Platelet-rich plasma injections for the management of knee osteoarthritis: The ESSKA-ICRS consensus. Recommendations using the RAND/UCLA appropriateness method for different clinical scenarios.

PURPOSE: The aim of this consensus was to develop evidence- and expert-based patient-focused recommendations on the appropriateness of intra-articular platelet-rich plasma (PRP) injections in different clinical scenarios of patients with knee osteoarthritis (OA). METHODS: The RAND/UCLA Appropriateness Method was used by the European Society of Sports Traumatology, Knee Surgery, and Arthroscopy (ESSKA), as well as the International Cartilage Regeneration and Joint Preservation Society (ICRS) to reach a consensus and produce recommendations for specific patient categories combining best available scientific evidence with the collective judgement of a panel of experts. RESULTS: Scenarios were defined based on first treatment vs first injective treatment vs second injective treatment, age (<50/50-65/66-80/>80), tibiofemoral vs patellofemoral involvement, OA level (Kellgren-Lawrence/KL 0-I/II-III/IV), and joint effusion (dry knee, minor-mild or major effusion). Out of 216 scenarios, in 84 (38.9%) the indication was considered appropriate, in 9 (4.2%) inappropriate and in 123 (56.9%) uncertain. The parameters associated with the highest consensus were PRP use after failed injective treatments (62.5%), followed by PRP after failed conservative treatments and KL 0-III scenarios (58.3%), while the highest uncertainty was found for PRP use as first treatment and KL IV OA (91.7% and 87.5% of uncertain scenarios, respectively). CONCLUSION: This ESSKA-ICRS consensus established recommendations on the appropriateness or inappropriateness of PRP injections for the treatment of knee OA, providing a useful reference for clinical practice. PRP injections are considered appropriate in patients aged ≤80 years with knee KL 0-III OA grade after failed conservative non-injective or injective treatments, while they are not considered appropriate as first treatment nor in KL IV OA grade. LEVEL OF EVIDENCE: Level I.

Assessing Bioprinted Functionalized Grafts for Biological Tendon Augmentation In Vitro.

Tendinopathy, characterized by inflammatory and degenerative changes, presents challenges in sports and medicine. In addressing the limitations of conservative management, this study focuses on developing tendon grafts using extrusion bioprinting with platelet-rich plasma (PRP)-infused hydrogels loaded with tendon cells. The objective is to understand paracrine interactions initiated by bioprinted tendon grafts in either inflamed or non-inflamed host tissues. PRP was utilized to functionalize methacrylate gelatin (GelMA), incorporating tendon cells for graft bioprinting. Bioinformatic analyses of overexpressed proteins, predictive of functional enrichment, revealed insights into PRP graft behavior in both non-inflamed and inflamed environments. PRP grafts activated inflammatory pathways, including Interleukin 17 (IL-17), neuroinflammation, Interleukin 33 (IL-33), and chemokine signaling. Interleukin 1 beta (IL-1b) in the graft environment triggered p38 mitogen-activated protein kinase (MAPK) signaling, nuclear factor kappa light chain enhancer of activated B cells (NF-kB) canonical pathway, and Vascular Endothelial Growth Factor (VEGF) signaling. Biological enrichment attributed to PRP grafts included cell chemotaxis, collagen turnover, cell migration, and angiogenesis. Acellular PRP grafts differed from nude grafts in promoting vessel length, vessel area, and junction density. Angiogenesis in cellular grafts was enhanced with newly synthesized Interleukin 8 (IL-8) in cooperation with IL-1b. In conclusion, paracrine signaling from PRP grafts, mediated by chemokine activities, influences cell migration, inflammation, and angiogenic status in host tissues. Under inflammatory conditions, newly synthesized IL-8 regulates vascularization in collaboration with PRP.

Wound-Microenvironment Engineering through Advanced-Dressing Bioprinting.

