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Muscle injuries and PRP: what does the science say?
  1. Kimberly G Harmon
  1. Correspondence to Dr Kimberly G Harmon, Hall Health Sports Medicine Clinic, Box 354410, University of Washington, Seattle, WA 98195, USA; kharmon{at}

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Muscle strains and contusions are extremely common in sport and account for significant time loss.1 2 The healing process can be slow, and reinjury is common.3 Recently there has been significant interest in the use of platelet-rich plasma (PRP) to enhance healing. In this issue, Mei-Dan et al (see page 618) discuss the biological background and clinical rationale for the use of PRP.4 This paper will address the use of PRP to enhance the speed and quality of repair in muscle injury.

First phase of healing

When muscle is injured, capillary rupture and bleeding leads to a sequence of highly coordinated events. The first phase is the degeneration/inflammation phase and is characterised by the rupture of myofibrils and their ensuing necrosis. A haematoma forms between the stumps of the ruptured myofibrils, and inflammatory cells invade.3 Platelets arrive, adhere to the exposed collagen, become activated and immediately begin to release growth factors and cytokines further amplifying the inflammatory process. Neutrophils begin to migrate to the area and arrive as early as 1–2 h after injury.5

The neutrophils are phagocytic and contain over 40 hydrolytic enzymes. Their activation leads to phagocytosis of debris, and also to the release of oxygen free radicals and proteases. This release of toxic molecules from the neutrophils can lead to secondary damage to the muscle.2 5 6 In fact, the time of peak muscle injury correlates to the time of maximal neutrophil invasion and not to the initial injury.5 In …

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