The effect of recombinant human platelet-derived growth factor BB-coated sutures on rotator cuff healing in a sheep model

Bioactive Scaffold With Spatially Embedded Growth Factors Promotes Bone-to-Tendon Interface Healing of Chronic Rotator Cuff Tear in Rabbit Model

BACKGROUND

Functional restoration of the bone-to-tendon interface (BTI) after rotator cuff repair is a challenge. Therefore, numerous biocompatible biomaterials for promoting BTI healing have been investigated.

PURPOSE

To determine the efficacy of scaffolds with spatiotemporal delivery of growth factors (GFs) to accelerate BTI healing after rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

An advanced 3-dimensional printing technique was used to fabricate bioactive scaffolds with spatiotemporal delivery of multiple GFs targeting the tendon, fibrocartilage, and bone regions. In total, 50 rabbits were used: 2 nonoperated controls and 48 rabbits with induced chronic rotator cuff tears (RCTs). The animals with RCTs were divided into 3 groups: (A) saline injection, (B) scaffold without GF, and (C) scaffold with GF. To induce chronic models, RCTs were left unrepaired for 6 weeks; then, surgical repairs with or without bioactive scaffolds were performed. For groups B and C, each scaffold was implanted between the bony footprint and the supraspinatus tendon. Four weeks after repair, quantitative real-time polymerase chain reaction and immunofluorescence analyses were performed to evaluate early signs of regenerative healing. Histological, biomechanical, and micro-computed tomography analyses were performed 12 weeks after repair.

RESULTS

Group C had the highest mRNA expression of collagen type I alpha 1, collagen type III alpha 1, and aggrecan. Immunofluorescence analysis showed the formation of an aggrecan+/collagen II+ fibrocartilaginous matrix at the BTI when repaired with scaffold with GFs. Histologic analysis revealed greater collagen fiber continuity, denser collagen fibers, and a more mature tendon-to-bone junction in GF-embedded scaffolds than those in the other groups. Group C demonstrated the highest load-to-failure ratio, and modulus mapping showed that the distribution of the micromechanical properties of the BTI repaired with GF-embedded scaffolds was comparable with that of the native BTI. Micro-computed tomography analysis identified the highest bone mineral density and bone volume/total volume ratio in group C.

CONCLUSION

Bioactive scaffolds with spatially embedded GFs have significant potential to promote the BTI healing of chronic RCTs in a rabbit model.

CLINICAL RELEVANCE

The scaffolds with spatiotemporal delivery of GF may serve as an off-the-shelf biomaterial graft to promote the healing of RCTs.

The Role of Nanomaterials and Biological Agents on Rotator Cuff Regeneration

The rotator cuff is a musculotendon unit responsible for movement in the shoulder. Rotator cuff tears represent a significant number of musculoskeletal injuries in the adult population. In addition, there is a high incidence of retear rates due to various complications within the complex anatomical structure and the lack of proper healing. Current clinical strategies for rotator cuff augmentation include surgical intervention with autograft tissue grafts and beneficial impacts have been shown, but challenges still exist because of limited supply. For decades, nanomaterials have been engineered for the repair of various tissue and organ systems. This review article provides a thorough summary of the role nanomaterials, stem cells and biological agents have played in rotator cuff repair to date and offers input on next generation approaches for regenerating this tissue.

Modelling gluteus medius tendon degeneration and repair in a large animal model

INTRODUCTION

Gluteus medius tendon tears often occur in the context of chronic tendinopathy and remain a difficult clinical problem. Surgical repair is challenging as it is often delayed and performed in degenerative tendons. No animal model currently exists to mimic the delayed repair of tendinopathic gluteus medius tears. The aims of this study were to develop a chronic model of gluteus medius tendinopathy and tear and then compare this model to an acute gluteus medius tear and repair.

MATERIALS AND METHODS

Six gluteus medius muscles were dissected and examined in mature sheep to confirm anatomical similarity to the human counterpart. Ten separate adult sheep underwent tendon detachment, followed by relook and histological sampling at 6 and 16 weeks to assess the extent of tendon degeneration. Six adult sheep underwent tendon repair at 6 weeks and were later assessed for healing of the tendon and compared to a further four adult sheep who underwent an acute tendon detachment and repair procedure.

RESULTS

The sheep gluteus medius muscle consisted of three compartments, the anterior, middle and posterior. All compartments inserted via the common tendon on the superolateral aspect of the greater trochanter. At both 6 and 16 weeks, there was significant tendinopathic changes on histology compared to controls as assessed by modified Movin's score (p = 0.018, p = 0.047) but no difference between the 6- and 16-week groups (p = 0.25). There were significant differences between delayed and acute repair in both histological appearance (p = 0.025) and biomechanical properties (p = 0.019), with acute repair superior in both.

CONCLUSIONS

Tendon detachment for 6 weeks is sufficient to produce histological changes similar to chronic tendinopathy and repair of this degenerative tendon results in significantly poorer healing when compared to an acute repair model. Animal models for gluteus medius tears should use a delayed repair model to improve clinical validity.

Mesenchymal Stem Cells From a Hypoxic Culture Can Improve Rotator Cuff Tear Repair

A rotator cuff tear is an age-related common cause of pain and disability. Studies including our previously published ones have demonstrated that mesenchymal stem cells cultured under hypoxic conditions [hypoxic multipotent stromal cells (MSCs)] facilitate the retention of transplanted cells and promote wound healing. However, there are very few, if any, reports targeting the punctured supraspinatus tendons to create more or equally serous wounds as age-related tears of rotator cuff. It remains to be determined whether transplantation of bone-marrow-derived hypoxic MSCs into the punctured supraspinatus tendon improves tendon repair and, when combined with ultrasound-guided delivery, could be used for future clinical applications. In this study, we used a total of 33 Sprague-Dawley rats in different groups for normal no-punched control, hypoxic MSC treatment, nontreated vehicle control, and MSC preparation, and then evaluated treatment outcomes by biomechanical testing and histological analysis. We found that the ultimate failure load of the hypoxic MSC-treated group was close to that of the normal tendon and significantly greater than that of the nontreated vehicle control group. In vivo tracking of cells labeled with superparamagnetic iron oxide (SPIO) nanoparticles revealed an enhanced retention of transplanted cells at the tear site. Our study demonstrates that hypoxic MSCs improve rotator cuff tear repair in a rat model.

Effect of a Porous Suture Containing Transforming Growth Factor Beta 1 on Healing After Rotator Cuff Repair in a Rat Model

BACKGROUND

The healing failure rate after rotator cuff repair is considerably high.

