Rotator Cuff Repair Model Research Articles

Effect of PARP-1 Inhibition on Rotator Cuff Healing: A Feasibility Study Using Veliparib in a Rat Model of Acute Rotator Cuff Repair

Background: PARP-1 (poly[ADP-ribose]) was shown to influence the inflammatory response after rotator cuff tear, leading to fibrosis, muscular atrophy, and fatty infiltration in mouse rotator cuff degeneration. So far, it is not known how PARP-1 influences enthesis healing after rotator cuff tear repair. Hypothesis/Purpose: This study aimed to examine the feasibility of oral PARP-1 inhibition and investigate its influence on rat supraspinatus enthesis and muscle healing after rotator cuff repair. The hypothesis was that oral PARP-1 inhibition would improve enthesis healing after acute rotator cuff repair in a rat model. Study Design: Controlled laboratory study. Methods: In 24 Sprague-Dawley rats, the supraspinatus tendon was sharply detached and immediately repaired with a single transosseous suture. The rats were randomly allocated into 2 groups, with the rats in the inhibitor group receiving veliparib with a target dose of 12.5 mg/kg/d via drinking water during the postoperative recovery period. The animals were sacrificed 8 weeks after surgery. For the analysis, macroscopic, biomechanical, and histologic methods were used. Results: Oral veliparib was safe for the rats, with no adverse effects observed. In total, the inhibitor group had a significantly better histologic grading of the enthesis with less scar tissue formation. The macroscopic cross-sectional area of the supraspinatus muscles was 10.5% higher (P = .034) in the inhibitor group, which was in agreement with an 8.7% higher microscopic muscle fiber diameter on histologic sections (P < .0001). There were no statistically significant differences in the biomechanical properties between the groups. Conclusion: This study is the first to investigate the influence of PARP-1 inhibition on healing enthesis. On the basis of these findings, we conclude that oral veliparib, which was previously shown to inhibit PARP-1 effectively, is safe to apply and has beneficial effects on morphologic enthesis healing and muscle fiber size. Clinical Relevance: Modulating the inflammatory response through PARP-1 inhibition during the postoperative healing period is a promising approach to improve enthesis healing and reduce rotator cuff retearing. With substances already approved by the Food and Drug Administration, PARP-1 inhibition bears high potential for future translation into clinical application.

OBESITY IMPAIRS ENTHESIS HEALING AFTER ROTATOR CUFF REPAIR IN A RAT MODEL

We hypothesised that diet-induced obesity (DIO) would result in inferior enthesis healing in a rat model of rotator cuff (RC) repair and that dietary intervention in the peri-operative period would improve enthesis healing.A total of 78 male Sprague-Dawley rats were divided into three weight-matched groups from weaning and fed either: control diet (CD), high-fat diet (HFD), or HFD until surgery, then CD thereafter (HF-CD). After 12 weeks, the left supraspinatus tendon was detached, followed by immediate surgical repair. At 2 and 12 weeks post-surgery, animals were culled, and RCs harvested for biomechanical and histological evaluation. Body composition and metabolic markers were assessed via DEXA and plasma analyses, respectively.DIO was established in the HFD and HF-CD groups before surgery and subsequently reversed in the HF-CD group after surgery. Histologically, the appearance of the repaired entheses was poorer in both the HFD and HF-CD groups compared with the CD group at 12 weeks after surgery, with semiquantitative scores of 6.2 (p&lt;0.01), 4.98 (p&lt;0.01), and 8.7 of 15, respectively. The repaired entheses in the HF-CD group had a significantly lower load to failure (P=0.03) at 12 weeks after surgery compared with the CD group, while the load to failure in the HFD group was low but not significantly different (P=0.10). Plasma leptin were negatively correlated with histology scores and load to failure at 12 weeks after surgery.DIO impaired enthesis healing in this rat RC repair model, with inferior biomechanical and histological outcomes. Restoring normal weight with dietary change after surgery did not improve healing outcomes. Circulating levels of leptin significantly correlated with poor healing outcomes. This pre-clinical rodent model demonstrates that obesity is a potentially modifiable factor that impairs RC healing and increases the risk of failure after RC surgery.

Subacromial bursa increases the failure force in a mouse model of supraspinatus detachment and repair.

