AP: Lower limb anatomy

• Framework: Overview and Surface Anatomy | The Hip Joint and Pelvis | The Gluteal Region | The Thigh and Femoral Triangle | The Knee | The Leg and Compartments | The Ankle and Foot
• Nerves and vessels: Lumbar and Sacral Plexuses | Sciatic, Tibial and Common Peroneal Nerves | Femoral, Obturator and Other Nerves | Root Lesions — Myotomes and Dermatomes | Arterial Supply and Pulses | Veins and Lymphatics | Gait and Clinically Important Injuries
• Revision: Lower Limb at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🦵 Lower limb anatomy — page 4 of the Anatomy and Physiology chapter. Lower limb anatomy underpins hip fractures, knee injuries, foot drop, sciatica, peripheral arterial disease, varicose veins and DVT — and procedures such as femoral access, IM injections and nerve blocks. Learn the blood supply of the femoral head, the knee ligaments, the leg compartments and the nerves around the fibula and buttock.
Your four questions for every lower limb problem: Is it a root, plexus or peripheral nerve lesion? Which bone or joint injury threatens which nerve or vessel? Is the blood supply adequate (arterial) and is the return adequate (venous)? How does it change the patient's gait?

Overview and Surface Anatomy

• Regions — gluteal region, hip, thigh, knee, leg (knee to ankle), ankle, foot.
• Bones — hip bone (ilium, ischium, pubis — fuse at the acetabulum), femur (the longest bone), patella (largest sesamoid), tibia (weight-bearing, medial), fibula (lateral — muscle attachment, little weight), 7 tarsals, 5 metatarsals, 14 phalanges.
• Compartments:
  • Thigh — anterior (extensors of the knee — femoral nerve), medial (adductors — obturator nerve), posterior (hamstrings — sciatic nerve).
  • Leg — anterior (dorsiflexors — deep peroneal), lateral (evertors — superficial peroneal), posterior superficial and deep (plantarflexors — tibial).
• Surface landmarks:
  • Anterior superior iliac spine (ASIS), iliac crest (highest point at L4 — lumbar puncture), pubic tubercle, ischial tuberosity, greater trochanter.
  • Inguinal ligament — ASIS to pubic tubercle.
  • Mid-inguinal point (halfway between ASIS and pubic symphysis) — femoral artery; the midpoint of the inguinal ligament (halfway between ASIS and pubic tubercle) — deep inguinal ring.
  • Head of the fibula — the common peroneal nerve winds around its neck.
  • Medial malleolus (tibia) and lateral malleolus (fibula — lower and more posterior).
• Safe IM injection — upper outer quadrant of the buttock (or ventrogluteal site / vastus lateralis) — avoids the sciatic nerve.

The Hip Joint and Pelvis

• Hip joint — ball-and-socket synovial joint between the femoral head and acetabulum (deepened by the labrum); very stable — strong ligaments (iliofemoral — the strongest ligament in the body, pubofemoral, ischiofemoral) and deep socket.
• Blood supply of the femoral head:
  • Mainly the medial circumflex femoral artery (from the profunda femoris) — retinacular vessels run up the femoral neck within the capsule.
  • Lateral circumflex femoral artery; the artery of ligamentum teres (small in adults).
  • Intracapsular (femoral neck) fractures disrupt the retinacular vessels → avascular necrosis and non-union — displaced fractures usually need hemiarthroplasty or total hip replacement; extracapsular (intertrochanteric) fractures keep the blood supply — fixation with a dynamic hip screw or nail.
• Hip fracture signs — shortened and externally rotated leg; pain on movement; inability to weight-bear.
• Hip dislocation — posterior (90% — dashboard injury, or after hip replacement) — leg shortened, flexed, adducted and internally rotated; sciatic nerve at risk; reduce urgently (AVN).
• Hip movements and muscles:
  • Flexion — iliopsoas (femoral nerve and L1–3), rectus femoris, sartorius.
  • Extension — gluteus maximus (inferior gluteal nerve), hamstrings.
  • Abduction — gluteus medius and minimus (superior gluteal nerve).
  • Adduction — adductor longus, brevis and magnus, gracilis (obturator nerve).
• Pelvis — a ring formed by the two hip bones and the sacrum (sacroiliac joints and pubic symphysis); pelvic ring fractures in major trauma can cause life-threatening haemorrhage (venous plexus) — pelvic binder; pubic rami fractures in older people after falls (fragility).
• Hip conditions by age — DDH (infants), transient synovitis and Perthes' (children), SCFE (adolescents), osteoarthritis and fracture (older adults); hip pain may refer to the knee (obturator nerve).

