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Capsule function following anterior dislocation: Implications for diagnosis of shoulder instability
Author(s) -
Rainis Carrie A.,
Browe Daniel P.,
McMahon Patrick J.,
Debski Richard E.
Publication year - 2013
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.22300
Subject(s) - dislocation , instability , capsule , medicine , function (biology) , anterior shoulder dislocation , anterior shoulder , physical medicine and rehabilitation , surgery , materials science , geology , physics , mechanics , biology , composite material , microbiology and biotechnology , paleontology
Abstract During shoulder dislocation, the glenohumeral capsule undergoes non‐recoverable strain, leading to joint instability. Clinicians use physical exams to diagnose injury and direct repair procedures; however, they are subjective and do not provide quantitative information. Our objectives were to: (1) determine the relationship between capsule function following anterior dislocation and non‐recoverable strain; and (2) identify joint positions at which physical exams can be used to detect non‐recoverable strain in specific capsule regions. Physical exams were simulated at three joint positions including external rotation (ER) using robotic technology before and after anterior dislocation. The resulting joint kinematics, strain distribution in the capsule, and non‐recoverable strain were determined. Following dislocation, anterior translation increased by as much as 48% (0° ER: p = 0.03; 30° ER: p = 0.03; 60° ER: p < 0.01). Capsule sub‐regions with less non‐recoverable strain required more ER to detect differences in the strain ratios between the intact and injured joint. Strain ratio changes on the humeral side of the posterior axillary pouch (0.31 ± 0.32) were significant at all joint positions (0° ER: p = 0.03; 30° ER: p = 0.048; 60° ER: p = 0.04), whereas strain ratio differences on the humeral side of the anterior axillary pouch (0.18 ± 0.21) were significant only at 60° of ER ( p = 0.03). Therefore, standardizing physical exams for joint position could help surgeons identify specific locations of non‐recoverable strain that may have been ignored. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 962–968, 2013