Anatomy chapters
Joints of the lower limb
Understand the stabilising ligaments, articular surfaces and movements that make the lower limb a weight-bearing chain.
- The hip gains stability from a deep socket and strong capsule.
- ACL limits anterior tibial movement; PCL limits posterior tibial movement.
- Ankle dorsiflexion/plantarflexion differs from intertarsal inversion/eversion.
On this page
Overview
Lower-limb joints transmit weight while permitting movement. The hip provides a deep, stable socket; the knee combines flexion with controlled rotation; the ankle and foot adapt the limb to the ground.
Separate the articulation, capsule, ligaments and moving muscles. A joint may look simple in a movement table while depending on several connected structures for stability.
Joint types
| Joint | Type and surfaces | Principal movement | Key stabiliser |
|---|---|---|---|
| Hip | Synovial ball-and-socket; femoral head and lunate acetabular surface | Three-axis movement | Labrum, capsule and surrounding muscles |
| Knee | Modified hinge tibiofemoral articulation plus patellofemoral gliding | Flexion/extension with rotation in flexion | Cruciates, collaterals and quadriceps |
| Proximal tibiofibular | Synovial plane; fibular head and lateral tibial condyle | Small gliding adjustments | Capsule and ligaments |
| Distal tibiofibular | Fibrous syndesmosis | Small mortise adjustments | Tibiofibular/interosseous ligaments |
| Talocrural ankle | Synovial hinge; tibia/fibula and talar trochlea | Dorsiflexion/plantarflexion | Mortise and collateral ligaments |
| Subtalar and transverse tarsal complex | Talus, calcaneum, navicular and cuboid articulations | Combined inversion/eversion | Interosseous and plantar ligaments |
| Metatarsophalangeal | Synovial condyloid; metatarsal heads and proximal phalanges | Flexion/extension, limited spreading | Collateral ligaments and plantar plates |
| Interphalangeal | Synovial hinge | Flexion/extension | Collateral ligaments and plantar restraints |
Snell describes the tibiofemoral articulation as a hinge and the patellofemoral articulation as gliding. “Modified hinge” highlights the additional rotation possible when the knee is flexed.
Hip surfaces, capsule and ligaments
The acetabular labrum deepens the socket. The articular lunate surface is horseshoe-shaped; the central acetabular fossa is non-articular. The transverse acetabular ligament bridges the inferior notch.
The capsule attaches around the acetabular margin. On the femur it reaches the intertrochanteric line anteriorly but only partway along the neck posteriorly. Retinacular vessels ascend along the intracapsular neck towards the head.
| Ligament | Attachments | Main restraint | Clinical note |
|---|---|---|---|
| Iliofemoral | AIIS region to intertrochanteric line, inverted Y | Hyperextension and lateral rotation | Helps maintain upright stance |
| Pubofemoral | Pubic region to inferior capsule/femoral attachment | Excess abduction and extension; Snell also emphasises lateral rotation | Inferomedial support |
| Ischiofemoral | Posterior acetabular/ischial region spiralling to femoral neck/trochanteric region | Extension and medial rotation | Posterior capsular reinforcement |
| Ligament of head | Acetabular notch/transverse ligament to fovea capitis | Limited mechanical restraint; carries a vessel | Its artery is not the principal adult supply |
The anterior hip capsule reaches the intertrochanteric line; posteriorly it stops along the femoral neck.
Iliopsoas flexes; gluteus maximus and hamstrings extend. Gluteus medius/minimus abduct and stabilise the pelvis. Adductors bring the thigh medially; short deep rotators turn it laterally.
The femoral nerve and vessels lie anterior to the hip region, with sciatic posteriorly. Femoral, obturator and sciatic pathways and the nerve to quadratus femoris contribute articular fibres. Circumflex femoral vessels supply the joint and proximal femur.
Knee ligaments
The patellar ligament continues the quadriceps mechanism from patella to tibial tuberosity. The medial collateral ligament joins femur to medial tibia and blends with the medial meniscus.
The lateral collateral joins femur to fibular head and is separated from lateral meniscus by popliteus tendon.
| Ligament | Tibial/femoral relationship | Main action | Test implication |
|---|---|---|---|
| ACL | Anterior tibial intercondylar area to medial surface of lateral femoral condyle | Limits anterior tibial translation and hyperextension | Anterior drawer/Lachman assess this restraint |
| PCL | Posterior tibial intercondylar area to lateral surface of medial femoral condyle | Limits posterior tibial translation | Posterior drawer and sag assess this restraint |
| MCL | Medial femur to medial tibia | Resists valgus stress | Medial opening suggests failure |
| LCL | Lateral femur to fibular head | Resists varus stress | Lateral opening suggests failure |
| Oblique popliteal | Expansion from semimembranosus across posterior capsule | Posterior reinforcement | Connects muscle and capsular stability |
The cruciates lie within the capsule but outside the synovial cavity. Their names follow their tibial attachments, not the femoral condyle to which they attach.
