Does a single application of PRP alter the expression of IGF-I in the early phase of tendon healing?

Effect of platelet-rich plasma in Achilles tendon allograft in rabbits

BACKGROUND

Achilles tendon is composed of dense connective tissue and is one of the largest tendons in the body. In veterinary medicine, acute ruptures are associated with impact injury or sharp trauma. Healing of the ruptured tendon is challenging because of poor blood and nerve supply as well as the residual cell population. Platelet-rich plasma (PRP) contains numerous bioactive agents and growth factors and has been utilized to promote healing in bone, soft tissue, and tendons.

OBJECTIVE

The purpose of this study was to evaluate the healing effect of PRP injected into the surrounding fascia of the Achilles tendon after allograft in rabbits.

METHODS

Donor rabbits (n = 8) were anesthetized and 16 lateral gastrocnemius tendons were fully transected bilaterally. Transected tendons were decellularized and stored at -80°C prior to allograft. The allograft was placed on the partially transected medial gastrocnemius tendon in the left hindlimb of 16 rabbits. The allograft PRP group (n = 8) had 0.3 mL of PRP administered in the tendon and the allograft control group (n = 8) did not receive any treatment. After 8 weeks, rabbits were euthanatized and allograft tendons were transected for macroscopic, biomechanical, and histological assessment.

RESULTS

The allograft PRP group exhibited superior macroscopic assessment scores, greater tensile strength, and a histologically enhanced healing process compared to those in the allograft control group.

CONCLUSIONS

Our results suggest administration of PRP on an allograft tendon has a positive effect on the healing process in a ruptured Achilles tendon.

Current progress in growth factors and extracellular vesicles in tendon healing

Tendon injury healing is a complex process that involves the participation of a significant number of molecules and cells, including growth factors molecules in a key role. Numerous studies have demonstrated the function of growth factors in tendon healing, and the recent emergence of EV has also provided a new visual field for promoting tendon healing. This review examines the tendon structure, growth, and development, as well as the physiological process of its healing after injury. The review assesses the role of six substances in tendon healing: insulin-like growth factor-I (IGF-I), transforming growth factor β (TGFβ), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and EV. Different growth factors are active at various stages of healing and exhibit separate physiological activities. IGF-1 is expressed immediately after injury and stimulates the mitosis of various cells while suppressing the response to inflammation. VEGF, which is also active immediately after injury, accelerates local metabolism by promoting vascular network formation and positively impacts the activities of other growth factors. However, VEGF's protracted action could be harmful to tendon healing. PDGF, the earliest discovered cytokine to influence tendon healing, has a powerful cell chemotaxis and promotes cell proliferation, but it can equally accelerate the response to inflammation and relieve local adhesions. Also useful for relieving tendon adhesion is TGF- β, which is active almost during the entire phase of tendon healing. As a powerful active substance, in addition to its participation in the field of cardiovascular and cerebrovascular vessels, tumour and chronic wounds, TGF- β reportedly plays a role in promoting cell proliferation, activating growth factors, and inhibiting inflammatory response during tendon healing.

Molecular and Biologic Effects of Platelet-Rich Plasma (PRP) in Ligament and Tendon Healing and Regeneration: A Systematic Review

Platelet-rich plasma (PRP) has been introduced and applied to a wide spectrum of acute and chronic ligament and tendon pathologic conditions. Although the biological effect of PRP has been studied thoroughly in both animal and human studies, there is no consensus so far on the exact mechanism of its action as well as the optimal timing and dosage of its application. Therefore, we conducted a systematic review aiming to evaluate the molecular effect of the administration of PRP in tendoligamentous injuries and degenerative diseases. The literature search revealed 36 in vitro and in vivo studies examining the healing and remodeling response of animal and human ligament or tendon tissues to PRP. Platelet-rich plasma added in the culture media was highly associated with increased cell proliferation, migration, viability and total collagen production of both ligament- and tendon-derived cells in in vitro studies, which was further confirmed by the upregulation of collagen gene expression. In vivo studies correlated the PRP with higher fibroblastic anabolic activity, including increased cellularity, collagen production and vascularity of ligament tissue. Similarly, greater metabolic response of tenocytes along with the acceleration of the healing process in the setting of a tendon tear were noticed after PRP application, particularly between the third and fourth week after treatment. However, some studies demonstrated that PRP had no or even negative effect on tendon and ligament regeneration. This controversy is mainly related to the variable processes and methodologies of preparation of PRP, necessitating standardized protocols for both investigation and ap-plication.

