Proximal first metatarsal opening wedge osteotomy: geometric analysis on saw bone models.

BACKGROUND: For hallux valgus correction, distal first metatarsal osteotomy is generally used for minor to moderate deformities, diaphyseal osteotomy for moderate deformities and basal osteotomy or arthrodesis for severe deformities. With the advent of locking plates, there has been renewed interest in opening wedge basal osteotomy.

OBJECTIVE: We undertook this study in order to understand the power and limitations of this osteotomy.

METHOD: Proximal opening wedge osteotomies were performed on saw bone models in four orientations, with three different wedge sizes: (1) perpendicular to the ground (PG); (2) perpendicular to the shaft (PS); (3) perpendicular to shaft with 30° declination (DEC); (4) 30° oblique (OB). Pre- and post-osteotomy measurements were made of axial and plantar translation and inter-metatarsal angle.

RESULTS: Plantar translation and intermetatarsal angle correction increased with increasing wedge size. The DEC osteotomy produced the greatest increase in length of metatarsal shaft, while the PS osteotomy gave the least. The most plantar translation was achieved with the DEC osteotomy. Overall, the PS osteotomy gave the largest correction of the intermetatarsal angle.

CONCLUSION: Although there are several published clinical case series of the proximal opening wedge osteotomy, this is the first study to fully evaluate its geometry.