OBJECTIVE: The purpose of this study was to investigate the distribution of the change of leg length (LL) after closed wedge high tibial osteotomy (CWHTO) and to identify the factors associated with the magnitude of postoperative change of LL. METHODS: A total of 70 consecutive knees of 58 patients with knee osteoarthritis who underwent CWHTO were retrospectively investigated. LL, hip-knee-ankle angle (HKAA), mechanical axis deviation (MAD), joint line convergence angle (JLCA), mechanical medial proximal tibial angle (mMPTA), and mechanical lateral distal femoral angle (mLDFA) were measured using the anteroposterior whole leg radiograph, and posterior tibial slope (PTS) and flexion contracture (FC) were measured using the lateral knee radiograph. The amount of change from preoperative to postoperative in each parameter was defined as Δ. RESULTS: Patients had a mean correction angle of 18.3 ± 6.6°, with a mean ΔLL of -0.8 ± 10.2 mm, ranging from - 22 mm to 24 mm. There were significant differences between the preoperative and postoperative mean values of HKAA, MAD, JLCA, mMPTA, and FC, whereas no significant differences were found in LL, mLDFA, and PTS. A significant correlation was found between ΔLL and postoperative FC (ρ=-0.28, P = 0.03). Moderate correlations were found between postoperative FC and preoperative FC (ρ = 0.61, P <
0.01) or postoperative PTS (ρ = 0.44, P <
0.01) and between ΔFC and postoperative FC (ρ = 0.54, P <
0.01), postoperative PTS (ρ = 0.60, P <
0.01) or ΔPTS (ρ = 0.55, P <
0.01). CONCLUSIONS: The mean change of LL after CWHTO was only - 0.8 mm, but it ranged widely, from - 22 mm to 24 mm. This variability highlights the importance of addressing factors such as FC and PTS, which are associated with LL changes. Surgeons should carefully control PTS during surgery and address FC to minimize LL change. However, these findings should be interpreted with caution due to the limited methodologies in the assessment of variables including LL and FC.