Musculoskeletal modelling for hip joint replacement

Author: Neha Saini

Saini, Neha, 2019 Musculoskeletal modelling for hip joint replacement, Flinders University, College of Science and Engineering

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Osteoarthritis (OA), specifically in the hip joint, is a progressive chronic joint disorder that leads to pathological changes including pain, limited mobility and muscle atrophy. Increasing prevalence of OA is a result of an ageing population and obesity. Total hip arthroplasty (THA), one of the most successful surgeries, is used to replace the degenerated articular surfaces providing pain relief and improved mobility. Conversely, several complications are associated with THA resulting in failure and revision surgery, leading to low quality of life and higher indirect and direct costs. Estimation of hip joint contact forces (HCF) can assist in preventing implant failure and consequent revision surgery. Musculoskeletal modelling has become a conventional method to predict HCF, however muscle symmetry is typically assumed in present studies. This assumption may not be a close representation of clinical observations. This thesis was designed to estimate resultant HCF and muscle forces by introducing abductor muscle asymmetry to imitate muscle atrophy.

OpenSim 4.0 was used with previously designed statistical shape scaled model (Bahl et al, 2019). Maximum isometric forces defined by Delp (1990) to introduce asymmetry in gluteus medius and minimus; 20%, 40% and 60%. Muscle asymmetry was introduced in the affected OA hip in six end-stage OA patients awaiting surgery by altering maximum isometric forces that are directly correlated to muscle cross sectional area.

Only one patient out of six showed a two peak profile while others showed only one peak profile in 100% gait cycle in the affected hip. For majority of the patients, insignificant changes were present in resultant HCF for all muscle asymmetry models. However, for 60% abductor muscle asymmetry model, evident changes in resultant HCF were present with a significant increase in two patients while a decrease in one patient. This was due to compensatory action by the individual muscles taking over for the weak abductors. Further assessing the anterior - posterior HCF, a direction change was present for one patient as the muscle asymmetry was increased.

An increasing trend in used available muscle force capacity was present in all abductors; gluteus medius, minimus, maximus and tensor fascia latae. Additionally, patients using their full abductor available muscle force capacity due to muscle asymmetry were further compensated by flexors and extensors. Low gait speeds were also associated with lower HCF but only true for some patients.

The results strongly indicated; the impact of abductor muscle asymmetry on the resultant HCF and individual muscle forces was very case dependent. Further suggesting various other factors can impact patient’s ability to withstand muscle weakness. In most cases, abductor muscles were reaching their maximum available force capacity may result in muscle fatigue, risk of dislocation and further volume reduction post THA.

This study has provided a method to predict resultant HCF and muscle forces with manipulating the muscle asymmetry in end-stage OA patients. Additionally, the impact of muscle asymmetry on the peak resultant HCF was also analysed to be case dependent. Therefore, future studies should be conducted with patient specific data for muscle volume and fatty infiltration using CT data.

Keywords: Musculoskeletal Modelling, Hip Joint Replacement, THR, OpenSim, Muscle Asymmetry

Subject: Engineering thesis

Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Mark Taylor