The biology of platelet-rich plasma and its application in trauma and orthopaedic surgery: a review of the literature

Platelet-rich plasma in tendon models: a systematic review of basic science literature

PURPOSE

To perform a systematic review of the basic science literature on the use of platelet-rich plasma (PRP) in tendon models.

METHODS

We searched the PubMed/Medline and Embase databases in June 2012 using the following parameters: ((tenocytes OR tendon OR tendinitis OR tendinosis OR tendinopathy) AND (platelet rich plasma OR PRP OR autologous conditioned plasma OR ACP)). The inclusion criteria for full-text review were in vivo and in vitro studies examining the effects of PRP on tendons and/or tenocytes. Clinical studies were excluded. Only studies published in peer-reviewed journals that compared PRP directly with a control were included. Data were extracted based on a predefined data sheet, which included information on PRP preparation, study methods, and results. Studies were analyzed for trends, comparing and contrasting the reported effects of PRP.

RESULTS

The search yielded 31 articles for inclusion in our review. Of the studies, 22 (71%) reported platelet concentrations in the PRP; 6 (19%) reported cytology. Eight in vivo studies found decreased tendon repair time, increased fiber organization, or both with PRP treatment. Eight in vitro studies reported that PRP treatment increased cell proliferation; 7 reported an increase in growth factor expression. Three in vivo studies found increased vascularity, and 4 found increased tensile strength with PRP treatment.

CONCLUSIONS

In the basic science studies evaluated, it appears that PRP confers several potential effects on tendon models compared with a control. However, the literature is inconsistent with regard to reporting the methods of preparation of PRP and in reporting platelet concentrations and cytology.

CLINICAL RELEVANCE

Establishing proof of concept for PRP may lead to further high-quality clinical studies in which the appropriate indications can be defined.

An orthopedic tissue adhesive for targeted delivery of intraoperative biologics

Tissue adhesives can bind together damaged tissues and serve as tools to deliver and localize therapeutics to facilitate regeneration. One emerging therapeutic trend in orthopedics is the use of intraoperative biologics (IOB), such as bone marrow (BM) and platelet-rich plasma (PRP), to stimulate healing. Here, we introduce the application of the biomaterial chondroitin sulfate succinimidyl succinate (CS-NHS) to deliver IOB in a hydrogel adhesive. We demonstrate the biomaterial's ability to bind various tissue types and its cellular biocompatibility with encapsulated human mesenchymal stem cells (hMSCs). Further, we examine in detail the CS-NHS adhesive combined with BM aspirate for use in bone applications. hMSCs were encapsulated in CS-BM and cultured for 5 weeks in osteogenic medium. Quantitative RT-PCR demonstrated osteogenesis via upregulation of the osteogenic transcription factor Runx2 and bone markers alkaline phosphatase and osteocalcin. Significant deposition of calcium and osteocalcin was detected using biochemical, histological, and immunohistochemical techniques. Shear testing demonstrated that the CS-BM adhesive exhibited an adhesive strength approximately an order of magnitude stronger than fibrin glue and approaching that of a cyanoacrylate adhesive. These results indicate that CS-NHS is a promising delivery tool for IOB in orthopedic applications requiring a strong, degradable, and biocompatible adhesive that supports bone growth.

Treatment options: biological basis of regenerative endodontic procedures

Dental trauma occurs frequently in children and often can lead to pulpal necrosis. The occurrence of pulpal necrosis in the permanent but immature tooth represents a challenging clinical situation because the thin and often short roots increase the risk of subsequent fracture. Current approaches for treating the traumatized immature tooth with pulpal necrosis do not reliably achieve the desired clinical outcomes, consisting of healing of apical periodontitis, promotion of continued root development, and restoration of the functional competence of pulpal tissue. An optimal approach for treating the immature permanent tooth with a necrotic pulp would be to regenerate functional pulpal tissue. This review summarizes the current literature supporting a biological rationale for considering regenerative endodontic treatment procedures in treating the immature permanent tooth with pulp necrosis.

Can platelet-rich plasma (PRP) improve bone healing? A comparison between the theory and experimental outcomes

The increased concentration of platelets within platelet-rich plasma (PRP) provides a vehicle to deliver supra-physiologic concentrations of growth factors to an injury site, possibly accelerating or otherwise improving connective tissue regeneration. This potential benefit has led to the application of PRP in several applications; however, inconsistent results have limited widespread adoption in bone healing. This review provides a core understanding of the bone healing mechanisms, and corresponds this to the factors present in PRP. In addition, the current state of the art of PRP preparation, the key aspects that may influence its effectiveness, and treatment outcomes as they relate specifically to bone defect healing are presented. Although PRP does have a sound scientific basis, its use for bone healing appears only beneficial when used in combination with osteoconductive scaffolds; however, neither allograft nor autograft appear to be appropriate carriers. Aggressive processing techniques and very high concentrations of PRP may not improve healing outcomes. Moreover, many other variables exist in PRP preparation and use that influence its efficacy; the effect of these variables should be understood when considering PRP use. This review includes the essentials of what has been established, what is currently missing in the literature, and recommendations for future directions.

Virally inactivated human platelet concentrate lysate induces regulatory T cells and immunosuppressive effect in a murine asthma model

BACKGROUND

Platelet concentrate lysates (PCLs) are increasingly used in regenerative medicine. We have developed a solvent/detergent (S/D)-treated PCL. The functional properties of this preparation should be unveiled. We hypothesized that, due to transforming growth factor-β1 (TGF-β1) content, PCLs may exert immunosuppressive and anti-inflammatory functions.

STUDY DESIGN AND METHODS

PCL was prepared by S/D treatment, oil extraction, and hydrophobic interaction chromatography. The content of TGF-β in PCL was determined by enzyme-linked immunosorbent assay. Cultured CD4+ T cells were used to investigate the effects of PCL on expression of transcription factor forkhead box P3 (Foxp3), the inhibition of T-cell proliferation, and cytokine production. The regulatory function of PCL-converted CD4+ T cells was analyzed by suppressive assay. The BALB/c mice were given PCL-converted CD4+ T cells before ovalbumin (OVA) sensitization and challenge using an asthma model. Inflammatory parameters, such as the level of immunoglobulin E (IgE), airway hyperresponsiveness (AHR), bronchial lavage fluid eosinophils, and cytokines were assayed. Recombinant human (rHu) TGF-β1 was used as control.

