Anatomy

Definition and Functions

• Support — the framework of the body
• Protection — skull for brain, thorax for heart and lungs, pelvis for viscera
• Movement — acts as levers for muscles
• Mineral store — 99% of body calcium and 85% of phosphate
• Haematopoiesis — red marrow
• Fat storage — yellow marrow

Classification BY Shape

Classification BY Development

• The clavicle is the first bone to ossify (5th–6th week) and the last to complete ossification (about 25 years)
• It is also the only long bone to ossify in membrane

Parts of a Long Bone

Types of Epiphysis

Growing End and the Law of Ossification

• Mnemonic — "To the elbow I go, from the knee I flee" describes the direction of the nutrient artery, which points away from the growing end
• So in the upper limb the nutrient foramen points toward the elbow; in the lower limb away from the knee

Blood Supply of a Long Bone

• Nutrient artery — the principal supply; enters the shaft obliquely through the nutrient foramen and supplies the inner two-thirds of the diaphysis and the marrow
• Periosteal arteries — supply the outer one-third of the cortex; numerous where muscles attach
• Metaphyseal and epiphyseal arteries — supply the ends; the metaphysis is richly vascular with sluggish flow
• Juxta-epiphyseal arteries

Applied Aspects

• Acute osteomyelitis in children characteristically begins in the metaphysis, because blood flow there is slow and the capillary loops are hairpin-shaped, allowing organisms to settle
• Fracture through the epiphyseal plate (Salter–Harris injury) may arrest growth and cause deformity or shortening
• Ossification centres are used to estimate age in medicolegal practice — the lower femoral epiphysis at birth, and fusion of the iliac crest at about 21 years
• Avascular necrosis follows interruption of a single end-arterial supply — head of femur, scaphoid, talus, lunate
• The periosteum is richly innervated, which is why fractures and subperiosteal collections are so painful, while the bone itself is relatively insensitive

Definition

Structural Classification

Fibrous Joints

• Synostosis = complete bony fusion of a former joint, as when sutures close in adult life

Cartilaginous Joints

Synovial Joints — Structure

• Articular cartilage — hyaline (fibrocartilage in the temporo­mandibular, sternoclavicular and acromioclavicular joints); avascular, aneural and alymphatic, nourished by synovial fluid
• Articular capsule — outer fibrous layer and inner synovial membrane
• Synovial membrane — lines everything except the articular cartilage; secretes synovial fluid
• Joint cavity — a potential space containing synovial fluid
• Ligaments — capsular, extracapsular, intracapsular
• Accessory structures — menisci, labra, fat pads, bursae, tendons
• A dialysate of plasma with hyaluronic acid added by synovial cells
• Functions — lubrication, nutrition of articular cartilage, shock absorption, removal of debris (by phagocytosis)
• Viscous and slightly alkaline; only 0.5–2 mL in a large joint

Types of Synovial Joint

Blood and Nerve Supply — Hilton’s Law

• Explains referred pain — hip disease refers pain to the knee, since both are supplied by the obturator and femoral nerves
• The nerve supply is sensory (pain and proprioception) and vasomotor; joints have no motor supply
• Articular arteries form a periarticular anastomosis, ensuring supply in all positions of the joint
• The capsule and ligaments are richly innervated; the articular cartilage and synovial membrane are insensitive

Factors Determining Range and Stability

Applied Aspects

• Articular cartilage has no blood supply and cannot regenerate; damage is repaired by fibrocartilage, which is mechanically inferior — the basis of osteoarthritis
• Aspiration of synovial fluid distinguishes septic arthritis (turbid, high neutrophils, low glucose) from gout (negatively birefringent needle crystals) and pseudogout (positively birefringent rhomboids)
• Haemarthrosis in haemophilia damages cartilage and leads to ankylosis
• Referred pain from the hip to the knee is a classic trap — always examine the hip in a child complaining of knee pain
• Dislocation is commonest where mobility is greatest — the shoulder, because stability has been traded for range

Types of Muscle

Classification of Skeletal Muscle BY Shape and Fibre Direction

Parts and Attachments

• Origin — the more fixed and proximal attachment; insertion — the more mobile and distal
• The two may reverse in function — in a pull-up, the insertion becomes fixed and the origin moves
• Belly — the fleshy contractile part
• Tendon — cord-like; aponeurosis — flattened sheet; raphe — where two flat muscles interdigitate

Functional Classification

• Reciprocal innervation — when the agonist contracts, the antagonist is reflexly inhibited
• Shunt and spurt muscles — a spurt muscle inserts far from the joint and produces movement (biceps); a shunt muscle inserts close and stabilises (brachioradialis)

Nerve Supply

• Motor fibres — large myelinated alpha motor neurones to extrafusal fibres; gamma efferents to intrafusal fibres of the muscle spindle
• Sensory fibres (about 40% of the nerve) — from muscle spindles (length) and Golgi tendon organs (tension); the basis of proprioception
• Sympathetic fibres — vasomotor
• Motor unit = one motor neurone and all the fibres it supplies; small in precise muscles (extraocular, 1:5) and large in powerful ones (gluteus maximus, 1:2000)
• The nerve usually enters at the "motor point", near the junction of the upper and middle thirds

