Impact of Osteotomy Gap Implant Selection on Prognosis Following Medial Opening Wedge Supramalleolar Osteotomy: A Retrospective Cohort Study.

BACKGROUND: Optimal management of the osteotomy gap during medial opening wedge supramalleolar osteotomy (MOWSMO) for varus ankle osteoarthritis remains uncertain. PURPOSE: To compare union and clinical outcomes among four gap-management strategies and examine whether gap height was associated with early union. STUDY DESIGN: Retrospective cohort study; Level of Evidence, III. METHODS: We reviewed 125 patients undergoing MOWSMO and grouped them by gap management: void retention (n = 15), metal cage (n = 35), structural allograft (n = 56), or autograft (n = 19). Clinical and radiographic outcomes, complications, satisfaction, and union at 3, 6, and 12 months were compared. Logistic regression evaluated gap height and 3-month union, adjusted for age and body mass index. RESULTS: Clinical scores improved in all groups (p < 0.001), without between-group differences at final follow-up (AOFAS, p = 0.127; FFI, p = 0.239; NRS, p = 0.405). At 3 months, union was observed in 1/15 (7%) void, 17/35 (49%) cage, 37/56 (66%) allograft, and 13/19 (68%) autograft cases (p < 0.001); 12-month union did not differ (p = 0.140). Greater gap height was associated with lower odds of 3-month union (odds ratio, 0.808; 95% confidence interval, 0.670-0.974; p = 0.025). Complication and satisfaction rates were similar among groups. CONCLUSIONS: Void retention showed slower early radiographic healing but similar 12-month union and final outcomes. The small void group and nonrandom allocation preclude a noninferiority conclusion. Larger prospective studies are needed.