Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Biomedical Engineering

Collaborative Specialization

Musculoskeletal Health Research

Supervisor

Johnson, James A.

Affiliation

St. Josephs Hospital - Hand and Upper Limb Center

Abstract

Hemiarthroplasties typically result in accelerated wear of the preserved side of the joint, resulting in suboptimal clinical outcomes and limited longevity. This in vitro study investigated the effects of hemiarthroplasty implant curvature on the early biological response of articular cartilage measured by proteoglycan release, histology, and surface morphology. Cartilage from boar radiocarpal joints were worn by metal pins of varying radii of curvature (RoC) using a pin-on-plate wear simulator. Histology and proteoglycan assays showed no significant differences between RoC treatment groups, and proteoglycan assays showed increased proteoglycan release 72 hours after wear testing in worn cartilage specimens compared to control specimens. Field emission scanning electron microscopy showed increased surface damage as RoC decreased. Results suggest that early wear mechanisms smoothen cartilage surface before causing damage. Delayed biological response implied that implant curvature affects early wear mechanics before cartilage biologics. Overall, this study improves our understanding of cartilage wear and cellular response.

Summary for Lay Audience

Joints that connect and provide movement to our skeletal structure deteriorate with age, use, injuries, and certain diseases; and in some cases, replacement of these joints with implants is required. According to the Canadian Joint Replacement Registry, demand for hip and knee replacements continues to increase in Canada, with about 130,000 surgeries costing $1.2 billion annually. However, with breaks or fractures it is sometimes not necessary to replace both sides of the joint; for example, in radial head fractures, the most common fracture around the elbow with an incidence rate of 2.5-2.8 for every 10,000 people per year. Hemiarthroplasty replaces only one articulating surface in a joint with an implant, as an alternative to replacing both surfaces in a total arthroplasty. This approach preserves the native joint, reduces costs, and minimises procedure risks and recovery time. However, hemiarthroplasty often results in accelerated cartilage wear of the original side of the joint due to the stiffness of implants relative to cartilage. Studies have suggested that more conforming implant designs reduce contact stress and cartilage wear, even though the biological response of cartilage to implant curvature is still unknown. There is an urgent clinical need for improved hemiarthroplasty implant design.

Our specific research questions are: “How do cartilage cells respond to mechanical wear, and how is this influenced by the implant design?”

The studies used a wear simulator to investigate effects of hemiarthroplasty implant curvature on the biological response of cartilage via proteoglycan release, histology, and field emission scanning electron microscopy. These outcomes assessed the cartilage response to mechanical wear using implant designs of different curvatures. Results showed a delayed biological response of 72 hours, which adds to the literature from a biological perspective, highlighting that cartilage cells respond to mechanical wear with a substantial delay. From that we can deduce that mechanical wear occurs before biological response. Additionally, results showed that implant pin curvature did not affect the biological response as expected. There were also implications that early wear mechanisms first act to smoothen the cartilage before causing damage. Overall, these studies provide a better understanding of early cartilage wear mechanisms.

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