Musculoskeletal shoulder modelling for clinical applications

Abstract

The shoulder is the most commonly dislocated joint in the human body, with the vast majority of these dislocations being located anteriorly. Anterior shoulder dislocations are commonly associated with capsuloligamentous injuries and osseous defects. Recurrent anterior instability is a common clinical problem and understanding the influence of structural damage on joint stability is an important adjunct to surgical decision-making. Clinical practice is guided by experience, radiology, retrospective analyses and physical cadaver experiments. As the stability of the shoulder is load dependent, with higher joint forces increasing instability, the aim of this thesis was to develop and validate computational shoulder models to simulate the effect of structural damage on joint stability under in-vivo loading conditions to aid surgical decision-making for patients with anterior shoulder instability. The UK National Shoulder Model, consisting of 21 upper limb muscles crossing 5 functional joints, was customised to accurately quantify shoulder loading during functional activities. Ten subject-specific shoulder models were developed from Magnetic Resonance Imaging and validated against electromyographic signals. These models were used to identify the best combination of anthropometric parameters that yield best model outcomes in shoulder loading through linear scaling of personalised shoulder models. These parameters were gender and the ratio of body height to shoulder width (p<0.04) and these model predictions are significantly improved (p<0.02) when compared to the generic model. The forces derived from the modelling were used in two subject-specific finite element models with an anatomically accurate representation of the labrum, to assess shoulder stability through concavity compression under physiological joint loading for pathologies associated with anterior shoulder instability. The key results from these studies were that there is a high risk of shoulder dislocation under physiological joint loading for patients with a 2 mm anterior or 4 mm anteroinferior osseous defect. The loss in anterior shoulder stability in overhead throwing athletes with intact glenoid following biceps tenodesis is compensated by a non-significant increase in rotator cuff muscle force which maintain shoulder stability across all overhead throwing sports, except baseball pitching, where biceps tenodesis has significantly decreased (p<0.02) anterior shoulder stability. The work in this thesis has advanced the technology of musculoskeletal modelling of the shoulder through the inclusion of concavity compression and has applied this to various relevant clinical questions through the further development of an anatomical atlas, and an atlas of tasks of daily living. The applications of such modelling are broader than those addressed here and therefore this work serves as the foundation for potential further studies, including the bespoke design of arthroplasty or other soft tissue procedures.