Fixation technique of biodegradable magnesium alloy suture anchor in the rotator cuff repair of the shoulder in a goat model: a technical note.

BACKGROUND: Shoulder disorders, particularly rotator cuff tears, are prevalent musculoskeletal conditions related to aging. Although the widely used suture anchor technique provides strong mechanical support to the tendon, it is associated with a risk of postoperative tendon retearing. The conventionally used titanium alloys can affect the interpretation of magnetic resonance imaging. Degradable magnesium alloys possess excellent biocompatibility, similar mechanical property to the bone, and stimulating bone formation ability from Mg2+. The purpose of this experiment was to develop innovative magnesium-based suture anchors to enhance rotator cuff repair by improving fixation materials, and to evaluate their feasibility in a goat model. METHODS: We developed fluoridized ZK60 suture anchors as the implantation material for two goats, who underwent rotator cuff repair surgery on both shoulders. Computed tomography (CT) and histological analysis were performed at 12 weeks postoperatively, and the results were compared between the magnesium and titanium alloy groups. Additionally, a hematological examination was conducted, which included assessments of red blood cells, white blood cells, platelets, coagulation function, liver function, kidney function, and magnesium ion concentration. RESULTS: The 12-week postoperative CT images showed intact MgF2 ZK60 suture anchors, effectively reconnecting the infraspinatus tendon to the humeral head. The anchors became less visible on CT scans, indicating absorption by surrounding tissues. New bone formation in the MgF2 group surpassed that in the Ti group, demonstrating superior osseointegration. The similarity between cortical bone and magnesium reduced stress-shielding and promoted bone regeneration. Histological analysis revealed successful tendon healing with MgF2 anchors, while the Ti group showed discontinuous interfaces and reduced collagen secretion. Hematological examination showed stable liver, renal function, and magnesium ion levels. CONCLUSIONS: The findings indicate that MgF2-coated suture anchors are feasible for rotator cuff repair and potentially other orthopedic applications. We hope that magnesium alloy anchors can become the solution for rotator cuff tendon repair surgery.

Biocompatibility of a Marine Collagen-Based Scaffold In Vitro and In Vivo.

Scaffold material is essential in providing mechanical support to tissue, allowing stem cells to improve their function in the healing and repair of trauma sites and tissue regeneration. The scaffold aids cell organization in the damaged tissue. It serves and allows bio mimicking the mechanical and biological properties of the target tissue and facilitates cell proliferation and differentiation at the regeneration site. In this study, the developed and assayed bio-composite made of unique collagen fibers and alginate hydrogel supports the function of cells around the implanted material. We used an in vivo rat model to study the scaffold effects when transplanted subcutaneously and as an augment for tendon repair. Animals' well-being was measured by their weight and daily activity post scaffold transplantation during their recovery. At the end of the experiment, the bio-composite was histologically examined, and the surrounding tissues around the implant were evaluated for inflammation reaction and scarring tissue. In the histology, the formation of granulation tissue and fibroblasts that were part of the inclusion process of the implanted material were noted. At the transplanted sites, inflammatory cells, such as plasma cells, macrophages, and giant cells, were also observed as expected at this time point post transplantation. This study demonstrated not only the collagen-alginate device biocompatibility, with no cytotoxic effects on the analyzed rats, but also that the 3D structure enables cell migration and new blood vessel formation needed for tissue repair. Overall, the results of the current study proved for the first time that the implantable scaffold for long-term confirms the well-being of these rats and is correspondence to biocompatibility ISO standards and can be further developed for medical devices application.

Therapeutic potential of exosomes in rotator cuff tendon healing.

Rotator cuff tears are common musculoskeletal injuries that can cause significant pain and disability. While the clinical results of rotator cuff repair can be good, failure of tendon healing remains a significant problem. Molecular mechanisms underlying structural failure following surgical repair remain unclear. Histologically, enhanced inflammation, disorganization of the collagen fibers, calcification, apoptosis and tissue necrosis affect the normal healing process. Mesenchymal stem cells (MSCs) have the ability to provide improved healing following rotator cuff repair via the release of mediators from secreted 30-100 nm extracellular vesicles called exosomes. They carry regulatory proteins, mRNA and miRNA and have the ability to increase collagen synthesis and angiogenesis through increased expression of mRNA and release of proangiogenic factors and regulatory proteins that play a major role in proper tissue remodeling and preventing extracellular matrix degradation. Various studies have shown the effect of exosomes on improving outcome of cutaneous wound healing, scar tissue formation, degenerative bone disease and Duchenne Muscular Dystrophy. In this article, we critically reviewed the potential role of exosomes in tendon regeneration and propose the novel use of exosomes alone or seeded onto biomaterial matrices to stimulate secretion of favorable cellular factors in accelerating the healing response following rotator cuff repair.

