By: 25 October 2011

Nyffeler R, Werner CML, Sukthankar A, Schmid MR, Gerber C.
Journal of Bone Joint Surgery Am. / 2006;88-A :800-5.

From their own observations these authors have observed that patients who have large acromions seen both on X-rays or during surgery tend to have rotator cuff tears . They suggest that such acromions contribute to rotator cuff tears.

The authors compared the preoperative x-rays of patients with surgically proven rotator cuff tears to 2 groups of patients with intact cuffs: those undergoing total shoulder replacement for osteoarthritis and an age and gender matched asymptomatic control group. X-ray measurements were made using three parallel vertical lines between the glenoid plane, the lateral acromion edge and the lateral edge of the greater tuberosity. They then measured the acromial index which was the gleno-acromial distance divided by the gleno-tuberosity distance.

They found that the index was significantly higher for patients with rotator cuff tears and lower for the two groups of patients with intact cuffs (p <0.0001).

The authors suggest that the lateral extension of the acromion influences the deltoid muscle force vector. A lateralised acromion causes a greater ascending force to be exerted by the deltoid fibres on the humerus during abduction. This reduces the acromial humeral space and impinges on the supraspinatus leading to degenerative tears.

Comparatively, a short lateral extension would lead to a smaller ascending force but a larger compression force on the glenoid which would explain the association with glenoid osteoarthritis.

The authors conclude that the lateral acromial extension could contribute to a rotator cuff tear however, further studies are required to confirm whether it is a cause or rather than a consequence.