Purpose: To determine whether a single dose of PRP could accelerate ligament healing and correspondingly improve histological characteristics and biomechanical properties when injected immediately postoperatively into the injured medial collateral ligament (MCL) of New Zealand White rabbits.
Study Design: Controlled laboratory study.
Methods: Eighty skeletally mature New Zealand White rabbits (160 knees) were used. The MCL was torn midbody to simulate a grade 3 tear. After an acute injury of the MCL, the administration of autologous PRP at 3 different platelet concentrations (0 million/uL, platelet-poor plasma [PPP]; 0.6 million/uL, 2 times the baseline [23 PRP]; and 1.2 million/uL, 4 times the baseline [43 PRP]) was performed and compared with a saline injection control in the contralateral knee. Histological analysis and a bio- mechanical endpoint characterization were utilized to assess ligamentous healing and compare it to a sham surgery group.
Results: The PPP (P = .001) and 43 PRP (P = .002) groups had a significantly lower collagen subscore than the sham surgery group. No other differences were observed among the treatment groups, including the vascularity subscore and overall ligament tissue maturity index score. Compared with saline-injected contralateral knees, the maximum load for PPP and 23 PRP was not significantly different (P = .788 and .325, respectively). The maximum load and stiffness for knees treated with 43 PRP were significantly less than for the saline-treated contralateral knees (P = .006 and .001, respectively).
Conclusion: One single dose of PPP or 23 PRP at the time of injury did not improve ligament healing. In addition, 43 PRP negatively affected ligament strength and histological characteristics at 6 weeks after the injury.
Clinical Relevance: The current practice of treating knee ligament injuries with PRP may not improve healing at low doses of PRP. The decreased mechanical properties and histological appearance of the torn MCL suggest that high doses of PRP decrease the quality of repair tissue. Further in vivo studies are necessary to determine the dosing and timing of PRP administration after a ligament injury before the widespread use of PRP to treat ligament injuries is recommended.