Resorbable electrospun polydioxanone fibres modify the behaviour of cells from both healthy and diseased human tendons.

Chronic tendinopathy in an active and ageing population represents an increasing burden to healthcare systems. Rotator cuff tendinopathy alone accounts for approximately 70 % of all shoulder pain. Tendinopathic tissue has a disorganised extracellular matrix, altered vasculature, and infiltration of fibroblasts and inflammatory cells. This altered biology may contribute to the limited success of surgical repair strategies. Electrospun resorbable scaffolds can potentially enhance endogenous repair mechanisms by influencing the tissue microenvironment. Polydioxanone (PDO) has an established safety profile in patients. We compared the response of healthy and diseased human tendon cells to electrospun PDO fibres using live cell imaging, proliferation, flow cytometry, and gene expression studies. Within 4 h of initial contact with electrospun PDO, healthy tendon cells underwent a marked transformation; elongating along the fibres in a fibre density dependent manner. Diseased tendon cells initially responded at a slower rate, but ultimately underwent a similar morphological change. Electrospun fibres increased the proliferation rate of diseased tendon cells and increased the ratio of type I:IIIcollagenmRNA expression. Flow cytometry revealed decreased expression of CD106, a marker of mesenchymal stem cells, and increased expression of CD10 on healthy versus diseased tendon cells. PDO electrospun scaffolds further promoted CD106negCD10pos expression of healthy tendon cells. Despite their behavioural differences, both healthy and diseased human tendon cells responded to electrospun PDO fibres. This encourages further work establishing their efficacy in augmenting surgical repair of diseased tendons.

Enhancement of rotator cuff tendon-bone healing with fibroblast growth factor 2 impregnated in gelatin hydrogel sheets in a rabbit model.

BACKGROUND: Application of fibroblast growth factor 2 (FGF-2) may improve the healing response after rotator cuff (RC) surgical repair. This study aimed to determine whether FGF-2-impregnated gelatin hydrogel sheet (GHS) incorporation into the bony trough on the greater tuberosity facilitates healing after RC surgical repair in rabbits. METHODS: We assigned 120 adult male Japanese white rabbits treated with unilateral surgery for supraspinatus tendon repair into the following groups: suture-only group (suture); suture and GHS with phosphate-buffered saline (carrier); suture and GHS with 3 µg of FGF-2 (F3); and suture and GHS with 30 µg of FGF-2 (F30). The effect of FGF-2 was assessed using histologic, biomechanical, and microcomputed tomography evaluations at 2, 6, and 12 weeks. RESULTS: At 12 weeks, loose fibrovascular tissues emerged at the repair site in the suture and carrier groups and dense tendon-like tissues in the F3 and F30 groups, which demonstrated significantly higher ultimate load-to-failure and stress-to-failure at 12 weeks than that in the suture and carrier groups. Microcomputed tomography imaging showed ectopic calcification formation in some specimens from each group. Appearances or frequencies were similar among groups. The histologic and biomechanical effects of FGF-2 on RC healing were obvious at ≥6 weeks postoperatively. CONCLUSION: FGF-2-impregnated GHS incorporation into the bony trough on the greater tuberosity before RC surgical repair is feasible and results in histologic and biomechanical improvements during RC healing in rabbits. No detrimental effect on ectopic calcification was observed.

Rotator Cuff Repair and Overlay Augmentation by Direct Interlocking of a Nonwoven Polyethylene Terephthalate Patch Into the Tendon: Evaluation in an Ovine Model.

