Description
【Objectives】
The increased patellofemoral pressure (PFP) after total knee arthroplasty (TKA) has been reported to induce patellar maltracking. The purpose of this study was to investigate the influence of the intraoperative PFP on the postoperative functional outcomes in TKA.
【Methods】
This study enrolled 26 patients with varus knee osteoarthritis who underwent cruciate-retaining TKAs with patellar-resurfacing (age [Mean ± SD]: 76.3 ± 5.2 years; females, n = 21; males, n = 5). After implantation of the femoral and tibial components, we fixed a custom-made patellar component which incorporated two ultrathin force sensors to the bone resection surface of the patellar remnant (Figure 1). Subsequently, the lateral and medial PFPs were separately measured at 0°, 90°, 120°, and 135° knee flexion. The functional outcomes were evaluated by measuring Knee injury and Osteoarthritis Outcome Score (KOOS)，Forgotten Joint Score (FJS)-12 and the maximal flexion and extension angles of the knee at 12 months postoperatively. Correlations between the PFPs and the postoperative functional outcomes were evaluated by calculating Spearman’s rank correlation coefficients (rs). Additionally, radiographic measurement to evaluate the component alignment was performed for a battery of postoperative radiographs, including a full-leg-length standing anteroposterior radiograph, a lateral knee radiograph and a skyline view. We also evaluated correlations between the PFPs and the radiographic measurement parameters by calculating rs. Statistical significance was set at p < 0.05.
【Results】
Mean lateral PFPs were 2.7 ± 2.2 N, 25.7 ± 14.0 N, 39.0 ± 20.8 N and 49.7 ± 28.2 N for knee flexion of 0°, 90°, 120° and 135°, respectively. Mean medial PFPs were 2.8 ± 3.1 N, 5.2 ± 5.9 N, 8.8 ± 9.2 N and 13.5 ± 14.2 N for knee flexion of 0°, 90°, 120° and 135°, respectively. The functional outcomes are listed in Table 1. The lateral PFP at the knee flexion of 120° was negatively correlated with the maximal flexion angle of the knee at 12 months postoperatively (rs = -0.45, p = 0.021). The Insall-Salvati ratio of a lateral knee radiograph was positively correlated with the lateral PFPs at the knee flexion of 90° (rs = 0.45, p = 0.022) and 120° (rs = 0.43, p = 0.031).
【Conclusions】
This study demonstrated that patella alta was the causative factor for high lateral PFP in the flexed-knee position, which induced decreased postoperative knee flexion after patellar-resurfacing TKA.
