A 36-year-old female patient presented with a 4-year history of right ankle pain. She had significate loss of weight and started physical activity just before the symptoms appeared four years ago. No history of trauma was reported. First diagnosis was synovitis, for which the patient underwent physical therapy with torpid outcome. She experienced paraesthesia along the posterior and medial aspect of the ankle and foot. Symptoms got worse at the end of the day, with cramping episodes in the foot. Physical examination revealed a positive dorsiflexion-eversion test provoking numbness of the foot. Tinel's sign was positive. Ankle range of motion was limited due to pain, scored 8 using the Visual Analog Score (VAS). The patient had a preoperative score of 40 points, according to the American Orthopaedic Foot and Ankle Society (AOFAS). Bilateral electromyography (EMG) was performed, disclosing abnormal adductor hallucis and adductor digiti quinti neurophysiologic parameters in comparison to the asymptomatic side.
Initial plain radiographs showed a considerable (1.8 cm) posterior bone fragment in relation with the talus (Figure 1). CT scan was then performed, which showed the presence of an articulated accessory bone. At this point, talus bipartitus (TB) diagnosis was suspected (Figure 2). MRI disclosed the presence of an inflammatory process, bone fragment covered with cartilage, and what appears to be a degenerative synchondrosis as a consequence of posteromedial impingement (Figure 3).
In this scenario, a surgical procedure was indicated due to increasing symptoms and several conservative treatment trials with no response.
Preoperatory assessment included three-dimensional CT scan images to get full awareness of the bone fragment's specific anatomy. Anatomic relationship between the tibial nerve, posterior tibial artery, flexor hallucis longus, flexor digitorium longus, and tibialis posterior tendon and the bone fragment was assessed with the help of MRI. Though fixation of the accessory bone has been previously reported, in the index case, this was not an option because of its particular shape, with a medial protuberance invading the tarsal tunnel.
Excision of the bone fragment was performed. A medial approach was used. Both tibialis posterior tendon and neurovascular bundle were identified and carefully preserved. The bone fragment was removed and the tunnel was released (Figure 4). Postoperative care included cast immobilization and a 30-day weight-bearing restriction. Postoperative radiographs showed the complete absence of residual bone fragment (Figure 5). Histological findings disclosed mature bone with articular cartilage surface. After 6 months of follow-up, the patient had a VAS score of 2 and an AOFAS score of 87. At a 2-year follow-up, VAS was 1 and AOFAS was 96. Patient had no residual pain and no recurrence of neurological symptoms.