Implantation of a porcine acellular dermal graft in a primate model of rotator cuff repair

Establishing a rabbit model with massive supraspinatus tendon defect for investigating scaffold-assisted tendon repair

BACKGROUND

Shoulder pain and disability from rotator cuff tears remain challenging clinical problem despite advancements in surgical techniques and materials. To advance our understanding of injury progression and develop effective therapeutics using tissue engineering and regenerative medicine approaches, it is crucial to develop and utilize animal models that closely resemble the anatomy and display the pathophysiology of the human rotator cuff. Among various animal models, the rabbit shoulder defect model is particularly favored due to its similarity to human rotator cuff pathology. However, a standardized protocol for creating a massive rotator cuff defect in the rabbits is not well defined. Therefore, the objective of our study was to establish a robust and reproducible model of a rotator cuff defect to evaluate the regenerative efficacy of scaffolds.

RESULTS

In our study, we successfully developed a rabbit model with a massive supraspinatus tendon defect that closely resembles the common rotator cuff injuries observed in humans. This defect involved a complete transection of the tendon, spanning 10 mm in length and encompassing its full thickness and width. To ensure stable scaffolding, we employed an innovative bridging suture technique that utilized a modified Mason-Allen suture as a structural support. Moreover, to assess the therapeutic effectiveness of the model, we utilized different scaffolds, including a bovine tendon extracellular matrix (ECM) scaffold and a commercial acellular dermal matrix (ADM) scaffold. Throughout the observation period, no scaffold damage was observed. Notably, comprehensive histological analysis demonstrated that the regenerative tissue in the tendon ECM scaffold group exhibited an organized and aligned fiber structure, indicating tendon-like tissue regeneration while the tissue in the ADM group showed comparatively less organization.

CONCLUSIONS

This study presents a comprehensive description of the implemented procedures for the development of a highly reproducible animal model that induces massive segmental defects in rotator cuff tendons. This protocol can be universally implemented with alternative scaffolds to investigate extensive tendon defects and evaluate the efficacy of regenerative treatments. The application of our animal model offers a standardized and reproducible platform, enabling researchers to systematically evaluate, compare, and optimize scaffold designs. This approach holds significant importance in advancing the development of tissue engineering strategies for effectively repairing extensive tendon defects.

Biomimetic gradient scaffolds for the tissue engineering and regeneration of rotator cuff enthesis

Rotator cuff tear is one of the most common musculoskeletal disorders, which often results in recurrent shoulder pain and limited movement. Enthesis is a structurally complex and functionally critical interface connecting tendon and bone that plays an essential role in maintaining integrity of the shoulder joint. Despite the availability of advanced surgical procedures for rotator cuff repair, there is a high rate of failure following surgery due to suboptimal enthesis healing and regeneration. Novel strategies based on tissue engineering are gaining popularity in improving tendon-bone interface (TBI) regeneration. Through incorporating physical and biochemical cues into scaffold design which mimics the structure and composition of native enthesis is advantageous to guide specific differentiation of seeding cells and facilitate the formation of functional tissues. In this review, we summarize the current state of research in enthesis tissue engineering highlighting the development and application of biomimetic scaffolds that replicate the gradient TBI. We also discuss the latest techniques for fabricating potential translatable scaffolds such as 3D bioprinting and microfluidic device. While preclinical studies have demonstrated encouraging results of biomimetic gradient scaffolds, the translation of these findings into clinical applications necessitates a comprehensive understanding of their safety and long-term efficacy.

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.

Decellularized Bovine Pericardial Patch Loaded With Mesenchymal Stromal Cells Enhance the Mechanical Strength and Biological Healing of Large-to-Massive Rotator Cuff Tear in a Rat Model

PURPOSE

The purpose of this study was to determine whether the addition of decellularized bovine pericardial patch loaded with mesenchymal stromal cells enhanced bone-to-tendon healing and improved the biomechanical strength of large-to-massive rotator cuff tears in a small animal model.

METHODS

Adipose-derived mesenchymal stromal cells (MSCs) from rat inguinal fat were isolated, cultured, and loaded onto decellularized bovine pericardium patches. To simulate large-to-massive tears, rats were managed with free cage activity for 6 weeks after tear creation. A total of 18 rats were randomly allocated to repair-only (control), repair with pericardial patch augmentation (patch), or repair with MSC loaded pericardial patch augmentation (patch-MSC). Each group had 6 rats (one shoulder of each rat was used for histological evaluation and another for biomechanical evaluation). MSCs seeded on the pericardial patches were traced on four shoulders from 2 other rats at 4 weeks after surgery. Histological evaluation for bone-to-tendon healing and biomechanical testing was carried out at 8 weeks after repair.

RESULTS

MSCs tagged with a green fluorescent protein were observed in the repair site 4 weeks after the repair. One shoulder each in the control and patch groups showed complete discontinuity between the bone and tendon. One shoulder in the control group showed attenuation with only a tenuous connection. Fibrocartilage and tidemark formation at the bone-to-tendon interface (P = .002) and collagen fiber density (P = .040) and orientation (P = .003) were better in the patch-MSC group than in the control or patch group. Load-to-failure in the patch-MSC and patch groups was higher than that in the control group (P = .001 and .009, respectively).

