An Update on Scaffold Devices for Rotator Cuff Repair

Novel Growth Factor Combination for Improving Rotator Cuff Repair: A Rat In Vivo Study

BACKGROUND

The lack of healing at the repaired tendon-bone interface is an important cause of failure after rotator cuff repair. While augmentation with growth factors (GFs) has demonstrated promise, the ideal combination must target all 3 tissue types at the tendon-bone interface.

HYPOTHESIS

The GF combination of transforming growth factor beta 1, Insulin-like growth factor 1, and parathyroid hormone will promote tenocyte proliferation and differentiation and improve the biomechanical and histological quality of the repaired tendon-bone interface.

STUDY DESIGN

Controlled laboratory study.

METHODS

In vitro, human tenocytes were cultured in the presence of the GF combination for 72 hours, and cell growth assays and the expression of genes specific to tendon, cartilage, and bone were analyzed. In vivo, adult rats (N = 46) underwent detachment and repair of the left supraspinatus tendon. A PVA-tyramine gel was used to deliver the GF combination to the tendon-bone interface. Histological, biomechanical, and RNA microarray analysis was performed at 6 and 12 weeks after surgery. Immunohistochemistry for type II and X collagen was performed at 12 weeks.

RESULTS

When treated with the GF combination in vitro, human tenocytes proliferated 1.5 times more than control (P = .04). The expression of scleraxis increased 65-fold (P = .013). The expression of Sox-9 (P = .011), type I collagen (P = .021), fibromodulin (P = .0075), and biglycan (P = .010) was also significantly increased, while the expression of PPARγ was decreased (P = .007). At 6 and 12 weeks postoperatively, the quality of healing on histology was significantly higher in the GF group, with the formation of a more mature tendon-bone interface, as confirmed by immunohistochemistry for type II and X collagen. The GF group achieved a load at failure and Young modulus >1.5 times higher at both time points. Microarrays at 6 weeks demonstrated upregulation of genes involved in leukocyte aggregation (S100A8, S100A9) and tissue mineralization (Bglap, serglycin, Fam20c).

CONCLUSION

The GF combination promoted protendon and cartilage responses in human tenocytes in vitro; it also improved the histological appearance and mechanical properties of the repair in vivo. Microarrays of the tendon-bone interface identified inflammatory and mineralization pathways affected by the GF combination, providing novel therapeutic targets for further research.

CLINICAL RELEVANCE

The use of this GF combination is translatable to patients and may improve healing after rotator cuff repair.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Biologics to Improve Healing in Large and Massive Rotator Cuff Tears: A Critical Review

Large and massive rotator cuff tears have the highest risk of retear. Common biologic modalities that can potentially reduce the retear rate and improve healing include platelet-rich plasma (PRP), scaffolds, and mesenchymal stem cells (MSCs). PRP has been studied for its role in improving rotator cuff healing and results of randomized controlled trials and meta-analyses show mixed results. Most studies in large and massivge tears show that PRP decreases the retear rate, but the connection between structural integrity and clinical outcomes is still unknown. Extracellular matrix (ECM) and synthetic scaffolds can increase healing in augmentation and bridging repair. Acellular dermal allografts have shown better healing rates and outcomes than xenografts in meta-analyses. Synthetic scaffolds augmented with bone marrow-derived stem cells have only been studied in vitro but are promising for the combination of mechanical stability and induction of a biological response. Superior capsule reconstruction is an exciting type of interposition graft reconstruction that has shown favorable early clinical outcomes for large and massive tears. Bone marrow-derived stem cells and adipose-derived stem cells improve the biomechanical characteristics of tendon repair and enhance the histological findings of the healing process in animal studies. However, evidence from human studies is lacking, especially in patients with large and massive tears. In summary, there are many biological options to augment rotator cuff repair in patients with large and massive tears. Due to mixed results and a lack of standardization in high-quality studies, we cannot recommend PRP at this time as an adjunct to rotator cuff repair. Both ECM and synthetic scaffolds, as well as SCR, can be used, especially in situations where native tendon is compromised, and additional mechanical augmentation is needed. Stem cells have been the least studied to date, so it is difficult to give recommendations for or against their use at this time.

Hip abductor tendon tears: where are we now?

Hip abductor tendon tear is a difficult problem to manage. The hip abductor mechanism is made up of the gluteus medius and minimus muscles, both of which contribute to stabilising the pelvis through the gait cycle. Tears of these tendons are likely due to iatrogenic injury during arthroplasty and chronic degenerative tendinopathy. Ultrasound and magnetic resonance imaging have provided limited clues regarding the pattern of disease and further work is required to clarify both the macro and microscopic pattern of disease. While surgery has been attempted over the last 2 decades, the outcomes are variable and the lack of high-quality studies have limited the uptake of surgical repair. Hip abductor tendon tears share many features with rotator cuff tears, hence, innovations in surgical techniques, materials and biologics may apply to both pathologies.

Macromechanics and polycaprolactone fiber organization drive macrophage polarization and regulate inflammatory activation of tendon in vitro and in vivo

Appropriate macrophage response to an implanted biomaterial is crucial for successful tissue healing outcomes. In this work we investigated how intrinsic topological cues from electrospun biomaterials and extrinsic mechanical loads cooperate to guide macrophage activation and macrophage-tendon fibroblast cross-talk. We performed a series of in vitro and in vivo experiments using aligned or randomly oriented polycaprolactone nanofiber substrates in both mechanically loaded and unloaded conditions. Across all experiments a disorganized biomaterial fiber topography was alone sufficient to promote a pro-inflammatory signature in macrophages, tendon fibroblasts, and tendon tissue. Extrinsic mechanical loading was found to strongly regulate the character of this signature by reducing pro-inflammatory markers both in vitro and in vivo. We observed that macrophages generally displayed a stronger response to biophysical cues than tendon fibroblasts, with dominant effects of cross-talk between these cell types observed in mechanical co-culture models. Collectively our data suggest that macrophages play a potentially important role as mechanosensory cells in tendon repair, and provide insight into how biological response might be therapeutically modulated by rational biomaterial designs that address the biomechanical niche of recruited cells.

