Chronic Effects of Pitching on Muscle Thickness and Strength of the Scapular Stabilizers in Professional Baseball Players.

Background: The posterior scapular muscles eccentrically contract to disperse the high forces observed in the deceleration phase of pitching. Muscular adaptations often occur following chronic eccentric loading, however, no study has evaluated the adaptations of the posterior scapular muscles with regard to throwing and their relationship with humeral retroversion (HR) in professional pitchers.

Hypothesis: Significant chronic adaptations in muscle thickness (MT) and strength of the trapezius and rhomboids would be observed in healthy professional baseball pitchers, and there would be a significant relationship between humeral adaptations (ie, HR) and posterior scapular muscle adaptations (ie, strength and MT).

Master swimmers with shoulder pain and disability have altered functional and structural measures.

Context: Supraspinatus tendinopathy and shoulder pain are common in competitive youth swimmers; however, no studies have investigated clinical and structural factors contributing to shoulder pain and disability in master level swimmers.

Objective: The objectives of this study were: 1) to determine the prevalence of shoulder pain and disability in master level swimmers, 2) to identify the most provocative special tests for shoulder pain, and 3) to determine if shoulder clinical and tissue specific measures, training variables and volume vary between those with and without shoulder pain, dissatisfaction and disability.

Design: Cross-sectional.

Movement Coordination During Humeral Elevation in Individuals With Newly Acquired Spinal Cord Injury.

Humeral elevation is a critical motion for individuals who use a manual wheelchair given that, in a typical day, wheelchair users reach overhead 5 times more often than able-bodied controls. Kinematic analyses in individuals with chronic spinal cord injury (SCI) have focused on weight-bearing tasks rather than overhead reaching. This technical report presents shoulder movement coordination during overhead reaching in individuals with newly acquired SCI.

Tendon Biomechanics and Crimp Properties Following Fatigue Loading Are Influenced by Tendon Type and Age in Mice.

In tendon, type-I collagen assembles together into fibrils, fibers, and fascicles that exhibit a wavy or crimped pattern that uncrimps with applied tensile loading. This structural property has been observed across multiple tendons throughout aging and may play an important role in tendon viscoelasticity, response to fatigue loading, healing, and development. Previous work has shown that crimp is permanently altered with the application of fatigue loading.

Dynamic Loading and Tendon Healing Affect Multiscale Tendon Properties and ECM Stress Transmission.

The extracellular matrix (ECM) is the primary biomechanical environment that interacts with tendon cells (tenocytes). Stresses applied via muscle contraction during skeletal movement transfer across structural hierarchies to the tenocyte nucleus in native uninjured tendons. Alterations to ECM structural and mechanical properties due to mechanical loading and tissue healing may affect this multiscale strain transfer and stress transmission through the ECM.

Nonsurgical treatment and early return to activity leads to improved Achilles tendon fatigue mechanics and functional outcomes during early healing in an animal model.

Achilles tendon ruptures are common and devastating injuries; however, an optimized treatment and rehabilitation protocol has yet to be defined. Therefore, the objective of this study was to investigate the effects of surgical repair and return to activity on joint function and Achilles tendon properties after 3 weeks of healing. Sprague-Dawley rats (N = 100) received unilateral blunt transection of their Achilles tendon.

Evaluating changes in tendon crimp with fatigue loading as an ex vivo structural assessment of tendon damage.

The complex structure of tendons relates to their mechanical properties. Previous research has associated the waviness of collagen fibers (crimp) during quasi-static tensile loading to tensile mechanical properties, but less is known about the role of fatigue loading on crimp properties. In this study (IACUC approved), mouse patellar tendons were fatigue loaded while an integrated plane polariscope simultaneously assessed crimp properties.

Exercise protocol induces muscle, tendon, and bone adaptations in the rat shoulder.

Background: a rat model of supraspinatus overuse has suggested mechanisms governing tendon degeneration; however, delineating which changes are pathologic or simply physiologic adaptations to increased loading remains a question. The objective of this study was to develop and characterize a rat exercise model that induces systemic and local shoulder adaptations without mechanical injury to the supraspinatus tendon.

Methods: exercise rats completed a treadmill training protocol for 12 weeks.

In situ fibril stretch and sliding is location-dependent in mouse supraspinatus tendons.

Tendons are able to transmit high loads efficiently due to their finely optimized hierarchical collagen structure. Two mechanisms by which tendons respond to load are collagen fibril sliding and deformation (stretch). Although many studies have demonstrated that regional variations in tendon structure, composition, and organization contribute to the full tendon׳s mechanical response, the location-dependent response to loading at the fibril level has not been investigated.

Effect of isolated hyperglycemia on native mechanical and biologic shoulder joint properties in a rat model.

Recently, diabetes has been linked to rotator cuff disease and adhesive capsulitis, conditions with increased stiffness and inflammation. Unfortunately, limited research exists examining how hyperglycemia affects the native shoulder (tendon and capsule) properties. Therefore, the objectives of this study were to compare shoulder joint mechanics, tendon properties (mechanics and immunohistochemistry), and capsule of healthy control and hyperglycemic rats 8 weeks following induction of hyperglycemia with a submaximal dose of streptozotocin (STZ).