The Gluteal Region

• Muscles:
  • Gluteus maximus — hip extension (climbing stairs, rising from sitting) — inferior gluteal nerve (L5–S2).
  • Gluteus medius and minimus — hip abduction — stabilise the pelvis when standing on one leg — superior gluteal nerve (L4–S1).
  • Piriformis and the short lateral rotators (obturator internus, gemelli, quadratus femoris).
• Trendelenburg sign — standing on the affected leg, the pelvis drops on the opposite (unsupported) side — weak hip abductors (superior gluteal nerve injury, hip OA, DDH, after hip surgery, L5 radiculopathy) → Trendelenburg gait (waddling if bilateral).
• Greater sciatic foramen — transmits structures from the pelvis to the buttock; piriformis passes through it:
  • Above piriformis — superior gluteal nerve and vessels.
  • Below piriformis — sciatic nerve, inferior gluteal nerve and vessels, pudendal nerve, posterior cutaneous nerve of the thigh.
• Sciatic nerve in the buttock — runs through the lower inner quadrant, midway between the greater trochanter and ischial tuberosity — at risk from misplaced injections, posterior hip dislocation and hip surgery.
• Piriformis syndrome — buttock pain and sciatica from compression by piriformis (diagnosis of exclusion).
• Greater trochanteric pain syndrome (trochanteric bursitis/gluteal tendinopathy) — lateral hip pain, tender greater trochanter, pain lying on that side.
• Pudendal nerve (S2–4) — perineal sensation and external sphincters — pudendal block in childbirth (ischial spine).

The Thigh and Femoral Triangle

• Anterior compartment — quadriceps femoris (rectus femoris, vastus lateralis, medialis, intermedius) → patellar tendon → tibial tuberosity — knee extension (rectus femoris also flexes the hip); sartorius (longest muscle — "tailor's" position); iliopsoas — all femoral nerve (L2–4).
• Medial compartment — adductors (longus, brevis, magnus), gracilis, pectineus — obturator nerve (L2–4); adductor strain in sport.
• Posterior compartment — hamstrings (biceps femoris, semitendinosus, semimembranosus) — knee flexion and hip extension — sciatic nerve (tibial part, except the short head of biceps — common peroneal); hamstring tears in sprinters.
• Femoral triangle:
  • Boundaries — inguinal ligament (superior), sartorius (lateral), adductor longus (medial).
  • Contents (lateral to medial) — "NAVY" — femoral Nerve, Artery, Vein, (empty space — femoral canal containing lymphatics — Cloquet's node), Y-fronts (midline).
  • The femoral artery, vein and canal lie in the femoral sheath; the nerve lies outside it.
• Clinical uses — femoral arterial puncture and access (angiography, ECMO), femoral venous lines (vein medial to the pulse), femoral nerve block (lateral to the artery).
• Femoral hernia — through the femoral canal, below and lateral to the pubic tubercle; narrow neck → high risk of strangulation; more common in women (inguinal hernias are still commoner overall).
• Adductor (subsartorial/Hunter's) canal — femoral artery and vein, saphenous nerve and nerve to vastus medialis → artery passes through the adductor hiatus to become the popliteal artery; adductor canal block for knee surgery.
• Femoral shaft fracture — high-energy; can lose 1–1.5 L of blood into the thigh; traction splint; fat embolism risk.

The Knee

• Knee joint — modified hinge joint (femur, tibia and patella); the largest synovial joint; flexion, extension and a little rotation ("screw-home" mechanism locks the knee in full extension — popliteus unlocks it).
• Stabilising structures:

  Structure	Function	Injury and test
  Anterior cruciate ligament (ACL)	Prevents anterior tibial translation	Twisting injury with a "pop", rapid swelling (haemarthrosis), instability — Lachman's test (most sensitive), anterior drawer
  Posterior cruciate ligament (PCL)	Prevents posterior tibial translation	Dashboard injury, fall on flexed knee — posterior drawer, posterior sag
  Medial collateral ligament (MCL)	Resists valgus stress	Blow to the lateral knee — valgus stress test; attached to the medial meniscus
  Lateral collateral ligament (LCL)	Resists varus stress	Varus stress test; may injure the common peroneal nerve
  Menisci (fibrocartilage)	Load distribution, stability	Twisting on a flexed knee — joint line pain, delayed swelling, locking (bucket-handle tear); McMurray's test; medial tears more common

