Anterior compartment of leg

Question 1

Describe the contents of the anterior extensor compartment including the superior extensor retinaculum.

Answer 1

• This compartment comprises the space between the deep fascia and the interosseous membrane, bounded medially by the extensor surface of the tibia and laterally by the extensor surface of the fibula and the anterior intermuscular septum.
• Its contents are muscles - tibialis anterior, extensor hallucis longus, extensor digitorum longus and peroneus tertius, together with the deep peroneal nerve and anterior tibial vessels.
• In its lower extent, the deep fascia is thickened to form the superior extensor retinaculum, which is attached to the anterior borders of the tibia and fibula.
• Deep to the retinaculum lie the tendons of tibialis anterior, extensor hallicus longus, extensor digitorum longus and peroneus tertius, in that order from medial to lateral, in front of the lower end of the tibia.
  Only the tibialis anterior tendon has a synovial sheath here.
• The anterior tibial vessels and deep peroneal nerve are also deep to the retinaculum, lying between extensor hallicus longus and extensor digitorum longus, with the vessels medial to the nerve.

Question 2

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

Answer 2

• Origin - upper 2/3 of lateral surface of tibia, from the interosseous membrane and from the deep fascia overlying it.
• Insertion - medial and inferior surfaces of the medial cuneiform and the adjacent base of the 1st metatarsal bone
• Nerve supply - deep peroneal and recurrent genicular nerves (L4).
• Action - combined dorsiflexion of the ankle joint and inversion of the foot. Also helps to maintain the medial longitudinal arch of the foot.

Question 3

Extensor hallucis longus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 3

• Origin - middle half of the anterior surface of the fibula and the adjacent interosseous membrane.
• Insertion - passes deep to the extensor retinaculum before inserting at the base of the distal phalanx of the big toe.
• Nerve supply - Deep peroneal nerve (L5).
• Action - extends the metatarsophalangeal and interphalangeal joints of the big toe and assist in the in the inversion of the foot and dorsiflexion of the ankle.

Question 4

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

Answer 4

• Origin - upper ¾ of the anterior surface of the fibula, a small area on the lateral condyle of the tibia and the interosseous membrane.
• Insertion - divides into four slips that insert into the proximal and distal phalanges of the lateral four digits of the foot - digits 2-5.
• Nerve supply - deep peroneal nerve (L5, S1).
• Action - dorsiflex (extend) the lateral four toes. Also assists in dorsiflexion of ankle.

Question 4

Peroneus tertius:
* Origin
* Insertion
* Nerve supply
* Action

Answer 4

• Origin - Distal half or third of the fibula, intermuscular septum.
• Insertion - tendon passes under the extensor retinaculum of the foot with the extensor digitorum longus tendon an inserts on the dorsal surface of the base of the 5th metatarsal.
• Nerve supply - deep peroneal nerve (L5, S1).
• Action - dorsiflex and evert foot.

Question 5

Outline the tibiofibular joints.

Answer 5

• The superior tibiofibular joint is a synovial joint between the lateral tibial condyle and the fibular head. The articuating surfaces are almost flat. The capsule is reinforced by anterior and posterior ligaments. The joint cavity may occasionally communicate posteriorly with the bursa deep to the popliteus tendon and thence with the knee joint.
• The interosseous membrane consists of strong fibres that slope steeply from the tibia down to the fibula, and are continuous distally with the interosseous tibiofibular ligament.
• The inferior tibiofibular joint is a fibrous joint (syndesmosis) between the convex medial surface of the distal end of the fibula and the concave fibular notch of the distal tibia. The bones are held together by anterior and posterior tibiofibular ligaments and are strongly bound by the interosseous tibiofibular ligament, whose fibres occupy the triangular area on each bone at the lower end of the interosseous border.
• Only slight movements occur at the tibiofibular joints, the fibula rotating laterally a little during dorsiflexion at the ankle.