Hyperosmolar irrigation solutions have been shown to decrease fluid extravasation during arthroscopic procedures and safety has been demonstrated in canine and human studies. Prospective, blinded, randomized controlled trial was performed to compare lactated Ringer's solution (273 mOsm/L) and a hyperosmolar (600 mOsm/L) irrigation solution for an exploratory medial femorotibial joint arthroscopy. Primary outcomes focused on the amount of periarticular fluid retention based on change in stifle girth and ultrasonographic (US) measurements. The water content of the tissue samples was assessed, and viability of the cartilage tissue was determined. The objectives of this study were to determine: (1) whether an irrigation solution that is hyperosmolar relative to synovial fluid decreases tissue extravasation during an arthroscopic protocol when compared to a relatively hypoosmolar solution, (2) the safety of a hyperosmolar solution by assessing the viability of joint tissues after joint irrigation, (3) if the use of a hyperosmolar solution decreases water content in stifle tissue. There was not a significant difference in joint swelling between hyperosmolar (Hyper) and lactated Ringer's solution (LRS) treatment groups. Percent increments in femorotibial joint dimensions (mean [plus or minus] S.D.) were seen in both treatment groups based on US (LRS, 83.9 [plus or minus] 84.6 percent; HYPER, 131.2 [plus or minus] 144.9 percent) and caliper measurements (LRS 5.5 [plus or minus] 4.3 percent; HYPER 7.5 [plus or minus] 5.8 percent) (p[less than or equal to]0.05). Chondrocyte viability and tissue water content were well maintained in both treatment groups, and differences were not statistically significant. These findings suggest that approximately doubling the osmolarity of the standard irrigation solution used for arthroscopy did not result in detrimental effects on chondrocyte viability or tissue water content, it did not significantly reduce tissue swelling.