- The optimal centrifugation protocol for production of rat PRP is 1300 rpm for 5 minutes.
- PRP administration in RCR improves tendon biomechanics in a rat model.
- Administration of NSAIDs following RCR has no significant effect on tendon biomechanical properties.
- NSAIDs may be co-administered with PRP without reducing efficacy of PRP.
- The role of PRP and NSAIDs in human RCR remains unclear.
Rotator cuff tears are a common source of shoulder pain and disability among older adults and athletes. Full-thickness tears alone occur in up to 30% of adults older than 60 years. 1 Surgical repair is plagued by an unpredictable rate of recurrence (range, 11%-94%). 1-10 As a result of improved suture materials, knotting patterns, and anchor designs, hardware issues are no longer the primary cause of rotator cuff repair (RCR) failures; now the principal mode of failure is biologic. 2 Animal model studies have found that, after injury and subsequent healing, the tendon–bone interface remains abnormal. 11 Rotator cuff research therefore has focused largely on biological enhancement of tendon-to-bone healing.
One means of biological augmentation is autologous platelet-rich plasma (PRP), which has supraphysiologic concentrations of platelets and their secreted growth factors. Although there is no consensus on the long-term efficacy of PRP, some studies suggest PRP accelerates healing over short and intermediate terms, which may contribute to a more rapid decrease in pain and more rapid return to normal activities. 12-18 Similarly, systemic nonsteroidal anti-inflammatory drugs (NSAIDs) have long been used to treat musculoskeletal injuries, including rotator cuff pathology. However, NSAIDs inhibit cyclooxygenase activity, and clinical and experimental data have shown that cyclooxygenase 2 function is crucial in normal tendon-to-bone healing. 19-21
Comprehensive studies have been conducted on the efficacy of both PRP and NSAIDs, but the interaction of concurrently used PRP and NSAIDs has not been determined. As many physicians use both modalities in the treatment of soft-tissue injuries, it is important to study the potential interactions when coadministered. Prior studies in small animal models suggest NSAIDs may impair tendon-to-bone healing in RCR, but there is no evidence regarding the effect of NSAIDs on the efficacy of PRP treatment. 21
We conducted a study to determine the interaction of PRP and NSAIDs when used as adjuncts to RCR in a rat model. We hypothesized that PRP would increase the strength of RCR and that NSAIDs would interfere with the effects of PRP. A preliminary study objective was to determine an appropriate centrifugation protocol for producing PRP from rat blood, for use in this study and in future rat-based studies of PRP.
Materials and Methods
Part A: Pretesting Determination of PRP Centrifugation Protocol
Fourteen adult male Fischer rats were used in part A of this study, which was conducted to determine an appropriate PRP centrifugation protocol. Traditional PRP centrifugation protocols are established for human blood, but rat red blood cells (RBCs) and human RBCs differ in size. 22 In our preliminary study, we wanted to determine the adjusted centrifuge speed and duration for producing clinically optimal PRP from rats. Clinically optimal PRP has reduced levels of RBCs, which decrease platelet affinity. Although the role of leukocytes in PRP preparations is debated, reducing the number of white blood cells (WBCs) decreases the number of matrix metalloproteinases and reactive oxygen species that may lead to inflammation. We used the platelet index (ratio of platelets to WBCs) and the RBC count to quantify the quality of our PRP sample.
Each rat in part A was anesthetized while supine. We used the Autologous Conditioned Plasma (ACP) system (Arthrex), which requires only 1 centrifugation cycle to create PRP. About 9 mL or 10 mL of blood was obtained by cardiac aspiration using an ACP Double Syringe (Arthrex). After blood retrieval, a thoracotomy was performed to confirm each rat’s death.