Biocompatibility of a polymer patch for rotator cuff repair

Application of Nondegradable Synthetic Materials for Tendon and Ligament Injury

Tendon and ligament injuries, prevalent requiring surgical intervention, significantly impact joint stability and function. Owing to excellent mechanical properties and biochemical stability, Nondegradable synthetic materials, including polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE), have demonstrated significant potential in the treatment of tendon and ligament injuries. These above materials offer substantial mechanical support, joint mobility, and tissue healing promotion of the shoulder, knee, and ankle joint. This review conclude the latest development and application of nondegradable materials such as artificial patches and ligaments in tendon and ligament injuries including rotator cuff tears (RCTs), anterior cruciate ligament (ACL) injuries, and Achilles tendon ruptures.

Animal Models of Rotator Cuff Injury and Repair: A Systematic Review

There are a large number of animal studies on rotator cuff injury and repair, but a lack of detailed research and evaluation on the animal models. This systematic review aims to provide a framework for animal studies and repair patches for rotator cuff injury. Four hundred nine animal studies were included, of which the most common animal model of rotator cuff injury is rat (53.56%), the most common site of rotator cuff injury is the supraspinatus tendon (62.10%), and the most common injury type (degree) is acute tear (full thickness) (48.41%). The most common research purpose is to evaluate the repair effect of the patch (24.94%), followed by the observation of pathophysiological changes after rotator cuff injury (20.87%). Among the five types of repair patch materials including nondegradable and degradable synthetic materials, autologous and allogeneic tissues, and naturally derived biomaterial, the last one is the mostly used (52.74%). For different animal models, the rodent models (rat and mouse) are the most commonly used and probably the most suitable species for preliminary studies of rotator cuff injury; the rabbit, canine, sheep, and goat models are more suitable for biomechanical performance testing, rehabilitation training, and validation of surgical methods; and the nonhuman primate models (monkey and baboon) are the closest to human, but it is more difficult to carry out the animal studies on them because of ethical issues, high feeding cost, and management difficulties.

Clinical outcomes and structural integrity rate of arthroscopic augmented rotator cuff repairs using extracellular porcine matrix patch

Background

Structural failure rate in rotator cuff repairs is still high. The purpose of the study is to assess the structural integrity of a series of augmented rotator cuff repairs with porcine matrix patch and report the functional outcomes.

Methods

Between 2014 and 2017, 44 consecutive patients underwent arthroscopic double-row repair of medium to massive rotator cuff tears with extracellular porcine dermal matrix augmentation. At one-year follow-up, magnetic resonance imaging scan was performed to assess the integrity of the repair. Oxford Shoulder Score (OSS), Constant Score (CS) and Visual Analogue Scale pain score, together with range of motion were used to assess patients.

Results

Patients mean age was 68 (53-82); mean follow-up was 17.2 (12-24) months. On magnetic resonance imaging scans, seven rotator cuff repair failures (15.9%) were observed: tear size was an independent predictor of re-rupture at one-year follow-up. Clinical scores showed a statistically significant improvement at three months and until final follow-up (p< 0.001). No complications occurred.

Conclusion

Observed structural failure rate of 15.9% is lower than those reported in the literature for standard rotator cuff repair of medium to massive tears in similar cohorts to ours. Extracellular matrix augmentation for rotator cuff repair was shown to be a safe and reliable support to the repairs and patients recovered good shoulder function.Level of Evidence: Level IV.

Evaluation of patches for rotator cuff repair: A systematic review and meta-analysis based on animal studies

Based on the published animal studies, we systematically evaluated the outcomes of various materials for rotator cuff repair in animal models and the potentials of their clinical translation. 74 animal studies were finally included, of which naturally derived biomaterials were applied the most widely (50.0%), rats were the most commonly used animal model (47.0%), and autologous tissue demonstrated the best outcomes in all animal models. The biomechanical properties of naturally derived biomaterials (maximum failure load: WMD 18.68 [95%CI 7.71-29.66]; P = 0.001, and stiffness: WMD 1.30 [95%CI 0.01-2.60]; P = 0.048) was statistically significant in the rabbit model. The rabbit model showed better outcomes even though the injury was severer compared with the rat model.

Physicochemical features assessment of acemannan-based ternary blended films for biomedical purposes

The exploitation of natural origin macromolecules, as complex physical mixtures or drugs, increases in biomedical or tissue engineering (TE) solutions. Aloe Vera is a highly explored medicinal plant, from which the main polysaccharide is acemannan (ACE). The ACE combination with chitosan and alginate results in interactions that lead to mixed junction zones formation, predicting membrane functionality improvement. This work proposes the development and characterization of ACE-based blended films as a promising strategy to design a nature-derived bioactive platform. The results confirmed that stable complex polyelectrolyte structures were formed through different intermolecular interactions. The films present good dimensional stability, flexibility, an adequate swelling ability with mostly radial water uptake, and a sustainable ACE release to the medium. Positive biological performance of the ACE-based blended films with L929 cells also suggested that they can be applied in TE solutions, with the potential to act as bioactive topical platforms.

