Predictive factors for the bone union disorder of intramedullary screw fixation in proximal fifth metatarsal bone fractures

Introduction Although intramedullary screw fixation likely leads to successful union of Jones fractures compared to that of nonoperative treatments, bony union disorder after surgical treatment remains to be elucidated. Methods Intramedullary screw fixation was performed for the surgical treatment of proximal fifth metatarsal stress fractures in this series. Between January 2008 and December 2019, the feet of 222 patients were investigated regarding the effective factors for postoperative bony union between the normal union group and the bony union disorder group according to the patients' physical status, radiological assessment, and screw size. The mean postoperative follow-up period was 11.1 months. Bone union disorder was defined as delayed union, nonunion, or a re-fracture recognized through a radiographic image. Results The prevalence rate of union disorders occurred in 14% (31/222) of the patients. The risk of bone union disorder significantly increased when using a small-diameter screw (odds ratio 4.81, 95% confidence interval [CI] 1.62-14.2, p = 0.004) and non-bone graft procedures (odds ratio 3.13, 95% CI 1.22-8.02, p = 0.02). Screw length, preoperative Torg's classification, or patients' physical status did not affect postoperative bony union. Conclusions Approximately 14.0% of the patients in our study had postoperative bone union disorder. Small-diameter screws and non-bone graft procedures increased the risk of bone union disorder in the intramedullary screw fixation technique of fifth metatarsal bone stress fractures.