The influence of variations of the coracoacromial arch on the development of rotator cuff tears.

In order to define the geometry of the coracoacromial arch in both its bony and soft parts and to bring it into relationship with rotator cuff tears, 54 cadaver shoulders (from subjects aged 47-90 years) were dissected and X-rayed (anteroposterior projection and supraspinatus outlet view). Partial rotator cuff tears were assessed additionally by transillumination and polarized microscopy. After transfixation of the coracoacromial arch with a polyurethane mould, sections were made along the coracoacromial ligament. The morphology of the acromion was described following the classification of Bigliani et al. [5]. Amongst other parameters, measurements were taken between the long axis of the scapula, the spina, and the acromion. In 19 of 22 cases, a traction osteophyte was associated with rotator cuff tears. In incomplete tears, spurs were completely encased within the ligament and did not impair the subacromial space. The number of rotator cuff tears was significantly increased in shoulders with "curved" acromia, flat acromial slope, and increased angle between the scapular plane and the spina (intact, mean 58 degrees; tears, mean 47 degrees). The morphology of the subacromial space was secondarily determined by this angle. In contrast to Bigliani et al. we were unable to find a "hooked" acromion. These results indicate that the combination of a flat and curved acromion or a position of the acromioclavicular joint above the cranial pole of the glenoid must be regarded as considerable risks for the development of rotator cuff tears. The concept of anterior acromioplasty is supported by our results.