Bioaugmentation in the surgical treatment of anterior cruciate ligament injuries: A review of current concepts and emerging techniques

Injuries involving the anterior cruciate ligament are among the most common athletic injuries, and are the most common involving the knee. The anterior cruciate ligament is a key translational and rotational stabilizer of the knee joint during pivoting and cutting activities. Traditionally, surgical intervention in the form of anterior cruciate ligament reconstruction has been recommended for those who sustain an anterior cruciate ligament rupture and wish to remain active and return to sport. The intra-articular environment of the anterior cruciate ligament makes achieving successful healing following repair challenging. Historically, results following repair were poor, and anterior cruciate ligament reconstruction emerged as the gold-standard for treatment. While earlier literature reported high rates of return to play, the results of more recent studies with longer follow-up have suggested that anterior cruciate ligament reconstruction may not be as successful as once thought: fewer athletes are able to return to sport at their preinjury level, and many still go on to develop osteoarthritis of the knee at a relatively younger age. The four principles of tissue engineering (cells, growth factors, scaffolds, and mechanical stimuli) combined in various methods of bioaugmentation have been increasingly explored in an effort to improve outcomes following surgical treatment of anterior cruciate ligament injuries. Newer technologies have also led to the re-emergence of anterior cruciate ligament repair as an option for select patients. The different biological challenges associated with anterior cruciate ligament repair and reconstruction each present unique opportunities for targeted bioaugmentation strategies that may eventually lead to better outcomes with better return-to-play rates and fewer revisions.

Vascularization and biocompatibility of poly(ε-caprolactone) fiber mats for rotator cuff tear repair

Rotator cuff tear is the most frequent tendon injury in the adult population. Despite current improvements in surgical techniques and the development of grafts, failure rates following tendon reconstruction remain high. New therapies, which aim to restore the topology and functionality of the interface between muscle, tendon and bone, are essentially required. One of the key factors for a successful incorporation of tissue engineered constructs is a rapid ingrowth of cells and tissues, which is dependent on a fast vascularization. The dorsal skinfold chamber model in female BALB/cJZtm mice allows the observation of microhemodynamic parameters in repeated measurements in vivo and therefore the description of the vascularization of different implant materials. In order to promote vascularization of implant material, we compared a porous polymer patch (a commercially available porous polyurethane based scaffold from Biomerix™) with electrospun polycaprolactone (PCL) fiber mats and chitosan-graft-PCL coated electrospun PCL (CS-g-PCL) fiber mats in vivo. Using intravital fluorescence microscopy microcirculatory parameters were analyzed repetitively over 14 days. Vascularization was significantly increased in CS-g-PCL fiber mats at day 14 compared to the porous polymer patch and uncoated PCL fiber mats. Furthermore CS-g-PCL fiber mats showed also a reduced activation of immune cells. Clinically, these are important findings as they indicate that the CS-g-PCL improves the formation of vascularized tissue and the ingrowth of cells into electrospun PCL scaffolds. Especially the combination of enhanced vascularization and the reduction in immune cell activation at the later time points of our study points to an improved clinical outcome after rotator cuff tear repair.

Application of a new polyester patch in arthroscopic massive rotator cuff repair-a prospective cohort study

BACKGROUND

Massive rotator cuff (RC) tears still present a clinically challenging problem, with reported rerupture rates in up to 94%. The study objective was to determine the impact of synthetic patch augmentation for massive RC tears.

METHODS

Between June 2012 and 2014, we performed 50 arthroscopic RC reconstructions augmented with a synthetic polyester patch. Pre- and postoperative imaging methods included arthrographic magnetic resonance imaging, arthrographic computed tomography, and ultrasound examination to determine tendon integrity or rerupture. Clinical outcome was evaluated using the Constant-Murley score and the subjective shoulder value. Mean clinical midterm and final follow-up was 22 months (9-35 months) and 52 months (25-74 months), respectively.

RESULTS

The mean Constant-Murley score increased significantly from 36.5 (±16.4 standard deviation [SD]) preoperatively to a midterm value of 81.2 (±9.6 SD; P < .0001) and further improved to a mean of 83.4 (±10.8 SD) at final follow-up. The mean subjective shoulder value increased from 40.3 (±24.3 SD) to 89.2 (±12.9 SD; P < .0001) at midterm and to 89.6 (±15.2 SD) at final follow-up. We observed 7 complete reruptures (14%). However, reruptures did not correlate with revision surgery, which was performed in 8 patients. The main reason for revision was frozen shoulder or arthrofibrosis with an intact reconstruction and patch, which was performed in 6 cases.

CONCLUSIONS

The retear rate of 14% compared favorably with nonaugmented RC repairs in the literature. Therefore, we conclude that patch augmentation in massive RC tears is feasible to reduce retears and to improve clinical outcome.

Influence of sutures configuration on the strength of tendon-patch joints for rotator cuff tears treatment

PURPOSE

Massive rotator cuff tears are common in the aging population. The incidence of failed rotator cuff repairs is still quite high, especially in the treatment of full-thickness tears or revision repairs. In this context, natural and synthetic meshes can be used as augmentation scaffolds or as devices to close the gap between a retracted tendon and the bone. The purpose of this work is to evaluate the ultimate tensile strength of different tendon-patch joints in order to consider their use in the treatment of massive cuff tears.

MATERIALS AND METHODS

Porcine tendons and a synthetic low-density polypropylene mesh have been used. A preliminary study on the tensile strength of tendons and patches has been performed. Different patch-tendon joints have been studied by modifying the number and the layout of the sutures. For every joint, the tensile test, performed through an electromechanical machine, has been repeated at least twice to obtain reliable data.

RESULTS

Experimental tensile tests on tendons and patches have given good results with very low dispersion data. Mean values of the calculated ultimate tensile stresses are, respectively, about 34 MPa and 16 MPa for tendons and patches. As regards the sutures arrangement, the staggered layout gave, for all joints, a higher tensile strength than the regular (aligned) one. Different ultimate tensile stress values, depending on the sutures number and layout, have been calculated for the joints.