BACKGROUND: Arthroscopic repair of large rotator cuff tendon tears is associated with high rates of retear. Construct failure often occurs at the suture-tendon interface. Patch augmentation can improve mechanical strength and healing at this interface. PURPOSE: To introduce a novel technique for suture-free attachment of an overlaid patch and evaluate its biomechanical strength and biological performance. STUDY DESIGN: Descriptive and controlled laboratory studies. METHODS: An established ovine model of partial infraspinatus tendon resection and immediate repair was used. After a nonwoven polyethylene terephthalate patch was overlaid to the resected tendon, a barbed microblade was used to draw fibers of the patch directly into the underlying tissue. In vivo histological assessment of healing was performed at 6 and 13 weeks after implantation. Ex vivo models were used to characterize primary repair strength of the suture-free patch fixation to tendon. Additional ex vivo testing assessed the potential of the technique for patch overlay augmentation of suture-based repair. RESULTS: The in vivo study revealed no macroscopic evidence of adverse tissue reactions to the interlocked patch fibers. Histological testing indicated a normal host healing response with minimal fibrosis. Uniform and aligned tissue ingrowth to the core of the patch was observed from both the tendon and the bone interfaces to the patch. There was no evident retraction of the infraspinatus muscle, lengthening of the tendon, or tendon gap formation over 13 weeks. Ex vivo testing revealed that direct patch interlocking yielded tendon purchase equivalent to a Mason-Allen suture (150 ± 58 vs 154 ± 49 N, respectively; P = .25). In an overlay configuration, fiber interlocked patch augmentation increased Mason-Allen suture retention strength by 88% (from 221 ± 43 N to 417 ± 86 N; P < .01) with no detectable difference in repair stiffness. CONCLUSION: Testing in an ovine model of rotator cuff tendon repair suggested that surgical interlocking of a nonwoven medical textile can provide effective biomechanical performance, support functional tissue ingrowth, and help avoid musculotendinous retraction after surgical tendon repair. CLINICAL RELEVANCE: The novel technique may facilitate patch augmentation of rotator cuff repairs.

Does augmentation with a reinforced fascia patch improve rotator cuff repair outcomes?

BACKGROUND: Scaffold devices are used to augment rotator cuff repairs in humans. While the strength of a novel poly-L-lactic acid-reinforced (human) fascia patch has been documented, it is unclear whether such patches will enhance the strength or likelihood of healing of rotator cuff repairs. QUESTIONS/PURPOSES: In a canine shoulder model, we asked: Do tendon repairs augmented with a reinforced fascia patch have (1) increased biomechanical properties at Time 0 and (2) less tendon retraction and increased cross-sectional area and biomechanical properties after 12 weeks of healing compared to repairs without augmentation? (3) Do the biomechanical properties of tendon repairs reach normal values by 12 weeks of healing? And (4) is the host response associated with use of the reinforced fascia patch biocompatible? METHODS: Eleven dogs underwent bilateral shoulder surgery with partial release and acute repair of the infraspinatus tendon, one shoulder with augmentation and one without augmentation. Repair retraction, cross-sectional area, biomechanical properties, and biocompatibility were assessed at 12 weeks. RESULTS: At Time 0, the mean ± SD ultimate load of augmented repairs was 296 ± 130 N (46% ± 25%) more than nonaugmented repairs, with no difference in stiffness between groups. At 12 weeks, the ultimate load of augmented repairs averaged 192 ± 213 N (15% ± 16%) less than nonaugmented repairs, with no difference in stiffness between groups. At the tendon repair site at 12 weeks, the fascia patch showed a biocompatible host tissue response. CONCLUSIONS: The biomechanical properties of repairs augmented with a reinforced fascia patch demonstrated greater ultimate load at Time 0 than nonaugmented repairs but remained essentially unchanged after 12 weeks of healing, despite improvements in the ultimate load of nonaugmented controls in the same time frame.

Fiber-aligned polymer scaffolds for rotator cuff repair in a rat model.