A Simplified Murine Model to Imitate Flexor Tendon Adhesion Formation without Suture

Peritendinous adhesion (PA) around tendons are daunting challenges for hand surgeons. Tenotomy with various sutures are considered classical tendon repair models (TRM) of tendon adhesion as well as tendon healing. However, potential biomimetic therapies such as anti-adhesion barriers and artificial tendon sheaths to avoid recurrence of PA are sometimes tested in these models without considering tendon healing. Thus, our aim is to create a simplified model without sutures in this study by using three 6 mm longitudinal and parallel incisions called the longitudinal incision model (LCM) in the murine flexor tendon. We found that the adhesion score of LCM has no significant difference to that in TRM. The range of motion (ROM) reveals similar adhesion formation in both TRM and LCM groups. Moreover, mRNA expression levels of collagen I and III in LCM shows no significant difference to that in TRM. The breaking force and stiffness of LCM were significantly higher than that of TRM. Therefore, LCM can imitate flexor tendon adhesion formation without sutures compared to TRM, without significant side effects on biomechanics with an easy operation.

Progress of Platelet Derivatives for Cartilage Tissue Engineering

Articular cartilage has limited self-regeneration ability for lacking of blood vessels, nerves, and lymph that makes it a great challenge to repair defects of the tissue and restore motor functions of the injured or aging population. Platelet derivatives, such as platelet-rich plasma, have been proved effective, safe, and economical in musculoskeletal diseases for their autologous origin and rich in growth factors. The combination of platelet derivatives with biomaterials provides both mechanical support and localized sustained release of bioactive molecules in cartilage tissue engineering and low-cost efficient approaches of potential treatment. In this review, we first provide an overview of platelet derivatives and their application in clinical and experimental therapies, and then we further discuss the techniques of the addition of platelet derivatives and their influences on scaffold properties. Advances in cartilage tissue engineering with platelet derivatives as signal factors and structural components are also introduced before prospects and concerns in this research field. In short, platelet derivatives have broad application prospects as an economical and effective enhancement for tissue engineering–based articular cartilage repair.

The effects of orthobiologics in the treatment of tendon pathologies: a systematic review of preclinical evidence

Purpose

The aim of this systematic review is to explore the current available knowledge about tendon disorders and orthobiologics derived by preclinical experiments to evaluate their role and efficacy in the different stages and conditions related to the tendon healing processes.

Methods

The systematic review was performed according to the PRISMA guidelines. Different electronic databases (MEDLINE, Web of Science, EMBASE) were searched for studies investigating orthobiologics (PRP and cell-based products from adipose tissue or bone marrow) in animal models or veterinary clinical trials for tendon pathologies (complete/partial tendon ruptures, rotator cuff tears, tendinopathy, enthesis-related injuries). Data regarding the specific product used, the treatment site/pathology, the host and the model were collected. The results were classified into the following categories: histological, biomechanical, molecular and imaging.

Results

A large pool of preclinical studies on tendon disorders have been found on platelet-rich plasma (PRP), while data about stromal vascular fraction (SVF) and bone marrow concentrate (BMAC) are still limited and frequently focused on expanded cells, rather than orthobiologics prepared at the point of care.

The effect of PRP is related to an acceleration of the healing process, without improvements in the final structure and properties of repaired tendon. Cell-based products have been reported to produce more durable results, but the level of evidence is currently insufficient to draw clear indications.

Conclusions

The preclinical results about orthobiologics applications to tendon pathologies would support the rationale of their clinical use and encourage the performance of clinical trials aimed to confirm these data in human subjects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00468-w.

