Tarsal tunnel syndrome after total ankle replacement—a report of 3 cases

Tarsal tunnel syndrome is an entrapment neuropathy of the tibial nerve and its branches within the tunnel formed by the flexor retinaculum on the medial side of the ankle. The possible etiologies include trauma, space-occupying lesions, metabolic disorders, and ankle deformities, but in many cases tarsal tunnel syndrome is idiopathic.

We have found some particular situations that tend to lead to tarsal tunnel syndrome, i.e. posterior tibial nerve strain due to anatomical change after TAR surgery. Coronal plane deformity of the ankle joint of over 10 degrees was observed in case 1 (varus deformity) and in case 2 (valgus deformity). These 2 cases suffered from instability for many years prior to TAR, which may have altered the soft tissue including the tarsal tunnel and its contents. The operation may have caused increased tension on the tibial nerve. Postoperative changes in alignment after TAR may cause entrapment of the tibial nerve. Trepman et al. (1999) reported the effects of foot and ankle position on tarsal tunnel compartmental pressure. Bracilovic et al. (2006) used MRI to measure mean tarsal tunnel volume and found reduction of tarsal tunnel volume with inversion or eversion of the ankle, compared to neutral positioning.

Case 3 had a poor clinical outcome after tarsal tunnel release. In this case, the tarsal tunnel syndrome may have occurred due to distraction injury of the tibial nerve that probably took place during correction of the shortening deformity. Alshami et al. (2008) have shown that excess strain on a tibial nerve results in reduced intraneural blood flow and abnormal action potential patterns, which may cause tarsal tunnel syndrome. Even slight compression, possibly caused by edema following a minor strain, could produce local vascular insufficiency and make a nerve lesion more likely.

We suspect that correction of ankle coronal plane deformity of more than 10 degrees and distraction of shortening deformity may cause tarsal tunnel syndrome after TAR. Thus, surgeons should perhaps inform the patients about the small risk of—and the symptoms of—tarsal tunnel syndrome and its operative treatment.