In patients with comorbidities, a large number of wounds become chronic, representing an overwhelming economic burden for healthcare systems. Engineering the microenvironment is a paramount trend to activate cells and burst-healing mechanisms. The extrusion bioprinting of advanced dressings was performed with novel composite bioinks made by blending adipose decellularized extracellular matrix with plasma and human dermal fibroblasts. Rheological and microstructural assessments of the composite hydrogels supported post-printing cell viability and proliferation over time. Embedded fibroblasts expressed steady concentrations of extracellular matrix proteins, including type 1, 3 and 4 collagens and fibronectin. ELISA assessments, multiplex protein arrays and ensuing bioinformatic analyses revealed paracrine activities corresponding to wound-healing activation through the modulation of inflammation and angiogenesis. The two modalities of advanced dressings, differing in platelet number, showed differences in the release of inflammatory and angiogenic cytokines, including interleukin 8 (IL-8), monocyte chemotactic protein 1 (MCP-1), vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF). The conditioned media stimulated human-dermal-cell proliferation over time. Our findings open the door to engineering the microenvironment as a strategy to enhance healing.

Overview of Current Advances in Extrusion Bioprinting for Skin Applications.

Bioprinting technologies, which have the ability to combine various human cell phenotypes, signaling proteins, extracellular matrix components, and other scaffold-like biomaterials, are currently being exploited for the fabrication of human skin in regenerative medicine. We performed a systematic review to appraise the latest advances in 3D bioprinting for skin applications, describing the main cell phenotypes, signaling proteins, and bioinks used in extrusion platforms. To understand the current limitations of this technology for skin bioprinting, we briefly address the relevant aspects of skin biology. This field is in the early stage of development, and reported research on extrusion bioprinting for skin applications has shown moderate progress. We have identified two major trends. First, the biomimetic approach uses cell-laden natural polymers, including fibrinogen, decellularized extracellular matrix, and collagen. Second, the material engineering line of research, which is focused on the optimization of printable biomaterials that expedite the manufacturing process, mainly involves chemically functionalized polymers and reinforcement strategies through molecular blending and postprinting interventions, i.e., ionic, covalent, or light entanglement, to enhance the mechanical properties of the construct and facilitate layer-by-layer deposition. Skin constructs manufactured using the biomimetic approach have reached a higher level of complexity in biological terms, including up to five different cell phenotypes and mirroring the epidermis, dermis and hypodermis. The confluence of the two perspectives, representing interdisciplinary inputs, is required for further advancement toward the future translation of extrusion bioprinting and to meet the urgent clinical demand for skin equivalents.

Freeze-Drying of Platelet-Rich Plasma: The Quest for Standardization.

The complex biology of platelets and their involvement in tissue repair and inflammation have inspired the development of platelet-rich plasma (PRP) therapies for a broad array of medical needs. However, clinical advances are hampered by the fact that PRP products, doses and treatment protocols are far from being standardized. Freeze-drying PRP (FD-PRP) preserves platelet function, cytokine concentration and functionality, and has been proposed as a consistent method for product standardization and fabrication of an off-the-shelf product with improved stability and readiness for future uses. Here, we present the current state of experimental and clinical FD-PRP research in the different medical areas in which PRP has potential to meet prevailing medical needs. A systematic search, according to PRISMA (Preferred Reported Items for Systematic Reviews and Meta-Analyses) guidelines, showed that research is mostly focused on wound healing, i.e., developing combination products for ulcer management. Injectable hydrogels are investigated for lumbar fusion and knee conditions. In dentistry, combination products permit slow kinetics of growth factor release and functionalized membranes for guided bone regeneration.

Wound Dressing Selection Is Critical to Enhance Platelet-Rich Fibrin Activities in Wound Care.