Blood Supply

• Muscles are richly vascular, with many anastomosing branches
• Vessels usually enter with the nerve at the neurovascular hilum
• Blood flow rises many-fold during exercise; capillary density reflects the muscle's oxidative type

Muscle Fibre Types

• Most human muscles are mixed; the proportion is genetically determined and modified by training
• Endurance training increases type I capacity; sprint training hypertrophies type II fibres

Applied Aspects

• Denervation causes rapid wasting with fibrillation; reinnervation within about 18 months may restore function, after which fibrosis is irreversible
• Volkmann ischaemic contracture — muscle necrosis from compartment ischaemia, followed by fibrosis and permanent deformity
• Intramuscular injection into the gluteal region must be in the upper outer quadrant to avoid the sciatic nerve; the deltoid and vastus lateralis are alternatives
• Muscle biopsy distinguishes myopathy from neuropathy — grouped atrophy indicates denervation
• Tendon transfer exploits the fact that a muscle retains its own nerve supply when its insertion is moved, restoring lost function after nerve injury

Types of Blood Vessels

• All vessels have three coats — tunica intima, media and adventitia
• Vasa vasorum supply the outer coats of large vessels; nervi vasorum are the sympathetic vasomotor nerves

Anastomosis

• Actual anastomosis — between vessels of appreciable size, giving effective collateral circulation
• Potential anastomosis — between very small branches; opens only slowly and may be inadequate for sudden occlusion

End Arteries

Important Anastomoses

Portosystemic Anastomoses

Veins and Their Special Features

• Valves are folds of intima that prevent backflow; numerous in the limbs, especially the lower, and absent in the venae cavae, portal vein, cerebral and vertebral veins
• Venae comitantes — paired veins accompanying a deep artery within a common sheath; arterial pulsation aids venous return
• Venous sinuses — channels with no muscular wall, as in the dura mater
• Perforating veins connect superficial to deep veins in the limbs, with valves directing flow inward; their incompetence causes varicose veins
• The vertebral venous plexus (Batson) is valveless and connects the pelvis to the skull — a route for the spread of prostatic and breast carcinoma to the vertebrae and brain

Applied Aspects

• Portal hypertension opens these channels; the oesophageal varices are the most dangerous, because the veins are submucosal and unsupported
• Central retinal artery occlusion causes sudden painless permanent blindness — the retina tolerates ischaemia for only a few minutes
• Coronary arteries are functional end arteries, which is why occlusion infarcts myocardium; gradual narrowing allows some collateral development
• Ligation of a vessel is safe only where anastomosis is good — the reason the classical sites of ligation are chosen where they are
• Arteriovenous fistula for dialysis is created surgically, exploiting the principle that a direct communication carries high flow
• Varicose veins result from incompetent valves in the perforating veins, so blood is forced outward into the superficial system on muscular contraction
• Deep vein thrombosis follows Virchow triad — stasis, endothelial injury and hypercoagulability; the calf veins are the usual site
• Watershed areas between two arterial territories are the first to infarct in hypotension — the splenic flexure of the colon is the classic example
• Atherosclerosis affects elastic and large muscular arteries preferentially, sparing the arterioles, which is why it causes infarction rather than diffuse ischaemia

Skin

• Mnemonic for epidermal layers — "Come, Let's Get Sun Burnt" from surface inward
• Stratum lucidum is present only in thick (glabrous) skin — palms and soles
• Melanocytes lie in the stratum basale; racial differences depend on melanin distribution and size of granules, not on the number of melanocytes
• Functions — protection, thermoregulation, sensation, excretion, vitamin D synthesis, immunological (Langerhans cells)

Superficial and Deep Fascia

• Superficial fascia has two layers in the lower abdomen — Camper (fatty) and Scarpa (membranous); Scarpa continues into the perineum as Colles fascia, which determines where extravasated urine can spread
• Deep fascia forms retinacula — the flexor retinaculum at the wrist and the extensor retinaculum at the ankle, holding tendons in place

The Lymphatic System

• Consists of lymph capillaries, vessels, nodes and lymphoid organs
• Lymph capillaries are blind-ended, more permeable than blood capillaries, and lack a basement membrane — which is why protein and cells enter them
• Absent from — central nervous system, cornea, cartilage, bone marrow, epidermis, nails, hair
• Functions — returns tissue fluid and protein to blood; absorbs fat from the gut (chyle); immune defence; a route of tumour spread
• Capsule with trabeculae; hilum where the efferent vessel leaves
• Cortex — lymphoid follicles with germinal centres; B lymphocytes
• Paracortex — T lymphocytes; expands in viral infection
• Medulla — medullary cords and sinuses; plasma cells
• Afferent vessels are many and enter the convex surface; the efferent is single and leaves at the hilum

Major Lymphatic Ducts

• The thoracic duct begins as the cisterna chyli at the level of L1–L2, and is about 45 cm long
• It is the largest lymphatic vessel in the body

