Synthetic Patch Rotator Cuff Repair: A 10-year Follow-Up

Application of Nondegradable Synthetic Materials for Tendon and Ligament Injury

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

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.

Reliability of a Novel Preoperative Protocol for Determining Graft Sizes for Superior Capsular Reconstruction Using Plain Film Radiography

BACKGROUND

Superior capsular reconstruction (SCR) for massive, irreparable rotator cuff tears involves anchoring a graft between the superior glenoid and the greater tuberosity of the humerus. Optimizing the graft size is important. We aimed (1) to evaluate the reliability of plain film radiography in determining graft size for SCR and (2) to create a database to help predict future graft sizes.

METHODS

An inter- and intra-rater reliability trial was conducted on 10 and 6 subjects with healthy shoulders, respectively, using plain film radiography to measure the distance between the superior glenoid and the supraspinatus footprint. The subjects were positioned upright with an abduction pillow modified to hold the shoulder at 30° abduction and 45° external rotation, afterwhich a true antero-posterior shoulder radiograph was captured. Thirty subjects were recruited for the database and grouped using the aforementioned protocol.

RESULTS

The inter-rater and intra-rater trial agreement was excellent, with intraclass correlation coefficients of 0.94 (95% CI) and 0.76 (95% CI), respectively. Three medio-lateral patch sizes, of 33 mm, 38 mm, and 47 mm, were proposed based on the protocol in 30 subjects.

CONCLUSIONS

Plain film radiography demonstrated excellent reliability in measuring the distance between the superior glenoid and the supraspinatus footprint. Three ordinal patch sizes are proposed.

Biomechanical and morphological comparison of two interposition graft rotator cuff repair techniques

BACKGROUND

Interposition graft rotator cuff repair is one option for the treatment of massive, otherwise irreparable rotator cuff tears. It is undetermined how different suturing techniques influence morphology at the patch-tendon interface in interposition rotator cuff repairs, particularly with respect to increased cross-sectional area at the repair site post-exposure to cyclic loading, which may influence healing. We aimed to analyze how the morphology of the grafts used in polytetrafluoroethylene (PTFE) interposition rotator cuff repairs differed according to whether the graft was secured using the multiple mattress technique or the weave technique respectively.

METHODS

Twelve PTFE interposition rotator cuff repairs (two groups, n = 6) were cyclically loaded. The thickness, width, cross-sectional area at the individual patches and at the repair site, and patch elongation were compared between repairs using the 'multiple mattress' technique and repairs that used the 'weave' technique.

RESULTS

At all loads, repair site cross-sectional area and thickness was greater in the weave group than in the multiple mattress group (P<0.05), despite repair site width being greater in the multiple mattress group (P<0.05). No significant differences in elongation were found between the multiple mattress and weave groups.

CONCLUSION

Greater repair site cross-sectional area under cyclic loading was observed in polytetrafluoroethylene interposition rotator repairs that used the weave technique than in those that used the multiple mattress technique. Increased repair site cross-sectional area in the weave group occurred due to increased thickness and decreased width relative to the multiple mattress group. No differences in cross-sectional area were found between groups at the individual patches.

A Knitted PET Patch Enhances the Maturation of Regenerated Tendons in Bridging Reconstruction of Massive Rotator Cuff Tears in a Rabbit Model

BACKGROUND

Although nondegradable synthetic grafts for bridging reconstruction of massive rotator cuff tears (MRCTs) have shown satisfactory clinical outcomes, their function and details on graft-tendon healing and enthesis regeneration have not been fully studied.

HYPOTHESIS

The knitted polyethylene terephthalate (PET) patch as a nondegradable synthetic graft could provide sustained mechanical support, facilitating enthesis and tendon regeneration in the treatment of MRCTs.

STUDY DESIGN

Controlled laboratory study.

