The Stress Distribution at the Undersurface of the Acromion in a Rotator Cuff Tear Shoulder using

CT Osteoabsorptiometry.

Abstract

CT osteoabsorptiometry is a method of predicting the long-standing stress distribution over individual joints by measuring the pattern of subchondral bone density. The purpose of this study is to predict the subacromial stress distribution in normal and rotator cuff tear shoulders using this method. CT image data of 9 shoulders with rotator cuff tears and 5 normal shoulders were prepared for this study. CT values of the undersurface of the acromion were measured on coronal view. For analysis, mapping data depicted by a gray scale were created from the CT values at each coordinate point. The distribution patterns were classified into 3 types according to the location of the high density area: Anterolateral type, anterior type, posterior type. In the cuff tear group,5 shoulders were classified in anterolateral type, and 4 in anterior type. In the control group,1 shoulder in antero-lateral type, and 4 in posterior type. The quantitative analysis was based on the ratio of the high bone density area of the undersurface of the acromion. The ratio of the high density area was significantly high at the anterolateral zone in the cuff tear group. In conclusion, the distribution of the high bone density at the antero-lateral part of the acromion was considered to reflect the long-standing stress by subacromial impingement in patients with rotator cuff tears. The difference of stress distribution types in cuff tear group was considered to suggest that the stress distribution area varied in each case.