CONCLUSION

Synthetic patches could be an interesting option to repair massive cuff tears and to improve, in a significant way, pain, range of motion and strength at time 0, so reducing the rehabilitation time. Obtained results demonstrated that joints with a suitable number and layout of sutures could ensure very good mechanical performances. The failure load of the tendon-patch joint, in fact, is higher than the working load on a healthy tendon.

Technologies to Augment Rotator Cuff Repair

Healing rates after rotator cuff repair vary widely. New technologies seek to improve tendon to bone healing with the addition of platelet-rich plasma, stem cells, and biological and synthetic grafts. Platelet-rich plasma and mesenchymal stem cells are used to help create a favorable environment for tendon to bone healing, and grafts and scaffolds provide structural support for repair. The efficacy of platelet-rich plasma and stem cell products seems to be variable, with different products offering different levels of cytokine and growth factors. Scaffold material is also variable with a wide range of synthetic and biological grafts.

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.

Biomaterials based strategies for rotator cuff repair

Tearing of the rotator cuff commonly occurs as among one of the most frequently experienced tendon disorders. While treatment typically involves surgical repair, failure rates to achieve or sustain healing range from 20 to 90%. The insufficient capacity to recover damaged tendon to heal to the bone, especially at the enthesis, is primarily responsible for the failure rates reported. Various types of biomaterials with special structures have been developed to improve tendon-bone healing and tendon regeneration, and have received considerable attention for replacement, reconstruction, or reinforcement of tendon defects. In this review, we first give a brief introduction of the anatomy of the rotator cuff and then discuss various design strategies to augment rotator cuff repair. Furthermore, we highlight current biomaterials used for repair and their clinical applications as well as the limitations in the literature. We conclude this article with challenges and future directions in designing more advanced biomaterials for augmentation of rotator cuff repair.

Single-cell analysis reveals a nestin+ tendon stem/progenitor cell population with strong tenogenic potentiality

The repair of injured tendons remains a formidable clinical challenge because of our limited understanding of tendon stem cells and the regulation of tenogenesis. With single-cell analysis to characterize the gene expression profiles of individual cells isolated from tendon tissue, a subpopulation of nestin⁺ tendon stem/progenitor cells (TSPCs) was identified within the tendon cell population. Using Gene Expression Omnibus datasets and immunofluorescence assays, we found that nestin expression was activated at specific stages of tendon development. Moreover, isolated nestin⁺ TSPCs exhibited superior tenogenic capacity compared to nestin^- TSPCs. Knockdown of nestin expression in TSPCs suppressed their clonogenic capacity and reduced their tenogenic potential significantly both in vitro and in vivo. Hence, these findings provide new insights into the identification of subpopulations of TSPCs and illustrate the crucial roles of nestin in TSPC fate decisions and phenotype maintenance, which may assist in future therapeutic strategies to treat tendon disease.

Effective healing of chronic rotator cuff injury using recombinant bone morphogenetic protein-2 coated dermal patch in vivo

Biologic augmentation for rotator cuff repair is a challenging treatment in patients with chronic large, massive, and irreparable rotator cuff injuries. Particularly, the use of an extracellular matrix (ECM) patch such as dermal tissue offered improved biomechanical properties in previous studies. Cytokines induce cell chemotaxis, proliferation, matrix synthesis, and cell differentiation. Moreover, osteoinductive growth factors such as bone morphogenetic protein-2 (BMP-2) affect the formation of new bone and fibrocartilage in lesions. However, the effects of using a dermal patch in combination with BMP-2 have not been evaluated to date, although many researchers have recognized the importance thereof. In this study, rhBMP-2-coated dermal patch (1 cm × 2 cm) isolated from human cadaveric donor was inserted in a rabbit model of chronic rotator cuff injury for in vivo evaluation. Bone mineral density and biomechanical strength were tested and histological and histomorphometric analyses were performed. The results showed that insertion of an rhBMP-2-coated acellular dermal patch not only significantly ameliorated new bone formation, it also improved biomechanical properties such as ultimate tensile strength. Thus, the use of this combination may improve the chronic rotator cuff injury-healing rate and clinical outcomes after rotator cuff repair. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1840-1846, 2017.

Massive Rotator Cuff Tears: Trends in Surgical Management

Compared with smaller tears, massive rotator cuff tears present significant clinical management dilemmas for the treating surgeon because they are often fraught with structural failure and poor outcomes. To optimize healing, current surgical methods look to optimize footprint coverage and enhance the biological environment for healing. Double-row techniques have demonstrated clear biomechanical advantages in controlled cadaveric studies, but have yet to demonstrate clear clinical efficacy over more simple repair techniques. When repairs for massive rotator cuff tears fail, options include revision repair or superior capsular reconstruction, an option to bridge the tissue gap with human dermal allograft or fascia lata autograft in hopes of containing the humeral head from superior migration and precluding rotator cuff arthropathy. Although latissimus transfers remain a reasonable option for massive, irreparable rotator cuff tears in appropriately indicated patients, clinical results are often unpredictable. Older patients with chronic, massive rotator cuff tears with pseudoparalysis can achieve predictable, often excellent clinical results with a reverse total shoulder arthroplasty. [Orthopedics. 2016; 39(3):145-151.].