Superior Capsule Reconstruction for Irreparable Rotator Cuff Tears: A Systematic Review

PURPOSE

To evaluate the preliminary clinical outcomes and complications of superior capsule reconstruction (SCR) for irreparable rotator cuff tears.

METHODS

A systematic review of PubMed, MEDLINE, EMBASE, and Cochrane databases was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies reporting clinical outcomes of irreparable rotator cuff tears managed by SCR were included. Clinical outcome analyses of pre- and postoperative range of motion, American Shoulder and Elbow Surgeons scores, visual analog scale pain scores, and acromiohumeral intervals (AHIs) were performed and reported as range or frequency.

RESULTS

Five studies (285 patients, 291 shoulders) of level III-IV evidence were included, with a weighted mean (± standard deviation) follow-up of 27.7 ± 17.3 months. Forward flexion improved from 91°-130° preoperatively to 147°-160° postoperatively, external rotation from 26°-41° to 41°-45°, and internal rotation from L4-L1 to L1. American Shoulder and Elbow Surgeons scores increased from 36-52.2 to 77.5-92, and visual analog scale pain scores decreased from 4.0-6.3 to 0.4-1.7. Radiographically, AHIs with acellular dermal allograft ranged from 4.5 to 7.1 mm preoperatively, improving to 7.6-10.8 mm immediately postoperation before decreasing to 6.7-9.7 mm by final follow-up. Complication and graft failure rates were 17.2% and 11.7%, respectively.

CONCLUSIONS

Preliminary results of SCR show consistent improvement in shoulder functionality and pain reduction. However, a decrease in postoperative AHIs indicates dermal allograft elongation and persistent superior migration of the humerus, potentially contributing to later graft failure. Studies with longer follow-up will be essential to evaluate the long-term utility of SCR in the treatment of irreparable rotator cuff tears.

LEVEL OF EVIDENCE

Level IV, systematic review of level III-IV studies.

Overlay repair with a synthetic collagen scaffold improves the quality of healing in a rat rotator cuff repair model

BACKGROUND

Augmenting repairs with extracellular matrix-based scaffolds is a common option for rotator cuff tears. In this study, a new collagen scaffold was assessed for its efficacy in augmenting rotator cuff repair.

METHODS

The collagen scaffold was assessed in vitro for cytocompatibility and retention of tenocyte phenotype using alamarBlue assays, fluorescent imaging, and real-time polymerase chain reaction. Immunogenicity was assessed in vitro by the activation of human monocytes. In vivo, by use of a modified rat rotator cuff defect model, supraspinatus tendon repairs were carried out in 40 animals. Overlay augmentation with the collagen scaffold was compared with unaugmented repairs. At 6 and 12 weeks postoperatively, the repairs were tested biomechanically to evaluate repair strength, as well as histologically to assess quality of healing.

RESULTS

The collagen scaffold supported human tendon-derived cell growth in vitro, with cells demonstrating proliferation and appearing morphologically tenocytic over the experimental period. No immunogenic responses were provoked compared with suture material control. In vivo, augmentation with the scaffold improved the histologic scores at 12 weeks (8.4 of 15 vs 6.4 of 15, P = .032). However, no significant difference was detected with mechanical testing.

CONCLUSION

The new collagen scaffold was supportive of cell growth in vitro and generated a minimal acute inflammatory response. In vivo, we observed an improvement in the histologic appearance of the repair at 12 weeks. However, a meaningful increase in biomechanical strength was not achieved. Further modification and improvement of the scaffold are required prior to consideration for clinical use.

In Vivo Evaluation of Different Collagen Scaffolds in an Achilles Tendon Defect Model

In the present study, a newly introduced bovine cross-linked collagen scaffold (test material) was investigated in vivo in an Achilles tendon defect model and compared to a commercially available porcine collagen scaffold (control material). In total, 28 male Sprague Dawley rats (about 400 g) were examined. The defined Achilles tendon defect of 5 mm of the right hind limb was replaced by one of the scaffold materials. After euthanasia, the hind limbs were transected for testing. Biomechanical evaluation was carried out via tensile testing (n = 8 each group, observation time: 28 days). Nonoperated tendons from the bilateral side were used as a control (native tendon, n = 4). For the histological evaluation, 12 animals were sacrificed at 14 and 28 days postoperatively (n = 3 each group and time point). Stained slices (Hematoxylin & Eosin) were evaluated qualitatively in terms of presence of cells and cell migration into scaffolds as well as structure and degradation of the scaffold. All transected hind limbs were additionally analyzed using MRI before testing to verify if the tendon repair using a collagen scaffold was still intact after the observation period. The maximum failure loads of both scaffold materials (test material: 54.5 ± 16.4 N, control: 63.1 ± 19.5 N) were in the range of native tendon (76.6 ± 11.6 N, p ≥ 0.07). The stiffness of native tendons was twofold higher (p ≤ 0.01) and the tear strength was approximately fivefold higher (p ≤ 0.01) compared to the repaired tendons with both scaffolds. Histological findings indicated that neither the test nor the control material induced inflammation, but the test material underwent a slower remodeling process. An overall repair failure rate of 48% was observed via MRI. The experimental data of the newly developed test material showed similar outcomes compared to the commercially available control material. The high repair failure rate indicated that MRI is recommended as an auxiliary measurement tool to validate experimental data.