Tendon properties remain altered in a chronic rat rotator cuff model.
ABSTRACT: Chronic rotator cuff tears are often associated with pain or poor function. In a rat with only a detached supraspinatus tendon, the tendon heals spontaneously which is inconsistent with how tears are believed to heal in humans.We therefore asked whether a combined supraspinatus and infraspinatus detachment in the rat would fail to heal and result in a chronic injury in the supraspinatus tendon.We acutely detached the supraspinatus and infraspinatus tendons in a rat model. At 4, 8, and 16 weeks post-detachment, biomechanical testing, collagen organization, and histological grading were evaluated for the detached supraspinatus and infraspinatus tendons and compared to controls.In the detached supraspinatus tendon, area and percent relaxation were increased at all time points while the modulus and stiffness were similar to those of controls at 4 and 8 weeks. Collagen disorganization increased at late time points while cellularity increased and cells were more rounded in shape. In the detached infraspinatus tendon, area and percent relaxation were also increased at late time points. However, the modulus values initially decreased followed by an increase in both modulus and stiffness at 16 weeks compared to control. In the detached infraspinatus, we also observed a decrease in collagen organization at all time points and increased cellularity and a more rounded cell shape.Due to the ongoing changes in mechanics, collagen organization and histology in the detached supraspinatus tendon compared to control animals at 16 weeks, this model may be useful for understanding the human chronic tendon tear.This rat rotator cuff chronic model can be used to test hypotheses regarding injury and repair mechanisms that cannot be addressed in human patients or in cadaveric studies.
Project description:Rotator cuff tears are common shoulder problems whose propagation is difficult to predict because of the structural and mechanical inhomogeneity of the supraspinatus tendon. We have previously shown that the supraspinatus and infraspinatus tendons interact mechanically when the supraspinatus tendon is intact or exhibits a full-thickness tear, so that an increase in supraspinatus tendon strain is paralleled by an increase in infraspinatus tendon strain. Such interaction is critical and suggests that an increase in infraspinatus tendon strain that accompanies an increase in supraspinatus tendon strain may shield the supraspinatus tendon from further injury, but increase the risk of injury to the infraspinatus tendon. In this study, the mechanical interactions between the supraspinatus and infraspinatus tendons were evaluated for the commonly occurring supraspinatus tendon partial-thickness tears through a range of rotation angles.For each joint rotation and supraspinatus tendon tear size evaluated, the supraspinatus tendon was loaded, and images corresponding to 5 N, 30 N, 60 N, and 90 N of supraspinatus tendon load were isolated for the speckle painted supraspinatus and infraspinatus tendons. A region of interest outlining the insertion site was isolated and displacements between the 5 N loaded image and each of the others were measured, from which normalized average principal strains were quantified in both tendons.The observed effect on infraspinatus tendon strain paralleled that observed on strain in the supraspinatus tendon. Introducing a supraspinatus tendon partial-thickness tear and increasing load caused an increase in normalized average maximum and a decrease in normalized average minimum principal strain in the infraspinatus tendon. Increasing rotation angle from internal to external rotation caused a general decrease in normalized average maximum and increase in normalized average minimum principal strain in both tendons.The supraspinatus and infraspinatus tendons mechanically interact for the intact and partially torn supraspinatus tendons for neutral and rotated glenohumeral joint.
Project description:The rotator cuff assists in shoulder movement and provides dynamic stability to the glenohumeral joint. Specifically, the anterior-posterior (AP) force balance, provided by the subscapularis anteriorly and the infraspinatus and teres minor posteriorly, is critical for joint stability and concentric rotation of the humeral head on the glenoid. However, limited understanding exists of the consequences associated with disruption of the AP force balance (due to tears of both the supraspinatus and infraspinatus tendons) on joint function and joint damage. We investigated the effect of disrupting the APforce balance on joint function and joint damage in an overuse rat model. Twenty-eight rats underwent 4 weeks of overuse to produce a tendinopathic condition and were then randomized into two surgical groups: Detachment of the supraspinatus only or detachment of the supraspinatus and infraspinatus tendons. Rats were then gradually returned to their overuse protocol. Quantitative ambulatory measures including medial/lateral, propulsion, braking, and vertical forces were significantly different between groups. Additionally, cartilage and adjacent tendon properties were significantly altered. These results identify joint imbalance as a mechanical mechanism for joint damage and demonstrate the importance of preserving rotator cuff balance when treating active cuff tear patients.
