Patients with High Chronic Postoperative Knee Pain 5 years after Total Knee Replacement Demonstrate Low-grad Inflammation, Impairment of Function and High Levels of Pain Catastrophizing

Objectives: Total knee replacement (TKR) normally provides improvements of physical function and reduces pain. However, approximately 20% of the patients report chronic postoperative knee pain. The aims of the present study were to assess the pain, physical function, and physiological characteristics 5 years after TKR surgery. Methods: Eighty patients were recruited 5 years after TKR and divided into two groups based on their average 24-hour knee pain intensity assessed on a visual analog scale (VAS 0-10) ("High Pain Group": VAS≥3; "Low Pain Group": VAS<3). The patients completed the painDETECT (PD-Q), Oxford Knee Score (OKS), Pain Catastrophizing Scale (PCS), and Forgotten Joint Score (FJS-12). Furthermore, the patients underwent a clinical examination of the knees and high sensitivity serum C-reactive protein (hs-CRP) was measured as an inflammatory marker. Results: 53% of the patients in the High Pain Group was not satisfied with the outcome, while only 11% of the patients in the Low Pain Group was not satisfied, and the pain intensities in the two groups were 5.1 (4.6-5-6) and 1.1 (0.6-1.5), (P<0.001), respectively. Furthermore, the High Pain Group demonstrates worse scores in: FJS-12 (P=0.001), OKS function (P<0.001), OKS pain (P<0.001), and PCS (P<0.001). The High Pain Group demonstrated increased level of hs-CRP (4.3mg/L (3.2-5.5) vs. 1.7mg/L (1.2-2.2), P<0.001), and decreased range of motion in the knee (110-degrees ROM vs. 119-degrees ROM, P=0.013). Discussion: Patients with high chronic postoperative knee pain 5 years after TKR demonstrate decreased physical function, higher levels of catastrophizing thoughts, and increased levels of inflammation.