Lower Limb Overview
| Region | Boundaries / Extent |
|---|---|
| Pelvic girdle and hip region | Hip bone (ilium, ischium, pubis) and proximal femur; connects the lower limb to the axial skeleton via the sacroiliac joint and pubic symphysis |
| Gluteal region | Posterior aspect of the hip, between the iliac crest and gluteal fold; houses the gluteal muscles and the sciatic nerve's exit point |
| Thigh (femoral region) | Hip to knee; femur, with anterior, medial, and posterior fascial compartments |
| Knee | Femoral condyles, tibial plateau, and patella; the largest and most complex synovial joint in the body |
| Leg (crural region) | Knee to ankle; tibia and fibula, with anterior, lateral, and posterior fascial compartments |
| Ankle | Distal tibia/fibula and talus; mortise joint between the malleoli and the talar dome |
| Foot | Tarsus, metatarsus, and phalanges; dorsum and sole, weight-bearing and propulsive |
- Pelvic girdle: hip bone (fused ilium, ischium, pubis)
- Thigh: femur, patella (sesamoid within the quadriceps tendon)
- Leg: tibia (medial, weight-bearing), fibula (lateral, non-weight-bearing, muscle attachment and ankle stability)
- Tarsus: 7 tarsal bones (talus, calcaneus, navicular, cuboid, 3 cuneiforms)
- Foot: 5 metatarsals, 14 phalanges (proximal, middle, distal, great toe lacks a middle phalanx, mirroring the thumb)
| Joint | Type | Key Movements |
|---|---|---|
| Sacroiliac | Synovial (plane) with strong ligamentous support | Minimal gliding; primarily weight transmission |
| Pubic symphysis | Secondary cartilaginous (symphysis) | Minimal movement; relaxes in pregnancy |
| Hip | Ball-and-socket synovial | Flexion/extension, abduction/adduction, medial/lateral rotation, circumduction |
| Knee | Modified hinge (synovial, with rotatory component) | Flexion/extension, and rotation when flexed |
| Superior tibiofibular | Plane synovial | Minor gliding |
| Inferior tibiofibular | Fibrous (syndesmosis) | Minimal movement; accommodates talar mortise widening |
| Ankle (talocrural) | Hinge synovial | Dorsiflexion/plantarflexion |
| Subtalar | Plane synovial | Inversion/eversion (with transverse tarsal joint) |
| Transverse tarsal (midtarsal) | Compound (talonavicular + calcaneocuboid) | Inversion/eversion, contributes to foot flexibility/rigidity switch during gait |
| Metatarsophalangeal (MTP) | Condyloid | Flexion/extension, limited abduction/adduction |
| Interphalangeal (PIP, DIP) | Hinge | Flexion/extension only |
- Thigh: anterior (extensor, femoral nerve), medial (adductor, obturator nerve), posterior (flexor/hamstring, sciatic nerve).
- Leg: anterior (dorsiflexor, deep fibular nerve), lateral (evertor, superficial fibular nerve), posterior (plantarflexor, tibial nerve, superficial and deep groups).
- Foot: four plantar layers plus dorsal muscles, supplied by the medial and lateral plantar nerves (plantar) and deep fibular nerve (dorsum).
Fascial compartments are bounded by deep fascia and intermuscular septa, clinically relevant to compartment syndrome, most classically in the anterior leg compartment.
| Nerve | Root Values | Chief Motor Function |
|---|---|---|
| Femoral | L2, L3, L4 | Anterior thigh (hip flexion, knee extension) |
| Obturator | L2, L3, L4 | Medial thigh (hip adduction) |
| Sciatic (tibial + common fibular components) | L4–S3 | Posterior thigh, entire leg and foot |
| Superior gluteal | L4, L5, S1 | Gluteus medius, minimus, tensor fasciae latae |
| Inferior gluteal | L5, S1, S2 | Gluteus maximus |
The sciatic nerve is the largest nerve in the body, splitting into the tibial nerve (posterior compartment of leg) and common fibular nerve (anterior and lateral compartments of leg), typically at or above the popliteal fossa.