RESULTS

PCL significantly enhanced the development of CD4+Foxp3+-induced regulatory T cells (iTregs). Converted iTregs produced neither Th1 nor Th2 cytokines and inhibited normal T-cell proliferation. PCL- and rHuTGF-β-converted CD4+ T cells prevented OVA-induced asthma. PCL- and rHuTGF-β-modified T cells both significantly reduced expression levels of OVA-specific IgE and significantly inhibited the development of AHR, airway eosinophilia, and Th2 responses in mice.

CONCLUSION

S/D-treated PCL promotes Foxp3+ iTregs and exerts immunosuppressive and anti-inflammatory properties. This finding may help to understand the clinical properties of platelet lysates.

The role of platelets in the treatment of Achilles tendon injuries

To systematically review the current in-vivo evidence for the use of platelet-concentrates (PRP) in the treatment of Achilles tendinopathy and Achilles tendon ruptures in animal models and human applications. A systematic search of PubMed, CINAHL, EMBASE, CCTR, and CDSR was performed for animal and human studies on the effect of platelet-concentrates in the treatment of Achilles tendinopathy and ruptures using the terms "Achilles tendon and platelet." The systematic search revealed a total of 149 papers. After excluding duplicates and cases of overlapping data, studies not focusing on in vivo evidence in terms of treatment or outcome, studies without any intervention, studies with unacceptable high attrition, one Chinese and one Swedish study, the remaining 14 manuscripts were included. The key finding of our study is evidence in support of a statistically significant effect of platelet concentrates in the treatment of Achilles tendon ruptures in vivo in animal models and human application, consistent with a medium to large sized effect. This effect is most likely attributable to fastened and enhanced scar tissue maturation. There was no evidence for a beneficial effect of platelets in Achilles tendinopathy.

The Potential Use of Allogeneic Platelet-Rich Plasma for Large Bone Defect Treatment: Immunogenicity and Defect Healing Efficacy

Autologous platelet-rich plasma (PRP) has been extensively investigated for large bone defect treatment, but its clinical application is harassed by controversial outcome, due to highly variable PRP quality among patients. Alternatively, allogeneic PRP from well-characterized donors cannot only generate more consistent and reliable therapeutic effect but also avoid harvesting large quantities of blood, an additional health burdens to patients. However, the use of allogeneic PRP for bone defect treatment is generally less investigated, especially for its immunogenicity in such application. Here, we meticulously investigated the immunogenicity of allogeneic PRP and evaluated its healing efficacy for critical-sized defect treatment. Allogeneic PRP contained 4.1-fold and 2.7- to 4.9-fold higher amount of platelets and growth factors than whole blood, respectively. The intramuscular injection of allogeneic PRP to rabbits did not trigger severe and chronic immunoresponse, evidenced by little change in muscular tissue microstructure and CD4+/CD8+ T lymphocyte subpopulation in peripheral blood. The implantation of allogeneic PRP/deproteinized bone matrix (DPB) constructs (PRP + DPB) successfully bridged 1.5-cm segmental radial defects in rabbits, achieving similar healing capacity as autologous MSC/DPB constructs (MSC + DPB), with greater bone formation (1.1–1.5x, p < 0.05) and vascularization (1.3–1.6x, p < 0.05) than DPB alone, shown by histomorphometric analysis, bone mineral density measurement, and radionuclide bone imaging. Furthermore, the implantation of both allogeneic PRP- and autologous MSC-mediated DPB constructs (PRP + MSC + DPB) resulted in the most robust bone regeneration (1.2–2.1x, p < 0.05) and vascularization (1.3–2.0x, p < 0.05) than others (PRP + DPB, MSC + DPB, or DPB alone). This study has demonstrated the promising use of allogeneic PRP for bone defect treatment with negligible immunogenicity, great healing efficacy, potentially more consistent quality, and no additional health burden to patients; additionally, the synergetic enhancing effect found between allogeneic PRP and autologous MSCs may shed a light on developing new therapeutic strategies for large bone defect treatment.

Regulation of hypoxia-induced cell death in human tenocytes

Degenerate shoulder tendons display evidence of hypoxia. However tendons are relatively avascular and not considered to have high oxygen requirements and the vulnerability of tendon cells to hypoxia is unclear. Cultured human tenocytes were exposed to hypoxia and the cellular response detected using QPCR, Western blotting, viability, and ELISA assays. We find that tenocytes respond to hypoxia in vitro by activating classical HIF-1α-driven pathways. Total hypoxia caused significant tenocyte apoptosis. Transcription factors typically involved in hypoxic response, HIF-1α and FOXO3A, were upregulated. Hypoxia caused sustained upregulation of several proapoptotic proteins known to mediate hypoxia-induced apoptosis, such as Bnip3 and Nix, but others were unchanged although they were reportedly hypoxia-sensitive in other cell types. Antiapoptotic proteins Bcl2 and Bcl-xL were unchanged by hypoxia. Normal human tenocytes expressed all isoforms of the hypoxia-induced vascular growth factor VEGF except VEGF-D. Hypoxia markedly upregulated VEGF-A mRNA, followed by increased VEGF protein secretion. However treatment with VEGF did not improve tenocyte survival. As a protective strategy for tenocytes at risk of hypoxic death we added prosurvival growth factors insulin or platelet rich plasma (PRP). Both agents strongly protected tenocytes from hypoxia-induced death over 48 h, suggesting possible efficacy in the acute postrupture tendon or integrating graft.

A preliminary study on the potential of manuka honey and platelet-rich plasma in wound healing

Aim. The purpose of this study was to determine the in vitro response of cells critical to the wound healing process in culture media supplemented with a lyophilized preparation rich in growth factors (PRGF) and Manuka honey. Materials and Methods. This study utilized cell culture media supplemented with PRGF, as well as whole Manuka honey and the medical-grade Medihoney (MH), a Manuka honey product. The response of human fibroblasts (hDF), macrophages, and endothelial cells (hPMEC) was evaluated, with respect to cell proliferation, chemotaxis, collagen matrix production, and angiogenic potential, when subjected to culture with media containing PRGF, MH, Manuka honey, and a combination of PRGF and MH. Results. All three cell types demonstrated increases in cellular activity in the presence of PRGF, with further increases in activity seen in the presence of PRGF+MH. hDFs proved to be the most positively responsive cells, as they experienced enhanced proliferation, collagen matrix production, and migration into an in vitro wound healing model with the PRGF+MH-supplemented media. Conclusion. This preliminary in vitro study is the first to evaluate the combination of PRGF and Manuka honey, two products with the potential to increase regeneration individually, as a combined product to enhance dermal regeneration.