CONCLUSION

Decellularized bovine pericardial patches loaded with adipose-derived and cultured mesenchymal stromal cells enhanced healing in terms of both histology and mechanical strength at 8 weeks following rotator cuff repair in a rat model.

CLINICAL RELEVANCE

Large-to-massive rotator tears need a strategy to prevent retear and enhance healing. The addition of decellularized bovine pericardial patch loaded with MSCs can enhance bone-to-tendon healing and improve biomechanical healing of large-to-massive rotator cuff tears following repair.

Large animal models for the study of tendinopathy

Tendinopathy has a high incidence in athletes and the aging population. It can cause pain and movement disorders, and is one of the most difficult problems in orthopedics. Animal models of tendinopathy provide potentially efficient and effective means to develop understanding of human tendinopathy and its underlying pathological mechanisms and treatments. The selection of preclinical models is essential to ensure the successful translation of effective and innovative treatments into clinical practice. Large animals can be used in both micro- and macro-level research owing to their similarity to humans in size, structure, and function. This article reviews the application of large animal models in tendinopathy regarding injuries to four tendons: rotator cuff, patellar ligament, Achilles tendon, and flexor tendon. The advantages and disadvantages of studying tendinopathy with large animal models are summarized. It is hoped that, with further development of animal models of tendinopathy, new strategies for the prevention and treatment of tendinopathy in humans will be developed.

Stem cell sheet interpositioned between the tendon and bone would be better for healing than stem cell sheet overlaid above the tendon-to-bone junction in rotator cuff repair of rats

BACKGROUND

Although stem cells might enhance natural enthesis healing in surgical rotator cuff repair, not much attention has been given to the delivery and location of delivering stem cells. The purpose of this study to know where to locate those stem cells during repair.

METHODS

Animal model of chronic rotator cuff tear was created in 24 rats. Adipose-derived stem cells were engineered as a sheet and transplanted 1) between a torn tendon and humerus (interposition group) or 2) over a repaired tendon-to-bone junction (overlay group) at the time of surgical repair. Tracking of stem cells with overexpression of green fluorescent protein (GFP) were carried out at the time of sacrifice in additional 4 shoulders in each group. Histological and Biomechanical evaluation was performed to compare the differences in tendon-to-bone healing.

RESULTS

Histology showed increased fibrocartilage, a clear boundary at the mineralized fibrocartilage, abundant collagen type III, and higher total scores, especially in the interposition group. GFP-overexpression was observed at the transplanted site at 2 weeks after repair. Although two groups where stem cell sheets applied showed higher load to failure than the repair-only group, the load to failure was not different between the interposition and overlay group.

CONCLUSION

In the chronic rotator cuff repair model, stem cell sheets enhanced regeneration of the tendon-to-bone junction. This regeneration was effective when the stem cell sheet was interpositioned at the tendon-to-bone interface.

LEVEL OF EVIDENCE

Basic Science Study; In Vivo Animal Model; Histology and Biomechanics.

Integration and functional performance of a decellularised porcine superflexor tendon graft in an ovine model of anterior cruciate ligament reconstruction

The objective was to evaluate the performance of decellularised porcine superflexor tendon (pSFT) as an anterior cruciate ligament (ACL) reconstruction device. The ACL of adult sheep was reconstructed with decellularised pSFT or ovine allograft SFT and animals sacrificed at 4, 12 and 26 weeks (n = 4 per group) for biological evaluation and 26 weeks (n = 6) for biomechanical evaluation of the grafts. Both grafts showed good in vivo performance with no major differences at macroscopic evaluation post euthanasia. Histopathology revealed an inflammatory reaction to both grafts at 4 weeks, which reduced by 26 weeks. There was advanced cellular ingrowth from 12 weeks, ligamentisation of intra-articular grafts, ossification and formation of Sharpey's fibers at the graft/bone junctions. Immunohistochemistry showed that at 4 and 12 weeks, the host response was dominated by CD163+ M2 macrophages and a cell infiltrate comprising α-SMA + myofibroblasts, CD34+ and CD271+ progenitor cells. At 26 weeks the biomechanical properties of decellularised pSFT and oSFT grafts were comparable, with all grafts failing in the intra-articular region. This study provides new insight into constructive remodelling of tendons used for ACL replacement and evidence of integration and functional performance of a decellularised xenogeneic tendon with potential as an alternative for ACL reconstruction.

Histologic Analysis of Porcine Dermal Graft Augmentation in Treatment of Rotator Cuff Tears

BACKGROUND

Biologic augmentation via extracellular matrix (ECM) scaffolds has been utilized to address rotator cuff tears with poor-quality tissue.

PURPOSE

To evaluate the cellular changes in graft explants taken from patients treated with porcine dermal grafts for rotator cuff tears.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Four graft biopsy specimens were obtained from patients treated with porcine dermal grafts in an interposition technique for rotator cuff tears and compared with a nonimplanted graft and a normal rotator cuff specimen. Biopsy of the graft site was performed at 18 days, 3 months, 7 months, and 10.5 months after implantation. Hematoxylin and eosin staining was used to evaluate for cellular and vascular changes. Picrosirius red (PSR) stain with 90° polarized light was performed to evaluate collagen fibril size and orientation. All biopsy specimens were analyzed by a pathologist.

