Human Anatomy
Knee Joint, Anterolateral Leg and Dorsum of Foot
Knee joint and anterolateral leg anatomy for MBBS: cruciate and collateral ligaments, menisci, dorsiflexors and foot drop, mapped to NMC codes AN18.1 to AN18.7.
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Knee Joint, Anterolateral Leg and Dorsum of Foot
Knee joint and anterolateral leg anatomy for MBBS: cruciate and collateral ligaments, menisci, dorsiflexors and foot drop, mapped to NMC codes AN18.1 to AN18.7.
This chapter covers the knee joint together with the anterolateral leg and dorsum of the foot. It details the cruciate and collateral ligaments and the menisci, the locking mechanism of the knee, the dorsiflexor and evertor compartments, and the peroneal nerves whose injury causes foot drop.
High-yield: Knee Joint, Anterolateral Leg and Dorsum of Foot
- The knee is a synovial hinge joint that also allows a small amount of rotation, chiefly between the femoral and tibial condyles.
- The anterior cruciate ligament prevents forward sliding of the tibia on the femur and is torn in twisting injuries.
- The posterior cruciate ligament prevents backward sliding of the tibia and is the stronger of the two.
- The medial meniscus is firmly attached to the tibial collateral ligament, so both are often injured together.
- The classic unhappy triad injures the tibial collateral ligament, the medial meniscus and the anterior cruciate ligament.
- The knee locks in full extension by medial rotation of the femur on the tibia, and popliteus releases this lock.
- The tibial collateral ligament resists valgus force and the fibular collateral ligament resists varus force.
- The anterior compartment of the leg contains the dorsiflexors, supplied by the deep peroneal nerve.
- Injury to the deep peroneal or common peroneal nerve causes foot drop with loss of dorsiflexion.
- The lateral compartment contains peroneus longus and brevis, which evert the foot, supplied by the superficial peroneal nerve.
- The dorsalis pedis pulse is felt lateral to the tendon of extensor hallucis longus on the dorsum of the foot.
- The extensor retinacula hold down the dorsiflexor tendons at the ankle.
- The common peroneal nerve is easily injured as it winds around the neck of the fibula.
- The dorsum of the foot is supplied mainly by the superficial peroneal nerve, except the first web space, supplied by the deep peroneal nerve.
Ligaments of the knee
- **Anterior cruciate:** Prevents forward slide of the tibia on the femur; torn in twisting injuries; positive anterior drawer sign.
- **Posterior cruciate:** Prevents backward slide of the tibia; the stronger cruciate; positive posterior drawer sign when torn.
- **Tibial collateral:** Resists valgus force; attached to the medial meniscus, so both are injured together.
- **Fibular collateral:** Resists varus force; cord-like and separate from the lateral meniscus.
NMC competencies in this chapter
- **AN18.1:** Type, articular surfaces and capsule of the knee joint
- **AN18.2:** Ligaments and menisci of the knee joint
- **AN18.3:** Movements and locking mechanism of the knee
- **AN18.4:** Muscles of the anterior compartment of the leg
- **AN18.5:** Muscles of the lateral compartment of the leg
- **AN18.6:** Nerves and vessels of the anterolateral leg and dorsum of foot
- **AN18.7:** Applied anatomy of the knee and foot drop
Frequently Asked Questions
What is the unhappy triad of the knee?
It is a combined injury of the tibial collateral ligament, the medial meniscus and the anterior cruciate ligament, typically from a blow to the outer side of a planted, slightly flexed knee.
How does the knee lock and then release?
In the last part of extension the femur rotates medially on the fixed tibia to lock the knee into a stable position. The popliteus muscle rotates the femur laterally to release this lock before flexion begins.
What causes foot drop?
Injury to the common peroneal nerve, often at the neck of the fibula, or its deep peroneal branch paralyses the dorsiflexors, so the foot drops and the patient develops a high-stepping gait.
Where is the dorsalis pedis pulse felt?
The dorsalis pedis pulse is palpated on the dorsum of the foot, just lateral to the tendon of extensor hallucis longus, between the first and second metatarsal bases.
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