Choi W, Kim JH, Byun SE, et al. - In this study, the impacts of vitamin D deficiency on the functional outcomes following a high tibial osteotomy (HTO) were tested. Researchers retrospectively examined clinical data of 209 patients (327 knees) who had undergone HTO done by a single surgeon. They examined 94 patients (94 knees) who had undergone HTO. They classified individuals into two groups according to their preoperative serum vitamin D levels (D- Deficiency and S- Sufficient); < 20 ng/ml (group D, N = 48) and ≥ 20 ng/ml (group S, N = 46) respectively. They evaluated a subjective form of International Knee Documentation Committee score, mechanical alignment, and cartilage status before and 1 year following HTO between groups. The data reveal that individuals with vitamin D deficiency had less satisfactory functional outcomes within 1 year from HTO surgery. The outcomes imply that preoperative serum vitamin D level is one of the factors influencing the outcome after HTO. In patients undergoing HTO, they recommended evaluating serum vitamin D levels as part of the routine workup.