It is unknown at which stage of rotator cuff tear the biomechanical environment is altered. The purpose of this study was to determine if a critical rotator cuff tear stage exists that alters glenohumeral joint biomechanics throughout the rotational range of shoulder motion, and to evaluate the biomechanical effect of parascapular muscle-loading.
Eight cadaver shoulders were used with a custom testing system. Four progressive rotator cuff tear stages were investigated on the basis of footprint anatomy. Three muscle-loading conditions were examined: rotator cuff only; rotator cuff with deltoid muscle; and rotator cuff, deltoid, pectoralis major, and latissimus dorsi muscles. Testing was performed in the scapular plane with 0°, 30°, and 60° of shoulder abduction. The maximum internal and external rotations were measured with 3.4 Nm of torque. The position of the humeral head apex with respect to the glenoid was calculated with use of a MicroScribe 3DLX digitizing system throughout the rotational range of motion. The abduction capability was determined as the abduction angle achieved with increasing deltoid load.
Tear of the entire supraspinatus tendon significantly increased maximum external rotation and significantly decreased abduction capability with higher deltoid loads (p < 0.05). Tear of the entire supraspinatus tendon and half of the infraspinatus tendon significantly shifted the humeral head apex posteriorly at the midrange of rotation and superiorly at maximum internal rotation (p < 0.05). Loading the pectoralis major and latissimus dorsi muscles decreased the amount of humeral head elevation due to deltoid loading.
Tear of the entire supraspinatus tendon was the critical stage for increasing rotational range of shoulder motion and for decreased abduction capability. Further tear progression to the infraspinatus muscle was the critical stage for significant changes in humeral head kinematics. The pectoralis major and latissimus dorsi muscles played an important role in stabilizing the humeral head as the rotator cuff tear progressed.
"Just as full-thickness rotator cuff tears are almost always preceded by partial tears and tendon degeneration (Oh et al., 2011), noninflammatory tendinosis and chronic tendinopathy predispose the Achilles tendon to complete rupture (Hess, 2010). In examining biopsy samples of patients undergoing open repair for torn Achilles tendons, Tallon et al. found that ruptured tendons were significantly more degenerated than tendinopathic tendons (Tallon et al., 2001). "
"These two-tendon tears may disrupt the force balance provided by the subscapularis anteriorly and infraspinatus posteriorly (Burkhart, 1991). This force balance disruption may lead to humeral head translations (Keener et al., 2009; Oh et al., 2011) and therefore increase the patient's risk of developing secondary joint damage, such as tear propagation, long head of the biceps (LHB) degeneration (Lakemeier et al., 2010a), articular cartilage degeneration (Hsu et al., 2003), or cuff tear arthropathy (Neer II et al., 1983). Clinical investigations have shown a correlation between two-tendon rotator cuff tears and secondary joint pathology (Keener et al., 2009), such as impaired joint function and LHB pain(Lakemeier et al., 2010a, 2010b). "
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Biomechanics 06/2013; 46(11). DOI:10.1016/j.jbiomech.2013.05.007 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rotator cuff injuries are common problems and a frequent reason for patients to present to primary care physicians. These injuries are seen more frequently now with the aging population. These muscles allow for movement of the arm in overhead activities and controlled movements through space. A thorough physical examination can lead to the diagnosis of rotator cuff pathology. Radiographic imaging may offer some insight into the underlying pathology, and magnetic resonance imaging provides for excellent visualization of the rotator cuff. Many rotator cuff tears, especially partial tears, will symptomatically improve with conservative management. Surgical treatment may offer improved pain relief and function in those patients for whom nonoperative care is insufficient. In cases in which rotator cuff repair is not possible, the reverse total shoulder arthroplasty is a possibility. New technologies are also under investigation that allow for biological augmentation of rotator cuff tears.
The Physician and sportsmedicine 05/2012; 40(2):73-86. DOI:10.3810/psm.2012.05.1967 · 1.09 Impact Factor
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