RESULTS

There was evidence of progressive remodeling of the porcine dermal grafts. The most mature grafts demonstrated vessel infiltration and extensive remodeling without evidence of inflammation, foreign body reaction, or tissue rejection. PSR demonstrated increased organization of collagen domains, resembling normal tendon by 10.5 months postoperatively.

CONCLUSION

This series suggests that ECM grafts may serve as an effective scaffold for host cell infiltration, collagen reorganization, and vascularization as a result of histologic changes demonstrated with retrieval of specimens from patients with rotator cuff tears that were augmented with porcine dermal grafts.

Use of biologics in rotator cuff disorders: Current concept review

Poor tendon to bone healing following rotator cuff repair has led to the continued interest and investigation into biological augmentation. The biology of tendinopathy is not fully understood and consequently the availability of disease modifying therapeutic targets is limited. A ceiling of benefit has been reached by mechanical optimisation of rotator cuff repair and thus, in order to improve healing rates, a biological solution is required. This review focuses on the strategies to biologically augment rotator cuff disorders with an emphasis on rotator cuff repair. Leucocyte rich platelet rich plasma has been shown to improve healing rates without clinically relevant improvements in outcome scores. Similarly, improved healing rates have also been reported with bone marrow stimulation and in long-term follow-up with bone marrow concentrate. Extracellular matrix (ECM) and synthetic scaffolds can increase healing through mechanical and or biological augmentation. A potential third category of scaffold is bio-inductive and has no mechanical support. Studies involving various scaffolds have shown promising results for augmentation of large to massive tears and is likely to be most beneficial when tendon quality is poor, however level I evidence is limited.

Decellularized xenografts in regenerative medicine: From processing to clinical application

Decellularized xenografts are an inherent component of regenerative medicine. Their preserved structure, mechanical integrity and biofunctional composition have well established them in reparative medicine for a diverse range of clinical indications. Nonetheless, their performance is highly influenced by their source (ie species, age, tissue) and processing (ie decellularization, crosslinking, sterilization and preservation), which govern their final characteristics and determine their success or failure for a specific clinical target. In this review, we provide an overview of the different sources and processing methods used in decellularized xenografts fabrication and discuss their effect on the clinical performance of commercially available decellularized xenografts.

Rotator cuff repair with biological graft augmentation causes adverse tissue outcomes

Background and purpose - Biological patches can be used to augment rotator cuff tendon repair in an attempt to improve healing and reduce rates of re-rupture. However, little is known about the in vivo tissue response to these patches. We assessed native rotator cuff tissue response after surgical repair and augmentation with 2 commercially available extracellular matrix (ECM) patches. Patients and methods - Patients underwent a rotator cuff repair augmented with either GraftJacket (Wright Medical), Permacol (Zimmer Biomet), or no patch (Control), applied using an onlay technique. A sample of supraspinatus tendon was collected intraoperatively and 4 weeks post-surgery, using ultrasound-guided biopsy. Histology and immunohistochemistry were performed on all samples. Results - The Permacol group (n = 3) and GraftJacket group (n = 4) demonstrated some changes in native tendon ECM compared with the control group (n = 3). Significant disruption of the extracellular matrix of the repaired native supraspinatus, underlying both patches, was observed. The patches did not generally increase cellularity, foreign body giant cell count, or vascularity compared to the control group. 1 patient in the Permacol group had an adverse tissue immune response characterized by extensive infiltration of IRF5+, CD68+, and CD206+ cells, suggesting involvement of macrophages with a pro-inflammatory phenotype. No significant differences in protein expression of CD4, CD45, CD68, CD206, BMP7, IRF5, TGFß, and PDPN were observed among the groups. Interpretation - Histological and immunohistochemical analysis of native tendon tissue after patch augmentation in rotator cuff repair raises some concerns about a lack of benefit and potential for harm from these materials.

Engineered Cell Sheets for the Effective Delivery of Adipose-Derived Stem Cells for Tendon-to-Bone Healing

BACKGROUND

Efforts are being made to treat rotator cuff tears (RCTs) that exhibit poor healing and high retear rates. Tendon-to-bone healing using mesenchymal stem cells is being explored, but research is needed to establish effective delivery options.

PURPOSE

To evaluate the effects of an adipose-derived stem cell (ADSC) sheet on mesenchymal stem cell delivery for tendon-to-bone healing of a chronic RCT in rats and to demonstrate that ADSC sheets enhance tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Mesenchymal stem cells were obtained from rat adipose tissue, and a cell sheet was prepared using a temperature-responsive dish. To evaluate the efficacy of stem cells produced in a sheet for the lesion, the experiment was conducted with 3 groups: repair group, cell sheet transplantation after repair group, and cell sheet-only group. Histological, biomechanical, and micro-computed tomography (micro-CT) results were compared among the groups.

