The influence of acromioclavicular joint morphology on rotator cuff tears

A detailed anatomic study of 123 shoulders was performed to define the loca tion of the acromioclavicular IAC) joint within the supraspinatus outlet an d to determine the correlation of AC joint morphologic characteristics with the presence of full-thickness rotator cuff tears (RCTs). The presence, lo cation, and extent of RCTs were first documented for each shoulder, and 2 a natomic landmarks consisting of the anterolateral acromial corner and the i nferior midpoint of the AC joint were identified and their positions digiti zed in 3 dimensions to calculate outlet space and clearance and AC joint lo cations. High resolution x-ray films were then obtained to determine the ex tent of degenerative changes including the location and size of inferior os teophytes and joint space. These specimens were cleaned of all soft tissues , and additional measurements were made. All data were entered into a compu terized database and analyzed with respect to age, sex, and the presence of RCT: Comparison of age-matched RCT versus non-RCT groups revealed no signi ficant differences in the position of the AC joint within the supraspinatus outlet. When AC joint morphologic characteristics were compared with those of a nontear, age-matched group, no significant differences with regard to joint space narrowing were found, but significantly larger and greater num ber of osteophytes were identified on both sides of the joint in the RCT gr oup. In conclusion, the position of the AC joint is fairly constant within the supraspinatus outlet and does not appear to predispose to RCTs. The mor phology of the AC joint contribution of the tears seems to be acquired in n ature rather than inherent in its location within the outlet.