290. GEOMETRIC ANALYSIS OF SCARFT OSTEOTOMY OF THE FIRST METATARSAL

Abstract

Purpose of the study: Osteotomy of the first metatarsal has become the gold standard treatment for hallux valgus. We report a study on the changes in radiographic findings as a function of the degree of translation of the distal fragment of the metatarsal during scarf distal wedge osteotomy.

Material and methods: From the cohort of patients who underwent hallux valgus surgery in our unit, we collected 118 anteroposterior x-rays of the forefoot. Computer-assisted image processing established a trigonometric analysis of each forefoot before and after standardised virtual surgery. Variations in standard morphological measurements (phalangeal valgus: M1P1; metatarsal varus: M1M2; orientation of the joint surfaces of the first metatarsal: proximally (PMAA) and distally (DMAA).

Results: The successive translations significantly modified all of the morphological measurements. For M1M2, intermediary translation corrected the metatarsal varus (< 5) in 72% of the cases, maximal translation in 97%. For the M1P1 angle, intermediary translation only corrected the phalangeal valgus (< 8) in 44% of cases, maximal translation in 31%. For the DMAA angle, intermediary translation corrected the distal articular orientation (< 6) in 66%, maximal translation in 97%. Distal translation of the first metatarsal aggravated the obliquity of the proximal joint surface from a mean 1.57±4.5 to 7.7±4.7, with intermediary translation and to 13.92±4.9 with maximal translation.

Discussion: Considering the large number of techniques proposed, the choice of one osetotomy model is reductive, but it does demonstrate via a geometric application the limits of osteotomy translation of the first metatarsal for the correction of hallux valgus.