RESULTS

Hematoxylin and eosin staining for histomorphological analysis revealed that the cell sheet transplantation after repair group (5.75 ± 0.95) showed statistically significant higher scores than the repair (2.75 ± 0.50) and cell sheet-only (3.25 ± 0.50) groups (P < .001). On safranin O staining, the cell sheet transplantation after repair group (0.51 ± 0.04 mm²) had a larger fibrocartilage area than the repair (0.31 ± 0.06 mm²) and cell sheet-only (0.32 ± 0.03 mm²) groups (P = .001). On micro-CT, bone volume/total volume values were significantly higher in the cell sheet transplantation after repair group (23.98% ± 1.75%) than in the other groups (P < .039); there was no significant difference in the other values. On the biomechanical test, the cell sheet transplantation after repair group (4 weeks after repair) showed significantly higher results than the other groups (P < .005).

CONCLUSION

Our study shows that engineered stem cells are a clinically feasible stem cell delivery tool for rotator cuff repair.

CLINICAL RELEVANCE

This laboratory study provides evidence that ADSCs are effective in repairing RCTs, which are common sports injuries.

Remnant Tendon Preservation Enhances Rotator Cuff Healing: Remnant Preserving Versus Removal in a Rabbit Model

PURPOSE

To assess whether anatomic repair preserving remnant tendon tissue can enhance tendon-to-bone healing biomechanically and histologically in a rabbit rotator cuff tear model.

METHODS

In this controlled laboratory study, bilateral infraspinatus tenotomy from the greater tuberosity, with remnant tendon on the footprint, was performed in 26 New Zealand white rabbits. An open transosseous technique was used to perform bilateral infraspinatus tendon repair 1 week later. Preservation and removal of the remaining tendon were performed on the left and right sides, respectively. Seven rabbits each were killed humanely for biomechanical testing and 6 rabbits each were killed humanely for histologic evaluation at 4 and 12 weeks.

RESULTS

Significantly superior biomechanical properties were shown in the remnant tissue-preservation group at 4 and 12 weeks in terms of maximum load (89.6 ± 24.3 N vs 68.2 ± 20.7 N at 4 weeks, P = .048; 120.8 ± 27.5 N vs 93.3 ± 25.1 N at 12 weeks, P = .035) and stiffness (25.3 ± 3.4 N/mm vs 17.7 ± 5.2 N/mm at 4 weeks, P = .009; 26.7 ± 5.2 N/mm vs 19.4 ± 5.2 N/mm at 12 weeks, P < .001). Improved bone-tendon interface histologic maturity scores (14.8 ± 0.9 vs 8.2 ± 1.5 at 4 weeks, P = .027; 16.8 ± 0.7 vs 10.5 ± 1.4 at 12 weeks, P = .027) and large metachromasia areas (0.117 ± 0.053 mm² vs 0.032 ± 0.017 mm² at 4 weeks, P = .022; 0.14 ± 0.046 mm² vs 0.037 ± 0.016 mm² at 12 weeks, P = .007) were obtained in the preservation group compared with the removal group at 4 and 12 weeks.

CONCLUSIONS

This study showed that preserving remnant tissue in anatomic repair can significantly improve rotator cuff healing compared with remnant tissue removal on the footprint in terms of biomechanical properties, bone-tendon interface histologic maturity scores, and metachromasia at 4 and 12 weeks after repair in a rabbit rotator cuff tear model.

CLINICAL RELEVANCE

The results suggest that preservation of remnant tissue on the footprint containing the native bone-tendon interface, when present, may be a better option for rotator cuff healing in rotator cuff repair surgery.

Small Subchondral Drill Holes Improve Marrow Stimulation of Rotator Cuff Repair in a Rabbit Model of Chronic Rotator Cuff Tear

BACKGROUND

Microfracture of the greater tuberosity has been proved effective for enhancing tendon-to-bone healing after rotator cuff repair. However, no standard diameter for the microfracture has been established.

PURPOSE/HYPOTHESIS

This study aimed to assess treatment with large- and small-diameter microfractures to enhance healing during rotator cuff repair surgery in a rabbit model of chronic rotator cuff tear. It was hypothesized that a small-diameter microfracture had advantages in terms of tendon-to-bone integration, bone-tendon interface maturity, microfracture healing, and biomechanical properties compared with a large-diameter microfracture.

STUDY DESIGN

Controlled laboratory study.

METHODS

Bilateral supraspinatus tenotomy from the greater tuberosity was performed on 21 New Zealand White rabbits. Bilateral supraspinatus repair was performed 6 weeks later. Small-diameter (0.5 mm) microfracture and large-diameter microfracture (1 mm) were performed on the left side and right side, respectively, in 14 rabbits as a study group, and simple repair without microfracture was performed in 7 rabbits as a control group. At 12 weeks later, 7 of 14 rabbits in the study group were sacrificed for micro-computed tomography evaluation and biomechanical testing. Another 6 rabbits were sacrificed for histological evaluation. In the control group, 3 of the 7 rabbits were sacrificed for histological evaluation and the remaining rabbits were sacrificed for biomechanical testing.

RESULTS

Significantly better bone-to-tendon integration was observed in the small-diameter microfracture group. Better histological formation and maturity of the bone-tendon interface corresponding to better biomechanical results (maximum load to failure and stiffness) were obtained on the small-diameter microfracture side compared with the large-diameter side and the control group. The large-diameter microfracture showed worse radiographic and histological properties for healing of the microfracture holes on the greater tuberosity. Additionally, the large-diameter microfracture showed inferior biomechanical properties but similar histological results compared with the control group.