METHODS

A knitted PET patch was fabricated for bridging reconstruction (PET group) in a New Zealand White rabbit model of MRCTs (negative control group), and an autologous Achilles tendon was used as a control (autograft group). The animals were sacrificed, and tissue samples were harvested for gross observation as well as histological and biomechanical analyses at 4, 8, and 12 weeks postoperatively.

RESULTS

Histological analysis showed no significant difference in the graft-bone interface score between the PET and autograft groups at 4, 8, and 12 weeks postoperatively. Interestingly, in the PET group, Sharpey-like fibers were observed at 8 weeks, while fibrocartilage formation and the ingrowth of chondrocytes were recognized at 12 weeks. Meanwhile, the tendon maturing score was significantly higher in the PET group than in the autograft group (19.7 ± 1.5 vs 15.3 ± 1.2, respectively; P = .008) at 12 weeks, with parallel-oriented collagen fibers around the knitted PET patch. Moreover, the ultimate failure load of the PET group was similar to that of a healthy rabbit tendon at 8 weeks (125.6 ± 13.6 vs 130.8 ± 28.6 N, respectively; P > .05) and no different from that of the autograft group at 4, 8, and 12 weeks.

CONCLUSION

The knitted PET patch could not only immediately reconstruct the mechanical support for the torn tendon postoperatively in the rabbit model of MRCTs but also enhanced maturation of the regenerated tendon by fibrocartilage formation and improved the organization of collagen fibers. Herein, the knitted PET patch could be a promising candidate graft adopted in bridging reconstruction of MRCTs.

CLINICAL RELEVANCE

A nondegradable knitted PET patch can safely bridge MRCTs with satisfactory mechanical strength and the promotion of tissue regeneration.

Synthetic polytetrafluoroethylene patches for irreparable rotator cuff tears-how are they doing at 5 years?

BACKGROUND

Treating massive and irreparable rotator cuff tears are problematic. Several studies have reported that polytetrafluoroethylene (PTFE) patches demonstrated excellent construct integrity and positive clinical and patient outcomes. However, these studies either had small sample sizes or short follow-up periods.

PURPOSE

To determine the survivorship, efficacy, and medium-term (2-19 years) outcomes of PTFE patch repairs.

METHODS

This retrospective study used prospectively collected data to establish the medium-term outcomes of PTFE interposition patch repairs for massive rotator cuff tears that could not be repaired by the standard technique. Patients included those who met the ≥2-year follow-up criteria post repair. Standardized assessments of patient-ranked shoulder pain and function and shoulder strength and passive range of motion (ROM) were performed preoperatively and at follow-up visits. Radiographs and ultrasonography were used to evaluate repair integrity, measure proximal humeral head migration, and determine glenohumeral arthritis scores.

RESULTS

Forty-one shoulders formed the study cohort at a mean follow-up period of 5 years (range: 2-19 years). The mean age of this group was 72 (standard deviation: 10; range: 50-88) and had 14 cm² tears at surgery. Twenty-five of 41 (61%) PTFE interposition patch repairs remained intact at an average of 5 years postrepair. Thirteen patches failed at the patch-tendon junction, 1 was removed, and 2 patients underwent reverse total shoulder replacement. Patient-ranked shoulder stiffness (P < .05), frequency of pain during activity and sleep (P < .001), pain levels during overhead activity and rest (P < .001), and overall shoulder function significantly improved from bad preoperatively to fair at the mean 5-year postoperative visit (P < .001). No significant improvements were demonstrated in dynamometer-measured shoulder strength maneuvers and passive ROM. All patients demonstrated proximal humeral head migration on shoulder radiographs regardless of repair integrity (mean Upper Migration Index = 1.2). Failed repairs were associated with higher mean preoperative glenohumeral arthritis grades compared with intact repairs (grade 2 in failed repairs compared with grade 1 in intact repairs) (P < .01).