Growth Factor Roles in Soft Tissue Physiology and Pathophysiology

Repair and healing of injured and diseased tendons has been traditionally fraught with apprehension and difficulties, and often led to rather unsatisfactory results. The burgeoning research field of growth factors has opened new venues for treatment of tendon disorders and injuries, and possibly for treatment of disorders of the aorta and major arteries as well. Several chapters in this volume elucidate the role of transforming growth factor β (TGFß) in pathogenesis of several heritable disorders affecting soft tissues, such as aorta, cardiac valves, and tendons and ligaments. Several members of the bone morphogenetic group either have been approved by the FDA for treatment of non-healing fractures or have been undergoing intensive clinical and experimental testing for use of healing bone fractures and tendon injuries. Because fibroblast growth factors (FGFs) are involved in embryonic development of tendons and muscles among other tissues and organs, the hope is that applied research on FGF biological effects will lead to the development of some new treatment strategies providing that we can control angiogenicity of these growth factors. The problem, or rather question, regarding practical use of imsulin-like growth factor I (IGF-I) in tendon repair is whether IGF-I acts independently or under the guidance of growth hormone. FGF2 or platelet-derived growth factor (PDGF) alone or in combination with IGF-I stimulates regeneration of periodontal ligament: a matter of importance in Marfan patients with periodontitis. In contrast, vascular endothelial growth factor (VEGF) appears to have rather deleterious effects on experimental tendon healing, perhaps because of its angiogenic activity and stimulation of matrix metalloproteinases-proteases whose increased expression has been documented in a variety of ruptured tendons. Other modalities, such as local administration of platelet-rich plasma (PRP) and/or of mesenchymal stem cells have been explored extensively in tendon healing. Though treatment with PRP and mesenchymal stem cells has met with some success in horses (who experience a lot of tendon injuries and other tendon problems), the use of PRP and mesenchymal stem cells in people has been more problematic and requires more studies before PRP and mesenchymal stem cells can become reliable tools in management of soft tissue injuries and disorders.

Biologics in the Treatment of Achilles Tendon

The treatment of Achilles tendinitis from conservative to minimally invasive to surgery gives patients a wide range of treatment options for this common pathology. The use and role of biologics to augment this treatment is emerging. The use of biologics may enhance the healing potential of the Achilles tendon when conservative treatment fails. There are a handful of biologics being investigated to obtain if improved outcomes can be maximized.

Biologics in the Treatment of Achilles Tendon Pathologies

Regenerative medicine is gaining more and more space for the treatment of Achilles pathologic conditions. Biologics could play a role in the management of midportion Achilles tendinopathy as a step between conservative and surgical treatment or as an augmentation. Higher-level studies are needed before determining a level of treatment recommendation for biologic strategies for insertional Achilles tendinopathy. Combining imaging with patient's functional requests could be the way to reach a protocol for the use of biologics for the treatment of midportion Achilles tendinopathy and, for this perspective, the authors describe the Foot and Ankle Reconstruction Group algorithm of treatment.

Efficacy of Combining PRP and MMP Inhibitors in Treating Moderately Damaged Tendons Ex Vivo

Platelet-rich plasma (PRP) and broad-spectrum matrix metalloproteinase inhibitors (MMPIs) have been used as therapeutic options for tendinopathy. However, mixed results have been reported regarding their efficacy. We posited that the combination of these two treatment strategies would be more beneficial for healing tendons than each treatment alone. Rat tail tendons were harvested and cultured without mechanical stress for 0, 4, or 10 days. Single and combination treatment with PRP and MMPIs with either broad- or narrow-spectrum (MMP-13 selective), was administered to 4-day stress-deprived (SD) tendons, an ex vivo model for moderate tendinopathy. This treatment was applied to the damaged tendons over 6 days. At the end of their culture time, the tendons were subjected to traction testing and pathohistology, immunohistochemistry, and viability assays. The results showed better histological features for the PRP + narrow-spectrum MMPI group compared with all individual treatment modalities. Moreover, higher fiber density, more elongated nucleus shape, smaller space between fibers, and a trend toward higher mechanical strength were noted for PRP + narrow-spectrum MMPI group compared with 10-day SD tendons. This study shows that the combination of PRP + narrow-spectrum MMPI is a potentially effective treatment approach for tendinopathy. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1838-1847, 2019.

