Objective – To identify quantifiable kinematical parameters that give an objective image of degree of lameness in horses after induced lameness of the tarso-crural joint with LPS and to test the effectiveness of an intra-articular administered opioid morphine. Study design – Randomized, blinded cross-over clinical study Animals – 8 clinically sound Dutch warm blood mares Procedure – Lameness was induced with an intra-articular (IA) injection of lipopolysaccharide (LPS). One hour after LPS injection the horses were treated with an IA injection of morphine (MOR) 120 mg diluted with NaCl to a solution of 20 ml or with 20 ml saline (SAL) as control. The horses had to walk and trot on a treadmill and kinematic measurements were made before and 4, 8 and 28 hours after LPS induced lameness. Kinematic measurements were made of the hoof, fetlock joint, tarsal joint, stifle joint, trochanter major (hip joint), tuber coxae and sacrum. Lameness was subjectively scored by an orthopaedic using a scale of the standard American Association of Equine Practitioners. Data are reported as mean ± SEM and were analyzed using SPSS. Differences were considered significant at P < 0,05. Results – After lameness induction the range of motion of the tarsal and fetlock joint significantly decreased in the control group and after IA administration of morphine the range of motion of the fetlock joint and the tarsal joint significant increased and returned to baseline levels. Significant compensatory effects were only seen in symmetry indices of the range of motion of the contralateral hind limb of the tarsal joint at walk. Fetlock joint extension at walk was decreased up to 28 hours after lameness induction. Subjective clinical lameness score showed a significant increase in lameness grade after LPS injection in the control group. A decrease in lameness grade after IA injection of morphine was seen at 4 and 8 hours after lameness induction in clinical lameness scores. Subjective clinical lameness score showed all horses to be sound at 28 hours after lameness induction with LPS. Conclusions and Clinical Relevance - Morphine had a strong clinical analgesic effect. The analgesic effect of IA morphine was seen in objective kinematical parameters as well. No systemic side effects could be detected after IA administered morphine. Subtle or slight lameness could be detected in some of the objective kinematical parameters up to 28 hours after lameness induction. In contrast, subjective lameness scoring showed all horses to be sound at 28 hours after lameness induction
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