It has been shown that subacromial bursa (SAB) harbors connective tissue progenitor cells. The purpose of this study was to evaluate the effects of implantation of SAB-derived cells (SBCs) suspended in a fibrin sealant bead and implantation of SAB tissue at rotator cuff repair site on biomechanical properties of the repair in a mouse (C57Bl/6) model of supraspinatus tendon (ST) detachment and repair. Part 1: Murine SAB tissue was harvested and cultured. Viability of SBCs suspended in 10 μL of fibrin sealant beads was confirmed invitro and invivo. Eighty mice underwent right ST detachment and repair augmented with either fibrin sealant bead (control group) or fibrin sealant bead with 100,000 SBCs (study group) applied at the repair site. Part 2: 120 mice underwent right ST detachment and repair and were randomized equally into 4 groups: (1) a tissue group, which received a piece of freshly harvested SAB tissue; (2) a cell group, which received SBCs suspended in fibrin sealant bead; (3) a fibrin sealant group, which received plain fibrin sealant bead without cells; and (4) a control group, which received nothing at the ST repair site. An equal number of mice in each group were killed at 2 and 4 weeks. Specimens underwent biomechanical testing to evaluate failure force (part 1 and 2) and histologic analysis of the repair site (part 1 only). Part 1: The mean failure force in the study group was significantly higher than controls at 2 and 4 weeks (3.25±1.03 N vs. 2.43±0.56 N, P=.01, and 4.08±0.99 N vs. 3.02±0.8 N, P=.004, respectively). Mean cell density of the ST at the repair site was significantly lower in the study group at 2 weeks than in controls (18,292.13±1706.41 vs. 29,501.90±3627.49, P=.001). Study group specimens had lower proteoglycan contents than controls, but this difference was not statistically significant. Part 2: There was no difference in failure force between cell and tissue groups at the 2- and 4-week time points (P=.994 and P=.603, respectively). There was no difference in failure force between fibrin sealant bead and control groups at the 2- and 4-week time points (P=.978 and P=.752, respectively). This study shows that the application of SBCs and SAB tissue at the rotator cuff repair site increases the strength of repair in a murine model of rotator cuff detachment and repair.

Mechanical stimulation improves rotator cuff tendon-bone healing via activating IL-4/JAK/STAT signaling pathway mediated macrophage M2 polarization.

BackgroundIt is well known that appropriate mechanical stimulation benefits tendon-bone (T-B) healing, however, the mechanisms behind this are still uncovered completely. Here, we aimed to explore whether the IL-4/JAK/STAT signaling pathway mediated macrophage polarization was involved in mechanical stimulation induced T-B healing.MethodC57BL/6 mice rotator cuff (RC) repair model was established, and the mice were randomly allocated to the following group. 1. Mice were allowed for free cage activities after surgery (FC group); 2. Mice received treadmill running initiated on postoperative day 7 (TR group); 3. Mice only received a local injection of hydrogel containing IL-4 neutralizing antibody without postoperative intervention (FC ​+ ​AF-404-SP group); 4. Mice received a local injection of hydrogel containing IL-4 neutralizing antibody and postoperative treadmill running (TR ​+ ​AF-404-SP group). The expression of IL-4 within supraspinatus tendon (SST) enthesis was measured by Enzyme-linked immunosorbent assay (ELISA). In addition, the activation of JAK/STAT signaling pathway in macrophages and identification of macrophage phenotype at the RC insertion site was detected by Flow cytometry and qRT-PCR. T-B healing quality in this RC repair model was evaluated by histological staining, Micro-computed tomography (Micro-CT) scanning, and biomechanical testing.ResultIn this study, using the RC repair model, we confirmed that generation of IL-4, activation of the JAK/STAT signaling pathway in macrophages, the ability of macrophages to polarize towards M2 subtype, and T-B healing quality were significantly enhanced in TR group compared to FC group. When comparing FC ​+ ​AF-404-SP group with TR ​+ ​AF-404-SP group, it was found that the mechanical stimulation induced this effect was depleted following the blockade of the IL-4/JAK/STAT signaling pathway.ConclusionOur finding suggested that mechanical stimulation could accelerate T-B healing via activating the IL-4/JAK/STAT signaling pathway that modulates macrophages to polarize towards M2 subtype.The translational potential of this articleThis is the first study to reveal a significant role of mechanical stimulation in the IL-4/JAK/STAT signaling pathway activation and macrophage polarization during RC T-B healing, which highlights the IL-4/JAK/STAT signaling pathway as a potential target to mediate macrophage M2 polarization and improves T-B healing for RC repair.

