293. INFLUENCE OF THE DISTAL METATARSAL ANGLE (DMMA) ON THE CORRECTION OF HALLUX VALGUS BY BASIMETATARSAL OSTEOTOMY

Abstract

Purpose of the study: Basimetatarsal osteotomy to correct hallux valgus deformity by subtraction of a lateral wedge does not take into account the distal angle of the first metatarsal (DMMA). The purpose of this study was to demonstrate that the preoperative DMMA has an effect on the correction of the metatarsophalangeal angle and the duration of the result.

Material and methods: This retrospective study included 76 patients, mean age 58 years (84 feet). The M1P1 angle of the first ray was 34 on average, the DMMA 10 (two-thirds of the patients had a DMAA > 10. The same operator used the same technique for all procedures: lateral wedge osteotomy of the base of the first metatarsal with metatarsophalangeal release. Basal osteotomy of the first phalanx was performed for severe deformity. Radiographic measures were made on the dorsoplantar anteroposterior images in the weight-bearing condition preoperatively, at four weeks and at last follow-up. All images were read by an independent observer. Mean follow-up was 11 months. The DMMA measurement was the angle between the distal joint surface of the first metatarsal and the alignment of its diaphysis.

Results: Mean postoperative correction of the hallux valgus was 25 with a mean M1P1 of 9. This result remained stable without loss of correction at last follow-up. The mean postoperative DMAA was 10 and remained unchanged.

Discussion: Determination of the DMAA can be difficult because of preoperative pronation of the forefoot, compromising the reliability of the measurement. The literature also reports intraobserver and interobserver variability of this angle. Mean follow-up was not greater than one year, but the loss of correction generally occurred during the first six postoperative months. The operative technique enabled sufficient and stable correction over time. A pathological value for DMAA, even if large and uncorrected, does not prevent a good correction of the M1P1 angle and to maintain that correction. The clinical result is also the same irrespective of the preoperative DMMA.

Conclusion: Wedge osteotomy of the base of the first metatarsal is a reliable procedure for the treatment of hallux valgus. The value of the DMAA has no effect, in our experience, on the quality of the correction, or on the duration of the result.