Chronic safety assessment of hemostatic self-expanding foam: 90-day survival study and intramuscular biocompatibility

BACKGROUND

Noncompressible hemorrhage is a significant cause of preventable death in trauma, with no effective presurgical treatments. We previously described the efficacy and 28-day safety of a self-expanding hemostatic foam in swine models. We hypothesized that the 28-day results would be confirmed at a second site and that results would be consistent over 90 days. Finally, we hypothesized that the foam material would be biocompatible following intramuscular implantation.

METHODS

Foam treatment was administered in swine following a closed-cavity splenic injury. The material was explanted after 3 hours, and the animals were monitored to 28 days (n = 6) or 90 days (n = 4). Results were compared with a control group with injury alone (n = 6 at 28 days, n = 3 at 90 days). In a separate study, foam samples were implanted in rabbit paravertebral muscle and assessed at 28 days and 90 days relative to a Food and Drug Administration-approved polyurethane mesh (n = 3 per group).

RESULTS

All animals survived the acute phase of the study, and the foam animals required enterorrhaphy. One animal developed postoperative ileus and was euthanized; all other animals survived to the 28-day or 90-day end point without clinically significant complications. Histologic evaluation demonstrated that remnant particles were associated with a fibrotic capsule and mild inflammation. The foam was considered biocompatible in 28-day and 90-day intramuscular implant studies.

CONCLUSION

Foam treatment was not associated with significant evidence of end-organ dysfunction or toxicity at 28 days or 90 days. Remnant foam particles were well tolerated. These results support the long-term safety of this intervention for severely bleeding patients.

Rotator cuff repair using a decellularized tendon slices graft: an in vivo study in a rabbit model

PURPOSE

Although varieties of surgical repair techniques and materials have been used to repair rotator cuff defects, re-tearing frequently occurs. The purpose of this study is to evaluate the postoperative outcomes of rotator cuff repairs with a decellularized tendon slices (DTSs) graft in a rabbit model.

METHODS

Large defects in the infraspinatus tendons were created bilaterally in 21 rabbits. The graft group underwent reconstruction of the defects with the DTSs grafts, while the defect group did not undergo any treatment. The specimens underwent histological observation, biomechanical testing, and magnetic resonance imaging (MRI) detection at 4, 8, and 12 weeks after surgery. In addition, 2 rabbits that were not operated on were used for MRI detection as a normal reference.

RESULTS

Histological analysis revealed that the graft promoted host cell ingrowth and tissue integration, and a tendon-like structure developed at 12 weeks. The ultimate tensile load had a significant difference between specimens at 4 and 12 weeks in the graft group, but there was no significant difference between the graft group and the defect group. In the graft group, the stiffness at 12 weeks was significantly greater than that at 4 or 8 weeks, and it was also greater than the stiffness in the defect group at 12 weeks. MRI demonstrated that the signal strength of the regenerative tissue from the graft group at 12 weeks was similar to that of normal infraspinatus tendon.

CONCLUSION

The DTSs graft allowed for incorporation of host tendon and improved the biomechanical performance of the regenerative tendon. Therefore, the graft could be a promising bioscaffold to enhance the surgical repair of large rotator cuff defects and consequently improve the clinical outcome of rotator cuff tears.

Naturally derived and synthetic scaffolds for skeletal muscle reconstruction

Skeletal muscle tissue has an inherent capacity for regeneration following injury. However, severe trauma, such as volumetric muscle loss, overwhelms these natural muscle repair mechanisms prompting the search for a tissue engineering/regenerative medicine approach to promote functional skeletal muscle restoration. A desirable approach involves a bioscaffold that simultaneously acts as an inductive microenvironment and as a cell/drug delivery vehicle to encourage muscle ingrowth. Both biologically active, naturally derived materials (such as extracellular matrix) and carefully engineered synthetic polymers have been developed to provide such a muscle regenerative environment. Next generation naturally derived/synthetic "hybrid materials" would combine the advantageous properties of these materials to create an optimal platform for cell/drug delivery and possess inherent bioactive properties. Advances in scaffolds using muscle tissue engineering are reviewed herein.

Validating whole slide digital morphometric analysis as a microscopy tool

Whole slide imaging (WSI) can be used to quantify multiple responses within tissue sections during histological analysis. Feature Analysis on Consecutive Tissue Sections (FACTS®) allows the investigator to perform digital morphometric analysis (DMA) within specified regions of interest (ROI) across multiple serial sections at faster rates when compared with manual morphometry methods. Using FACTS® in conjunction with WSI is a powerful analysis tool, which allows DMA to target specific ROI across multiple tissue sections stained for different biomarkers. DMA may serve as an appropriate alternative to classic, manual, histologic morphometric measures, which have historically relied on the selection of high-powered fields of views and manual scoring (e.g., a gold standard). In the current study, existing preserved samples were used to determine if DMA would provide similar results to manual counting methods. Rodent hearts (n=14, left ventricles) were stained with Masson's trichrome, and reacted for cluster of differentiation 68 (CD-68). This study found no statistical significant difference between a classic, manual method and the use of digital algorithms to perform the similar counts (p=0.38). DMA offers researchers the ability to accurately evaluate morphological characteristics in a reproducible fashion without investigator bias and with higher throughput.

Results of reconstruction of massive irreparable rotator cuff tears using a fascia lata allograft

BACKGROUND

Despite the advances in surgical treatment options, massive rotator cuff (r-c) tears still represent a challenge for orthopedic surgeons. This study assesses the effectiveness of fascia lata allograft in reconstruction of massive and irreparable r-c tear and to evaluate the healing and functional outcomes.

