Capsaicin Instillation for Postoperative Pain following Total Knee Arthroplasty
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Capsaicin Instillation for Postoperative Pain following Total Knee Arthroplasty A Preliminary Report of a Randomized, Double-Blind, Parallel-Group, Placebo-Controlled, Multicentre Trial Craig T. Hartrick, Cecile Pestano, Nickole Carlson and Susan Hartrick Anesthesiology Research, Oakland University William Beaumont School of Medicine, Beaumont Health System, Royal Oak and Troy, MI, USA
Abstract
Background: Pain following total knee arthroplasty (TKA) interferes with rehabilitation. Capsaicin applied in high concentration to nociceptors can cause relatively selective C-fibre desensitization for a period of weeks to months. Resultant long-lasting analgesia might facilitate rehabilitation. Objective: The objective of this study was to determine if direct instillation of a high-concentration capsaicin preparation into the wound following TKA would provide pain relief, improve physical functioning and rehabilitation, and reduce opioid requirements. Methods: This was a randomized, double-blind, parallel-group, placebocontrolled, multicentre, phase II trial carried out in a teaching hospital system. Non-opioid-tolerant males or females aged 18–85 years with a body mass index (BMI) £45 kg/m2, American Society of Anesthesiologists (ASA) physical status 1–3 and end-stage osteoarthritis who were scheduled for primary unilateral TKA were included. Patients received placebo vehicle or capsaicin 15 mg (Anesiva 4975) by instillation immediately prior to wound closure. Surgery was conducted under spinal anaesthesia and femoral nerve block. Postoperative rescue analgesia consisted of intravenous patientcontrolled analgesia with morphine for 24 hours; oral oxycodone was provided thereafter as needed. It was hypothesized prior to data collection that capsaicin instillation would reduce postoperative pain scores and result in improved patient satisfaction and ambulation. The primary outcome was the area under the numerical rating scale (NRS) for pain score-time curve from 4 to 24 hours (AUC4–24). NRS for pain scores were obtained every 4 hours for 24 hours then daily with ambulation and physical therapy for 3 days. Function and patient satisfaction were assessed at 14, 28 and 42 days. Results: Data from 14 patients (seven per group) from a single centre (data were not available from other sites because of sponsor bankruptcy) were available for this preliminary report. AUC4–24 was not significantly different clinically (placebo 70.3; capsaicin 65.7) in this sample; however, a significant
Hartrick et al.
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opioid-sparing effect was seen in the capsaicin group despite the fact that patients in this group had higher BMIs. Pain scores tended to be lower in the capsaicin group, despite the fact that patients in this group received significantly less rescue opioid medication. Morphine use from 12–24 hours was lower (capsaicin group mean 13.4 mg; 95% confidence interval [CI] 7.4, 19.5; range 10–21 mg vs placebo group mean 25.9 mg; 95% CI 19.8, 32.0; range 15–3
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