Lymphatics, Dermatomes and Surface Anatomy

Superficial lymphatics:

• Two main groups, following the two saphenous veins.
• The majority accompany the great saphenous vein → drain into the superficial inguinal nodes (medial group, along the vein's termination).
• A smaller group accompanies the small saphenous vein → drains into the popliteal nodes first, then onward to the deep system.

Deep lymphatics:

• Accompany the deep veins/arteries (anterior tibial, posterior tibial, popliteal, femoral) directly to the popliteal nodes (a few small nodes along the popliteal vessels) and then the deep inguinal nodes.

Superficial inguinal nodes:

• Arranged in a horizontal group (along the inguinal ligament, also receiving lymph from the lower anterior abdominal wall, buttock, external genitalia, and perineum) and a vertical group (along the terminal great saphenous vein, receiving the bulk of lower limb superficial drainage).
• Efferents drain to the deep inguinal nodes and external iliac nodes.

Deep inguinal nodes:

• Small group (1–3 nodes, including the node of Cloquet/Rosenmüller) within the femoral canal, along the femoral vein.
• Receive deep lymphatics of the limb and efferents from the superficial inguinal nodes; drain onward to the external iliac nodes.

Popliteal nodes:

• Small, deep group within the popliteal fossa, along the popliteal vessels.
• Receive the small saphenous vein's superficial lymphatic territory (posterolateral leg/foot) and the deep lymphatics of the leg; drain onward to the deep inguinal nodes.

Drainage pathways (overall):

Foot/leg → superficial (great or small saphenous-associated) or deep lymphatics → [popliteal nodes, for the small saphenous/deep leg territory] → inguinal nodes (superficial and deep) → external iliac nodes → para-aortic nodes.

Note the parallel with the upper limb: great saphenous ≈ basilic vein pathway (via an intermediate node group before the main regional nodes); small saphenous ≈ cephalic vein pathway is not a precise analogy, but both illustrate that lymphatic drainage broadly follows venous drainage territory.

The lower limb dermatomes descend along the front of the limb (L1 at the groin to L5 at the great toe) and ascend back up the back of the limb (S1 at the heel to S2/S3 at the buttock/posterior thigh), reflecting the limb's embryological rotation, mirrored but opposite in direction to the upper limb's spiral.

Bony landmarks:

• ASIS: palpable anterior pelvic landmark; origin of sartorius and inguinal ligament attachment.
• Greater trochanter: lateral hip prominence, palpable; a horizontal line between the two greater trochanters normally passes through the S2 vertebral level (relevant to lumbar puncture landmark estimation, via the intercristal/Tuffier's line at the iliac crests rather than trochanters directly, but both are commonly taught together).
• Ischial tuberosity: deep to gluteus maximus in standing, becomes subcutaneous and weight-bearing in sitting.
• Patella: anterior knee, easily palpable, moves with knee flexion/extension.
• Tibial tuberosity: palpable just below the patella; patellar ligament insertion.
• Head of fibula: palpable posterolateral to the knee, just below the lateral joint line; common fibular nerve passes around its neck just distal to this point.
• Tibial crest (anterior border): subcutaneous the entire length of the shin.
• Medial malleolus: distal tibia, medial ankle prominence.
• Lateral malleolus: distal fibula, lateral ankle prominence, extends more distally than the medial malleolus.
• Calcaneal tuberosity: heel, Achilles tendon insertion.

Muscle and tendon landmarks:

• Achilles (calcaneal) tendon: prominent posterior ankle structure, palpable and visible; common rupture site (see Applied Anatomy).
• Patellar ligament: palpable between patella and tibial tuberosity.
• Hamstring tendons: palpable posterolaterally (biceps femoris, to the fibular head) and posteromedially (semitendinosus, semimembranosus) at the popliteal fossa margins, especially with resisted knee flexion.
• Tibialis anterior tendon: palpable anteromedial ankle with resisted dorsiflexion.
• Extensor tendons: visible on the dorsum of the foot with toe extension.

Vascular landmarks:

• Femoral pulse: at the midinguinal point (midpoint between the ASIS and pubic symphysis), a key landmark for femoral artery access (catheterisation, CPR compressions reference, arterial blood sampling).
• Popliteal pulse: deep in the popliteal fossa, often difficult to palpate given the artery's depth; best felt with the knee slightly flexed.
• Dorsalis pedis pulse: dorsum of the foot, lateral to the extensor hallucis longus tendon, between the 1st and 2nd metatarsal bases.
• Posterior tibial pulse: posterior to the medial malleolus.
• Dorsalis pedis and posterior tibial pulses are the standard sites for assessing distal lower limb perfusion (e.g., in peripheral arterial disease, trauma, or post-vascular procedure monitoring).
• Great and small saphenous veins: visible/palpable along their respective courses, particularly in individuals with varicose veins or on a tourniquet-engorged limb.