Proximal fragment intermetatarsal angle (PFIA) increases after SCARF osteotomy

Abstract

Category: Bunion Introduction/Purpose: Instability of the joint between the medial cuneiform and the first metatarsal is considered as one of the progression factors of Hallux valgus and its recurrence in some cases. We believe that we must increase the intermetatarsal angle of the proximal fragment during the correction by the SCARF osteotomy, seeking the greater degree of instability of this joint. Doing that, we can prevent further varus displacement, as we have reached the greater degree of instability. The purpose of this study was to evaluate if the SCARF osteotomy is able to increase the varus position of the base of the first metatarsal. Methods: This is a retrospective study with 32 patients with mild, moderate and severe hallux valgus, who were submitted to surgical treatment by the SCARF technique. All patients were operated by the same surgeon. Anteroposterior radiographs of the loaded foot were analyzed in the pre and postoperative (3 months) moments. We developed two measures to evaluate the position of the base of the first metatarsal: The Proximal Fragment Intermetatarsal Angle (PFIA), and the distance between the lateral cortex of the first metatarsal and the medial cortex of the second metatarsal (3 cm from the base of the first metatarsal). All measurements were made with a virtual ruler on magnified digital images and rounded to the nearest 0.1 mm. A 95% confidence interval was considered for statistical significant results (p<0,05). Results: The mean age of the sample was 44 years, with a predominance of females (62%). The mean pre-operative intermetatarsal angle was 14.9°, while in the postoperative period it was 5.2°, showing that there was correction of the metatarsal positioning. However, the PFIA increased to 17.8° at the post-operative period (p<0,05), showing a greater instability of the first metatarsal cuneiform joint, as the base of the first metatarsal was positioned in a more varus condition. In addition, we observed that there was an increase in the distance between the base of the first metatarsus and the second metatarsus after the surgical procedure, from 13.7 to 16 millimeters (p<0,05). Conclusion: We concluded that the SCARF osteotomy is able to increase the varus position of the base of the first metatarsal, leading to more instability at the first metatarsal cuneiform joint, and, in our opinion, less chance of recurrence in the long-term. A prospective and long-term is needed to prove this statement.