Characterization of time‐dependent changes in the subchondral bone density distribution of the proximal tibia following high tibial osteotomy

Purpose This study aimed to evaluate the time‐dependent changes in the medial and lateral subchondral bone density distribution of the tibial joint surface before and after high tibial osteotomy (HTO) using computed tomography‐osteoabsorptiometry. Methods This study included 17 patients (20 knees) (8 men and 9 women; mean age: 55 years) who underwent HTO for medial compartment osteoarthritis. Computed tomography‐osteoabsorptiometry was conducted to measure the subchondral bone density distribution in the tibial joint surface. The high‐density area (HDA), defined as the region corresponding to the highest Hounsfield unit values that comprises 20% of the total region, was calculated. Medial ratio was defined as the proportion of the HDA in the medial compartment relative to the total HDA of both compartments. Measurements were performed preoperatively and at 3, 6, 12 and 24 months post‐operatively, and a generalized linear regression analysis with a gamma distribution model was conducted. Results The medial ratios (mean ± standard deviation) were 89 ± 9% preoperatively, 73 ± 12% at 3 months, 78 ± 13% at 6 months, 78 ± 10% at 12 months and 77 ± 17% at 24 months. Based on the gamma distribution, the non‐linear model was expressed as follows: Y = 82.8 × t − 0.04 × exp(−0.004 × t ). This finding indicated that the medial ratio had a decreasing trend, reaching its minimum at 10.2 months post‐operatively. Conclusion This study showed time‐dependent changes in the subchondral bone density on the tibial side after HTO. The changes in the bone density distribution on the medial and lateral tibial joint surface, which are associated with alignment correction, stabilized at approximately 10.5 months post‐operatively. Therefore, the optimal timing for evaluating subchondral bone density in response to stress redistribution may be after 10.2 months. Level of Evidence Level IV.