Proximal crescentic metatarsal osteotomy: the effect of saw blade orientation on first ray elevation

BACKGROUND: Moderate and severe hallux valgus deformities generally require a proximal metatarsal osteotomy to correct a widened intermetatarsal angle. Although excellent results have been reported using the proximal crescentic osteotomy, concerns have been raised about the incidence of postoperative dorsal malunion, which may lead to transfer lesions. The objectives of this paper were to evaluate the influence of saw blade angulation on the final position of the first metatarsal and to test a new technique used to ensure proper orientation of the osteotomy. METHODS: For part I of the study, 26 Sawbones specimens with hallux valgus deformities were corrected using a proximal crescentic osteotomy with the saw blade position incrementally rotated in the coronal plane. The sagittal change in the final position of the metatarsal was quantified radiographically and correlated to the saw blade orientation. For part II of the study, a Kirschner wire was placed in a vertical position into the medial cuneiform to serve as a guide for the crescentic saw blade in 13 cadaver feet with hallux valgus. Metatarsus primus elevatus was measured after surgical correction. RESULTS: Part I of the study demonstrated a highly linear relationship (R2=0.95) between first metatarsal elevation and the orientation of the saw blade. Every 10-degree of saw blade angulation resulted in a 2-mm change in the sagittal position of the first metatarsal. In part II of the study, the average change in metatarsus primus elevation for the 13 specimens after surgical correction of the hallux valgus deformity was only 1.1 mm (range -3.9 to +4.9 mm). Eleven of the 13 specimens had less than 2.5 mm of elevatus. CONCLUSION: Dorsal malunion of the first metatarsal after proximal crescentic osteotomy is a recognized complication. The final position of the hallux metatarsal is influenced by the coronal plane orientation of the saw. A new technique is described to aid the surgeon in proper alignment of the saw and help prevent excessive first ray elevation.