CONCLUSION

Small-diameter microfracture showed advantages with enhanced rotator cuff healing for biomechanical, histological, and radiographic outcomes compared with large-diameter microfracture, and large-diameter microfracture may worsen the rotator cuff healing.

CLINICAL RELEVANCE

This animal study suggested that a smaller diameter microfracture may be a better choice to enhance healing in clinical rotator cuff repair surgery in humans.

Arthroscopic Superior Capsular Reconstruction With Acellular Porcine Dermal Xenograft for the Treatment of Massive Irreparable Rotator Cuff Tears

Purpose

To evaluate the short-term clinical outcomes and the complications related to arthroscopic superior capsular reconstruction (SCR) with acellular porcine dermal xenograft for the treatment of irreparable massive rotator cuff tears.

Methods

A prospective observational study of patients treated with arthroscopic SCR for irreparable massive rotator cuff tears in the period from 2016 to 2017 was performed. Range of motion and Shoulder Pain and Disability Index (SPADI) scores were assessed preoperatively, at 6 months postoperatively, and at 12 months postoperatively.

Results

A total of 20 shoulders in 19 patients, with an average age of 60 years, were included in the study. Twelve patients met the criterion for the minimal clinically important difference in the SPADI score. The mean SPADI score showed significant improvement from 51.3% to 10.4% at 1-year follow-up. Active abduction improved from 65.4° to 149.3° and active forward flexion improved from 68.6° to 151.4° at 1-year follow-up. The procedure had a 30% complication rate, including a 15% rate of immunologic rejection of the xenograft. Five patients underwent revision procedures, including arthroscopic debridement and removal of xenograft residuals, implantation of a balloon spacer, and revision SCR with a fascia lata autograft.

Conclusions

Arthroscopic SCR with an acellular porcine dermal xenograft led to a successful outcome in 60% of cases. The procedure showed a quite high complication rate; the most severe cases were related to acute immunologic rejection of the xenograft.

Level of Evidence

Level IV, case series.

Minimally invasive fascia lata harvesting in ASCR does not produce significant donor site morbidity

PURPOSE

The aim of this study was to prospectively evaluate donor site morbidity in arthroscopic superior capsular reconstruction using a minimally invasive harvested fascia lata autograft.

METHODS

Fifteen consecutive patients underwent arthroscopic superior capsular reconstruction by the senior author using a fascia lata autograft harvested in a minimally invasive fashion. All patients were prospectively evaluated at 1 week, 6 and 18 months postoperatively. The subjects' body mass index, age, actual or previous corticosteroid therapy history and active smoking habits were evaluated. Functional outcomes were assessed by the non-arthritic hip score applied to the harvested and contralateral thighs. Every patient completed standardized subjective satisfaction questionnaires at all evaluations. The median patient age was 65.5 years (range 47-77). Nine patients (60%) were females, and six (40%) were males. One patient (6.7%) was within the normal range of weight, nine (60%) were overweight, four (27%) were obese, and one (6.7%) was extremely obese. Two patients (13%) were active smokers. No patients had an active or previous record of corticosteroid therapy. No patients required postoperative lower limb physical therapy.

RESULTS

In terms of overall and cosmetic satisfaction, most patients reported that they were satisfied or very satisfied at all evaluations, and the proportion of very satisfied patients increased over time (p < 0.001). The harvested thigh's functional scores were 91% (p = 0.003) and 94% (p = 0.008) of the healthy thigh's score at 6 and 18 months, respectively. The complications reported were mild, and their proportions decreased in the first 18 months after surgery (p = 0.04).

CONCLUSIONS

The minimally invasive fascia lata harvesting technique for arthroscopic superior capsular reconstruction leads to donor site satisfactory subjective results and good functional outcomes at 18 months after surgery. According to these findings, donor site morbidity is not a valid argument against the use of this autograft for arthroscopic superior capsular reconstruction.

LEVEL OF EVIDENCE

Case series, level IV.

Surgical repair of large-to-massive rotator cuff tears seems to be a better option than patch augmentation or débridement and biceps tenotomy: a prospective comparative study

BACKGROUND

This prospective study compared the outcomes after 3 different treatments for large and massive rotator cuff tears.

METHODS

Patients with a diagnosis of large-to-massive rotator cuff tears were prospectively included. Patients were allocated in 3 groups: (1) arthroscopic complete repair (repair group), (2) open repair and xenograft patch augmentation (patch group), and (3) arthroscopic débridement and tenotomy of the long head of the biceps (débridement group). Patients were evaluated preoperatively and postoperatively at 3, 6, 12 and 24 months. The primary outcome measure was the Constant-Murley score.

RESULTS

The study included 32 consecutive patients. The mean improvement in the Constant-Murley score was +29.1 for the repair group (P < .01), +32.2 for the patch group (P < .01), and +20.1 for the débridement group (P < .01) at the final follow-up examination. No differences were found between the repair and patch groups, but the difference became significant between the débridement group and the patch group (P < .001) and also between the débridement group and the repair group (P < .002) at 12 months and the final follow-up. Moreover, 5 complications occurred in 11 patients in the patch group, whereas there was only 1 complication in the repair group and no complications in the débridement group.

