Use of a geometric formula to improve the radiographic correction achieved by the scarf osteotomy

Background: Many procedures for hallux valgus treatment have high recurrence rates, often related to operative considerations such as accuracy of deformity correction, soft tissue balancing and sesamoid alignment. Inadequate distal metatarsal-articular angle (DMAA) correction is common with uni- and bi-planar osteotomies which principally address the inter-metatarsal angle (IMA). The scarf osteotomy is a tri-planar osteotomy which corrects the DMAA and IMA, thereby achieving a more anatomical correction and potentially reducing the recurrence rate. Our hypothesis was that by controlling the length and relative proximal and distal translations of the scarf with a geometric formula, more accurate correction of the IMA and DMAA is possible. Methods: A formula was generated to determine the specific adjustments required to correct the deformity. A prospective trial was performed to assess the accuracy of this formula. Thirty-four adult patients were enrolled in the study. Seventeen patients underwent a standard scarf procedure; 17 were operated on using the corrections prescribed by the formula. Results: Hallux valgus angle (HVA), IMA and DMAA corrections improved with the formula (p = 0.036, p = 0.049, and p = 0.006, respectively). Patient and procedure selection has changed in our unit as a result of this study, which identified some preoperative deformities as beyond the capabilities of the scarf procedure. Conclusion: The formula allows precise, reproducible, anatomical correction of IMA and DMAA deformities. The degree of correction attainable with the scarf is dependent on the first metatarsal width and the preoperative deformities. The formula highlighted the limitations of the scarf, thereby aiding in appropriate patient and procedure selection.