Hyperosmolar Irrigation Compared with a Standard Solution in an Equine Stifle Arthroscopy Model. Hayden L1, McCracken M1, Johnson P<sup>1, Stoker A2. 1University of Missouri, Veterinary Health Center, Columbia, MO; 2University of Missouri, Department of Orthopedic Surgery, Columbia, MO.
A hyperosmolar irrigation solution has been reported to be safe and has potential benefits for use during arthroscopy in human and canine studies. We hypothesized that joint irrigation using a relatively hyperosmolar irrigation solution would decrease fluid extravasation and periarticular joint swelling, without compromising the viability of joint tissues. A prospective, blinded, randomized controlled trial was performed to compare isotonic (LRS, 273 mOsm/L) and hyperosmolar (Hyper, 600 mOsm/L) irrigation solutions used for 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 using the Invitrogen microscopic fluorescent cell viability staining system. There was not a significant difference in joint swelling between Hyper and LRS treatment groups. The mean percentage change in stifle US measurements (Hyper 131.2%, LRS 83.9%) and caliper measurements of the femorotibial joint (Hyper 7.5%, LRS 5.5%) were significantly increased in both the treatment groups (P ≤ 0.041). Chondrocyte viability and tissue water content were well maintained in both treatment groups, and differences were not statistically significant. These findings suggest that whereas 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. Limitations included the number of subjects, and the model utilized does not directly apply to diseased joints or provide long-term outcome measures.