Project description:Latissimus dorsi tendon transfer is an effective option for young and active patients with massive irreparable posterosuperior rotator cuff tears and intact subscapularis tendon. This approach has been shown to relieve pain and improve shoulder function in both the short and long term. We describe a surgical technique using an acromial osteotomy to better expose the greater tuberosity for the tendon transfer without disrupting the deltoid muscle. The latissimus dorsi tendon is reinforced with a human dermal collagen matrix (GraftJacket; Wright Medical Group) for additional augmentation of the muscle to gain more excursion for the tendon transfer to the greater tuberosity. The transferred tendon is fixed to the supraspinatus and infraspinatus footprints on the greater tuberosity using suture anchors. The acromial osteotomy is repaired back anatomically with several No. 5 braided sutures (FiberWire; Arthrex).
Project description:Large rotator cuff tears (supraspinatus and infraspinatus) are common in patients who perform overhead activities (laborers, athletes). In addition, following large cuff tears, these patients commonly attempt to return to pre-injury activity levels. However, there is a limited understanding of the damaging effects on the uninjured joint tissues when doing so. Therefore, the objective of this study was to investigate the effect of returning to overuse activity following a supraspinatus and infraspinatus tear on shoulder function and the structural and biological properties of the intact tendons and glenoid cartilage. Forty rats underwent 4 weeks of overuse followed by detachment of the supraspinatus and infraspinatus tendons and were then randomized into two groups: return to overuse or cage activity. Ambulatory measurements were performed over time and structural and biological properties of the adjacent tendons and cartilage were evaluated. Results demonstrated that animals returning to overuse activity did not have altered shoulder function but despite this, did have altered cartilage and tendon properties. These mechanical changes corresponded to altered transcriptional regulation of chondrogenic genes within cartilage and tendon. This study helps define the mechanical and biological mechanisms leading to joint damage and provides a framework for treating active cuff tear patients.
Project description:Rotator cuff tears affect millions of individuals each year, often requiring surgical intervention. However, repair failure remains common. We have previously shown that pulsed electromagnetic field (PEMF) therapy improved tendon-to-bone healing in a rat rotator cuff model. The purpose of this study was to determine the influence of both PEMF frequency and exposure time on rotator cuff healing.Two hundred ten Sprague-Dawley rats underwent acute bilateral supraspinatus injury and repair followed by either Physio-Stim PEMF or high-frequency PEMF therapy for 1, 3, or 6 hours daily. Control animals did not receive PEMF therapy. Mechanical and histologic properties were assessed at 4, 8, and 16 weeks.Improvements in different mechanical properties at various endpoints were identified for all treatment modalities when compared with untreated animals, regardless of PEMF frequency or duration. Of note, 1 hour of Physio-Stim treatment showed significant improvements in tendon mechanical properties across all time points, including increases in both modulus and stiffness as early as 4 weeks. Collagen organization improved for several of the treatment groups compared with controls. In addition, improvements in type I collagen and fibronectin expression were identified with PEMF treatment. An important finding was that no adverse effects were identified in any mechanical or histologic property.Overall, our results suggest that PEMF therapy has a positive effect on rat rotator cuff healing for each electromagnetic fundamental pulse frequency and treatment duration tested in this study.
Project description:BACKGROUND:Previous studies have shown that ibuprofen is detrimental to tissue healing after acute injury; however, the effects of ibuprofen when combined with noninjurious exercise are debated. HYPOTHESIS:Administration of ibuprofen to rats undergoing a noninjurious treadmill exercise protocol will abolish the beneficial adaptations found with exercise but will have no effect on sedentary muscle and tendon properties. STUDY DESIGN:Controlled laboratory study. METHODS:A total of 167 male Sprague-Dawley rats were divided into exercise or cage activity (sedentary) groups and acute (a single bout of exercise followed by 24 hours of rest) and chronic (2 or 8 weeks of repeated exercise) response times. Half of the rats were administered ibuprofen to investigate the effects of this drug over time when combined with different activity levels (exercise and sedentary). Supraspinatus tendons were used for mechanical testing and histologic assessment (organization, cell shape, cellularity), and supraspinatus muscles were used for morphologic (fiber cross-sectional area, centrally nucleated fibers) and fiber type analysis. RESULTS:Chronic intake of ibuprofen did not impair supraspinatus tendon organization or mechanical adaptations (stiffness, modulus, maximum load, maximum stress, dynamic modulus, or viscoelastic properties) to exercise. Tendon mechanical properties were not diminished and in some instances increased with ibuprofen. In contrast, total supraspinatus muscle fiber cross-sectional area decreased with ibuprofen at chronic response times, and some fiber type-specific changes were detected. CONCLUSION:Chronic administration of ibuprofen does not impair supraspinatus tendon mechanical properties in a rat model of exercise but does decrease supraspinatus muscle fiber cross-sectional area. This fundamental study adds to the growing literature on the effects of ibuprofen on musculoskeletal tissues and provides a solid foundation on which future work can build. CLINICAL RELEVANCE:The study findings suggest that ibuprofen does not detrimentally affect regulation of supraspinatus tendon adaptations to exercise but does decrease muscle growth. Individuals should be advised on the risk of decreased muscle hypertrophy when consuming ibuprofen.