PURPOSE

To evaluate the effect of a porous suture containing transforming growth factor beta 1 (TGF-β1) on the sustained release of TGF-β1 and rotator cuff healing in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A porous suture was developed, and its tensile strength was measured. TGF-β1 was delivered using the porous suture, and a TGF-β1 release test and human fibroblast proliferation assay were performed. For the animal experiment, 30 rats were randomly allocated into 3 groups (n = 10 each). A bilateral supraspinatus tendon tear was made in all the rats, and repair was performed. Group 1 received repair only; group 2, repair and a single injection of TGF-β1; and group 3, repair using the porous suture containing TGF-β1. Eight weeks after repair, biomechanical and histological analyses were performed.

RESULTS

The porous suture was successfully developed with mechanical properties compatible with the conventional suture, and the sustained release of TGF-β1 from the porous suture was confirmed. In addition, the cell proliferation assay confirmed the biological safety of the porous suture. In the animal experiment, group 3 biomechanically exhibited the largest cross-sectional area and the highest ultimate failure load and ultimate stress (all P < .05). Histological examination revealed that group 3 showed significantly better collagen fiber density and tendon-to-bone maturation than did groups 1 and 2 (all P < .05).

CONCLUSION

The porous suture containing TGF-β1 could sustainedly and safely release TGF-β1, and its use during rotator cuff repair could improve rotator cuff healing, as assessed on the basis of the biomechanical and histological changes in the rat model in this study. Considering the effectiveness, safety, and convenience of the porous suture without extra effort in surgery, the findings of the present study will have a far-reaching effect on the treatment of rotator cuff tears.

CLINICAL RELEVANCE

The porous suture containing TGF-β1 might improve healing after rotator cuff repair.

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

A Novel Strategy to Enhance Microfracture Treatment With Stromal Cell-Derived Factor-1 in a Rat Model

Background

Microfracture is one of the most widely used techniques for the repair of articular cartilage. However, microfracture often results in filling of the chondral defect with fibrocartilage, which exhibits poor durability and sub-optimal mechanical properties. Stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for mesenchymal stem cells (MSCs) and is expressed at high levels in bone marrow adjacent to developing cartilage during endochondral bone formation. Integrating SDF-1 into an implantable collagen scaffold may provide a chondro-conductive and chondro-inductive milieu via chemotaxis of MSCs and promotion of chondrogenic differentiation, facilitating more robust hyaline cartilage formation following microfracture.

Objective

This work aimed to confirm the chemoattractive properties of SDF-1 in vitro and develop a one-step method for incorporating SDF-1 in vivo to enhance cartilage repair using a rat osteochondral defect model.

Methods

Bone marrow-derived MSCs (BMSCs) were harvested from the femurs of Sprague–Dawley rats and cultured in low-glucose Dulbecco’s modified Eagle’s medium containing 10% fetal bovine serum, with the medium changed every 3 days. Passage 1 MSCs were analyzed by flow cytometry with an S3 Cell Sorter (Bio-Rad). In vitro cell migration assays were performed on MSCs by labeling cells with carboxyfluorescein diacetate, succinimidyl ester (CFDA-SE; Bio-Rad). For the microfracture model, a 1.6-mm-diameter osteochondral defect was created in the femoral trochleae of 20 Sprague–Dawley rats bilaterally until bone marrow spillage was seen under saline irrigation. One knee was chosen at random to receive implantation of the scaffold, and the contralateral knee was left unfilled as an empty control. Type I collagen scaffolds (Kensey Nash) were coated with either gelatin only or gelatin and SDF-1 using a dip coating process. The rats received implantation of either a gelatin-only scaffold (N = 10) or gelatin-and-SDF-1 scaffold (N = 10) at the site of the microfracture. Femurs were collected for histological analyses at 4- and 8-week time points post-operatively, and sections were stained with Safranin O/Fast Green. The samples were graded blindly by two observers using the Modified O’Driscoll score, a validated scoring system for chondral repair. A minimum of 10 separate grading scores were made per sample and averaged. Quantitative comparisons of cell migration in vitro were performed with one-way ANOVA. Cartilage repair in vivo was also compared among groups with one-way ANOVA, and the results were presented as mean ± standard deviation, with P-values < 0.05 considered as statistically significant.

Results

MSC migration showed a dose–response relationship with SDF-1, with an optimal dosage for chemotaxis between 10 and 100 ng/ml. After scaffold implantation, the SDF-1-treated group demonstrated complete filling of the cartilage defect with mature cartilage tissue, exhibiting strong proteoglycan content, smooth borders, and good incorporation into marginal cartilage. Modified O’Driscoll scores after 8 weeks showed a significant improvement of cartilage repair in the SDF-1 group relative to the empty control group (P < 0.01), with a trend toward improvement when compared with the gelatin-only-scaffold group (P < 0.1). No significant differences in scores were found between the empty defect group and gelatin-only group.

Conclusion

In this study, we demonstrated a simple method for improving the quality of cartilage defect repair in a rat model of microfracture. We confirmed the chemotactic properties of SDF-1 on rat MSCs and found an optimized dosage range for chemotaxis between 10 and 100 ng/ml. Furthermore, we demonstrated a strategy to incorporate SDF-1 into gelatin–collagen I scaffolds in vivo at the site of an osteochondral defect. SDF-1-treated defects displayed robust hyaline cartilage resurfacing of the defect with minimal fibrous tissue, in contrast to the empty control group. The results of the in vitro and in vivo studies together suggest that SDF-1-mediated signaling may significantly improve the quality of cartilage regeneration in an osteochondral defect.

Assessment of whether the rabbit subscapularis tendon model is suitable for studying the human chronic rotator cuff pathology: Discovery of a new ligament connecting the glenoid and subscapularis tendon

OBJECTIVE

This study aimed to investigate the anatomical relationship between the subscapularis tendon and glenosubscapularal ligament (GSL) that we accidentally identified from our previous study on a rabbit shoulder model and to determine whether this anatomical relationship has an impact on the rabbit shoulder model for studying the human chronic rotator cuff pathology.

METHODS

In this study, 15 male New Zealand rabbits aged 12 weeks and weighing 2.5 kg were used. Moreover, 3 rabbits were sacrificed for the anatomical and histological investigation of the relationship between the subscapularis tendon and GSL at baseline. The remaining 12 rabbits underwent the subscapularis tendon tenotomy from the lesser tuberosity using a standardized procedure. The GSL was cut on the left side and preserved on the right side. For histomorphometric analysis, 6 rabbits were first sacrificed at 6 weeks and then the remaining 6 rabbits at 12 weeks.

