tendon sheath and inserts onto the terminal tendon of the extensor mechanism and extends the DIP joint when the PIP joint is extended.
9. The triangular ligament joins the two lateral bands before they join together to become the terminal tendon. They prevent volar subluxation of the lateral bands.
10. The extensor tendon is held centrally by the sagittal bands at the level of the MCP joint. They arise from the volar plate and intermetacarpal ligaments volarly and attach to the extensor tendon dorsally.

Figure 11. Extensor tendon / Dorsal digital expansion. The extensor tendon and dorsal digital expansion.

Other important ligaments in the hand

1. Deep Transverse Metacarpal Ligament: Interconnect 2nd to 5th metacarpal heads at volar plate and prevent them from splaying apart (abduction).
2. Natatory ligament (Superficial Transverse Metacarpal Ligament): Runs form the distal metacarpal to proximal phalanx and resists abduction.
3. Triangular ligament: Present between the two lateral bands over the dorsal side distal to the PIPJ and counteracts pull of oblique retinacular ligament, preventing lateral subluxation of the common extensor mechanism.
4. Volar Plate: This is a thickening of the joint capsule volar to the MCPJ and PIPJ. It prevents hyperextension of the joint.
5. Anterior oblique ligament: This is a primary stabilizer of the trapeziometacarpal joint and is taut in abduction, extension and pronation. It originates from the tuberosity of the trapezium and inserts on the volar ulnar edge of the thumb metacarpal base.
6. Ulnar collateral ligament of thumb: This runs along the ulnar side of the MCP joint of the thumb and is on the radial side of the wrist joint but the ulnar side of the thumb. It originates from the metacarpal head and inserts into the medial aspect and the base of the proximal phalanx of the thumb.

1. The thumb has two annular and one oblique pulley.
2. The A1 annular pulley overlies the MCPJ and the A2 over the distal part of the proximal phalanx.
3. The oblique pulley, which is the most important and prevents bowstringing of flexor pollicis longus tendon is between the A1 and A2 pulleys, centered over the proximal phalanx and is in continuity with the adductor pollicis insertion.

Zones are used to describe the location of tendon injuries. There are nine zones of injury:

Flexor zones (Verdan’s zone):

Extensor compartments of the wrist: (Figure 12)

Figure 12. Extensor tendon compartments. The dorsal wrist compartments and contents

1. The major structures from forearm pass into the hand through the carpal tunnel. The volar surface of the carpal bones form a concavity and this concavity is roofed over by a thick fibrous band, the flexor retinaculum converting the concavity into a tunnel through which structures pass.

Flexor retinaculum/transverse carpal ligament

This is a distal continuation of two sheets of fascia: the deep fascia of the forearm and fascia over flexor digitorum superficialis. These two sheets come together and later become continuous with the palmar aponeurosis.

The attachments are:

Medial: pisiform, hook of hamate

Lateral: tubercle of scaphoid, ridge of trapezium

Deep: medial lip of a groove on the trapezium.

Functions of the retinaculum:

• Acts as a protracting and restraining device which is essential to stop bowstringing of the long tendons

• It gives partial insertion to some muscles (PL, FCU)

• It gives partial origin to some muscles (thenar and hypothenar muscles).

Structures passing superficial to the retinaculum: (medial to lateral)

• Tendon of FCU (attached to pisiform bone)

• Ulnar nerve and vessels (close to pisiform bone)

• Palmar cutaneous branches of the ulnar nerve

• Tendon of palmaris longus (middle of retinaculum)

• Palmar cutaneous branch of the median nerve.

Structures passing through the carpal tunnel:

• The four tendons of the FDS pass through in two layers, with the middle and ring lying in front of index and little fingers.

• The four tendons of FDP lie all on the same plane deep on the carpal bones

• The tendon of FCR passes down to the base of metacarpals 2 and 3

• The median nerve passes beneath flexor retinaculum on the lateral side of

FDS (middle finger tendon), between it and FCR.

• The tendon of FPL lies in its own synovial sheath as it passes through the radial side of the tunnel.

The anatomical snuffbox is a triangular deepening on the dorso-radial aspect of the hand at the level of the carpal bones.

Boundaries

Dorsal: EHL (extensor pollicis longus)

Volar: APL and EPB (abductor pollicis longus and extensor pollicis brevis)

Proximal: Radial styloid

Distal: Apex of the triangle where dorsal and volar borders meet.

Floor: Scaphoid and trapezium

Contents

• Radial artery

• Cephalic vein

• Dorsal cutaneous br. of radial nerve

Extensor zones

Zones are used to describe the location of tendon injuries. There are nine zones of injury:

The major blood supply of the scaphoid is derived from dorsal carpal branches of the radial artery entering the dorsal ridge by vascular foramina from ligamentous and capsular attachments. This supplies the 70-80% of distal scaphoid in a retrograde fashion including the proximal pole.

A second major group, palmar and superficial palmar branches of the radial artery enters the scaphoid tubercle volarly and perfuses only the distal 20–30% of bone. The proximal pole is the region with the most tenuous blood supply owing to the distal to proximal (retrograde) vascular supply. There are no anastomoses between dorsal and palmar vessels. Fractures across the waist can result in avascular necrosis of the proximal fragment.

The brachial plexus is a network of nerves formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5-T1). After emerging from the spine it proceeds through the neck, the axilla and into the arm.

The brachial plexus can be divided into parts as shown below.

• Roots:

The five roots are the five anterior rami of the spinal nerves and are situated between anterior and middle scalene muscle.

• Trunks:

The five roots merge to form three trunks arranged from top to bottom and hence their name. They lie in the posterior triangle of the neck.

1. Superior or upper trunk (C5-C6)

2. Middle trunk (C7)

3. Inferior or lower trunk (C8, T1)

• Divisions

Each trunk then splits in two (anterior and posterior divisions) to form a total of six divisions. Divisions lie behind the clavicle:

• Cords

These six divisions re-group to become the three cords. The cords are named by their position with respect to the axillary artery.

1. Lateral,

2. Medial,

3. Posterior (formed by all three posterior divisions)

• Branches

Branches arise from the roots, trunks and cords. The cords themselves end as terminal branches.

Figure 13. Brachial plexus.Steps to draw the brachial plexus.

From the Roots

1. Dorsal scapular nerve (C5): Supplies rhomboid muscles and levator scapulae.

2. Long thoracic nerve (C5, C6, C7): Supplies serratus anterior muscle (nerve damage causes medial scapula winging). Enters the axilla by passing down over the lateral border of the first rib behind the axillary vessels. Descends over the superficial surface of serratus anterior muscle.

3. Suprascapular nerve (C5, C6): Supplies supraspinatus and infraspinatus muscles. Arises in the posterior triangle of the neck and runs downwards and laterally inferior to trapezius and omohyoid. Enters the suprascapular fossa by passing through the suprascapular notch beneath the superior transverse scapular ligament.

Compression in the suprascapular notch causes wasting of supraspinatus and infraspinatus muscles. The suprascapular nerve also sends some filaments to supply the shoulder joint and capsule.