Lymphatic Drainage of Some Key Regions

• The testis drains to para-aortic nodes while the scrotum drains to inguinal nodes — a favourite examination point, explained by the descent of the testis from the posterior abdominal wall

Appendages of the Skin

Applied Aspects

• Lymphoedema follows obstruction — after axillary clearance, radiotherapy, or filariasis, which causes elephantiasis and is endemic in parts of India
• Lymphatic spread of carcinoma determines staging and surgical clearance; the sentinel node is the first node draining a tumour
• Chylothorax follows injury to the thoracic duct, as in oesophageal surgery or trauma
• Cellulitis and lymphangitis show as red streaks tracking toward the draining nodes
• Knowledge of drainage directs examination — a lesion on the lateral side of the foot drains to the popliteal nodes, not the inguinal, and would otherwise be missed

Definition and Formation

• Prefixed plexus — contribution from C4; postfixed — contribution from T2
• Arranged in five stages: Roots, Trunks, Divisions, Cords, Branches
• Mnemonic — "Read That Damn Cadaver Book"

Cord Formation

Branches

• Dorsal scapular nerve (C5) → rhomboids, levator scapulae
• Long thoracic nerve of Bell (C5, C6, C7) → serratus anterior
• Contributions to the phrenic nerve (C5)
• Suprascapular nerve (C5, C6) → supraspinatus and infraspinatus
• Nerve to subclavius (C5, C6)

• Mnemonic for the posterior cord — "ultra": Upper subscapular, Lower subscapular, Thoracodorsal, Radial, Axillary
• Mnemonic for the lateral cord — "LML"; for the medial cord — "MMMUM"

Relations

• The plexus enters the axilla through the cervico-axillary canal
• In the neck it lies in the interscalene groove, between scalenus anterior and scalenus medius, with the subclavian artery
• The subclavian vein lies anterior to scalenus anterior, separated from the plexus — the anatomical basis of the supraclavicular approach
• The cords are named by their relation to the second part of the axillary artery

Injuries — Upper Plexus (erb–duchenne)

• C5 and C6 roots, at Erb's point where they unite
• Cause — undue increase in the angle between the neck and shoulder: birth injury with shoulder dystocia, a fall on the shoulder, or traction on the arm
• Muscles paralysed — deltoid, supraspinatus, infraspinatus, biceps, brachialis, brachioradialis, supinator
• Deformity — the "policeman's tip" or "waiter's tip" hand:Arm adducted (deltoid, supraspinatus paralysed)
• Medially rotated (infraspinatus, teres minor paralysed)
• Elbow extended (biceps, brachialis paralysed)
• Forearm pronated (supinator, biceps paralysed)
• Sensory loss over the lateral side of the arm and forearm

Injuries — Lower Plexus (klumpke)

• C8 and T1 roots
• Cause — undue abduction of the arm: a breech delivery with the arm extended, clutching at something when falling, or a cervical rib
• Muscles paralysed — all the small muscles of the hand, and the long flexors
• Deformity — claw hand: hyperextension at the metacarpophalangeal joints with flexion at the interphalangeal joints
• HORNER syndrome may accompany it — ptosis, miosis, anhidrosis and enophthalmos — because the T1 sympathetic contribution is damaged
• Sensory loss along the medial side of the forearm and hand

Applied Aspects

• Winging of the scapula — injury to the long thoracic nerve (serratus anterior), classically after axillary surgery or radical mastectomy; the medial border of the scapula projects when pushing against a wall
• Brachial plexus block — performed by the interscalene, supraclavicular, infraclavicular or axillary route for upper limb surgery
• Cervical rib compresses the lower trunk and the subclavian artery → thoracic outlet syndrome, with wasting of the small hand muscles and vascular signs
• Erb palsy has a better prognosis than Klumpke, and most birth injuries recover with physiotherapy
• The posterior cord supplies all the extensors and the lateral and medial cords the flexors — a consequence of the limb bud rotating during development

Definition

Boundaries

• The anterior fold is formed by the lower border of pectoralis major; the posterior fold by latissimus dorsi and teres major

Contents

• Axillary artery and its branches
• Axillary vein and its tributaries
• Cords and branches of the brachial plexus
• Axillary lymph nodes — five groups
• Long thoracic nerve (on serratus anterior) and intercostobrachial nerve
• Axillary fat and areolar tissue
• The axillary tail of Spence of the breast pierces the deep fascia to enter the axilla

Axillary Artery

• Continuation of the subclavian artery at the outer border of the first rib; becomes the brachial artery at the lower border of teres major
• Divided into three parts by pectoralis minor — a useful rule: the number of branches equals the number of the part

• The subscapular artery is the largest branch
• The posterior circumflex humeral artery passes through the quadrangular space with the axillary nerve

Axillary LYMPH Nodes

Clavipectoral Fascia

• A strong sheet extending from the clavicle above to the axillary fascia below, enclosing subclavius and pectoralis minor
• Structures piercing it — mnemonic "LCTC":Lateral pectoral nerve
• Cephalic vein
• Thoraco-acromial artery
• Cephalic lymphatics
• Its lower part is the suspensory ligament of the axilla, which holds the axillary fascia up and produces the hollow of the armpit

