Description
Flexor hallucis longus is a powerful muscle located on the posterior aspect of the fibular below the deep fascia of the calf. In its own synovial sheath, the tendon passes downwards, deep to the flexor retinaculum, crossing the posterior ankle joint, lateral to flexor digitorum longus. The tendon wraps around the lower end of the of the tibia, the back of the talus, and the inferior surface of the sustentaculum tali, where its passes through a fibrous, synovial-lined tunnel.[1]
As the tendon enters into the sole of the foot it lies superficial to the spring ligament passing forward deep to the tendon of flexor digitorum longus. It then enters the fibrous sheath of the great toe passing between the two sesamoid bones to insert at the base of the distal phalanx.[1]
Origin
Lower two-thirds of posterior fibula.
Insertion
Plantar surface at the base of the first distal phalanx.
Nerve
Branch of the tibial nerve (root S1 and S2).
Cutaneous supply from root S2.
Artery
Peroneal artery[2]
Function
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.[2]
Clinical relevance
Flexor hallucis longus produces the final thrush from the foot in the toe-off phase of the gait cycle. At this point in the cycle, trcieps surae have already maximally contracted and flexor digitorum longus is completing its contraction. Therefore great toe flexion is the final act before the foot is lifted from the floor before swing phase.
The muscle contributes to maintaining the medial longitudinal arch.
Fractures of the sustentaculum tali can cause entrapment of the flexor hallucis longus or flexor digitorum longus tendons amongst other abnormalities that may indicate reconstructive surgery. Post-operative management includes the use of a lower leg splint for 5-7 days, partial weight-bearing with 20 kg for 6-8 weeks in the patient’s own footwear, early range of motion exercises of the ankle, subtalar and mid-tarsal joints. Outcomes are generally good with those sustaining isolated fractures performing better.[3]
Assessment
Palpation
Palpation is impossible due to the muscles depth and the structures obstruct surface palpation.
Power
Resisted flexion of great toe with the foot in neutral or dorsiflexion.
Length
In supine or seated, with ankle in dorsiflexed position. Stabilise proximal bone of joint to be measured. Extend the joint to be measured through available ROM.[4]
Treatment
Strengthening
A common exercise for foot strength is performed using a towel. Ask the patient to sit and place a towel under their foot, then ask the patient to grip the towel with their great toe thereby moving the towel along the floor.
The muscle can be strengthened by utilising its role in balance. Providing a patient with a suitably challenging balance exercise such as using wobble board makes exercise more functional.
Further in rehabilitation, walking or running on different surfaces such as grass or sand will further challenge the function of flexor digitorum longus.
Stretching
A stretch can be performed by pulling the great toe into a extended position and the ankle into a dorsiflexed position. Similar to strengthening, a towel may be useful if the patient is struggling to reach forward. It can be wrapped around the toes and ball of the foot.
References
- ↑ 1.01.1 Palastanga N, Soames R. Anatomy and Human Movement: Structure and Function. 6th ed. London, United Kingdom: Churchill Livingstone; 2012.
- ↑ 2.02.1 Saladin K. Anatomy & physiology: The Unity of Form and Function. 5th ed. New York: McGraw-Hill; 2010.
- ↑ Dürr C, Zwipp H, Rammelt S. Fractures of the sustentaculum tali. Operative Orthopädie und Traumatologie. 2013 Dec;25(6):569–78.
- ↑ Reese NB, Bandy WD, B WD, Y MM. Joint range of motion and muscle length testing. Philadelphia: Saunders (W.B.) Co; 2002 Jan 15. ISBN: 9780721689425.
