Hallux Valgus Correction: Comparison of Minimally Invasive Transverse and Chevron Distal Metatarsal Osteotomy Constructs

CATEGORY: Basic Sciences/Biologics; Bunion INTRODUCTION/PURPOSE: Hallux valgus is one of the most common surgically corrected forefoot deformities. Compared to open procedures, minimally invasive treatment of hallux valgus has resulted in decreased operative time, reduced complication rates, and greater patient satisfaction. Until recently in the United States, distal chevron osteotomies have been the standard for hallux valgus correction of moderate deformity. To the best of the authors’ knowledge, no studies have evaluated biomechanical strength of transverse and chevron distal metatarsal osteotomy constructs. The purpose of this study was to evaluate the biomechanical strength of transverse and chevron minimally invasive osteotomy techniques using 9 matched cadaveric pairs. METHODS: A total of nine matched cadaveric specimens were randomized to transverse or chevron distal metatarsal osteotomies. Each minimally invasive surgical technique was performed by a fellowship trained orthopedic foot and ankle surgeon. Anterior- posterior and lateral radiographic images were obtained following surgical fixation. Biomechanical testing was performed on an Instron Mechanical System. Ultimate load to failure, yield load, and stiffness were assessed across the fixation construct with fulcrum within the metatarsal shaft proximal to screw fixation and compression load at the sesamoid bones. A pre-load of 10N was applied to the sesamoid bones by the compression post to stabilize the sample. Subsequently, a compression rate was applied to the sample at 10mm/min until failure was observed. Mean and standard deviations were assessed and compared across cohorts. RESULTS: All nine cadaveric specimens were male. There was no difference in average percent metadiaphyseal shift among transverse (36%) and chevron (38%) osteotomies. The most common mode of failure among transverse and chevron osteotomies was fracture at screw insertion site (55.6%), followed by failure at osteotomy site (44.4%). One paired sample was noted to have poor bone quality prior to biomechanical testing. There was a trend towards increased ultimate load to failure (p=0.480) and stiffness (p=0.438) among transverse osteotomy compared to chevron osteotomy, however, no statistically significant difference was observed. CONCLUSION: Biomechanical testing demonstrates no statistical difference in ultimate load to failure and stiffness between minimally invasive transverse and chevron distal metatarsal osteotomy constructs. A trend towards increased ultimate load and stiffness in the transverse osteotomy cohort was observed. Chevron osteotomies violate the entire plantar cortex and may result in early failure by relative ease of cutout through cancellous bone compared to transverse osteotomies in which failure would require cortical bone cutout. Future studies are required to evaluate strength of construct in a larger sample. Analysis is limited, healing may provide additional strength that is not simulated in cadaveric studies.