Model Development and Analysis of the Rat Supraspinatus Muscle-Tendon-Bone Unit
Open Access
- Author:
- Cush, Coleman
- Area of Honors:
- Biomedical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Meghan Vidt, Thesis Supervisor
Jian Yang, Thesis Honors Advisor
Julianna Simon, Faculty Reader - Keywords:
- finite element model
shoulder tear
sensitivity analysis
tendinopathy treatments
dry needling
focused ultrasound
rat
supraspinatus muscle-tendon-bone unit - Abstract:
- Shoulder injuries, including tendinopathy, are one of the most common injuries that occur, affecting 30% of the general population and at least 50% of patients over the age of 70 years. Current treatments have mixed success rates, thus, development of new treatments are needed. A finite element model of the muscle-tendon-bone unit of the supraspinatus would enable in silico investigation of new treatments for tendinopathy reducing the burdens and resources required for in vivo and ex vivo experiments. The goal of this study is to develop and test a finite element model in COMSOL Multiphysics software to examine the effects of dry needling (DN) and focused ultrasound (fUS-1, fUS-2, fUS-3) treatments on stress in the supraspinatus tendon. Five separate models were created for each treatment option (Sham, DN, fUS-1, fUS-2, fUS-3). The geometry of the model was obtained from a rat MRI scan using 3D-Doctor software. Material properties of the muscle, aponeurosis, tendon, enthesis, and bone domains were assigned based on literature and mechanical testing performed in a previous study. To validate the model, a body load was applied to the enthesis and tendon, consistent with prior mechanical testing, and predicted tendon displacement values were compared to those obtained from experiments. A sensitivity analysis was performed to examine the model’s response to variation of the force magnitude, including the magnitude and location of the maximum principal stress. An additional analysis was performed to examine the sensitivity of principal stress to variation in force direction. Paired two sample t-tests for means were performed to analyze the model-produced tendon displacements to validate the model. The slopes and intercepts of peak magnitude of stress as a function of force magnitude for each treatment model were compared using heterogeneity of slopes and intercepts tests. Peak magnitude of stress in response to force direction changes was computed using two 1-way ANOVAs (treatment group, force rotation). T-tests were performed with Microsoft Excel (v16, Microsoft Corp., Redmond, WA, USA), heterogeneity of slopes and intercepts with MATLAB (v9.12, MathWorks, Natick, MA, USA), and 1-way ANOVAs with SAS software (v9.4, SAS, Inc., Cary, NC, USA), with significance indicated by p < 0.05. No significant difference was found between the mechanical testing displacements and the model-predicted displacements for each treatment group model. Comparisons between treatment group’s linear slopes of maximum principal stress versus force magnitude were different between Sham and DN (p < 0.001); Sham and fUS-1 (p < 0.001); Sham and fUS-2 (p < 0.001); Sham and fUS-3 (p < 0.001); DN and fUS-1 (p < 0.001); DN and fUS-3 (p = 0.003); fUS-1 and fUS-2 (p < 0.001); fUS-1 and fUS-3 (p < 0.001); and fUS-2 and fUS-3 (p < 0.001). Comparisons between the intercepts of the linear relationships were not significantly different. For this analysis, the maximum principal stress was located on the anterior-medial aspect of the enthesis-bone junction in all cases. In force direction analysis, there were differences in principal stress magnitude between DN and fUS-1 (p = 0.0015); Sham and DN (p = 0.0333); fUS-1 and fUS-2 (p = 0.0094); and fUS-1 and fUS-3 (p = 0.0306). There were no differences across groups in principal stress magnitude when the force direction was changed. In all cases except one, the maximum principal stress occurred on the anterior-medial aspect of the enthesis-bone junction; maximum principal stress occurred at the anterior-lateral aspect of the enthesis-bone junction for one simulation. Magnitudes of principal stress in the fUS-1 model were lower than those of Sham for both force magnitude and direction changes, suggesting this treatment has a possible advantage to withstand loading and maintain function following treatment. Ongoing work includes performing additional sensitivity analyses to examine stress magnitude in response to other permutations of force magnitude and force direction.