From the Upper trunk

1. Nerve to subclavius (C5, C6): Supplies subclavius. Descends posterior to clavicle and anterior to the brachial plexus and subclavian artery. May give a contribution to the phrenic nerve (C5), named the accessory phrenic nerve if present.

From the Lateral cord

1. Lateral pectoral nerve (C5, C6, C7): Supplies pectoralis major muscle.

2. Musculocutaneous nerve (C5, C6, C7): Terminal branch of the lateral cord. It arises obliquely behind the lower fibres of pectoralis minor, lying lateral to the axillary artery and passes between the two conjoined heads of coracobrachialis. It runs laterally between biceps and brachialis adherent to the deep surface of biceps. It pierces the deep fascia, continuing on as the lateral cutaneous nerve of the forearm (lateral to the cephalic vein) supplying skin on the lateral aspect of the forearm.

Motor supply is to coracobrachialis, biceps brachii and brachialis. It is protected during the anterior (Henry’s) approach to the shoulder by avoiding vigorous retraction of the conjoined tendon and avoiding dissection medial to the coracobrachialis muscle.

3. Lateral head of median nerve (see median nerve).

From the Posterior cord

1. Upper subscapular nerve (C5): Supplies the upper part of subscapularis.

2. Lower subscapular nerve (C6): Supplies the lower part of subscapularis and teres major.

3. Thoracodorsal nerve (C6, C7, C8): Supplies the latissimus dorsi muscle. It runs

downwards on subscapularis accompanied by the subscapular vessels.

4. Axillary nerve (C5, C6): Terminal branch of the posterior cord. The axillary nerve is just inferior to the shoulder capsule and it is protected during shoulder surgery by adduction and external rotation of the arm. The nerve is prone to injury during anterior dislocation of the shoulder owing to its close relationship with the inferior capsule. At the lower border of subscapularis it turns backwards and passes through the quadrangular space and then winds around the surgical neck of humerus with the posterior circumflex humeral vessels. After giving off a branch to the shoulder joint it divides into anterior and posterior branches. The anterior branch runs forward around the humerus in contact with the periosteum to enter the deep surface of deltoid. The posterior branch supplies teres minor and winds around the posterior border of deltoid. It ends as the upper lateral cutaneous nerve of the arm supplying the skin over the inferior half of the deltoid (regimental badge area).

5.Radial nerve (C5, C6, C7, C8, T1): The larger terminal branch of the posterior cord (largest branch of the brachial plexus). It crosses the lower border of the posterior axillary wall, lying on latissimus dorsi and teres major. It passes through a triangular space. It leaves the axilla and descends in the posterior compartment of the arm. It spirals around the humerus (medial to lateral) in the spiral groove between medial and lateral heads of triceps along with the profunda brachii artery. It pierces the lateral intermuscular septum at the midpoint of the humerus to reach the anterior compartment between the brachialis and brachioradialis. It crosses the anterior aspect of the lateral epicondyle (where it supplies anconeus) and enters the forearm, dividing into deep and superficial branches. At the elbow the radial nerve lies on the elbow capsule at the mid portion of the capitellum, making it prone to injury during arthroscopic capsular release.

It supplies: In Axilla

• Long, medial and lateral heads of triceps

• Posterior cutaneous nerve of arm (posterior upper arm skin)

• Lower lateral cutaneous nerve of arm (lower lateral arm skin). In posterior compartment of the arm

• Motor to brachioradialis, brachialis (small supply), extensor carpi radialis longus.

• Posterior cutaneous nerve of forearm (posterior forearm skin). 

The radial nerve divides into a deep (posterior interosseous nerve – PIN) and superficial branch.

• Posterior interosseous nerve: The PIN does not have a cutaneous branch and passes between the two heads of supinator to enter the posterior compartment. It reaches the interosseous membrane and ends on the back of the carpus. It supplies all the extensor muscles except extensor carpi radialis longus.

• Superficial branch of radial nerve: This runs over supinator, pronator teres and FDS and lies under brachioradialis, running with the radial artery on its medial side from about half way down the forearm. It passes deep to brachialis, proximal to the radial styloid and over the tendons of the snuffbox to reach the dorsal radial aspect of the hand.

From the Medial cord

1. Medial pectoral nerve (C8, T1): Arises from the medial cord behind the first part of the axillary artery and enters the deep surface of pectoralis minor. It perforates pectoralis minor to enter the pectoralis major muscle.

2. Medial cutaneous nerve of arm (C8, T1): Supplies anterior and medial aspects of the arm.

3. Medial cutaneous nerve of forearm (C8, T1): Supplies the medial aspect of the forearm.

4. Medial root of median nerve (C8, T1) (see median nerve): Crosses the axillary artery to join the lateral head

5. Median nerve (C6, C7, C8, T1):

This arises in the lower axilla by two roots, which clasp the axillary artery. The nerve initially lies anterior to the axillary artery then lateral to it. At the level of the mid-humerus the median nerve crosses the brachial artery, usually anteriorly to lie medial to the artery in the cubital fossa.

It lies on coracobrachialis and then brachialis. It passes beneath the bicipital aponeurosis at the elbow, leaving the cubital fossa between the two heads of pronator teres. It descends deep to the flexor digitorum superficialis on flexor digitorum profundus. Near the wrist it becomes superficial, passing between FDS and flexor carpi radialis. It travels deep to the palmaris longus tendon and enters the carpal tunnel where it divides into a lateral and medial branch. The lateral branch gives off the recurrent (muscular) branch and then breaks up into three palmar digital nerves, two for the thumb and one for the index, the last one also supplying the first lumbrical. The medial branch divides into two common palmar digital nerves for the index, middle and radial half of ring finger and the last one also supplies the second lumbrical. Palmar digital nerves supply not only the whole palmar aspect of the finger but also the distal half of the dorsal aspect of each finger as well. The median nerve does not give off any branches in the arm.

1 It supplies all the flexor muscles of the forearm except flexor carpi ulnaris and the medial half of flexor digitorum profundus (ulnar nerve). It also supplies the thenar eminence and the first and second lumbrical muscles.

2  Anterior interosseous nerve: This arises just below the two heads of pronator teres to run on the interosseous membrane between flexor digitorum profundus and flexor pollicis longus to reach pronator quadratus. It supplies these muscles, except for the medial half of flexor digitorum profundus. It also sends an articular branch to the wrist joint. This nerve does not have a cutaneous branch. Anterior interosseus nerve palsy presents principally as weakness of the thumb and index finger. (OK sign)

3 Palmar cutaneous branch of the median nerve: This arises just proximal to flexor retinaculum and becomes cutaneous between palmaris longus and flexor carpi radialis. It passes superficial to the flexor retinaculum to supply the lateral aspect of the palm (skin). It helps to determine the level of a median nerve injury; numbness over the thenar eminence may indicate a high lesion, whilst intact sensation with loss of function in the recurrent and palmar digital branches may indicate a more distal lesion, e.g. carpal tunnel (this is not entirely reliable owing to the anatomical variations).

