Participants with mild, moderate, or severe pain following total hip arthroplasty. A sub-study of the PANSAID trial on paracetamol and ibuprofen for postoperative pain treatment

Abstract

Objectives: In this sub-study of the 'Paracetamol and Ibuprofen in Combination' (PANSAID) trial, in which participants were randomised to one of four different non-opioids analgesic regimen consisting of paracetamol, ibuprofen, or a combination of the two after planned primary total hip arthroplasty, our aims were to investigate the distribution of participants' pain (mild, moderate or severe), integrate opioid use and pain to a single score (Silverman Integrated Approach (SIA)-score), and identify preoperative risk factors for severe pain.

Methods: We calculated the proportions of participants with mild (VAS 0-30 mm), moderate (VAS 31-60 mm) or severe (VAS 61-100 mm) pain and the SIA-scores (a sum of rank-based percentage differences from the mean rank in pain scores and opioid use, ranging from -200 to 200%). Using logistic regression with backwards elimination, we investigated the association between severe pain and easily obtainable preoperative patient characteristics.

Results: Among 556 participants from the modified intention-to-treat population, 33% (95% CI: 26-42) (Group Paracetamol + Ibuprofen (PCM + IBU)), 28% (95% CI: 21-37) (Group Paracetamol (PCM)), 23% (95% CI: 17-31) (Group Ibuprofen (IBU)), and 19% (95% CI: 13-27) (Group Half Strength-Paracetamol + Ibuprofen (HS-PCM + IBU)) experienced mild pain 6 h postoperatively during mobilisation. Median SIA-scores during mobilisation were: Group PCM + IBU: -48% (IQR: -112 to 31), Group PCM: 40% (IQR: -31 to 97), Group IBU: -5% (IQR: -57 to 67), and Group HS-PCM + IBU: 6% (IQR: -70 to 74) (overall difference: p=0.0001). Use of analgesics before surgery was the only covariate associated with severe pain (non-opioid: OR 0.50, 95% CI: 0.29-0.82, weak opioid 0.56, 95% CI: 0.28-1.16, reference no analgesics before surgery, p=0.02).

Conclusions: Only one third of participants using paracetamol and ibuprofen experienced mild pain after total hip arthroplasty and even fewer experienced mild pain using each drug alone as basic non-opioid analgesic treatment. We were not able, in any clinically relevant way, to predict severe postoperative pain. A more extensive postoperative pain regimen than paracetamol, ibuprofen and opioids may be needed for a large proportion of patients having total hip arthroplasty. SIA-scores integrate pain scores and opioid use for the individual patient and may add valuable information in acute pain research.

Keywords: ibuprofen; integrated pain score and opioid use; paracetamol; postoperative pain; prediction of pain; total hip arthroplasty.