The use of platelet-rich fibrin (PRF) is investigated in ulcer management because it provides a healing milieu rich in growth factors and cytokines. Although crucial, the relevance of secondary dressings is under-researched and no data support the use of any particular dressing in preference to another. We assessed the properties of different dressing categories, including alginates, hydrocolloids, foams, hydrofibers, films, meshes and gauzes, in terms of affinity for PRF, releasate management (retention/extrusion) and the kinetics of cytokine release as well as the influence of each combination product, [PRF + dressing], on dermal cell behaviour, aiming to provide useful information for choosing the most adequate dressing for each particular patient. Active dressings including alginates, hydrofibers, foams and hydrocolloids blend with PRF, creating a diverse combination of products with different performances. Alginate and hydrofiber showed the highest affinity but moderate retention of releasate, without interfering with cell functions. Instead, the foam sequestered the releasate and hindered the release of growth factors, thereby compromising cell activities. Film and mesh presented very poor releasate retention and performed similarly to PRF by itself. Affinity index and releasate management explained 79% of platelet-derived growth factor (PDGF-BB) concentration variability, p < 0.001. Cell proliferation depended on the ability of the combination product to retain/release supernatant, PDGF-BB concentration and cell adhesion R2 = 0.91, p = 0.014.

Platelet-rich plasma for the treatment of diabetic foot ulcers: A meta-analysis.

Foot ulcer is a major complication of diabetes mellitus and often precedes leg amputation. Among the different methods to achieve ulcer healing, the use of platelet-rich plasma, which is rich in multiple growth factors and cytokines and may have similarities to the natural wound healing process, is gaining in popularity. A systematic review with meta-analyses was performed to evaluate the safety and clinical effectiveness of platelet-rich plasma for the treatment of diabetic foot ulcers compared to standard treatment or any other alternative therapy. The electronic databases Medline, EMBASE, CINAHL, and Cochrane Central Register of Controlled Trials were consulted in March 2017 with no restrictions placed on the publication date. Predefined criteria were used to determine inclusion of studies and to assess their methodologic quality. Eight randomized clinical trials and two prospective longitudinal-observational studies with control group were included. Platelet-rich plasma treatment increased the likelihood of chronic wound healing (RR = 1.32; 95% CI: 1.11, 1.57, I2 = 15%) while the volume of the ulcer (MD = 0.12 cm2 ; 95% CI: 0.08, 0.16; p < 0.01; I2 = 0%) and time to complete wound healing (MD = -11.18 days; 95% CI: -20.69, -1.68; I2 = 53%) decreased. Regarding safety profile, platelet-rich plasma did not differ from standard treatment in terms of probability of occurrence of wound complications (RR = 0.57; 95% CI: 0.25, 1.28; I2 = 0%) or recurrences (RR = 2.76; 95% CI: 0.23, 33.36; p = 0.43; I2 = 82%) but it decreased the rate of adverse events (RR = 0.80; 95% CI: 0.66, 0.96; p = 0.02; I2 = 0%). Cumulative meta-analysis revealed that there is enough evidence to demonstrate a statistically significant benefit. However, studies included presented serious methodologic flaws. According to the results, platelet-rich plasma could be considered a candidate treatment for nonhealing of diabetic foot ulcers.

Needle tenotomy with PRP versus lidocaine in epicondylopathy: clinical and ultrasonographic outcomes over twenty months.

OBJECTIVE: To investigate whether pathological changes in elbow epicondylopathy, as assessed by conventional ultrasonography and clinical outcomes, could be modified following tenotomy with platelet-rich plasma (PRP) versus tenotomy with lidocaine. METHODS: This prospective sub-study was part of a patient- and assessor-blinded, superiority-type, randomized, lidocaine-controlled trial that was performed in a tertiary hospital to assess the effectiveness of PRP versus lidocaine as tenotomy adjuvants in patients with epicondylopathy. Patients were followed after two sessions of tenotomy with either PRP or lidocaine adjuvants (4 ml) within a 2-week interval. Tendon thickness, echotexture, and neovascularization were assessed as secondary outcome measurements at baseline and at 3, 6, 12, and 20 months after treatment, and correlations with clinical outcomes were examined. RESULTS: Twenty months after treatment, tenotomy induced changes in tendon structure, thickness (± = 0.0006), vascularity (p < 0.0001), and echotexture (p < 0.0001). In Disabilities of the Arm, Shoulder and Hand (DASH-E) and pain (VAS-P) scores, 80.85% and 90.91% of patients showed a meaningful clinical improvement, respectively, without differences between PRP and lidocaine. There were significant differences in between-group changes in vascularity over time, p = 0.037 and p = 0.049 in the unadjusted and adjusted models, respectively. There was no relationship between pain or function and sonographic entities at the various time points. CONCLUSIONS: Two successive needle tenotomies induced structural changes in recalcitrant epicondylopathy, with PRP displaying more vascularization and increased thickness over time compared to lidocaine. PRP compared with lidocaine did not result in improved function or decreased pain over 20 months.