RESULTS

In all the rabbits, GSL was identified, connecting the upper portion of glenoid and subscapularis muscle-tendon junction. The mean thickness of the middle portion of GSL was 1.1±0.2 mm; the mean length of GSL was 8.4±2.3 mm. The mean widths of the proximal and distal attachments were 2.4±0.3 and 4.2±0.5 mm, respectively. The mean size of the native subscapularis muscle fibers was 122.6±4.3 μm2. The mean size of the muscle fibers in shoulders with tenotomy alone was 112.6±6.2 and 102.6±4.8 μm2 at 6 and 12 weeks, respectively. The mean size of the muscle fibers in shoulders with tenotomy plus GSL cut severing was 88.3±9.7 and 56.4±5.2 μm2 at 6 and 12 weeks, respectively. The significant muscle atrophy was observed both at 6 and 12 weeks in the shoulders with tenotomy plus GSL cut compared with those with tenotomy alone as well as those with the native subscapularis. However, the muscle atrophy was not significantly different in the shoulders with tenotomy alone at different time points.

CONCLUSION

Because GSL may prevent the subscapularis retraction, the rabbit subscapularis tendon model may not be suitable for studying the human chronic rotator cuff pathology if GSL is neglected or preserved.

Implementation of Endogenous and Exogenous Mesenchymal Progenitor Cells for Skeletal Tissue Regeneration and Repair

Harnessing adult mesenchymal stem/progenitor cells to stimulate skeletal tissue repair is a strategy that is being actively investigated. While scientists continue to develop creative and thoughtful ways to utilize these cells for tissue repair, the vast majority of these methodologies can ultimately be categorized into two main approaches: (1) Facilitating the recruitment of endogenous host cells to the injury site; and (2) physically administering into the injury site cells themselves, exogenously, either by autologous or allogeneic implantation. The aim of this paper is to comprehensively review recent key literature on the use of these two approaches in stimulating healing and repair of different skeletal tissues. As expected, each of the two strategies have their own advantages and limitations (which we describe), especially when considering the diverse microenvironments of different skeletal tissues like bone, tendon/ligament, and cartilage/fibrocartilage. This paper also discusses stem/progenitor cells commonly used for repairing different skeletal tissues, and it lists ongoing clinical trials that have risen from the implementation of these cells and strategies. Lastly, we discuss our own thoughts on where the field is headed in the near future.

Current Progress in Tendon and Ligament Tissue Engineering

Background

Tendon and ligament injuries accounted for 30% of all musculoskeletal consultations with 4 million new incidences worldwide each year and thus imposed a significant burden to the society and the economy. Damaged tendon and ligament can severely affect the normal body movement and might lead to many complications if not treated promptly and adequately. Current conventional treatment through surgical repair and tissue graft are ineffective with a high rate of recurrence.

Methods

In this review, we first discussed the anatomy, physiology and pathophysiology of tendon and ligament injuries and its current treatment. Secondly, we explored the current role of tendon and ligament tissue engineering, describing its recent advances. After that, we also described stem cell and cell secreted product approaches in tendon and ligament injuries. Lastly, we examined the role of the bioreactor and mechanical loading in in vitro maturation of engineered tendon and ligament.

Results

Tissue engineering offers various alternative ways of treatment from biological tissue constructs to stem cell therapy and cell secreted products. Bioreactor with mechanical stimulation is instrumental in preparing mature engineered tendon and ligament substitutes in vitro.

Conclusions

Tissue engineering showed great promise in replacing the damaged tendon and ligament. However, more study is needed to develop ideal engineered tendon and ligament.

Augmenting endogenous repair of soft tissues with nanofibre scaffolds

As our ability to engineer nanoscale materials has developed we can now influence endogenous cellular processes with increasing precision. Consequently, the use of biomaterials to induce and guide the repair and regeneration of tissues is a rapidly developing area. This review focuses on soft tissue engineering, it will discuss the types of biomaterial scaffolds available before exploring physical, chemical and biological modifications to synthetic scaffolds. We will consider how these properties, in combination, can provide a precise design process, with the potential to meet the requirements of the injured and diseased soft tissue niche. Finally, we frame our discussions within clinical trial design and the regulatory framework, the consideration of which is fundamental to the successful translation of new biomaterials.

Stem Cell Therapy for Tendon Regeneration: Current Status and Future Directions

In adults the healing tendon generates fibrovascular scar tissue and recovers never histologically, mechanically, and functionally which leads to chronic and to degenerative diseases. In this review, the processes and mechanisms of tendon development and fetal regeneration in comparison to adult defect repair and degeneration are discussed in relation to regenerative therapeutic options. We focused on the application of stem cells, growth factors, transcription factors, and gene therapy in tendon injury therapies in order to intervene the scarring process and to induce functional regeneration of the lesioned tissue. Outlines for future therapeutic approaches for tendon injuries will be provided.

Biomaterials for the Treatment of Tendon Injury

Background

Most tendon injuries are occurring from a gradual wearing and tearing of the tendon tissues from overuse. Such injuries are usually seen in sports, exercising, or daily activities that involve a high mechanical load and weight bearing. However, owing to the lack of both cellularity and blood vessels in tendons, the process of tendon repair is slow and inefficient. Although various conservative (non-surgical) and surgical management options are conducted by the clinicians, a gold standard of these approaches does not exist. In this regard, the treatment of tendon injuries is challenging.

Method

Here, we describe the recent advances of biomaterial-based approaches for the treatment of injured tendons.

Results

Regenerative medicine is an emerging multidisciplinary research that specializes in the repair of damaged tendon tissues through the delivery of regenerative factors by biomaterials.

Conclusion

Although current biomaterial-based treatment strategies have shown their potential for tendon healing, future research and clinical applications should focused on finding the optimum combinations of regenerative factors with ideal biomaterials for the repair of tendons.

Nanofiber-based matrices for rotator cuff regenerative engineering

The rotator cuff consists of a cuff of soft tissue responsible for rotating the shoulder. Rotator cuff tendon tears are responsible for a significant source of disability and pain in the adult population. Most rotator cuff tendon tears occur at the bone-tendon interface. Tear size, patient age, fatty infiltration of muscle, have a major influence on the rate of retear after surgical repair. The high incidence of retears (up to 94% in some studies) after surgery makes rotator cuff injuries a critical musculoskeletal problem to address. The limitations of current treatments motivate regenerative engineering approaches for rotator cuff regeneration. Various fiber-based matrices are currently being investigated due to their structural similarity with native tendons and their ability to promote regeneration. This review will discuss the current approaches for rotator cuff regeneration, recent advances in fabrication and enhancement of nanofiber-based matrices and the development and use of complex nano/microstructures for rotator cuff regeneration. STATEMENT OF SIGNIFICANCE: Regeneration paradigms for musculoskeletal tissues involving the rotator cuff of the shoulder have received great interest. Novel technologies based on nanomaterials have emerged as possible robust solutions for rotator cuff injury and treatment due to structure/property relationships. The aim of the review submitted is to comprehensively describe and evaluate the development and use of nano-based material technologies for applications to rotator cuff tendon healing and regeneration.