4 Recurrent motor (thenar) branch of the median nerve: This supplies abductor pollicis brevis, flexor pollicis brevis and opponens pollicis. It loops around the distal border of flexor retinaculum and enters the thenar muscles.

5 Ulnar nerve (C8, T1): The ulnar nerve arises medial to the axillary artery and continues medial to the brachial artery, lying on coracobrachialis to the midpoint of the humerus where it leaves the anterior compartment by passing posteriorly through the medial intermuscular septum with the superior ulnar collateral artery to enter the posterior compartment of the arm. It runs anterior to the medial head of triceps, passing posterior to the medial humeral epicondyle to enter the forearm between the two heads of flexor carpi ulnaris.

It runs deep to flexor carpi ulnaris on the flexor digitorum profundus with the ulnar artery on its lateral side from one-third of the way down the forearm.

In the distal forearm it becomes superficially covered only by fascia and skin passing superficial to the flexor retinaculum with the ulnar artery. It then passes lateral to the pisiform and grooves the hook of the hamate. The deep branch of the ulnar nerve pierces between abductor digiti minimi and the flexor digiti minimi brevis.

Branches of the ulnar nerve

• No branches in the arm

• Articular branches to elbow joint

• Flexor carpi ulnaris and medial half of flexor digitorum profundus

• Palmar cutaneous branch (skin over hypothenar eminence)

• Dorsal cutaneous branch (medial skin dorsum of hand and 11⁄2 digits).

It arises 5 cm proximal to the wrist, passes deep to FCU onto the medial aspect of te dorsum of the hand 

aspect of the dorsum of the hand.

• Superficial branch of the ulnar nerve: supplies palmaris brevis and then

carries on as the superficial palmar branch to innervate the palmar 11⁄2 digits.

• Deep branch of the ulnar nerve: supplies wrist joint, flexor digiti minimi,

abductor digiti minimi, opponens digiti minimi, palmar and dorsal interossei, two medial lumbricals, adductor pollicis and deep head of flexor pollicis brevis.

Guyon’s canal

Fibrosseous tunnel approximately 4 cm long.

Boundries:

• Proximal: proximal edge of transverse carpal ligament at pisiform bone

• Distal: aponeurotic arch of origin of hypothenar muscles

• Medial wall: pisiform and fibrous attachments of pisohamate ligament

• Lateral wall: hook of hamate

• Roof: volar carpal ligament

The ulnar nerve divides within the canal into superficial (more ulnar) and deep (more radial) branches at the level of the pisiform.

There are four sites of compression:

1. Guyon’s canal – sensory loss of the palmar 11⁄2 digits. Spared dorsal medial hand and fingers (dorsal cutaneous branch) and proximal ulnar palm (palmar cutaneous branch). Motor: all ulnar hand muscles.

2. Distal to Guyon’s canal (proximal deep terminal branch) (pure motor). Motor: all ulnar hand muscles. Sensory: normal.

3. Hook of hamate (distal deep terminal branch) (pure motor). Motor: spares hypothenar muscles. Sensory: normal.

4. Superficial terminal branch – sensory loss of the palmar 11⁄2 digits. Motor: normal.

LOWER LIMB OSTEOLOGY and JOINTS

The bony pelvis is formed posteriorly by the sacrum and the coccyx and laterally and anteriorly by a pair of hip bones. Each hip bone consists of 3 sections, ilium, ischium, and pubis.

The two hip bones are joined anteriorly at the pubic symphysis by a fibrous cartilage covered by a hyaline cartilage, the interpubic disk, within which a non- synovial cavity might be present.

Two ligaments, the superior and inferior pubic ligaments, reinforce the symphysis.

Both sacroiliac joints, formed between the articular surfaces of the sacrum and the two hip bones are amphiarthroses; almost immobile joints enclosed by very taut joint capsules. This capsule is strengthened by the ventral, interosseous, and dorsal sacroiliac ligaments. The most important accessory ligaments of the sacroiliac joint are the sacrospinous and sacrotuberous ligaments which stabilize the hip bone on the sacrum and prevent the promonotory from tilting forward.

Additionally, these two ligaments transform the greater and lesser sciatic notches into the greater and lesser foramina, a pair of important pelvic openings. The iliolumbar ligament is a strong ligament which connects the tip of the transverse process of the fifth lumbar vertebra to the posterior part of the inner lip of the iliac crest. It can be thought of as the lower border of the thoracolumbar fascia.

1. Anterior sacroiliac ligament

This is a thin band that connects the anterior surface of the lateral part of the sacrum to the ilium.

2. Posterior sacroiliac ligaments

These are very strong ligaments forming the main bond of union between bones. They are divided into short (intrinsic) and long (extrinsic) ligaments. The short

posterior sacroiliac ligament passes from the first and second transverse tubercles of the sacrum to the tuberosity of the ilium. The long posterior sacroiliac ligament, which is oblique in direction, attaches from the third transverse tubercle of the sacrum to the posterior superior iliac spine (PSIS).

3. Sacrotuberous ligament

This is flat and triangular, attaches to posterior border of the ilium and the posterior superior and posterior inferior iliac spines, to the transverse tubercles of the sacrum below the articular surface, and to the upper part of the coccyx. Passing obliquely downward, forward and lateral, it becomes narrow and thick, to insert into the thinner margin of the ischial tuberosity.

4. Sacrospinous ligament

This lies on the pelvic aspect of the sacrotuberous ligament. It attaches to the side of the lower part of the sacrum and the upper part of the coccyx. The apex is attached to the spine of the ischium.

5. Sacrotuberous and sacrospinous ligaments

The sacrotuberous and sacrospinous ligaments, with the lesser sciatic notch of the ischium, enclose the lesser sciatic foramen, whose lateral part is occupied by the obturator internus.

6. Iliolumbar ligament

This is a V-shaped ligament. The apex is attached to the transverse process of the L5 vertebra. The upper band of the base passes to the iliac crest and the lower band runs laterally and downwards to blend with the front of the anterior sacroiliac ligament.

1.Iliofemoral ligament:

This Y shaped ligament is strongest in hip joint.

Prevents excessive adduction and internal rotation. Prevents the trunk from falling backward without the need for muscular activity in standing position.

2.Ischiofemoral:

Restricts internal rotation

3.Pubofemoral:

Restricts abduction and internal rotation

4 Ligamentum teres (intra-articular):

Blood supply through foveal artery

Figure 14. The hip joint ligaments

The hip joint is a synovial joint formed by the articulation of femoral head contained in the acetabulum. The acetabular labrum further extends beyond the equator increasing this containment.

The capsule of hip joint is attached to the acetabulum outside the labrum making it an intra-articular structure. It is attached to the femoral neck and allows for large range of movement in the joint.

The circular fibers of the capsule form a collar around the femoral neck called the zona orbicularis. The longitudinal retinacular fibers in the capsule travel along the neck and carry blood vessels.

The blood supply to the femoral head comes from the medial and lateral circumflex femoral arteries (MCF and LCF) which are both branches of the deep / profunda femoris artery (branch of femoral artery). There are minor contributions from the superior and inferior gluteal arteries.