CONCLUSION

The use of porcine dermis patches to augment repairs of massive and irreparable rotator cuff tears is not recommended because there is no benefit compared with repair without augmentation and patches result in more complications.

Evaluation of Decellularized Bovine Tendon Sheets for Achilles Tendon Defect Reconstruction in a Rabbit Model

BACKGROUND

Achilles tendon (AT) defects frequently occur in trauma and chronic injuries. Currently, no method can satisfactorily reconstruct the AT with completely restored function.

PURPOSE

To evaluate the postoperative outcomes of AT defect reconstruction with decellularized bovine tendon sheets (DBTSs) in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

DBTSs were prepared from bovine tendons after compression, decellularization, antigen extraction, freeze drying, and sterilization. Platelet-rich plasma (PRP) was obtained by differential centrifugation. Sixty-three rabbits were used in this study, and the AT defect model was created bilaterally. All rabbits were divided into 3 groups (n = 21). In the DBTS group and the DBTS + PRP group, 2-cm-long AT was excised and reconstructed by DBTSs or PRP-treated DBTSs. In the control group, the rabbits underwent AT transection, and stumps were sutured. After surgery, all rabbits were assessed by ultrasonography and magnetic resonance imaging and then sacrificed for histological examination and biomechanical testing at 4, 8, or 12 weeks.

RESULTS

Gross observations demonstrated the absence of immunologic incompatibility and rejection. Histological examination showed that DBTSs promoted host cell infiltration and new fibrous tissue integration as compared with the control group. In each group, there was an AT-like structure formation and aligned collagen fiber deposition at 12 weeks. Mechanical properties of the reconstructed AT were not significantly different among the 3 groups at 4, 8, and 12 weeks after surgery ( P > .05). Ultrasonography and magnetic resonance imaging results illustrated that the reconstructed AT from each group maintained remodeling, and there was no significant difference in the echogenicity scoring ( P > .05) and percentages of good and excellent ( P > .05) among the 3 groups.

CONCLUSION

DBTSs, which retain the native tendon structure and bioactive factors, had the ability to remodel and integrate into the rabbit AT and improve the healing process.

CLINICAL RELEVANCE

DBTSs could serve as an effective bioscaffold to reconstruct AT defects.

Orthopaedic regenerative tissue engineering en route to the holy grail: disequilibrium between the demand and the supply in the operating room

Orthopaedic disorders are very frequent, globally found and often partially unresolved despite the substantial advances in science and medicine. Their surgical intervention is multifarious and the most favourable treatment is chosen by the orthopaedic surgeon on a case-by-case basis depending on a number of factors related with the patient and the lesion. Numerous regenerative tissue engineering strategies have been developed and studied extensively in laboratory through in vitro experiments and preclinical in vivo trials with various established animal models, while a small proportion of them reached the operating room. However, based on the available literature, the current strategies have not yet achieved to fully solve the clinical problems. Thus, the gold standards, if existing, remain unchanged in the clinics, notwithstanding the known limitations and drawbacks. Herein, the involvement of regenerative tissue engineering in the clinical orthopaedics is reviewed. The current challenges are indicated and discussed in order to describe the current disequilibrium between the needs and solutions made available in the operating room. Regenerative tissue engineering is a very dynamic field that has a high growth rate and a great openness and ability to incorporate new technologies with passion to edge towards the Holy Grail that is functional tissue regeneration. Thus, the future of clinical solutions making use of regenerative tissue engineering principles for the management of orthopaedic disorders is firmly supported by the clinical need.

Preliminary Results of Arthroscopic Superior Capsule Reconstruction with Dermal Allograft

PURPOSE

The purpose of this study was to evaluate the short-term outcomes of arthroscopic superior capsule reconstruction (SCR) with dermal allograft for the treatment of irreparable massive rotator cuff tears (MRCTs).

METHODS

A multicenter study was performed on patients undergoing arthroscopic SCR for irreparable MRCTs. The minimum follow-up was 1 year. Range of motion and functional outcome according to visual analog scale (VAS) pain, American Shoulder and Elbow Surgeons (ASES) score, and subjective shoulder value (SSV) score were assessed preoperatively and at final follow-up. Radiographs were used to evaluate the acromiohumeral interval (AHI).

RESULTS

Fifty-nine patients with a mean age of 62.0 years had a minimum follow-up of 1 year. Twenty-five patients (42.4%) had a prior rotator cuff repair. Forward flexion improved from 130° preoperative to 158° postoperative, and external rotation improved from 36° to 45°, respectively (P < .001). Compared with preoperative values, the VAS decreased from 5.8 to 1.7, the ASES score improved from 43.6 to 77.5, and the SSV score improved from 35.0 to 76.3 (P < .001). The AHI was 6.6 mm at baseline and improved to 7.6 mm at 2 weeks postoperatively but decreased to 6.7 mm at final follow-up. Based on postoperative magnetic resonance imaging, 45% (9 of 20) of the grafts demonstrated complete healing. Forty-six (74.6%) cases were considered a success. Eleven patients (18.6%) underwent a revision procedure including 7 reverse shoulder arthroplasties.

