BACKGROUND: Pre-operative opioid use has been suggested to increase post-operative pain and opioid consumption after total knee arthroplasty (TKA), but previous studies are either retrospective or inhomogeneous with regard to surgical procedures or control of analgesic regimes, or with few opioid-treated patients, hindering firm conclusions.

METHODS: In a prospective observational study, we investigated the effect of > 4 weeks pre-operative opioid use [none vs. low dose (< 30 mg morphine equivalents (eq.)) vs. high dose (> 30 mg morphine eq.] in patients scheduled for primary, unilateral TKA. All patients had well-defined multimodal opioid-sparring perioperative analgesic therapy, and continued any pre-operative opioid medication. The primary outcome was differences between groups in pain at rest and during walk for the first 6 post-operative days.

RESULTS: Among 123 patients included, 115 were available for final analysis (93% follow-up rate). Post-operative pain during walk was significantly increased in both opioid-treated groups vs. non-opioid-treated patients (P < 0.009). Secondary analysis of combining all pre-operatively opioid-treated patients vs. opioid-free patients, showed significantly increased pain at rest and walk and increased post-operative opioid requirement - excluding pre-operative dosage - during the first post-operative week in opioid-treated patients (P = 0.001 and P = 0.007, respectively).

CONCLUSION: Pre-operative opioid use increases the risk for post-operative pain at rest and walk, and increased opioid consumption after TKA.