BACKGROUND: Repair techniques of rotator cuff tendon tears have improved in recent years; nonetheless, the failure rate remains high. Despite the availability of various graft materials for repair augmentation, there has yet to be a biomechanical study using fiber-aligned scaffolds in vivo. The objective of this study was to evaluate the efficacy of fiber-aligned nanofibrous polymer scaffolds as a potential treatment-delivery vehicle in a rat rotator cuff injury model. MATERIALS AND METHODS: Scaffolds with and without sacrificial fibers were fabricated via electrospinning and implanted to augment supraspinatus repair in rats. Repairs without scaffold augmentation were also performed to serve as controls. Rats were sacrificed at 4 and 8 weeks postoperatively, and repairs were evaluated histologically and biomechanically. RESULTS: Both scaffold formulations remained in place, with more noticeable cellular infiltration and colonization at 4 and 8 weeks after injury and repair for scaffolds lacking sacrificial fibers. Specimens with scaffolds were larger in cross-sectional area compared with controls. Biomechanical testing revealed no significant differences in structural properties between the groups. Some apparent material properties were significantly reduced in the scaffold groups. These reductions were due to increases in cross-sectional area, most likely caused by the extra thickness of the implanted scaffold material. No differences were observed between the 2 scaffold groups. CONCLUSIONS: No adverse effect of surgical implantation of overlaid fiber-aligned scaffolds on structural properties of supraspinatus tendons in rat rotator cuff repair was demonstrated, validating this model as a platform for targeted delivery.

Effectiveness of Bone Marrow-Derived Platelet-Rich Fibrin on Rotator Cuff Healing in a Rabbit Degenerative Model.

BACKGROUND: Platelet-rich fibrin (PRF) is a second-generation platelet concentrate. Although peripheral blood-derived PRF (P-PRF) is commonly applied in biological augmentation, there is no report about the therapeutic effect of bone marrow-derived PRF (BM-PRF) for degenerative rotator cuff tears (RCTs). PURPOSE/HYPOTHESIS: To examine the effects of platelet-rich plasma (PRP), P-PRF, and BM-PRF during rotator cuff repair (RCR) in degenerative RCTs in rabbits. We hypothesized that BM-PRF would accelerate the bone-tendon healing after RCR. STUDY DESIGN: Controlled laboratory study. METHODS: Degenerative RCT models were created 2 weeks before beginning the study, and 68 juvenile rabbits were divided into 4 groups: the control, PRP, P-PRF, and BM-PRF groups. RCR without augmentation was done in the control group. PRP was prepared by centrifuging peripheral blood twice using a plastic tube. P-PRF and BM-PRF were prepared by centrifuging peripheral blood and bone marrow, respectively, using a glass tube. Rabbits from PRP, P-PRF, and BM-PRF groups were administered the augmentation in a similar fashion for RCR, between the rotator cuff and the footprint of the humerus. At 4, 8, and 12 weeks, rabbits were euthanized and histologically assessed using hematoxylin and eosin staining, Alcian blue staining, and immunohistochemical staining for type I and III collagen. The sections were also evaluated with immunofluorescence staining of vascular endothelial growth factor (VEGF) at 4 weeks. RESULTS: The continuity was significantly better in the BM-PRF group at 4 weeks (P < .05). Immunofluorescence staining demonstrated that VEGF-positive stained cells were significantly greater in the BM-PRF group than in the control group (P < .01). The modified tendon maturing score was significantly greater in the BM-PRF group than in the control and PRP groups at 12 weeks (P < .05). There was no significant difference in the modified tendon maturing score of the P-PRF group compared with the control group. CONCLUSION: The rabbit model of degenerative RCTs demonstrated that RCR combined with BM-PRF enhanced tendon-bone continuity and increased the VEGF-positive cells at 4 weeks and obtained preferable tendon-bone maturation at 12 weeks. CLINICAL RELEVANCE: RCR augmented with BM-PRF has the potential to improve clinical outcomes for RCTs.

Evaluation of tumor necrosis factor α blockade on early tendon-to-bone healing in a rat rotator cuff repair model.