Biologic and mechanical aspects of tendon fibrosis after injury and repair

Tendon injuries of the hand that require surgical repair often heal with excess scarring and adhesions to adjacent tissues. This can compromise the natural gliding mechanics of the flexor tendons in particular, which operate within a fibro-osseous tunnel system similar to a set of pulleys. Even combining the finest suture repair techniques with optimal hand therapy protocols cannot ensure predictable restoration of hand function in these cases. To date, the majority of research regarding tendon injuries has revolved around the mechanical aspects of the surgical repair (i.e. suture techniques) and postoperative rehabilitation. The central principles of treatment gleaned from this literature include using a combination of core and epitendinous sutures during repair and initiating motion early on in hand therapy to improve tensile strength and limit adhesion formation. However, it is likely that the best clinical solution will utilize optimal biological modulation of the healing response in addition to these core strategies and, recently, the research in this area has expanded considerably. While there are no proven additive biological agents that can be used in clinical practice currently, in this review, we analyze the recent literature surrounding cytokine modulation, gene and cell-based therapies, and tissue engineering, which may ultimately lead to improved clinical outcomes following tendon injury in the future.

Platelet-Rich Plasma

Platelet-rich plasma (PRP) is a promising treatment for musculoskeletal maladies and clinical data to date have shown that PRP is safe. However, evidence of its efficacy has been mixed and highly variable depending on the specific indication. Additional future high-quality large clinical trials will be critical in shaping our perspective of this treatment option. The heterogeneity of PRP preparations, both presently and historically, leads sweeping recommendations about its utility impossible to make. This heterogeneity has also made interpreting existing literature more complicated.

Growth Factors and Cell Homing in Dental Tissue Regeneration

Purpose of Review

To summarize current views on the role and therapeutic potential of growth factors (GFs) within endodontic cell homing.

Recent Findings

Cell homing/revitalization techniques aim to regenerate dentin and pulp using endogenous cells. Clinically, revitalization has successfully created new vital tissue in necrotic permanent teeth with an open apex; however, there is no evidence of new odontoblasts, pulp tissue, or predictable extension in root length. Although the response is reparative rather than regenerative, exciting opportunities to improve these biologically-based strategies remain by (1) efficiently sequestering dentin-matrix-components (DMCs) using irrigants and dental materials (2) designing next-generation GF-releasing scaffold materials and (3) utilizing other sources of GF such as cells and plasma-rich plasma and plasma-rich fibrin.

Summary

GFs can promote reparative-dentinogenesis and pulp-like tissue formation. The future development and clinical approval of GF-functionalized-scaffolds is a priority; however, current focus should be to harness DMCs and target the interaction of stem cells and GFs.

A review on animal models and treatments for the reconstruction of Achilles and flexor tendons

Tendon is a connective tissue mainly composed of collagen fibers with peculiar mechanical properties essential to functional movements. The increasing incidence of tendon traumatic injuries and ruptures-associated or not with the loss of tissue-falls on the growing interest in the field of tissue engineering and regenerative medicine. The use of animal models is mandatory to deepen the knowledge of the tendon healing response to severe damages or acute transections. Thus, the selection of preclinical models is crucial to ensure a successful translation of effective and safe innovative treatments to the clinical practice. The current review is focused on animal models of tendon ruptures and lacerations or defective injuries with large tissue loss that require surgical approaches or grafting procedures. Data published between 2000 and 2016 were examined. The analyzed articles were compiled from Pub Med-NCBI using search terms, including animal model(s) AND tendon augmentation OR tendon substitute(s) OR tendon substitution OR tendon replacement OR tendon graft(s) OR tendon defect(s) OR tendon rupture(s). This article presents the existing preclinical models - considering their advantages and disadvantages-in which translational progresses have been made by using bioactive sutures or tissue engineering that combines biomaterials with cells and growth factors to efficiently treat transections or large defects of Achilles and flexor tendons.

PRP Treatment Efficacy for Tendinopathy: A Review of Basic Science Studies

Platelet-Rich Plasma (PRP) has been widely used in orthopaedic surgery and sport medicine to treat tendon injuries. However, the efficacy of PRP treatment for tendinopathy is controversial. This paper focuses on reviewing the basic science studies on PRP performed under well-controlled conditions. Both in vitro and in vivo studies describe PRP's anabolic and anti-inflammatory effects on tendons. While some clinical trials support these findings, others refute them. In this review, we discuss the effectiveness of PRP to treat tendon injuries with evidence presented in basic science studies and the potential reasons for the controversial results in clinical trials. Finally, we comment on the approaches that may be required to improve the efficacy of PRP treatment for tendinopathy.

