Knee Joint Line Obliquity Continues to Regress Beyond 1 Year and Stabilizes at 3 Years After Open Wedge High Tibial Osteotomy Without Correlation to Clinical Outcome.

Purpose: To evaluate midterm serial postoperative changes in the knee and adjacent joints, with a focus on the knee joint obliquity (KJLO).

Methods: Patients undergoing open wedge high tibial osteotomy (OWHTO) between January 2011 and December 2018 were retrospectively reviewed. Those with a follow-up duration of ≥5 years and serial long-standing hip-to-ankle radiographs were included. KJLO and joint line convergence angle (JLCA) were measured at the knee joint. The influence of the hip joint was assessed using the hip abduction angle (HAA), and the influence of the ankle joint was evaluated using the ankle joint line obliquity (AJLO) and the tibiotalar angle (TAA). Serial changes in the radiographic parameters (preoperative, 3-month, 1-year, 3-year, and 5-year postoperative) were analyzed using repeated measures correlation. Clinical outcomes were evaluated using the Knee Society objective and functional scores.

Results: A total of 105 knees were followed up for 90.2 ± 27.2 months (range, 60-151 months). KJLO increased from -0.7 ± 0.2° (mean ± standard error) preoperatively to 2.5 ± 0.3° at 3 months postoperatively and to 3.0 ± 0.2° at 1 year postoperatively (p=0.026, vs. 3-month postoperative), but subsequently decreased to 2.9 ± 0.2° at 3 years postoperatively (p<0.001, vs. 1-year postoperative) and to 2.7 ± 0.3° at 5 years postoperatively, with no significant difference between the 3- and 5-year values (p=0.609, vs. 3-year postoperative). Similarly, HAA increased until 1 year postoperatively (p<0.001, vs. 3-month postoperative), and then decreased significantly until 5 years postoperatively (p<0.001, vs. 1-year postoperative). However, AJLO showed a significant decrease between 3 months and 1 year postoperatively (p<0.001), with no further significant changes observed between 1 and 5 years postoperatively (p=0.225). According to the repeated measures correlation, the factors significantly correlating with changes in KJLO were HAA (p<0.001), AJLO (p<0.001), and JLCA (p=0.028). Five-year postoperative KJLO did not have significant correlations with the Knee Society objective (p=0.845) and functional (p=0.361) scores.

Conclusion: KJLO increased after OWHTO and began to decrease from 1 year postoperatively, with no significant difference observed between 3 and 5 years. This change did not correlate with clinical outcomes. HAA showed a similar pattern, increasing until 1 year and then continuing to decrease significantly throughout the midterm follow-up. AJLO showed a significant decrease within the first postoperative year, with no further changes thereafter.

Level of evidence: Level III, retrospective case series.