Use of affinity allows anti-inflammatory and anti-microbial dual release that matches suture wound resolution

Surgical sutures are vulnerable to bacterial infections and biofilm formation. At the suture site, pain and undesirable, excess inflammation are additionally detrimental to wound healing. The development of a polymerized cyclodextrin (pCD) coated surgical suture introduces the capability to locally deliver both anti-inflammatory and anti-microbial drugs throughout the phases of acute and chronic healing. Local delivery allows for the improvement of wound healing while reducing related systemic side effects and drug resistance. Through testing, it has been shown that the fabrication of our pCD coating minimally affects the suture's mechanical properties. In vitro studies show measurable and consistent drug delivery for nearly 5 weeks. The therapeutic level of this delivery is sufficient to show inhibition of bacterial growth for 4 weeks, and free-radical scavenging (an in vitro anti-inflammatory activity approximation) for 2 weeks. With this pCD coating technique, we maintain clinical performance standards while also introducing a long-term dual delivery system relevant to the wound healing timeframe. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Use of stem cells and growth factors in rotator cuff tendon repair

The management of rotator cuff tears continues to prove challenging for orthopaedic surgeons. Such tears affect most age groups and can lead to significant morbidity in patients. The aetiology of these tears is likely to be multifactorial; however, an understanding of the mechanisms involved is still under review. Despite advancements in surgical operative techniques and the materials used, post-operative recurrence rates after surgical repair remain high. A growing area of research surrounds biological adjuncts used to improve the healing potential of the repaired tissues. This review of recent publications focuses on the strengths and limitations of using stem cells and growth factors in rotator cuff repair.

Long-term local PDGF delivery using porous microspheres modified with heparin for tendon healing of rotator cuff tendinitis in a rabbit model

In this study, we prepared the platelet-derived growth factor-containing porous microspheres modified with heparin (PDGF/Hep-PMSs) and investigated their anti-inflammatory and tendon healing effects on rotator cuff (RC) tendinitis rabbit model. PDGF/Hep-PMSs suppressed the mRNA levels of six pro-inflammatory cytokines (i.e., MMP-3, MMP-13, COX-2, ADAMTS-5, IL-6, and TNF-α) in inflamed tenocytes. Long-term local delivery of PDGF/Hep-PMSs into tendon tissues of RC tendinitis decreased the mRNA levels of six pro-inflammatory cytokines and increased the mRNA levels of anti-inflammatory cytokines including IL-4, IL-10, and IL-13. Anti-inflammatory effects of PDGF/Hep-PMSs might have contributed to enhance the collagen content, tenogenic markers, stiffness, and tensile strength of tendons, eventually leading to tendon restoration. Our findings suggest that the long-term local PDGF delivery of PDGF/Hep-PMSs have a great potential to enhance tendon healing of RC tendinitis by suppressing inflammation responses.

Effect of connective tissue growth factor delivered via porous sutures on the proliferative stage of intrasynovial tendon repair

Recent growth factor, cell, and scaffold-based experimental interventions for intrasynovial flexor tendon repair have demonstrated therapeutic potential in rodent models. However, these approaches have not achieved consistent functional improvements in large animal trials due to deleterious inflammatory reactions to delivery materials and insufficient induction of targeted biological healing responses. In this study, we achieved porous suture-based sustained delivery of connective tissue growth factor (CTGF) into flexor tendons in a clinically relevant canine model. Repairs with CTGF-laden sutures were mechanically competent and did not show any evidence of adhesions or other negative inflammatory reactions based on histology, gene expression, or proteomics analyses at 14 days following repair. CTGF-laden sutures induced local cellular infiltration and a significant biological response immediately adjacent to the suture, including histological signs of angiogenesis and collagen deposition. There were no evident widespread biological effects throughout the tendon substance. There were significant differences in gene expression of the macrophage marker CD163 and anti-apoptotic factor BCL2L1; however, these differences were not corroborated by proteomics analysis. In summary, this study provided encouraging evidence of sustained delivery of biologically active CTGF from porous sutures without signs of a negative inflammatory reaction. With the development of a safe and effective method for generating a positive local biological response, future studies can explore additional methods for enhancing intrasynovial tendon repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2052-2063, 2018.

Rotator cuff repair with a novel mesh suture: An ex vivo assessment of mechanical properties

Surgical repair is a common treatment for rotator cuff tear; however, the retear rate is high. A high degree of suture repair strength is important to ensure rotator cuff integrity for healing. The purpose of this study was to compare the mechanical performance of rotator cuffs repaired with a mesh suture versus traditional polydioxanone suture II and FiberWire sutures in a canine in vitro model. Seventy-two canine shoulders were harvested. An infraspinatus tendon tear was created in each shoulder. Two suture techniques-simple interrupted sutures and two-row suture bridge-were used to reconnect the infraspinatus tendon to the greater tuberosity, using three different suture types: Mesh suture, polydioxanone suture II, or FiberWire. Shoulders were loaded to failure under displacement control at a rate of 20 mm/min. Failure load was compared between suture types and techniques. Ultimate failure load was significantly higher in the specimens repaired with mesh suture than with polydioxanone suture II or FiberWire, regardless of suture technique. There was no significant difference in stiffness among the six groups, with the exception that FiberWire repairs were stiffer than polydioxanone suture II repairs with the simple interrupted technique. All specimens failed by suture pull-out from the tendon. Based on our biomechanical findings, rotator cuff repair with the mesh suture might provide superior initial strength against failure compared with the traditional polydioxanone suture II or FiberWire sutures. Use of the mesh suture may provide increased initial fixation strength and decrease gap formation, which could result in improved healing and lower re-tear rates following rotator cuff repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:987-992, 2018.

The Role of Biologic Therapy in Rotator Cuff Tears and Repairs

PURPOSE OF REVIEW

The purpose of this review was to establish the foundation of the major biologic adjuvants to rotator cuff repairs and review recent scientific findings.