External iliac artery → femoral artery → popliteal artery → anterior tibial artery + posterior tibial artery (via the tibiofibular trunk, which also gives the fibular artery) → dorsalis pedis (from anterior tibial) and medial/lateral plantar arteries (from posterior tibial) → plantar arch → digital arteries.
- Named transition points: inguinal ligament (external iliac → femoral), adductor hiatus in adductor magnus (femoral → popliteal), lower border of popliteus (popliteal → anterior tibial + posterior tibial/tibiofibular trunk).
- Anastomotic networks around the hip (trochanteric and cruciate anastomoses), knee (genicular anastomosis), and ankle (malleolar anastomoses).
- Superficial system: dorsal venous arch of foot → great saphenous vein (medial, longest vein in the body, drains into the femoral vein at the saphenofemoral junction) and small saphenous vein (posterolateral, drains into the popliteal vein at the saphenopopliteal junction).
- Deep system: venae comitantes of the anterior tibial, posterior tibial, and fibular arteries → popliteal vein → femoral vein → external iliac vein.
- Perforating veins connect the superficial to the deep system, containing valves that normally direct flow inward (superficial to deep); incompetence contributes to varicose veins and venous insufficiency.
- Superficial lymphatics largely accompany the great saphenous vein → superficial inguinal nodes.
- A smaller group accompanies the small saphenous vein → popliteal nodes → deep lymphatics.
- Deep lymphatics accompany the deep vessels → popliteal nodes → deep inguinal nodes → external iliac nodes.
- All lower limb lymph drains toward the inguinal nodes (superficial and deep) → external iliac nodes → para-aortic nodes.
| Root | Approximate Area |
|---|---|
| L1 | Inguinal region, upper anterior thigh |
| L2 | Anterior and upper lateral thigh |
| L3 | Lower anterior thigh, knee |
| L4 | Medial leg, medial malleolus (down the "inside" line) |
| L5 | Lateral leg, dorsum of foot, great toe |
| S1 | Lateral foot, little toe, posterior calf |
| S2 | Posterior thigh and leg (midline strip) |
| Movement | Root Value |
|---|---|
| Hip flexion | L1, L2, L3 |
| Hip extension | L5, S1 |
| Hip abduction | L4, L5, S1 |
| Knee extension | L3, L4 |
| Knee flexion | L5, S1 |
| Ankle dorsiflexion | L4, L5 |
| Ankle plantarflexion | S1, S2 |
| Great toe extension | L5 |
Anterior superior iliac spine (ASIS), pubic tubercle, greater trochanter, ischial tuberosity, patella, tibial tuberosity, head of fibula, medial and lateral malleoli, Achilles tendon, femoral and popliteal pulses, dorsalis pedis and posterior tibial pulses. Full palpation detail is covered in the Surface Anatomy section.
- Hip: transmits body weight from the trunk to the limb; the gluteal muscles (especially gluteus medius/minimus) stabilise the pelvis in the coronal plane during single-limb stance, failure produces a Trendelenburg gait.
- Knee: alternates between a locked, stable extended position (standing, "screw-home mechanism") and a flexible flexed position (swing phase), unlocked by popliteus.
- Ankle and subtalar joints: dorsiflexion/plantarflexion at the ankle proper; inversion/eversion at the subtalar and transverse tarsal joints, allowing the foot to adapt to uneven ground while remaining a rigid lever for push-off.
- Foot: functions as a shock absorber (flexible, pronated) at heel strike and a rigid lever (supinated, arches locked) at toe-off, mediated by the plantar aponeurosis and the arches of the foot ("windlass mechanism").
- Overall limb design reflects its role in weight-bearing, propulsion, and balance: contrasting with the upper limb's emphasis on mobility and manipulation.