MATERIALS AND METHODS

68 patients (38 men, 30 women, mean age 64.9 years) with massive or irreparable r-c tears were treated with placement of fascia lata allograft to fill the defect between February 2006 and February 2010. At 43 months followup they were evaluated clinically using the constant score, preoperatively and postoperatively. Magnetic resonance imaging (MRI) and ultrasound were used postoperatively, to assess the integrity of the allograft at the repair site. Postoperatively, standard rehabilitation protocol was followed with gradual restoration.

RESULTS

Postoperative constant score increased from 32.5 preoperatively to 88.7 postoperatively. The most important was the pain relief from 2.4 preoperatively to 14.1 postoperatively and range of motion. The results of the MRI were not reliable, but the ultrasound was satisfactory. Finally, there was no infection or rejection of the graft in any of the patients.

CONCLUSIONS

Despite advances in surgical methods, there is still not a universally accepted treatment for massive and irreparable rotator cuff tears, because the standard methods have dubious results, with excessive retear rates and poor outcomes, necessitating the need for new repair strategies. We documented significant clinical improvement using fascia lata allograft in the repair of massive irreparable r-c tear, acting as scaffold to bridge the defect, enhancing the healing at the repair site.

Synthetic and degradable patches: an emerging solution for rotator cuff repair

The use of rotator cuff augmentation has increased dramatically over the last 10 years in response to the high rate of failure observed after non-augmented surgery. However, although augmentations have been shown to reduce shoulder pain, there is no consensus or clear guideline as to what is the safest or most efficacious material. Current augmentations, either available commercially or in development, can be classified into three categories: non-degradable structures, extra cellular matrix (ECM)-based patches and degradable synthetic scaffolds. Non-degradable structures have excellent mechanical properties, but can cause problems of infection and loss of integrity in the long-term. ECM-based patches usually demonstrate excellent biological properties in vitro, but studies have highlighted complications in vivo due to poor mechanical support and to infection or inflammation. Degradable synthetic scaffolds represent the new generation of implants. It is proposed that a combination of good mechanical properties, active promotion of biological healing, low infection risk and bio-absorption are the ideal characteristics of an augmentation material. Among the materials with these features, those processed by electrospinning have shown great promis. However, their clinical effectiveness has yet to be proven and well conducted clinical trials are urgently required.

Rotator cuff repair augmentation with local autogenous bone marrow via humeral cannulation in a rat model

BACKGROUND

Growth factors have been shown to improve healing after rotator cuff repair. Bone marrow is a potential vehicle for growth factor augmentation, yet methods of delivering marrow to cuff repair sites are still under-researched. We hypothesized that a cannulated humeral implant would deliver local bone marrow and thereby improve healing in a rat model.

METHODS

Twenty-eight rats underwent bilateral rotator cuff injury and repair. Each rat acted as its own control, randomized to a cannulated humeral implant in one shoulder and a solid implant in the other. Rats were euthanized at 4 and 8 weeks to create 4 time-treatment cohorts. Tendon healing was evaluated by dimensional measurements, biomechanical testing, and histology.

RESULTS

Tendon thickness, all biomechanical measures, and semi-quantitative histologic scores improved over time (P < .05) but not with treatment. The most common site of biomechanical tendon failure was midsubstance in the 8-week cannulated cohort and at the tendon footprint in the other 3 cohorts. Intraluminal bone growth was evident in all cannulated implants.

CONCLUSIONS

Humeral cannulation did not quantifiably improve tendon-to-bone healing in a rat model. The diminutive size of implants in rats, however, may have prevented sufficient delivery of local autogenous bone marrow; hence, further study in a larger animal is recommended.

Open repair of isolated traumatic subscapularis tendon tears with a synthetic soft tissue reinforcement

BACKGROUND

Missed or chronic subscapularis tendon ruptures may have muscle atrophy and tendon retraction resulting in a large defect with high risk of re-tear after a surgical repair. To improve the clinical results of this challenging surgery, the repaired tendon could be augmented with endogenous or exogenous materials. The purpose of this study was to evaluate the structural tendon integrity and clinical outcomes after an open subscapularis tendon repair with a synthetic soft tissue reinforcement.

MATERIALS AND METHODS

Ten patients were managed with an open repair of the subscapularis tendon with augmentation by means of SportMesh, a readily available synthetic degradable poly(urethaneurea) scaffold. Clinical findings were assessed for all patients preoperatively and postoperatively with use of the visual analog scale for pain and the DASH scoring system. All patients had an ultrasonographic study at the latest follow-up.

RESULTS

The visual analog scale for pain (mean ± standard deviation) improved significantly (P < 0.01) from 7.9 ± 1.1 preoperatively to 1.95 ± 1.85 at the latest clinical follow-up evaluation. The mean DASH score at the latest clinical follow-up was 12.63 %. Ultrasound imaging revealed a structural intact repair at follow-up in 9 shoulders (90 %) with average 5.4 mm in thickness (4.3 mm in the contralateral healthy side).

CONCLUSIONS

At a median follow-up of 23 months, 80 % (8 of 10) of patients had a good or excellent result after an open subscapularis tendon repair with a soft tissue reinforcement. As a synthetic material, SportMesh Soft Tissue Reinforcement eliminates the risk of collagen reactions, which may result from collagen or dermis patches. Although the follow-up is relatively short, our series shows a promising durable repair with a 10 % re-tear rate at an average of 23 postoperative months. Level of evidence Case Series, Treatment Study, Level IV.

