Correlation Between Changes in Subchondral Bone Density Distribution and Clinical Outcomes at 2 Years After Opening-Wedge High Tibial Osteotomy.

BACKGROUND: High tibial osteotomy (HTO) for medial knee osteoarthritis corrects lower limb alignment, redistributing knee joint stress from the medial to the lateral compartment and improving clinical outcomes. Subchondral bone density reflects joint stress distribution. While redistribution of subchondral bone density after HTO has been reported, the relationship between computed tomography-osteoabsorptiometry (CT OAM)-derived changes in subchondral bone density distribution and postoperative clinical outcomes has not been well-established. PURPOSE: To investigate the relationship between subchondral bone density distribution across the knee joint and clinical outcomes at 2 years after opening-wedge HTO (OW HTO). STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: This retrospective study included 27 patients (27 knees) with medial knee osteoarthritis who underwent OW HTO. Radiographic parameters and clinical outcomes were assessed preoperatively and 2 years postoperatively. Subchondral bone density was evaluated using CT OAM, analyzing the high-density area (HDA) in the medial and lateral tibial compartments. The medial ratio was defined as the proportion of HDA in the medial compartment relative to total HDA. Correlations between changes in the medial ratio (Δ medial ratio) and clinical outcomes were analyzed. RESULTS: Postoperative alignment and medial ratio were significantly altered, with a reduced medial ratio compared with preoperative values (preoperative, 82.2%; postoperative, 74.6%; P < .001). Change in medial ratio correlated with postoperative percentage of mechanical axis (%MA) (r = 0.414; P = .03) and change in hip-knee-ankle angle (ΔHKA angle) (r = 0.502; P = .008). Partial correlation analysis revealed that Δ medial ratio significantly correlated with postoperative Lysholm score (partial r = 0.463; P = .02) and Knee injury and Osteoarthritis Outcome Score (KOOS) Sport and Recreation subscale (partial r = 0.538; P = .006), and Quality of Life subscales (partial r = 0.558; P = .004) and KOOS summary (42-item weighted mean) (partial r = 0.527; P = .006), after adjusting for postoperative %MA and Δ HKA angle. CONCLUSION: Our study demonstrated that a greater reduction in the medial ratio after OW HTO is associated with improved clinical outcomes, indicating that CT OAM-based subchondral bone density redistribution may reflect mechanical adaptation to postoperative load redistribution. Overall, Δ medial ratio may serve as a potential imaging marker of medial compartment unloading after OW HTO.