Objectives: (1) To report the clinical and synovial effects of a platelet-rich product (PRPr) in normal equine joints, (2) to assess the persistence of platelets within synovial fluid after intra-articular injection, (3) to compare responses to different preparations of that product, and (4) to evaluate a gravity filtration system for PRPr preparation in horses. Study Design: Experimental. Methods: A platelet-rich saline product (PRPr) was prepared from 7 normal horses using a proprietary preparation device and was divided into 3 treatments: resting, CaCl2-activated (23mM, final), and bovine thrombin-activated (10U/mL, final). Each horse had 3 concurrent randomly assigned intra-articular PRPr treatments administered in their metacarpophalangeal/metatarsophalangeal joints; the fourth limb was injected with saline (0.9% NaCl) solution as a control. Clinical assessments, cytologic analysis of synovial fluid and hemograms were performed at 6, 24, 48, and 96hours after injection. PRPr composition and growth factor content were analyzed. Results: The gravity filtration system produced a moderately concentrated PRPr. At 6 and 24hours, when compared to control values, all PRPr treatments caused a significant increase in synovial WBC concentration (P<.0059) and neutrophil percentage (P<.0005). Bovine thrombin-activated PRPr injection consistently caused increased effusion scores and periarticular signs. At all time points, the synovial WBC concentration after thrombin-activated PRPr was significantly greater (P<.001) than for the control, CaCl2-activated or resting PRPr. Intact platelets could be observed in synovial fluid for up to 5 days after intra-articular PRPr injection. Conclusions: Resting and CaCl2-activated PRPr may be safely used to treat equine joints, but bovine thrombin activation is not recommended at 10U/mL. A PRPr can be prepared using a gravity filtration system, eliminating the need for centrifugation.
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