• "Unhappy triad" — ACL, MCL and medial meniscus injury together (lateral blow to a planted knee).
• Acute haemarthrosis (swelling within 2 hours) — ACL tear, fracture (lipohaemarthrosis), patellar dislocation; slower swelling (hours to a day) suggests a meniscal tear.
• Extensor mechanism — quadriceps tendon, patella, patellar tendon — rupture or patellar fracture → can't straight-leg raise.
• Bursae — prepatellar ("housemaid's knee" — kneeling), infrapatellar ("clergyman's knee"); Baker's (popliteal) cyst — posterior knee; rupture mimics DVT.
• Popliteal fossa — diamond-shaped; contents (superficial to deep) — tibial nerve, popliteal vein, popliteal artery (deepest); popliteal artery aneurysm (pulsatile mass — often bilateral, with AAA); posterior knee dislocation can tear the popliteal artery (check ABPI).
• Ottawa knee rules — X-ray if age 55 or more, isolated patellar tenderness, fibular head tenderness, can't flex to 90°, or can't weight-bear 4 steps.

The Leg and Compartments

• Four compartments (enclosed by tight fascia — compartment syndrome risk):

  Compartment	Muscles	Action	Nerve and artery
  Anterior	Tibialis anterior, extensor hallucis longus, extensor digitorum longus	Dorsiflexion, toe extension, inversion (TA)	Deep peroneal; anterior tibial artery
  Lateral	Peroneus (fibularis) longus and brevis	Eversion	Superficial peroneal; peroneal artery branches
  Superficial posterior	Gastrocnemius, soleus (→ Achilles tendon), plantaris	Plantarflexion	Tibial
  Deep posterior	Tibialis posterior, flexor digitorum longus, flexor hallucis longus	Inversion, toe flexion, plantarflexion	Tibial; posterior tibial artery

• Compartment syndrome — raised pressure within a compartment → ischaemia of muscle and nerve:
  • Causes — tibial fractures (commonest), crush injury, tight casts, reperfusion after vascular surgery, burns, prolonged immobilisation (long lie), IV drug injection.
  • Features — pain out of proportion to the injury, pain on passive stretch of the muscles (earliest sign), tense swelling, paraesthesia (first web space numbness — deep peroneal nerve in anterior compartment syndrome); pulses are usually present — pulselessness is very late.
  • Management — remove dressings and split casts to skin, limb at heart level, measure compartment pressures if unclear (delta pressure — diastolic BP minus compartment pressure — under 30 mmHg), urgent fasciotomy of all four compartments.
• Achilles tendon rupture — sudden pain "like being kicked" during sport, weak plantarflexion, palpable gap — Simmonds' (Thompson's) test (squeezing the calf doesn't plantarflex the foot); risk with fluoroquinolones and steroids.
• Tibial fractures — the tibia is subcutaneous anteromedially — open fractures are common; poor blood supply to the distal third (delayed union).
• Shin splints (medial tibial stress syndrome) and stress fractures in runners and military recruits.

The Ankle and Foot

• Ankle (talocrural) joint — hinge between the tibia, fibula and talus (mortise) — dorsiflexion and plantarflexion; most stable in dorsiflexion.
• Subtalar and midtarsal joints — inversion and eversion.
• Ligaments:
  • Lateral — anterior talofibular (ATFL — the most commonly sprained ligament — inversion injury), calcaneofibular, posterior talofibular.
  • Medial — deltoid ligament (strong — avulses the medial malleolus rather than tearing).
  • Syndesmosis — links the distal tibia and fibula (high ankle sprain; Weber C fractures).
• Ottawa ankle rules — X-ray if bone tenderness at the posterior edge or tip of either malleolus (distal 6 cm) or unable to weight-bear 4 steps; foot X-ray if tenderness at the base of the 5th metatarsal or navicular.
• Weber classification (lateral malleolus fractures — relative to the syndesmosis) — A (below — stable), B (at the level — may be unstable), C (above — unstable, syndesmosis torn — surgery); Maisonneuve — proximal fibular fracture with ankle syndesmosis injury.
• Tarsal tunnel (behind the medial malleolus) — contents from front to back: Tibialis posterior, flexor Digitorum longus, posterior tibial Artery (and veins), tibial Nerve, flexor Hallucis longus — "Tom, Dick And Nervous Harry"; posterior tibial pulse midway between the medial malleolus and the heel; tarsal tunnel syndrome (tibial nerve compression).
• Arches of the foot — medial longitudinal (tibialis posterior — tibialis posterior dysfunction → acquired flat foot), lateral longitudinal, transverse.
• Foot conditions — plantar fasciitis (heel pain worse with first steps), Morton's neuroma (between 3rd and 4th metatarsal heads), hallux valgus (bunion), gout (1st MTP), Charcot foot (neuropathic — diabetes), 5th metatarsal base fracture (peroneus brevis avulsion) vs Jones fracture (poor healing), calcaneal fractures (fall from height — check spine).
• Diabetic foot — neuropathy (10 g monofilament), ischaemia and infection — daily checks; urgent referral for ulcers or a hot, swollen foot.

