Lateral Plantar Nerve Neuropraxia after FHL Tendoscopy: Case Report and Anatomic Evaluation

Background: FHL tendoscopy has been described as a minimally invasive method used to treat some pathologies or facilitate some surgeries. As we have encountered lateral plantar nerve neurapraxia, we investigated the cause of lateral plantar nerve injury during Zone 2 flexor digitorum longus (FHL) tendoscopy with a cadaveric model. Materials and Methods: Eight feet of 4 embalmed cadavers were used for this study. Posterior ankle endoscopy (Zone 1 FHL tendoscopy) was performed with posteromedial and posterolateral portals. A 4.0-mm metal rod was inserted into the Zone 2 tendon sheath through the posteromedial portal. The distance between the posteromedial portal and the posterior tibial nerve was measured with the ankle in neutral position. Then, the shortest distance between the posterior tibial nerve and the rod was measured with the ankle in three positions: 20 degrees plan-tarflexion, neutral, and 20 degrees dorsiflexion. Result: The average distance between the posterior tibial nerve and the posteromedial portal was 9.3 mm. The average shortest distance between the posterior tibial nerve and the metal rod was 5 mm with the ankle in 20 degrees plantarflexion, 4.5 mm with ankle in neutral position, and 1.1 mm with the ankle in 20 degrees dorsiflexion. In three specimens, the nerve was in direct contact with the rod with the ankle in 20 degrees dorsiflexion. Conclusion: Ankle dorsiflexion brings the posterior tibial nerve in contact with the arthroscope during Zone 2 tendoscopy. Clinical Relevance: In order to avoid potential nerve injury during Zone 2 FHL tendoscopy, ankle dorsiflexion should be avoided.