PURPOSE: The purpose was to determine whether systemic tumor necrosis factor α (TNF-α) blockade can improve rotator cuff healing in a rat model. METHODS: One hundred twenty Lewis rats underwent unilateral detachment and repair of the supraspinatus. Rats were randomized into 2 groups. The experimental group received injections of pegylated soluble tumor necrosis factor receptor type I (3.0 mg/kg every other day for 3 doses). The control group received saline solution on the same dosing schedule. At 2, 4, and 8 weeks, 20 animals in each group were killed (4 for histologic assessment and 16 for biomechanical testing). Outcomes included qualitative histologic assessment to determine new fibrocartilage formation and collagen fiber organization. Immunohistochemical staining was performed to localize TNF-α, ED1 and ED2 macrophages, and tartrate-resistant acidic phosphatase. Biomechanical testing was performed to determine the ultimate load to failure, stiffness, cross-sectional area, and ultimate stress to failure. RESULTS: Qualitative assessments of histology showed that the experimental group had more cartilage formation at 4 weeks but not at 2 or 8 weeks. There was less TNF-α staining in the experimental group at 4 and 8 weeks, and there were fewer ED1 macrophages at 4 weeks compared with controls. The ultimate load to failure was greater in the experimental group compared with controls at 2 weeks (13.3 ± 2.6 N v 11.2 ± 2.7 N, P = .05) and at 4 weeks (21.7 ± 4.6 N v 18.5 ± 2.1 N, P = .04). The experimental group also had a higher stiffness at 2 weeks (7.2 ± 2.3 N/mm v 5.8 ± 1.4 N/mm, P = .04) and at 4 weeks (10.5 ± 2.7 N/mm v 8.4 ± 1.7 N/mm, P = .01). There were no differences in any biomechanical variable at 8 weeks. CONCLUSIONS: TNF-α blockade can improve the biomechanical strength of tendon-bone healing in a rat rotator cuff model at early time points, which corresponded with modest qualitative improvements in histology. However, these differences were not maintained at 8 weeks. CLINICAL RELEVANCE: TNF-α blockade may influence rotator cuff tendon healing.

Arthroscopic GraftJacket repair of rotator cuff tears.

HYPOTHESIS: Management of massive, degenerative, and irreparable rotator cuff tears is challenging. Excessive re-tear rates and poor clinical outcome after standard repair have led to alternative methods of treatment. Tendon transfers and shoulder arthroplasty have had mixed results; both are invasive procedures with high potential morbidity. We began performing rotator cuff augmentation and replacement using GraftJacket allograft acellular human dermal matrix as a biologic minimally invasive alternative in this difficult population almost 6 years ago. This article highlights our preferred arthroscopic technique and early results. MATERIALS AND METHODS: From January 2004 to June 2007, 45 patients (36 men, 9 women) with massive rotator cuff tears were treated arthroscopically with the GraftJacket allograft. All patients completed a preoperative University of California, Los Angeles (UCLA) score. Follow-up was a minimum of 2 years (range, 24-68 months) and patients completed UCLA, Western Ontario Rotator Cuff (WORC), and American Shoulder and Elbow Surgeons (ASES) scores. RESULTS: Analysis was performed using the 3 validated outcomes measurement scores. The mean UCLA score increased from 18.4 preoperatively to 27.5 postoperatively (P < .000). The average WORC score was 75.2, and the ASES score was 84.1 at the final follow-up. DISCUSSION: Evidence-based data to outline an algorithm for management of irreparable rotator cuff tears is being developed. We documented significant clinical improvement with arthroscopic rotator cuff reconstruction using the GraftJacket allograft acellular human dermal matrix. The procedure is safe and associated with high patient satisfaction, without the morbidity of tendon transfer or arthroplasty. For those few cases where further surgery is required, no bridges are burned. The early success of this procedure warrants further study with more patients, longer follow-up, and higher levels of evidence-based investigation.

Histological evaluation of cellular response to a multifilament electrospun suture for tendon repair.

BACKGROUND: Rotator cuff tendon repair in humans is a commonly performed procedure aimed at restoring the tendon-bone interface. Despite significant innovation of surgical techniques and suture anchor implants, only 60% of repairs heal successfully. One strategy to enhance repair is the use of bioactive sutures that provide the native tendon with biophysical cues for healing. We investigated the tissue response to a multifilament electrospun polydioxanone (PDO) suture in a sheep tendon injury model characterised by a natural history of failure of healing. METHODOLOGY AND RESULTS: Eight skeletally mature English Mule sheep underwent repair with electrospun sutures. Monofilament sutures were used as a control. Three months after surgery, all tendon repairs healed, without systemic features of inflammation, signs of tumour or infection at necropsy. A mild local inflammatory reaction was seen. On histology the electrospun sutures were densely infiltrated with predominantly tendon fibroblast-like cells. In comparison, no cellular infiltration was observed in the control suture. Neovascularisation was observed within the electrospun suture, whilst none was seen in the control. Foreign body giant cells were rarely seen with either sutures. CONCLUSION: This study demonstrates that a tissue response can be induced in tendon with a multifilament electrospun suture with no safety concerns.