CONCLUSIONS

Arthroscopic SCR using dermal allograft provides a successful outcome in approximately 70% of cases in an initial experience. The preliminary results are encouraging in this difficult to manage patient population, but precise indications are important and graft healing is low in our initial experience.

LEVEL OF EVIDENCE

Level IV, case series.

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.

Induced Remodeling of Porcine Tendons to Human Anterior Cruciate Ligaments by α-GAL Epitope Removal and Partial Cross-Linking

This review describes a novel method developed for processing porcine tendon and other ligament implants that enables in situ remodeling into autologous ligaments in humans. The method differs from methods using extracellular matrices (ECMs) that provide postoperative orthobiological support (i.e., augmentation grafts) for healing of injured ligaments, in that the porcine bone-patellar-tendon-bone itself serves as the graft replacing ruptured anterior cruciate ligament (ACL). The method allows for gradual remodeling of porcine tendon into autologous human ACL while maintaining the biomechanical integrity. The method was first evaluated in a preclinical model of monkeys and subsequently in patients. The method overcomes detrimental effects of the natural anti-Gal antibody and harnesses anti-non-gal antibodies for the remodeling process in two steps: Step 1. Elimination of α-gal epitopes—this epitope that is abundant in pigs (as in other nonprimate mammals) binds the natural anti-Gal antibody, which is the most abundant natural antibody in humans. This interaction, which can induce fast resorption of the porcine implant, is avoided by enzymatic elimination of α-gal epitopes from the implant with recombinant α-galactosidase. Step 2. Partial cross-linking of porcine tendon with glutaraldehyde—this cross-linking generates covalent bonds in the ECM, which slow infiltration of macrophages into the implant. Anti-non-gal antibodies are produced in recipients against the multiple porcine antigenic proteins and proteoglycans because of sequence differences between human and porcine homologous proteins. Anti-non-gal antibodies bind to the implant ECM, recruit macrophages, and induce the implant destruction by directing proteolytic activity of macrophages. Partial cross-linking of the tendon ECM decreases the extent of macrophage infiltration and degradation of the implant and enables concomitant infiltration of fibroblasts that follow the infiltrating macrophages. These fibroblasts align with the implant collagen fibers and secrete their own collagen and other ECM proteins, which gradually remodel the porcine tendon into human ACL. This ligamentization process lasts ∼2 years and the biomechanical integrity of the graft is maintained throughout the whole period. These studies are the first, and so far the only, to demonstrate remodeling of porcine tendon implants into permanently functional autologous ACL in humans.

Novel fiber-based pure chitosan scaffold for tendon augmentation: biomechanical and cell biological evaluation

One possibility to improve the mechanical properties after tendon ruptures is augmentation with a scaffold. Based on wet spinning technology, chitosan fibres were processed to a novel pure high-grade multifilament yarn with reproducible quality. The fibres were braided to obtain a 3D tendon scaffold. The CS fibres and scaffolds were evaluated biomechanically and compared to human supraspinatus (SSP) tendons. For the cytobiological characterization, in vitro cell culture experiments with human mesenchymal stem cells (hMSC) were performed. Three types of 3D circular braided scaffolds were fabricated. Significantly, higher ultimate stress values were measured for scaffold with larger filament yarn, compared to scaffold with smaller filament yarn. During cultivation over 28 days, the cells showed in dependence of isolation method and/or donor a doubling or tripling of the cell number or even a six-fold increase on the CS scaffold, which was comparable to the control (polystyrene) or in the case of cells obtained from human biceps tendon even higher proliferation rates. After 14 days, the scaffold surface was covered homogeneously with a cell layer. In summary, the present work demonstrates that braided chitosan scaffolds constitute a straightforward approach for designing tendon analogues, maintaining important flexibility in scaffold design and providing favourable mechanical properties of the resulting construct.

[Biomaterials in orthopedics]

Biomaterials are artificial or natural materials, which are used in living organisms for a wide variety of reasons. Currently, there are biomaterials available for practically all types of tissue and can fulfill temporary and permanent functions. Ideally, materials used for temporary roles should be completely resorbed after the fulfilling the function and those with a permanent role should remain stable within the body. Many of the currently available biomaterials do not possess these optimal features. Those with temporary roles often remain unchanged within the organism or only induce an incomplete regeneration and those with permanent roles suffer biological alterations which reduce the function. Despite the enormous number of biomaterials, it must always be considered whether the therapeutic target can be achieved without using an implant.

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.

Mini-open suture bridge repair with porcine dermal patch augmentation for massive rotator cuff tear: surgical technique and preliminary results

Background

The aim of this study was to describe the mini-open suture bridge technique with porcine dermal patch augmentation for massive rotator cuff tear and to assess preliminary clinical and radiological results.

Methods

Five patients with massive rotator cuff tear for which it was not possible to restore the anatomical footprint underwent mini-open suture bridge repair using a porcine dermal patch. The patients' average age was 53.4 years (range, 45 to 57 years), and the average duration of follow-up was 20.6 months (range, 14 to 26 months). Patients were evaluated with preoperative and postoperative outcome measures, including a visual analog scale (VAS) for pain, the University of California Los Angeles (UCLA) score, and the American Shoulder and Elbow Surgeons (ASES) score. The structural integrity of repaired rotator cuffs was assessed by magnetic resonance imaging 6 months postoperatively.

