Mid-range shoulder instability modeled as a cam-follower mechanism

Laurent Willemot, Andrew Thoreson, Breighner Ryan Breighner, Alexander Hooke, Olivier Verborgt, Kai Nan An

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


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 r2 of 0.88 and 0.90 for the small and large humeral head sizes, respectively. Comparison of the lateral displacement resulted in r2 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 30N, 60N, and 90N resulted in r2 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.

Original languageEnglish (US)
Pages (from-to)2227-2231
Number of pages5
JournalJournal of Biomechanics
Issue number10
StatePublished - Jul 16 2015


  • Glenohumeral instability
  • Kinematics
  • Modeling

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine
  • Biomedical Engineering
  • Rehabilitation


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