Ability of an intentionally smaller anterior than posterior gap to reduce the sagittal tibial slope in opening wedge high tibial osteotomy

BACKGROUND: We utilized in vivo 3- dimensional (D) computed tomography (CT) to determine whether the preoperatively planned anterior and posterior opening gap heights correlated with the real gaps following opening wedge high tibial osteotomy (HTO), as well as the relationships between anterior and posterior gap heights and change in sagittal tibial slope. METHODS: This prospective study involved 41 patients (41 knees) undergoing navigation HTO for primary medial osteoarthritis. Mechanical axis (MA), weight-bearing line (WBL) ratio, and posterior tibial slope were measured on radiographs preoperatively and after 3 months. The anterior and posterior opening gaps created by osteotomy were measured using in vivo 3D CT and the patients were classified into a larger anterior or posterior gap group. RESULTS: Of the 41 patients, 24 (59 %) had larger anterior and 17 (41 %) had larger posterior gaps. There were no between group differences in preoperative and postoperative slopes, or in change in slope. The correlation between preoperatively planned and postoperative posterior gaps was good, whereas the correlation of anterior gaps was only fair. Bland-Altman plots showed poor agreement for both preoperative and postoperative anterior and posterior gaps. The mean systematic difference (bias) was 2.3 mm (p < 0.001) for anterior and -1.0 mm (p = 0.033) for posterior gaps. CONCLUSIONS: Preoperatively calculated opening gaps, which were planned to be larger posteriorly than anteriorly to minimize the change in slope after surgery, did not correspond with postoperative opening gaps on 3D CT. In addition, postoperative tibial slope did not increase, even when the anterior gap was larger than the posterior gap. TRIAL REGISTRATION: Trial registration number: KCT0001905, April 29, 2016.