Background:Medial opening wedge high tibial osteotomy (HTO) is a well-described treatment in early medial compartmental osteoarthritis of the knee. However, two undesirable sequelae may follow –patella baja and changes in the posterior tibial slope (TS).Materials and Methods:We conducted a retrospective study in patients who underwent HTO in our center between September 2009 and February 2017. Preoperative and 6-week postoperative long-leg weight bearing films and lateral knee radiographs were assessed. Pre- and postoperative radiological measurements include the Caton-Deschamps Index (CDI), the mechanical axis deviation (MAD), and the posterior TS. Independant t-test and Pearson correlation test were performed.Results:A total of 106 knees were recruited. The mean age was 48.8 ± 10.8 years. 66 (62.3%) and 40 (37.7%) knees were from males and females, respectively. The mean pre- and postoperative measurements was (−9.70° ± 3.67° to 0.08° ± 2.80°) (−varus; +valgus) for the MAD, (7.14° ± 1.78° to 8.72° ± 3.11°) for posterior TS, and (0.93° ± 0.084° to 0.82° ± 0.13°) for CDI (P ≤ 0.001 for all). The association between patella height change and the level of osteotomy (supra-tubercle vs. infra-tubercle) was statistically significant (P < 0.001). A supra-tubercle osteotomy cut significantly lowering patella height (P = 0.011). There was otherwise no statistically significant correlations between patella height changes and the correction angle (P = 0.187) or posterior TS change (P = 0.744).Conclusions:A medial opening wedge HTO above the tibial tubercle was significantly associated with lowering patella height or reducing CDI postoperatively. Based on our results, we would recommend the use of an infra-tubercle osteotomy during the corrective surgery to prevent the complication of patella baja.