Effect of autologous platelet-rich plasma-releasate on intervertebral disc degeneration in the rabbit anular puncture model: a preclinical study

INTRODUCTION

Platelet-rich plasma (PRP) is a fraction of plasma in which several growth factors are concentrated at high levels. The active soluble releasate isolated following platelet activation of PRP (PRP-releasate) has been demonstrated to stimulate the metabolism of IVD cells in vitro. The in vivo effect of PRP-releasate on degenerated IVD remains unknown. The purpose of this study was to determine the reparative effects of autologous PRP-releasate on degenerated intervertebral discs (IVDs).

METHODS

To induce disc degeneration, New Zealand white rabbits (n = 12) received anular puncture in two noncontiguous discs. Autologous PRP and PPP (platelet-poor plasma) were isolated from fresh blood using two centrifugation techniques. Four weeks after the initial puncture, releasate isolated from clotted PPP or PRP (PPP- or PRP-releasate), or phosphate-buffered saline (PBS; control) was injected into the punctured discs. Disc height, magnetic resonance imaging (MRI) T2-mapping and histology were assessed.

RESULTS

Anular puncture produced a consistent disc narrowing within four weeks. PRP-releasate induced a statistically significant restoration of disc height (PRP vs. PPP and PBS, P<0.05). In T2-quantification, the mean T2-values of the nucleus pulposus (NP) and anulus fibrosus (AF) of the discs were not significantly different among the three treatment groups. Histologically, the number of chondrocyte-like cells was significantly higher in the discs injected with PRP-releasate compared to that with PBS.

CONCLUSIONS

The administration of active PRP-releasate induced a reparative effect on rabbit degenerated IVDs. The results of this study suggest that the use of autologous PRP-releasate is safe and can lead to a clinical application for IVD degeneration.

Injuries of the elbow and the current treatment of tendon disease

OBJECTIVE

Overuse and traumatic injuries of the elbow are common, occurring in both athletes and nonathletes. This article will discuss the commonly encountered soft-tissue and osseous pathologic abnormalities around the elbow and their imaging appearance on MRI and ultrasound.

CONCLUSION

The current treatment of tendon disease of the elbow is reviewed, with a focus on platelet-rich plasma injection.

Towards biological anulus repair: TGF-β3, FGF-2 and human serum support matrix formation by human anulus fibrosus cells

Closure and biological repair of anulus fibrosus (AF) defects in intervertebral disc diseases is a therapeutic challenge. The aim of our study was to evaluate the anabolic properties of bioactive factors on cartilaginous matrix formation by AF cells. Human AF cells were harvested from degenerated lumbar AF tissue and expanded in monolayer culture. AF cell differentiation and matrix formation was initiated by forming pellet cultures and stimulation with hyaluronic acid (HA), human serum (HS), fibroblast growth factor-2 (FGF-2), transforming growth factor-β3 (TGF-β3) and TGF-β3/FGF-2 for up to 4 weeks. Matrix formation was assessed histologically by staining of proteoglycan, type I and type II collagens and by gene expression analysis of typical extracellular matrix molecules and of catabolic matrix metalloproteinases MMP-2 and MMP-13. AF cells, stimulated with HS, FGF-2 and most pronounced with TGF-β3 or TGF-β3/FGF-2 formed a cartilaginous matrix with significantly enhanced expression of matrix molecules and of MMP-13. Stimulation of AF cells with TGF-β3 was accompanied by induction of type X collagen, known to occur in hypertrophic cartilage cells having mineralizing potential. HA did not show any chondro-inductive characteristics. These findings suggest human serum, FGF-2 and TGF-β3 as possible candidates to support biological treatment strategies of AF defects.

The Augmentation of a Collagen/Glycosaminoglycan Biphasic Osteochondral Scaffold with Platelet-Rich Plasma and Concentrated Bone Marrow Aspirate for Osteochondral Defect Repair in Sheep: A Pilot Study

OBJECTIVE

This study investigates the combination of platelet-rich plasma (PRP) or concentrated bone marrow aspirate (CBMA) with a biphasic collagen/glycosaminoglycan (GAG) osteochondral scaffold for the treatment of osteochondral defects in sheep.

DESIGN

Acute osteochondral defects were created in the medial femoral condyle (MFC) and the lateral trochlea sulcus (LTS) of 24 sheep (n = 6). Defects were left empty or filled with a 6 × 6-mm scaffold, either on its own or in combination with PRP or CBMA. Outcome measures at 6 months included mechanical testing, International Cartilage Repair Society (ICRS) repair score, modified O'Driscoll histology score, qualitative histology, and immunohistochemistry for type I, II, and VI collagen.

RESULTS

No differences in mechanical properties, ICRS repair score, or modified O'Driscoll score were detected between the 4 groups. However, qualitative assessments of the histological architecture, Safranin O content, and collagen immunohistochemistry indicated that in the PRP/scaffold groups, there was a more hyaline cartilage-like tissue repair. In addition, the addition of CBMA and PRP to the scaffold reduced cyst formation in the subchondral bone of healed lesions.

CONCLUSION

There was more hyaline cartilage-like tissue formed in the PRP/scaffold group and less subchondral cystic lesion formation in the CBMA and PRP/scaffold groups, although there were no quantitative differences in the repair tissue formed.

Plasma rich in growth factors in human extraction sockets: a radiographic and histomorphometric study on early bone deposition

OBJECTIVES

To determine whether and to what extent the additional application of plasma rich in growth factors (PRGF) to an extraction socket may influence the early bone deposition, as assessed by micro-computed tomography (micro-CT) scan as well as histomorphometric markers.

MATERIAL AND METHODS

Twenty-eight patients (age range: 34-74 years) contributing 36 extraction sockets were included in the study. Sockets were either treated with PRGF (PRGF group; 18 sites in 11 patients) or left to spontaneous healing (control group; 18 sites in 17 patients). Radiographic and histomorphometric analysis was performed on bone cores trephined from each healing socket after 4-6 (T1) or 7-10 (T2) weeks of healing.