Branches from the MCF and LCF anastomose to form an extra capsular arterial ring. This gives rise to ascending cervical branches, which travel up the capsule of hip joint as retinacular arteries. The retinacular arteries anastomose again to form a subsynovial intra articular ring, which gives off epiphyseal arterial branches that pierce and supply the femoral head.

There are minor contributions from the artery of ligamentum teres (foveal artery), a branch of obturator artery.

Figure 15. Blood supply to femoral head

The knee is the largest synovial joint in the body. It is enclosed by a capsule, which attaches about 15 mm distal to the articular surface of the tibia. The patella that articulates with the femoral condyle is the largest sesamoid bone in the body.

• The vascular supply to the knee is mainly through an anastomosis formed by:
• The descending and genicular branches of the femoral, popliteal and lateral circumflex femoral arteries from above (the thigh region).
• Circumflex fibular artery and branches of the anterior tibial artery from below (the leg).
• It is innervated by branches from the obturator, femoral, tibial and common fibular nerves.

The menisci serve to deepen the concavity of the tibial side of the joint and therefore provide some stability. Other functions include protection and assisting in rotation of the knee. They are avascular except in the peripheral third.

Medial meniscus:

This is a ‘C’shaped structure which is anchored to the tibia via the meniscotibial (coronary) ligaments.

• The anterior part is attached just below the tibial articular surface. Anteriorly it also connects with the lateral meniscus via a transverse ligament.

• In the mid portion it is attached to the deep fibres of the MCL.

• Posteriorly, it is anchored to the posterior intercondylar area.

Lateral Meniscus:

Compared to the medial meniscus the lateral meniscus is more ‘O’ shaped, is smaller and more mobile. There is no attachment to the adjacent LCL.

Posteriorly it is attached in the intercondylar area to the medial femoral condyle via the ligaments of Humphry (anterior menisco-femoral ligament) and Wrisberg (posterior menisco-femoral ligament).

Stability of the knee joint

Stability is provided mainly by the cruciate and collateral ligaments(Figure 16). The patella stability is mainly through the medial patellofemoral ligament (MPFL).

1. Medial collateral ligament (MCL)

This is a flat triangular band composed of two portions, superficial and deep.

The superficial MCL proximally is attached to the posterior aspect of the medial femoral condyle. This attachment is a few millimeters proximal and posterior to the medial epicondyle. Distally it is attached to the metaphyseal region of the tibia, about four fingers-breath below the joint, lying beneath the pes anserinus. The superficial MCL can be divided into anterior and posterior portions. The posterior part forms the posterior oblique ligament.

The superficial MCL is the primary restraint to valgus force.

The deep MCL is divided into menisco-femoral and menisco-tibial ligaments and inserts directly into the edge of the tibial plateau and meniscus.

2 Lateral collateral ligament (LCL)

This is cord-like, attached superiorly to the lateral femoral epicondyle (below the lateral head of gastrocnemius and above the popliteus). Inferiorly, it attaches to the head of the fibula and is overlapped by the biceps femoris. It lies free from the capsule and lateral meniscus, being separated from the meniscus by the tendon of popliteus inside the joint and the inferior lateral genicular vessels outside the joint.

The cruciate ligaments lie within the capsule (but not synovial membrane) of the knee joint.

3 Anterior cruciate ligament (ACL)

Attaches to the anterior part of the tibial plateau between the attachment of anterior horns of medial and lateral meniscus. The ACL ascends posterolaterally, twisting on itself, to attach to the posteromedial aspect of the lateral femoral condyle. The ACL is made up two bundles , the anteromedial and posterolateral. The anteromedial bundle is tight in flexion and the posterolateral is tight in extension.

4. The posterior cruciate ligament (PCL)

Compared to the ACL, the PCL is stronger, shorter, broader and less oblique. It attaches to a small impression at the posterior part of the intercondylar area of the tibia. It lies between the ligaments of Humphrey and Wisberg. It ascends anteromedially to attach to the anterolateral aspect of the medial femoral condyle. The PCL has an anterolateral portion that is tight in flexion and a posteromedial portion that is tight in extension.

5 Posterolateral corner (PLC)

This PLC complex comprises of static and dynamic components. The static stabilisers are: the arcuate ligament, popliteus tendon, posterolateral capsule, lateral collateral ligament, the fabello-fibular ligament and the politeofibular ligament. The dynamic component consists of the ilio-tibial band, the biceps femoris and the lateral head of the gastrocnemius.

6. Anterolateral ligament (ALL)

This is a term used to describe the soft tissue stabilizing structures in the anterolateral region of the knee. Recent studies have described this structure as passing antero-distally from an attachment proximal and posterior to the lateral femoral epicondyle to the margin of the lateral tibial plateau, approximately midway between Gerdy’s tubercle and the head of the fibula.(2) The ALL has been has been implicated as being the cause of the ‘segond fracture’. It is also thought to be injured frequently together with the ACL.

7 Medial patellofemoral ligament (MPFL)

The medial patellar retinaculum inserts into the upper 2/3 of the medial margin of the patella. Within the middle layer out of three, two distinct condensations of fibres are classically described. The medial patellotibial ligament(MPTL) which inserts into the medial meniscus and tibia and, more importantly, the MPFL, which inserts into a point 10mm posterior and proximal to the medial femoral epicondyle (although some authors say it attaches to the medial epicondyle). From here it attaches to the upper third of the patella. On the patella the mid-point is located 40% of the distance from the proximal tip of the patella. The upper extent can be identified by the way it blends with the distal insertion of the VMO into the patella. The lower extent of the MPFL is a distinct thickening within the fascial layer. (3)

The MPFL provides the major restraining force to lateral patellar dislocation when the knee is between 0 and 30 deg of flexion.

8 Pes anserinus:

Pes anserinus refers to the conjoined tendons of three muscles sartorius, gracilis and semitendinosus that insert onto the anteromedial surface of the proximal tibia. The appearance of the insertion looks like ‘goose foot’ and hence the name.

Figure 16. Ligaments of the knee

The popliteal fossa is a diamond-shaped depression behind the knee joint.

Boundaries

• Superior/lateral- biceps femoris; superior/medial- semitendinosus and semimembranosus; inferior/medial and lateral- medial and lateral heads of gastrocnemius

• Roof: deep fascia of the thigh

• Floor: from above downwards – popliteal surface of femur, posterior capsule of the knee joint and popliteus muscle.

Contents

1. Tibial nerve
2. Common peroneal nerve
3. Popliteal vein
4. Popliteal artery.

The tibial nerve is most superficial and the popliteal artery deepest, with the popliteal vein in between.

The tibial nerve runs vertically down the middle of the fossa and disappears by passing between the heads of gastrocnemius. The nerve enters the calf by passing beneath the fibrous arch in the origin of soleus. The common peroneal nerve runs downwards and laterally, medial to the biceps tendon, and disappears into the substance of peroneus longus to lie on the neck of the fibula. It ends by dividing into deep and superficial peroneal nerves.