Axillary Vein and Nerve Relations

• The axillary vein is formed by the union of the basilic vein and the venae comitantes of the brachial artery, at the lower border of teres major
• It lies medial and anterior to the artery, and becomes the subclavian vein at the outer border of the first rib
• The cephalic vein ends in it after piercing the clavipectoral fascia
• The vein is a common site for central venous access, and its wall is held open by fascia, so a tear can cause air embolism
• The three cords surround the second part of the artery, which is how they are named; the median nerve is formed in front of the third part

Applied Aspects

• Axillary lymph node clearance in breast carcinoma risks injury to the long thoracic nerve (winged scapula) and the thoracodorsal nerve, and causes lymphoedema of the arm
• Sentinel node biopsy has largely replaced routine clearance, sparing these complications
• Axillary abscess must be drained through the medial wall, to avoid the vessels and nerves laterally
• The axillary artery can be compressed against the humerus in the lateral wall to control bleeding
• Intercostobrachial nerve injury causes numbness over the medial arm after axillary surgery — a common and often unwarned complaint

Type and Articulation

• The most mobile joint in the body, and correspondingly the least stable
• The glenoid cavity is shallow and holds only about a third of the humeral head
• Deepened by the glenoid labrum, a fibrocartilaginous rim
• Both articular surfaces are covered with hyaline cartilage

Capsule and Synovial Membrane

• Attached medially to the margin of the glenoid cavity, beyond the labrum
• Laterally to the anatomical neck, except inferiorly where it descends about 1 cm onto the surgical neck
• Lax inferiorly to permit abduction — and therefore the weakest part
• Two deficiencies — for the tendon of the long head of biceps, and for communication with the subscapular bursa
• The synovial membrane sheathes the long head of biceps as it traverses the joint; the tendon is intracapsular but extrasynovial

Ligaments

Stability — the Rotator Cuff

• The chief stabilisers are muscles, not ligaments — the price of mobility

• Mnemonic — sits. Note that only subscapularis inserts into the lesser tubercle, and it is the only medial rotator of the four
• The cuff is deficient inferiorly, which is exactly why dislocation occurs in that direction

Movements and Muscles

• Scapulo-humeral rhythm — for every 3° of abduction, 2° occurs at the glenohumeral joint and 1° by scapular rotation

Blood and Nerve Supply

• Arteries — anterior and posterior circumflex humeral, suprascapular and circumflex scapular
• Nerves — axillary, suprascapular and lateral pectoral
• Hilton law applies — the nerves supplying a joint also supply the muscles acting on it and the skin over their insertions

Bursae Around the Shoulder

• A communicating subacromial bursa indicates a complete rotator cuff tear, since only a full-thickness defect connects them — the basis of the arthrogram sign

Applied Aspects

• Dislocation is commonest at the shoulder, and is usually anterior-inferior (subcoracoid) — the head is driven downward through the weak inferior capsule, then pulled forward by muscle action
• The axillary nerve is at risk in dislocation and in fracture of the surgical neck → deltoid paralysis and loss of sensation over the "regimental badge" area. Always test it before and after reduction
• Supraspinatus tendinitis and rotator cuff tear — the tendon is impinged beneath the coraco-acromial arch; gives a painful arc between 60° and 120° of abduction
• Frozen shoulder (adhesive capsulitis) — the capsule contracts, restricting all movements, and lateral rotation first
• Recurrent dislocation follows a Bankart lesion (avulsion of the anterior labrum) or a Hill–Sachs defect of the humeral head
• Posterior dislocation is rare and is classically missed; suspect it after an epileptic fit or electrocution, where the arm is held internally rotated

Definition

Boundaries

Contents — Lateral to Medial

• Radial nerve (in the lateral corner, between brachioradialis and brachialis) — divides here into superficial and deep branches
• Tendon of biceps brachii
• Brachial artery — divides at the level of the neck of the radius into radial and ulnar arteries
• Median nerve — leaves between the two heads of pronator teres
• Mnemonic from lateral to medial — "Really Need Beer To Be At My Nicest", or simply tan (Tendon, Artery, Nerve) for the three central structures
• Also present — the deep lymph nodes and the beginning of the radial and ulnar arteries

Compartments of the Arm

• The two compartments are separated by the medial and lateral intermuscular septa
• Brachialis is the chief flexor of the elbow; biceps is the chief supinator, most powerful with the elbow flexed
• Brachialis has a dual nerve supply — musculocutaneous and a twig from the radial nerve, since it develops partly from the extensor compartment

Brachial Artery

• Continuation of the axillary artery at the lower border of teres major
• Ends at the level of the neck of the radius by dividing into radial and ulnar arteries
• Relations — the median nerve crosses it from lateral to medial in the middle of the arm; it lies on triceps, then brachialis
• Branches — profunda brachii, nutrient, superior and inferior ulnar collateral, muscular
• Superficial throughout its course, covered only by skin and fascia in the cubital fossa — the reason it is used for blood pressure measurement