The recombinant human fibroblast growth factor-18 (sprifermin) improves tendon-to-bone healing by promoting chondrogenesis in a rat rotator cuff repair model.

Rotator cuff healing is improved by reconstructing the fibrocartilaginous structure of the tendon-to-bone enthesis. Fibroblast growth factor (FGF)-18 (sprifermin) is a well-known growth factor that improves articular cartilage repair via its anabolic effect. This study aimed to investigate the effect of recombinant human FGF-18 (rhFGF-18) on the chondrogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) invitro and tendon-to-bone healing in a rat model of rotator cuff repair. Histological and reverse transcription-quantitative real-time polymerase chain reaction analyses of chondral pellets cultured with different concentrations of rhFGF-18 were performed. Bilateral detachment and repair of the supraspinatus tendon were performed on rats. The rats were administered 0.2mL of sodium alginate (SA) hydrogel with (rhFGF-18/SA group, n=12) or without (SA group, n=12) 20μg of rhFGF-18 into the repaired side. The simple repair group (n=12) served as a control. At 4 and 8weeks after surgery, histological analysis and biomechanical tests were performed. After chondrogenesis induction, compared with the control group, 10ng/mL of rhFGF-18 increased pellet volume significantly (P=.002), with improved histological staining. It was noted that 10ng/mL of rhFGF-18 upregulated the mRNA expression (relative ratio to control) of aggrecan (2.59±0.29, P<.001), SRY-box transcription factor 9 (1.88±0.05, P<.001), and type II collagen (1.46±0.18, P=.009). At 4 and 8weeks after surgery, more fibrocartilage and cartilaginous extracellular matrix was observed in rhFGF-18/SA-treated rats. The semiquantitative data from picrosirius red staining test were 31.1±4.5 vs. 61.2±4.1 at 4weeks (P<.001) and 61.5±2.8 vs. 80.5±10.5 at 8weeks (P=.002) (control vs. rhFGF-18/SA). Ultimate failure load (25.42±3.61N vs. 18.87±2.71N at 4weeks and 28.63±5.22N vs. 22.15±3.11N at 8weeks; P=.006 and P=.03, respectively) and stiffness (18.49±1.38N/mm vs. 14.48±2.01N/mm at 8weeks, P=.01) were higher in the rhFGF-18/SA group than in the control group. rhFGF-18 promoted chondrogenesis in the hBMSCs invitro. rhFGF-18/SA improved tendon-to-bone healing in the rats by promoting regeneration of the fibrocartilage enthesis. rhFGF-18 (sprifermin) may be beneficial in improving tendon-to-bone healing after rotator cuff repair.

Poster 130: Tendon-to-bone Healing in a CCR2 Knockout Mouse Model of Delayed Rotator Cuff Repair

Poster 130: Tendon-to-bone Healing in a CCR2 Knockout Mouse Model of Delayed Rotator Cuff Repair

Chitosan-platelet-rich plasma implants improve rotator cuff repair in a large animal model: Pilot study.

Freeze-dried formulations of chitosan can be solubilized in platelet-rich plasma (PRP) to form injectable implants that are used as an adjunct treatment during surgical repair of the rotator cuff. The purpose of the current study was to assess chitosan-PRP implant residency, test safety, and assess efficacy over standard-of-care controls in a sheep model of rotator cuff repair. The infraspinatus tendon was transected unilaterally and immediately repaired with suture anchors in 22 skeletally mature ewes. In treatment groups, formulations containing chitosan, trehalose, and calcium chloride were solubilized with autologous leukocyte-rich PRP and injected at the tendon-bone interface and on top of the repaired site (1mL or 2mL doses). Implant residency was assessed histologically at 1 day. Outcome measures included MRI assessment at baseline, 6weeks, and 12weeks, histopathology and clinical pathology. Chitosan-PRP implants were resident at the injection site at 1 day and induced recruitment of polymorphonuclear cells. The tendon gap, which corresponds to the length of abnormally hyperintense tissue attached to the humeral head, was decreased by treatment with the 2mL dose when compared to controls at 12weeks on MRI images. Some histological features were improved by the 2mL dose treatment compared to controls at 12weeks. There was no treatment-specific effect on all standard safety outcome measures, which suggests high safety. This study provides preliminary evidence on the safety and efficacy of chitosan-PRP implants in a large animal model that could potentially be translated to a clinical setting.