Lumbar and Sacral Plexuses

• Lumbar plexus (L1–4) — forms within psoas major:
  • Iliohypogastric and ilioinguinal (L1) — lower abdominal wall, groin, scrotum or labia (injury in hernia repair — groin numbness and pain).
  • Genitofemoral (L1–2) — cremaster muscle (cremasteric reflex) and skin of the upper thigh and scrotum.
  • Lateral cutaneous nerve of the thigh (L2–3) — skin of the lateral thigh — meralgia paraesthetica (compressed under the inguinal ligament near the ASIS — obesity, tight belts, pregnancy).
  • Femoral nerve (L2–4) — posterior divisions.
  • Obturator nerve (L2–4) — anterior divisions.
• Sacral plexus (L4–S4) — on the posterior pelvic wall (lumbosacral trunk L4–5 joins S1–4):
  • Superior gluteal (L4–S1) and inferior gluteal (L5–S2) nerves.
  • Sciatic nerve (L4–S3) — the largest nerve in the body.
  • Posterior cutaneous nerve of the thigh (S1–3).
  • Pudendal nerve (S2–4) — "S2, 3, 4 keeps the penis off the floor" — and continence.
  • Pelvic splanchnic nerves (S2–4 — parasympathetic to the bladder, rectum and genitals).
• Lumbosacral plexopathy — diabetic amyotrophy (painful proximal weakness and wasting in the thigh — older people with type 2 diabetes), pelvic tumours, retroperitoneal haematoma (anticoagulants — femoral neuropathy), radiotherapy, obstetric injury.
• Psoas abscess — fever, back or groin pain, hip held flexed (pain on extension — psoas sign); TB or Staph. aureus.

Sciatic, Tibial and Common Peroneal Nerves

• Sciatic nerve (L4–S3):
  • Leaves the pelvis through the greater sciatic foramen below piriformis → buttock → posterior thigh (supplies hamstrings) → divides (usually above the knee) into the tibial and common peroneal nerves.
  • Complete lesion — weak knee flexion and all muscles below the knee (flail foot); sensory loss below the knee except the medial leg (saphenous); absent ankle jerk.
  • Causes — posterior hip dislocation, hip replacement, misplaced IM injection, pelvic fractures, tumours.
• Common peroneal (fibular) nerve (L4–S2):
  • Winds around the neck of the fibula (superficial — very vulnerable) → divides into deep peroneal (anterior compartment — dorsiflexion; sensation to the first web space) and superficial peroneal (lateral compartment — eversion; sensation to the dorsum of the foot).
  • Lesion — foot drop (weak dorsiflexion and eversion; inversion preserved — tibialis posterior is tibial nerve), numb dorsum of foot, high-stepping gait; ankle jerk normal.
  • Causes — fibular neck fracture, tight plaster casts, prolonged leg crossing, squatting, weight loss, lithotomy position, kneeling, knee dislocation.
• Tibial nerve (L4–S3):
  • Through the popliteal fossa → deep posterior compartment → behind the medial malleolus (tarsal tunnel) → medial and lateral plantar nerves (sole).
  • Supplies — calf muscles (plantarflexion, inversion via tibialis posterior, toe flexion), intrinsic muscles of the sole; sensation of the sole.
  • Lesion — weak plantarflexion and inversion (can't stand on tiptoe), numb sole, absent ankle jerk.
• Sural nerve (tibial and common peroneal branches) — lateral foot and ankle; used for nerve biopsy and grafts.
• Foot drop — differential:

  Lesion	Weakness	Other clues
  Common peroneal nerve	Dorsiflexion, eversion; inversion normal	Dorsum of foot numb; reflexes normal
  L5 radiculopathy	Dorsiflexion, eversion and inversion, hip abduction	Back pain, sciatica, L5 dermatome
  Sciatic nerve	All below the knee plus hamstrings	Absent ankle jerk
  Upper motor neurone	Pyramidal pattern	Brisk reflexes, extensor plantar (stroke, MS)
  Peripheral neuropathy / MND	Bilateral, symmetrical or patchy	Glove and stocking loss; fasciculations