Dual-modal magnetic resonance and photoacoustic tracking and outcome of transplanted tendon stem cells in the rat rotator cuff injury model.

Stem cells have been used to promote the repair of rotator cuff injury, but their fate after transplantation is not clear. Therefore, contrast agents with good biocompatibility for labeling cell and a reliable technique to track cell are necessary. Here, we developed a micron-sized PLGA/IO MPs to label tendon stem cells (TSCs) and demonstrated that PLGA/IO MPs were safe and efficient for long-term tracking of TSCs by using dual-modal MR and Photoacoustic (PA) imaging both in vitro and in rat rotator cuff injury. Moreover, TSCs improved the repair of injury and the therapeutic effect was not affected by PLGA/IO MPs labeling. We concluded that PLGA/IO particle was a promising dual-modal MR/PA contrast for noninvasive long-term stem cell tracking.

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.

Pro-chondrogenic and immunomodulatory melatonin-loaded electrospun membranes for tendon-to-bone healing.

Reconstructing the native structure of the tendon-to-bone insertion site (enthesis) in rotator cuff repair has always been a great challenge for orthopedic surgeons. Difficulty arises mainly due to the limited enthesis regenerative capability and severe inflammatory cell infiltration, which result in fibrovascular scar formation instead of native cartilage-like enthesis. Therefore, tissue engineering scaffolds with pro-chondrogenic and immunomodulatory capabilities may offer a new strategy for native enthesis regeneration. In this study, melatonin-loaded aligned polycaprolactone (PCL) electrospun fibrous membranes were fabricated. The sustained release of melatonin from this membrane significantly promoted the chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) in a long-term chondroid pellet model. After the membranes were implanted in a rat acute rotator cuff tear model, melatonin-loaded PCL membranes inhibited macrophage infiltration in the tendon-to-bone interface at the early healing phase, increasing chondroid zone formation, promoting collagen maturation, decreasing fibrovascular tissue formation and eventually improving the biomechanical strength of the regenerated enthesis. Taken together, melatonin-loaded PCL membranes possess great clinical application potential for tendon-to-bone healing.

Enhanced tendon-to-bone repair through adhesive films.

Tendon-to-bone surgical repairs have unacceptably high failure rates, possibly due to their inability to recreate the load transfer mechanisms of the native enthesis. Instead of distributing load across a wide attachment footprint area, surgical repairs concentrate shear stress on a small number of suture anchor points. This motivates development of technologies that distribute shear stresses away from suture anchors and across the enthesis footprint. Here, we present predictions and proof-of-concept experiments showing that mechanically-optimized adhesive films can mimic the natural load transfer mechanisms of the healthy attachment and increase the load tolerance of a repair. Mechanical optimization, based upon a shear lag model corroborated by a finite element analysis, revealed that adhesives with relatively high strength and low stiffness can, theoretically, strengthen tendon-to-bone repairs by over 10-fold. Lap shear testing using tendon and bone planks validated the mechanical models for a range of adhesive stiffnesses and strengths. Ex vivo human supraspinatus repairs of cadaveric tissues using multipartite adhesives showed substantial increase in strength. Results suggest that adhesive-enhanced repair can improve repair strength, and motivate a search for optimal adhesives. STATEMENT OF SIGNIFICANCE: Current surgical techniques for tendon-to-bone repair have unacceptably high failure rates, indicating that the initial repair strength is insufficient to prevent gapping or rupture. In the rotator cuff, repair techniques apply compression over the repair interface to achieve contact healing between tendon and bone, but transfer almost all force in shear across only a few points where sutures puncture the tendon. Therefore, we evaluated the ability of an adhesive film, implanted between tendon and bone, to enhance repair strength and minimize the likelihood of rupture. Mechanical models demonstrated that optimally designed adhesives would improve repair strength by over 10-fold. Experiments using idealized and clinically-relevant repairs validated these models. This work demonstrates an opportunity to dramatically improve tendon-to-bone repair strength using adhesive films with appropriate material properties.