New biotechnologies for musculoskeletal injuries.

The practice of any sport is inherently associated with the risk of musculoskeletal lesions. We describe regenerative medicine technologies, including cellular therapies, gene therapies and multimolecular preparations of growth factors and cytokines, which are expected to advance the field of orthopaedics and sports medicine. Gene therapy involves the introduction of genetic information in the injured tissue to help that tissue to heal and, possibly, regenerate. Cell therapies used in clinical practice are based on the transplantation of adult human cells, which can be at different stages of differentiation. Currently, the stromal vascular fraction, containing stem cells and other niche components, has been injected in the articular cartilage of the knee or delivered via arthroscopy. Bone marrow concentrate (BMC) has been used to manage focal chondral defects via arthroscopy with promising clinical results. In addition, purified mesenchymal stem cells (MSCs) have been injected or delivered as an adjuvant to arthroscopic microfractures, and patients have shown improved clinical outcomes. Laboratory-expanded MSCs injected in osteoarthritis moderately improved pain and functional outcomes. MSC treatment in the form of stromal vascular fraction (SVF) or BMC or laboratory expanded adhesive cells (bone marrow and adipose derived stem cells, BM-MSCs and ADSCs) has been proven to be safe. Despite their safety, expensive regulatory complexities required to implement cell-based therapies make these treatments unavailable for most patients. At present, although some results are promising, all biological interventions are experimental, and cost/efficacy has not been demonstrated yet. Moreover, short follow-up in most studies questions the durability of treatments.

Blood-Derived Products for Tissue Repair/Regeneration.

Medical interest in "blood-derived products for tissue repair/regeneration" has old roots, starting with chronic wounds in the 1980s, and boosted by sports medicine at the beginning of the millennium, when elite athletes treated with platelet rich plasma (PRP) resumed competition earlier than expected [...].

Autologous platelet-rich plasma in the treatment of venous leg ulcers in primary care: a randomised controlled, pilot study.

OBJECTIVE: To examine the potential efficacy and safety of autologous platelet-rich plasma (PRP) in comparison with the conventional treatment (standard care, SoC) for the treatment of leg ulcers in patients with chronic venous insufficiency, in a primary health-care setting. METHOD: A Phase I-II, open-label, parallel-group, multicentre, randomised pilot study was conducted. The outcome variables at baseline and at weeks five and nine included reduction in the ulcer area, Chronic Venous Insufficiency Quality of Life Questionnaire score, cost of the treatment for up to nine weeks and average weekly cure rate. RESULTS: A total of eight patients, each with at least a six-month history of venous leg ulcer (VLUs), were included in the study. A total of 12 ulcers were treated with either autologous PRP or standard SoC. Patients treated with PRP required wound care only once per week. In the SoC group, patients required intervention 2-3 times per week. A reduction in the mean ulcer size in the PRP group was 3.9cm2 compared with the SoC group at 3.2cm 2 , although the sample size was insufficient to reach statistical significance. Improvement in quality of life (QoL) score was observed in the patients in the PRP group. CONCLUSION: This study offers proof-of-concept of the feasibility and safety of PRP treatment to inform larger clinical trials in patients with VLUs. Our preliminary results suggest that PRP delivers a safe and effective treatment for VLU care that can be implemented in primary health-care settings.

Some patients (and some of us) respond better to some biological therapies: the as yet unsolved conundrum.

