Radiographic Evaluation of Time to Union in Minimally Invasive Hallux Valgus Correction

Category: Bunion; Lesser Toes Introduction/Purpose: Surgical correction of hallux valgus can be achieved through various techniques with minimally invasive surgery (MIS) gaining popularity in recent years amongst surgeons. The use of MIS 1st distal transverse metatarsal and Akin osteotomy has been associated with good functional outcomes and low complication rates. However, there is limited literature on the time to union following moderate and severe hallux valgus repair using this technique. Literature in orthopedic trauma has indicated that 3 neocortices on postoperative radiographs were associated with high likelihood of union. In this study, we conducted a retrospective analysis to investigate the time to union and its relationship with cortical formation and post-operative degree of displacement of the 1st metatarsal in patients undergoing HV repair. Methods: We retrospectively analyzed seventy-two consecutive patients with moderate to severe hallux valgus who underwent MIS 1st distal metatarsal and Akin osteotomy between 2019 and 2022. The procedures were performed by three fellowship-trained foot and ankle orthopedic surgeons. Postoperative weightbearing X-rays were taken at 6 weeks, 3 months, 6 months, and 12 months to assess time to radiographic union and overall union rate. Two orthopedic surgeons independently reviewed the radiographs. Radiographic measurements included the scale of displacement between the proximal and distal portions of the first metatarsal and the degree of cortex formation. Complete union was defined as the presence of three new cortices on postoperative X-ray films. Patients were divided into four groups based on the percentage of shift on the first metatarsal head (0-25, 25-50, 50-75, 75-100%) for the purpose of our analysis. Results: The cohort consisted of 63 women and 9 men, with an average age of 56.6 years. The mean BMI was 25.96. On average, 2 cortices were observed at 16.9 weeks, and 3 cortices were observed at 26.8 weeks. When the metatarsal shift was greater than 50%, two cortices were observed at an average of 20.14 weeks, compared to 13.7 weeks when the shift was less than 30% (p=0.004). Further analysis of the time required to observe 3 cortices showed no statistically significant difference between metatarsal shifts greater (25.26 weeks) and less than (23.74 weeks) 50% (p=0.4734). In all patients, 4 cortices were observed at the medial, lateral, superior, and inferior aspects of the first metatarsal at the 6-month and 12-month time points. Conclusion: In patients who underwent MIS 1st metatarsal distal transverse and Akin osteotomies for HV repair, the degree of displacement between the proximal and distal portions of the 1st metatarsal is not associated with statistically significant delay in new cortical formation, with an average time to union of 26.9 weeks across all groups, regardless of the percentage of displacement. Independent evaluations of union were consistent with the time points at which 2 and 3 cortices were formed on postoperative radiographs.