This is a synovial joint which is usually described as a hinge joint but its movements are not quite that of a hinge as the axis of rotation is not fixed but changes between the extremes of plantar flexion and dorsiflexion.

The stabilizing surfaces are those of the medial and lateral malleoli, which grip the sides of the talus. The capsule is attached to the articular margins off all three bones except the anterior part of the talus where it is fixed some distance away from the articular margin at the neck of the talus.

Ankle ligaments

The deltoid (medial) ligament (Figure 17) 

• Consists of two layers
• The deep part is a narrow rectangular band extending from the medial malleolus to the side of the talus (anterior and posterior tibiotalar ligaments).
• The superficial part is triangular-shaped and fans downwards from the borders of the medial malleolus to a continuous attachment on the sustentaculum tali and spring ligament (very strong) to the tuberosity of the navicular (weak).(tibionavicular and tibiocalcaneal).

The lateral ligament (Figure 18)

• Consists of three separate bands radiating from the lateral malleolus.
• The anterior (anterior talofibular ligament, ATFL) and posterior bands (posterior talofibular ligament) pass to the talus, and the intermediate band to the calcaneus (calcaneofibular).
• The ATFL is the weakest and is intracapsular.

Figure 17. The medial ligament complex of ankle joint

Figure 18. The lateral ligament complex of ankle joint

Whilst many of the extrinsic muscles attach to the dorsum of the foot, there are only two intrinsic muscles located in this compartment:

• Extensor digitorum brevis
• Extensor hallucis brevis

They are mainly responsible for assisting some of the extrinsic muscles in their actions.

Both muscles are innervated by the deep fibula nerve.

Figure 19. Dorsum of foot.The  extensor retinaculum and anterior compartment muscles and NV bundle

Osteology and blood supply of the talus

• The head has a large distal articular surface, which is ovoid, convex and directed forwards and medially. Its inferior surface has two facets. The medial is for the plantar calcaneonavicular ligament. The lateral facet articulates with the corresponding facet on the upper surface of the anterior part of the calcaneus
• The inferior surface of the body has two articular surfaces, which are separated by a smooth ridge.
• The posterior calcaneal surface is large and oval, articulating with the corresponding facet on the upper surface of the calcaneus.
• The middle calcaneal surface is small, oval and slightly convex, resting on the sustentaculum tali of the calcaneum.
• The upper surface of the body carries an articular area, the trochlea, which is convex from front to back but with a shallow central groove.
• The trochlea is broad in front and narrow behind. The trochlear surface is continued down over each side of the body for articulation with the malleoli.
• Behind the trochlea the talus is projected into a posterior process, which is grooved, by flexor hallucis longus.
• The inferior surface of the neck is grooved to fit over the corresponding groove on the calcaneum to make the tarsal sinus and gives attachment to the talocalcaneum ligament.
• Laterally the neck gives attachment to the cervical ligament and the anterior talofibular ligament. The neck of the talus is very short and is directed forwards and medially.

The talar blood supply is from intraosseous and extraosseous sources.

• The main blood supply is the ‘artery of the tarsal canal’ arising from the posterior tibial artery 1 cm proximal to the division into the medial and lateral plantar arteries. It passes anteriorly between FDL and FHL to enter the tarsal canal and continues to the lateral part of the tarsus sinus, where it anastomoses with the artery of the tarsal sinus, forming a vascular sling under the talar neck.
• A branch of the artery of the tarsal canal known as the deltoid branch passes deep to the deltoid ligament and supplies the medial aspect of the talar body. Occasionally this artery arises from the posterior tibial artery or medial plantar artery. In talar fractures it may be the only remaining arterial supply to the talus.
• The dorsalis pedis supplies the superior aspect of the talar neck and gives off the artery of the tarsal sinus.
• The peroneal artery gives off small branches, which form a plexus posteriorly with branches of the posterior tibial artery.
• The intraosseous blood supply of the talar head comes medially from the dorsalis pedis artery and laterally from the anastomoses between the artery of the tarsal canal and tarsal sinus.
• The middle and lateral third of the talar body is supplied by this anastomotic sling in the tarsal canal. The medial third of the talar body is supplied by the deltoid artery, a branch of the artery of the tarsal canal.

1. The sinus tarsi is an anatomical space bounded by the talus and calcaneum, the talocalcaneonavicular joint anteriorly and posterior facet of the subtalar joint posteriorly. It is medially continuous with the much narrower tarsal canal.
2. The sinus tarsi contains the cervical ligament and the three roots of the inferior extensor retinaculum.
3. The tarsal canal contains the interosseous talocalcaneal ligament and the deep and intermediate roots of the inferior extensor retinaculum.
4. Both the sinus and the canal contain nerves and blood vessels.which are important for the nutrition of the talus.

The extensor digitorum brevis and bifurcate ligament lie anterior to the sinus tarsi.

The tarsal tunnel is a fibro-osseous space posterior to the medial malleolus lying deep to the flexor retinaculum

Borders          

Anterior: medial malleolus

Lateral: talus and calcaneus

Covered by flexor retinaculum

Contents          

Tib Post          FDL      Artery  Vein     Nerve       FHL

Obturator nerve (L2, 3, 4)

This emerges from the medial border of psoas major on the ala of the sacrum to pass behind the common iliac vessels. It runs over the pelvic brim on the lateral wall of the sacrum to enter the thigh through the obturator foramen. It has anterior and posterior branches, which lie between the adductor brevis:

• Anterior branch: runs on the anterior aspect of adductor brevis deep to pectineus and then deep to adductor longus to end by becoming subcutaneous at the lower border of adductor longus

1. Motor to adductor longus, adductor brevis and gracilis. Occasional twig to pectineus
2. Sensory medial side of the thigh

• Posterior branch: runs deep to adductor on adductor magnus.

1. Motor to obturator externus, part of adductor magnus (adductor portion), adductor brevis (variable).

The obturator nerve can be damaged during hip and acetabular surgery (screw placement in the anteroinferior quadrant), leading to loss of hip adduction and decreased sensation of the medial thigh.

Lateral cutaneous nerve of the thigh (L2, 3)

• This emerges from the lateral border of psoas major below the iliac crest, crosses the iliacus muscle obliquely and runs towards the ASIS where it passes under the inguinal ligament into the thigh. In the thigh it divides into anterior and posterior branches about 10 cm below the inguinal ligament.
• Branches from the anterior division distribute and supply the skin of the anterior and lateral parts of the thigh, as far as the knee joint. The posterior branch pierces fascia lata and supplies skin from the level of the greater trochanter to the middle of the thigh.
• Bernhardt-Roth syndrome (meralgia paraesthetica) is a condition characterized by numbness and paraesthesia along the distribution of the lateral cutaneous nerve caused by entrapment of the nerve during its course into the thigh.

Femoral nerve (L2, 3, 4)

The femoral nerve arises from posterior divisions of the ventral rami of L2, L3 and L4. It is formed within psoas major and emerges from its lateral border lying in the iliac fossa. It reaches the thigh by running beneath the inguinal ligament lateral to the femoral artery lying on the psoas and iliacus tendon.