Results

The average VAS pain score, UCLA score, and ASES score improved from 6.8, 15.4, and 39.4 preoperatively to 0.8, 31.2, and 86.4 postoperatively (p = 0.041, 0.042, and 0.043, respectively). Magnetic resonance images obtained at an average of 8 months after surgery showed that four patients had intact repair integrity with graft incorporation. One patient had a re-tear with partial healing but still had a satisfactory clinical outcome. There was no intraoperative or postoperative complication in any patient.

Conclusions

Mini-open suture bridge repair with porcine dermal patch augmentation can be an option in young patients with high physical demands and massive rotator cuff tears for which it is not possible to restore the anatomical footprint.

The role of animal models in tendon research

Tendinopathy is a debilitating musculoskeletal condition which can cause significant pain and lead to complete rupture of the tendon, which often requires surgical repair. Due in part to the large spectrum of tendon pathologies, these disorders continue to be a clinical challenge. Animal models are often used in this field of research as they offer an attractive framework to examine the cascade of processes that occur throughout both tendon pathology and repair. This review discusses the structural, mechanical, and biological changes that occur throughout tendon pathology in animal models, as well as strategies for the improvement of tendon healing.

Cite this article: Bone Joint Res 2014;3:193–202.

Factors influencing the long-term behavior of extracellular matrix-derived scaffolds for musculoskeletal soft tissue repair

Musculoskeletal connective tissues such as tendon, ligament, and cartilage possess a limited ability for self-repair. Tissue engineering seeks to use combinations of cells, bioactive molecules, and biomaterials to develop new treatment options for the repair or replacement of damaged tissues. The use of native extracellular matrix as scaffold material for tissue engineering has become increasingly attractive because such tissues can not only provide structural support, but also regulate cell behavior. Although demineralized bone matrix has long been recognized for its osteoinductive abilities, recent studies have identified the ability of cartilage and tendon extracellular matrices to stimulate the differentiation of mesenchymal or adipose-derived adult stem cells toward chondrogenic or tenogenic lineages, respectively. This review discusses the motivation for fabricating scaffolds from musculoskeletal tissues, the in vitro and in vivo efficacy of these tissue-derived scaffolds, and various processing techniques such as decellularization or cross-linking that can mitigate immunogenic responses, moderate the degradation profile, and enhance the mechanical properties of these constructs following long-term implantation in vivo.

Application of acellular dermal xenografts in full-thickness skin burns

The aim of this study was to explore the clinical value of the porcine acellular dermal xenograft (ADX) in combination with autologous split-thickness skin and pure autologous split-thickness skin grafting applied in deep full-thickness burns and scar wounds. A total of 30 patients with deep burns were randomly divided into experimental and control groups following escharectomy. The patients were separately treated with porcine acellular dermal xenograft (ADX) in combination with autologous split-thickness skin and pure autologous split-thickness skin graft. The wound healing was observed routinely and the scores were evaluated using Vancouver scar scale at different times following transplant surgery. The samples of cograft regions and the control group (pure transplant split-thickness skin autograft) were observed using light microscopy and electron microscopy, and the follow-up results were recorded. No conspicuous rejections on the cograft wound surface were observed. Compared with the control group, the cograft wounds were smooth, presented no scar contracture and exhibited good skin elasticity and recovery of the joint function. The cografted skin combined well and displayed a clear and continuous basal membrane, as well as gradually combined skin structure, a mature stratum corneum, downward extended rete pegs, a mainly uniform dermal collagen fiber structure, regular alignment, and fewer blood capillaries. Clear desmosome cograft regions were identified among heckle cells, as well as a clear and continuous basal membrane. The cografted skin of the combined split-thickness autograft and the acellular heterologous (porcine) dermal matrix showed an improved shape and functional recovery compared with the pure split-thickness skin autograft. The combination of the meshed ADX and the split-thickness skin autograft applied in deep full-thickness burns and scar wounds may induce tissue regeneration via dermis aiming. This method also has superior shape and functional recovery, and has an extensive clinical application value.

Confocal laser scanning microscopy evaluation of an acellular dermis tissue transplant (Epiflex®)

The structure of a biological scaffold is a major determinant of its biological characteristics and its interaction with cells. An acellular dermis tissue transplant must undergo a series of processing steps, to remove cells and genetic material and provide the sterility required for surgical use. During manufacturing and sterilization the structure and composition of tissue transplants may change.

The composition of the human cell-free dermis transplant Epiflex® was investigated with specific attention paid to its structure, matrix composition, cellular content and biomechanics.

We demonstrated that after processing, the structure of Epiflex remains almost unchanged with an intact collagen network and extracellular matrix (ECM) protein composition providing natural cell interactions. Although the ready to use transplant does contain some cellular and DNA debris, the processing procedure results in a total destruction of cells and active DNA which is a requirement for an immunologically inert and biologically safe substrate. Its biomechanical parameters do not change significantly during the processing.

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.