Posterior Tibial Slope Increase Is Associated with Patellofemoral Joint Metabolic Alteration After Opening-Wedge High Tibial Osteotomy

Background/Objectives: Opening-wedge high tibial osteotomy (OWHTO) may alter patellar position and patellofemoral (PF) loading, raising concerns about postoperative PF deterioration. This study evaluated compartment-specific changes in SPECT/CT bone tracer uptake (BTU), a marker of subchondral osteoblastic activity, and factors associated with increased PF BTU. Methods: This retrospective study included 35 knees in 34 patients. SPECT/CT was obtained preoperatively and 12–24 months postoperatively. An exploratory 20% relative-change threshold was used to classify BTU responses. Clinical and radiographic variables were compared between PF BTU-increased and non-increased groups. Exploratory multivariable binary logistic regression was used to assess factors associated with a >20% increase in PF BTU, coded as 1, versus no such increase, coded as 0. Results: Mean medial BTU decreased (4.61 ± 2.46 to 3.38 ± 1.50; p = 0.005), whereas mean lateral and PF BTU did not change significantly. PF BTU increased by >20% in 12 knees (34%), decreased by >20% in 16 knees (46%), and remained within ±20% in 7 knees (20%). The increased group had a greater posterior tibial slope angle (PTSA) increase (2.87 ± 1.79° vs. 0.73 ± 2.93°; p = 0.029). In exploratory multivariable logistic regression, greater PTSA change was associated with higher odds of a >20% increase in PF BTU (adjusted OR = 1.5275; 95% CI, 1.0003–2.3325; p = 0.04985). International Knee Documentation Committee (IKDC) and anterior knee pain (AKP) scores did not differ significantly between groups. Conclusions: An exploratory association between PF BTU increase and PTSA change was observed, but it was sensitive to the analysis conditions. No significant between-group differences in short-term clinical scores were detected. These findings do not establish cartilage degeneration, causation, or a preventive benefit from controlling PTSA. Longer-term metabolic, structural, and clinical validation is needed.