RESULTS

Patients treated with PRGF application showed (i) similar bone volume and tissue mineral content, (ii) a trend, although not statistically significant, toward a greater number of CD68+ cells (at T1 and T2) and vVW+ cells (at T1), and (iii) a similar OCN staining score throughout the study, when compared with control group.

CONCLUSIONS

Plasma rich in growth factors-treated group did not show any enhancement in early (4 and 8 weeks) bone deposition compared with control group.

Platelet-rich plasma combined with hydroxyapatite for lumbar interbody fusion promoted bone formation and decreased an inflammatory pain neuropeptide in rats

STUDY DESIGN

A prospective interventional trial, using a rat model of lumbar interbody fusion.

OBJECTIVE

To examine the potential efficacy of platelet-rich plasma (PRP) for lumbar interbody fusion, using hydroxyapatite (HA).

SUMMARY OF BACKGROUND DATA

PRP is an autologous product containing a high concentration of platelets in a small volume of plasma and has osteoinductive effects. HA has osteoconductive ability and has been used in combination with autogenous bone for spine fusion. However, reports using PRP with HA for spine fusion are very few. The purpose of this study was to examine the efficacy of PRP with HA for spinal interbody fusion and at the same time to estimate the change in immunoreactivity of the inflammatory neuropeptide, calcitonin gene-related peptide (CGRP), in dorsal root ganglion (DRG) neurons innervating spinal discs.

METHODS

A total of 35 Sprague-Dawley rats were used in this study. Twenty-one rats were used for conducting interbody fusion experiments, 7 rats were used as immunostaining controls, and 7 other rats were used as blood donors for making PRP. L5-L6 interbody fusion was performed on 21 rats using HA + PRP (n = 7), HA + platelet-poor plasma (n = 7), or HA + saline (n = 7). Simultaneously, Fluoro-Gold neurotracer was applied to the intervertebral space to detect DRG neurons innervating the discs. L5-L6 lumbar radiographs were obtained and lumbar DRGs were immunostained for CGRP. The rate of bone union and the change in CGRP immunoreactive DRG neurons innervating the discs were evaluated and compared among groups.

RESULTS

All L5-L6 lumbar discs were fused in the PRP + HA group (fused 7/total 7), whereas only 1 case was fused in the platelet-poor plasma group (1 of 7) and no cases in the HA-only group (0 of 7), which was a significant difference. Upon immunohistochemical analysis, CGRP-positive neurons innervated L5-L6 intervertebral discs in nonunion cases, and these were significantly increased compared with those in union cases.

CONCLUSION

Our study suggests that using PRP with HA was beneficial for spine fusion. This combination may promote bone union and also decrease inflammatory neuropeptide in sensory neurons innervating the discs.

The biomechanical and histologic effects of platelet-rich plasma on rat rotator cuff repairs

BACKGROUND

Rotator cuff tears are common injuries that are often treated with surgical repair. Because of the high concentration of growth factors within platelets, platelet-rich plasma (PRP) has the potential to enhance healing in rotator cuff repairs.

HYPOTHESIS

Platelet-rich plasma would alter the biomechanical and histologic properties of rotator cuff repair during an acute injury response.

STUDY DESIGN

Controlled laboratory study.

METHODS

Platelet-rich plasma was produced from inbred donor rats. A tendon-from-bone supraspinatus tear was created surgically and an immediate transosseous repair performed. The control group underwent repair only. The PRP group underwent a repair with PRP augmentation. Rats in each group were sacrificed at 7, 14, and 21 days. The surgically repaired tendons underwent biomechanical testing, including failure load, stiffness, failure strain, and stress relaxation characteristics. Histological analysis evaluated the cellular characteristics of the repair tissue.

RESULTS

At 7- and 21-day periods, augmentation with PRP showed statistically significant effects on the biomechanical properties of the repaired rat supraspinatus tear, but failure load was not increased at the 7-, 14-, or 21-day periods (P = .688, .209, and .477, respectively). The control group had significantly higher stiffness at 21 days (P = .006). The control group had higher failure strain at 7 days (P = .02), whereas the PRP group had higher failure strain at 21 days (P = .008). Histologically, the PRP group showed increased fibroblastic response and vascular proliferation at each time point. At 21 days, the collagen fibers in the PRP group were oriented in a more linear fashion toward the tendon footprint.

CONCLUSION

In this controlled, rat model study, PRP altered the tissue properties of the supraspinatus tendon without affecting the construct's failure load.

CLINICAL RELEVANCE

The decreased tendon tissue stiffness acutely and failure to enhance tendon-to-bone healing of repairs should be considered before augmenting rotator cuff repairs with PRP. Further studies will be necessary to determine the role of PRP in clinical practice.

The positive effects of different platelet-rich plasma methods on human muscle, bone, and tendon cells

BACKGROUND

Clinical application of platelet-rich plasma (PRP) in the realm of orthopaedic sports medicine has yielded variable results. Differences in separation methods and variability of the individual may contribute to these variable results.

PURPOSE

To compare the effects of different PRP separation methods on human bone, muscle, and tendon cells in an in vitro model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Blood collected from 8 participants (mean ± SD age 31.6 ± 10.9 years) was used to obtain PRP preparations. Three different PRP separation methods were used: a single-spin process yielding a lower platelet concentration (PRP(LP)), a single-spin process yielding high platelet and white blood cell concentrations (PRP(HP)), and a double-spin that produces a higher platelet concentration and lower white blood cell concentration (PRP(DS)). Human bone, muscle, and tendon cells obtained from discarded tissue samples during shoulder surgery were placed into culture and treated with the 3 PRP preparations, control media (2% fetal bovine serum [FBS] and 10% FBS), and native blood. Radioactive thymidine assays were obtained to examine cell proliferation, and testing with enzyme-linked immunosorbent assay was used to determine growth factor concentrations.