As it enters the femoral triangle it divides into a superficial and deep group.

Superficial group: This comprises of two cutaneous and two muscular branches.

• Intermediate femoral cutaneous nerve (anterior thigh skin)
• Medial femoral cutaneous nerve (medial thigh skin).
• There is a nerve to pectineus and a nerve to sartorius.

Deep group: There are four muscular nerves and one cutaneous nerve.

• The saphenous nerve supplies the skin of the medial knee, medial calf and shin, and medial forefoot. It descends in the femoral triangle to reach the adductor canal where it spirals over the femoral artery to lie medial to it. It pierces the deep fascia on the medial side of the knee after emerging between sartorius and gracilis. It continues down the medial side of the leg with the long saphenous vein. It passes in front of the medial malleolus and along the medial border of the foot to the big toe.
• The four muscular nerves are nerves to rectus femoris, vastus medialis, vastus lateralis and vastus intermedius.

Sciatic nerve (L4–S3)

The sciatic nerve arises from the ventral rami of L4–S3 and descends through the greater sciatic foramen to enter the gluteal region, emerging from below the piriformis muscle more laterally than the inferior gluteal and pudendal vessels.

• It descends through the posterior compartment of the thigh and ends by dividing into tibial and common peroneal nerves, usually just above the popliteal fossa. Occasionally there is a high division at the piriformis muscle.
• The nerve lies on the ischium, superior gemellus, obturator internus, inferior gemellus, quadriceps femoris and adductor magnus. It is overlaid by the long head of biceps.
• This nerve does not supply any structure in the gluteal region.
• The common peroneal portion has one innervation in the thigh – the short head of biceps femoris. The short head of biceps femoris was developed in the extensor compartment but migrated to the flexor compartment for functional reasons, retaining its nerve supply.
• The tibial portion supplies the hamstring muscles (semimembranous, semitendinosus, biceps) as well as the hamstring part of the adductor magnus.

Nerve to quadratus femoris (L4, L5, S1)

This arises from the anterior surface of the sciatic nerve. It leaves the pelvis through the lower part of the greater sciatic notch and runs deep to obturator internus and inferior gemelli before entering quadratus femoris.

Nerve to obturator internus (L5, S1, S2)

This arises from the anterior surface of the sciatic nerve. It leaves the pelvis through the greater sciatic notch below piriformis and medial to the sciatic nerve. It passes over the ischial spine and sends a branch to the superior gemellus before turning forward to pass through the lesser sciatic notch and then penetrating and supplying obturator internus.

Common peroneal nerve (L4–S2)

• This is the smaller terminal branch of the sciatic nerve. It begins just above the apex of the popliteal fossa and descends underneath the medial border of biceps femoris muscle.
• It crosses plantaris, lateral head of gastrocnemius, popliteus tendon inside the knee joint capsule and the fibular origin of soleus. It leaves the fossa, passing into peroneus longus where it divides into superficial and deep peroneal nerves. Before dividing, the nerve gives off five branches (three cutaneous and two articular):
• Lateral sural cutaneous nerve (upper lateral calf skin)
• Peroneal communicating nerve
• Recurrent genicular nerve (skin over patella)
• Superior and inferior genicular nerves.
• The common peroneal supplies no muscles as it is a nerve of the extensor compartment. It is vulnerable to injury where it lies on the neck of the fibula.

Deep peroneal nerve (L4–S2)

• This begins within peroneus longus and winds around the fibular neck deep to extensor digitorum longus. It enters the anterior compartment by piercing the interosseous membrane and descends between EDL and tibialis anterior lateral to the anterior tibial vessels.
• In the middle of the leg the deep peroneal nerve lies on the interosseous membrane between TA and EHL.
• At the lower part of the tibia, EHL crosses over the nerve so that two muscles lie on either side of the neurovascular bundle (TA, EHL medially and EDL, peroneus tertius laterally). It ends by supplying the skin of the first web space.
• It supplies the muscles of the extensor compartment of the leg: tibialis anterior, extensor digitorum longus, extensor hallucis longus, peroneus tertius and extensor digitorum brevis.

Superficial peroneal nerve

• The superficial peroneal nerve begins in the substance of peroneus longus on the lateral side of the fibular neck. It descends first between peroneus longus and peroneus brevis, and then between peroneus longus and extensor digitorum longus.
• It supplies peroneus longus and brevis and pierces the deep fascia in the distal third of the leg.
• It divides into medial and lateral cutaneous branches.
• The medial branch supplies skin on the distal part of anterior leg, skin on the dorsum of the foot (except the first web space), the medial side of the big toe and adjacent sides of the second and third toes.
• The lateral branch also supplies skin of the dorsum of the foot, and adjacent sides of the third, fourth and fifth toes.

Tibial nerve (L4–S2)

• This is the terminal branch of the sciatic nerve. It begins just above the popliteal fossa, descends almost vertically through the fossa, lying first on the lateral side of the popliteal artery, then posterior to it and finally medial to it.
• The popliteal vein lies between the nerve and artery throughout its course.
• At the lower border of the popliteus muscle, it passes deep to the tendinous arch of the soleus muscle accompanied by the tibial vessels.
• It runs straight down the midline of the calf, deep to soleus, lying on the fibular aponeurosis of flexor digitorum longus.
• The nerve accompanies the posterior tibial artery and lies first on its medial side, then crosses posterior to it and finally lies on its lateral side.
• It leaves the posterior compartment of the leg under the flexor retinaculum behind the medial malleolus and then divides into the medial and lateral plantar nerves.
• The tibial nerve innervates all the muscles of the foot except the extensor digitorum brevis (supplied by the peroneal nerve).

• In the popliteal space it gives off five muscular, three articular (genicular nerves) and one cutaneous nerve:
• Popliteus muscle, two heads of gastrocnemius, soleus and plantaris?
• Upper and lower medial and middle genicular nerves?
• Medial sural cutaneous nerve, which joins with the peroneal communicating branch of the common peroneal nerve to form the sural nerve.
• In the posterior compartment it supplies four muscles:?Soleus, tibialis posterior, flexor digitorum longus and flexor hallucis longus.
• The nerve passes behind the medial malleolus between FDL and FHL under cover of the flexor retinaculum where it divides into medial and lateral plantar nerves.

Medial plantar nerve: (counterpart of the median nerve in the hand).

• Runs forward deep to the abductor hallucis with the medial plantar artery on its medial side.
• Supplies abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and the first lumbrical.
• The nerve gives off three sensory branches (common plantar digital nerves) that supply the medial 31⁄2 digits, including the dorsal skin and nail bed of the distal phalanges.

Lateral plantar nerve: (counterpart of the ulnar nerve in the hand).

• Crosses the sole obliquely just deep  to the first layer of muscles and supplies flexor accessorius and abductor digiti minimi.
• Near the base of the fifth metatarsal bone it divides into superficial and deep branches:
• The superficial branch supplies three muscles: flexor digiti minimi brevis and the two interossei of the fourth space (third plantar and fourth dorsal).
• The deep branch supplies the remaining interossei, transverse head of adductor hallucis and the lateral three lumbricals.

