Proximal Flexor Hallucis Longus Transfer to Peroneus Brevis for Treatment of Peroneal Muscle Paralysis

Abstract

Category: Hindfoot; Ankle; Other Introduction/Purpose: Equinovarus foot deformities typically present with equinus contractures, hindfoot varus, dorsiflexion of the medial midfoot, and adduction deformities of the forefoot. Whether of neurologic or muscular origin, all forms result muscular imbalance. Flexor hallucis longus (FHL) transfer to peroneus brevis (PB) is indicated when both peroneal muscles are in unrepairable condition to restore active eversion. However, in cases of muscle paralysis where the PB is still in continuity, we recommend a novel technique where FHL is tenodesed proximal to the peroneal retinaculum within the leg to avoid the additional morbidity associated with more distal fixation or tenodesis. Methods: Surgical intervention first involved a posterolateral approach to the ankle and an Achilles tendon Z-lengthening to fix her equinus contracture. The ankle and subtalar joint capsules were contracted requiring release. Flexor digitorum longus (FDL) and FHL were tenotomized, which immediately corrected her claw toes. Since the tendon had already been released, we were able to deliver the FHL tendon into the posterolateral leg wound. The peroneal fascia and sheath were opened proximal to the superior peroneal retinaculum to prevent tendon subluxation. PB was identified by confirming that it produced foot eversion and by visualizing the peroneus longus (PL). The tension of PB was confirmed by observing that it did not cause tension at PL insertion on the plantar 1st ray. FHL was then transferred to the PB utilizing a Pulvertaft weave technique with the tendon appropriately tensioned in mid eversion in the middle of the Blix curve (Figure 1). Results: After FHL transfer, the patient was immediately allowed to weight bear as tolerated in a short leg cast. This was due to her deconditioned state to limit atrophy and the effects of prolonged recumbency in this medically fragile young woman. The patient ultimately was casted for 10 weeks total as she was unable to tolerate a CAM boot or other orthotic due to the weight and problems with the fit. At 4 months follow up, her foot is corrected and she is able to stand in a neutral, plantigrade position. Using a new AFO, she can walk without issue. Her foot remains well balanced and plantigrade. Conclusion: This simple FHL transfer technique decreases morbidity since the transfer occurs within the leg, proximal to the superficial peroneal retinaculum (SPR). The transfer pulls on the paralyzed, but intact PB instead of routing the FHL to the 5th metatarsal base or PB stump. This technique is only recommended if PB is intact but non-functional. It should be noted that adequate tensioning is essential for a successful transfer. Benefits of this procedure include no cluttering under the SPR and no risk of scarring that region which can lead to decreased tendon excursion.