Muscular Pronation in First Metatarsal After Hallux Valgus Osteotomies: A Biomechanical Simulation Study.

Metatarsal pronation has been reported to be a significant recurrence factor for hallux valgus after corrective osteotomies. However, the extent of pronation correction with distal metatarsal I osteotomies varies greatly from patient to patient without the reason being known. The objective of this study was to describe the effect of the metatarsal I osteotomy angle on muscular torque, acting on the first metatarsal. The primary hypothesis was that a varying angle for the transversal cut affects the muscular pronating torque in the first metatarsal. Therefore, three different 3-dimensional foot models have been created, and a distal metatarsal I corrective osteotomy was simulated. The transverse cut of the osteotomy was varied from three different angles (-10°, 0°, 10°). Torque and the pro-/supinating component of eight muscles acting on the first metatarsal have been calculated. No significant difference in pro-/supinating torque acting on the first metatarsal was found between different osteotomy angles. Nevertheless, the lateral shift of the osteotomized metatarsal-I-head in ReveL osteotomy increased supinating torque in almost all analysed muscles, regardless of the angle of the osteotomy. Hence, a tendency (p = 0.082) towards less muscular pronating torque could be shown for all ReveL osteotomies compared to the non-osteotomized status quo. This increased supination was significant especially for the analysed flexors and adductor hallucis caput obliquus.