Human Anatomy
Lower Limb Joints and Surface Marking
Lower limb joints for MBBS: ankle joint, popliteal fossa, arches of the foot, and surface marking of vessels and nerves, mapped to NMC codes AN20.1 to AN20.10.
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Lower Limb Joints and Surface Marking
Lower limb joints for MBBS: ankle joint, popliteal fossa, arches of the foot, and surface marking of vessels and nerves, mapped to NMC codes AN20.1 to AN20.10.
This chapter draws together the joints of the lower limb, their stability and movements, and the surface marking of the main vessels and nerves. It covers the ankle joint and its ligaments, the popliteal fossa, the arches of the foot and the clinical anatomy of sprains and the saphenous vein.
High-yield: Lower Limb Joints and Surface Marking
- The ankle is a hinge joint between the lower tibia and fibula above and the talus below.
- The ankle is most stable in dorsiflexion, when the wider front of the talus is gripped in the mortise.
- The medial (deltoid) ligament of the ankle is strong and resists eversion, so it is less often torn.
- The lateral ligament of the ankle is weaker, and the anterior talofibular part is the most commonly sprained.
- Inversion injuries are the commonest ankle sprains and damage the lateral ligament.
- Subtalar and transverse tarsal joints allow inversion and eversion of the foot.
- The popliteal fossa is a diamond-shaped hollow behind the knee bounded by the hamstrings above and the two heads of gastrocnemius below.
- From superficial to deep in the popliteal fossa lie the tibial nerve, the popliteal vein and the popliteal artery.
- The popliteal artery is the deepest structure and is closely applied to the joint capsule, so it is hard to palpate.
- The great saphenous vein runs in front of the medial malleolus, a constant site for venous cut-down.
- The medial longitudinal arch is higher and more important than the lateral longitudinal arch.
- The surface marking of the femoral artery is the upper two-thirds of a line from the mid-inguinal point to the adductor tubercle.
- The sciatic nerve is marked from a point midway between the ischial tuberosity and the greater trochanter down the midline of the thigh.
- The saphenous opening lies about 3 to 4 cm below and lateral to the pubic tubercle.
Popliteal fossa and ankle
- **Popliteal fossa boundaries:** Biceps femoris above and laterally, semimembranosus and semitendinosus above and medially, two heads of gastrocnemius below.
- **Popliteal contents:** Tibial nerve (most superficial), popliteal vein, then popliteal artery (deepest, on the capsule).
- **Ankle stability:** Most stable in dorsiflexion; deltoid ligament resists eversion; lateral ligament weaker and commonly sprained.
- **Great saphenous vein:** In front of the medial malleolus; constant site for venous cut-down.
NMC competencies in this chapter
- **AN20.1:** Ankle joint: type, ligaments and movements
- **AN20.2:** Subtalar and other joints of the foot
- **AN20.3:** Boundaries and contents of the popliteal fossa
- **AN20.4:** Arches of the foot
- **AN20.5:** General features and movements of the lower limb
- **AN20.6:** Venous and lymphatic drainage of the lower limb
- **AN20.7:** Surface marking of vessels and nerves of the lower limb
- **AN20.8:** Radiographs of the lower limb
- **AN20.9:** Dermatomes of the lower limb
- **AN20.10:** Applied anatomy of lower limb joints
Frequently Asked Questions
Why is the ankle most stable in dorsiflexion?
The talus is wider in front than behind. In dorsiflexion the wider anterior part is gripped firmly in the mortise between the malleoli, making the joint most stable in that position.
Which ankle ligament is most often sprained?
The lateral ligament, and specifically its anterior talofibular part, is the most commonly sprained, because most ankle injuries occur through inversion of the foot.
What are the contents of the popliteal fossa from superficial to deep?
From superficial to deep lie the tibial nerve, the popliteal vein and the popliteal artery. The artery is deepest, lying on the joint capsule, which makes its pulse hard to feel.
Where is the great saphenous vein at the ankle?
The great saphenous vein passes in front of the medial malleolus in a constant position, making it a reliable site for a venous cut-down in emergencies.
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