CONCLUSION

PTFE interposition patch repairs for massive and irreparable tears had good construct integrity and clinical outcomes at 2 years. These outcomes were not maintained. PTFE patch repairs often failed at the patch-tendon junction at 4 years and beyond and were ineffective in (1) preventing proximal humeral head migration, (2) stopping progression of glenohumeral arthritis, and (3) improving shoulder strength and ROM.

The clinical results of lower trapezius tendon transfer with the peroneus longus allograft augmentation combined with interpositional repair with fascia lata in massive irreparable rotator cuff tears

OBJECTIVES

To investigate the clinical results of lower trapezius (LT) tendon transfer and interpositional repair that were performed simultaneously in patients with massive irreparable rotator cuff tears.

METHODS

Between 2018 and 2020 years, 16 patients with massive irreparable rotator cuff tears that were treated with LT tendon transfer and interpositional repair at the same time were included in this study. The mean follow-up period was 29±3 months (24-39 months) and the mean age of patients was 62±9 years (42-73 years). The acromio-humeral distance, active range of motions, Visual Analog Scale (VAS) scores, University of California-Los Angeles (UCLA) scores and Constant-Murley scores were made preoperatively and at the final follow-up.

RESULTS

At the final follow-up, forward flexion was increased from 109˚±24.7 to 144˚±22.21 (p=0.005), abduction from 60˚±16.33 to 135˚±16.33 (p=0.005) and external rotation from 12˚±16.87 to 35˚±14.34 (p=0.005). Total UCLA scores were 5.9±2.13 to 22.7±5.29 (p=0.005), Constant-Murley scores were 24±9.43 to 50.2±14.28 (p=0.008), VAS scores were 6.1±1.1 to 2.4±1.35 (p=0.007), mean acromio-humeral distances were 4.64±0.85 mm (3.42-6.23 mm) to 6.58 mm (5.25-8.21 mm) (p=0.005) preoperatively and at the final follow-up. Except one patient who had a frozen shoulder any significant complication was detected.

CONCLUSION

Adding interpositional repair to the LT tendon transfer in patients with posterior superior irreparable rotator cuff tear seems to have satisfactory short to mid-term clinical outcomes without an increase in complications.

Biomechanical Comparison of Synthetic Polytetrafluoroethylene (PTFE) vs Human Dermal Allograft (HDA), 2 vs 3 Glenoid Anchors, and Suture vs Minitape in Superior Capsule Reconstruction

Background: Superior capsule reconstruction (SCR) is an option for the treatment of massive, irreparable rotator cuff tears. However, which materials yield the strongest constructs remains undetermined. Purposes: We sought to investigate whether SCR with polytetrafluoroethylene (PTFE) or human dermal allograft (HDA), 2 or 3 glenoid anchors, and suture or minitape resulted in better failure load properties at the patch-glenoid interface. Methods: We conducted a biomechanical study in 30 glenoid-sided SCR repairs in Sawbones models divided into 5 groups. Each was pulled to failure to assess mode of failure, peak load (N), stiffness (N/mm), yield load (N), peak energy (N m), and ultimate energy (N m). The 5 groups were as follows: group 1-PTFE, 2 anchors, and suture; group 2-PTFE, 2 anchors, and minitape; group 3-HDA, 2 anchors, and suture; group 4-HDA, 2 anchors, and minitape; group 5-PTFE, 3 anchors, and minitape. Results: Repairs failed by button-holing of suture/minitape. Group 5 had greater peak load, stiffness, yield load, and peak energy (384 ± 62 N; 24 ± 3 N/mm; 343 ± 42 N; 4 ± 2 N m) than group 3 (226 ± 67 N; 16 ± 4 N/mm; 194 ± 74 N; 2 ± 1 N m) or group 4 (274 ± 62 N; 17 ± 4 N/mm; 244 ± 50 N; 2 ± 1 N m) and greater ultimate energy (8 ± 3 N m) than all other groups. Conclusions: This biomechanical study of SCR repairs in Sawbones models found that yield load was greater in PTFE than HDA, 3 anchors were better than 2, and minitape was no better than suture.

