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Individuals with knee osteoarthritis (OA) who have indicators of high vs low/no levels of neuropathic pain may be at elevated risk for chronic pain after total knee replacement (TKR) surgery, according to findings published in The Journal of Pain.
Whether neuropathic pain symptoms before TKR are predictive of chronic pain after surgery has remained unclear. While elusive, the goal of identifying patients who are likely to experience postoperative knee pain is an important one for clinicians and researchers, and this study attempted to fill that gap.
A total of 50 patients with knee OA (mean age, 66.4 years; 60% women) scheduled for TKR and 22 healthy individuals without OA (mean age, 56.7 years; 59.1% women) were included in the study. Patients were asked to complete the PainDETECT questionnaire at the start of the longitudinal trial. PainDETECT scores ≥19 (high pain) were indicative of likely neuropathic pain, and scores <19 (low pain) indicated nociceptive pain or mixed pain phenotypes. Quantitative sensory testing — including pain detection thresholds, pain tolerance, temporal summation of pain, conditioned pain modulation, and pressure pain thresholds — and assessment of pain intensity using a visual analog scale (VAS) were performed preoperatively and 6 months after TKR.
Of the 50 participants with OA, 30% were categorized as having high pain before TKR, indicating neuropathic pain likely driven by centralized processing. Compared with patients in the low pain group and healthy study participants, individuals in the high pain group displayed facilitated temporal summation of pain and lower pressure pain thresholds (P <.001).
After surgery, patients in the high vs low pain group reported more elevated VAS scores (P =.0003), as well as a facilitation of the temporal summation of pain when compared with the control group (P =.022), with 30.4% of patients meeting the criteria for chronic postoperative pain (VAS >4). Participants in both pain groups showed significant improvement in PainDETECT scores after surgery compared with their preoperative levels (P =.002 and P <.0001 for high and low pain, respectively). Participants in both the high and low pain groups had lower pressure pain thresholds compared with the control group (P <.0001 and P =.001, respectively). There were no significant differences in pain detection thresholds or pressure pain thresholds between participants in the high and low pain groups, nor between either of these groups and healthy controls.
Significant associations were found between postoperative pain and preoperative PainDETECT scores (r =0.397; P =.003), VAS (r =0.413; P =.004), pressure pain thresholds (r =-0.262; P =.039), and induced temporal summation of pain (r =0.343; P =.010). After regression analysis, only preoperative PainDETECT scores remained an independent predictor of postoperative pain (adjusted coefficient, 0.397; P =.006).
Study limitations included a small sample size, risk for follow-up loss inherent to longitudinal studies, substantial age difference between the patient with OA and control groups, and lack of evaluation of sensory deficits.
Experiencing neuropathic pain before surgery indicated a poorer prognosis regarding postoperative pain. “This study has shown that PainDETECT classifications are associated [with] central pain mechanisms in OA pain,” noted the authors, adding, “The PainDETECT questionnaire may have an additional role as an added construct to [quantitative sensory testing] measures alongside subjective VAS scores and in identifying a subgroup of patients [in whom] chronic postoperative pain [is likely to develop] after TKR surgery.”
Reference
Kurien T, Arendt-Nielsen L, Petersen KK, Graven-Nielsen T, Scammell BE. Preoperative neuropathic pain like symptoms and central pain mechanisms in knee osteoarthritis predicts poor outcome 6 months after total knee replacement surgery [published online June 16, 2018]. J Pain. doi:10.1016/j.jpain.2018.05.011
