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AN20.1-10 | General Features, Joints, radiographs & surface marking (Lower Limb) — Summary & Reflection

REFLECT

Imagine you are examining a 65-year-old diabetic patient in an urban medical college OPD. He has numbness in both feet, his dorsalis pedis pulses are absent bilaterally, and he has a painless ulcer on the sole of the right foot. Using your knowledge of lower limb surface anatomy, dermatomes, and vascular supply: (1) Which pulses would you check and where exactly? (2) What dermatomal pattern would sensory loss follow if the tibial nerve is affected? (3) Why is the ulcer painless despite its severity? (4) What is the risk if the posterior tibial pulse is also absent?

KEY TAKEAWAYS

  1. Ankle joint: Synovial hinge; tibiofibular mortise + talar trochlea. Lateral ligament (ATFL-CFL-PTFL) weaker → inversion sprains common. Deltoid ligament strong → avulsion fractures. Movements: plantarflexion/dorsiflexion only (inversion/eversion = subtalar).
  1. Subtalar joint: Primary joint for inversion/eversion. Transverse tarsal (Chopart) = talonavicular + calcaneocuboid joints.
  1. Fascia lata: IT band on lateral thigh. Retinacula at ankle hold tendons. Dermatomes: L4 medial leg/foot; L5 dorsum; S1 lateral/plantar.
  1. Varicose veins: Valve incompetence → reflux → venous hypertension → medial malleolus ulcer. DVT starts in soleal sinuses (Virchow's triad).
  1. Lymphatics: Scrotal → inguinal; testicular → para-aortic. Inguinal nodes drain the entire lower limb + lower abdominal wall + genitalia.
  1. Radiographs: Know normal Shenton's line (hip), joint space (knee), mortise uniformity (ankle 3mm), Bohler's angle (calcaneus 20-40°).
  1. Bony landmarks: Iliac crest = L4; PSIS = S2; fibula head = common peroneal nerve; medial malleolus = 1cm higher than lateral.
  1. Arterial pulses: Femoral (mid-inguinal point), popliteal (deep in fossa), posterior tibial (posterior to medial malleolus), dorsalis pedis (dorsum between 1st/2nd MT, lateral to EHL).
  1. Common peroneal nerve: Winds around fibula neck → most vulnerable major nerve in LL → foot drop.
  1. LL development: Medial rotation 90° in week 5-6 explains extensor = anterior. Club foot from arrested rotation. Testes → para-aortic (not inguinal) because of abdominal origin.