Effect of Patient Specific Parameters on Degenerative Shoulder Diseases

Osteoarthritis and rotator cuff tears are two common and wide spread shoulder diseases leading to significant restrictions in the daily life of the affected. The pathogenesis is not fully understood yet. A chronic process triggered by multiple causes is assumed including inflammation, metabolic disturbances, and mechanical contributions. Several studies described as mechanical cause a statistically important impact of the scapula shape. The appearance of osteoarthritis and rotator cuff tears could be linked with specific anatomic parameters. The aim of this thesis was to improve the understanding of the mechanical contribution to the development of osteoarthritis and rotator cuff tears by the means of computational modelling. In this work, we focused on the lateral extension of the acromion and the glenoid inclination. Three numerical shoulder models were developed to analyse these two parameters. A musculoskeletal model was used to evaluate muscle and joint reaction forces acting on the glenohumeral joint. The underlying algorithm calculated joint torques for a given movement based on an inverse dynamics approach and solved the undetermined problem of muscle coordination with a nullspace optimization routine. The calculated joint forces were then used as input for a finite element cartilage model. Cartilage was modelled as incompressible hyperelastic material characterized with experimental data. The model provided values for cartilage strain and humeral head translations. The humeral head translation and supraspinatus force were used in a third model of the supraspinatus tendon. The constitutive equations for tendon tissue were derived from an anisotropic hyperelastic strain energy potential. Material parameters were identified in both fibre direction and the transverse plane. The elasticity tensor was approximated using a forward differentiation algorithm. Using the finite element method, tendon strains and tendon impingement were evaluated. The biomechanical variables cartilage strain, subacromial space, and tendon strain were analysed for different anatomic configurations. All models were validated with available clinical data. The biomechanical variables were more sensitive to changes of the acromion length than to changes of the glenoid inclination. The numerical study could explain the statistical association for osteoarthritis for short acromion by an increase in cartilage strains. A long acromion increased superior humeral head translation, which is associated to tendon impingement and related tears. We also observed increasing tendon strains close to the tendon insertion for a short acromion. Clinical studies did not correlate tendon tears to a short acromion. However, the clinical studies did not distinguish between the different types of tendon tears. At this point, further clinical studies would be necessary to clarify the numerical results. A better understanding about physiologic anatomic parameters could help to improve the treatment of osteoarthritis and rotator cuff tears. Prosthesis design and positioning during total shoulder arthroplasty, tendon repair techniques, and conservative treatment could be improved to compensate negative effects of excessive anatomic parameters

Active Stability of Glenohumeral Joint Diminishes during the End-range Motions

The lack of congruence between the involved articular surfaces causes the inherent instability of the glenohumeral joint. This joint is therefore the most commonly dislocated joint in the human body. Anterior instability accounts for over 90% of the shoulder dislocations. The reason of this almost unidirectional dislocation remains unknown. Few studies have quantitatively discussed the joint stability utilizing musculoskeletal models. Other studies mainly utilized either purely clinical or cadaveric approaches to address the joint stability. The aim of this study is to identify the key factors contributing to anterior instability through a quantitative analysis of the shoulder's dynamic stabilizers

Development of a 3D finite element muscle model

Stability of the shoulder, more precisely the glenohumeral joint, can only be achieved in case of healthy and well coordinated muscular activity in the upper limb. Degenerative deseases like osteoarthritis, muscle deficiencies or injuries can lead to instability problems of the humeral head. To analyse human shoulder stability, numerical models have been developped at the LBO that allow the simulation of humeral head translation in the glenoid cavity. As muscles play an important role, the aim of that project is to refine the muscle modelling by developping a new 3D muscle model. This new muscle model will then be included into an existing shoulder model. The first part of this project is to study muscle anatomy, physiology and existing constitutive laws. In a second step, the modelling of the muscle and the implementation of appropriate user subroutines will be done in Abaqus. Basic knowledge of finite element analyses and programming are recommended

Patient specific numerical shoulder model based on medical imaging

The shoulder is often described as the most complex human joint because of its anatomy and the high number of muscles participating in arm movements. The anatomy and the development of muscles depend on personal characteristics and the style of living. The aim of this project is to take into account the individual anatomy and to analyse the effects on shoulder mechanics. Therefore, patient specific numerical shoulder models will be generated out of medical imaging data. In the beginning the project will focus on how to obtain the patient specific shoulder properties out of medical imaging data. The obtained patient specific datasets will then be used to build patient specific numerical shoulder models in Abaqus. Basic knowledge in programming is recommended

Second asymptomatic carotid surgery trial (ACST-2) : a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86-1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91-1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable