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Title:Effects of rotator cuff tears on glenohumeral capsule strain
Author(s):Rahman, Hafizur
Director of Research:Kersh, Mariana
Doctoral Committee Chair(s):Kersh, Mariana
Doctoral Committee Member(s):Wagoner Johnson, Amy J.; Toussaint, Kimani; Harley, Brendan
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Rotator cuff tear
glenohumeral capsule
activities of daily living
Abstract:Rotator cuff tears (RCTs) account for more than 4.5 million physician visits annually in the United States and are a primary source of shoulder pain and dysfunction. Approximately 250,000 rotator cuff repair surgeries are performed each year, and the success rate of repair is variable with 20% to 65% resulting in a re-tear. RCT is a tear of one or more of the rotator cuff tendons (supraspinatus, infraspinatus, teres minor, and subscapularis). While the tear is often considered to be an injury to the tendons, and is consequently treated as such, there is evidence that the structural and mechanical properties of the injured rotator cuff tendons, remaining intact tendons and glenoid cartilage are affected by RCTs. However, despite the fact that glenohumeral (GH) capsule is a primary passive stabilizer of the shoulder joint, the biomechanical consequences of RCTs on the GH capsule have not been well defined. Further, the kinematics of the normal shoulder joint have been shown to be different than that of a shoulder with an RCT, indicating a possible change in the loading condition of the shoulder. Together, the changes in kinematics of the shoulder after RCT and alteration in shoulder stability may contribute to the poor success rate associated with RCT repairs. It is therefore important to know how the changes in kinematics due to RCTs affect the mechanical state of the GH capsule and its contribution to shoulder joint function and stability. The objective of this in vitro study was to (1) quantify the strain distributions of the GH capsule for two functional tasks (forward reach and functional pull), and (2) identify how this strain distribution is affected by RCTs. To perform the biomechanical testing, a 6 degree-of-freedom actuator was developed from a 5-axis computer numerical control (CNC) machine to replicate shoulder motion in cadaveric specimens. The human shoulder joint (humerus-capsule-scapula, n=5) was mounted into the CNC machine and the kinematics of four tasks was replicated: forward reach and functional pull from subjects without an RCT (controls), and the same two tasks from subjects with an RCT. Gleonhumeral capsule strain was measured using digital image correlation by applying a random speckle pattern on the anterior and posterior regions of the GH capsule. High-speed camera images of the capsule were recorded during the experiments, and processed to calculate the dynamic strain along the medial-lateral and superior inferior directions. For both healthy forward reach and functional pull, the strain distributions were inhomogeneous throughout the capsule and the peak strain occurred at the most extreme position of the task. During forward reach, the peak strain (0.610 +/ 0.177) occurred near the fully extended reach position (44% of cycle) while it occurred at the end of the functional pull (0.416 +/ 0.157, 49% of cycle). For both tasks, the peak strain was most often found at either the humeral or glenoid insertion. Both anterior and posterior sides of the capsule were under the biaxial tension during forward reach. However, during functional pull, both sides were in uniaxial tension: the anterior side was loaded along the medial-lateral direction while the posterior side was loaded along the superior-inferior directions. The peak superior-inferior strain in the superior-humeral regions of the posterior side was lower for forward reach compared to functional pull (p = 0.046). The remaining regions were not significantly different. The kinematics associated with RCTs showed similar trends in terms of the loading state of the capsule; both sides were in biaxial tension during forward reach and uniaxial tension during functional pull. However, the strain distribution in the capsule was significantly different under the RCT kinematics. In some regions, strains increased while in other regions strains decreased for both the anterior and posterior sides of the capsule. These changes were spatially heterogeneous. Forward reach mechanically challenges the glenohumeral capsule more than functional pull as shown by the increased strain and its biaxial nature. In terms of rotator cuff tears, our results elucidate how RCTs may change the overall shoulder joint stability as a result of focally specific changes in the GH capsule strain. Understanding the biomechanical effects of RCTs on shoulder joint function is essential for optimal rotator cuff repair surgery outcome. The methodology developed in this research could be used to investigate the sensitivity of capsule strain to tear progression and evaluate options for improving RCT surgical techniques or rehabilitation protocols.
Issue Date:2018-07-11
Rights Information:Copyright 2018 Hafizur Rahman
Date Available in IDEALS:2018-09-27
Date Deposited:2018-08

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