Pretest

Introduction

Tarsal coalition presents as painful hindfoot, with limited motion, usually in valgus position, and often with protective peroneal spasm. Differential diagnosis includes: tarsal coalition, inflammation (osteochondroses, JRA), infection, tumor (osteoid osteoma), and trauma. Tarsal coalition results from the failure of segmentation of primitive mesenchyme. Histological examination reveals fibrous, cartilaginous or osseus tissue. Presentation occurs in adolescence as tarsal bones and coalitions become increasingly ossified. Most common coalitions are the talocalcaneal (medial facet) and calcaneonavicular.

Talocalcaneal (TC) coalition usually presents with constant, activity related pain, a marked reduction in subtalar motion and is tender to palpation over medial subtalar joint. Calcaneonavicular (CN) coalition usually has intermittent symptoms. It may present with a minimal reduction in subtalar motion, but will demonstrate a significant decrease in transverse tarsal motion and tenderness over the sinus tarsi.

Coalitions may present with history of multiple ankle sprains. Acute cases are easy to differentiate from ankle sprain, but may coexist. Late cases should have a complete ankle examination because the patient may have developed laxity secondary to the decreased subtalar motion. Rigid congenital coalitions may result in ball and socket ankle. The pathomechanics of the coalition involve the subtalar motion, which is a combination of rotational and gliding movements. As the coalition ossifies and stiffens, these movements are diminished resulting in adaptive changes at adjacent joints, i.e. talonavicular beaking.

Diagnosis through radiographs may be difficult because coalitions are not easily visualized; adaptive changes are noted, but not degenerative. Oblique x-rays can show CN coalitions. CT scans are the test of choice for TC coalition. It requires fine cuts in frontal plane, showing obliquity of joint. The role of bone scans and MRIs is still not clear. It has been found that in CN cases, 50% are symptomatic and in TC cases, 89% are symptomatic, with 20% being severe.

Treatment

The treatment regimen for the asymptomatic patient is no treatment - leave it alone. For the symptomatic patient, conservative measures such as decreased activity, orthosis, medication and/or casting is recommended. Surgical options depend upon the coalition, adaptive changes in mid and forefoot, and soft tissue contracture. Surgical treatment for CN, coalition, involves excision of coalition with interposition of extensor brevis. This results in relief of pain and return of motion. Surgical intervention for TC, intra-articular coalition, involves resection of the coalition if it involves less than 50% of the subtalar joint. The purpose is to resect and interpose fat and the results are variable. Postoperative management includes initial protection with early motion. Salvage surgery should not be taken to a triple if a lessor fusion is indicated, i.e. subtalar.

Bibliography

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