Anastomosis Around the Elbow

• Between branches of the brachial and profunda brachii above, and the radial, ulnar and interosseous recurrent arteries below
• Permits collateral circulation if the brachial artery is occluded below the profunda
• The corresponding scapular anastomosis permits ligation of the third part of the subclavian or first part of the axillary artery

Nerves of the Arm — Course and Relations

• The musculocutaneous nerve continues as the lateral cutaneous nerve of the forearm
• Only the radial and musculocutaneous nerves supply muscles in the arm; the median and ulnar pass through without branching

Applied Aspects

• Blood pressure is measured over the brachial artery in the cubital fossa, and the pulse felt medial to the biceps tendon
• The median cubital vein is the standard site for venepuncture and intravenous access; the bicipital aponeurosis separates it from the brachial artery and is therefore called the "grace of God" tendon
• Supracondylar fracture of the humerus — common in children; may injure the brachial artery or the median nerve, and cause Volkmann ischaemic contracture if the compartment is not decompressed
• Volkmann contracture — ischaemic necrosis of the flexor muscles followed by fibrosis, giving a permanently flexed, clawed hand
• Radial nerve injury in the spiral groove (mid-shaft humeral fracture) → wrist drop, with triceps spared because its branches arise higher
• The cubital fossa is the site of arterial cannulation for cardiac catheterisation by the brachial route, and of arteriovenous fistula formation for dialysis
• Biceps tendon rupture at the long head gives the "Popeye sign" — the muscle belly bunches distally
• Tennis elbow (lateral epicondylitis) affects the common extensor origin; golfer’s elbow the common flexor origin
• The ulnar nerve lies behind the medial epicondyle, so it is at risk in any medial approach to the elbow

Small Muscles of the Hand

• Mnemonic — "dab and pad": Dorsal ABduct, Palmar ADduct
• The ulnar nerve supplies all the small muscles of the hand except the thenar group and the lateral two lumbricals — the single most useful statement about hand innervation
• Lumbricals flex the metacarpophalangeal and extend the interphalangeal joints, the position of writing

Fascial Spaces of the Palm

• The palmar aponeurosis is a triangular thickening of deep fascia, continuous with the tendon of palmaris longus
• Two septa divide the palm into thenar, hypothenar and central compartments

Synovial Sheaths

• Ulnar bursa — encloses all the long flexor tendons; extends from proximal to the flexor retinaculum into the palm, continuing to the little finger
• Radial bursa — encloses the tendon of flexor pollicis longus
• Digital sheaths of the index, middle and ring fingers are separate
• So infection of the little finger or thumb can spread proximally into the forearm, whereas that of the other fingers is usually confined

Arches of the Hand

• The superficial arch is more distal; the deep arch more proximal
• The superficial arch gives common palmar digital arteries; the deep arch gives palmar metacarpal arteries and the princeps pollicis
• Allen test checks the patency of both arteries before radial artery cannulation, relying on this anastomosis

Nerve Supply of the Skin

• Median — lateral part of the palm, palmar surface of the lateral three and a half digits, and their nail beds dorsally
• Ulnar — medial one and a half digits, both palmar and dorsal
• Radial — dorsum of the lateral three and a half digits, excluding the nail beds

Nerve Lesions and Their Deformities

• The ulnar paradox — a lesion at the wrist gives a more marked claw than one at the elbow, because in the high lesion flexor digitorum profundus is also paralysed and cannot flex the interphalangeal joints

Skin and Grips of the Hand

• Palmar skin is thick, hairless, rich in sweat glands, and firmly bound to the palmar aponeurosis by fibrous septa — so it does not slip when gripping
• Dorsal skin is thin and loose, which is why oedema collects there and why dorsal swelling occurs in palmar infection
• Power grip — the whole hand around an object; long flexors and the ulnar-supplied intrinsics
• Precision grip — between the thumb and finger pulps; depends on opposition, and therefore on the median nerve
• Hook grip — carrying a bag; long flexors alone
• The opposable thumb accounts for about 40–50% of hand function, which is why its loss is compensated by pollicisation surgery

Applied Aspects

• Carpal tunnel syndrome — compression of the median nerve beneath the flexor retinaculum; nocturnal pain and paraesthesiae in the lateral three and a half digits, thenar wasting, positive Tinel and Phalen tests
• Froment sign — in ulnar palsy, adductor pollicis fails, so the thumb flexes at the interphalangeal joint when gripping paper
• Dupuytren contracture — fibrosis and shortening of the palmar aponeurosis, drawing the ring and little fingers into flexion
• Felon (pulp space infection) is a surgical emergency — the closed space raises tension and causes necrosis of the terminal phalanx
• The hand is the organ of the intellect: precision grip depends on the opposable thumb, which depends on the median nerve — which is why median nerve injury is functionally the most disabling of the three
• Trigger finger — nodular thickening of a flexor tendon catching at the A1 pulley, so the finger snaps on extension
• Mallet finger — avulsion of the extensor insertion into the distal phalanx, which then drops
• Boutonni re and swan-neck deformities of rheumatoid arthritis result from disruption of the extensor expansion at different levels

