Sagittal Patellar Offset Ratio Can Be a Predictor of Anterior Knee Pain after Primary Total Knee Arthroplasty without Patella Resurfacing.

Abstract

Anterior knee pain (AKP) is an issue that persists even after successful total knee arthroplasty (TKA). In some patients, reasons for AKP occurrence are known, but it is unexplained in some others despite the patellofemoral joint being thought to be the main focus of pain. We investigated the relationship between unexplained AKP and the patellofemoral joint in the sagittal plane after primary TKA. We evaluated 372 knees of 317 patients retrospectively, who had completed a minimum 24-month follow-up. We divided them into two groups according to the presence of AKP. Sagittal patellar offset ratio (SPOR), anterior femoral offset ratio (AFOR), and Insall-Salvati ratio (ISR) were measured on lateral X-rays. Clinical outcomes were evaluated using the Oxford knee score (OKS) and WOMAC pre-and postoperatively, and AKP was evaluated using a visual analog scale (VAS) postoperatively. Between non-AKP and AKP groups, SPOR (p<0.001) and AFOR (p=0.03) were significantly different but not ISR (p=0.89). SPOR and AFOR were found to be two independent risk factors that may predict the likelihood of AKP. Receiver operating characteristic (ROC) analysis revealed that AFOR is a poor value, whereas SPOR is a reasonable predictive value. No correlation between SPOR and postoperative OKS (p=0.92) and WOMAC (p=0.25) and no correlation between AFOR and postoperative OKS (p=0.44) and WOMAC (p=0.58) were found. We found that SPOR is a good predictive tool with a cutoff value of 46.4% and 91.5% sensitivity for AKP and its increased ratio increases the probability of AKP following TKA. Considering that the patellar offset will not change, especially in patients without patella resurfacing, care should be taken not to increase the anterior femoral offset.