Volume and Distribution of Early Knee Effusion After TKA with a PEEK-Based Knee Prosthesis

Background: Early knee effusion is a common phenomenon after total knee arthroplasty (TKA), with potential clinical implications. Unlike traditional alloy knee prostheses, the polyetheretherketone (PEEK) knee system has radiographic transparency on magnetic resonance (MR) scans, which allows analysis of prosthetic knee effusion. We aimed to identify the distribution and volume of knee effusion after TKA with the PEEK prosthesis with use of MR imaging and to analyze whether dynamic changes in effusion were correlated with serum inflammatory marker changes and knee function recovery. Methods: Nine patients with osteoarthritis who were 59 to 74 years old underwent unilateral TKA with the PEEK prosthesis between June 2021 and August 2021. Dynamic early postoperative changes in the volume and distribution of knee effusion were evaluated with use of 3D MR stereoscopic images. Serum inflammatory markers were measured via blood tests, and joint function was evaluated with use of the subjective functional score of the Knee Society Score (KSS) and knee range of motion (ROM). Linear regression analyses were performed to assess for correlations between knee effusion volume and inflammatory markers and between knee effusion volume and joint function. Results: The mean serum inflammatory marker levels increased significantly at 1 week after TKA with the PEEK prosthesis and then gradually decreased with time from 1 to 6 months. The mean total knee effusion volume gradually decreased over time. Concurrently, the mean KSS subjective functional score and mean knee ROM improved with time. Total knee effusion volume was positively correlated with C-reactive protein level (R 2 = 0.16; p = 0.007) and negatively correlated with the change in KSS score between the preoperative and postoperative time points (R 2 = 0.19; p = 0.003). Using the 1-week total knee effusion volume as a reference, a positive correlation was observed between the reduction in total knee effusion volume and the actual value of the ROM (R 2 = 0.36; p = 0.0001) from 3 to 24 months postoperatively. Conclusions: Through 3D MR imaging, the precise distribution and volume of, and dynamic changes in, knee effusion after TKA with the PEEK prosthesis were confirmed and were found to be correlated with inflammation and joint function in the early postoperative period. The results demonstrate the potential clinical benefit of the PEEK-based knee system for future use. Level of Evidence: Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.