Three-dimensional analysis of different first metatarsal osteotomies in a hallux valgus model.

BACKGROUND: This study evaluates and compares three-dimensional (3-D) changes in geometry of the first metatarsal (MT1) independent of soft tissue corrections of 5 common osteotomies: three distal (Chevron, Mitchell, and Wilson), one proximal (Stephens basal), and one combined proximal/distal (Scarf), using standardized synthetic bone models.

MATERIALS AND METHODS: A digitizing system was used to measure and record points on the synthetic bone models in 3-D space. Computer vector analysis calculated 3-D rotations and translations of the MT1 head plus the conventional intermetatarsal angle (IMA) and distal metatarsal articular angle (DMAA).

RESULTS: The Wilson and Mitchell's osteotomies produced significant shortening (p < 0.001) in contrast to the three other osteotomies. All the osteotomies produced a reduction in the 3-D IMA. The Scarf and Stephens basal osteotomies reduced the DMAA. All of the osteotomies resulted in lateral translations and depression of the MT1 head. While there were no significant (p > 0.05) translational differences between the Scarf and Stephens basal osteotomies, there were rotational differences, with the Stephens basal producing significantly more plantar flexion (p = 0.000) and pronation (p < 0.001) than the Scarf.

CONCLUSION: This geometric study indicated many of the MT1 head changes following metatarsal osteotomy to be out-of-plane translational and multiplanar rotations which cannot be determined using AP radiographs alone.

CLINICAL RELEVANCE: We advocate judicious choice of osteotomy to achieve the desired correction of hallux valgus in each individual.