Saphenous nerve (L3, L4)

• The saphenous nerve is the continuation of the femoral nerve from the thigh.
• In the leg it travels with the great saphenous vein and passes in front of the medial malleolus into the foot where it supplies sensation over the medial border of the leg and foot as far as the ball of the big toe.
• The nerve can be damaged during knee surgery (especially the infrapatellar branch) as it becomes subcutaneous on the medial side of the knee between the sartorius and the gracilis.

Femoral artery

• The femoral artery is a continuation of the external iliac artery, beginning posterior to the inguinal ligament at the mid-inguinal point (halfway between ASIS and pubic symphysis). It ends as it passes through the adductor hiatus in the adductor magnus to become the popliteal artery. It emerges from under the inguinal ligament with the femoral vein medial to it, both within the femoral sheath.
• It lies on psoas major. As the artery enters the adductor canal it lies on adductor longus then adductor magnus.
• Four branches arise from the artery in the femoral triangle: Superficial epigastric artery,superficial circumflex iliac artery, superficial external pudendal artery and
• deep external pudendal artery.
• The profunda femoris artery is the main branch of the femoral artery and is given off posterolaterally just below the femoral sheath. It is the main blood supply to the thigh. It runs posteriorly between pectineus and adductor longus. It gives off medial and lateral circumflex femoral branches.

Popliteal artery

• The popliteal artery begins as the continuation of the femoral artery as it passes through the adductor magnus hiatus and ends as it passes under the fibrous arch of soleus where it divides into anterior and posterior tibial arteries.
• The popliteal artery is the deepest neurovascular structure in the popliteal fossa, lying with only fat between it and the popliteal surface of the femur. Biceps femoris is medial and semimembranosus medial.
• Lower down it lies between the two heads of gastrocnemius. At all levels the popliteal vein lies between the artery and the tibial nerve.
• It is crossed laterally to medially by the tibial nerve.

Anterior tibial artery

• This supplies structures in the extensor compartment of the lower leg.
• It descends on the interosseous membrane and crosses the lower tibia at the ankle joint midway between the malleoli.
• Initially it lies between tibialis anterior (medially) and EDL (laterally), then between tibialis anterior and EHL.
• The deep peroneal nerve is initially lateral to the artery but passes anterior to it before again becoming lateral.

Posterior tibial artery

• The posterior tibial artery travels downwards on tibialis posterior, FDL, the tibia and the ankle joint.
• It lies deep to gastocnemius, soleus, flexor retinaculum and abductor hallucis. It ends under the flexor retinaculum by dividing into medial and lateral plantar arteries.

Dorsalis pedis artery

• This is a direct continuation of the anterior tibial artery.
• It begins midway between the malleoli and runs anteromedially, deep to the inferior extensor retinaculum between EHL and EDL tendons.

The osteology of the spine involves the cervical, the thoracic, the lumbar and the sacral spinal vertebrae. The typical spinal vertebrae are very similar and have almost identical features in comparison to the other vertebrae of the same region of the spine. The atypical vertebrae differ from the other vertebrae in a few key components.

Typical cervical vertebra C3-C6

The features of the cervical vertebra are as follows-

Shape

• The body of the vertebra is small and is broader from side to side in comparison from front to back.
• Short and bifid spinous processes.
• The vertebral foramen is large and triangular in shape.

Articulations

• The superior and inferior articulating facets for articulation between the vertebrae.
• The articular facets are flat and oval in shape.
• The superior articular facets face backward,upward and slightly medially.
• The corresponding orientation of the inferior facets in order to help articulate with the superior facets of the next vertebrae is facing forward, downward and slightly laterally.

Distinguishing features

• The transverse processes have a foramen transversarium, which allows passage of the vertebral artery and the vertebral vein along with a plexus of sympathetic nerves.
• The anterior tubercle of the sixth cervical vertebrae is known as the carotid tubercle or the Chassaignac tubercle. This tubercle is significant in separating the carotid artery from the vertebral artery. This tubercle is used as a landmark for anesthesia of the brachial or the cervical plexus of nerves.
• The cervical nerves emerge above the designated vertebrae. For example the third cervical nerve C3, passes above the third cervical vertebrae.

Atypical Vertebra Atlas/C1

The first cervical vertebra is unique in the following aspects-

Shape

• The shape of the vertebra is similar to a ring. This ring comprises of the following parts-
• The anterior arch- forming the anterior wall of the ring.
• The posterior arch- forming the posterior wall of the ring.
• The lateral masses- forming the lateral walls.
• The transverse processes on either side housing the transverse foramen- these foramen transmit the vertebral artery and the vertebral vein along with a plexus of sympathetic nerves.

• There is no body of this vertebra. The dens of the second vertebra is embryologically derived from the body of the first vertebra.
• The central vertebral foramen is divided into 2 parts by the transverse atlantal ligament (TAL). The anterior part is smaller and houses the odontoid process (dens) of the second cervical vertebra. The posterior part is larger and houses the spinal cord and its membranes.
• This transverse atlantal ligament is prone to inflammatory degeneration in patients with rheumatoid arthritis causing atlanto-axial instability. Attempts at intubating these patients can result in damage to the spinal cord.

Articulations

• The lateral masses have two articular facets.
• The superior articular facets are large and articulate with the corresponding condyles of the occipital bone
• The inferior facets are slightly flattened to convex and articulate with the axis / C2 vertebra.

Atypical vertebra Axis/C2

The second cervical vertebra is unique the following aspects-

The Dens

• Also called the odontoid process and is shaped like a peg.
• The anterior surface articulates with the anterior arch of the atlas bone.
• The posterior surface has a transverse groove for the transverse atlantal ligament (TAL). TAL ligament stabilizes the dens and limits it from compressing the spinal cord.
• The apex of the dens gives attachment to the apical odontoid ligament and the alar ligaments on either side, which join the dens to the occipital bone.

Other distinguishing features

• The central foramen is larger than the typical cervical vertebrae.
• The lamina is very thick and strong.
• The transverse processes are very small and have a perforation on either side or the vertebral foramen.
• The spinous process is large, very strong and has a bifurcated tip.

Atypical vertebra C7

The unique features of the C7 vertebra are:

• The spinous process is long and prominent but is not bifid.
• The vertebral artery passes anterior to the transverse process rather than inside the transverse foramen, but variations are known to occur.

Typical thoracic vertebrae T2 to T8

• The bodies of the vertebrae are heart shaped.
• The laminae are broad and thick and overlap the adjacent laminae like tiles on a roof.
• The pedicels are directed backward and slightly upward.
• The spinous process is long and directed downwards. The cross section of the process is triangular.
• The transverse processes are thick, strong and long. They are directed obliquely backward and lateral. The ends if the processes are clubbed.
• The transverse processes have a small concave surface close to the clubbed ends for articulation of the ribs.