Intra-Articular Injections of Platelet-Rich Plasma versus Hyaluronic Acid in the Treatment of Osteoarthritic Knee Pain: A Randomized Clinical Trial in the Context of the Spanish National Health Care System

Intra-articular injection of platelet-rich plasma (PRP) has been established as a suitable treatment for knee osteoarthritis. Here, we present a double-blind randomized controlled clinical trial, conducted in a public Hospital of the Spanish National Health Care System, to evaluate the efficacy of injecting autologous PRP versus hyaluronic acid (HA) in knee osteoarthritis. PRP was manufactured in Malaga’s Regional Blood Center (Spain). Patients that met the eligibility criteria were randomized into a PRP group or a HA group. Pain and functional improvements were assessed pre- and post-treatment (three and six months follow-up) using the Visual Analogue Scale (VAS); the Knee and Osteoarthritis Outcome System (KOOS) scale and the European Quality of Life scale (EUROQOL). Both groups presented pain reduction at six months. The VAS scores for the PRP group improved by at least 50% from their initial value, particularly at three months following the final infiltration, with results resembling those of the HA group at six months. PRP was more effective in patients with lower osteoarthritis grades. Both treatments improved pain in knee osteoarthritis patients without statistically significant differences between them. However, PRP injection was proved to improve pain three months after the final infiltration and to be more effective in lower osteoarthritis grades.

Plantar fascia rupture in a professional soccer player

We report the case of a 29-year-old male professional soccer player who presented with symptoms of plantar fasciitis. His symptoms occurred with no remarkable triggers and gradually worsened despite conservative treatments including taping, use of insoles, and physical therapy. Local corticosteroid injection was given twice as a further intervention, but his plantar fascia partially ruptured 49 days after the second injection. He was treated conservatively with platelet-rich plasma, and magnetic resonance imaging showed regenerative change of the ruptured fascia. Five months after the rupture, he returned to his original level of training. If professional athletes find it difficult to refrain from athletic activity, as in the present case, the risk of rupture due to corticosteroid injection should not be overlooked.

Platelet-Rich Plasma Augmentation of Arthroscopic Hip Surgery for Femoroacetabular Impingement: A Prospective Study With 24-Month Follow-up

PURPOSE

The objective of this study is to evaluate the clinical and immunologic effects of intra-articular doses of platelet-rich plasma (PRP) in arthroscopic hip surgery for femoroacetabular impingement.

METHODS

Preoperatively, patients were randomized either to receive an intra-articular injection of PRP (group I, n = 30) or not to receive PRP (group II, n = 27) at the end of hip arthroscopic surgery. To evaluate the clinical outcome and follow-up, we used the modified Harris Hip Score (mHHS) 3, 6, and 24 months after surgery. Pain was evaluated using a visual analog scale 24 hours, 48 hours, 3 months, and 6 months after surgery. The radiologic outcome was analyzed using radiographs and magnetic resonance imaging (MRI) obtained before surgery and 6 months after surgery. Labral integration and joint effusion were evaluated with MRI at 6 months. For statistical analysis, an independent t test and the Wilcoxon rank sum test were used (P < .05 was considered statistically significant).

RESULTS

The visual analog scale score 48 hours after surgery was 3.04 in group I compared with 5.28 in group II (P < .05). At the 3-month follow-up, the mHHS was 91.79 in group I versus 90.97 in group II (P = .65). At the 24-month follow-up, the mHHS was 93.41 in group I (P = .56) versus 92.32 in group II (P = .52). At the 6-month follow-up, MRI showed no effusion in 36.7% of patients in group I versus 21.1% of patients in group II (P = .013). Regarding labral integration, no statistical differences were observed between the groups (P = .76).

CONCLUSIONS

In this randomized study, PRP resulted in lower postoperative pain scores at 48 hours and fewer joint effusions at 6 months. These findings suggest that PRP may have a benefit regarding postoperative inflammation; however, the long-term clinical benefit is unclear.

