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

R. Kugan, V. Currall, P. Johal, C.I. Clark

Introduction: For hallux valgus correction, a general consensus exists with regards to the use of distal first metatarsal osteotomy for minor to moderate deformities and diaphyseal osteotomy for moderate to severe deformities, with basal osteotomy reserved for severe deformities with a large intermetatarsal angle. Several types of basal osteotomy have been described, but all have disadvantages, so there has been renewed interest in opening wedge basal osteotomy. Little has been written about the geometry of this osteotomy, so we undertook this study in order to understand its power and limitations.

Methods: Proximal opening wedge osteotomies were performed in four orientations on saw bone models: 1. Perpendicular to the ground (PG); 2. Perpendicular to the shaft (PS); 3. Perpendicular to shaft with 30 degrees of declination (DEC); 4. 30 degree oblique (OB). Pre- and post-osteotomy measurements were made using reference wires to compare axial and plantar translation and change in intermetatarsal angle.

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

Conclusion: The proximal metatarsal opening wedge osteotomy is a powerful osteotomy in achieving hallux valgus correction. An osteotomy perpendicular to shaft is ideal for achieving correction of the intermetatarsal angle and plantar translation with minimal lengthening. This study provides useful information about the geometry of the basal opening wedge osteotomy of the first metatarsal, which may be used for correction of a severe hallux valgus deformity, often in conjunction with a distal chevron and/or Akin osteotomy.