RESULTS

Addition of PRP(LP) to osteocytes, myocytes, and tenocytes significantly increased cell proliferation (P ≤ .05) compared with the controls. Adding PRP(DS) to osteoblasts and tenocytes increased cell proliferation significantly (P ≤ .05), but no significance was shown for its addition to myocytes. The addition of PRP(HP) significantly increased cell proliferation compared with the controls only when added to tenocytes (P ≤ .05). Osteoblasts: Proliferation was significantly increased by addition of PRP(LP) compared with all controls (2% FBS, 10% FBS, native blood) (P ≤ .05). Addition of PRP(DS) led to significantly increased proliferation compared with all controls, native blood, and PRP(HP) (P ≤ .05). Proliferation was significantly less when PRP(HP) was added compared with PRP(DS) (P ≤ .05). Myocytes: Proliferation was significantly increased by addition of PRP(LP) compared with native blood (P ≤ .05). Adding PRP(HP) or PRP(DS) to myocytes showed no significant increase in proliferation compared with the controls or the other separations. Tenocytes: Proliferation was significantly increased by addition of PRP(LP) compared with all controls (2% FBS, 10% FBS, native blood) (P ≤ .05). Addition of PRP(DS) showed a significant increase compared with the controls and native blood. For tenocytes, there was a significant increase (P ≤ .05) seen when PRP(HP) was added compared with the controls and native blood but not compared with the other separations.

CONCLUSION

The primary findings of this study suggest the application of different PRP separations may result in a potential beneficial effect on the clinically relevant target cells in vitro. However, it is unclear which platelet concentration or PRP preparation may be optimal for the treatment of various cell types. In addition, a "more is better" theory for the use of higher platelet concentrations cannot be supported. This study was not intended to prove efficacy but to provide a platform for future research to be built upon.

CLINICAL RELEVANCE

The utilization of different PRP separations may result in a potentially beneficial effect on the clinically relevant target cells in vitro, but it is unclear which platelet concentration or PRP preparation may be optimal for the treatment of various cell types.

Using platelet-rich plasma for the treatment of symptomatic cervical ectopy

OBJECTIVE

To evaluate the effectiveness of autologous platelet-rich plasma (PRP) applications in the treatment of benign cervical ectopy.

METHODS

Symptomatic women with benign cervical ectopy (n=120) were randomized to a PRP or a laser group. In the PRP group, PRP was applied twice on the cervical erosion with a 1-week interval. In the laser group, an Nd-YAG laser was used once for tissue vaporization.

RESULTS

The complete cure rates were 93.7% for the PRP and 92.4% for the laser group (P>0.05). The mean time to re-epithelialization was significantly shorter in the PRP (6.41 ± 2.05 weeks) than in the laser group (8.28 ± 1.72 weeks) (P<0.01). The rate of adverse treatment effects (i.e. vaginal discharge or vaginal bleeding) was much lower in the PRP than that in the laser group (P<0.01) and the effects were milder. Eleven patients in the PRP group had mild or moderate vaginal bleeding after treatment but none had heavy bleeding. Of 25 patients with vaginal bleeding in the laser group, 2 had heavy bleeding necessitating tamponade.

CONCLUSION

Autologous PRP applications appear promising for the treatment of cervical ectopy in symptomatic women, as they generate a shorter tissue healing time and milder adverse effects than laser treatment.

Platelet gel: applications in dental regenerative surgery

BACKGROUND

Platelet growth factors obtained from platelet-rich plasma (PRP) are used in prosthetic and periodontal regenerative therapy in dentistry. Increased microvascular proliferation in the first 20 days is followed by enhanced osteoblast activity and immature osteoid formation within 3-6 weeks, improving the quality and quantity of newly formed bone tissue. The aim of this study was to evaluate, through three-dimensional X-ray monitoring, the amount of bone obtained after bone regeneration treatment with platelet gel from autologous PRP.

MATERIALS AND METHODS

Patients eligible for regenerative treatment of atrophic alveolar bone of the maxilla or mandible were studied. The patients' autologous whole blood was collected at the Department of Immunology and Transfusion of San Matteo Hospital for the preparation of platelet gel. The bone at the treated sites was analysed prior to and 4 months after the treatment using the three-dimensional X-ray system Galileos.

RESULTS

Over a period of 6 years, 133 patients were treated: 304 implants were inserted and there were five cases of failure. The regenerated bone area consisted of histologically immature osteoid tissue composed of thin trabeculae of vital bone and nuclei of osteocytes, associated with fibro-connective tissue.

DISCUSSION

This co-operative trial between the Transfusion Centre, for standardised production and validation of the platelet gel, and the Dental Surgery room for its application showed that the technique appears effective and safe. Although difficulties were encountered because of the small sample size and the inability to carry out long-term histological controls, the use of small amounts of PRP (5-10%) combined with autologous bone (15-20%) and alloplastic material appears to reduce the need for bone grafting.

Platelet-rich plasma: the PAW classification system

Platelet-rich plasma (PRP) has been the subject of hundreds of publications in recent years. Reports of its effects in tissue, both positive and negative, have generated great interest in the orthopaedic community. Protocols for PRP preparation vary widely between authors and are often not well documented in the literature, making results difficult to compare or replicate. A classification system is needed to more accurately compare protocols and results and effectively group studies together for meta-analysis. Although some classification systems have been proposed, no single system takes into account the multitude of variables that determine the efficacy of PRP. In this article we propose a simple method for organizing and comparing results in the literature. The PAW classification system is based on 3 components: (1) the absolute number of Platelets, (2) the manner in which platelet Activation occurs, and (3) the presence or absence of White cells. By analyzing these 3 variables, we are able to accurately compare publications.

The role of platelet rich plasma in musculoskeletal science

The idea of using platelet rich plasma (PRP) in medicine has been around since the 1970s. It is only more recently that its use has been employed in the area of musculoskeletal science. Platelet rich plasma in this area has received much media attention being used by many celebrity sports athletes for musculoskeletal injuries. Therefore it is important for the musculoskeletal practitioner to be aware of the concepts surrounding its use and application. In this article we cover what platelet rich plasma is, how it is prepared and administered, its potential clinical application, and what the current literature discusses in the various areas of musculoskeletal science.

Drugs for bone healing

INTRODUCTION

The biological process of fracture healing is complex with influences that are both patient-dependent and related to the trauma experienced and stability of the fracture. Fracture healing complications negatively affect the patient's quality of life, even more when fractures occur in the elderly osteoporotic patients.