Definition

Boundaries

• Older descriptions include adductor brevis in the floor

Contents — Lateral to Medial

• Mnemonic — NAVEL
• N — Femoral nerve and its branches (outside the femoral sheath)
• A — Femoral artery and branches
• V — Femoral vein and tributaries
• E — Empty space (the femoral canal)
• L — Lymphatics — deep inguinal nodes including the node of Cloquet
• Also — femoral branch of the genitofemoral nerve, lateral cutaneous nerve of thigh, and the terminal part of the great saphenous vein

Femoral Sheath

• Anterior wall — from the fascia transversalis; posterior wall — from the fascia iliaca
• Divided by two septa into three compartments

• The femoral nerve is outside the sheath, lying on iliopsoas — a point frequently asked

Femoral Canal and Ring

• The femoral canal is the medial compartment, about 1.25 cm long; its upper opening is the femoral ring, closed by the femoral septum
• Function — a dead space allowing the femoral vein to expand during increased venous return, and a route for lymphatics

Femoral Artery

• Continuation of the external iliac artery at the mid-inguinal point — midway between the anterior superior iliac spine and the pubic symphysis
• Becomes the popliteal artery at the adductor hiatus
• Branches — superficial epigastric, superficial circumflex iliac, superficial and deep external pudendal, and the profunda femoris (the largest, from the lateral side about 4 cm below the inguinal ligament)
• Profunda femoris gives the medial and lateral circumflex femoral arteries and four perforating arteries

Saphenous Opening and LYMPH Nodes

• The saphenous opening is a gap in the fascia lata about 4 cm below and lateral to the pubic tubercle, with a sharp falciform margin
• It is closed by the cribriform fascia, pierced by the great saphenous vein and lymphatics — hence the name
• Superficial inguinal nodes lie in the superficial fascia — a horizontal group below the inguinal ligament draining the anterior abdominal wall below the umbilicus, perineum, external genitalia (not testis), lower anal canal and buttock; and a vertical group along the saphenous vein draining the lower limb
• Deep inguinal nodes lie medial to the femoral vein, the highest being the node of Cloquet in the femoral canal
• All drain onward to the external iliac nodes

Applied Aspects

• Femoral hernia — lies below and lateral to the pubic tubercle; commoner in women (wider pelvis); high risk of strangulation because the ring is narrow and rigid
• Inguinal hernia lies above and medial to the pubic tubercle — the single reliable clinical distinction
• The femoral artery is the standard site for arterial puncture — cardiac catheterisation, angiography, and femoral arterial blood gas sampling
• Femoral vein cannulation uses the same landmarks — the vein lies immediately medial to the artery
• Femoral nerve block is given lateral to the artery, remembering the nerve is outside the sheath
• Psoas abscess tracks beneath the inguinal ligament and presents as a swelling in the femoral triangle, mimicking a hernia; it has a cross-fluctuant swelling above the ligament
• Saphena varix at the saphenous opening may also mimic a hernia, but has a fluid thrill on coughing and vanishes on lying down

Type and Articulation

• Designed for stability and weight transmission, in contrast to the shoulder, which is designed for mobility
• The acetabulum is deepened by the acetabular labrum, and completed below by the transverse acetabular ligament
• The acetabular fossa is non-articular and contains the Haversian fat pad
• Articular cartilage of the acetabulum is horseshoe-shaped (lunate surface); that of the head covers all but the fovea

Capsule

• Proximally — to the acetabular margin and the transverse ligament
• Distally — anteriorly to the intertrochanteric line; posteriorly only to the medial two-thirds of the neck, not reaching the intertrochanteric crest
• Some fibres are reflected along the neck as retinacula, carrying the crucial retinacular vessels

Ligaments

Blood Supply

• The medial circumflex femoral artery is the most important
• The supply is essentially retrograde — from the neck toward the head — which is why an intracapsular fracture is so dangerous

Movements and Muscles

Nerve Supply and Relations

• Femoral, obturator, superior gluteal and nerve to quadratus femoris — illustrating Hilton's law
• Anterior relations — iliopsoas, pectineus, femoral vessels
• Posterior relations — sciatic nerve, piriformis, obturator internus, quadratus femoris
• Superior — gluteus minimus, reflected head of rectus femoris
• Inferior — obturator externus

Weight Transmission and the Angle of Inclination

• The angle of inclination between the neck and shaft is about 125° in the adult, more in the child
• Coxa vara — the angle is reduced; the limb is shortened and a Trendelenburg gait results
• Coxa valga — the angle is increased
• The angle of femoral torsion (anteversion) is about 15°; excess causes an in-toeing gait in children
• The neck is the weakest part of the femur, and trabeculae are arranged along lines of stress, leaving Ward's triangle as an area of relative weakness

