Types of Chronic Pain After Total Knee Arthroplasty and Their Relationship with Pain Intensity, Disability, and Quality of Life

OBJECTIVE: To determine the prevalence of different pain mechanisms, including nociplastic pain, and to evaluate the associations of these mechanisms with pain intensity, disability, pain catastrophizing, and quality of life in patients with chronic pain after total knee arthroplasty (TKA).MATERIALS and METHODS: This single-center cross-sectional observational study included 200 consecutive patients with chronic post-TKA pain between November 2022 and January 2023. Chronic post-TKA pain was defined as patient-reported pain in the operated knee persisting or recurring for more than three months after primary TKA, with a visual analog scale (VAS) score greater than 0 at the study visit. Neuropathic pain was identified using the painDETECT questionnaire. In patients not classified as possible or likely neuropathic pain, nociplastic pain affecting the musculoskeletal system was identified using the clinical criteria and grading system proposed by Kosek et al., including clinical history and bedside sensory examination for static mechanical allodynia, dynamic mechanical allodynia, thermal allodynia, and hyperalgesia. Patients were assigned to one dominant pain phenotype according to an a priori analytic hierarchy: neuropathic, nociplastic, and nociceptive pain. Pain intensity was assessed using the VAS, pain catastrophizing by the Pain Catastrophizing Scale, disability by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and quality of life by the 36-item Short Form Health Survey (SF-36).RESULTS: According to the classification hierarchy, 29 patients (14.5%) had possible neuropathic pain, 22 (11.0%) had neuropathic pain, 35 (17.5%) had possible nociplastic pain, 61 (30.5%) had probable nociplastic pain, and 53 (26.5%) had nociceptive pain. VAS, WOMAC, and Pain Catastrophizing Scale scores differed significantly across pain phenotype groups (all p<0.001). Patients with possible neuropathic, neuropathic, and probable nociplastic pain generally showed greater pain intensity, disability, and pain catastrophizing than those with nociceptive pain. SF-36 physical and mental component scores also differed significantly between groups, with the lowest scores generally observed in the probable nociplastic and possible neuropathic groups.CONCLUSION: Chronic pain after TKA is mechanistically heterogeneous, and approximately three quarters of the present cohort showed possible or likely neuropathic or nociplastic features. These findings support structured mechanism-based evaluation before and after TKA, while also emphasizing the need for prospective studies including preoperative pain phenotyping and standardized sensory testing.