|Abstract / Summary|
Knee arthroplasty (KA) surgeries are effective and successful but about 20% of the patients report dissatisfaction in the form of persistent pain or functional limitations after the operation. The evidence suggests that pain catastrophizing may influence the outcome after a KA, but much is still unknown and only few studies have assessed the predictive value of pain catastrophizing on physical function or physical activity after a KA. Furthermore, only little is known about the potential of a cognitive-behavioural therapy (CBT) based intervention for patients with high levels of preoperative pain catastrophizing.
The overall aim of this PhD thesis was to examine the influence of pain catastrophizing on pain, physical function, physical activity, muscle mass and general health both among patients with clinical symptoms of knee osteoarthritis (OA) and among patients referred for KA. Furthermore, to examine whether the severity of radiographic OA is associated with the degree of physical symptoms and whether it is associated with being operated on or not. Finally, to investigate the effectiveness of a patient education based on CBT given to patients with high levels of preoperative pain catastrophizing undergoing a total knee arthroplasty (TKA).
This thesis consists of four studies. Study I was a cross-sectional study including 325 patients referred to the Orthopaedic Outpatient Knee Clinic with clinical symptoms of knee OA. The patients completed EuroQol-5D (EQ-5D), The Short Form-36 (SF-36(PF)), The Oxford Knee Score (OKS) and The Pain Catastrophizing Scale (PCS) and the severity of radiographic OA was graded with the Kellgren–Lawrence Scale (KLS). Study II was a cohort study including 615 patients scheduled for KA. The patients completed the PCS prior to surgery and the OKS, the SF-36 (PF) and the EQ-5D prior to surgery, and 4 and 12 months after the surgery. Study III was a randomized controlled trial including 60 patients referred for TKA with high levels of pain catastrophizing. The patients were randomized to either CBT based pain education or usual care. The primary outcome measure was pain under activity measured with the Visual Analog Scale (VAS). All outcomes were measured preoperatively, at 3 months, and at 1 year after surgery. Study IV was a cohort study including 58 patients referred for TKA due to OA. Physical activity was measured with a tri-axial accelerometer before surgery and 3 and 12 months after the surgery. Other outcome measures consisted of Knee Injury and Osteoarthritis Outcome Score (KOOS), 6-Minutes’ Walk Test (6MWT), 30 seconds Chair Stand Test (30CST) and Dual-energy X-ray Absorptiometry (DXA) scans.
Among patients with knee OA, we found that high PCS was associated with higher levels of pain and lower physical function. We found, however, no correlations between radiographic OA and physical symptoms except for a weak correlation between KLS and SF-36. Among patients that had undergone a KA, we found that patients with high preoperative PCS had larger improvements in physical function from before surgery to 12 months after surgery than patients with low PCS. However, patients with high PCS reported significantly lower physical function and health related quality of life both preoperatively and 4 and 12 months postoperatively. Furthermore, we found that high pain catastrophizing was associated with higher levels of pain 12 months after the surgery. Preoperative pain catastrophizing did not influence objectively measured physical activity (PA) 12 months after a TKA, but preoperatively patients with high PCS had lower scores in the KOOS subscales; symptoms, pain and ADL. Moreover, they had statistically significantly higher BMI and percent fat mass and lower percent muscle mass than patients with low PCS. For patients with high PCS, participation in a CBT-based patient education in addition to usual care did not result in better outcomes 12 months after TKA.
In the future, further research is warranted to identify preoperative predictors of persistent pain as well as interventions for the approximately 20% of the patients with persisting pain after a TKA.