Comparison of plantar pressure, clinical, and radiographic changes of the forefoot after biplanar Austin osteotomy and triplanar Boc osteotomy in patients with mild hallux valgus

Background: Boc's modification of the Austin procedure is a triplane distal osteotomy that achieves shortening and plantarflexion of the first metatarsal with a lateral translation of the metatarsal head. The clinical results and influence of the Austin and Boc osteotomies on plantar pressure have been compared retrospectively. Materials and Methods: The patients were divided into two groups: 30 Austin and 30 Boc osteotomies were performed with a mean followup of 37 (range, 29 to 56) months. Results: Sixty patients with mild hallux valgus deformities and central metatarsalgia, took part in the study. Pressure measurements were performed with a Diagnostic Support system (R) footplate. The average postoperative American Orthopaedic Foot and Ankle Society score of the Austin group was 81.9 and 86.4 for the Boc group. The pressure distributions under the fourth and fifth metatarsal head were comparable in both groups (p > 0.05). The Austin group showed decreased load bearing under the hallux and the first metatarsal head (p < 0.01), consistent with a persistent overloading of the second and third metatarsal head (p > 0.05). The Boc group showed decreased weightbearing under the hallux with better load distribution beneath the second and the third metatarsal head (p < 0.05). Correlation of the American Orthopaedic Foot and Ankle Society scores and pressure variables confirmed a significant negative correlation with altered hallux and central metatarsal head loading (p < 0.01). Conclusion: The Boc triplane osteotomy seems to restore more physiologic loading of the forefoot in comparison to the Austin procedure, reducing the incidence of painful callus under the second and third metatarsal head.