Evaluation of a cross-linked acellular porcine dermal patch for rotator cuff repair augmentation in an ovine model.

In this study we evaluated 2 commercially available rotator cuff repair augmentation patches in an in vivo sheep model using mechanical testing and histologic techniques. Bilateral infraspinatus tears were created and repaired in 2 groups of 8 adult ewes. Each group (killed at 9 or 24 weeks) included 5 repaired with suture alone, 6 repaired and augmented with a cross-linked acellular porcine dermal (PD) patch (Zimmer Collagen Repair Patch), and 5 repaired and augmented with a porcine small intestine submucosa (SIS) patch (Restore Orthobiologic Soft Tissue Implant; DePuy Orthopaedics). At 3 weeks, sheep with suture repair and an SIS patch had significant elevation of plasma fibrinogen levels (P < .05) whereas sheep with suture repair and a PD patch elicited no elevation in plasma fibrinogen levels. At 9 weeks, the mean failure load was 201 +/- 60 lb for suture repairs, 182 +/- 63 lb for PD repairs, and 137 +/- 16 lb for SIS repairs. Within any individual sheep, the shoulder undergoing PD repair always had a higher failure load than the contralateral suture or shoulder undergoing SIS repair. At 9 weeks, macrophages were seen on all PD surfaces whereas most of the SIS materials were resorbed. At 24 weeks, failure loads were identical between groups. Macrophages had disappeared from the PD groups, and integration of the PD patch into the surrounding tissue with vascular and fibroblastic invasion was seen. For the SIS group, diverse tissue types (including ectopic bone) were seen.

Stimulation of Rotator Cuff Repair by Sustained Release of Bone Morphogenetic Protein-7 Using a Gelatin Hydrogel Sheet.

Bone morphogenetic protein-7 (BMP-7) promotes not only osteogenesis but also matrix production in chondrocytes and tenocytes. However, because of its short half-life, maintaining local concentrations of BMP-7 is difficult. We examined the use of a gelatin hydrogel sheet (GHS) for the sustained release of BMP-7 in stimulating rotator cuff repair at the tendon-to-bone insertion. Twelve-week-old male Sprague-Dawley rats were used. Radiolabeled BMP-7 ((125)I-BMP-7) was injected into the subacromial bursa in the (125)I-BMP-7 group, whereas a GHS impregnated with (125)I-BMP-7 was implanted on the tendon attached to the tendon-to-bone insertion in the (125)I-BMP-7+GHS group. Levels of (125)I-BMP-7 in the tendon-to-bone insertion were assessed at 1, 3, 7, 14, and 21 postoperative days. The BMP-7 concentrations were significantly higher in the (125)I-BMP-7+GHS group than in the (125)I-BMP-7 group. Next, the bilateral supraspinatus tendons were resected and sutured to the greater tuberosity of the humerus using the Mason-Allen technique. Treatment groups were created as follows: either phosphate-buffered saline (PBS) or BMP-7 was injected into the subacromial bursa in the PBS and BMP-7 groups, whereas a GHS impregnated with either PBS or BMP-7 was implanted on the repaired tendon attached to the tendon-to-bone insertion in the PBS+GHS and BMP-7+GHS groups. The resected specimens were stained at 2, 4, and 8 postoperative weeks with hematoxylin and eosin as well as Safranin O, and tissue repair was evaluated histologically by using the tendon-to-bone maturing score. Tissue repair was assessed biomechanically at 4 and 8 postoperative weeks. The BMP-7+GHS group at 8 postoperative weeks demonstrated a favorable cartilage matrix production and tendon orientation; moreover, the tendon-to-bone maturing score and the ultimate force-to-failure were the highest in this group. The ability of GHS to provide controlled release of various growth factors has been previously reported. We confirmed that the GHS releases BMP-7 in a sustained manner in the rat shoulder joint. At 8 postoperative weeks, the repaired tissue was mostly restored, both histologically and biomechanically, in the BMP-7+GHS group. We therefore conclude that the sustained release of BMP-7 from a GHS can stimulate rotator cuff repair.

Experimental rotator cuff repair. A preliminary study.

