A prospective, randomized, double-blind, controlled study was conducted to assess the efficacy of intra-articular bupivacaine and diamorphine. Ninety-six day-case patients were allocated randomly to receive intra-articular injections of either 20 mL 0.9% saline (control, n = 35), 20 mL 0.5% plain bupivacaine (n = 31), or 20 mL 0.9% saline with 5 mg diamorphine (n = 30) prior to tourniquet release. Visual analogue scales (VAS) were completed at 1 h, 3 h (discharge) and 24 h, and supplementary analgesia noted. Intra-articular analgesics conferred a noticeable improvement in patient comfort. First, the quantity of supplementary analgesia required prior to discharge was significantly reduced (P = 0.016); second, patients reported a less disturbed night's sleep (P = 0.034).