154. NEUROPATHIC PAIN AFTER KNEE ARTHROPLASTY

Abstract

Purpose of the study: The favourable outcome with knee arthroplasty can be compromised by persistent unexplained pain. Postoperative pain accounts for about 30% of the complaints of chronic pain present in 25% of the general population and would be to a large extent of neuropathic origin (DCN). The purpose of this work was to evaluate pain before and after knee arthroplasty in terms of intensity and clinical expression.

Material and methods: A prospective monocentric epidemiology study was conducted to validate self-administrated questionnaires which, over a six month period, were completed by knee arthroplasty patients. A numerical scale (Nu) from 0 to 10, a 7-item questionnaire screening for neuropathic pain (burns, painful cold, electrical discharge, tingling, pins and needles, numbness, itching) scored 0 or 1 and positive if the score is ≥3 (DN4), an abridged qualitative pain questionnaire (QDSA) divided into a sensorial score (QDSAs) and an affective score (QDSAa), and a scale evaluating anxiety and depression (HAD) were recorded preoperatively, (T0), at 3rd postoperative day (PO), 1st (M1), 3rd (M2) and 6th (M6) postoperative month. Outcome was expressed as mean±SD or median and range.

Results: Eight men and 39 women, mean age 66.6±10.7 years were included. These patients. Fourteen of 47 (25.9%) had DCN postoperatively (2 DN4 successively ≥3). The “tingles” item for postoperative DN4 was significantly predictive of DCN (specificity 88.9%, sensitivity 83.3%). Preoperatively, the median intensity of pain was 6 (5–10) and was significantly higher in patients with DCN compared with those without DCN at M1 (4 [1–8] vs 3 [0–7]) and M3 (4 [1–8] vs 2 [0–6]) (p < 0,009) including 3/14 patients with Nu > 7 at M3. At M6, 12.7 % (n = 6/47) patients still had DN4 ≥3. The QDSAs score was higher in patients with DCN at M1 (11.8±4.4 vs 4.8±4.5; p < 0.001) and M3 (10.2±6 vs 3.5±3.2; p < 0.001). There was no significant difference between the QDSAa scores and the HAD.

Conclusion: The persistence of unusually intense pain after knee arthroplasty would suggest the pain could result from a neuropathological source which would require specific treatment because of the general insensitivity to analgesics.