Automated Assessment of Cell Infiltration and Removal in Decellularized Scaffolds - Experimental Study in Rabbits

Objective  Semiquantitative and automated measurement of nuclear material removal and cell infiltration in decellularized tendon scaffolds (DTSs). Method  16 pure New Zealand rabbits were used, and the gastrocnemius muscle tendon was collected bilaterally from half of these animals (16 tendons collected); 4 were kept as control and 12 were submitted to the decellularization protocol (DTS). Eight of the DTSs were used as an in vivo implant in the experimental rotator cuff tear (RCT) model, and the rest, as well as the controls, were used in the semiquantitative and automated evaluation of nuclear material removal. The eight additional rabbits were used to make the experimental model of RCT and subsequent evaluation of cellular infiltration after 2 or 8 weeks, within the DTS. Results  The semiquantitative and automated analysis used demonstrated a removal of 79% of nuclear material ( p  < 0.001 and power > 99%) and a decrease of 88% (p < 0.001 and power >99%) in the area occupied by nuclear material after the decellularization protocol. On cell infiltration in DTS, an increase of 256% (p < 0.001 and power >99%) in the number of cells within the DTS was observed in the comparison between 2 and 8 weeks postoperatively. Conclusion  The proposed semiquantitative and automated measurement method was able to objectively measure the removal of nuclear material and cell infiltration in DTS.

Rotator Cuff Repair With Patch Augmentation: What Do We Know?

BACKGROUND

Repair of massive rotator cuff tears remains a challenging process with mixed success. There is a growing interest in the use of patches to augment the repair construct and the potential to enhance the strength, healing, and associated clinical outcomes. Such patches may be synthetic, xenograft, or autograft/allograft, and a variety of techniques have been tried to biologically enhance their integration and performance. The materials used are rapidly advancing, as is our understanding of their effects on rotator cuff tissue. This article aims to evaluate what we currently know about patch augmentation through a comprehensive review of the available literature.

METHODS

We explore the results of existing clinical trials for each graft type, new manufacturing methods, novel techniques for biological enhancement, and the histological and biomechanical impact of patch augmentation.

RESULTS

There are promising results in short-term studies, which suggest that patch augmentation has great potential to improve the success rate. In particular, this appears to be true for human dermal allograft, while porcine dermal grafts and some synthetic grafts have also had promising results.

CONCLUSION

However, there remains a need for high-quality, prospective clinical trials directly comparing each type of graft and the effect that they have on the clinical and radiological outcomes of rotator cuff repair.

Healing and Functional Results of Dermal Allograft Augmentation of Complex and Revision Rotator Cuff Repairs

BACKGROUND

Primary rotator cuff repairs in complex cases (older patient age, larger tear sizes, chronic tears) and revision repairs are at high risk for failure of healing.

PURPOSE

To examine clinical outcomes and healing rates in complex and revision rotator cuff repairs with dermal allograft augmentation.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A retrospective study was made of cases performed by 3 fellowship-trained surgeons via a uniform technique involving rotator cuff repairs with allograft augmentation. In all cases, a 1.5-mm, human, decellularized dermal graft was tied on top of the tendon at the medial row and compressed to the rotator cuff footprint using a double-row technique. Postoperative magnetic resonance imaging (MRI) was performed at a minimum of 6 months and American Shoulder and Elbow Surgeons (ASES), Single Assessment Numeric Evaluation (SANE), and 12-Item Short Form Health Survey scores were collected at a minimum of 2 years postoperatively.

