Adaptation strategies of horses with induced forelimb lameness walking on a treadmill.

BACKGROUND: There is a paucity of research describing the gait pattern of lame horses at the walk. OBJECTIVES: To describe the changes in motion pattern and vertical ground reaction forces (GRFz) in horses with induced forelimb lameness at the walk and compare those changes with the changes observed at the trot. STUDY DESIGN: Experimental study. METHODS: In 10 clinically sound Warmblood horses, moderate forelimb lameness was induced using a sole pressure model followed by trot and walk on a treadmill. Kinematic data were collected using 3D optical motion capture (OMC), and GRFz by an instrumented treadmill. Mixed models were used to compare sound baseline versus forelimb lameness (significance was set at P < .05). RESULTS: Lameness induction significantly reduced peak GRFz on the second force peak, and vertical impulse in the lame limb. Stride and stance duration in all limbs were reduced. Lameness significantly affected the vertical movement symmetry of the head and withers. Maximum limb retraction angle, fetlock extension and protraction speed were reduced in the lame limb. Body centre of mass (COM) translation was reduced in the side-to-side direction and increased in the vertical and fore-aft directions. Several compensatory kinetic and kinematic changes were observed in the nonlame limbs. The observed changes in both kinetics and kinematics were generally smaller at walk with fewer variables being affected, compared to the trot. MAIN LIMITATIONS: Only one degree and type of orthopaedic pain (sole pressure) was studied. CONCLUSIONS: Compensatory strategies of forelimb lameness at the walk include alteration of several kinetic and kinematic parameters and have some specific patterns and inter-individual differences that are not seen at the trot. However, much like at the trot, head movement and forelimb vertical force symmetry seem to be the most useful parameters to detect forelimb lameness at walk.

Analgesic efficacy of intra-articular morphine in experimentally induced radiocarpal synovitis in horses.

OBJECTIVE: To compare the analgesic effect of intra-articular (IA) and intravenous (IV) morphine in horses with experimentally induced synovitis. ANIMALS: Eight adult horses. STUDY DESIGN: Randomized, observer blinded, double dummy trial with sequential crossover design. METHODS: Radiocarpal synovitis was induced by IA injection of lipopolysaccharide on two occasions separated by a 3-week washout period. In one study period horses received treatment IA; morphine IA (0.05 mg kg(-1)) plus saline IV and in the other study period they received treatment IV; saline IA plus morphine IV (0.05 mg kg(-1)). Lameness and pain were evaluated repeatedly by two observers throughout each of the two 168-hour study periods. Pain was evaluated by use of a visual analogue scale of pain intensity (VAS) and a composite measure pain scale (CMPS). Comparison of treatments was performed by analysis of variance with repeated measurements. Significance level was set to p < or = 0.05. Inter-observer agreement and agreement between the VAS and CMPS was assessed by use of the Bland-Altman method. RESULTS: Intra-articular injection of LPS elicited a marked synovitis resulting in lameness and pain. IA morphine resulted in significantly less lameness than IV morphine (p = 0.03). CMPS (p = 0.09) and VAS (p = 0.10) pain scores did not differ significantly between treatments. Inter-observer agreement of the CMPS was classified as good, but only fair for the VAS. Agreement between the two pain scales was considered fair. CONCLUSIONS AND CLINICAL RELEVANCE: An analgesic effect of IA morphine was demonstrated by significantly reduced lameness scores. The results support the common practice of including IA morphine in a multimodal analgesic protocol after arthroscopic surgery, although further studies in clinical cases are needed. The employed CMPS had good reproducibility, and was easy to use, but may have limited sensitivity at mild intensity pain.

Pharmacokinetics of intra-articular morphine in horses with lipopolysaccharide-induced synovitis.

OBJECTIVE: To describe the pharmacokinetics of intra-articularly (IA) administered morphine. STUDY DESIGN: Experimental randomized, cross-over study. ANIMALS: Eight adult healthy mixed breed horses aged 6.5 +/- 2.3 (mean +/- SD) years and weighing 535 +/- 86 kg. METHODS: Unilateral radiocarpal synovitis was induced by IA injection of 3 microg lipopolysaccharide (LPS) on two occasions (right and left radiocarpal joint, respectively) separated by a 3-week wash-out period. Treatments were administered 4 hours post-LPS-injection: Treatment IA; preservative free morphine IA (0.05 mg kg(-1)) plus saline intravenous (IV) and treatment IV; saline IA plus preservative free morphine IV (0.05 mg kg(-1)). Concentrations of morphine, morphine-3-glucuronide and morphine-6-glucuronide (M6G) were determined repeatedly in serum and synovial fluid (SF) by high-performance liquid chromatography mass spectrometry, at 2 and 4 hours and then at 4 hours intervals until 28 hours post-treatment. RESULTS: Injection of LPS elicited a marked and comparable synovitis in all LPS-injected radiocarpal joints. IA administered morphine was detectable in SF of all eight joints 24 hours post-treatment and in 6/8 joints 28 hours post-treatment. The terminal half-life of morphine in SF was estimated to be 2.6 hours. IA administration of morphine resulted in mean serum concentrations of morphine below 5 ng mL(-1) from 2 to 28 hours after treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Intra-articularly administered morphine remained within the joint for at least 24 hours. At the same time only very low serum concentrations of morphine and M6G were detected. The present results suggest that IA morphine at 0.05 mg kg(-1) may be used for IA analgesia lasting at least 24 hours and give strong support to the theory that previously observed analgesic and anti-inflammatory effects of IA morphine in horses are most likely to be mediated peripherally.

Anti-inflammatory effects of intra-articular administration of morphine in horses with experimentally induced synovitis.

OBJECTIVE: To compare the effects of intra-articular (IA) versus IV administration of morphine on local and systemic inflammatory responses in horses with experimentally induced acute synovitis. ANIMALS: 8 horses. PROCEDURES: Each horse received the following 2 treatments 4 hours after synovitis was induced: IA administration of morphine (0.05 mg/kg) with IV administration of 1 mL of saline (0.9% NaCl) solution/100 kg, and IA administration of 1 mL of saline solution/100 kg with IV administration of morphine (0.05 mg/kg). Treatments were administered in randomized order with a washout period of 3 weeks between treatments. Before each treatment, aseptic synovitis was induced by injection of lipopolysaccharide into a radiocarpal joint. For the second treatment, the contralateral radiocarpal joint was selected. Joint swelling and skin temperature over the treated joints were recorded. Clinical examinations were performed, and blood WBC count, serum amyloid A (SAA) concentration, serum cortisol concentration, synovial fluid WBC count, synovial fluid total protein (TP) concentration, and synovial fluid SAA concentration were measured before and repeatedly during each of the two 168-hour study periods. Data were analyzed by use of ANOVA with repeated measures. RESULTS: IA administration of morphine resulted in significantly less joint swelling and lower synovial fluid TP and serum and synovial fluid SAA concentrations, and blood WBC count than did IV administration of morphine. CONCLUSIONS AND CLINICAL RELEVANCE: IA administration of morphine exerted anti-inflammatory properties in horses with experimentally induced acute synovitis, supporting its use as a part of a balanced analgesic protocol.