Association of Undercorrection With Residual Proinflammatory Gene Expressions and Clinical Outcomes After Medial Open Wedge Proximal Tibial Osteotomy.

BACKGROUND Accumulating evidence suggests that synovial inflammation plays a pivotal role in knee osteoarthritis. Although biomechanical findings have shown that medial open-wedge proximal tibial osteotomy (OWPTO) decreases medial compartment loading by correcting knee alignment, the relationship between knee alignment and synovial inflammation in the biological microenvironment has not yet been elucidated. PURPOSES To investigate the relationship between preoperative and postoperative knee alignment and synovial gene expression and to determine the cutoff point of postoperative knee alignment at which gene expression of synovial inflammation improves. STUDY DESIGN Cohort study; Level of evidence, 3. METHODS A total of 36 patients with osteoarthritis who underwent OWPTO between June 2018 and May 2020 were enrolled. Synovial tissue was collected from affected knees during initial OWPTO and plate removal surgeries, and gene expression associated with the pathogenesis of osteoarthritis in the synovial tissue was investigated using real-time polymerase chain reaction. The correlation between weightbearing line ratio (WBLR) and synovial gene expression was determined. Receiver operating characteristic curve analysis was used to determine the cutoff values of WBLR for improving gene expression. The participants were divided into 2 groups, according to the cutoff values of their WBLR, and compared according to Knee injury and Osteoarthritis Outcome Score (KOOS) and synovial gene expression. RESULTS Postoperative WBLR was correlated with gene expression of interleukin 1β (IL1B) (ρ = -0.43; P = .008) and of interleukin 6 (IL6) (ρ = -0.41; P = .01). The cutoff value to predict improvement of IL6 was postoperative WBLR of 52%, with an area under the curve of 0.74 (P = .03). Patients with WBLR of <52% showed higher postoperative inflammatory gene (IL1B [P = .04] and IL6 [P = .03]) and inferior postoperative KOOS values compared with those with WBLR of >52%. CONCLUSION The novel cutoff alignment for biological improvement after OWPTO in patients with medial compartment osteoarthritis was determined to be WBLR of 52%, and WBLR of <52% was associated with higher residual intra-articular inflammation and poor clinical outcomes. After accounting for surgical errors, the surgeon should set the target surgical alignment so that the postoperative WBLR does not fall below 52%.