RECENT FINDINGS

Platelet-rich plasma (PRP) overall has no significant impact on functional outcomes and repair integrity, but may be more advantageous in small to medium tears. Further studies should focus on leukocyte-rich versus poor preparations and the use of PRP in patients that are high risk for repair failure. Biologic and synthetic patches or augments provide mechanical stability for large and massive rotator cuff tears and decrease re-tear rates. Mesenchymal stem cells have demonstrated improved healing rates without an impact on outcomes. Cytokines and growth factors show promise in animal models, but require human trials to further evaluate. In massive or revision repairs, allograft or synthetic patch augmentation should be considered. Platelet-rich plasma may have benefit in smaller tears. Further studies are needed to evaluate the value of mesenchymal stem cells and various cytologic chemical signals.

Regenerative Engineering of the Rotator Cuff of the Shoulder

Rotator cuff tears often heal poorly, leading to re-tears after repair. This is in part attributed to the low proliferative ability of the resident cells (tendon fibroblasts and tendon-stem cells) upon injury to the rotator cuff tissue and the low vascularity of the tendon insertion. In addition, surgical outcomes of current techniques used in clinical settings are often suboptimal, leading to the formation of neo-tissue with poor biomechanics and structural characteristics, which results in re-tears. This has prompted interest in a new approach, which we term as "Regenerative Engineering", for regenerating rotator cuff tendons. In the Regenerative Engineering paradigm, roles played by stem cells, scaffolds, growth factors/small molecules, the use of local physical forces, and morphogenesis interplayed with clinical surgery techniques may synchronously act, leading to synergistic effects and resulting in successful tissue regeneration. In this regard, various cell sources such as tendon fibroblasts and adult tissue-derived stem cells have been isolated, characterized, and investigated for regenerating rotator cuff tendons. Likewise, numerous scaffolds with varying architecture, geometry, and mechanical characteristics of biologic and synthetic origin have been developed. Furthermore, these scaffolds have been also fabricated with biochemical cues (growth factors and small molecules), facilitating tissue regeneration. In this Review, various strategies to regenerate rotator cuff tendons using stem cells, advanced materials, and factors in the setting of physical forces under the Regenerative Engineering paradigm are described.

Growth factor delivery strategies for rotator cuff repair and regeneration

The high incidence of degenerative tears and prevalence of retears (20-95%) after surgical repair makes rotator cuff injuries a significant health problem. This high retear rate is attributed to the failure of the repaired tissue to regenerate the native tendon-to-bone insertion (enthesis). Biological augmentation of surgical repair such as autografts, allografts, and xenografts are confounded by donor site morbidity, immunogenicity, and disease transmission, respectively. In contrast, these risks may be alleviated via growth factor therapy, which can actively influence the healing environment to promote functional repair. Several challenges have to be overcome before growth factor delivery can translate into clinical practice such as the selection of optimal growth factor(s) or combination, identification of the most efficient stage and duration of delivery, and the design considerations for the delivery device. Emerging insight into the injury-repair microenvironment and our understanding of growth factor mechanisms in healing are informing the design of advanced delivery scaffolds to effectively treat rotator cuff tears. Here, we review potential growth factor candidates, design parameters and material selection for growth factor delivery, innovative and dynamic delivery scaffolds, and novel therapeutic targets from tendon and developmental biology for the structural and functional healing of rotator cuff repair.

Effectiveness of Biologic Factors in Shoulder Disorders

Background:

Shoulder pathology can cause significant pain, discomfort, and loss of function that all interfere with activities of daily living and may lead to poor quality of life. Primary osteoarthritis and rotator cuff diseases with its sequalae are the main culprits. Management of shoulder disorders using biological factors gained an increasing interest over the last years. This interest reveals the need of effective treatments for shoulder degenerative disorders, and highlights the importance of a comprehensive and detailed understanding of the rapidly increasing knowledge in the field.

Methods:

This study will describe most of the available biology-based strategies that have been recently developed, focusing on their effectiveness in animal and clinical studies.

Results:

Data from in vitro work will also be briefly presented; in order to further elucidate newly acquired knowledge regarding mechanisms of tissue degeneration and repair that would probably drive translational work in the next decade. The role of platelet rich-plasma, growth factors, stem cells and other alternative treatments will be described in an evidence-based approach, in an attempt to provide guidelines for their clinical application. Finally, certain challenges that biologic treatments face today will be described as an initiative for future strategies.

Conclusion:

The application of different growth factors and mesenchymal stem cells appears as promising approaches for enhancing biologic repair. However, data from clinical studies are still limited, and future studies need to improve understanding of the repair process in cellular and molecular level and evaluate the effectiveness of biologic factors in the management of shoulder disorders.

Antimicrobials tethering on suture surface through a hydrogel: a novel strategy to combat postoperative wound infections

The present study aimed to develop a novel biocompatible suture biomaterial from Eri silk waste to avoid surgical site infections.

Rotator cuff repair: a review of surgical techniques, animal models, and new technologies under development

Rotator cuff tears are the most common musculoskeletal injury occurring in the shoulder. Current surgical repair fails to heal in 20% to 95% of patients, depending on age, size of the tear, smoking, time of repair, tendon quality, muscle quality, healing response, and surgical treatments. These problems are worsened by the limited healing potential of injured tendons attributed to the presence of degenerative changes and relatively poor vascularity of the cuff tendons. Development of new techniques to treat rotator cuff tears requires testing in animal models to assess safety and efficacy before clinical testing. Hence, it is important to evaluate appropriate animal models for rotator cuff research with degeneration of tendons, muscular atrophy, and fatty infiltration similar to humans. This report reviews current clinical treatments and preclinical approaches for rotator cuff tear repair. The review will focus on current clinical surgical treatments, new repair strategies under clinical and preclinical development, and will also describe different animal models available for rotator cuff research. These findings and future directions for rotator cuff tear repair will be discussed.

Platelet-Rich Plasma Injections With Needle Tenotomy for Gluteus Medius Tendinopathy: A Registry Study With Prospective Follow-up

BACKGROUND

Gluteal tendinopathy is a prevalent condition that can be associated with significant pain and disability. To date, no studies have prospectively assessed the efficacy of intratendinous platelet-rich plasma (PRP) injections as a minimally invasive treatment for gluteus medius tendinopathy.

