The effect of first metatarsal extension osteotomy on foot alignment in patients with pes cavus: A three-dimensional anatomical model study

Objective: Pes cavus is high medial arch of the foot that does not flatten under weight-bearing. This study aimed to investigate the effects of variations of first metatarsal extension osteotomy, performed virtually on three-dimensional anatomical models, on foot alignment and to develop a treatment algorithm. Materials and Methods: Three-dimensional models were created from weight-bearing CT scans of 10 patients diagnosed with pes cavus. Extension osteotomies were performed at 1 cm and 2 cm distal to the tarsometatarsal joint as 3 mm, 5 mm, and 7 mm wedge sizes. Meary's angle, calcaneal pitch angle, and tibiocalcaneal angle were evaluated pre- and post-osteotomy. Results: Virtual osteotomies performed at 1 cm resulted in a decrease in Meary's angle by 6.65°±1.18, 10.94°±1.87, 15.13°±2.53, in calcaneal pitch angle by 2.14°±0.48, 3.57°±0.57, 4.89°±0.93, and in tibiocalcaneal angle by 4.92°±1.33, 8.27°±1.92, 11.6°±2.62 for 3 mm, 5 mm, and 7 mm osteotomies. Osteotomies performed at 2 cm resulted in a decrease in Meary's angle by 6.62°±1.02, 10.56°±1.81, 14.3°±2.32, in calcaneal pitch angle by 2.09°±0.38, 3.34°±0.51, 4.52°±0.7, and in tibiocalcaneal angle by 4.84°±1.01, 7.78°±1.38, 10.74°±2.1. No significant difference was found on foot alignment effects between osteotomies performed at 1 cm and 2 cm. Conclusion: A preoperative planning algorithm was developed to determine the appropriate first metatarsal extension osteotomy based on the severity of the pes cavus deformity. Keywords: Pes cavus, first metatarsal extension osteotomy, 3D modeling, preoperative planning.