RESULTS

A total of 35 patients (23 revision repairs, 12 primary complex repairs) were included. The mean patient age was 57.9 years (range, 41.0-70.5 years). All shoulders had 2-tendon tears (supraspinatus and infraspinatus), and 8 included the upper 50% of the subscapularis. At a minimum of 2 years after surgery (mean, 3.2 years), mean ASES and SANE scores improved from 42.4 and 35.3 to 77.6 and 73.5, respectively (P < .001). In the 23 patients (66%) with postoperative MRI evaluation, 11 (48%) had images showing the tendons were retorn. ASES (89.7 vs 66.4; P = .04) and SANE (84.1 vs 50.5; P = .02) scores were higher in healed patients than those with retears. The retear group had a higher degree of preoperative fatty atrophy of the infraspinatus (P = .024).

CONCLUSION

Double-row arthroscopic repair with dermal allograft augmentation of complex and revision rotator cuff tears led to improved functional outcomes. Approximately half of patients experienced a failure of healing, which was associated with poorer functional results.

Interposition Graft Repair of Irreparable Rotator Cuff Tears: A Review of Biomechanics and Clinical Outcomes

Managing massive irreparable rotator cuff tears is a challenge. Interposition graft repairs to bridge the torn defect are a promising solution. Many graft materials are available for interposition repairs including the following: allografts, autografts, extracellular matrix, and synthetic grafts. Currently, it is unknown how these materials compare biomechanically or in their clinical outcomes when used for interposition graft repairs of massive irreparable rotator cuff tears. Most allografts and autografts are similar, in maximal load and stiffness, to intact rotator cuff tendons. Synthetic grafts have similar maximal load but lower stiffness, whereas extracellular matrix grafts are lower in maximal load and stiffness compared with intact rotator cuff tendons. Overall interposition graft repairs have shown some promising 2-year outcomes in patient and physician-reported functional outcomes, regardless of graft type. Few reported complications or repair failure associated with interposition graft repairs of massive irreparable rotator cuff tears at 2 years postsurgery have been noted.

Patch Augmentation in Rotator Cuff Repair

PURPOSE OF THE REVIEW

Rotator cuff repair has excellent outcomes for many patients but continues to be suboptimal for large, retracted tears, and revision procedures. In these situations, patch augmentation may be considered in order to improve healing. The purpose of this article is to review the history, graft options, indications, surgical technique, outcomes, and complications associated with arthroscopic patch augmentation for rotator cuff repair.

RECENT FINDINGS

Patch augmentation has been shown in several studies to improve healing rates. After multiple investigations into different materials available for patch augmentation, acellular dermal allograft seems to be the graft with the best scientific support. While multiple techniques have been presented, few studies have compared their performance. While the arthroscopic technique for patch augmentation can be challenging, we present a systematic approach to this procedure with the potential to reliably and predictably perform patch augmentation. This technique is a valuable tool for surgeons that treat rotator cuff pathology.

Evaluating the Outcomes of Rotator Cuff Repairs With Polytetrafluoroethylene Patches for Massive and Irreparable Rotator Cuff Tears With a Minimum 2-Year Follow-up

BACKGROUND

Massive and irreparable rotator cuff tears are difficult to manage surgically. One technique is to use a synthetic polytetrafluoroethylene (PTFE) patch to bridge the tear. However, there is little information regarding the outcomes of this procedure.

PURPOSE

To determine the ≥2-year outcomes of patients for whom synthetic patches were used as tendon substitutes to bridge irreparable rotator cuff defects.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

This retrospective cohort study used prospectively collected data. Patients included those with a synthetic patch inserted as an interposition graft for large and/or irreparable rotator cuff tears with a minimum 2-year follow-up. Standardized assessment of shoulder pain, function, range of motion, and strength was performed preoperatively, at 6 and 12 weeks, and at 6 months and ≥2 years. Radiograph and ultrasound were performed preoperatively, at 6 months, and ≥2 years.