Healing rates for challenging rotator cuff tears utilizing an acellular human dermal reinforcement graft

PURPOSE

This study presents a retrospective case series of the clinical and structural outcomes (1.5 T MRI) of arthroscopic rotator cuff repair with acellular human dermal graft reinforcement performed by a single surgeon in patients with large, massive, and previously repaired rotator cuff tears.

MATERIALS AND METHODS

Fourteen patients with mean anterior to posterior tear size 3.87 ± 0.99 cm (median 4 cm, range 2.5-6 cm) were enrolled in the study and were evaluated for structural integrity using a high-field (1.5 T) MRI at an average of 16.8 months after surgery. The Constant-Murley scores, the Flexilevel Scale of Shoulder Function (Flex SF), scapular plane abduction, and strength were analyzed.

RESULTS

MRI results showed that the rotator cuff repair was intact in 85.7% (12/14) of the patients studied. Two patients had a Sugaya Type IV recurrent tear (2 of 14; 14.3%), which were both less than 1 cm. The Constant score increased from a preoperative mean of 49.72 (range 13-74) to a postoperative mean of 81.07 (range 45-92) (P value = 0.009). Flexilevel Scale of Shoulder Function (Flex SF) Score normalized to a 100-point scale improved from a preoperative mean of 53.69 to a postoperative mean of 79.71 (P value = 0.003). The Pain Score improved from a preoperative mean of 7.73 to a postoperative mean of 13.57 (P value = 0.008). Scapular plane abduction improved from a preoperative mean of 113.64° to a postoperative mean of 166.43° (P value = 0.010). The strength subset score improved from a preoperative mean of 1.73 kg to a postoperative mean of 7.52 kg (P value = 0.006).

CONCLUSIONS

This study presents a safe and effective technique that may help improve the healing rates of large, massive, and revision rotator cuff tears with the use of an acellular human dermal allograft. This technique demonstrated favorable structural healing rates and statistically improved functional outcomes in the near term.

LEVEL OF EVIDENCE

4. Retrospective case series.

Rotator cuff: biology and current arthroscopic techniques

The present article summarizes current trends in arthroscopic rotator cuff repairs focusing on the used repair technique, potential influencing factors on the results, and long-term outcome after reconstruction of the rotator cuff. Moreover, different treatment options for the treatment for irreparable rotator cuff ruptures were described, and the results of additional augmentation of the repairs with platelet-rich plasma were critically analyzed. Based on the current literature, double-row repairs did not achieve superior clinical results compared to single-row repairs neither in the clinical results nor in the re-rupture rate. Multiple factors such as age, fatty infiltration, and initial rupture size might influence the results. If the rupture is not repairable, various options were described including cuff debridement, partial repair, tuberoplasty, or tendon transfers. The additional augmentation with platelet-rich plasma did not reveal any significant differences in the healing rate compared to conventional rotator cuff repairs.

LEVEL OF EVIDENCE

IV.

Scaffold devices for rotator cuff repair

Rotator cuff tears affect 40% or more of those aged older than 60 years, and repair failure rates of 20% to 70% remain a significant clinical challenge. Hence, there is a need for repair strategies that can augment the repair by mechanically reinforcing it, while at the same time biologically enhancing the intrinsic healing potential of the tendon. Tissue engineering strategies to improve rotator cuff repair healing include the use of scaffolds, growth factors, and cell seeding, or a combination of these approaches. Currently, scaffolds derived from mammalian extracellular matrix, synthetic polymers, and a combination thereof, have been cleared by the U.S. Food and Drug Administration and are marketed as medical devices for rotator cuff repair in humans. Despite the growing clinical use of scaffold devices for rotator cuff repair, there are numerous questions related to their indication, surgical application, safety, mechanism of action, and efficacy that remain to be clarified or addressed. This article reviews the current basic science and clinical understanding of commercially available synthetic and extracellular matrix scaffolds for rotator cuff repair. Our review will emphasize the host response and scaffold remodeling, mechanical and suture-retention properties, and preclinical and clinical studies on the use of these scaffolds for rotator cuff repair. We will discuss the implications of these data on the future directions for use of these scaffolds in tendon repair procedures.

Animal models for translational research on shoulder pathologies: from bench to bedside

Several animal models have been used for in vivo and in vitro shoulder research. In vitro models, consisting of cadaveric specimens, are useful in providing basic understanding of the functioning of the shoulder and for biomechanical experiments. In vivo models provide the means to model living phenomena, such as tendon healing process, tendinopathy, instability, and adaptive responses to surgery. However, intrinsic differences among different species make translation to human shoulder pathologies difficult. Most of the animals used in experimental settings are quadrupeds, using the forelimbs for weight-bearing during locomotion, with no or minimal overhead activity. The various animal models already used to study shoulder pathologies are presented in this article. However, there is a lack of validation for these animal models, which provides challenge to the further research in this field.

