This study demonstrated that orthopedic surgeons with fellowship training in shoulder surgery have fair to moderate interobserver reliability in determining the presence of an enthesophyte. However, the measurement of these enthesophytes showed only poor interobserver reliability. The interobserver reliability in determining acromial morphology was found to be moderate.
As in most reliability studies, the intraobserver reliability was generally better than the interobserver reliability [20
]. The intraobserver reliability for determining the presence of an enthesophyte was moderate. Similar to the interobserver findings, intraobserver reliability using the enthesophyte length technique was poor. However, the intraobserver reliability of measuring the enthesophyte–humeral distance was moderate. Intraobserver reliability in determining acromial morphology was determined to be good.
It is not clear why the radiographic methods of measuring the size of the acromial enthesophyte were unreliable. It is possible that it is difficult to reliably determine the inferior cortex of the acromion on two-dimensional radiographs. It is also possible that the reliability of this method would be improved using digital radiographs with a computerized measuring device. Computed tomography may be a more reliable method of measuring acromial enthesophytes, but this does not appear to be practical from a clinical standpoint.
This study was potentially limited by the inclusion of non-consecutive patients. The methodology of this study would be improved by having the investigators review a series of consecutive radiographs that were not previewed by the principal investigator. The difficulty with this proposed study design is that the true incidence of acromial enthesophytes is not well known. It may take >100 consecutive patients to have enough radiographic images to evaluate the presence of an acromial enthesophyte and all three acromial morphologies. In an attempt to limit the inclusion of potential bias, all of the investigators were blinded to the classifications determined by all other investigators including the principal investigator that selected the radiographic series.
The presence of an acromial enthesophyte was first noted in 1922 when Graves described a plaque of bone on the undersurface of the acromion. Graves suggested that it was an ossification of the coracoacromial ligament [6
]. Further studies have noted the presence of the acromial enthesophyte [1
]. The presence of enthesophytes ranges from 7% to 43.7% [3
]. While most studies suggest that acromial spur incidence and size increase with age [14
], two studies indicate no correlation of age and the prevalence of acromial enthesophytes [32
]. Shoulders with type III acromial morphology have been associated with a statistically increased presence of an entheophyte [14
Bigliani et al. stressed the importance of distinguishing between spurs, which were probably acquired, and the variations in the native architectural type of the acromion [6
]. Others have supported this distinction between native acromial morphology and the presence of an acquired acromial enthesophyte [14
]. However, some believe that the hooked acromion (type III) is primarily an acquired characteristic and is a result of a degenerative change that occurs with aging [8
]. Edelson [8
] supports this theory through his finding that no hooked acromions were found in cadaveric specimens under the age of 30 and that as age increased hooks became more common and larger. No longitudinal studies on acromial morphology have been recorded, and so the impact of the aging process on acromial morphology remains theoretical [31
Although there are no other studies found in the literature that assess reliability in determining the presence or size of an acromial enthesophyte, there are several studies that have examined the reliability of determining acromial morphology [4
]. The interobserver reliability of this study was as good as or better than that of the previously published studies. An author of one of these studies felt that one of the difficulties with determining acromial morphology is the presence of acromial spurs which may confound the classification of the acromial morphology [4
]. When a spur is present, the true acromial edge may appear indistinct, which may influence its classification. The current study is the first published reliability study that attempts to differentiate between native acromial morphology and the presence of an acromial enthesophyte.
Several studies have noted a correlation with the presence of a type III acromion and the increased prevalence and severity of rotator cuff disease [2
]. Similar findings have been found correlating the presence of acromial enthesophytes and rotator cuff disease [2
]. However, other studies debate the correlation of rotator cuff disease with acromial morphology or acromial enthesophytes [18
]. When examining the success of non-operative treatment of impingement syndrome, acromial morphology has been shown to influence the outcome scores and the need for surgical intervention [28
]. The presence of an acromial enthesophyte was not found to be statistically related to worse outcomes of the non-operative management of impingement syndrome [40
It is possible that the enthesophyte size and the distance between the enthesophyte and the humeral head is correlated with rotator cuff pathology; however, it has not been documented thus far. The authors believe that future studies should be performed to examine the role of the enthesophyte in the development of symptoms and the ability of treating rotator cuff tears associated with acromial enthesophytes. This current study may be helpful in developing these future studies.