Instability of the first metatarsal-cuneiform joint: diagnosis and discussion of an independent pain generator in the foot.

BACKGROUND: First metatarsocuneiform (MC) instability is recognized as a pathologic contributor to hallux valgus. There are no studies identifying the first MC joint as an independent pain generator in the foot that may require surgical arthrodesis for its management. MATERIALS AND METHODS: The authors reviewed the records of all patients with this newly described pathology in the first MC joint. There were 61 patients with 85 feet who underwent a fluoroscopically guided local anesthetic injection into the first metatarsocuneiform joint to assess pain relief. Patient's complaints, physical exam findings, treatment decisions, patient characteristics, and radiographic findings were evaluated. RESULTS: Seventy-nine percent of patients (67/85) injected had relief of their symptoms. Eight or these 67 patients were eventually treated with first MC arthrodesis with complete relief of symptoms. The average time from onset of symptoms to presentation was 21 (range, 1 to 72) months. Eighty-five percent of feet (72/85) had multiple previous diagnoses. Radiographic plantar widening of the first M-C joint on weightbearing views was inconsistent with pathology. CONCLUSION: The first MC joint is an independent pain generator in the foot that can have variable presentations. Radiographic data can often be helpful, but clinical exam findings are paramount in the diagnosis. Fluoroscopically-guided long acting local anesthetic injections of this joint are helpful in the diagnosis, especially in the patient with multiple possible pain generators in the foot and ankle. Failure to recognize the first MC joint as a source of pain may lead to delay in treatment, misdiagnosis, and mistreatment of foot pathology.