AREAS COVERED

In the polytherapy for bone regeneration, a high success rate was obtained with the use of growth factors, osteogenic cells, and osteoconductive factors. There have been high expectations that treatment with drugs active on bone remodeling would be efficient for acceleration of fracture healing. A literature search was undertaken using wording like "drug or pharmacology of fracture healing." This report will review the systemic pharmacological agents for which clinical trials documenting their efficacy on bone healing have been carried out or are underway.

EXPERT OPINION

At present the use of systemic pharmacological agents to enhance fracture healing in the clinical setting is still controversial. However, future clinical trials will offer the possibility to obtain data that will make possible the registration of a drug as a "healer."

Bone graft substitutes: What are the options?

Currently, a number of bone grafting materials are available in the clinical setting to enhance bone regeneration, varying from autologous bone to several bone graft substitutes. Although autologous bone remains the "gold standard" for stimulating bone repair and regeneration, the morbidity from its harvesting and its restricted availability generated the need for the development of other materials or strategies either to substitute autologous bone graft or expand its limited supply. Bone graft substitutes can possess one or more components: an osteoconductive matrix, acting as a scaffold; osteoinductive proteins and other growth factors to induce differentiation and proliferation of bone-forming cells; and osteogenic cells for bone formation. Based on their distinct properties, all these bone grafting alternatives have specific indications, and can be used either alone or in combination. In this review, we summarise the available bone grafting materials, focussing mainly on the various bone substitutes and their characteristics, in an effort to specify the indications for their use.

Human platelet-rich plasma stimulates migration and chondrogenic differentiation of human subchondral progenitor cells

In cartilage repair, platelet-rich plasma (PRP) is used in one-step approaches utilizing microfracture and matrix-induced chondrogenesis procedures, bone marrow-derived cell transplantation, or intra-articular injection. The aim of our study was to evaluate the effect of human PRP on the migration and chondrogenic differentiation of human subchondral progenitors. Human progenitors were derived from subchondral cortico-spongious bone (CSP), were analyzed for their migration capacity upon PRP treatment in 96-well chemotaxis assays and cultured in high-density pellet cultures under serum-free conditions in the presence of 5% PRP. Chemotaxis assays showed that 0.1-100% PRP significantly (p < 0.05) stimulate the migration of CSP compared to untreated controls. Histological staining of proteoglycan and immuno-staining of type II collagen indicated that progenitors stimulated with PRP show significantly increased cartilage matrix formation compared to untreated progenitors. Real-time gene expression analysis of typical chondrocyte marker genes as well as osteogenic and adipogenic markers like osteocalcin and fatty acid binding protein showed that PRP induces the chondrogenic differentiation sequence of human progenitors in high-density pellet cultures, while osteogenic or adipogenic differentiation was not evident. These results suggest that human PRP may enhance the migration and stimulate the chondrogenic differentiation of human subchondral progenitor cells known from microfracture.

A positive-margin resection model recreates the postsurgical tumor microenvironment and is a reliable model for adjuvant therapy evaluation

Up to 30% of cancer patients undergoing curative surgery develop local recurrences due to positive margins. Patients typically receive adjuvant chemotherapy, immunotherapy and/or radiation to prevent such relapses. Interestingly, evidence supporting these therapies is traditionally derived in animal models of primary tumors, thus failing to consider surgically induced tumor microenvironment changes that may influence adjuvant therapy efficacy. To address this consideration, we characterized a murine model of local cancer recurrence. This model was reproducible and generated a postoperative inflammatory tumor microenvironment that resembles those observed following human cancer surgery. To further validate this model, antagonists of two pro-inflammatory mediators, TGFβ and COX-2, were tested and found to be effective in decreasing the growth of recurrent tumors. We appreciated that preoperative TGFβ inhibition led to wound dehiscence, while postoperative initiation of COX-2 inhibition resulted in a loss of efficacy. In summary, although not an exact replica of all human cancer surgeries, our proposed local recurrence approach provides a biologically relevant and reliable model useful for preclinical evaluation of novel adjuvant therapies. The use of this model yields results that may be overlooked using traditional preclinical cancer models that fail to incorporate a surgical component.

Repeated platelet concentrate injections enhance reparative response of microfractures in the treatment of chondral defects of the knee: an experimental study in an animal model

PURPOSE

To assess the histology and biomechanics of repair cartilage after microfractures with and without repeated local injections of platelet concentrate for the treatment of full-thickness focal chondral defects of the knee.

METHODS

A full-thickness chondral lesion on the medial femoral condyle was created in 30 sheep and treated with microfractures. Animals were divided into 2 groups, according to postoperative treatment: in group 1 we performed 5 weekly injections of autologous conditioned plasma, whereas group 2 did not undergo further treatments. Animals were killed at 3, 6, and 12 months after treatment. Macroscopic, histologic, and biomechanical evaluations were performed. Differences between groups at each time interval and differences over time within groups were analyzed for each outcome. Significance was set at P < .05.

RESULTS

Group 1 showed significantly better macroscopic, histologic, and biomechanical results than group 2 at each time interval. Analysis of time effect within groups showed that in group 1, quality of repair tissue significantly improved from 3 to 6 months after treatment and remained stable over time for all the outcomes; in group 2 a significant histologic and mechanical deterioration was observed between 6 and 12 months' follow-up.

CONCLUSIONS

Five repeated local injections of autologous conditioned plasma after microfractures in the treatment of full-thickness cartilage injuries promoted a better and more durable reparative response than isolated microfractures, although they did not produce hyaline cartilage.

CLINICAL RELEVANCE

Periodical intra-articular injections of platelet concentrate after microfractures may improve cartilage repair and prevent further degenerative changes.

A cell-free scaffold-based cartilage repair provides improved function hyaline-like repair at one year

BACKGROUND

Bone marrow stimulation techniques in cartilage repair such as drilling are limited by the formation of fibrous to hyaline-like repair tissue. It has been suggested such techniques can be enhanced by covering the defect with scaffolds. We present an innovative approach using a polyglycolic acid (PGA)-hyaluronan scaffold with platelet-rich-plasma (PRP) in drilling.

QUESTIONS/PURPOSES

We asked whether (1) PRP immersed in a cell-free PGA-hyaluronan scaffold improves patient-reported 1-year outcomes for the Knee injury and Osteoarthritis Score (KOOS), and (2) implantation of the scaffold in combination with bone marrow stimulation leads to the formation of hyaline-like cartilage repair tissue.

