Fate of the Contralateral Knee After Unilateral High Tibial Osteotomy

Background: No research has reported on the prognosis and risk factors related to the non-operated contralateral knee after unilateral high tibial osteotomy (HTO). 
Hypothesis/Purpose: The primary aim of this study was to assess radiologic parameters that affect OA progression and the need for surgery in the non-operated knee following unilateral HTO, with concurrent assessment of the operated knee. 
Study Design: Case series; Level of evidence, 4.
Methods: From July 2000 to September 2021, 231 patients with knee OA who underwent unilateral HTO were retrospectively investigated. Radiologic parameters, such as the Kellgren-Lawrence grade (K-L grade), hip-knee-ankle angle (HKAA), weight-bearing line ratio (WBLR), joint line convergence angle (JLCA), and joint line obliquity angle were assessed preoperatively and postoperatively from 1 to 4 years. OA progression was defined as an increase in K-L grade. Clinical failure or surgery was defined as undergoing joint replacement or osteotomy. 
Results: Postoperatively higher WBLR (P = .030) and smaller JLCA (P = .008) in the operated knee were significant risk factors for undergoing surgery in the non-operated knee. Postoperatively smaller JLCA (P = .051) in the operated knee was a marginally significant risk factor for OA progression in the non-operated knee. Postoperatively larger JLCA (P = .030) in the operated knee was a significant risk factor for clinical failure in the operated knee, whereas HKAA and WBLR were not. Pre- and postoperative changes in JLCA needed to be less than -0.75° (P = .004) and greater than -4.1° (P = .004) to reduce OA progression in both knees.
Conclusion: Increased postoperative valgus alignment and medial joint opening in the operated knee after unilateral HTO were associated with a higher risk of surgery and osteoarthritis progression in the non-operated knee. A small medial joint opening in the operated knee was associated with a higher risk of clinical failure in the operated knee. For a balanced medial joint opening, if the pre- and postoperative changes in JLCA were between -4.1° and -0.75°, a favorable prognosis for OA progression in both knees could be anticipated.