Applied Aspects

• Referred pain to the knee — both joints are supplied by the obturator and femoral nerves, so always examine the hip in a child with knee pain; a missed slipped capital femoral epiphysis or Perthes disease is a classic error
• Posterior dislocation is the commonest, from a dashboard injury with the hip flexed and adducted; the limb is flexed, adducted, medially rotated and shortened, and the sciatic nerve is at risk
• Fracture neck of femur — the limb is shortened and laterally rotated; intracapsular fractures risk avascular necrosis and are often treated by replacement rather than fixation
• Developmental dysplasia of the hip — screened by the Ortolani and Barlow tests in the newborn; early treatment in a Pavlik harness prevents lifelong disability
• Trendelenburg sign — the pelvis droops on the unsupported side when the gluteus medius and minimus of the standing side are weak
• Perthes disease — idiopathic avascular necrosis of the femoral head in children of 4 to 8 years, presenting with a limp and knee pain
• Slipped capital femoral epiphysis — in obese adolescents; the limb is laterally rotated and shortened, and the diagnosis is missed if only the knee is examined
• Arthroplasty and hemiarthroplasty are chosen over internal fixation for displaced intracapsular fractures in the elderly, precisely because the blood supply is already destroyed
• Fracture neck of femur is a disease of osteoporosis, and carries high mortality in the elderly from immobility rather than from the fracture itself

Type and Articulation

• Really three joints in one capsule — two tibiofemoral (medial and lateral) and one patellofemoral
• Articular surfaces are markedly incongruent, which is why menisci and ligaments matter so much
• Stability depends on ligaments and muscles, not on bony fit

Ligaments

• The cruciates are named after their tibial attachment, and they cross each other like the limbs of an X
• They are intracapsular but EXTRAsynovial

Menisci

• Functions — deepen the articular surface, distribute weight over a wider area, absorb shock, and assist lubrication
• Blood supply reaches only the outer third ("red zone"); tears of the inner avascular part do not heal and must be excised

Locking and Unlocking

• Popliteus is the "key that unlocks the knee" — the single most asked fact about this muscle
• Locking is completed by quadriceps, particularly vastus medialis

Bursae

Blood and Nerve Supply

• Genicular anastomosis — five genicular branches of the popliteal, with the descending genicular, descending branch of the lateral circumflex femoral, and the anterior tibial recurrent
• Nerves — femoral, tibial, common peroneal and obturator

Movements and Muscles

• Rotation is possible only when the knee is flexed, since the ligaments are taut in extension
• Vastus medialis obliquus prevents lateral patellar dislocation; it is the first to waste in knee disease and the last to recover

Applied Aspects

• Unhappy triad of O'Donoghue — a lateral blow to the abducted, flexed knee tears the tibial collateral ligament, the medial meniscus (attached to it) and the anterior cruciate
• Meniscal tear — twisting on a flexed weight-bearing knee; gives locking, clicking, joint-line tenderness and a positive McMurray test
• Anterior cruciate rupture — an audible pop, immediate haemarthrosis, and a positive Lachman test; the knee gives way on turning
• Effusion is detected by the patellar tap for a large effusion and the bulge test for a small one; the suprapatellar bursa must be emptied first
• Genu valgum (knock knee) and genu varum (bow leg) alter the mechanical axis and predispose to osteoarthritis of one compartment
• Osteoarthritis of the knee is very common in India, aggravated by squatting and floor sitting, and typically affects the medial compartment first

Definition

Boundaries

Contents

• From superficial to deep — tibial nerve, popliteal vein, popliteal artery
• Mnemonic — the artery is deepest and most medial; the nerve is most superficial and lateral
• Common peroneal (fibular) nerve — along the medial border of biceps femoris
• Popliteal lymph nodes — drain the lateral side of the foot, the heel and the deep tissues of the leg
• Genicular vessels and nerves; the small saphenous vein pierces the fascia to end in the popliteal vein
• Popliteal fat

The Sciatic Nerve

• Leaves the pelvis through the greater sciatic foramen below piriformis
• Descends midway between the ischial tuberosity and the greater trochanter
• Lies on obturator internus, gemelli, quadratus femoris and adductor magnus
• Divides into the tibial and common peroneal nerves, usually at the upper angle of the popliteal fossa, though the division may be higher
• It is really two nerves in one sheath from the start — the tibial (anterior divisions) and common peroneal (posterior divisions)

Common Peroneal Nerve and Foot Drop

• Winds round the neck OF the fibula, where it is subcutaneous and the most commonly injured nerve in the lower limb
• Divides into superficial peroneal (peroneus longus and brevis; skin of the dorsum) and deep peroneal (anterior compartment; first web space)
• Causes — a tight plaster cast, fracture of the fibular neck, prolonged squatting or crossing the legs, pressure from a lithotomy position, leprosy
• Eversion is lost as well as dorsiflexion, which distinguishes it from an isolated deep peroneal lesion

Sciatic Nerve Injury

• Complete lesion — paralysis of the hamstrings and all muscles below the knee; foot drop; sensory loss below the knee except the medial side (saphenous, from the femoral nerve)
• Knee flexion is weakened but retained, by gracilis and sartorius
• Causes — posterior dislocation of the hip, fracture of the pelvis, badly placed intramuscular injection, penetrating wounds
• Piriformis syndrome — compression by a hypertrophied piriformis, particularly when the nerve pierces the muscle (a variation in about 10%)