BACKGROUND: The repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Prospective studies comparing different repair techniques are difficult to design and carry out because of the many factors that influence structural and clinical outcomes. The objective of this study was to develop a suitable animal model for evaluation of the efficacy of different repair techniques for massive rotator cuff tears and to use this model to compare a new repair technique, tested in vitro, with the conventional technique. METHODS: We compared two techniques of rotator cuff repair in vivo using the left shoulders of forty-seven sheep. With the conventional technique, simple stitches were used and both suture ends were passed transosseously and tied over the greater tuberosity of the humerus. With the other technique, the modified Mason-Allen stitch was used and both suture ends were passed transosseously and tied over a cortical-bone-augmentation device. This device consisted of a poly(L/D-lactide) plate that was fifteen millimeters long, ten millimeters wide, and two millimeters thick. Number-3 braided polyester suture material was used in all of the experiments. RESULTS: In pilot studies (without prevention of full weight-bearing), most repairs failed regardless of the technique that was used. The simple stitch always failed by the suture pulling through the tendon or the bone; the suture material did not break or tear. The modified Mason-Allen stitch failed in only two of seventeen shoulders. In ten shoulders, the suture material failed even though the stitches were intact. Thus, we concluded that the modified Mason-Allen stitch is a more secure method of achieving suture purchase in the tendon. In eight of sixteen shoulders, the nonaugmented double transosseous bone-fixation technique failed by the suture pulling through the bone. The cortical-bone-augmentation technique never failed. In definite studies, prevention of full weight-bearing was achieved by fixation of a ten-centimeter-diameter ball under the hoof of the sheep. This led to healing in eight of ten shoulders repaired with the modified Mason-Allen stitch and cortical-bone augmentation. On histological analysis, both the simple-stitch and the modified Mason-Allen technique caused similar degrees of transient localized tissue damage. Mechanical pullout tests of repairs with the new technique showed a failure strength that was approximately 30 percent of that of an intact infraspinatus tendon at six weeks, 52 percent of that of an intact tendon at three months, and 81 percent of that of an intact tendon at six months. CONCLUSIONS: The repair technique with a modified Mason-Allen stitch with number-3 braided polyester suture material and cortical-bone augmentation was superior to the conventional repair technique. Use of the modified Mason-Allen stitch and the cortical-bone-augmentation device transferred the weakest point of the repair to the suture material rather than to the bone or the tendon. Failure to protect the rotator cuff post-operatively was associated with an exceedingly high rate of failure, even if optimum repair technique was used. CLINICAL RELEVANCE: Different techniques for rotator cuff repair substantially influence the rate of failure. A modified Mason-Allen stitch does not cause tendon necrosis, and use of this stitch with cortical-bone augmentation yields a repair that is biologically well tolerated and stronger in vivo than a repair with the conventional technique. Unprotected repairs, however, have an exceedingly high rate of failure even if optimum repair technique is used. Postoperative protection from tension overload, such as with an abduction splint, may be necessary for successful healing of massive rotator cuff tears.

Reconstruction of a defect of the rotator cuff with polytetrafluoroethylene felt graft. Recovery of tensile strength and histocompatibility in an animal model.

We reconstructed defects in the infraspinatus tendon u sing polytetrafluoroethylene (PTFE) felt grafts in 31 beagle dogs and examined the mechanical responses and histocompatibility. Except for one infected specimen, all the reconstructed infraspinatus tendons healed. We examined eight specimens each immediately after surgery and at six and 12 weeks. The ultimate tensile strength of the reconstructed tendons was 60.84 N, 172.88 N, and 306.51 N immediately after surgery and at six and 12 weeks, respectively. The stiffness of the specimens at the PTFE felt-bone interface was 9.61 kN/m, 64.67 kN/m, and 135.09 kN/m immediately after surgery and at six and 12 weeks, respectively. Six tendons were examined histologically at three, six, 12 and 24 weeks. Histological analysis showed that there was ingrowth of fibrous tissue between the PTFE fibres. Foreign-body reactionswere found at the margin of the PTFE-bone interface between 12 and 24 weeks. The mechanical recovery and tissue affinity of PTFE felt to bone and to tendon support its use for reconstruction of the rotator cuff. The possible development of a foreign-body reaction should be borne in mind.