Risk Factors for Increase in Posterior Slope After Medial Open-Wedge High Tibial Osteotomy

Background:Whether lateral hinge fracture (LHF) after open-wedge high tibial osteotomy (OWHTO) is associated with the change in tibial posterior slope (PS) has not been determined. Risk factors for PS increase are still unknown. Hypothesis:There will be no difference in patient characteristics and radiographic factors when stratified by change in tibial PS (Delta PS). Study Design:Cohort study; Level of evidence, 3. Methods:We reviewed the records of 148 patients who underwent OWHTO with locking-plate fixation from 2010 to 2016. Included were those with a minimum 2-year follow-up and true lateral radiographs before and at 1 year after surgery. Delta PS was defined as a difference between preoperative and 1-year postoperative PS, with positive values indicating PS increase. Delta PS was classified into <3 degrees, 3 degrees to <6 degrees, and >= 6 degrees. Any LHFs were grouped by Takeuchi classification as stable (type 1) or unstable (types 2 and 3). Risk factors for PS increase were evaluated using ordinal logistic regression analyses. Clinical outcomes according to Delta PS were evaluated using the Hospital for Special Surgery score. Results:There were 79 (53.4%) patients with Delta PS <3 degrees, 44 (29.7%) with 3 degrees <= Delta PS < 6 degrees, and 25 (16.9%) with Delta PS >= 6 degrees. LHFs were observed in 41 (27.7%) patients: 32 with type 1 and 7 and 2 with types 2 and 3, respectively. Results of the multivariate ordinal logistic regression analysis indicated that Delta PS was associated with unstable LHF (P = .005, exp[beta] = 6.34), preoperative PS (P = .028, exp[beta] = 0.90), and correction angle (P = .037, exp[beta] = 1.09). Delta PS >= 6 degrees was seen in 4 of 9 (44.4%) patients with unstable LHF, 9 of 32 (28.1%) with stable LHF, and 12 of 107 (11.2%) with no LHF (P = .017). The mean correction angle was 11.3 degrees +/- 3.6 degrees in patients with Delta PS >= 6 degrees, 9.4 degrees +/- 4.6 degrees in cases of 3 degrees <= Delta PS < 6 degrees, and 8.8 degrees +/- 3.6 degrees in cases of Delta PS <3 degrees (P = .019). Hospital for Special Surgery scores did not differ according to Delta PS. Conclusion:LHF type and correction angle were associated with Delta PS after OWHTO, and unstable LHF and large correction angle were risk factors for PS increase. There was no significant difference in clinical outcomes according to Delta PS.