LEVEL OF EVIDENCE

Level II, lesser-quality randomized controlled trial.

Platelet-Rich Plasma Promotes Axon Regeneration, Wound Healing, and Pain Reduction: Fact or Fiction

Platelet-rich plasma (PRP) has been tested in vitro, in animal models, and clinically for its efficacy in enhancing the rate of wound healing, reducing pain associated with injuries, and promoting axon regeneration. Although extensive data indicate that PRP-released factors induce these effects, the claims are often weakened because many studies were not rigorous or controlled, the data were limited, and other studies yielded contrary results. Critical to assessing whether PRP is effective are the large number of variables in these studies, including the method of PRP preparation, which influences the composition of PRP; type of application; type of wounds; target tissues; and diverse animal models and clinical studies. All these variables raise the question of whether one can anticipate consistent influences and raise the possibility that most of the results are correct under the circumstances where PRP was tested. This review examines evidence on the potential influences of PRP and whether PRP-released factors could induce the reported influences and concludes that the preponderance of evidence suggests that PRP has the capacity to induce all the claimed influences, although this position cannot be definitively argued. Well-defined and rigorously controlled studies of the potential influences of PRP are required in which PRP is isolated and applied using consistent techniques, protocols, and models. Finally, it is concluded that, because of the purported benefits of PRP administration and the lack of adverse events, further animal and clinical studies should be performed to explore the potential influences of PRP.

New and emerging strategies in platelet-rich plasma application in musculoskeletal regenerative procedures: general overview on still open questions and outlook

Despite its pervasive use, the clinical efficacy of platelet-rich plasma (PRP) therapy and the different mechanisms of action have yet to be established. This overview of the literature is focused on the role of PRP in bone, tendon, cartilage, and ligament tissue regeneration considering basic science literature deriving from in vitro and in vivo studies. Although this work provides evidence that numerous preclinical studies published within the last 10 years showed promising results concerning the application of PRP, many key questions remain unanswered and controversial results have arisen. Additional preclinical studies are needed to define the dosing, timing, and frequency of PRP injections, different techniques for delivery and location of delivery, optimal physiologic conditions for injections, and the concomitant use of recombinant proteins, cytokines, additional growth factors, biological scaffolds, and stems cells to develop optimal treatment protocols that can effectively treat various musculoskeletal conditions.

Platelet-rich plasma in orthopedic therapy: a comparative systematic review of clinical and experimental data in equine and human musculoskeletal lesions

BACKGROUND

This systematic review aimed to present and critically appraise the available information on the efficacy of platelet rich plasma (PRP) in equine and human orthopedic therapeutics and to verify the influence of study design and methodology on the assumption of PRP's efficacy. We searched Medline, PubMed, Embase, Bireme and Google Scholar without restrictions until July 2013. Randomized trials, human cohort clinical studies or case series with a control group on the use of PRP in tendons, ligaments or articular lesions were included. Equine clinical studies on the same topics were included independently of their design. Experimental studies relevant to the clarification of PRP's effects and mechanisms of action in tissues of interest, conducted in any animal species, were selected.

RESULTS

This review included 123 studies. PRP's beneficial effects were observed in 46.7% of the clinical studies, while the absence of positive effects was observed in 43.3%. Among experimental studies, 73% yielded positive results, and 7.9% yielded negative results. The most frequent flaws in the clinical trials' designs were the lack of a true placebo group, poor product characterization, insufficient blinding, small sampling, short follow-up periods, and adoption of poor outcome measures. The methods employed for PRP preparation and administration and the selected outcome measures varied greatly. Poor study design was a common feature of equine clinical trials. From studies in which PRP had beneficial effects, 67.8% had an overall high risk of bias. From the studies in which PRP failed to exhibit beneficial effects, 67.8% had an overall low risk of bias.

CONCLUSIONS

Most experimental studies revealed positive effects of PRP. Although the majority of equine clinical studies yielded positive results, the human clinical trials' results failed to corroborate these findings. In both species, beneficial results were more frequently observed in studies with a high risk of bias. The use of PRP in musculoskeletal lesions, although safe and promising, has still not shown strong evidence in clinical scenarios.

