Humeroscapular Positions and Motion.

Last updated Wednesday, January 26, 2005

Figure 1 - The "sleeve"

Figure 2 - Tightness of the posterior capsule

Figure 3 - Localized abrasion

Figure 4 - Repeated forced contact

Humeroscapular motion interface

Smooth motion

In addition to the motion at the glenohumeral joint, the upper end of the humerus, biceps tendon and rotator cuff must glide smoothly inside a sleeve consisting of the acromion, deltoid, coracoid, coracoacromial ligament, and the muscles originating from the coracoid. This motion is described as motion at the humeroscapular motion interface.

Excursions of up to 4 cm take place at this nonarticular interface.

Loss of smooth motion

Smooth motion at this interface is required for normal shoulder function. Loss of this smooth motion can result from alterations in the normal postural relationships of the humerus and scapula. Tightness of the posterior capsule can produce obligate superior translation of the humerus on elevation, forcing abrasive contact between the cuff and the undersurface of the coracoacromial arch. Cuff deficiency may also allow superior translation of the humerus in relation to the scapula, creating localized abrasion of the proximal humerus beneath the unyielding acromion. Repeated forced contact of the cuff or proximal humerus with the undersurface of the anterior acromion may grind up the remaining interposed rotator cuff tissue and humeral articular cartilage. Destruction of the joint surface associated with the excessively superior position of the humeral head in massive cuff deficiency is known as cuff tear arthropathy.

Roughness of the superficial aspect of the motion interface (the undersurface of the coracoacromial arch) may also result from developmental or acquired abnormalities in the shape of the acromion. Roughness of the deep aspect of the interface may result from complete or partial thickness cuff tears involving the upper surface of the tendon, by sutures or lumpy tendon attachments following cuff repair, by prominent tendon calcifications, or by abnormal prominence of the tuberosities. Finally, roughness at the humeroscapular interface can result from a thickened subacromial bursa or from posttraumatic or postsurgical scarring.

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