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.
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ABSTRACT: No clear recommendations exist regarding optimal humeral component version and deltoid tension in reverse total shoulder arthroplasty (TSA). A biomechanical shoulder simulator tested humeral versions (0°, 10°, 20° retroversion) and implant thicknesses (-3, 0, +3 mm from baseline) after reverse TSA in human cadavers. Abduction and external rotation ranges of motion as well as abduction and dislocation forces were quantified for native arms and arms implanted with 9 combinations of humeral version and implant thickness. Resting abduction angles increased significantly (up to 30°) after reverse TSA compared with native shoulders. With constant posterior cuff loads, native arms externally rotated 20°, whereas no external rotation occurred in implanted arms (20° net internal rotation). Humeral version did not affect rotational range of motion but did alter resting abduction. Abduction forces decreased 30% vs native shoulders but did not change when version or implant thickness was altered. Humeral center of rotation was shifted 17 mm medially and 12 mm inferiorly after implantation. The force required for lateral dislocation was 60% less than anterior and was not affected by implant thickness or version. Reverse TSA reduced abduction forces compared with native shoulders and resulted in limited external rotation and abduction ranges of motion. Because abduction force was reduced for all implants, the choice of humeral version and implant thickness should focus on range of motion. Lateral dislocation forces were less than anterior forces; thus, levering and inferior/posterior impingement may be a more probable basis for dislocation (laterally) than anteriorly directed forces.Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 04/2011; 21(4):483-90. · 1.93 Impact Factor
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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. · 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 02/2012; 30(9):1430-4. · 2.88 Impact Factor