Use of ultrasound-targeted microbubble destruction to transfect IGF-1 cDNA to enhance the regeneration of rat wounded Achilles tendon in vivo

The purpose of this study was to determine whether using ultrasound-targeted microbubble destruction (UTMD) to transfect rat wounded Achilles tendon with insulin-like growth factor-1 (IGF-1) cDNA would enhance tissue regeneration. Forty rats with injured Achilles tendons were transfected with IGF-1 cDNA and divided into: (1) control group, (2) plasmid-only group, (3) plasmid+ultrasound group and (4) plasmid+microbubbles+ultrasound group. The IGF-1 cDNA expression of the Achilles tendons was evaluated by histological adhesion finding, quantitative real-time reverse transcription PCR examination and biomechanical test. The adhesion scores in group 4 were lowest at weeks 2 and 8 (P<0.05). The IGF-1 expression in the Achilles tendons was highest in group 4 at weeks 2 and 8 (P<0.05). Compared with those of other three groups, the granulation tissues and inflammatory-cell infiltration were lighter in group 4 at week 2, and the scars on the tendons in group 4 were less evident at week 8. The messenger RNA (mRNA) of IGF-1 of group 4 was upregulated at weeks 2 and 8 (P<0.01). Groups 4 and 3 showed a greater maximum load, stiffness and ultimate stress (P<0.05). Maximum load, stiffness and ultimate stress of healing Achilles tendons in group 4 were highest at weeks 2 and 8 (P<0.05).

Treatment of tendinopathies with platelet-rich plasma

Pain and dysfunction related to tendinopathy are often refractory to traditional treatments and offer a unique challenge to physicians, because no gold standard treatment exists. Injectable biologics may represent a new modality in conjunction with a multifaceted treatment approach. Platelet-rich plasma (PRP) injections are not associated with the systemic or tendon degradation risks of corticosteroids or the inherent risks of surgery. Studies are promising but have not been replicated with high-powered evidence at the clinical level. Further evidence to expand understanding of the role of PRP in the treatment of tendinopathy is needed.

Effectiveness of xenogenous-based bovine-derived platelet gel embedded within a three-dimensional collagen implant on the healing and regeneration of the Achilles tendon defect in rabbits

BACKGROUND AND OBJECTIVE

Tissue engineering is an option in reconstructing large tendon defects and managing their healing and regeneration. We designed and produced a novel xenogeneic-based bovine platelet, embedded it within a tissue-engineered collagen implant (CI) and applied it in an experimentally induced large tendon defect model in rabbits to test whether bovine platelets could stimulate tendon healing and regeneration in vivo.

METHODS

One hundred twenty rabbits were randomly divided into two experimental and pilot groups. In all the animals, the left Achilles tendon was surgically excised and the tendon edges were aligned by Kessler suture. Each group was then divided into three groups of control (no implant), treated with CI and treated with collagen-platelet implant. The pilot groups were euthanized at 10, 15, 30 and 40 days post-injury (DPI), and their gross and histologic characteristics were evaluated to study host-graft interaction mechanism. To study the tendon healing and its outcome, the experimental animals were tested during the experiment using hematologic, ultrasonographic and various methods of clinical examinations and then euthanized at 60 DPI and their tendons were evaluated by gross pathologic, histopathologic, scanning electron microscopic, biophysical and biochemical methods.

RESULTS

Bovine platelets embedded within a CI increased inflammation at short term while it increased the rate of implant absorption and matrix replacement compared with the controls and CI alone. Treatment also significantly increased diameter, density, amount, alignment and differentiation of the collagen fibrils and fibers and approximated the water uptake and delivery behavior of the healing tendons to normal contralaterals (p < 0.05). Treatment also improved echogenicity and homogenicity of the tendons and reduced peritendinous adhesion, muscle fibrosis and atrophy, and therefore, it improved the clinical scores and physical activity related to the injured limb when compared with the controls (p < 0.05).

CONCLUSION

The bovine platelet gel embedded within the tissue-engineered CI was effective in healing, modeling and remodeling of the Achilles tendon in rabbit. This strategy may be a valuable option in the clinical setting.

