Edited by Marcus Coe, MD
Transferring the flexor hallucis longus (FHL) tendon to the peroneus brevis may be indicated when there is loss of function in the two peroneal tendons (peroneus brevis and peroneus longus) resulting in ankle or foot instability or pain. The FHL tendon normally flexes the big toe. The peroneal tendons normally serve to pull the foot out to the side (evert the foot). Dysfunction of the peroneal tendons can occur from severe inflammation and irritation of the peroneal tendons (tendonitis), leading to a rupture of the peroneal tendons over time. Alternatively, paralysis of the peroneal muscles may be an indication for this type of surgery. These indications are quite uncommon, and usually when one of the peroneal tendons is torn or dysfunctional, the other tendon can compensate or be substituted in its place.
The flexor hallucis longus tendon is cut or detached from its insertion. This is often performed through two incisions. The FHL is first identified on the outside (posterolateral) part of the ankle. Through an incision, the muscle belly and then the tendon are identified. It is possible to release the tendon here, although it is often released through a second incision; a small incision on the inside (medial side) of the foot can be used to identify the tendon. The tendon is then cut near the base of the big toe in the sole of the foot. The cut FHL tendon is brought out through the initial incision behind the ankle.
Once the FHL tendon has been harvested, it is re-routed behind the ankle to where the peroneus brevis tendon normally inserts at the base of the small toe on the outside of the foot. The FHL tendon is then sutured into the stump of the peroneus brevis tendon or anchored into bone at the the base of the small toe.
For this procedure to be successful, the FHL tendon needs to heal completely to its newly transferred position. This usually takes a minimum of six weeks, and during this time, immobilization (in a cast or a walking boot) and limited or no weight bearing is required. Following this healing period, the FHL tendon must be retrained to do its new job: everting the foot. This can be challenging as the brain is used to having the muscle flex the great toe and now it is being asked to evert the foot. Often the FHL never fully regains normal function, but can still provide the strength to stabilize the foot and ankle and relieve pain.
Specific complications associated with the flexor hallucis longus transfer to the peroneus brevis may include:
- Great toe weakness. This procedure can result in some increased weakness of great toe flexion. However, this is usually not a clinically significant problem as there is another tendon that flexes the great toe.
- Failure to fully restore function of the peroneal muscles. It is unrealistic to expect to regain full strength in eversion equivalent to normal peroneal function, but the procedure can usually stabilize the ankle and foot adequately even without restoring full strength
- Nerve injuries. There is a major nerve in the back part of the foot called the tibial nerve which supplies the sensation to the sole of the foot as well as to some muscles in the sole of the foot. In rare instances, this can be injured with resulting pain and/or loss of function of this nerve.
Edited August 15, 2015