RESULTS

At a mean of 36 months, 58 of 68 eligible patients were followed up, and 53 of 58 (90%) patches remained in situ. Three patches failed at the patch-tendon interface, while 1 patient (2 shoulders/patches) went on to have reverse total shoulder replacements. Patient-ranked shoulder stiffness ( P < .001), frequency of pain with activity and sleep ( P < .0001), level of pain at rest and overhead ( P < .0001), and overall shoulder function improved from bad to very good ( P < .0001) by 6 months. Supraspinatus (mean ± SEM: 29 ± 16 N to 42 ± 13 N) and external rotation (39 ± 13 N to 59 ± 15 N) strength were the most notable increases at the ≥2-year follow-up ( P < .0001). Passive range of motion also improved by 49% to 67%; forward flexion, from 131° to 171°; abduction, from 117° to 161°; external rotation, from 38° to 55°; and internal rotation, from L3 to T10 ( P < .0001) preoperatively to ≥2 years. The most improvement in passive range of motion occurred between 12 months and ≥2 years. The mean (SD) Constant-Murley score was 90 (12), while the American Shoulder and Elbow Surgeons score was 95 (8).

CONCLUSION

At 36 months postoperatively, patients who had synthetic patches used as tendon substitutes to bridge irreparable rotator cuff defects reported less pain and greater overall shoulder function as compared with preoperative assessments. They demonstrated improved range of passive motion and improved strength. The data support the hypothesis that the technique of using a synthetic PTFE patch to bridge a large and/or irreparable tear has good construct integrity and improves patient and clinical outcomes.

A Comparison of Two Arthroscopic Techniques for Interpositional Polytetrafluoroethylene Patch Repair for Massive Irreparable Rotator Cuff Tears: Speed and Biomechanics

BACKGROUND

Interpositional synthetic patch repairs are a novel method of treating massive irreparable rotator cuff tears. However, surgeons experience difficulty in the arthroscopic insertion of these patches.

QUESTIONS/PURPOSES

We compared two methods of arthroscopic interpositional synthetic patch repair: the newly devised slide-and-grip technique, using pre-loaded sliding knots and no arthroscopic knots, and the weave technique, using less arthroscopic knot tying than the earlier mattress technique. Study questions were as follows: (1) Would the slide-and-grip technique take less time than the weave technique? (2) Would the biomechanical strength of the two methods be comparable?

METHODS

Fourteen paired ovine infraspinatus tendon ex vivo models of the degenerative human rotator cuff underwent timed repair with a synthetic polytetrafluoroethylene (PTFE) patch, using either the weave technique (n = 7) or the slide-and-grip technique (n = 7). Each was pulled to failure using a tensile testing machine, the Instron 8874.

RESULTS

The time to complete the slide-and-grip repairs was shorter (12 ± 0.9 min) than that of the weave repairs (23 ± 1 min). Ultimate load to failure was comparable for the slide-and-grip and weave techniques (211 ± 27 N vs. 295 ± 35 N, respectively), and the slide-and-grip was less stiff (14 ± 1 N/mm vs. 19 ± 1 N/mm).

CONCLUSIONS

The slide-and-grip technique took less time than the weave technique for the interpositional patch repair of massive irreparable rotator cuff tears and when correctly performed had comparable biomechanical strength.

Regenerative Engineering of the Rotator Cuff of the Shoulder

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

Tendon injury and repair - A perspective on the basic mechanisms of tendon disease and future clinical therapy

Tendon is an intricately organized connective tissue that efficiently transfers muscle force to the bony skeleton. Its structure, function, and physiology reflect the extreme, repetitive mechanical stresses that tendon tissues bear. These mechanical demands also lie beneath high clinical rates of tendon disorders, and present daunting challenges for clinical treatment of these ailments. This article aims to provide perspective on the most urgent frontiers of tendon research and therapeutic development. We start by broadly introducing essential elements of current understanding about tendon structure, function, physiology, damage, and repair. We then introduce and describe a novel paradigm explaining tendon disease progression from initial accumulation of damage in the tendon core to eventual vascular recruitment from the surrounding synovial tissues. We conclude with a perspective on the important role that biomaterials will play in translating research discoveries to the patient.

