Optimal Target Angle in Oblique Diaphyseal Osteotomy of the Fifth Metatarsal for Symptomatic Bunionette: A Retrospective Analysis.

Abstract

Background: The effects of the osteotomy angle during oblique diaphyseal osteotomy of the fifth metatarsal on the clinical outcomes remain unclear. This study aimed to clarify the clinical and radiographic outcomes of this procedure, with a focus on the intraoperative osteotomy angle.

Methods: This retrospective study included 30 female patients who underwent oblique diaphyseal osteotomy of the fifth metatarsal with single-screw fixation for symptomatic bunionette (36 feet, mean age, 68.3 years; mean follow-up, 22.5 months). The angles between the osteotomy line and the fifth metatarsal and screw insertion axes were measured as the osteotomy and screw insertion angles, respectively. Receiver operating characteristic curve analysis was performed to determine the cutoff value for the osteotomy angle. The metatarsophalangeal angle (MTPA) and intermetatarsal angle (IMA) between the fourth and fifth metatarsals were measured on dorsoplantar images. The Japanese Society for Surgery of the Foot (JSSF) scale was scored at the preoperative and final follow-up visits.

Results: Screw backout was identified in 14 feet (38.9 %). The osteotomy and screw insertion angles were 35.9 and 62.2 degrees in the screw backout group and 24.6 and 71.2 degrees in the control group, respectively (P < .05). The osteotomy angle >31.1 degrees was a cutoff value of postoperative screw backout (sensitivity, 0.79; specificity, 0.96; area under the curve, 0.92). The mean MTPA and IMA were 21.0 and 12.3 degrees preoperatively and 9.3 and 8.2 degrees at the final follow-up, respectively. The mean JSSF scale score improved significantly from 59.9 to 95.3.

Conclusion: The osteotomy angle was greater and the screw was inserted more shallowly against the osteotomy line in the screw backout group compared with the control group. The optimal target angle of the osteotomy line to the fifth metatarsal axis should be <30 degrees intraoperatively for single-screw fixation.