ACL attaches to the lateral femoral condyle; PCL to the medial femoral condyle.
Menisci, bursae and locking
Menisci are fibrocartilaginous pads that improve congruence and distribute load. The medial meniscus is less mobile because of its capsular and MCL attachment. The lateral meniscus is more mobile and more nearly circular.
The suprapatellar pouch communicates with the joint beneath quadriceps. Prepatellar bursa lies between skin and patella; superficial infrapatellar bursa lies between skin and patellar ligament; deep infrapatellar bursa lies between ligament and tibia.
The semimembranosus-related bursa may communicate with the joint. Its expansion can produce a posteromedial cystic swelling.
In terminal weight-bearing extension, the femur rotates medially on the tibia and the knee locks. Popliteus unlocks it by laterally rotating the femur on the fixed tibia. With the foot off the ground, the equivalent unlocking action is medial tibial rotation.
Popliteus unlocks the knee; specify whether femur or tibia is moving.
Knee articular nerves include femoral, obturator, tibial and common fibular branches. Genicular vessels form its periarticular network. The popliteal artery lies directly behind the joint region and is vulnerable during dislocation.
Ankle and tibiofibular stability
The distal tibia and malleoli form a mortise around the talus. The anterior talar trochlea is wider, so dorsiflexion wedges it more securely into the mortise. The syndesmosis preserves the tibia–fibula relationship.
The medial deltoid ligament extends from the medial malleolus to talus, calcaneum and navicular/spring-ligament region. Laterally, anterior talofibular, calcaneofibular and posterior talofibular ligaments connect the lateral malleolus to talus and calcaneum.
Dorsiflexion uses anterior-compartment muscles; plantarflexion chiefly uses the calf with assistance from long flexors and fibularis muscles. Tibial and deep fibular branches supply the ankle; malleolar branches of the leg arteries contribute blood.
Inversion and eversion are chiefly intertarsal movements, not pure hinge movements at the ankle.
Foot joints and arch supports
The subtalar joint links talus and calcaneum. Talonavicular/talocalcaneonavicular and calcaneocuboid articulations form the main transverse tarsal complex. Other intertarsal and tarsometatarsal joints permit smaller adjustments.
The spring ligament spans sustentaculum tali to navicular and supports the talar head. Long and short plantar ligaments support the lateral side; the long plantar reaches beyond cuboid towards metatarsal bases.
The medial longitudinal arch contains calcaneum, talus, navicular, cuneiforms and medial three metatarsals. The lateral arch contains calcaneum, cuboid and lateral two metatarsals. The transverse arch includes cuneiforms, cuboid and metatarsal bases.
Plantar aponeurosis, ligaments and muscle tendons work together. Tibialis posterior and anterior support the medial arch; fibularis longus crosses the sole and helps support the transverse arch. Toe interossei use the second toe as the reference axis.
Clinical relevance
Posterior hip dislocation
How it happens: axial force through a flexed hip drives the head posteriorly, sometimes fracturing the posterior acetabular rim.
What you see: a shortened, adducted, internally rotated limb, with possible sciatic deficit and compromised femoral-head circulation.
Meniscal injury
How it happens: rotation of a loaded knee traps or tears fibrocartilage, especially the less mobile medial meniscus.
What you see: joint-line pain, swelling and sometimes mechanical catching or locking. Not every painful knee that feels stiff is mechanically locked.
Lateral ankle sprain
How it happens: inversion, often in plantarflexion, loads the lateral restraints, particularly anterior talofibular ligament.
What you see: lateral swelling and pain; greater disruption may create instability. Bony tenderness raises a separate fracture concern.
Predict instability from a failed ligament and give the direction relative to the tibia or femur. Distinguish intracapsular from intrasynovial structures, and ankle hinge motion from intertarsal rotation. Link hip capsule attachment and retinacular vessels to intracapsular neck fractures.
Quick revision
- Hip labrum deepens the socket; iliofemoral ligament resists extension.
- ACL restrains anterior tibial movement; PCL restrains posterior movement.
- Medial meniscus is attached to MCL; lateral is separated from LCL.
- Cruciates are intracapsular but extrasynovial.
- Popliteus unlocks the knee.
- Spring ligament supports talar head and medial arch.
Sources: Snell's Clinical Anatomy by Regions, supplied Lower Limb joint and arch sections; current functional terminology and examination conventions where noted. UHS PGET Paper I MBBS TOS. Picture links are visual study resources. Text and tables written independently for The House Job.
FAQ
Does the fibula articulate with the femur at the knee?
No. Its proximal articulation is with the tibia. Its distal end contributes to the ankle mortise.
Which knee meniscus is attached to a collateral ligament?
The medial meniscus is attached to MCL. Popliteus tendon separates the lateral meniscus from LCL.
Why is the ankle more stable in dorsiflexion?
The wider anterior talar trochlea fits tightly within the tibiofibular mortise.
Which structure supports the head of the talus from below?
The plantar calcaneonavicular, or spring, ligament, together with the surrounding capsuloligamentous and tendon supports.