title: Mid-range shoulder instability modeled as a cam-follower mechanism.
abstract: In this paper, we model a simplified glenohumeral joint as a cam-follower mechanism during experimental simulated dislocation. Thus, humeral head trajectory and translational forces are predicted using only contact surface geometry and compressive forces as function inputs. We demonstrate this new interpretation of glenohumeral stability and verify the accuracy of the method by physically testing a custom-molded, idealized shoulder model and comparing data to the output of the 2D mathematical model. Comparison of translational forces between experimental and mathematical approaches resulted in r(2) of 0.88 and 0.90 for the small and large humeral head sizes, respectively. Comparison of the lateral displacement resulted in r(2) of 0.99 and 0.98 for the small and larger humeral head sizes, respectively. Comparing translational forces between experiments and the mathematical model when varying the compressive force to 30 N, 60 N, and 90 N resulted in r(2) of 0.90, 0.82, and 0.89, respectively. The preliminary success of this study is motivation to introduce the effects of soft tissue such as cartilage and validation with a cadaver model. The use of simple mathematical models such as this aid in the set-up and understanding of experiments in stability research and avoid unnecessary depletion of cadaveric resources.
authors: Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors: Laurent
authors: L
authors: Willemot
authors: Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors: Andrew
authors: A
authors: Thoreson
authors: Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors: Ryan Breighner
authors: Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors: Alexander
authors: A
authors: Hooke
authors: Department of Orthopaedic Surgery and Traumatology, AZ Monica, Antwerp, Belgium.
authors: Olivier
authors: O
authors: Verborgt
authors: Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA. Electronic address: an@mayo.edu.
authors: Kai-Nan
authors: KN
authors: An
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D058430:Humeral Head / Q000503:physiopathology; D007593:Joint Instability / Q000503:physiopathology*; D008954:Models, Biological; D016059:Range of Motion, Articular; D012782:Shoulder / Q000503:physiopathology; D012785:Shoulder Joint / Q000503:physiopathology*
keywords: Glenohumeral instability; Kinematics; Modeling