Very often, treatment for many common musculoskeletal conditions is only palliative, or involves surgery with major shortcomings. Biological interventions-in particular, platelet-rich plasma (PRP) therapies-may well provide more effective treatments, but their actual efficacy is under scrutiny. PRP is biologically unique to each individual depending on endogenous and exogenous factors, including, but not limited to, demographic factors (i.e. age), immune status (i.e. microbiota), metabolic diseases and concomitant medications. All these potential modifiers of the ultimate effects of PRP have been poorly explored, and their relationship with efficacy has not been established.

Adjuvant Biological Therapies in Chronic Leg Ulcers.

Current biological treatments for non-healing wounds aim to address the common deviations in healing mechanisms, mainly inflammation, inadequate angiogenesis and reduced synthesis of extracellular matrix. In this context, regenerative medicine strategies, i.e., platelet rich plasmas and mesenchymal stromal cell products, may form part of adjuvant interventions in an integral patient management. We synthesized the clinical experience on ulcer management using these two categories of biological adjuvants. The results of ten controlled trials that are included in this systematic review favor the use of mesenchymal stromal cell based-adjuvants for impaired wound healing, but the number and quality of studies is moderate-low and are complicated by the diversity of biological products. Regarding platelet-derived products, 18 controlled studies investigated their efficacy in chronic wounds in the lower limb, but the heterogeneity of products and protocols hinders clinically meaningful quantitative synthesis. Most patients were diabetic, emphasizing an unmet medical need in this condition. Overall, there is not sufficient evidence to inform routine care, and further clinical research is necessary to realize the full potential of adjuvant regenerative medicine strategies in the management of chronic leg ulcers.

Hyperuricemia in Tendons.

Hyperuricemia, particularly gout, and the immune inflammatory response are highly integrated. Both, long standing hyperuricemia and monosodium urate (MSU) crystal deposition can challenge tendon homeostasis because of their potential to cause inflammation to the host. Knowledge is emerging from clinical imaging research depicting where MSU crystals deposit, including patellar tendon, triceps and quadriceps tendons. Remarkably, subclinical tendon inflammation and damage are also present in asymptomatic hyperuricemia. Monosodium urate crystals act as danger activating molecular patterns (DAMPs), activating the inflammasome and inducing the secretion of IL-1beta, a key mediator of the inflammatory response. The crucial role of IL-1beta in driving the inflammatory events during gout attacks is supported by the clinical efficacy of IL-1beta blockade. Some data implicating IL-1beta as an initiator of tendinopathy exist, but the link between hyperuricemia and the development of tendinopathy remains to be validated. Further knowledge about the interactions of uric acid with both innate immune and tendon cells, and their consequences may help to determine if there is a subclass of hyperuricemic-tendinopathy.

Tendons Involvement in Congenital Metabolic Disorders.

Congenital metabolic disorders are consequence of defects involving single genes that code for enzymes. Blocking metabolic pathways, the defect leads to the shortage of essential compounds, and/or to the accumulation of huge quantities of precursors, which interfere with normal functions. Only few of these diseases are characterized by a clinically significant tendon involvement.Heterozygous Familial Hypercholesterolaemia results from the inheritance of a mutant low-density lipoprotein receptor gene; patients show high cholesterol levels, precocious coronary artery disease, and may develop tendon xanthomata (mainly in Achilles tendon). The detection of xanthomata is important, because it allows an early diagnosis and treatment of the disorder. Cerebrotendinous Xanthomatosis is a rare genetic metabolic disorder of cholesterol and bile acid metabolism, characterized by accumulation of cholestanol in brain and tendons. Tendon abnormalities are similar to those reported in Heterozygous Familial Hypercholesterolaemia. Alkaptonuria is caused by a deficiency of the enzyme homogentisic acid oxidase. Due to the accumulation of the homogentisic acid, tendons and ligaments are characterized by a typical ochre/yellow pigmentation (ochronosis), with ensuing inflammation, calcification and rupture. In Congenital Hypergalactosemia an increased tendon collagen cross-linking by non-enzymatic galactosylation can be observed. Finally, Congenital Hypophosphatasia may be associated to deposition of hydroxyapatite crystals in rotator cuff, elbow, and Achilles tendons.

