3.9: Posterior Leg

Cutaneous supply (504,2)

Upper half = posterior femoral cutaneous nerve (sacral plexus, S123)

Lower = sural & sural communicating nerves (from tibial and common peroneal)

Medial side = saphenous (from front of femoral nerve in subsartorial canal)

Veins (509)

Short saphenous: drains lateral dorsal venous arch and lateral side of foot

-           lies with sural nerve behind lateral malleolus (medial to the nerve in calf, lateral at the malleolus)

-           passes up in subcut fat to midline of calf ¨ pierces deep fascia ¨ ends in popliteal vein

-           communicates with deep channels to GSV

Fascia

Thickened above heel.  Attached to tibia and fibula across AchillesÕ tendon separated by bursa.

Flexor retinaculum (493) is another thickening; bridges deep flexors and neurovascular bundles

-           extends from tip of medial malleolus to medial process of calcaneus (heads posteroinferior).

Muscles

Superficial and Deep with deep transverse fascia of leg between them.

-           this fascia extends from soleal line and medial margin of tibia to posterior fibula.

Superficial = gastroc, plantaris and soleus; all ¨ tendo-Achilles.

Deep = popliteus, FDL, FHL, tib posterior ¨ under flexor retinaculum into sole of foot.

Nerve

Tibial part of sciatic

Arteries

Posterior tibial and its peroneal branch.

 

Superficial Muscles (481-3)

(1) Gastrocnemius

Arises: two heads each separated from femur by a bursa.

-           lateral ¨ from lateral side of lateral femoral condyle above popliteus

-           medial ¨ from back of medial condyle and shaft of femur

-           ¨ heads converge. Medial head longest. Short saphenous lies in gutter between.

Inserts: aponeurosis between gastroc & soleus forms AchillesÕ ¨ middle 1/3 posterior calcaneus. 

-           a bursa lies here between tendon and calcaneus.

(2) Plantaris

Arises: vestigial muscle from above lateral condyle of femur

Inserts: tendon between medial gastroc & soleus ¨ fuses with medial side of tendo calcaneus. 

-           absent in 10%; used in tendon grafting

(3) Soleus

The equivalent of FDS in the forearm.  Powerful, multipennate.

Arises: upper fibula and soleus line of tibia, with fibrous arch between that bridges over the popliteal vessels and tibial nerve.

-           flat muscle with aponeuroses on each surface; superficial lamella ¨ tendo calcaneus.

-           perforating veins from LSV enter soleus as a rich venous plexus ¨ muscle pump. 

 

Innervation: All 3 are supplied by tibial nerve (S1,2); each gets a branch in the popliteal fossa.

-           lateral branch usually supplies plantaris as well.

-           Soleus gets two branches; one from above pop fossa, other in deep surface in calf ¨ cut both in cases of intractable intermittent claudication.

 

Action: chief plantarflexor; gastroc also flexes knee.  Soleus is antigravity; contracts alternately in standing: obliquity of multipennate fibres mean it is strong but slow cf rapid gastrocnemius.

-           one strolls quietly with soleus, long jumps with gastroc.

Test: plantarflexion against resistance.

Deep Muscles

See written notes for remainder.

 

Popliteus is included in this group.

Tibialis posterior, FHL lie deep & run parallel to destinations.

FDL lies superficial to them; medial in calf ¨ between two at ankle ¨ lateral 4 toes.

Tendons of FHL and FDL insert into bases of TPÕs of hallux and lateral 4 toes respectively.

Tibialis posterior ¨ navicular.

These muscles supplied by tibial nerve. 

Tibioperoneal trunk

Popliteal divides at lower border of popliteus into anterior tibial & tibioperoneal arteries.  Latter 2-3cm long, lies on tibialis posterior. Surrounded by interconnecting veins ¨ dissect with care.  Anterior tibial vein must be formally ligated to expose the trifurcation.  Nerve initially lies posterolateral ¨ crosses to lie medial.   

Posterior tibial artery

Main branch; passes under arch of soleus (which must be divided for access) ¨ runs down between FDL aponeurosis and FHL, deep to soleus ¨ divides at flexor retinaculum into medial & lateral plantar arteries.  Palpable below medial malleolus 2.5cm anterior to medial border of calcaneus. 

Access: at origin, and posterior to medial malleolus.

Branches:

Nutrient to tibia

Muscular to soleus

Peroneal arises 2.5cm below bifurcation ¨ runs in fibrous tunnel.  Gives off muscular branches, ends in interosseous and lateral calcaneal branches.  Can be approached at origin and in middle 1/3 by excising mid-fibula. 

Relations of artery at ankle  (medial ¨ lateral)

Timothy (TP) frightens (FDL) all (artery) very (vein) nervous (tibial nerve) housemaids (FHL)

Tibial nerve

Runs down midline of calf deep to soleus.  Posterior tibial artery initially lies lateral ¨ passes deep to lie medially. 

Nerve to flexor compartment; cutaneous twigs given off to skin of heel.