STATEMENT OF SIGNIFICANCE

Tendon and ligament problems represent the most frequent musculoskeletal complaints for which patients seek medical attention. Current therapeutic options for addressing tendon disorders are often ineffective, and the need for improved understanding of tendon physiology is urgent. This perspective article summarizes essential elements of our current knowledge on tendon structure, function, physiology, damage, and repair. It also describes a novel framework to understand tendon physiology and pathophysiology that may be useful in pushing the field forward.

Biomechanical comparison of expanded polytetrafluoroethylene (ePTFE) and PTFE interpositional patches and direct tendon-to-bone repair for massive rotator cuff tears in an ovine model

BACKGROUND

Massive irreparable rotator cuff tears are a difficult problem. Modalities such as irrigation and debridement, partial repair, tendon transfer and grafts have been utilized with high failure rates and mixed results. Synthetic interpositional patch repairs are a novel and increasingly used approach. The present study aimed to examine the biomechanical properties of common synthetic materials for interpositional repairs in contrast to native tendon.

METHODS

Six ovine tendons, six polytetrafluoroethylene (PTFE) felt sections and six expanded PTFE (ePTFE) patch sections were pulled-to-failure to analyze their biomechanical and material properties. Six direct tendon-to-bone surgical method repairs, six interpositional PTFE felt patch repairs and six interpositional ePTFE patch repairs were also constructed in ovine shoulders and pulled-to-failure to examine the biomechanical properties of each repair construct.

RESULTS

Ovine tendon had higher load-to-failure (591 N) and had greater stiffness (108 N/mm) than either PTFE felt (296 N, 28 N/mm) or ePTFE patch sections (323 N, 34 N/mm). Both PTFE felt and ePTFE repair techniques required greater load-to-failure (225 N and 177 N, respectively) than direct tendon-to-bone surgical repairs (147 N) in ovine models.

CONCLUSIONS

Synthetic materials lacked several biomechanical properties, including strength and stiffness, compared to ovine tendon. Interpositional surgical repair models with these materials were significantly stronger than direct tendon-to-bone model repairs.

The biomechanical effects of polytetrafluoroethylene suture augmentations in lateral-row rotator cuff repairs in an ovine model

BACKGROUND

This study investigated the biomechanical effects of expanded polytetrafluoroethylene (ePTFE) suture augmentation patches in rotator cuff repair constructs.

METHODS

The infraspinatus tendon in 24 cadaveric ovine shoulders was repaired using an inverted horizontal mattress suture with 2 knotless bone anchors (ArthroCare, Austin, TX, USA) in a lateral-row configuration. Four different repair groups (6 per group) were created: (1) standard repair using inverted horizontal mattress sutures, (2) repair with ePTFE suture augmentations on the bursal side of the tendon, (3) repair with ePTFE suture augmentations on the articular side, and, (4) repair with ePTFE suture augmentations on both sides of the tendon. Footprint contact pressure, stiffness, and the load to failure of the repair constructs were measured.

RESULTS

Repairs with ePTFE suture augmentations on the bursal side exerted significantly more footprint contact pressure (0.40 ± 0.01 MPa) than those on the articular side (0.34 ± 0.02 MPa, P = .04) and those on both sides (0.33 ± 0.02 MPa, P = .01). At 15 degrees of abduction, ePTFE-augmented repairs on the bursal side had higher footprint contact pressure (0.26 ± 0.03 MPa) compared with standard repairs (0.15 ± 0.02 MPa, P = .01) and with ePTFE-augmented repairs on the articular side (0.18 ± 0.02 MPa, P = .03). The ePTFE-augmented repairs on the bursal side demonstrated significantly higher failure loads (178 ± 18 N) than standard repairs (120 ± 17 N, P = .04).

CONCLUSIONS

Inverted horizontal mattress sutures augmented with ePTFE patches on the bursal side of the tendon enhanced footprint contact pressures and the ultimate load to failure of lateral-row rotator cuff repairs in an ovine model.