How Obesity Affects Tendons?

Several epidemiological and clinical observations have definitely demonstrated that obesity has harmful effects on tendons. The pathogenesis of tendon damage is multi-factorial. In addition to overload, attributable to the increased body weight, which significantly affects load-bearing tendons, systemic factors play a relevant role. Several bioactive peptides (chemerin, leptin, adiponectin and others) are released by adipocytes, and influence tendon structure by means of negative activities on mesenchymal cells. The ensuing systemic state of chronic, sub-clinic, low-grade inflammation can damage tendon structure. Metabolic disorders (diabetes, impaired glucose tolerance, and dislipidemia), frequently associated with visceral adiposity, are concurrent pathogenetic factors. Indeed, high glucose levels increase the formation of Advanced Glycation End-products, which in turn form stable covalent cross-links within collagen fibers, modifying their structure and functionality.Sport activities, so useful for preventing important cardiovascular complications, may be detrimental for tendons if they are submitted to intense acute or chronic overload. Therefore, two caution rules are mandatory: first, to engage in personalized soft training program, and secondly to follow regular check-up for tendon pathology.

Biological approach for the management of non-healing diabetic foot ulcers.

OBJECTIVE: To show an approach to profit of the main components of platelet rich plasma (PRP), i.e. the signaling proteins, and the fibrin scaffold and discuss the intervention within TIME (Tissue, Inflammation/Infection, Moisture, Edges) framework. METHODS: Two patients with diabetic foot ulcers are treated with both liquid and gelled PRP, and the rationale for the PRP intervention is described herein. Autologous blood is withdrawn and, PRP is separated by single spinning and activated with CaCl2 prior to application. PRP is injected in an activated liquid form, i.e. freshly activated, before coagulation, within the wound edges. In fibrotic tissue PRP is introduced performing a needling procedure. In addition, PRP, clotted ex-vivo, is applied in the wound bed as a primary dressing. RESULTS: Both patients responded positively to PRP intervention. Case 1 healed after five weekly PRP applications. Case 2 healed after eight weekly PRP applications. Patient satisfaction was high in both cases. The procedure had no complications, is well tolerated and easy to perform in any medical setting. CONCLUSION: PRP intervention is safe and if associated with correct tissue debridement and preparation of the host tissue it may help to decrease the burden of diabetic foot ulcers. Carefully designed randomized clinical trials with special attention to the PRP procedure are needed to assess the efficacy of these interventions.

Three-Dimensional Platelet-Rich Plasma Hydrogel Model to Study Early Tendon Healing.

Since the experimental conditions of cell cultures may bias results, it is critical to use suitable models. This is also true in the context of tendon cell biology and the study of platelet-rich plasma (PRP) therapies and PRP-augmented cell-based therapies. We compared the culture of human tendon cells in 2 dimensions (2D) with PRP-supplemented media to culture in matching 3-dimensional (3D) PRP hydrogels. Cell proliferation, cell shape, and the pattern of gene and protein expression were examined. Our data revealed modifications in cell shape and enhanced expression of tenomodulin and scleraxis in 3D hydrogels. Additionally, protein secretion analysis using glass-based arrays specific for angiogenesis revealed differences in interleukin (IL)-6 and IL-8 protein expression between 2D cultures and 3D hydrogels, while the secretion of other angiogenic or inflammatory cytokines was unaffected. Our study suggests that 3D hydrogels are physiologically more relevant than 2D cultures in the study of tendon cells, based on cell shape, support of tenocyte proliferation, phenotype, and the pattern of gene and protein expression.

Platelet-rich plasma modulates the secretion of inflammatory/angiogenic proteins by inflamed tenocytes.

