Does reducing the concentration of bupivacaine when performing therapeutic shoulder joint injections impact the clinical outcome?

OBJECTIVE: Mixtures of local anesthetics and steroids are routinely injected intraarticularly to temporarily relieve joint pain, even though local anesthetics have been reported to cause chondrocyte death in a dose- and time-dependent manner. This study aimed to determine if intraarticular injections of bupivacaine 0.5% and bupivacaine 0.25% would provide similar pain relief. MATERIALS AND METHODS: All fluoroscopically guided glenohumeral joint injections performed using 2.5 mL of bupivacaine and 0.5 mL (20 mg) of triamcinolone acetonide over a 42-month period were included if a pain score was recorded before, 5.10 minutes after, and 1 week after injection. Pain reduction of more than 2 points was considered much improved clinically with pain reduction of more than 1 point considered the minimum clinically important difference (MCID) threshold. RESULTS: Statistically significant and much improved pain reduction was achieved using both bupivacaine 0.5% and 0.25% 5.10 minutes (-3.7 points; 95% CI, -3.4 to -4.0 points; p ≤ 0.001; and.3.3 points; 95% CI, -3.0 to -3.5 points; p ≤ 0.001) and 1 week (-2.5 points; 95% CI, -2.2 to -2.9 points; p ≤ 0.001; and -2.1 points; 95% CI, -1.8 to -2.3 points; p ≤ 0.001) after injection, respectively. Adjusting for age, sex, pain score before injection, and indication, the mean decrease in pain was greater in the bupivacaine 0.5% group by 0.30 points 5.10 minutes after injection (95% CI, -0.03 to 0.63 points; p = 0.08) and 0.46 points 1 week after injection (95% CI, 0.13.0.77 points; p = 0.01). CONCLUSION: Both bupivacaine 0.5% and bupivacaine 0.25% provide statistically significant and much improved pain relief 5.10 minutes and 1 week after intraarticular glenohumeral injections. Bupivacaine 0.5% provided greater pain relief than bupivacaine 0.25%, but the difference was less than 0.5 points and therefore did not meet the MCID threshold.