@article{73aa718bd51b47f5a7c8eb3a2f6500c6,
title = "Mechanical environment associated with rotator cuff tears",
abstract = "A simplified 2-dimensional finite element model was used to investigate the stress environment in the supraspinatus tendon. The extrafibrillar matrix and collagen fiber were modeled with fiber-reinforced composite elements. The stress was evaluated at humeroscapular elevation angles of 0°, 30°, and 60°. Two acromion conditions were simulated. In the first set of conditions there was no subacromial impingement. In the second set there was subacromial impingement of the bursal side. Impingement was simulated by producing a 1-mm indentation on the bursal surface, an indentation similar to the type of impingement associated with deltoid contraction. The results demonstrated that subacromial impingement generates high stress concentrations in and around the critical zone. Such high stress could initiate a tear; tears that result from stress point to an extrinsic mechanism. However, we found that high stress and potential tears caused by impingement may occur on the bursal side, the articular side, or within the tendon. This result is unaccounted for by traditional mechanical models in which only bursal-sided partial tears are initiated by subacromial impingement.",
author = "Luo, {Zong Ping} and Hsu, {Horng Chaung} and Grabowski, {John J.} and Morrey, {Bernard F.} and An, {Kai Nan}",
note = "Funding Information: The intrinsic mechanism proposed by Codmanr postulates that degenerative changes in the rotator cuff result in tears. This theory has been supported by several recent studies.*Jl3,{\textquoteleft}7 In a study involving 306 cadaver+ specimens, Uhthoff et all7 stated that the maiority of cuff tears were initiated on the articular side. This implies that the initial tears were degenerative in nature and that extrinsic causes played a secondary role. Ozaki et all3 correlated the changes on the undersurface of the acromion of ZOO shoulder specimens with pathologic changes of the rotator cuff. They found that specimens that had a partial rotator cuff tear on the articular side usually had an intact acromial undersurface. in addition, the severity of the pathologic findings on the undersurface was correlated with the severity of the cuff tear. Ozaki et all3 concluded that lesions that appeared on the anterior third of the under-surface of the acromion seemed to represent a secondary change that followed cuff tears of the bursal side. A vicious cycle then developed, such that the irregularity of the acromial undersurface abraded the cuff and vice versa. Lohr and Uhthoff* reported a microvascular study of 18 shoulder specimens that also tended to support the intrinsic model. Their study revealed that within the critical zone almost no vessels were present on the articular side of the tendon. Small, penetrating vessel branches were observed to extend from the humeral head toward the more proximal tendinous branches. However, in all cases, these branches failed to reach their destination. Such shortcomings in vascularization make the cuff more susceptible to degenerative changes and functional failure.",
year = "1998",
doi = "10.1016/S1058-2746(98)90010-6",
language = "English (US)",
volume = "7",
pages = "616--620",
journal = "Journal of Shoulder and Elbow Surgery",
issn = "1058-2746",
publisher = "Mosby Inc.",
number = "6",
}