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Knee dislocation may be associated with an injury to the common peroneal nerve with a subsequent foot drop. Previous studies have demonstrated good functional results after posterior tibial tendon transfer in patients with foot drop. No studies, to our knowledge, have focused exclusively on knee dislocation as the cause of common peroneal nerve injury leading to foot drop.We determined the percentage of patients developing common peroneal nerve paresis after knee dislocation, the symptom improvement rate in these patients, and patient-reported outcomes (American Orthopaedic Foot and Ankle Society [AOFAS] ankle-hindfoot score), ankle dorsiflexion strength, and ROM in patients with no symptom improvement treated with posterior tibial tendon transfer.Two hundred forty-seven patients with knee dislocation, defined as an injury to both the ACL and PCL with an additional injury to the lateral and/or medial ligaments (Schenck Classification II to IV), were registered in a single institution's database between 1996 and 2011. The database was queried for the frequency of documented injuries to the common peroneal nerve and, among those, the frequency of spontaneous resolution after this injury. Patients demonstrating no active dorsiflexion 12 months after injury generally were offered posterior tibial tendon transfer. Postoperatively, patients were evaluated for AOFAS score, ankle dorsiflexion strength, and ROM.Forty-three patients (17%) had a common peroneal nerve paresis at admission. At 1-year followup, 15 of 43 patients (35%) had experienced symptom improvement. One patient experienced spontaneous improvement later than 1 year after injury. One patient was lost to followup. A below-knee amputation was performed in one patient due to the initial trauma. Seven patients were satisfied with their function using a brace or had medical contraindications to surgical treatment, while four patients refused the proposed operation with a tendon transfer, leaving 14 patients treated with posterior tibial tendon transfer. In the 12 patients available for evaluation, mean AOFAS score was 91 of 100. Mean (± SD) dorsiflexion strength was 118 (± 55) Nm on the operated side and 284 (± 94) Nm on the unaffected side (p < 0.001). Mean ROM was 67° (± 15°) on the operated side and 93° (± 14°) on the unaffected side (p < 0.001).Based on these findings, we recommend posterior tibial tendon transfer for treatment of foot drop that persists at least 1 year after knee dislocation.Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.