Bioengineered stromal cell-derived factor-1α analogue delivered as an angiogenic therapy significantly restores viscoelastic material properties of infarcted cardiac muscle.

Ischemic heart disease is a major health problem worldwide, and current therapies fail to address microrevascularization. Previously, our group demonstrated that the sustained release of novel engineered stromal cell-derived factor 1-a analogue (ESA) limits infarct spreading, collagen deposition, improves cardiac function by promoting angiogenesis in the region surrounding the infarct, and restores the tensile properties of infarcted myocardium. In this study, using a well-established rat model of ischemic cardiomyopathy, we describe a novel and innovative method for analyzing the viscoelastic properties of infarcted myocardium.

Disruption of the anterior-posterior rotator cuff force balance alters joint function and leads to joint damage in a rat model.

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.

Analysis of collagen organization in mouse achilles tendon using high-frequency ultrasound imaging.

Achilles tendon ruptures are traumatic injuries, and techniques for assessing repair outcomes rely on patient-based measures of pain and function, which do not directly assess tendon healing. Consequently, there is a need for a quantitative, in vivo measure of tendon properties. Therefore, the purpose of this study was to validate ultrasound imaging for evaluating collagen organization in tendons.

Biceps detachment decreases joint damage in a rotator cuff tear rat model.

Background: Pathology in the long head of the biceps tendon often occurs in patients with rotator cuff tears. Arthroscopic tenotomy is the most common treatment. However, the role of the long head of the biceps at the shoulder and the consequences of surgical detachment on the remaining shoulder structures remain unknown.

Biomechanical and structural response of healing Achilles tendon to fatigue loading following acute injury.

Achilles tendon injuries affect both athletes and the general population, and their incidence is rising. In particular, the Achilles tendon is subject to dynamic loading at or near failure loads during activity, and fatigue induced damage is likely a contributing factor to ultimate tendon failure. Unfortunately, little is known about how injured Achilles tendons respond mechanically and structurally to fatigue loading during healing.

The dynamics of collagen uncrimping and lateral contraction in tendon and the effect of ionic concentration.

Under tensile loading, tendon undergoes a number of unique structural changes that govern its mechanical response. For example, stretching a tendon is known to induce both the progressive "uncrimping" of wavy collagen fibrils and extensive lateral contraction mediated by fluid flow out of the tissue. However, it is not known whether these processes are interdependent.

Returning to overuse activity following a supraspinatus and infraspinatus tear leads to joint damage in a rat model.

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.

Effect of age and proteoglycan deficiency on collagen fiber re-alignment and mechanical properties in mouse supraspinatus tendon.

Collagen fiber realignment is one mechanism by which tendon responds to load. Re-alignment is altered when the structure of tendon is altered, such as in the natural process of aging or with alterations of matrix proteins, such as proteoglycan expression. While changes in re-alignment and mechanical properties have been investigated recently during development, they have not been studied in (1) aged tendons, or (2) in the absence of key proteoglycans.

Effect of return to overuse activity following an isolated supraspinatus tendon tear on adjacent intact tendons and glenoid cartilage in a rat model.

Rotator cuff tears are common conditions that can alter shoulder mechanics and may lead to damage of intact joint tissues. These injuries are of particular concern in populations who perform tasks requiring repetitive overhead activity (e.g.

Mathematically engineered stromal cell-derived factor-1α stem cell cytokine analog enhances mechanical properties of infarcted myocardium.

Objective: The biomechanical response to a myocardial infarction consists of ventricular remodeling that leads to dilatation, loss of contractile function, abnormal stress patterns, and ultimately heart failure. We hypothesized that intramyocardial injection of our previously designed pro-angiogenic chemokine, an engineered stromal cell-derived factor-1α analog (ESA), improves mechanical properties of the heart after infarction.

Methods: Male rats (n = 54) underwent either sham surgery (n = 17) with no coronary artery ligation or ligation of the left anterior descending artery (n = 37).

Glenoid cartilage mechanical properties decrease after rotator cuff tears in a rat model.

Rotator cuff repairs are commonly performed to reduce pain and restore function. Tears are also treated successfully without surgical intervention; however, the effect that a torn tendon has on the glenohumeral cartilage remains unknown. Clinically, a correlation between massive rotator cuff tears and glenohumeral arthritis has often been observed.

Restoration of anterior-posterior rotator cuff force balance improves shoulder function in a rat model of chronic massive tears.

The rotator cuff musculature imparts dynamic stability to the glenohumeral joint. In particular, the balance between the subscapularis anteriorly and the infraspinatus posteriorly, often referred to as the rotator cuff "force couple," is critical for concavity compression and concentric rotation of the humeral head. Restoration of this anterior-posterior force balance after chronic, massive rotator cuff tears may allow for deltoid compensation, but no in vivo studies have quantitatively demonstrated an improvement in shoulder function.