Posterior compartment of leg

Question 1

Gastrocnemius:
* Origin
* Insertion
* Nerve supply
* Action

Answer 1

• Origin - lateral head - outer aspect of the lateral condyle of the femur, just superior and posterior the lateral epicondyle.The fabella is an accessory ossicle most always found in the lateral head of the gastrocnemius. Medial head - back of the medial condyle and the popliteal surface of the shaft of the femur.
• Insertion - fuses with the soleus tendon to form the upper part of tendocalcaneus.
  This broad tendon then narrows until it reaches the the calcaneous where it expands again for its insertion on the middle part of the posterior surface of the calcaneus.
• Nerve supply - Tibial nerve (S1, 2).
• Action - plantarflexion of ankle. Knee flexion.

Question 2

Plantaris:
* Origin
* Insertion
* Nerve supply
* Action

Answer 2

• Origin - lower part of the lateral supracondylar line of the femur.
• Insertion - inserts medially, in association with the Achilles tendon on the calcaneus, or independently on calcaneus.
• Nerve supply - Tibial nerve (S1, 2).
• Action - acts with the gastrocnemius but is insignificant as either a flexor of the knee, or a plantar flexor of the ankle.

Question 3

Soleus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 3

• Origin - posterior surface of the head and upper 1/3 of the shaft of the fibula;
  Middle 1/3 of the medial border of the tibia, tendinous arch between tibia and fibula.
• Insertion - posterior surface of the calcaneus via the Achilles tendon.
• Nerve supply - Tibial nerve (S1, 2).
• Action - plantarflexion of foot at ankle.

Question 4

Flexor digitorum longus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 4

• Origin - medial portion of the posterior surface of the tibia, inferior to the soleal line.
• Insertion - on the plantar surface at the base of the distal phalanges of the second, third, fourth and fifth toes.
• Nerve supply - tibial nerve (S1, 2).
• Action - flexes the second to fifth toes first at the distal interphalangeal joint, then the proximal interphalangeal joint and finally the metatarsophalangeal joint. Aids with plantarflexion of the foot at the ankle. Assists in maintaining the medial longitudinal arch of the foot.

Question 5

Flexor hallicus longus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 5

• Origin - lower two-thirds of posterior fibula and interosseous membrane.
• Insertion - plantar surface at the base of the first distal phalanx.
• Nerve supply - tibial nerve (S1, 2).
• Action - flexes all the joints of the great toe as the foot is raised from the ground. Additionally stabilises the first metatarsal head and keeps distal pad of the great toe in contact with ground in toe-off and when on tip-toe.
  Aids in plantarflexion at the ankle joint. Assists in maintaining the medial longitudinal arch of the foot.

Question 6

Tibialis posterior:
* Origin
* Insertion
* Nerve supply
* Action

Answer 6

• Origin - arises from the interosseous membrane and the adjoining surface of tibia/fibula below the origin of soleus.
• Insertion - the major insertion is onto the navicular. Tendinous slips also pass to the sustentaculum tali, all 3 cuneiforms, the cuboid and the 2nd, 3rd and 4th metatarsals.
• Nerve supply - tibial nerve (L4).
• Action - to plantarflex and invert the ankle. It also plays an important role in stabilising the medial longitudinal arch.