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.

BackgroundAlthough 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.MethodsAnimal 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.ResultsHistology 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.ConclusionIn 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 evidenceBasic Science Study; In Vivo Animal Model; Histology and Biomechanics.

Pegylated insulin-like growth factor-1 biotherapeutic delivery promotes rotator cuff regeneration in a rat model.

Tears in the rotator cuff are challenging to repair because of the complex, hypocellular, hypovascular, and movement-active nature of the tendon and its enthesis. Insulin-like Growth Factor-1 (IGF-1) is a promising therapeutic for this repair. However, its unstable nature, short half-life, and ability to disrupt homeostasis has limited its clinical translation. Pegylation has been shown to improve the stability and sustain IGF-1 levels in the systemic circulation without disrupting homeostasis. To provide localized delivery of IGF-1 in the repaired tendons, we encapsulated pegylated IGF-1 mimic and its controls (unpegylated IGF-1 mimic and recombinant human IGF-1) in polycaprolactone-based matrices and evaluated them in a pre-clinical rodent model of rotator cuff repair. Pegylated-IGF-1 mimic delivery reestablished the characteristic tendon-to-bone enthesis structure and improved tendon tensile properties within 8 weeks of repair compared to controls, signifying the importance of pegylation in this complex tissue regeneration. These results demonstrate a simple and scalable biologic delivery technology alternative to tissue-derived grafts for soft tissue repair.

Effect of Mechanical Stimulation Combined With Platelet-Rich Plasma on Healing of the Rotator Cuff in a Murine Model

Background: Mechanical stimulation and platelet-rich plasma (PRP) have been shown to be beneficial for healing of the bone-tendon interface (BTI), but few studies have explored the efficacy of a combination of these applications. We investigated the effect of mechanical stimulation combined with PRP on rotator cuff repair in mice. Hypothesis: Mechanical stimulation combined with PRP can enhance BTI healing in a murine model of rotator cuff repair. Study Design: Controlled laboratory study. Methods: A total of 160 C57BL/6 mice were used. Overall, 40 mice were used to prepare PRP, while 120 mice underwent acute supraspinatus tendon (SST) repair. The animals were randomly assigned to 4 groups: control group, mechanical stimulation group, PRP group, and mechanical stimulation combined with PRP group (combination group). At 4 and 8 weeks postoperatively, animals were sacrificed, the eyeballs were removed to collect blood, and the SST–humeral complexes were collected. Histological, biomechanical, immunological, and bone morphometric tests were performed. Results: Histologically, at 4 and 8 weeks after surgery, the area of the fibrocartilage layer at the BTI in the combination group was larger than in the other groups. The content and distribution of proteoglycans in this layer in the combination group were significantly greater than in the other groups. At 8 weeks postoperatively, trabecular number, and trabecular bone thickness of the subchondral bone area of interest at the BTI of the combination group were greater than those of the other groups, bone volume fraction of the combination group was greater than the control group. On biomechanical testing at 4 and 8 weeks after surgery, the failure load and ultimate strength of the SST–humeral complex in the combination group were higher than in the other groups. Enzyme-linked immunosorbent assay results showed that, at 4 weeks postoperatively, the serum concentrations of transforming growth factor beta 1 and platelet-derived growth factor (PDGF) in the combination group were significantly higher than in the other groups; at 8 weeks, the PDGF-AB concentration in the combination group was higher than in the control and mechanical stimulation groups. Conclusion: Mechanical stimulation combined with PRP can effectively promote the early stage of healing after a rotator cuff injury. Clinical Relevance: These findings imply that mechanical stimulation combined with PRP can serve as a potential therapeutic strategy for rotator cuff healing.

Caffeine intake does not appear to impair tendon-to-bone healing strength in a rat rotator cuff repair model.