Femoral, Obturator and Other Nerves

• Femoral nerve (L2–4):
  • Forms in psoas → under the inguinal ligament (lateral to the artery) → femoral triangle.
  • Supplies — quadriceps (knee extension), iliacus, sartorius, pectineus; sensation of the anterior thigh and, via the saphenous nerve, the medial leg and medial foot (runs with the great saphenous vein — injured in varicose vein surgery and vein harvest).
  • Lesion — weak knee extension (knee gives way, difficulty climbing stairs), absent knee jerk, numb anterior thigh and medial leg.
  • Causes — retroperitoneal or iliacus haematoma (anticoagulation, haemophilia), femoral catheterisation, hip surgery, pelvic surgery (retractors), diabetic amyotrophy.
  • Femoral nerve vs L3–4 radiculopathy — L4 also weakens hip adduction (obturator) and tibialis anterior.
• Obturator nerve (L2–4):
  • Through the obturator foramen (canal) → medial thigh.
  • Supplies — adductors; small area of skin on the medial thigh; branches to the hip and knee (hip pain referred to the knee).
  • Lesion — weak adduction (leg swings outwards — circumduction); causes — pelvic surgery, obstetric injury, obturator hernia (elderly thin women — Howship–Romberg sign — medial thigh pain).
• Lateral cutaneous nerve of the thigh — meralgia paraesthetica — burning numbness of the lateral thigh, purely sensory; weight loss, loosen belts.
• Superior gluteal nerve — Trendelenburg gait; inferior gluteal — weak hip extension (difficulty rising from a chair or climbing stairs).
• Saphenous nerve block (adductor canal) and femoral and fascia iliaca blocks — knee and hip surgery and hip fractures.

Root Lesions — Myotomes and Dermatomes

• Lumbar disc prolapse — usually L4/5 (compresses L5) or L5/S1 (compresses S1) — posterolateral prolapse compresses the traversing root (the lower one); far-lateral prolapse compresses the exiting root.
• Sciatica — leg pain worse than back pain, below the knee, dermatomal; straight leg raise positive (L5, S1); femoral stretch test (L2–4).
• Cauda equina syndrome — compression of the lumbosacral roots below L1/2 (central disc, tumour, abscess, haematoma) — bilateral sciatica, saddle anaesthesia, bladder dysfunction (retention or reduced sensation), bowel dysfunction, sexual dysfunction, reduced anal tone — emergency MRI and decompression.
• Spinal cord ends at L1/2 in adults (conus medullaris) — LP below L3; lesions above cause UMN signs, below LMN signs (cauda equina); conus lesions — mixed signs, early sphincter problems.
• Spinal stenosis — neurogenic claudication (leg pain on walking, relieved by sitting or bending forward — "shopping trolley sign"; pulses normal) vs vascular claudication (relieved by standing still; pulses reduced).

⚠️ Safety Pearl: Back pain with bilateral leg symptoms, saddle numbness or any new bladder or bowel disturbance is cauda equina syndrome until an urgent MRI proves otherwise. Waiting for retention to develop means waiting for permanent damage.

Arterial Supply and Pulses

• Course — abdominal aorta (bifurcates at L4) → common iliac → external iliac (internal iliac supplies the pelvis and buttock) → femoral artery (under the inguinal ligament at the mid-inguinal point) → gives off the profunda femoris (deep thigh; circumflex femoral arteries) → superficial femoral artery (adductor canal — commonest site of atherosclerotic occlusion) → popliteal artery → divides below the knee into the anterior tibial (→ dorsalis pedis) and the tibioperoneal trunk (→ posterior tibial and peroneal arteries).
• Pulses:
  • Femoral — mid-inguinal point.
  • Popliteal — deep in the fossa — knee slightly flexed, press with fingertips of both hands (easily felt — consider aneurysm).
  • Posterior tibial — behind the medial malleolus.
  • Dorsalis pedis — lateral to extensor hallucis longus on the dorsum of the foot (absent in about 10% of healthy people).
• Peripheral arterial disease:
  • Intermittent claudication — calf pain on walking relieved by rest (superficial femoral disease); buttock and thigh claudication with aorto-iliac disease (Leriche syndrome — with erectile dysfunction).
  • Critical (chronic limb-threatening) ischaemia — rest pain (worse at night, relieved by hanging the leg down), ulcers, gangrene.
  • ABPI (ankle–brachial pressure index) — normal 0.9–1.3; claudication about 0.5–0.9; critical ischaemia under 0.5; falsely high (over 1.3) with calcified arteries (diabetes, CKD); Buerger's test (pallor on elevation, rubor on dependency).
• Acute limb ischaemia — "6 Ps" — Pain, Pallor, Pulseless, Perishingly cold, Paraesthesia, Paralysis (late — irreversible) — embolism (AF) or thrombosis — heparin and urgent vascular surgery.
• Popliteal artery — at risk in knee dislocation and supracondylar femoral fractures.

