Humeral head translation decreases with muscle loading
ABSTRACT This study was conducted to determine the effect of in vitro passive and active loading on humeral head translation during glenohumeral abduction. A shoulder simulator produced unconstrained active abduction of the humerus in 8 specimens. Loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and anterior, middle, and posterior deltoid muscles was simulated by use of 4 different sets of loading ratios. Significantly greater translations of the humeral head occurred both in 3 dimensions (P < .001) and in the sagittal plane (P < .005) during passive motion when compared with active motion from 30 degrees to 70 degrees of abduction. In the sagittal plane, passive abduction experienced a resultant translation of 3.8 +/- 1.0 mm whereas the active loading ratios averaged 2.3 +/- 1.0 mm. There were no significant differences in the translations that were produced by the 4 sets of muscle-loading ratios used to achieve active motions. This study emphasizes the importance of the musculature in maintaining normal ball-and-socket kinematics of the shoulder.
SourceAvailable from: Milad Masjedi[Show abstract] [Hide abstract]
ABSTRACT: Musculoskeletal shoulder models allow non-invasive prediction of parameters that cannot be measured, particularly the loading applied to morphological structures and neurological control. This insight improves treatment and avoidance of pathology and performance evaluation and optimisation. A lack of appropriate validation and knowledge of model parameters' accuracy may cause reduced clinical success for these models. Instrumented implants have recently been used to validate musculoskeletal models, adding important information to the literature. This development along with increasing prevalence of shoulder models necessitates a fresh review of available models and their utility. The practical uses of models are described. Accuracy of model inputs, modelling techniques and model sensitivity is the main technical review undertaken. Collection and comparison of these parameters are vital to understanding disagreement between model outputs. Trends in shoulder modelling are highlighted: validation through instrumented prostheses, increasing openness and strictly constrained, optimised, measured kinematics. Future directions are recommended: validation through focus on model sub-sections, increased subject specificity with imaging techniques determining muscle and body segment parameters and through different scaling and kinematics optimisation approaches.Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine 07/2013; 227(10):1041-57. DOI:10.1177/0954411913492303 · 1.14 Impact Factor
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ABSTRACT: We evaluated coracoacromial ligament (CAL) displacement during motion in shoulders with supraspinatus tendon tears by dynamic ultrasonography (US). Twenty subjects with unilateral, full-thickness supraspinatus tendon tears (SST group) and 20 subjects with intact supraspinatus tendons (control group) underwent dynamic US. The CAL displacement in their bilateral shoulders was measured in the transverse US view during passive and active shoulder abduction and internal rotation (SAIR). In the SST group, the CAL displacement was significantly greater in the affected shoulders than in the intact ones (1.9 mm ± 0.8 mm vs. 1.5 mm ± 0.5 mm, p = 0.01) during passive SAIR, but was not significantly different between the shoulders (1.7 mm ± 0.7 mm vs. 1.7 mm ± 0.4 mm, p = 0.81) during active SAIR. In the control group, no difference in the CAL displacement between the shoulders was noted during passive and active SAIR. Thus, dynamic US revealed greater CAL displacement in shoulders with supraspinatus tendon tears than in intact ones during passive SAIR. Dynamic US may help to detect abnormal kinematics in shoulders with such injury.Journal of Orthopaedic Research 09/2012; 30(9):1430-4. DOI:10.1002/jor.22084 · 2.97 Impact Factor
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ABSTRACT: Background: Supraspinatus tears are common in pitchers. However, the effect of these tears on glenohumeral (GH) mechanics is incompletely understood. Purpose/Hypothesis: To describe the effect of supraspinatus tears and repairs on GH kinematics during an abbreviated throwing motion using the intact shoulder girdle. The hypothesis was that supraspinatus tears would lead to an increase of GH translation in the coronal plane and supraspinatus repairs would restore GH kinematics. Study Design: Controlled laboratory study. Methods: Six shoulders from 3 fresh-frozen cadavers were tested in a novel 7 degrees of freedom robotic testing system. Torsos were mounted and the wrist was pinned to an actuator mounted on an upper frame. After the deltoid was removed, the shoulders were studied during an abbreviated throwing motion (ATM) from maximum external rotation to the midcoronal plane to establish a baseline. The ATM was repeated after creation of a 1-cm supraspinatus tear, after creation of a 3-cm supraspinatus tear, and after repair with a transosseous equivalent (TOE) technique. Retroreflective bone markers and high-speed infrared cameras were used to measure GH kinematics and calculate the center of rotation of the GH joint (CORGH) instantaneously. Results: The 1- and 3-cm supraspinatus tears did not significantly alter GH translation. The TOE repair shifted the CORGH posteriorly, as evidenced by a significant decrease in the overall GH translation in all 3 planes (P = .003, .019, and .026, for x-y, y-z, and x-z planes, respectively). Conclusion: In contrast to a TOE repair of the supraspinatus tendon, isolated supraspinatus tears did not perturb GH kinematics in this cadaveric model of the throwing shoulder. Clinical Relevance: In throwing athletes, treatment of rotator cuff tears should be addressed with caution to avoid an unintended alteration in GH kinematics due to overtightening of the tendon.The American Journal of Sports Medicine 09/2014; 42(10). DOI:10.1177/0363546514547348 · 4.70 Impact Factor