PURPOSE

To prospectively assess the efficacy of intratendinous PRP injections as treatment for chronic recalcitrant gluteus medius tendinopathy.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

During the study period between July 2011 and November 2015, data were collected from the Hospital for Special Surgery Center for Hip Preservation Outcomes Registry on participants who underwent ultrasound-guided intratendinous PRP injections for recalcitrant gluteus medius tendinosis and/or partial tears of the tendon associated with moderate to severe lateral hip pain for longer than 3 months. All participants were assessed pre- and postinjection with 4 outcome measures: modified Harris Hip Score (mHHS), Hip Outcome Score-Activities of Daily Living subscale (HOS-ADL), Hip Outcome Score-Sport-Specific subscale (HOS-Sport), and the International Hip Outcome Tool-33 (iHOT-33). Demographic data, including age, sex, height, weight, body mass index, and smoking status, were also collected.

RESULTS

A total of 21 patients were included in the study, with a mean follow-up of 19.7 months (range, 12.1-32.3 months). The mean improvements from preinjection to postinjection follow-up were 56.73 to 74.17 for mHHS, 68.93 to 84.14 for HOS-ADL, 45.54 to 66.72 for HOS-Sport, and 34.06 to 66.33 for iHOT-33. All mean outcome measure improvements were clinically and statistically significant (P < .001). Length of follow-up was positively correlated with improvements in HOS-ADL (P = .021) and HOS-Sport (P = .004) scores. No adverse events were observed during or after the procedure.

CONCLUSION

In this registry study with prospective follow-up, we found ultrasound-guided intratendinous PRP injections to be a safe and effective treatment option for chronic recalcitrant gluteus medius tendinopathy due to moderate to severe tendinosis and/or partial tendon tears. Well-powered randomized controlled studies are warranted to confirm our findings and further define the ideal candidates for this treatment.

Advances in biologic augmentation for rotator cuff repair

Rotator cuff tear is a very common shoulder injury that often necessitates surgical intervention for repair. Despite advances in surgical techniques for rotator cuff repair, there is a high incidence of failure after surgery because of poor healing capacity attributed to many factors. The complexity of tendon-to-bone integration inherently presents a challenge for repair because of a large biomechanical mismatch between the tendon and bone and insufficient regeneration of native tissue, leading to the formation of fibrovascular scar tissue. Therefore, various biological augmentation approaches have been investigated to improve rotator cuff repair healing. This review highlights recent advances in three fundamental approaches for biological augmentation for functional and integrative tendon-bone repair. First, the exploration, application, and delivery of growth factors to improve regeneration of native tissue are discussed. Second, applications of stem cell and other cell-based therapies to replenish damaged tissue for better healing are covered. Finally, this review will highlight the development and applications of compatible biomaterials to both better recapitulate the tendon-bone interface and improve delivery of biological factors for enhanced integrative repair.

Surgical Sutures with Porous Sheaths for the Sustained Release of Growth Factors

Surgical sutures with highly porous sheaths are developed using a swelling and freeze-drying procedure without compromising their mechanical properties. The modified sutures show a high capacity for loading biofactors and are able to release the loaded biofactors in a sustained manner.

Biologic Treatments for Sports Injuries II Think Tank-Current Concepts, Future Research, and Barriers to Advancement, Part 2: Rotator Cuff

Rotator cuff tears are common and result in considerable morbidity. Tears within the tendon substance or at its insertion into the humeral head represent a considerable clinical challenge because of the hostile local environment that precludes healing. Tears often progress without intervention, and current surgical treatments are inadequate. Although surgical implants, instrumentation, and techniques have improved, healing rates have not improved, and a high failure rate remains for large and massive rotator cuff tears. The use of biologic adjuvants that contribute to a regenerative microenvironment have great potential for improving healing rates and function after surgery. This article presents a review of current and emerging biologic approaches to augment rotator cuff tendon and muscle regeneration focusing on the scientific rationale, preclinical, and clinical evidence for efficacy, areas for future research, and current barriers to advancement and implementation.

Coated Sutures

The addition of specific proteins or growth factors onto sutures would provide a direct application of exogenous factors to promote tissue repair. The higher levels of growth factors and cytokines may optimize the healing environment and promote tissue recovery. Despite this proposed benefit, the current orthopedic literature on the use of coated sutures is limited. Although several of the published studies investigating healing improvement by coated sutures have shown promising results, these data are only based on in vitro or small animal experiments. Recent meta-analyses have reported positive effects of triclosan-coated antimicrobial sutures in regards to reduction of surgical site complications. However, biologically coated sutures are not yet widely accepted due to several unanswered questions (concentration, release kinematics, tissue reactions, etc.) in addition to the high costs of such products. Further studies are needed to demonstrate the efficacy of coated sutures in orthopedic surgery.

Local Application of Gelatin Hydrogel Sheets Impregnated With Platelet-Derived Growth Factor BB Promotes Tendon-to-Bone Healing After Rotator Cuff Repair in Rats

PURPOSE

To determine whether the local application of platelet-derived growth factor BB (PDGF-BB) in hydrogel sheets would promote healing and improve histologic characteristics and biomechanical strength after rotator cuff (RC) repair in rats.

METHODS

To assess the effect of PDGF-BB on tendon-to-bone healing we divided 36 adult male Sprague-Dawley rats treated with bilateral surgery to repair the supraspinatus tendon at its insertion site into 3 groups: group 1 = suture-only group; group 2 = suture and gelatin hydrogel sheets impregnated with phosphate-buffered saline (PBS); and group 3 = suture and gelatin hydrogel sheets impregnated with PDGF-BB (0.5 μg). Semiquantitative histologic evaluation was carried out 2, 6, and 12 weeks later; cell proliferation was assessed 2 and 6 weeks postoperatively by immunostaining for proliferating cell nuclear antigen (PCNA), and biomechanical testing, including ultimate load to failure, stiffness, and ultimate stress to failure, was performed 12 weeks after the operation.

RESULTS

At 2 weeks, the average percentage of PCNA-positive cells at the insertion site was significantly higher in group 3 (40.5% ± 2.4%) than in group 1 (32.1% ± 6.9%; P = .03) and group 2 (31.9% ± 3.7%; P = .02). At 2 and 6 weeks, the histologic scores were similar among the 3 groups. At 12 weeks, the histologic score was significantly higher in group 3 (10.3 ± 0.8) than in group 1 (8.5 ± 0.5; P = .002) or group 2 (8.8 ± 0.8; P = .009), whereas ultimate load to failure, stiffness, and ultimate load to stress (normal control population, 44.73 ± 9.75 N, 27.59 ± 4.32 N/mm, and 21.33 ± 4.65 N/mm(2), respectively) were significantly higher in group 3 (28.28 ± 6.28 N, 11.05 ± 2.37 N/mm, and 7.99 ± 2.13 N/mm(2), respectively) than in group 1 (10.44 ± 1.98 N, 4.74 ± 1.31 N/mm, and 3.28 ± 1.27 N/mm(2), respectively; all P < .001) or group 2 (11.85 ± 2.89 N, 5.86 ± 1.75 N/mm, and 3.31 ± 0.80 N/mm(2), respectively; all P < .001).