Decellularized human dermis to treat massive rotator cuff tears: in vitro evaluations

Interest is increasing in biological scaffolds for tissue regeneration such as extracellular matrix membranes, developed through soft tissue decellularization. Extracellular matrix membranes were developed to heal different tendon and soft tissue lesions that are very frequent in the general population with high health-care costs and patient morbidity. The aim of this research was to evaluate a human dermal matrix (HDM) decellularized by a chemico-physical method. A primary culture of rat tenocytes was performed: tenocytes were seeded on HDM samples and on polystyrene wells as controls (CTR). Cell viability and synthetic activity were evaluated at 3 and 7 days. An in vitro microwound model was used to evaluate HDM bioactivity: after tenocyte expansion, artificial wounds were created, HDM extracts were added, and closure time and decorin synthesis were monitored histomorphometrically at 1, 4, 24, and 72 hr. A significant higher amount of collagen I was observed when cells were cultured on HDM in comparison with that on CTR (3 days: p < 0.0001; 7 days: p < 0.05). In HDM group, fibronectin synthesis was significantly higher at both experimental times (p < 0.0001). At 3 days, proteoglycans and transforming growth factor-β1 releases were significantly higher on HDM (p < 0.0001 and p < 0.005, respectively). The artificial microwound closure time and decorin expression were significantly enhanced by the addition of 50% HDM extract (p < 0.05). In vitro data showed that the decellularization technique enabled the development of a matrix with adequate biological and biomechanical properties.

Biologic augmentation of rotator cuff repair

Rotator cuff repair is a common orthopedic procedure. Despite advances in surgical technique, the rotator cuff tendons often fail to heal after surgery. In recent years, a number of biologic strategies have been developed and tested to augment healing after rotator cuff repair. These strategies include allograft, extracellular matrices (ECMs), platelet rich plasma (PRP), growth factors, stem cells, and gene therapy. This chapter reviews the most current research on biologic augmentation of rotator cuff repair using these methods.

Augmentation of a rotator cuff suture repair using rhPDGF-BB and a type I bovine collagen matrix in an ovine model

BACKGROUND

Rotator cuff tears are a common source of shoulder pain. High rates (20%-94%) of structural failure of the repair have been attributed to multiple factors, including poor repair tissue quality and tendon-to-bone integration. Biologic augmentation using growth factors has potential to promote tendon-to-bone integration, improving the function and long-term success of the repair. One such growth factor is platelet-derived growth factor-BB (PDGF-BB), which has been shown to improve healing in tendon and bone repair models.

HYPOTHESIS

Recombinant human PDGF-BB (rhPDGF-BB) combined with a highly porous type I bovine collagen matrix will improve the biomechanical function and morphologic appearance of the repair in a dose-dependent manner, relative to a suture-only control, after 12 weeks in an acute ovine model of rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

An interpositional graft consisting of rhPDGF-BB and a type I collagen matrix was implanted in an ovine model of rotator cuff repair. Biomechanical and histologic analyses were performed to determine the functional and anatomic characteristics of the repair after 12 weeks.

RESULTS

A significant increase in the ultimate load to failure was observed in repairs treated with 75 µg (1490.5 ± 224.5 N, P = .029) or 150 µg (1486.6 ± 229.0 N, P = .029) of rhPDGF-BB, relative to suture-only controls (910.4 ± 156.1 N) and the 500-µg rhPDGF-BB group (677.8 ± 105.9 N). The 75-µg and 150-µg rhPDGF-BB groups also exhibited increased tendon-to-bone interdigitation histologically. No differences in inflammation or cellularity were observed among treatments.

CONCLUSION

This study demonstrated that an interpositional graft consisting of rhPDGF-BB (75 or 150 µg) and a type I collagen matrix was able to improve the biomechanical strength and anatomic appearance in an ovine model of rotator cuff repair compared to a suture-only control and the 500-µg rhPDGF-BB group.

CLINICAL RELEVANCE

Recombinant human PDGF-BB combined with a type I collagen matrix has potential to be used to augment surgical repair of rotator cuff tears, thereby improving clinical success.

Rotator cuff repair augmentation using a novel polycarbonate polyurethane patch: preliminary results at 12 months' follow-up

BACKGROUND

Preventing anatomic failure after rotator cuff repair (RCR) remains a challenge. Augmentation with a surgical mesh may permanently reinforce the repair and decrease failure rates. The purpose of this study is to assess the postoperative outcomes of open RCR augmented with a novel reticulated polycarbonate polyurethane patch.

MATERIALS AND METHODS

Ten patients with supraspinatus tendon tears underwent open RCR augmented with a polycarbonate polyurethane patch secured in a 6-point fixation construct placed over the repaired tendon. Patients were evaluated with preoperative and postoperative outcome measures, including the Simple Shoulder Test, visual analog pain scale, American Shoulder and Elbow Surgeons shoulder score, Cumulative Activities of Daily Living score, and University of California, Los Angeles shoulder scale, as well as range of motion. Postoperative magnetic resonance imaging was used to evaluate repair status.

RESULTS

Patients showed significant improvements in visual analog pain scale, Simple Shoulder Test, and American Shoulder and Elbow Surgeons shoulder scores at both 6 and 12 months postoperatively (P < .05 and P < .01, respectively). The University of California, Los Angeles postoperative score was good to excellent in 7 patients at 6 months and in 8 patients at 12 months. Range of motion in forward flexion, abduction, internal rotation, and external rotation was significantly improved at both 6 and 12 months postoperatively (P < .05 and P < .01, respectively). Magnetic resonance imaging at 12 months showed healing in 90%; one patient had a definitive persistent tear. We found no adverse events associated with the patch, including the absence of fibrosis, mechanical symptoms, or visible subacromial adhesions.

DISCUSSION

The polycarbonate polyurethane patch was designed to support tissue in growth and enhance healing as shown by preclinical animal studies. Clinically, the patch is well tolerated and shows promising efficacy, with a 10% retear rate at the 12-month time point.

Human tendon cell response to 7 commercially available extracellular matrix materials: an in vitro study

PURPOSE

To evaluate the response of human tenocytes in culture to 7 commercially available extracellular matrix (ECM) patches.

