Purpose of the study: To evaluate the effect of acromial morphology, as assessed on radiographs, on rotator cuff tears.
Material: A total of 200 patients surgically treated for shoulder disorders were enrolled. All were older than 40 years and had good quality shoulder radiographs. Two groups were composed: First, a clinical model group of 136 patients to be investigated for three parameters of rotator cuff injury that was divided into two subgroups. One included 68 patients, with an average age of 53.5 years, in whom surgery revealed no injury to the rotator cuff; the other subgroup of 68 patients, with an average age of 58 years, had a ruptured supraspinatus tendon. Subsequently, a control group of 64 patients (32 with rotator cuff injury and 32 without it) was used to verify the results of the model group.
Methods: Three parameters describing the acromion, i.e., acromion index (AI), lateral acromion angle and acromial slope, were measured on standard radiographs. Tangential antero-posterior and scapular "Y" (supraspinatus outlet) views were taken, the images were digitalised and evaluated using a TomoCon 3.0 Viewer programme, and the results of the two groups were statistically analysed and compared.
Results: The difference between the patients with rotator cuff injury and those without it was best shown, in both groups, by significant differences in the acromion index. This was true for both the men and women. The AI values for the patients with rotator cuff injury were 0.66 and 0.65 in the model and control groups, respectively. The same AI value of 0.76 was found for uninjured rotator cuffs in both groups. The two other parameters investigated did not appear to be of any significant validity for assessment of rotator cuff tears.
Discussion: The aetiology of injury to the rotator cuff has not been fully understood yet but, undoubtedly, the causes will be many. The shape of the acromion is regarded as one of the important factors. We agree with Nyffeler et al. that a lateral extension of the acromion is most often associated with rotator cuff tears and that the acromion index proposed by these authors is a good parameter to assess this morphological change.
Conclusions: A lateral extension of the acromion plays an important role in the aetiology of degenerative tears of the supraspinatus tendon. The acromion index appears to be the best instrument for assessing this morphological change.