A DYNAMIC SHOULDER MODEL FOR BIOMECHANICA L MEASUREMENTS

The article discusses a dynamic shoulder model capable of simulating t he forces generated by the rotator cuff and the deltoid muscle, and el evation movements of the glenohumeral joint using, a computer-aided se rvohydraulic unit. In 10 cadaver shoulder specimen, the effects of the loss of function of the supraspinatus muscle on maximum elevation was determined with an ultrasound system. Changes in the so-called imping ement pressure below the coracoacromial arch were determined with the aid of capacitive pressure sensors. With the supraspinatus muscle inac tive/absent, the maximum elevation of the humerus showed a decrease of 6 % (p < 0,05), which, however, was overcome by an increase in deltoi d power of only one-third of the supraspinatus muscle power loss. For a Simulated isolated supraspinatus defect, the subacromial pressure be low the coracoacromial arch decreased by 8 % (p > 0,05). These results confirm clinical investigations showing that isolated lesions affecti ng the supraspinatus tendon often fail to produce symptoms and thus re quire no surgical reconstruction.