Typical lumbar vertebrae

• The superior articular processes are thin plates of bone projecting upward from the junctions of the pedicles and laminae.
• The superior articular facets are directed backward, laterally and upward.
• The inferior articular facets are fused to an extent with the laminae. Their facets are directed forward, downward and medial.
• These vertebrae constitute the largest segment of the vertebral column.
• The main components of these vertebrae are-
• Vertebral body-
• This is large and wider from side to side.
• It is thicker in front than the back.
• It is flattened or slightly concave from above and below.
• It is concave on the behind and deeply constricted in the front and the sides.
• Vertebral arch- this vertebral arch consists of-
• A pair of pedicels
• Pedicles are strong and directed backward from the upper body.
• The sagittal width of pedicles increases from upper lumbar to lower lumbar region.
• The angulation in axial plane increases from 10 degrees to 20 degrees.
• A pair of laminae- that are broad short and strong.
• They form the posterior portion of the vertebral arch.
• The laminae connect the spinous process to the pedicels.
• Vertebral foramen
• This foramen is smaller than the cervical vertebrae, but larger than the thoracic vertebrae.
• The Spinous Processes
• These spinous processes are thick, broad and quadrilateral in cross section.
• It is projected backwards and ends in a rough border.
• It has well defined superior and inferior articular facets.

Important ligaments

Anterior longitudinal ligament

• This extends from the basiocciput of the skull and anterior tubercle of the atlas to the front of the upper part of the sacrum.
• It is firmly attached to the periosteum of the vertebral bodies but less so over the intervertebral discs.

Posterior longitudinal ligament

• This extends from the back of the vertebral body of the axis to the anterior wall of the upper sacral canal.
• It is broader and more firmly attached over the intervertebral discs but narrower and more loosely attached to the vertebral bodies.

Ligamentum flavum

• These are a pair of yellowish (high content of elastic tissue) ligaments that join the contiguous borders of adjacent lamina.
• They are attached above to the front of the upper lamina and below to the back of the lower lamina.
• They are long, thin and broad in the cervical region, thicker in the thoracic region and thickest in the lumbar region.

Supraspinous ligaments

• These join the tips of the adjacent spinous processes from C7 to the sacrum. They are strong cord-like bands of white fibrous tissue. At the back of the neck they merge with the ligamentum nuchae.
• The ligament nuchae is a strong broad triangular septum of fibroelastic tissue attached to the external occipital crest, bifid spines of the cervical vertebrae and the investing layer of deep cervical fascia, which encloses the trapezius muscles.

Interspinous ligaments

• These unite the spinous processes of the vertebrae along their adjacent borders. They are well developed only in the lumbar region and they fuse with the supraspinous ligaments.

Intertransverse ligaments

• Weak sheets of fibrous tissue joining the transverse processes of vertebrae along their adjacent borders.

Apical ligament

• This joins the apex of the dens to the anterior margin of the foramen magnum, and is a fibrous remnant of the notochord.

Alar ligaments

• The alar ligaments lie obliquely on either side of the apical ligament.
• They diverge from the side of the dens to the foramen magnum.
• They are very strong ligaments and limit rotation of the head.

• The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.
• It extends from the foramen magnum and continues through to the conus medullaris near the second lumbar vertebra, terminating in a fibrous extension known as the filum terminale, which anchors the spinal cord to the coccyx.
• The cauda equina (“horse’s tail”) is the name for the collection of nerves in the vertebral column that continue to travel through the vertebral column below the conus medullaris.
• The spinal cord has 2 enlargements:

1 Cervical enlargement – corresponds roughly to the brachial plexus nerves, which innervate the upper limb. It includes spinal cord segments from about C4 to T1. The vertebral levels of the enlargement are roughly the same (C4 to T1).

2 Lumbosacral enlargement – corresponds to the lumbosacral plexus nerves, which innervate the lower limb. It comprises the spinal cord segments from L2 to S3 and is found about the vertebral levels of T9 to T12.

The spinal cord is protected by three spinal meninges:

1. The duramater is the outermost layer, and it forms a tough protective coating. The space between the vertebral column and the duramater is called the epidural space, which contains adipose tissue and blood vessels. The space between duramater and arachnoid mater is called subdural space.
2. The arachnoid mater is the middle protective layer. The space between the arachnoid and the underlying piamater is called the subarachnoid space. The subarachnoid space contains cerebrospinal fluid (CSF).
3. The piamater is the innermost protective layer. It is very delicate and it is tightly associated with the surface of the spinal cord.

• The cord is stabilized within the dura mater by the connecting denticulate ligaments, which extend from the piamater laterally between the dorsal and ventral roots. The dural sac ends at the vertebral level of the second sacral vertebra.
• In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor neurons. Internal to this peripheral region is the grey matter, which surrounds the central canal, which is an extension of the fourth ventricle and contains CSF.
• The white matter consists almost totally of myelinated motor and sensory axons.
• The grey matter is shaped like a butterfly and consists of cell bodies of interneurons, motor neurons, neuroglia cells and unmyelinated axons.
• The spinal cord has a shape that is compressed dorso-ventrally, giving it an elliptical shape. The cord has grooves in the dorsal (posterior median sulcus) and ventral sides (anterior median fissure).

Spinal cord segments

• Spinal cord is divided into 31 segments. At every segment, right and left pairs of spinal nerves (mixed, sensory and motor) emerge.
• Motor nerve rootlets emerge from the ventro lateral sulci and combine to form the motor nerve root.
• The sensory nerve rootlets arise form the dorso lateral sulci and form sensory nerve roots. Each segment of the spinal cord is associated with a pair of ganglia, called dorsal root ganglia, which are situated just outside the spinal cord. These ganglia contain cell bodies of sensory neurons.
• The ventral (motor) and dorsal (sensory) roots combine to form spinal nerves one on each side of the spinal cord and exit from the intervertebral foramen.
• In the upper part of the vertebral column, spinal nerves exit directly from the spinal cord, whereas in the lower part of the vertebral column the nerves pass further down the column before exiting.

• The spinal cord is supplied by three arteries that run along its length starting in the brain.  These are:

1. Anterior spinal artery,
2. Right posterior spinal artery
3. Left posterior spinal artery

• There are also many arteries that approach it through the sides of the spinal column.
• These travel in the subarachnoid space and send branches into the spinal cord. They form anastomoses via the anterior and posterior segmental medullary arteries, which enter the spinal cord at various points along its length.
• The actual blood flow through these arteries, derived from the posterior cerebral circulation, is inadequate to maintain the spinal cord below the cervical segments.
• The major contribution to the arterial blood supply of the spinal cord below the cervical region comes from the radially arranged posterior and anterior radicular arteries, which run into the spinal cord alongside the dorsal and ventral nerve roots. These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses and supplement the blood flow to the spinal cord.
• The largest of the anterior radicular arteries is known as the artery of Adamkiewicz, or anterior radicularis magna (ARM) artery, which usually arises between L1 and L2, but can arise anywhere from T9 to L5. Impaired blood flow through these critical radicular arteries, especially during surgical procedures that involve abrupt disruption of blood flow through the aorta, for example during aortic aneursym repair, can result in spinal cord infarction and paraplegia.