arises from distal femoral epiphysis, on lateral surface of lateral condyle, by tendon that leaves smooth pit above popliteus
medial head
arises via tendon from smooth shallow pit on medial condyle at distal end of supracondylar ridge, & via fleshy fibres from popliteal surface of femur
medial & lateral heads form medial & lateral borders of distal half of popliteal fossa
They converge to lie side by side, with deep surface covered by aponeurosis which rubs on soleus aponeurosis
lateral head blends with soleal aponeurosis distally, but medial head is separate, & has tendon of plantaris interposed between it & soleus fascia
Insertion:
tendon of insertion rotates through 90°, (DAMP), & inserts into middle third of posterior surface of calcaneus, separated from it by bursa. spiraling of tendon helps in storing energy
Innervation
tibial nerve (S1, S2).
Plantaris
This vestigial muscle is seen in 93%
Origin
above gastrocnemius on lateral supracondylar ridge & its thin, twisted ribbon of tendon runs down between soleus & medial head of gastroc to insert into common tendon
Innervation
tibial nerve (S1, S2)
Soleus
Origin:
Arises from tibia (mostly) & fibula.
fibular origin
upper fourth, including head, then there is fibrous arch which spans tibial NV bundle (much like FDS) to reach tibia
tibial origin
middle third, down to hands breadth below lower end of soleal line
muscle is flat with deep & superficial aponeurosis; between aponeuroses short thick fibres run from anterosuperior down & posteriorly, & tendon of insertion arises from posterior layer
On anterior surface of deep aponeurosis is slender bipennate muscle belly attached to centre of aponeurosis. This belly lies on NV bundle, in groove between FDL medially & FHL laterally
muscle fibres of soleus contain deep venous plexus that can give rise to DVTs
Innervation:
two separate branches of tibial nerve (S1, S2)
Structure of Achilles tendon
mostly type I collagen,
< 4% strain
no damage
4-8% strain
microscopic damage
> 8% strain
macroscopic rupture occurs
Type III collagen is found post rupture, & is not as strong
Blood supply of Achilles tendon
controversial
density of blood vessels is lower in middle 1/3 of tendon