PATIENTS AND METHODS

We reviewed 52 patients who had arthroscopic implantation of the PGA-hyaluronan scaffold immersed with PRP in articular cartilage defects of the knee pretreated with Pridie drilling. Patients were assessed by KOOS. At 9 months followup, histologic staining was performed in specimens obtained from five patients to assess the repair tissue quality.

RESULTS

The KOOS subscores improved for pain (55 to 91), symptoms (57 to 88), activities of daily living (69 to 86), sports and recreation (36 to 70), and quality of life (38 to 73). The histologic evaluation showed a homogeneous hyaline-like cartilage repair tissue.

CONCLUSIONS

The cell-free PGA-hyaluronan scaffold combined with PRP leads to cartilage repair and improved patient-reported outcomes (KOOS) during 12 months of followup. Histologic sections showed morphologic features of hyaline-like repair tissue. Long-term followup is needed to determine if the cartilage repair tissue is durable.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Platelet activation: ultrastructure and morphometry in platelet-rich plasma of horses

This study was conducted to investigate the activation ability of the platelet-rich plasma (PRP) by pharmacological agents, as well as to verify the need or not of this activation for therapeutic use. The PRP was obtained from four healthy crossbred geldings aged 13 to 16 years (15±1years), and was processed for observation and quantification of the platelet morphology by using the transmission electron microscopy. All PRP samples were activated with 10% calcium chloride (CaCl2) solution, pure bovine thrombin or associated with CaCl2. The control (pure PRP) was not pharmacologically activated. In the pure PRP samples, 49% of the platelets were classified as state of activation uncertain, 41% as resting, 9% as fully activated and 1% as irreversibly damaged. Treatment with 10% CaCl2 provided a distribution of 54% platelets in state of activation uncertain, 24% as fully activated, 20% as resting, and 2% as irreversibly damaged. The platelet morphology of the bovine thrombin treated samples did not fit into classification adopted, as showing irregular shape with emission of large filamentous pseudopods, appearance of ruptured and whole granules in the remaining cytoplasm and extracellular environment. There was effect of the treatment on the platelet morphology (P=0.03). The 10% CaCl2 is an adequate platelet-activating agent. However, in cases the use of PRP under its liquid form is necessary, the use of pure PRP is recommended, since besides presenting an adequate percentage of fully activated platelets it also has significant amount of the resting type, which can be activated by substances found in the injured tissue.

The role of platelet-rich plasma in rotator cuff repair

The shoulder is a common source of disability resulting from traumatic and degenerate tears of the rotator cuff, subacromial impingement, and osteoarthritis. Nonoperative management has focused on treatment of the predisposing factors, the use of analgesics and anti-inflammatory medication usually in association with local anesthetic and steroid injections. Surgical intervention allows debridement of the degenerate cuff and partial thickness cuff tears, subacromial bursitis, impinging bone spurs and osteophytes together with rotator cuff repairs. Repairs of degenerate and torn tissue are often prone to failure due to many intrinsic and extrinsic factors. It is assumed that some biological therapies might improve clinical, mechanical, and histologic outcomes. Injections of platelet-rich plasma (PRP) have led to reduced pain and improved recovery in other degenerate pathologies areas together with the restoration of function. This study reviews the current literature on PRP and in particular discusses its relevance in the treatment of rotator cuff tears.

Cell therapy in bone healing disorders

In addition to osteosynthetic stabilizing techniques and autologous bone transplantations, so-called orthobiologics play an increasing role in the treatment of bone healing disorders. Besides the use of various growth factors, more and more new data suggest that cell-based therapies promote local bone regeneration. For ethical and biological reasons, clinical application of progenitor cells on the musculoskeletal system is limited to autologous, postpartum stem cells. Intraoperative one-step treatment with autologous progenitor cells, in particular, delivered promising results in preliminary clinical studies. This article provides an overview of the rationale for, and characteristics of the clinical application of cell-based therapy to treat osseous defects based on a review of existing literature and our own experience with more than 100 patients. Most clinical trials report successful bone regeneration after the application of mixed cell populations from bone marrow. The autologous application of human bone marrow cells which are not expanded ex vivo has medico-legal advantages. However, there is a lack of prospective randomized studies including controls for cell therapy for bone defects. Autologous bone marrow cell therapy seems to be a promising treatment option which may reduce the amount of bone grafting in future.

Tissue engineered strategies for skeletal muscle injury

Skeletal muscle injuries are common in athletes, occurring with direct and indirect mechanisms and marked residual effects, such as severe long-term pain and physical disability. Current therapy consists of conservative management including RICE protocol (rest, ice, compression and elevation), nonsteroidal anti-inflammatory drugs, and intramuscular corticosteroids. However, current management of muscle injuries often does not provide optimal restoration to preinjury status. New biological therapies, such as injection of platelet-rich plasma and stem-cell-based therapy, are appealing. Although some studies support PRP application in muscle-injury management, reasons for concern persist, and further research is required for a standardized and safe use of PRP in clinical practice. The role of stem cells needs to be confirmed, as studies are still limited and inconsistent. Further research is needed to identify mechanisms involved in muscle regeneration and in survival, proliferation, and differentiation of stem cells.

Incorporating platelet-rich plasma into electrospun scaffolds for tissue engineering applications

Platelet-rich plasma (PRP) therapy has seen a recent spike in clinical interest due to the potential that the highly concentrated platelet solutions hold for stimulating tissue repair and regeneration. The aim of this study was to incorporate PRP into a number of electrospun materials to determine how growth factors are eluted from the structures, and what effect the presence of these factors has on enhancing electrospun scaffold bioactivity. PRP underwent a freeze-thaw-freeze process to lyse platelets, followed by lyophilization to create a powdered preparation rich in growth factors (PRGF), which was subsequently added to the electrospinning process. Release of protein from scaffolds over time was quantified, along with the quantification of human macrophage and adipose-derived stem cell (ADSC) chemotaxis and proliferation. Protein assays demonstrated a sustained release of protein from PRGF-containing scaffolds at up to 35 days in culture. Scaffold bioactivity was enhanced as ADSCs demonstrated increased proliferation in the presence of PRGF, whereas macrophages demonstrated increased chemotaxis to PRGF. In conclusion, the work performed in this study demonstrated that the incorporation of PRGF into electrospun structures has a significant positive influence on the bioactivity of the scaffolds, and may prove beneficial in a number of tissue engineering applications.

