The ratio of mechanical axis shift to the correction angle differs in preoperative planning, but actual postoperative alignment is comparable between opening wedge and closed wedge high tibial osteotomy

Background: The purpose of this study was to investigate the relationship between the bony correction angle and mechanical axis change and their differences between closed wedge high tibial osteotomy (CWHTO) and open wedge high tibial osteotomy (OWHTO). Methods: A total of 100 knees of 89 patients who underwent OWHTO (50 knees) or CWHTO (50 knees) were investigated. The femorotibial angle (FTA), % mechanical axis deviation (MAD), % anatomical tibial axis deviation (ATAD), % mechanical tibial axis deviation (MTAD), mechanical medial proximal tibial angle (mMPTA), and joint line convergence angle (JLCA) were measured on preoperative and postoperative radiographs. The amount of change from preoperative to postoperative in each measurement is represented as Δ. Results: CWHTO resulted in a greater increase of Δ(%MTAD - %ATAD)/ΔmMPTA than OWHTO (P<0.05), and a greater decrease of ΔJLCA/ΔmMPTA than OWHTO (P<0.05). However, no significant difference was found in the Δ%MAD/ΔmMPTA between CWHTO and OWHTO. When the osteotomy was planned with the same bony correction angle, %MA passed more laterally in OWHTO than in CWHTO (P<0.05). These results suggested a lesser valgus bony correction ratio due to greater medial shift of the tibial axis and greater valgus compensation of the soft tissue in CWHTO compared to OWHTO. Conclusions: The ratio of mechanical axis shift to the correction angle differed in preoperative planning, but postoperative alignment was comparable between opening wedge and closed wedge high tibial osteotomy.