Project description:Passing suture during a rotator cuff repair requires proper orientation and purchase of the rotator cuff tendon. Our technique uses a new portal to improve access to the supraspinatus and infraspinatus and uses additional portals for a circumferential repair of the tear, thereby restoring the footprint. Using a penetrating suture passer through the anterior, posterior, and superomedial portals allows 270° of coverage. The lateral anchors complete the circumferential repair. Sutures from the medial anchors are passed in a retrograde fashion using 3 small incisions with no cannula. A spinal needle is used to localize the orientation of each portal. The N+4 portal is the workhorse portal, allowing access to the supraspinatus and infraspinatus. The suture retriever enters the trapezius 5 cm from the medial border of the acromion and 1 cm anterior to the spine of the scapula. It enters the subacromial space on top of the supraspinatus. This provides protection to the suprascapular nerve in the supraspinatus fossa. The cuff is lifted with a grasper to allow perpendicular passage of suture. The suture is retrieved for tying. The tissue purchase and location of suture placement help restore the footprint of the supraspinatus and infraspinatus. Additional sutures are passed anteriorly through the subclavian portal and posteriorly through the high posteromedial portal. The repair is completed with lateral-row anchors as needed.
Project description:Tendon injuries heal as scar tissue with significant dysfunction and propensity to re-injure, motivating efforts to develop stem cell-based therapies for tendon regeneration. For these therapies to succeed, effective cues to guide tenogenesis are needed. Our aim is to identify these cues within the embryonic tendon microenvironment. We recently demonstrated embryonic tendon elastic modulus increases during development and is substantially lower than in adult. Here, we examined how these embryonic mechanical properties influence tenogenically differentiating cells, by culturing embryonic tendon progenitor cells (TPCs) within alginate gel scaffolds fabricated with embryonic tendon mechanical properties. We showed that nano- and microscale moduli of RGD-functionalized alginate gels can be tailored to that of embryonic tendons by adjusting polymer concentration and crosslink density. These gels differentially regulated morphology of encapsulated TPCs as a function of initial elastic modulus. Additionally, higher initial elastic moduli elicited higher mRNA levels of scleraxis and collagen type XII but lower levels of collagen type I, whereas late tendon markers tenomodulin and collagen type III were unaffected. Our results demonstrate the potential to engineer scaffolds with embryonic mechanical properties and to use these scaffolds to regulate the behavior of tenogenically differentiating cells.
Project description:The objective of this study was to understand the effect of pre-repair rotator cuff chronicity on post-repair healing outcomes using a chronic and acute multi-tendon rat rotator cuff injury model. Full-thickness dual tendon injuries (supra- and infraspinatus) were created unilaterally in adult male Sprague Dawley rats, and left chronically detached for 8 or 16 weeks. After chronic detachment, tears were repaired and acute dual tendon injuries were created and immediately repaired on contralateral shoulders. Tissue level outcomes for bone, tendon, and muscle were assessed 4 or 8 weeks after repair using histology, microcomputed tomography, biomechanical testing, and biochemical assays. Substantial gap formation was seen in 35% of acute repairs and 44% of chronic repairs. Gap formation negatively correlated with mechanical and structural outcomes for both healing time points regardless of injury duration. Bone and histomorphometry, as well as biomechanics, were similar between acute and chronic injury and repair regardless of chronicity and duration of healing. This study was the first to implement a multi-tendon rotator cuff injury with surgical repair following both chronic and acute injuries. Massive tear in a rodent model resulted in gap formation regardless of injury duration which had detrimental effects on repair outcomes.