The growth factors involved in flexor tendon repair and adhesion formation

Flexor tendon injuries remain a significant clinical problem, owing to the formation of adhesions or tendon rupture. A number of strategies have been tried to improve outcomes, but as yet none are routinely used in clinical practice. Understanding the role that growth factors play in tendon repair should enable a more targeted approach to be developed to improve the results of flexor tendon repair. This review describes the main growth factors in tendon wound healing, and the role they play in both repair and adhesion formation.

Platelet-rich plasma: does it help reduce tunnel widening after ACL reconstruction?

PURPOSE

The purpose of this study was to evaluate the efficacy of platelet-rich plasma (PRP) in reducing femoral and tibial tunnel enlargement in patients operated on for anterior cruciate ligament reconstruction with hamstrings.

METHODS

Forty male patients, in which both femoral and tibial 9-mm tunnels were performed because of the graft size, were enrolled in this prospective study. They were randomly assigned to group A (20 patients, PRP group) and group B (20 patients, control group). All patients were followed up at a median of 14.7 months (range 10-16 months), with a physical examination, the Tegner, Lysholm and objective IKDC scoring scales, and with the KT-1000 arthrometer. Moreover, they underwent a CT evaluation in order to assess the amount of tunnel enlargement.

RESULTS

Femoral tunnel diameter increased from 9.0 ± 0.1 mm to 9.8 ± 0.3 mm in group A (p = 0.032) and from 9.0 ± 0.1 mm to 9.4 ± 0.5 mm in group B (p = 0.043). Tibial tunnel diameter increased from 9.0 ± 0.2 mm to 10.9 ± 0.2 mm in group A (p = 0.029) and from 9.1 ± 0.1 mm to 10.1 ± 0.4 mm in group B (p = 0.028). Physical examination as well as the evaluation scales used showed no differences between the two groups.

CONCLUSIONS

The use of PRP does not seem to be effective in preventing tunnel enlargement.

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.

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.

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.

Platelet-rich plasma reverses the inhibition of tenocytes and osteoblasts in tendon-bone healing

The purpose of this study was to investigate the effect of platelet-rich plasma on the proliferation of osteoblasts and tenocytes in tendon-bone healing. We cultured osteoblasts and tenocytes in an indirect coculture system with Transwell filters (Merck Millipore, Billerica, Massachusetts). The proliferation was examined using Cell Counting Kit-8 (Dojindo Chemistry Research Institute, Kumamoto, Japan).Four groups were studied: group 1, one cell type cultured without platelet-rich plasma; group 2, two cell types cultured together in an indirect coculture system without platelet-rich plasma; group 3, cells in the outer chamber and platelet-rich plasma in the inner chamber; and group 4, two different cell types in each of the 2 chambers with platelet-rich plasma in the inner chamber. The proliferation rates of groups 3 and 4 were the highest, followed by group 1 and then group 2, which was the lowest.Platelet-rich plasma abolishes the inhibition of osteoblasts or tenocytes in an indirect coculture system and improves the cell proliferation rate.

Platelet-rich plasma: a milieu of bioactive factors

Platelet concentrates such as platelet-rich plasma (PRP) have gained popularity in sports medicine and orthopaedics to promote accelerated physiologic healing and return to function. Each PRP product varies depending on patient factors and the system used to generate it. Blood from some patients may fail to make PRP, and most clinicians use PRP without performing cell counts on either the blood or the preparation to confirm that the solution is truly PRP. Components in this milieu have bioactive functions that affect musculoskeletal tissue regeneration and healing. Platelets are activated by collagen or other molecules and release growth factors from alpha granules. Additional substances are released from dense bodies and lysosomes. Soluble proteins also present in PRP function in hemostasis, whereas others serve as biomarkers of musculoskeletal injury. Electrolytes and soluble plasma hormones are required for cellular signaling and regulation. Leukocytes and erythrocytes are present in PRP and function in inflammation, immunity, and additional cellular signaling pathways. This article supports the emerging paradigm that more than just platelets are playing a role in clinical responses to PRP. Depending on the specific constituents of a PRP preparation, the clinical use can theoretically be matched to the pathology being treated in an effort to improve clinical efficacy.