Excision of a Middle Facet Tarsal Coalition
Authors: Li Shuyuan , Myerson Mark S. 
Published: February 2020

Background:
Middle facet tarsal coalition is one of the commonly seen tarsal coalitions in clinical practice that can cause pain and associated flatfoot deformity. Excision of the coalition is one of the treatment options for symptomatic cases. Although symptoms may subside in children following a period of immobilization, resection should be considered as a treatment alternative for children and adolescents because of the potential for restoration of subtalar joint movement. The indications for excision of the coalition are not consistently reported in the literature, and the procedure is not always easy to perform. In this article, we describe the steps for a successful excision of a middle facet tarsal coalition.

Description:
The incision is marked from 1 cm inferior to the medial malleolus, extending distally to the navicular tuberosity and inferior to the level of the posterior tibial tendon. The coalition is first located by retracting the flexor tendons and the neurovascular bundle. The bone on the surface of the coalition is gradually removed to expose the middle facet. A 2-mm guide pin and a cannulated dilator probe inserted through the sinus tarsi into the tarsal canal that exits anterior to the posterior facet help with identifying the margins of the coalition. The middle facet is then removed either partially or totally, depending on the size, shape, and location of the coalition, until the posterior facet is visualized. Following excision, bone wax is used on the exposed surfaces or fat is inserted to prevent adhesion and recurrent bone formation. If there is an associated flatfoot deformity, additional surgeries, including a medial translational osteotomy or a lateral column lengthening of the calcaneus, a Cotton osteotomy, an arthroereisis, or a calcaneus stop procedure, may be necessary.

Alternatives:
The alternative treatment for managing a middle facet coalition is immobilization of the foot in a boot or cast for 6 to 8 weeks to decrease pain. This will not improve the function of the hindfoot, which remains stiff, but may alleviate pain temporarily. Excision of the coalition in combination with other procedures for correction of the flatfoot is an alternative to an arthrodesis of the subtalar joint and works well in children and adolescents, particularly in those with reasonable subtalar joint flexibility. A triple arthrodesis is rarely performed for an isolated middle facet coalition, even in adults, unless there is peritalar arthritis and more severe abduction of the talonavicular joint with associated stiffness.

Rationale:
The rationale for excision of a middle facet tarsal coalition is to maximize the mobility of the hindfoot, in particular, the subtalar joint. The success of excision of the coalition is associated with the rigidity of the hindfoot and the presence of a flatfoot deformity. The stiffer the hindfoot and the flatter the foot, the less likely is excision of the coalition to be successful. Since the alternative to resection of a middle facet coalition is arthrodesis of the subtalar joint, one must distinguish between feet in which there is mobility, and excision is more likely to be successful, and those that are rigid, for which arthrodesis is preferable. In many feet, however, the size of the coalition is not associated with the flexibility of the hindfoot, and in an extremely rigid hindfoot, we recommend an arthrodesis, even in an adolescent patient. Rigidity increases with increasing age, and it is uncommon to excise the middle facet coalition in adult patients or in a patient in whom subtalar arthritis is evident.