CONCLUSIONS

The placement of a PDGF-BB-impregnated hydrogel sheet just lateral to a transected and acutely reattached supraspinatus tendon produced significantly more PCNA-positive cells at 2 weeks and greater collagen fiber orientation, ultimate failure loads, stiffness, and stress to failure at 12 weeks than did a PBS-impregnated hydrogel sheet. No differences in vascularity or cellularity were observed.

CLINICAL RELEVANCE

The local application of PDGF-BB-impregnated gelatin hydrogel may help to promote tendon-to-bone healing after RC repair in humans.

Biologics for tendon repair

Tendon injuries are common and present a clinical challenge to orthopedic surgery mainly because these injuries often respond poorly to treatment and require prolonged rehabilitation. Therapeutic options used to repair ruptured tendons have consisted of suture, autografts, allografts, and synthetic prostheses. To date, none of these alternatives has provided a successful long-term solution, and often the restored tendons do not recover their complete strength and functionality. Unfortunately, our understanding of tendon biology lags far behind that of other musculoskeletal tissues, thus impeding the development of new treatment options for tendon conditions. Hence, in this review, after introducing the clinical significance of tendon diseases and the present understanding of tendon biology, we describe and critically assess the current strategies for enhancing tendon repair by biological means. These consist mainly of applying growth factors, stem cells, natural biomaterials and genes, alone or in combination, to the site of tendon damage. A deeper understanding of how tendon tissue and cells operate, combined with practical applications of modern molecular and cellular tools could provide the long awaited breakthrough in designing effective tendon-specific therapeutics and overall improvement of tendon disease management.

Platelet-rich plasma and other cellular strategies in orthopedic surgery

The use of biologics in the treatment of musculoskeletal disease has become increasingly more common as research studies continue to provide further elucidation of their mechanisms in healing. Platelet-rich plasma, patches, growth factors, and stem cells are among the many biologics under active investigation and have varying levels of success in augmenting surgical or nonoperative interventions. However, the limitations of these treatments exist, and clear guidelines for their indications and application have yet to be established. Well-designed clinical trials will help determine the appropriate future use of biologics to ensure consistent outcomes.

Factors affecting healing after arthroscopic rotator cuff repair

Rotator cuff repair has been shown to have good long-term results. Unfortunately, a significant proportion of repairs still fail to heal. Many factors, both patient and surgeon related, can influence healing after repair. Older age, larger tear size, worse muscle quality, greater muscle-tendon unit retraction, smoking, osteoporosis, diabetes and hypercholesterolemia have all shown to negatively influence tendon healing. Surgeon related factors that can influence healing include repair construct-single vs double row, rehabilitation, and biologics including platelet rich plasma and mesenchymal stem cells. Double-row repairs are biomechanically stronger and have better healing rates compared with single-row repairs although clinical outcomes are equivalent between both constructs. Slower, less aggressive rehabilitation programs have demonstrated improved healing with no negative effect on final range of motion and are therefore recommended after repair of most full thickness tears. Additionally no definitive evidence supports the use of platelet rich plasma or mesenchymal stem cells regarding improvement of healing rates and clinical outcomes. Further research is needed to identify effective biologically directed augmentations that will improve healing rates and clinical outcomes after rotator cuff repair.

Augmentation of tendon-to-bone healing

Tendon-to-bone healing is vital to the ultimate success of the various surgical procedures performed to repair injured tendons. Achieving tendon-to-bone healing that is functionally and biologically similar to native anatomy can be challenging because of the limited regeneration capacity of the tendon-bone interface. Orthopaedic basic-science research strategies aiming to augment tendon-to-bone healing include the use of osteoinductive growth factors, platelet-rich plasma, gene therapy, enveloping the grafts with periosteum, osteoconductive materials, cell-based therapies, biodegradable scaffolds, and biomimetic patches. Low-intensity pulsed ultrasound and extracorporeal shockwave treatment may affect tendon-to-bone healing by means of mechanical forces that stimulate biological cascades at the insertion site. Application of various loading methods and immobilization times influence the stress forces acting on the recently repaired tendon-to-bone attachment, which eventually may change the biological dynamics of the interface. Other approaches, such as the use of coated sutures and interference screws, aim to deliver biological factors while achieving mechanical stability by means of various fixators. Controlled Level-I human trials are required to confirm the promising results from in vitro or animal research studies elucidating the mechanisms underlying tendon-to-bone healing and to translate these results into clinical practice.

Comparison of rotator cuff muscle architecture between humans and other selected vertebrate species

In this study, we compare rotator cuff muscle architecture of typically used animal models with that of humans and quantify the scaling relationships of these muscles across mammals. The four muscles that correspond to the human rotator cuff - supraspinatus, infraspinatus, subscapularis and teres minor - of 10 commonly studied animals were excised and subjected to a series of comparative measurements. When body mass among animals was regressed against physiological cross-sectional area, muscle mass and normalized fiber length, the confidence intervals suggested geometric scaling but did not exclude other scaling relationships. Based on the architectural difference index (ADI), a combined measure of fiber length-to-moment arm ratio, fiber length-to-muscle length ratio and the fraction of the total rotator cuff physiological cross-sectional area contributed by each muscle, chimpanzees were found to be the most similar to humans (ADI=2.15), followed closely by capuchins (ADI=2.16). Interestingly, of the eight non-primates studied, smaller mammals such as mice, rats and dogs were more similar to humans in architectural parameters compared with larger mammals such as sheep, pigs or cows. The force production versus velocity trade-off (indicated by fiber length-to-moment arm ratio) and the excursion ability (indicated by fiber length-to-muscle length ratio) of humans were also most similar to those of primates, followed by the small mammals. Overall, primates provide the best architectural representation of human muscle architecture. However, based on the muscle architectural parameters of non-primates, smaller rather than larger mammals may be better models for studying muscles related to the human rotator cuff.