The effect of platelet concentrates on graft maturation and graft-bone interface healing in anterior cruciate ligament reconstruction in human patients: a systematic review of controlled trials

PURPOSE

To systematically review the current evidence for the effects of platelet concentrates on (1) graft maturation and (2) graft-bone interface healing in anterior cruciate ligament (ACL) reconstruction in human, controlled trials and for ensuing differences in clinical outcomes.

METHODS

A systematic search of PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Embase, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews was performed for controlled trials of human ACL reconstruction with and without platelet concentrates. Data validity was assessed, and data were collected on graft maturation, graft-bone interface healing, and clinical outcome.

RESULTS

Eight studies met the inclusion criteria. Seven studies reported on graft maturation with significantly better outcomes in the platelet groups in 4, and there were large differences in means in an additional 2 studies. Five studies reported on tunnel healing, and 4 found no difference between groups. Three studies assessed clinical outcome but found no differences, regardless of whether they had shown a beneficial effect (1 of 3) or no effect (2 of 3) of platelets on graft and tunnel healing.

CONCLUSIONS

The current best evidence suggests that the addition of platelet concentrates to ACL reconstruction may have a beneficial effect on graft maturation and could improve it by 20% to 30% on average, but with substantial variability. The most likely mode of action is that treatment with platelets accelerates graft repopulation and remodeling, and this interpretation is supported by the existing data and is biologically plausible. However, the current evidence also shows only a very limited influence of platelet concentrates on graft-bone interface healing and no significant difference in clinical outcomes.

LEVEL OF EVIDENCE

Level III, systematic review of Level I, II, and III studies.

Platelet-rich plasma activation in combination with biphasic osteochondral scaffolds-conditions for maximal growth factor production

PURPOSE

The combination of scaffolds and biological factors may enhance articular cartilage repair. Little is known regarding the activation and subsequent growth factor release of platelet-rich plasma (PRP) in contact with biosynthetic scaffolds. The purpose of this study was i) to identify whether the addition of thrombin was required to activate PRP in the presence of a collagen osteochondral scaffold and ii) to compare the activity of PRP when applied to both collagen- and polylactide-based osteochondral scaffolds.

METHODS

Equal combined volumes of test substances were used (n = 3): 500 μl PRP alone or on scaffolds; 375 μl PRP + 125 μl autologous thrombin on scaffolds; 455 μl PRP + 45 μl bovine thrombin on scaffolds. Scaffolds and/or PRP were cultured in vitro in DMEM/F12 medium for 10 days. TGF-β1, PDGF-AB and bFGF were measured using ELISA.

RESULTS

A similar cumulative release profile in all growth factors was found over the 10-day period i.e. a burst release and further physiological prolonged release. A significantly higher release of PDGF-AB was seen in the PRP + collagen scaffold groups at all time points, compared to scaffold + PRP + thrombins (P < 0.001). A significantly increased cumulative volume of PDGF-AB was released from the collagen scaffold compared to the polylactide scaffold (P < 0.001).

CONCLUSION

This study shows that polylactide and particularly collagen osteochondral scaffolds activate PRP in vitro. If PRP is combined with these scaffolds clinically, no exogenous activation with thrombin is required to achieve growth factor release, which may be of benefit for articular cartilage repair applications.

Optimization of ingredients, procedures and rehabilitation for platelet-rich plasma injections for chronic tendinopathy

SUMMARY There is considerable interest amongst clinicians and researchers to create the optimal platelet product to maximize outcomes with platelet-rich plasma (PRP) injections. PRP has been widely introduced as a safe alternative for treating tendinopathies. However, there is still limited clinical evidence describing the components of the platelet product and supporting its use in clinical trials. This article reviews the current literature regarding the role of PRP injections in the treatment of recalcitrant tendinopathies and the different factors in the platelet product that could affect the outcome, including the platelet count, presence of leukocytes, activators used, pH of solution and delivery method, among others. In addition, we address important concepts regarding rehabilitation after PRP procedures, which has little consensus to date and is the subject of much debate. Based on the phases of soft tissue healing, basic science research on platelets, as well as our clinical experience in treating over 500 patients with PRP, we will suggest guidelines regarding the optimal progression of rehabilitation and timing for return to previous activity following the procedure.

Platelet-rich plasma protects tenocytes from adverse side effects of dexamethasone and ciprofloxacin

BACKGROUND

Ruptured tendons heal very slowly and complete recovery from injury is uncertain. Platelet-rich plasma (PRP), a rich source of growth factors, is currently being widely tested as a soft tissue healing agent and may accelerate tendon repair. The authors assessed the ability of PRP to prevent in vitro adverse effects of 2 drugs commonly linked to tendon rupture and tendinopathy, glucocorticoids and fluoroquinolone antibiotics.

HYPOTHESIS

The pro-healing response induced by PRP protects human tenocytes against the cytotoxic effects of dexamethasone and ciprofloxacin.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human primary hamstring tenocytes were exposed to different doses of ciprofloxacin and dexamethasone with and without PRP. AlamarBlue, β-galactosidase assay, and live/dead stain were used to measure, respectively, viability, senescence, and death in tenocyte culture.

RESULTS

The viability of cells exposed to high doses of ciprofloxacin was significantly decreased compared with controls, with no induced senescence but increased cell death. Dexamethasone reduced viable cell number without inducing overt cell death, but the number of senescent cells increased considerably. After co-treatment with 10% PRP, viable cell number increased significantly in both conditions and the number of dead cells decreased in ciprofloxacin-treated cultures. Moreover, dexamethasone-induced senescence was markedly reduced by co-treatment with 10% PRP.

CONCLUSION

This study demonstrates that ciprofloxacin and dexamethasone have differing adverse effects on human tenocytes, with ciprofloxacin inducing cell death while dexamethasone primarily induces senescence. The authors showed that PRP can protect cultured human tenocytes against cell death or senescence induced by these drugs.

CLINICAL RELEVANCE

Both ciprofloxacin and dexamethasone are highly effective in treatment of inflammatory and infectious conditions, therefore new strategies to minimize their adverse effects are of strong interest. These findings suggest the potential for local administration of PRP to enhance tendon healing in patients undergoing glucocorticoid or fluoroquinolone treatment.