BACKGROUND: Platelet-rich plasma therapies for tendinopathy appear to provide moderate pain reduction. However, the biological mechanisms behind the observed clinical effects remain poorly characterized. QUESTIONS/PURPOSES: The purpose of this study was to explore whether platelet-rich plasma modifies the inflammatory/angiogenic status of already inflamed tenocytes by examining (1) gene expression; (2) modulation of chemokine and interleukin secretion; and (3) differences between healthy and tendinopathic tenocytes. METHODS: Cells from both healthy and tendinopathic tendons were exposed to interleukin (IL)-1ß and after treated with platelet-rich plasma. Modifications in the expression of selected genes were assessed by real-time reverse transcription-polymerase chain reaction and changes in secretion of angiogenic/inflammatory molecules by enzyme-linked immunosorbent assay. Platelet-rich plasma-induced changes in tendinopathic cells were compared with normal after normalizing platelet-rich plasma data against IL-1ß status in each specific sample. RESULTS: In IL-1ß-exposed cells, platelet-rich plasma downregulates expression of IL-6/CXCL-6 (mean, 0.015; 95% confidence interval [CI], 0.005-0.025; p = 0.026), IL-6R (mean, 0.61; 95% CI, 0.27-0.95; p = 0.029), and IL-8/CXCL-8 (mean, 0.02; 95% CI, 0.007-0.023; p = 0.026). Secretion of IL-6/CXCL6, 0.35 (95% CI, 0.3-0.4; p = 0.002), IL-8/CXCL8, 0.55 (95% CI, 0.5-0.7; p = 0.01), and monocyte chemoattractant protein-1/CCL2, 0.40 (95% CI, 0.2-0.6; p = 0.001) was reduced by platelet-rich plasma, whereas vascular endothelial growth factor increased by twofold, (95% CI, 1.7-2.3; p < 0.001). RANTES/CCL5 increased by10-fold (95% CI, 4-17) and hepatocyte growth factor by 21-fold (95% CI, 0.2-42) in tendinopathic and by 2.3-fold (95% CI, 2-3) and threefold (95% CI, 1-5) in normal cells (p = 0.005 for both). CONCLUSIONS: Platelet-rich plasma induces an immunomodulatory and proangiogenic phenotype consistent with healing mechanisms with few differences between tendinopathic and normal cells. CLINICAL RELEVANCE: Platelet-rich plasma injections in pathological and nearby tissue might help to recover tendon homeostasis.

Muscle and tendon injuries: the role of biological interventions to promote and assist healing and recovery.

PURPOSE: To summarize clinical studies after platelet-rich plasma (PRP) therapy for tendinopathy, plantar fasciopathy, and muscle injuries; to review PRP formulations used across studies; and to identify knowledge deficits that require further investigation. METHODS: After a systematic review in PubMed, we identified clinical studies assessing PRP efficacy in tendon and muscle during the past decade. We standardized data extraction by grouping studies based on anatomic location; summarized patient populations, PRP formulations, and clinical outcomes; and identified knowledge deficits that require further investigation. RESULTS: Overall, 1,541 patients had been treated with PRP in 58 clinical studies; of these, 26 addressed upper limb tendinopathies and 32 addressed the lower limb (810 patients and 731 patients treated with PRP, respectively). The quality of research is higher for the upper limb than for the lower limb (23 controlled studies, of which 17 are Level I, v 19 controlled studies, of which 6 are Level I, respectively). Patients have been treated mostly with leukocyte-platelet-rich plasma, except in the arthroscopic management of the rotator cuff. The safety and efficacy of PRP for muscle injuries has been addressed in 7 studies including 182 patients. Differences across results are mainly attributed to dissimilarities between tissues and different stages of degeneration, numbers of PRP applications, and protocols. CONCLUSIONS: Given the heterogeneity in tendons and tendinopathies, currently, we are not able to decide whether PRP therapies are useful. Despite advances in PRP science, data are insufficient and there is a clear need to optimize protocols and obtain more high-quality clinical data in both tendinopathies and muscle injuries before making treatment recommendations. LEVEL OF EVIDENCE: Level IV, systematic review of Level I through IV studies.