BackgroundTendon-to-bone (TtB) healing is essential for successful rotator cuff repair (RCR). This study aimed to investigate if caffeine intake impaired TtB healing in a rat RCR model.MethodsSeventy-two rats were randomized into a caffeinated group or a noncaffeinated group. Specimens received one week of oral caffeine solution or normal saline before RCR. All rats then underwent bilateral RCR. Caffeination or saline gavages continued until rats were sacrificed at 2, 4, and 8 weeks postoperatively. Load-to-failure (primary outcomes measure), maximum stress, and stiffness of the TtB interface were measured for one shoulder of each specimen. Six random shoulders from each group underwent histological assessment of TtB healing.ResultsLoad-to-failure and maximum stress of RCR did not appear to differ between groups at any time point. No difference in RCR stiffness was found between groups at 2 and 4 weeks; however, stiffness in the caffeinated group did appear to lower at 8 weeks (P = .04).ConclusionPerioperative caffeine intake did not appear to affect load-to-failure strength of RCR in an animal model. Although our secondary outcome measures of maximum stress and stiffness also did not appear to be influenced by perioperative caffeine intake, there did appear to be a trend toward decreased RCR stiffness at 8 weeks postoperatively in specimens that received caffeine.

Injection of Micronized Human Amnion/Chorion Membrane Results in Increased Early Supraspinatus Muscle Regeneration in a Chronic Model of Rotator Cuff Tear.

Surgical repair of severe rotator cuff tear often results in retear due to unaddressed muscle degeneration. The objective of this study was to test the regenerative potential of micronized dehydrated Human Amnion/Chorion Membrane (dHACM), in a clinically relevant delayed reattachment model of rotator cuff repair. Micronized dHACM was injected into rat supraspinatus muscle during tendon re-attachment surgery, three weeks after original tendon injury. One week after material injection, inflammatory and mesenchymal stem cell infiltration into supraspinatus muscles was assessed via flow cytometry. Histological methods were utilized to assess structural and regenerative changes in muscle one and three weeks after material injection. Micronized dHACM injection resulted in increased M1-like macrophages (17.1 [Formula: see text] fold change over contralateral controls) and regenerating muscle fibers (4.3% vs 1.7% in saline treated muscles) one week after injection compared to saline treated muscles. Tendon reattachment itself exhibited intrinsic healing in this model, demonstrated by a general return of muscle weight and reduced fibrosis. Our results indicate that injection of micronized dHACM may initiate an inflammatory response in degenerated muscle that promotes early muscle regeneration, and that our animal model may be a suitable platform for studying treatments in muscle at early timepoints, before intrinsic healing occurs.

Pulsed electromagnetic field therapy alters early healing in a rat model of rotator cuff injury and repair: Potential mechanisms.

Rotator cuff repair failure remains common due to poor tendon healing, particularly at the enthesis. We previously showed that pulsed electromagnetic field (PEMF) therapy improved the mechanical properties of the rat supraspinatus tendon postoperatively. However, little is known about the mechanisms behind PEMF-dependent contributions to improved healing in this injury model. The objective of this study was to determine the influence of PEMF treatment on tendon gene expression and cell composition, as well as bone microarchitecture and dynamic bone metabolism during early stages of healing. We hypothesized that PEMF treatment would amplify tendon-healing related signaling pathways while mitigating inflammation and improve bone metabolism at the repair site. Rats underwent rotator cuff injury and repair followed by assignment to either control (non-PEMF) or PEMF treatment groups. Gene and protein expression as well as tendon and bone histological assessments were performed 3, 7, 14, 21, and 28 days after injury. Gene expression data demonstrated an upregulation in the bone morphogenetic protein 2 signaling pathway and increases in pro-osteogenic genes at the insertion, supporting important processes to re-establish the tendon-bone interface. PEMF also downregulated genes related to a fibrotic healing response. Anti-inflammatory effects were demonstrated by both gene expression and macrophage phenotype. PEMF significantly increased the rate of kinetic bone formation directly adjacent to the tendon enthesis as well as the number of cuboidal surface osteoblasts (active osteoblasts) in the humeral head. This study has provided insight into how PEMF affects cellular and molecular processes in the supraspinatus tendon and adjacent bone after injury and repair.

Rotator cuff repair using a bioresorbable nanofiber interposition scaffold: a biomechanical and histologic analysis in sheep.

