title: A rigid body model for the assessment of glenohumeral joint mechanics: Influence of osseous defects on range of motion and dislocation.
abstract: The purpose of this study was to employ subject-specific computer models to evaluate the interaction of glenohumeral range-of-motion and Hill-Sachs humeral head bone defect size on engagement and shoulder dislocation. We hypothesized that the rate of engagement would increase as defect size increased, and that greater shoulder ROM would engage smaller defects. Three dimensional computer models of 12 shoulders were created. For each shoulder, additional models were created with simulated Hill-Sachs defects of varying severities (XS=15%, S=22.5%, M=30%, L=37.5%, XL=45% and XXL=52.5% of the humeral head diameter, respectively). Rotational motion simulations without translation were conducted. The simulations ended if the defect engaged the anterior glenoid rim with resultant dislocation. The results showed that the rate of engagement was significantly different between defect sizes (0.001<p<0.032). Defect engagement occurred for all specimens when defects size XL and XXL were simulated. Size M or L defects engaged in some (but not all) specimens. Defect engagement occurred at mean horizontal extension angles of -23.6±9.3°, -17.9±10.8°, -4.5±9.0°, and +6.4±8.8° for M, L, XL, and XXL defect sizes, respectively. Differences in engagement angle between defect sizes were significant for all comparisons (p<0.001). The model showed that XS and S size defects do not engage when only rotational motions are considered. Since engagement of XS and S size Hill-Sachs defects is believed to occur clinically, we suspect that some amount of joint translation may be occurring, causing these defects to engage. Therefore, further studies on clinical pre-operative joint laxity and ROM may enable the prediction of engagement.
authors: Bioengineering Research Laboratory, Roth | McFarlane Hand and Upper Limb Centre, St. Joseph׳s Health Care, Western University, London, ON, Canada.
authors: Mark F
authors: MF
authors: Welsh
authors: Bioengineering Research Laboratory, Roth | McFarlane Hand and Upper Limb Centre, St. Joseph׳s Health Care, Western University, London, ON, Canada; Department of Mechanical Engineering, Binghamton University, Binghamton, NY, USA.
authors: Ryan T
authors: RT
authors: Willing
authors: Bioengineering Research Laboratory, Roth | McFarlane Hand and Upper Limb Centre, St. Joseph׳s Health Care, Western University, London, ON, Canada; Department of Mechanical Engineering, Imperial College London, London, UK.
authors: Joshua W
authors: JW
authors: Giles
authors: Bioengineering Research Laboratory, Roth | McFarlane Hand and Upper Limb Centre, St. Joseph׳s Health Care, Western University, London, ON, Canada.
authors: George S
authors: GS
authors: Athwal
authors: Bioengineering Research Laboratory, Roth | McFarlane Hand and Upper Limb Centre, St. Joseph׳s Health Care, Western University, London, ON, Canada. Electronic address: jajohnso@uwo.ca.
authors: James A
authors: JA
authors: Johnson
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D006801:Humans; D058430:Humeral Head / Q000502:physiology / Q000503:physiopathology; D007593:Joint Instability / Q000473:pathology / Q000503:physiopathology; D008297:Male; D055595:Mechanical Phenomena; D008875:Middle Aged; D008953:Models, Anatomic; D016059:Range of Motion, Articular; D012399:Rotation; D012540:Scapula / Q000502:physiology / Q000503:physiopathology; D012783:Shoulder Dislocation / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery; D012785:Shoulder Joint / Q000033:anatomy & histology* / Q000502:physiology* / Q000601:surgery; D055815:Young Adult
keywords: Dislocation; Hill–Sachs; Instability; Multibody models; Shoulder