Frequency of neuropathic pain in patients with knee osteoarthritis

Objective: The aims of this study are to evaluate the frequency of neuropathic pain in patients with knee osteoarthritis (OA), assess the impact of neuropathic pain on knee-related disability and quality of life in knee OA, and objectively assess the impairment of light touch sensation due to possible nerve damage in the knee using the Semmes-Weinstein (SW) monofilament test. Materials and Methods: The study included 113 patients diagnosed with knee (OA) and 126 healthy controls. The age, gender, BMI, education level, and pain duration of both the patient and control groups were surveyed. Patients with knee OA were assessed using the Four-Question Neuropathic Pain Questionnaire (DN-4) to evaluate the presence of neuropathic pain components and were divided into two groups: those with neuropathic pain and those without. Radiological osteoarthritis severity was assessed using the Kellgren-Lawrence grading scale, pain intensity was measured using the Numeric Rating Scale (NRS), knee-related disability was evaluated using the WOMAC scale, and the quality of life of the patients was assessed using the SF-36 scale. The presence of possible tactile hypoesthesia in the knee was evaluated using the Semmes-Weinstein monofilament test in both the knee OA patients and the control group. Results: Neuropathic pain was detected in 30.08% of patients with knee OA. No statistically significant differences were found between the knee OA patients with and without neuropathic pain in terms of average age, gender, average BMI, and education level (p > 0.05). In patients with knee OA and neuropathic pain, both resting and movement Numeric Rating Scale (NRS) scores were significantly higher (p < 0.001). In the group with neuropathic pain, WOMAC pain, physical function, stiffness, and total scores were significantly higher (p < 0.05). In knee OA patients with neuropathic pain, the scores for total pain, physical functioning, physical role difficulty, emotional role difficulty, and social functioning from the SF-36 scale were significantly lower compared to those without neuropathic pain (p < 0.05). The average pain duration in the group with neuropathic pain was significantly longer than that in the group without neuropathic pain (p < 0.001). Radiological OA stages of knee OA patients with neuropathic pain were found to be more advanced compared to those without neuropathic pain (p < 0.05). The average Semmes-Weinstein monofilament test scores in patients with knee OA and neuropathic pain were higher across all regions of the knee compared to those without neuropathic pain and the controls (p < 0.001). Conclusion: This study detected a neuropathic pain component in 30.08% of patients with knee OA. In patients with neuropathic pain, it was observed that pain intensity and knee-related disabilities were higher, while physical functioning and quality of life were lower. In our study, based on the average values of the Semmes-Weinstein monofilament test, a quantitative sensory testing tool, it was shown that light touch sensation was impaired in all compartments of the knee in both all knee OA patients and those with concomitant neuropathic pain. Keywords: Knee osteoarthritis, Neuropathic pain, Quality of life