The articular involvement, or the joints affected by the tarsal coalition, is likely the most important factor when one is considering the surgical options for the treatment of a tarsal coalition. Tarsal coalitions may be divided into those that are extra-articular (i.e., those occurring outside normal joints) and those that are intra-articular (i.e., those occurring within normal joints). The most common extra-articular tarsal coalition is the calcaneonavicular bar since there is not a normal articulation between the calcaneus and the navicular. Conversely, the most common intra-articular tarsal coalition is the middle facet talocalcaneal coalition since this abnormal union directly disrupts the subtalar joint.
Extra-articular coalitions are generally more responsive to resection because their excision does not destroy or alter the existing tarsal joint articulations. In contrast, intra-articular coalitions are generally less amenable to resection because their excision alters an already abnormal tarsal joint.1
The presence or absence of arthritic or adaptive changes in the joints surrounding a tarsal coalition has a clinically significant impact on the selection of a surgical treatment plan. These changes are believed to result from the restricted motion and altered biomechanics created by the tarsal coalition, and are therefore termed secondary arthritic or adaptive changes.
Many of these changes classically occur in patients with tarsal coalitions. For example, talonavicular joint arthritis is a secondary change, which occasionally occurs with a middle facet talocalcaneal joint coalition. Narrowing of joint spaces, joint lipping or osteophyte formation and adaptive changes in osseous structures and joints are all frequent secondary arthritic or adaptive changes that may be associated with a tarsal coalition. Intuitively, the greater the severity of the secondary arthritic or adaptive changes present with a tarsal coalition, the more difficult the surgical procedure will be for correction of that coalition.
Further, with more secondary arthritic and/or adaptive changes, the tarsal area will be less responsive to simple resection of the tarsal coalition. Secondary adaptive changes, which are deemed non-arthritic, are less problematic and have less of an effect on the foot after surgical resection of the coalition. Resection of a tarsal coalition in the presence of significant secondary arthritic changes could necessitate further biomechanical adjustment in an already mechanically compensated foot. This generally results in further aggravation of any existing symptom complex. Therefore, when severe secondary arthritic or adaptive changes are associated with a tarsal coalition, arthrodesis is usually considered the operation of choice.1
Does Size Matter With Tarsal Coalitions?
Tarsal coalitions have traditionally been classified based upon their tissue composition as follows.
• Synostosis – osseous coalition
• Synchondrosis – cartilaginous coalition
• Syndesmosis – fibrous coalition
This categorization is somewhat antiquated as coalitions are rarely, if ever, entirely cartilaginous or fibrous in nature. Therefore, a tarsal coalition is better termed as either complete (i.e., an entirely osseous coalition) or incomplete (i.e., a fibrocartilaginous coalition). For extra-articular coalitions, such as the calcaneonavicular bar, the tissue composition and size of the coalition seem to have little bearing on the ultimate surgical approach. However, this is not the case for an intra-articular tarsal coalition such as the middle facet talocalcaneal coalition.