SLR - March 2019 - Robby Caballes

Talus Bipartitus: A Rare Anatomical Variant Presenting as an Entrapment Neuropathy of the Tibial Nerve Within the Tarsal Tunnel

Reference: Abrego, De Cicco, Gimenez, Marquesini, Sotelano, Carrasco, Santini Araujo. Talus Bipartitus: A Rare Anatomical Variant Presenting as an Entrapment Neuropathy of the Tibial Nerve Within the Tarsal Tunnel. Hindawi Case Reports in Orthopedics. 2018, Sep 12.

Scientific Literature Review

Reviewed By: Robby Caballes, DPM
Residency Program: Bethesda Hospital, Boynton Beach FL

Podiatric Relevance: Tarsal tunnel syndrome (TTS) is defined as an entrapment neuropathy of the tibial nerve within the tarsal tunnel lying deep to the flexor retinaculum. Many factors are thought to contribute to TTS, including biomechanical factors (equinus and flat feet) as well as "space-occupying lesions," such as soft-tissue masses. Clinical symptoms manifest in a positive Tinel's Sign, burning, cramping or pain along the plantar foot. Although rarely reported, suspicion of a rare anomalous bipartite talus bone (Talus Bipartitus/TB) must be considered when there is no alleviation of symptoms. Utilization of multiple diagnostic modalities (CT, MRI and EMG) to identify TTS early on as the primary etiology may support further use of imaging studies in association with physical exam to reach a precise diagnosis.

Methods: This level V case report describes a 36-year-old female patient with a four-year history of right ankle pain presenting with symptoms of a tarsal tunnel syndrome unresolved by multiple conservative treatment modalities. The patient related no trauma upon interview, but experienced paresthesias along the plantar and medial aspect of the foot and ankle. Physical examination findings were positive for tarsal tunnel syndrome and included a positive Tinel's Sign as well as positive dorsiflexion-eversion test eliciting symptoms in the foot. Initial plain radiographs revealed a 1.8 cm posterior bone fragment in relation with the talus. CT imaging showed presence of an articulated accessory bone. MRI showed findings of a degenerative synchondrosis possibly as a sequela of posterior-medial impingement. EMG studies showed abnormal adductor hallucis/digiti quinti neurophysiologic parameters. Surgical excision of the bone fragment was planned through a medial approach to the tarsal tunnel. The fragment was subsequently removed and the tunnel was released. Postoperative care included cast immobilization and a 30-day weightbearing restriction. Pathological analysis had disclosed mature bone with articular cartilage surface.

Results: Preoperatively, the patient's VAS score was 8 with an AOFAS score of 40. Postoperatively at six months, the VAS score improved to 2 with an AOFAS score of 87. At the two-year follow-up, the VAS was 1 and AOFAS was 96. At final follow-up visit, the patient reported no residual pain and no recurrence of the neurological symptoms.

Conclusions: To the authors' knowledge, only one case of TTS secondary to a skeletal anomaly (accessory ossicle) has been reported. This case report illustrates the vital importance of paired clinical examination in addition to imaging modalities/examinations (CT, MRI and EMG) to correctly diagnose and treat TTS. There are various etiologies described in the literature for TTS, including perineural fibrosis, systemic disease, ganglion, neuroma, tendinopathy, lipoma and venous pathology. However, few cases have identified this skeletal anomaly as the source of unresolved TTS. This case report highlights the use of further imaging in addition to clinical exam and provocative testing to make a correct diagnosis of tarsal tunnel syndrome in patients with chronic unresolved pain. A thorough understanding of the foot's anatomy and its skeletal variations may help the treating physician in providing an earlier, more accurate diagnosis of TTS and treatment plan.

Educational Opportunities