OBJECTIVE: Intra-articular injection of local anesthetic and/or corticosteroid is an adjunct treatment for arthritic and inflammatory orthopedic conditions. Despite potential benefits, there is growing concern that these medications may cause significant morbidity, including potential toxicity to intra-articular chondrocytes and synoviocytes. DESIGN: Twenty dogs underwent intra-articular injection of the shoulder joint using ultrasound guidance, with the following injectates (n = 5 each): negative control (saline), methylprednisolone/1.0% lidocaine, triamcinolone/1.0% lidocaine, and triamcinolone/0.0625% bupivacaine. The dogs were euthanized 24 hours postinjection for reasons unrelated to this study. Synovium/cartilage explants were harvested under sterile conditions and assessed immediately or cultured for 7 days. Synoviocyte and chondrocyte viability was determined on day 1 and day 7 using Calcien AM and Sytox Blue live/dead fluorescent stains, and cell metabolism determined on day 2 using the alamar blue additive test. Results were compared statistically. RESULTS: On day 1 synovium exposed to 1%L/M demonstrated a significant decrease in cell metabolism (P = 0.0107) and subjective synoviocyte viability scores (P = 0.013) compared with the negative control. Cartilage exposed to 1%L/M demonstrated decreased chondrocyte viability and cell metabolism versus all other groups, although not significantly. After 7 days of culture, cartilage viable cell density in the 1%L/M group was significantly (P ≤ 0.001) lower than the negative control. Subjective synoviocyte viability scores was significantly lower in the 1%L/M (P = 0.013), 1%L/T (P ≤ 0.001), and 0.0625%B/T groups (P = 0.006) compared with the negative control. CONCLUSIONS: This study suggests potential negative effects of combination local anesthetic/corticosteroid on intra-articular cell viability and cell metabolism. Further study is needed before determining definitive clinical recommendations.