Veins and Lymphatics

• Superficial veins:
  • Great (long) saphenous vein — starts anterior to the medial malleolus (cutdown site) → up the medial leg and thigh (with the saphenous nerve) → joins the femoral vein at the saphenofemoral junction (about 3–4 cm below and lateral to the pubic tubercle); used for coronary bypass grafts.
  • Small (short) saphenous vein — behind the lateral malleolus → up the back of the calf (with the sural nerve) → popliteal vein (saphenopopliteal junction).
• Deep veins — accompany the arteries (venae comitantes below the knee) → popliteal → femoral → external iliac; soleal and gastrocnemius venous sinuses (where DVT often starts).
• Perforating veins — connect superficial to deep, with one-way valves (blood flows superficial → deep).
• Calf muscle pump — calf contraction squeezes deep veins; valves stop backflow — fails with immobility (DVT) and with valve damage.
• Chronic venous disease:
  • Varicose veins — incompetent valves (often at the saphenofemoral junction) — duplex ultrasound; endovenous ablation.
  • Venous insufficiency — oedema, haemosiderin staining, lipodermatosclerosis ("inverted champagne bottle"), venous eczema, venous ulcers (gaiter area — medial malleolus — compression bandaging after checking ABPI).
• Deep vein thrombosis — Virchow's triad (stasis, endothelial injury, hypercoagulability) — Wells score, D-dimer, proximal leg vein ultrasound; May–Thurner syndrome (left common iliac vein compressed by the right common iliac artery — left-sided DVT).
• Lymphatics — superficial vessels follow the great saphenous vein → superficial inguinal nodes (also drain the lower abdominal wall below the umbilicus, buttock, perineum, external genitalia, anal canal below the pectinate line, and lower vagina) → deep inguinal → external iliac nodes; testis drains to para-aortic nodes (not inguinal); popliteal nodes drain the lateral foot (small saphenous territory).

Gait and Clinically Important Injuries

• Gait cycle — stance phase (about 60% — heel strike to toe-off) and swing phase (40%).
• Abnormal gaits:

  Gait	Features	Causes
  Antalgic	Short stance on the painful leg	Pain — arthritis, fracture
  Trendelenburg	Pelvis drops on the swing side; trunk lurches	Weak hip abductors — hip OA, superior gluteal nerve, L5
  High-stepping	Lifts the knee high; foot slaps	Foot drop — common peroneal, L5, neuropathy
  Spastic / hemiplegic	Stiff leg circumducts	Stroke, MS
  Scissoring	Legs cross	Cerebral palsy, cord lesions
  Parkinsonian	Shuffling, reduced arm swing, festination, turning en bloc	Parkinson's
  Ataxic (cerebellar)	Broad-based, unsteady; can't tandem walk	Cerebellar disease, alcohol
  Sensory ataxic	Stamping; worse in the dark; Romberg positive	Dorsal column loss, neuropathy
  Waddling	Bilateral Trendelenburg	Proximal myopathy, bilateral DDH, pregnancy
  Apraxic ("magnetic")	Feet stuck to the floor	Normal pressure hydrocephalus, vascular dementia

• Key injuries and what they threaten:
  • Intracapsular neck of femur fracture — femoral head blood supply (AVN).
  • Posterior hip dislocation — sciatic nerve; femoral head blood supply.
  • Pelvic ring fracture — internal iliac vessels and venous plexus (haemorrhage), bladder and urethra.
  • Femoral shaft fracture — blood loss, fat embolism.
  • Knee dislocation — popliteal artery and common peroneal nerve.
  • Fibular neck fracture — common peroneal nerve.
  • Tibial fracture — compartment syndrome.
  • Calcaneal fracture (fall from height) — associated spinal fractures.