Below-the-Knee Amputation With Targeted Muscle Reinnervation: Operative Technique and Technical Pearls of an Interfascicular Superficial Peroneal Nerve Targeted Muscle Reinnervation

Abstract

INTRODUCTION: Targeted muscle reinnervation (TMR) is a nerve transfer technique by which the severed ends of sensory nerves are transferred to expendable donor motor nerves to minimize pain. TMR has successfully been used to reduce residual limb and phantom limb pain in patients with upper and lower extremity amputations. For patients with below-the-knee amputations (BKAs), the tibial nerve and superficial peroneal nerve (SPN) are the most common sensory nerves addressed with TMR. Although the tibial nerve coaptation is well-protected by the deep posterior musculature, the SPN coaptation is commonly positioned at the weight-bearing portion of the stump without significant soft tissue padding. This study details a novel interfascicular SPN TMR technique performed through a proximal incision at the fibular head. TECHNIQUE: TMR performed primarily at time of BKA is offered to all patients preoperatively to prophylactically reduce pain. TMR is also offered secondarily to patients who develop severe neuroma or phantom limb pain after their amputation. When performed primarily, TMR is performed on the SPN and tibial nerve. When performed secondarily, TMR is performed on the involved nerves based on clinical exam. The SPN TMR is performed through an approach to the common peroneal nerve (CPN) at the fibular head. Accessing the CPN at this level allows for complete decompression of the CPN through the peroneal tunnel. An internal neurolysis is performed, and a nerve stimulator is used to map the motor fascicles to identify an expendable target. The extensor digitorum longus is preferentially selected since it is not critical to tibial padding. The SPN is then translocated from the distal wound into the peroneal tunnel incision and an antegrade nerve transfer is performed to the motor target, typically with a close size match (Video). RESULTS: This technique for primary TMR for BKAs was performed in 109 patients over a 2-year period from January 1, 2018 to December 31, 2019. The SPN was transferred to the extensor digitorum longus 78.5% of the time, peroneus brevis 9.3%, redundant branch of tibialis anterior 6.5%, and peroneus longus 5.6%. The tibial nerve was transferred to the tibialis posterior 66.7% of the time, soleus 10.0%, flexor digitorum longus 8.3%, flexor hallucis longus 8.3%, and unspecified muscle of the deep flexor compartment 6.7%. No primary DPN, sural, or saphenous TMRs were performed. There were no added surgical complications attributable to the TMR portion of the case: no surgical site infections at the fibular head incision or reoperation for seromas or hematomas. If patients developed pain in the saphenous or sural distributions a secondary TMR was performed, but this was only required in 2 patients. CONCLUSIONS: TMR has been demonstrated to greatly improve amputees’ pain and ambulation following a major lower extremity amputation. This article provides insight into the technical pearls of the unique interfascicular SPN TMR, which places the coaptation away from the weight-bearing stump and allows for a close size match. This technique has been used with excellent clinical outcomes and no procedure-specific complications in over 100 patients.