Background:The purpose of this study was to evaluate the mechanical, structural, and histologic quality of rotator cuff repairs augmented with an interposition electrospun nanofiber scaffold composed of polyglycolic acid (PGA) and poly-L-lactide-co-ε-caprolactone (PLCL) in an acute sheep model.Methods:Forty acute infraspinatus tendon detachment and repair procedures were performed in a sheep infraspinatus model using a double-row transosseous-equivalent anchor technique either with an interposition nanofiber scaffold composed of polyglycolic acid–poly-L-lactide-co-ε-caprolactone or with no scaffold. Animals were euthanized at the 6-week (20 samples) and 12-week (20 samples) postoperative time points to assess the biomechanical and histologic properties of the repairs and to compare differences within each group.Results:Within the scaffold-treated group, there was a significant increase in ultimate failure force (in newtons) from 6 to 12 weeks (P < .01), a significant increase in ultimate failure load from 6 to 12 weeks (P < .01), and a significant increase in ultimate failure stress (in megapascals) from 6 to 12 weeks (P < .01). At 6 weeks, the tendon-bone attachment was most consistent with an “indirect” type of insertion, whereas at 12 weeks, a visible difference in the progression and re-formation of the enthesis was observed. Compared with controls, animals in the scaffold-treated group displayed an insertion of the fibrous tendon with the humeral footprint that was beginning to be organized in a manner similar to the “native” direct/fibrocartilaginous insertion of the ovine infraspinatus tendon. In the majority of these animals treated with the scaffold, prominent perforating collagen fibers, similar to Sharpey fibers, were present and extending through a region of calcified fibrocartilage and attaching to the humeral footprint. No surgical complications occurred in any of the 40 sheep, including delayed wound healing or infection.Conclusions:In a sheep acute rotator cuff repair model, securing a nanofiber scaffold between the tendon and the bone using a double-row transosseous-equivalent anchor fixation technique resulted in greater failure strength. Additionally, at the enthesis, Sharpey fiber–like attachments (ie, collagen fibers extending from the tendon into the calcified fibrocartilage of the humerus) were observed, which were not seen in the control group.Level of evidence:Basic Science Study; Biomechanical/Histology

A Weaving Rip-Stop Technique Leads to a Significantly Increased Load to Failure and Reduction in Suture-Tendon Cut-Through in a Biomechanical Model of Rotator Cuff Repair

PurposeTo present an alternative arthroscopic rip-stop technique with a single suture tape weaved through the tendon from anterior to posterior and to biomechanically test its strength against a control technique consisting of a single-row repair with simple sutures.MethodsThis was a controlled biomechanical study. Dissection and harvesting of the supraspinatus muscle-tendon unit were performed along the cable in 9 matched-pair cadaveric shoulders. Samples were divided into 2 groups: simple suture repair only (SSR) and simple suture repair with rip-stop (SSPR). Biomechanical testing was performed with an initial preload, followed by cyclic loading and then ramp to failure. Peak-to-peak displacement, stiffness (in newtons per millimeter), load at failure (in newtons), and failure mechanism were recorded. Data were compared using the paired-sample t test.ResultsThe average peak-to-peak displacement for SSR samples was not significantly different from that of SSPR samples (P = .96). Similarly, elongation in the SSR and SSPR groups was not significantly different (P = .82). Stiffness was significantly different between the SSR and SSPR groups (P = .0054): SSR samples were less stiff than SSPR samples. Moreover, SSR samples failed at significantly lower forces than did SSPR samples (P = .028). A larger percentage of failures occurred due to tendon cut-through among SSR samples versus suture breakage among SSPR samples.ConclusionsAn alternative rip-stop technique is presented in this biomechanical model that may assist surgeons to better deal with difficult rotator cuff repairs. Weaving a suture tape as a rip-stop can increase stiffness, achieve higher failure loads when compared with simple suture repair with no rip-stop, and reduce tendon cut-through.Clinical RelevanceThis study provides insight into a variation of rip-stop stitch techniques that may help solve the clinical problem of failure occurring at the suture-tendon interface, specifically tendon cut-through.