METHODS

Four samples of each ECM were incubated in human tenocyte cultures by use of standard methods. Cell adhesion, cell proliferation, and cellular production of type I and type III collagen, decorin, and scleraxis were measured for each sample according to established experimental methods. Histologic samples were examined to measure the migration of the tenocytes into the ECM.

RESULTS

Tenocytes adhered more to samples of layered submucosal pig intestine than the 6 other ECM materials (P < .002). Tenocytes proliferated more and produced more matrix proteins when cultured on ECM derived from unaltered dermal specimens of human or porcine origin (P < .001). Cells were not seen to have migrated into the matrix of any ECM sample.

CONCLUSIONS

Human tenocytes reacted most favorably to dermal ECM samples that were not chemically cross-linked by the manufacturer. Less favorable responses of the human cells were seen when cultured with equine or synthetic ECM, which showed favorable biologic responses in nonhuman models. Cellular migration into the matrix of the ECM is a complex process and cannot be replicated in this model entirely.

CLINICAL RELEVANCE

The results of this study suggest that dermal ECM may more favorably react with human tendon tissue than ECM of other origins. This may have great relevance as research continues in the field of augmenting surgical soft-tissue repair.

Preclinical models for translating regenerative medicine therapies for rotator cuff repair

Despite improvements in the understanding of rotator cuff pathology and advances in surgical treatment options, repairs of chronic rotator cuff tears often re-tear or fail to heal after surgery. Hence, there is a critical need for new regenerative repair strategies that provide effective mechanical reinforcement of rotator cuff repair as well as stimulate and enhance the patient's intrinsic healing potential. This article will discuss and identify appropriate models for translating regenerative medicine therapies for rotator cuff repair. Animal models are an essential part of the research and development pathway; however, no one animal model reproduces all of the features of the human injury condition. The rat shoulder is considered the most appropriate model to investigate the initial safety, mechanism, and efficacy of biologic treatments aimed to enhance tendon-to-bone repair. Whereas large animal models are considered more appropriate to investigate the surgical methods, safety and efficacy of the mechanical-or combination biologic/mechanical-strategies are ultimately needed for treating human patients. The human cadaver shoulder model, performed using standard-of-care repair techniques, is considered the best for establishing the surgical techniques and mechanical efficacy of various repair strategies at time zero. While preclinical models provide a critical aspect of the translational pathway for engineered tissues, controlled clinical trials and postmarketing surveillance are also needed to define the efficacy, proper indications, and the method of application for each new regenerative medicine strategy.

Biomechanical analysis of an ovine rotator cuff repair via porous patch augmentation in a chronic rupture model

BACKGROUND

Rotator cuff repair is a commonly performed procedure, but many of these repairs fail in the postoperative term. Despite advances in surgical methods to optimize the repair, failure rates still persist clinically, thereby suggesting the need for novel mechanical or biological augmentation strategies. Nonresorbable implants provide an appealing approach because patch materials may confer acute mechanical stability and act as a conductive scaffold for tissue ingrowth at the site of the tendon insertion.

HYPOTHESIS

The polyurethane scaffold mesh will confer greater biomechanical function relative to a nonaugmented repair after 12 weeks in vivo using a chronic ovine model of rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

After development of the chronic rupture model, the tensile failure properties of the nonresorbable mesh-augmented repair (n, 9) were compared with those of a surgical control in an ovine model (n, 8).

RESULTS

Rotator cuff repair with the scaffold mesh in the chronic model resulted in a significant 74.2% increase in force at failure relative to the nonaugmented surgical control (P = .021). Apparent increases in stiffness (55.4%) and global displacement at failure (21.4%) in the mesh-augmented group relative to nonaugmented controls were not significant (P = .126 and P = .123, respectively). At the study endpoint, the augmented shoulders recovered 37.8% and 40.7% of the force at failure and stiffness, respectively, of intact, nonoperated controls.

CONCLUSION

Using the previously described chronic rupture model, this study demonstrated that repair of a chronic tendon tear with the polyurethane scaffold mesh provides greater mechanical strength in the critical healing period than that of traditional suture anchor repair.

CLINICAL RELEVANCE

This device could be used to enhance the surgical repair of the rotator cuff and consequently improve long-term clinical outcome.

Tendon augmentation grafts: a systematic review

INTRODUCTION

Several biomaterials are available to bridge large tendon defects or reinforce tenuous tendon repairs.

METHODS

We performed a comprehensive search of PubMed, Medline, Cochrane, CINAHL, and Embase databases using various combinations of the commercial names of each scaffold and the keywords 'tendon', 'rotator cuff', 'supraspinatus tendon', 'Achilles tendon', 'scaffold', 'biomaterials', 'extracellular matrix', 'substitute', and 'devices' over the years 1966-2009. All articles relevant to the subject were retrieved, and their bibliographies hand searched for further references in the context to biomaterials for tendon repair.

RESULTS

Many biomaterials are available for tendon augmentation. Scanty evidence is available for the use of these scaffolds.

DISCUSSION

The emerging field of tissue engineering holds the promise to use biomaterials for tendon augmentation. Preliminary studies support the idea that these biomaterials have the ability to provide an alternative for tendon augmentation. However, available data are lacking to allow definitive conclusion on the use of biomaterials for tendon augmentation. Additionally, the prevalence of postoperative complications encountered with their use varies within the different studies.

CONCLUSION

Rather than providing strong evidence for or against the use of these materials for tendon augmentation, this study instead generates potential areas for additional prospective investigation.