The Impact of Lower Extremity Mechanical Axis Alignment on the Success of Platelet-Rich Plasma Injections in Knee Osteoarthritis Patients

Abstract

Objectives Knee osteoarthritis (OA) is a common cause of pain and disability, and conventional conservative treatments often provide only limited and temporary relief. Platelet-rich plasma (PRP) injections have emerged as a promising biological therapy; however, patient response is highly variable, and biomechanical factors such as lower extremity malalignment may influence treatment outcomes. This study aimed to evaluate the effect of the lower extremity mechanical axis angle (MAA) on the clinical efficacy of PRP injection therapy in improving knee function and pain in patients with OA. Methods A total of 210 patients with knee OA who consented to PRP treatment between January 1, 2018, and January 1, 2023, were enrolled. Patients were stratified into three groups according to baseline varus angle: Group 1, 0 degrees-5 degrees (n = 70); Group 2, 6 degrees-10 degrees (n = 70); and Group 3, 11 degrees-15 degrees (n = 70). Clinical evaluations were performed at baseline and at 1, 3, 6, 12, and 24 months post-treatment using the Knee Injury and Osteoarthritis Outcome Score (KOOS), Kujala Patellofemoral Score, knee joint range of motion (ROM), MAA measurement, and a Visual Analogue Scale (VAS) for pain. Results All groups demonstrated significant improvements in pain and functional scores over the 24-month follow-up compared to baseline (p < 0.001), with the most notable gains observed at 3 and 6 months. At 3, 6, and 12 months, Group 1 achieved significantly better VAS and KOOS Pain subscale scores than Group 3 (p < 0.05). Both Groups 1 and 2 had higher KOOS Total scores than Group 3 at these time points (p < 0.05). Spearman correlation analysis revealed moderate negative associations between baseline MAA and changes from baseline to 6 months in VAS (rho = -0.58), KOOS Total (rho = -0.54), and Kujala scores (rho = -0.53) (all p < 0.001). Statistical analyses were conducted using ANOVA or Kruskal-Wallis tests as appropriate, and effect sizes (Cohen's d) with 95% confidence intervals were calculated. Conclusion PRP injection therapy yields significant improvements in pain and functional outcomes in patients with knee OA. However, increased MAA is associated with reduced clinical benefit, indicating that baseline lower extremity alignment should be considered in treatment planning.