The effect of the platelet-rich plasma and ozone therapy on tendon-to-bone healing in the rabbit rotator cuff repair model

BackgroundThe aim of this study is to histologically and biomechanically investigate the effects of local PRP and ozone therapy (O2O3) on tendon-to-bone healing in a rabbit model of the supraspinatus tendon tear.MethodsFour groups were formed to have seven rabbits in each group: repair, R; repair + PRP, RP; repair + ozone, RO; and repair + PRP + ozone, RPO. The supraspinatus tendon was detached by sharp dissection from the footprint and an acute tear pattern was created. Thereafter, tendon repair was performed with the transosseous technique. In the RP group, PRP, and in the RPO group, PRP + O2O3 mixture was injected to the tendon repair site. In the RO group, O2O3 gas mixture was injected into subacromial space three times a week for a total of 4 weeks. The study was ended at postoperative 6th week.ResultsWhen compared with the R group, a statistically significant increase was observed in the biomechanical strength of the RP and RPO groups. The highest increase in biomechanical strength was detected in the RPO group. The histology of the RO and RPO groups showed better collagen fiber continuity and orientation than the R and RP groups.ConclusionsThe results obtained from this study show that the ozonized PRP can be used as biological support to increase tendon-to-bone healing. However, these results need to be supported by clinical studies.

The Serum from Patients with Secondary Frozen Shoulder Following Rotator Cuff Repair Induces Shoulder Capsule Fibrosis and Promotes Macrophage Polarization and Fibroblast Activation.

PurposeDisorders with systematic inflammation were prognostic for secondary frozen shoulder (sFS) following rotator cuff repair (RCR); however, how systematic inflammation affects sFS remains unclear. The aim of this study was to observe the effect of pre-operative serum from patients with sFS and the serum from those without on shoulder capsule in mice, and on macrophages and fibroblasts in vitro.MethodsSerum samples of a consecutive cohort of patients for RCR were collected pre-operatively. Three months after RCR, patients who developed sFS (Group S) were identified. Serum samples from gender- and age-matched controls without sFS (group NS) were also picked out. Firstly, the effect of serum on shoulder capsule fibrosis was observed histologically and biomechanically in a mouse model of RCR. Secondly, the roles of the serum on macrophage polarization and fibroblast activation were investigated, and the potentially involved signaling pathways were identified. Finally, inflammation and fibrosis-related cytokines in serum were quantified.ResultsIn our cohort, all patients had free pre-operative shoulder range of motion. Seven patients developed sFS at 3 months after surgery. Seven matched patients without sFS were selected as control. The inter-group difference of basic characteristics was not significant. Compared to the serum of group NS, the serum of group S significantly induced hypercellularity, capsular thickening, and range of motion deficiency in mice shoulders after RCR. Compared to the serum of group NS, samples of group S significantly promoted M2 polarization of THP-1 human macrophages and the activation of human capsule-derived fibroblasts. Meanwhile, Smad3 and p-Smad3 in macrophages and fibroblasts were significantly up-regulated. On the other hand, levels of inflammation and fibrosis-related cytokines were not significantly different between serum in group S and group NS.ConclusionAlthough all patients in this cohort had free range of motion pre-operatively, the pre-operative serum from patients with sFS at 3 months after RCR could act as a trigger of shoulder capsule fibrosis post-operatively. This effect may be related to its promotion on macrophage polarization to M2 phenotype and fibroblast activation.

The effect of estrogen-like compound on rotator cuff tendon healing in a murine model.

Estrogen deficiency has been shown to negatively influence rotator cuff tendon healing. Therefore, the addition of an estrogen-like-compound (ELC) in a nonestrogen-deficient animal may improve the quality of a rotator cuff repair. The purpose of this study was to evaluate the effects of an ELC, diethylstilbestrol (DES), on tendon healing in a murine rotator cuff repair model. Thirty-three male wild-type mice (C57BL/6NJ) were randomly divided into three study groups. Group 1-unoperated mice with normal rotator cuff tendons. Groups 2 and 3 consisted of surgically repaired rotator cuff tendons; Group 2 (repair-only) was the standard repair group (no DES injected), whereas Group 3 (repair + DES) was the experimental repair group (injected with DES). Comparing the maximal thickness of calcified fibrocartilage to uncalcified fibrocartilage, the ratios for the control (intact tendon), repair-only, and repair + DES groups were 2:1, 0.9:1, and 1.7:1. RNA expression data demonstrated upregulation of chondrogenic, angiogenic, and tendon modulation genes in the repair- only group compared to the control (intact tendon) group (p < 0.04 for all), and that addition of DES further increased the osteogenic, angiogenic, and tendon modulation gene expression compared to the repair-only group (p < 0.02). Immunohistochemical analysis indicated that the addition of DES further increased osteogenic, angiogenic, and tendon maturation protein expression at the enthesis compared to standard repairs.

