The effect of immediate and delayed injection of platelet-rich plasma (PRP) on muscle contusion healing in the rat

Objectives: Muscle contusions are among the most common injuries in sport. Though typically self-limiting, more severe types of contusions can lead to marked pain and diminished function with significant delay in return-to-play. Current therapy is usually limited to NSAIDs and/or use of the RICE principle. Other forms of treatment that can potentially accelerate the rate of healing are desirable. Platelet-rich plasma (PRP) is a novel therapy produced from autologous whole blood that holds promise for treating muscle injuries. However, data both at the translational and clinical level is still limited. This study seeks to investigate the effects of PRP on muscle contusion healing in rats and to determine if the timing of injection plays any role in recovery. Methods: Forty-six (46) male Lewis rats each underwent blunt, non-penetrating impact to the gastrocnemius muscle via a drop-tower model. The rats were separated into 4 groups, with each rat undergoing injection into the injured gastrocnemius muscle according to the following schema: those in Group 1 underwent a single injection of 100ul of rat PRP on the day of injury; those in Group 2(controls) underwent a single injection of 100ul of saline on the day of injury; those in Group 3 underwent a single injection of 100ul rat PRP on post-injury day #1; those in Group 4 underwent a single injection of 100ul of rat PRP on post-injury day #3. After the injury, rats were allowed unrestricted activity. The primary outcome measurement was maximal isometric torque strength of the injured muscle, which was performed prior to impaction injury as well as on post-injury days 1, 4, 7, 10, and 14. All animals were sacrificed on post-injury day 15. Results: Mean rat weight was 319 (±15) grams. The mean platelet concentration in the PRP solution was 2.19x106 (±2.69x105) per ul, which was greater than 4 times whole blood baseline levels and the concentration of PDGF-AB, VEGF, and TGF-β was increased by a factor of 2.6, 1.8, and 2.7, respectively. Each group demonstrated statistically significant decreases in maximal isometric torque strength after injury, followed by significant increases back towards baseline values by post-injury day 14 (figure 1). There were no statistically significant differences between the treatment and control groups at any of the time-points. Conclusion: PRP is being used clinically to treat numerous soft tissue injuries, though clinical data is limited. In this rat contusion model, local injection of PRP into the injured gastrocnemius muscle resulted in no significant differences in maximal isometric torque strength at various post-injury time-points, indicating no likely benefit to healing. Additionally, there was no significant difference between immediate or delayed administration of PRP. Further translational and clinical investigation needs to be performed before PRP can be recommended for the treatment of muscle contusion injuries.