LAMENESS
Cryotherapy: Analgesia or Just Anti-inflammatory? By Paul Basilio Cryotherapy’s effects on inflammation are well known in both human and veterinary medicine, but an accurate analgesic picture is still unclear. To help fill in the gaps, Vivian Quam, MA, DVM, and colleagues designed an induced-lameness model applicable to sport horses in competition. “The ultimate objective is to understand how best to utilize cryotherapy as a tool for multimodal analgesia in our patients, as well as for a tool for safely managing the sport horse in competition,” said Dr. Quam, from the Department of Veterinary Clinical Sciences at The Ohio State University. In human sports medicine, cryotherapy has been employed commonly as an alternative or complementary therapy in elite athletes that face drug screening. It decreases synovial inflammation and knee pain in nonseptic joints for more than 24 hours, and intermittent cryotherapy improves pain, function and swelling in closed soft-tissue injuries. “It has also been shown to increase the pain threshold and pain tolerance at the site of cryotherapy application as well as at distal locations,” Dr. Quam said. “This suggests that a reduction in nerve conduction velocity is the mechanism of action for the analgesic effect of cryotherapy.”
Testing the Unknown
Dr. Quam’s team hypothesized that 60 minutes of cryotherapy in an ice water slurry would produce an analgesic effect that could be observed with a noninvasive sensor in horses with an induced forelimb lameness. The researchers selected 10 mature research horses with a normal physical examination and a negligible degree of observed lameness when trotted on a straight line, and all experimental procedures were conducted in accordance with IACUC standards. Study horses were sedated with IV acepromazine. The first dose was administered prior to a 100-m baseline jog on grass, and the second dose was administered while in stocks halfway through the treatment hour. Each horse was assigned to the cryotherapy or control group during the first treatment period, and they were then crossed over following a 2-week washout. A farrier applied steel keg shoes to both forefeet. The medial and lateral shoe branches had pre-drilled holes at the level of the heel bulbs to induce an AAEP Grade 3 lameness via screw application. It should be noted that their transient lameness model was successful, in that a similar lameness level was noted before lameness induction and shortly after the study period. The affected distal forelimbs were maintained at 6° C using a cryotherapy boot filled with an ice slurry 14
Issue 11/2020 | ModernEquineVet.com
in the experimental group or at ambient temperature in the control group. The contralateral limbs in each group were outfitted with a standard gel orthotic. “After the treatment hour, the degree of lameness was assessed at 5, 10, 15, 20, 30, 45, and 60 minutes post-treatment,” Dr. Quam said. “The screw was removed and lameness was assessed following removal to ensure that the method of lameness induction was not causing excessive pressure and pain that would persist following removal.”
Results
Cryotherapy was maintained without difficulty for the duration of treatment, and no changes in heart rate that would indicate pain from treatment were seen. The degree of induced lameness did not differ between cryotherapy and control groups, indicating that lameness induction was successful and both groups had the same degree of lameness before and after induction. “Both treatment groups experienced a reduction in lameness following the treatment hour,” Dr. Quam said. “However, the cryotherapy had a statistically significant lameness improvement at 5 and 10 minutes after the treatment period, indicating that the degree of lameness was improved at these points.” In the control group, however, there was only statistical significance at 5 minutes post-treatment. No significant improvement in lameness was noted for either group 15 minutes following treatment or in subsequent assessments. At 15 minutes, the lameness improvement was greater for the cryotherapy group than for the control group. After 1 hour, the treatment group had a longer duration of improved lameness vs. controls. In addition, 1° of lameness improvement was detectable in the cryotherapy group, but only at 15 minutes of treatment. “This study showed a modest reduction in lameness following 1 hour of cryotherapy, while the therapeutic effect diminished over the post-treatment hour,” she said. “Significant lameness improvement could be detected at least 10 minutes after cryotherapy.” This work serves as groundwork for further research that should determine the ideal method, duration and temperature for provision of analgesia, she said. “We could have missed a small analgesic effect over a longer period in the study due to the small number of [horses] and high individual variability. Alternatively, the time of cryotherapy in this model may have been insufficient to maintain an optimal effect of the hypothermia.” Dr. Quam discussed her research at the AAEP 65th Annual Convention & Trade Show in Denver. MeV