The Enhancement Effect of Acetylcholine and Pyridostigmine on Bone-Tendon Interface Healing in a Murine Rotator Cuff Model

Background: How to improve rotator cuff healing remains a challenge. Little is known about the effect of the parasympathetic transmitter acetylcholine (ACh) and the acetylcholinesterase inhibitor pyridostigmine (PYR), both of which have anti-inflammatory properties, in the healing process of rotator cuff injury. Hypothesis: ACh and PYR could enhance bone-tendon interface healing in a murine model of rotator cuff repair. Study Design: Controlled laboratory study. Methods: A total of 160 C57BL/6 mice underwent unilateral rotator cuff repair surgery. Fibrin gel (FG) was used as a drug carrier. The mice were randomly assigned to 4 groups with 40 mice per group: FG group (received FG alone), 10-5 M ACh group (received FG containing 10-5 M ACh), 10-6 M ACh group (received FG containing 10-6 M ACh), and PYR group (received FG containing 25 µg of PYR). Ten mice in each group were euthanized at 2, 4, 8, and 12 weeks postoperatively. Histologic, immunohistochemical, and biomechanical evaluations were performed for analysis. Results: Histologically, fibrocartilage-like tissue was shown at the repaired site. The proteoglycan content of the 10-5 M ACh group was significantly increased compared with the FG group at 4 weeks. M2 macrophages were identified at the repaired site for all groups at 2 and 4 weeks. At 8 weeks, M2 macrophages withdrew back to the tendon in the FG group, but a number of M2 macrophages were retained at the repaired sites in the ACh and PYR groups. Biomechanically, failure load and stiffness of the ACh and PYR groups were significantly higher than those of the FG group at 4 weeks. The stiffness of the ACh and PYR groups was significantly increased compared with the FG group at 8 weeks (P < .001 for all). At 12 weeks, most of the healing properties of the ACh and PYR groups were not significantly different compared with the FG group. Conclusion: ACh and PYR enhanced the early stage of bone-tendon insertion healing after rotator cuff repair. Clinical Relevance: These findings imply that ACh and PYR could serve as potential therapeutic strategies for rotator cuff healing.

In Vivo Imaging of Fibroblast Activity Using a 68Ga-Labeled Fibroblast Activation Protein Alpha (FAP-α) Inhibitor: Study in a Mouse Rotator Cuff Repair Model.

Rotator cuff repair site failure is a well-established clinical concern. Tendon-to-bone healing is initiated by inflammatory mediators followed by matrix synthesis by fibroblasts. The kinetics of fibroblast accumulation and activity are currently poorly understood. Ninety-six mice underwent supraspinatus tendon repair. Six were used for imaging using a novel 68Gallium (Ga)-labeled fibroblast activation protein alpha (FAP-α) inhibitor and positron emission tomography-computed tomography (PET/CT) at days 0 (before surgery), 3, 7, 14, and 28. Sixty-eight animals were divided into 4 groups to be evaluated at 3, 7, 14, or 28 days. Twenty-two native shoulders from mice without surgery were used as the control group (intact tendon). Six animals from each group were used for histological analysis; 6 from each group were used for evaluation of fibroblastic response-related gene expression; and 10 mice each from the intact, 14-day, and 28-day groups were used for biomechanical testing. There was minimal localization of 68Ga-labeled FAP-α inhibitor in the shoulders at day 0 (before surgery). There was significantly increased uptake in the shoulders with surgery compared with the contralateral sides without surgery at 3, 7, and 14 days. 68Ga-labeled FAP-α inhibitor uptake in the surgically treated shoulders increased gradually and peaked at 14 days followed by a decrease at 28 days. Gene expression for smooth muscle alpha (α)-2 (acta2), FAP-α, and fibronectin increased postsurgery followed by a drop at 28 days. Immunohistochemical analysis showed that FAP-α-positive cell density followed a similar temporal trend, peaking at 14 days. All trends matched closely with the PET/CT results. Biomechanical testing demonstrated a gradual increase in failure load during the healing process. 68Ga-labeled FAP-α inhibitor PET/CT allows facile, high-contrast in vivo 3-dimensional imaging of fibroblastic activity in a mouse rotator cuff repair model. Noninvasive imaging of activated fibroblasts using labeled radiotracers may be a valuable tool to follow the progression of healing at the bone-tendon interface.