The Popliteal Artery and Vein

• Popliteal artery — the continuation of the femoral artery from the adductor hiatus to the lower border of popliteus, where it divides into anterior and posterior tibial arteries
• The deepest structure in the fossa, lying on the popliteal surface of the femur and the capsule
• Branches — five genicular (superior medial and lateral, middle, inferior medial and lateral), muscular and sural
• These form the genicular anastomosis around the knee
• Popliteal vein lies between the artery and the tibial nerve, formed by the union of the venae comitantes of the tibial arteries; receives the small saphenous vein
• The pulse is felt with the knee flexed to relax the popliteal fascia, pressing the artery against the tibia

Applied Aspects

• Intramuscular injections must be given in the upper outer quadrant of the buttock, or better into the ventrogluteal or deltoid site, to avoid the sciatic nerve — injection palsy remains a preventable cause of disability in children
• Sciatica is most often due to a prolapsed intervertebral disc compressing a root (L5 or S1), not to the nerve trunk; the straight leg raising test is positive
• Popliteal aneurysm is the commonest peripheral aneurysm; it may thrombose and threaten the limb, and is often bilateral
• Baker cyst may rupture and mimic a deep vein thrombosis
• Foot drop is treated with an ankle-foot orthosis while the nerve recovers; leprosy remains an important cause in India
• The tibial nerve is rarely injured because it lies deep and protected; when it is, the result is loss of plantar flexion and of sensation over the sole, which is far more disabling for walking than a foot drop
• Deep vein thrombosis of the calf veins is the commonest source of pulmonary embolism, and the popliteal vein is the usual conduit

The Arches of the Foot

Factors Maintaining the Arches

• Ligaments are the chief passive support; muscles are the chief active support
• Tibialis posterior is the most important dynamic supporter of the medial arch — its dysfunction is a common cause of acquired flat foot in adults
• Peroneus longus crosses the sole obliquely and supports the transverse arch, acting like a stirrup with tibialis anterior

Weight Transmission

Muscles of the Sole

• Nerve supply — the medial plantar nerve supplies abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and the first lumbrical; the lateral plantar nerve supplies all the rest
• The medial plantar nerve is the equivalent of the median nerve; the lateral plantar of the ulnar
• In the foot the interossei abduct and adduct about the second toe, not the third

Plantar Aponeurosis

• A thick triangular sheet from the medial tubercle of the calcaneus, fanning out into five slips to the toes
• Functions — protects the sole, supports the longitudinal arches, and acts as a tie beam
• Windlass mechanism — dorsiflexion of the toes at toe-off tightens the aponeurosis, raising the arch and making the foot a rigid lever

Arterial Supply of the Sole

• Posterior tibial artery divides beneath the flexor retinaculum into medial and lateral plantar arteries
• The lateral plantar artery forms the plantar arch, completed by the dorsalis pedis through the first interosseous space
• Dorsalis pedis pulse is felt lateral to the tendon of extensor hallucis longus; posterior tibial pulse midway between the medial malleolus and the heel

Joints of Inversion and Eversion

• The axis of inversion and eversion is oblique, so inversion is accompanied by adduction and plantar flexion (together called supination), and eversion by abduction and dorsiflexion (pronation)
• The spring ligament supports the head of the talus; its stretching is a major factor in acquired flat foot

Applied Aspects

• Flat foot (pes planus) — loss of the medial arch; may be flexible (normal in children under 3, arch reappears on tiptoe) or rigid; caused in adults by tibialis posterior dysfunction
• Pes cavus — an abnormally high arch, often with an underlying neurological cause such as Friedreich ataxia or Charcot–Marie–Tooth disease
• Plantar fasciitis — pain at the medial calcaneal tubercle, worst on the first steps in the morning; a calcaneal spur may be seen but is not the cause
• Club foot (congenital talipes equinovarus) — the foot is plantar flexed, inverted and adducted; treated early by the Ponseti method of serial casting
• Diabetic foot — neuropathy removes protective sensation and ulcers form at the pressure points of the tripod, particularly under the head of the first metatarsal
• Peripheral pulses must be examined in every diabetic and every patient with leg pain — the dorsalis pedis is congenitally absent in about 10% of people, so its absence alone is not diagnostic
• March (stress) fracture of the second or third metatarsal follows unaccustomed walking; the radiograph is normal at first and callus appears later
• Hallux valgus — lateral deviation of the great toe with a bunion over the prominent first metatarsal head, aggravated by narrow footwear
• Ingrowing toenail and interdigital infection are common and become serious in the neuropathic or ischaemic foot
• Sole skin is thick and firmly bound to the aponeurosis, so infection there is intensely painful and swelling appears on the dorsum instead
• Footwear advice is a genuine clinical intervention in diabetes — well-fitting shoes and daily inspection of the feet prevent more amputations than any drug
• The arches are not present at birth; the infant foot is normally flat, and the medial arch develops as the child begins to walk