Comparison of the effect of intra-tendon applications of recombinant human platelet-derived growth factor-BB, platelet-rich plasma, steroids in a rat achilles tendon collagenase model

This study compared the effect of intra-tendon (IT) delivery of recombinant human platelet-derived growth factor-BB (rhPDGF-BB), platelet-rich plasma (PRP) and corticosteroids in a rat tendinopathy model. Seven days after collagenase induction of tendinopathy, a 30-µl IT injection was administered. Treatments included: saline; 3 µg rhPDGF-BB; 10 µg rhPDGF-BB; PRP; and 300 µg triamcinolone acetonide (TCA). Outcomes were assessed 7 and 21 days after treatment. All groups exhibited good to excellent repair. Relative to saline, cell proliferation increased 65% in the 10 µg rhPDGF-BB group and decreased 74% in the TCA group; inflammation decreased 65% in the TCA group. At 7 days, maximum load-to-failure was increased in the 3 µg rhPDGF-BB group relative to saline, PRP, and TCA (p < 0.025). On day 21, maximum load-to-rupture was increased in the 10 µg rhPDGF-BB group relative to saline, PRP, and TCA (p < 0.035) and in the 3 µg rhPDGF-BB group compared to saline and TCA (p < 0.027). Stiffness in the 10 µg rhPDGF-BB group was increased compared to saline, PRP, and TCA (p < 0.038). Histology demonstrated similar repair in all groups. PRP and TCA did not improve mechanical properties compared to saline. Injections of rhPDGF-BB increased maximum load-to-failure (3 and 10 µg) and stiffness (10 µg) relative to controls and commonly used treatments. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:145-150, 2014.

Review article: Regenerative techniques for repair of rotator cuff tears

The failure rate of rotator cuff repair is high. Regenerative techniques using material scaffolds, stem cells, and growth factors help augment repair and regenerate tissue. We reviewed the literature of various regenerative techniques in terms of (1) enhancing the repair process, (2) tissue regeneration, (3) mechanical strength, and (4) clinical outcome.

Are platelet-rich products necessary during the arthroscopic repair of full-thickness rotator cuff tears: a meta-analysis

Background

Platelet-rich products (PRP) are widely used for rotator cuff tears. However, whether platelet-rich products produce superior clinical or radiological outcomes is controversial. This study aims to use meta-analysis to compare clinical and radiological outcomes between groups with or without platelet-rich products.

Methods

The Pubmed, Embase, and Cochrane library databases were searched for relevant studies published before April 20, 2013. Studies were selected that clearly reported a comparison between the use or not of platelet-rich products. The Constant, ASES, UCLA, and SST scale systems and the rotator cuff retear rate were evaluated. The weighted mean differences and relative risks were calculated using a fixed-effects model.

Results

Seven studies were enrolled in this meta-analysis. No significant differences were found for the Constant scale (0.73, 95% CI, −1.82 to 3.27, P = 0.58), ASES scale (−2.89, 95% CI, −6.31 to 0.53, P = 0.1), UCLA scale (−0.79, 95% CI, −2.20 to 0.63, P = 0.28), SST scale (0.34, 95% CI, −0.01 to 0.69, P = 0.05), and the overall rotator cuff retear rate (0.71, 95% CI, 0.48 to 1.05, P = 0.08). Subgroup analysis according to the initial tear size showed a lower retear rate in small- and medium-sized tears (0.33, 95% CI, 0.12 to 0.91, P = 0.03) after platelet-rich product application but no difference for large- and massive-sized tears (0.86, 95% CI, 0.60 to 1.23, P = 0.42).

Conclusion

In conclusion, the meta-analysis suggests that the platelet-rich products have no benefits on the overall clinical outcomes and retear rate for the arthroscopic repair of full-thickness rotator cuff tears. However, a decrease occurred in the rate of retears among patients treated with PRP for small- and medium-sized rotator cuff tears but not for large- and massive-sized tears.

Level of Evidence

Level II

The science of rotator cuff tears: translating animal models to clinical recommendations using simulation analysis

PURPOSE

The purpose of this article is to review basic science studies using various animal models for rotator cuff research and to describe structural, biomechanical, and functional changes to muscle following rotator cuff tears. The use of computational simulations to translate the findings from animal models to human scale is further detailed.

METHODS

A comprehensive review was performed of the basic science literature describing the use of animal models and simulation analysis to examine muscle function following rotator cuff injury and repair in the ageing population.

RESULTS

The findings from various studies of rotator cuff pathology emphasize the importance of preventing permanent muscular changes with detrimental results. In vivo muscle function, electromyography, and passive muscle-tendon unit properties were studied before and after supraspinatus tenotomy in a rodent rotator cuff injury model (acute vs chronic). Then, a series of simulation experiments were conducted using a validated computational human musculoskeletal shoulder model to assess both passive and active tension of rotator cuff repairs based on surgical positioning.

CONCLUSION

Outcomes of rotator cuff repair may be improved by earlier surgical intervention, with lower surgical repair tensions and fewer electromyographic neuromuscular changes. An integrated approach of animal experiments, computer simulation analyses, and clinical studies may allow us to gain a fundamental understanding of the underlying pathology and interpret the results for clinical translation.

Dose-response effect of an intra-tendon application of recombinant human platelet-derived growth factor-BB (rhPDGF-BB) in a rat Achilles tendinopathy model

The purpose of this study was to assess whether intra-tendon delivery of recombinant human platelet-derived growth factor-BB (rhPDGF-BB) would improve Achilles tendon repair in a rat collagenase-induced tendinopathy model. Seven days following collagenase induction of tendinopathy, one of four intra-tendinous treatments was administered: (i) Vehicle control (sodium acetate buffer), (ii) 1.02 µg rhPDGF-BB, (iii) 10.2 µg rhPDGF-BB, or (iv) 102 µg rhPDGF-BB. Treated tendons were assessed for histopathological (e.g., proliferation, tendon thickness, collagen fiber density/orientation) and biomechanical (e.g., maximum load-to-failure and stiffness) outcomes. By 7 days post-treatment, there was a significant increase in cell proliferation with the 10.2 and 102 µg rhPDGF-BB-treated groups (p=0.049 and 0.015, respectively) and in thickness at the tendon midsubstance in the 10.2 µg of rhPDGF-BB group (p=0.005), compared to controls. All groups had equivalent outcomes by Day 21. There was a dose-dependent effect on the maximum load-to-failure, with no significant difference in the 1.02 and 102 µg rhPDGF-BB doses but the 10.2 µg rhPDGF-BB group had a significant increase in load-to-failure at 7 (p=0.003) and 21 days (p=0.019) compared to controls. The rhPDGF-BB treatment resulted in a dose-dependent, transient increase in cell proliferation and sustained improvement in biomechanical properties in a rat Achilles tendinopathy model, demonstrating the potential of rhPDGF-BB treatment in a tendinopathy application. Consequently, in this model, data suggest that rhPDGF-BB treatment is an effective therapy and thus, may be an option for clinical applications to treat tendinopathy.