Biomechanical Data Concerning the Shoulder Impingement Syndrome

Abstract

This study evaluates forces underneath the coracoacromial vault during elevation of the arm, using a dynamic shoulder model. Muscle forces at the glenohumeral joint were simulated with hydrodynamic cylinders and applied to the deltoid muscle and to the rotator cuff through wire cables in ten anatomic specimens. Computerized regulation initiated precise, time-controlled cycles of glenohumeral joint motion. The position of the arm in all spatial orientations was measured with an ultrasonic device. Forces underneath the coracoacromial vault were recorded with capacitive sensors. The mean force during one cycle of elevation averaged 13.9 N 2 12.5 N underneath the acromion, 0.43 N ? 0.51 N underneath the coracoacromial ligament, and 3.44 N 2 4.37 N underneath the coracoid process. The peak force averaged 37.8 N 2 33.2 N underneath the acromion, 3.03 N 2 2.62 N underneath the coracoacromial ligament, and 6.93 N ? 7.38 N underneath the coracoid process. Forces under the coracoid process exceeded forces under the acromion in some specimens. A marked increase in forces was observed a t the final stage of arm elevation and during early reverse-elevation in most specimens. The authors believe that these force values represent the pathomechanics of the shoulder impingement syndrome.

The influence of the acromial coverage index in rotator cuff tears

“…Bigliani et al 3 defined 3 distinct types of acromions and the relationship between acromial morphology and the incidence of rotator cuff tears in cadavers. Their classification has been corroborated by different studies 3,12,16,23,30,34,35 and has also been the subject of discussion by several authors who believe that the type III acromion is not an anatomic variant but results from ossification in the attachment of the coracoacromial ligament or is agerelated. 7,28,33 Other authors support the extrinsic mechanism by defining different patterns of contact that may lead to cuff compromise, such as the anterior slope of the acromion, 1 the coracoid process as another possible site of soft-tissue impingement, 10 the relationship between the lateral acromion angle and rotator cuff disease, 2,13,17,31 impingement of the deep surface of the rotator cuff on the posterosuperior border of the glenoid, 32 the anterosuperior impingement of the deep surface of the subscapularis, 11 and the influence of glenoid version on rotator cuff tears.…”

The coracoacromial ligament: Morphology and study of acromial enthesopathy

“…1,3,4,8,9,14,17,20,21,25,27,28,30,31 The CAL may form a small ridge at the inferolateral margin of the acromion that contributes toward rotator cuff pathology. Acromion enthesopathy (spur formation within the CAL at the anterior margin of the acromion) has been attributed to forces transmitted through the CAL via traction.…”

Options Before Reverse Total Shoulder Replacement

“…A tuberoplasty might also be considered in this patients group. Coraco-acromial ligament, a major restraint against superior migration of the humeral head, should be handled with care, and can be detached but should not be resected in this group of patients [65,66]. A biceps tenotomy, with or without tenodesis seems to be a safe additional procedure, helping decreasing the pain associated with massive cuff tears [64].…”