Program fits smooth surfaces onto estimated healthy knee shape to create implants ready for computer-assisted manufacturing.

People whose knees have been affected by osteoarthritis, also known as the “wear and tear” arthritis, often have to get knee implants to repair the damage. But if a knee implant does not fit the specific individual, it could lead to soft tissue damage, collapsing of the underlying bone, loosening of the implant and an increased likelihood of joint pain after an operation.

“One possible solution is to design implants that are patient-specific, anatomically accurate, reproduce normal knee motion and are ultimately repeatable,” said Dr. Johan van der Merwe, a lecturer in the Department of Mechanical and Mechatronic Engineering at Stellenbosch University (SU). Van der Merwe, who is also a member of the Biomedical Engineering Research Group in the same department, recently obtained his doctorate in Mechatronic Engineering at SU. He focused on developing a repeatable, semi-automated method of generating patient-specific implant components that reproduces an individual’s healthy anatomy to facilitate natural joint movement after an operation.

Van der Merwe pointed out that the knee is one of the joints most susceptible to osteoarthritis, a form of arthritis that occurs when the protective cartilage in joints breaks down.

Van der Merwe said for localized osteoarthritis, surgical reconstruction or replacement of only the damaged part of the knee (Unicompartmental Knee Arthroplasty) may be preferred over the replacement of the entire joint (Total Knee Arthroplasty). Projections are that by 2030 three million knee replacement surgeries will be done globally. Current knee replacements usually last for 10 years.

“Replacing or repairing only the damaged part may result in faster recovery, improved post-operative joint movement, retains as much of the joint’s natural anatomy as possible and is done at a lower cost,” he said. “But designing patient-specific Unicompartmental Knee Replacements ultimately rely on a technician’s interpretation and skill in order to consistently reproduce healthy knee shapes. This is a difficult problem—what is considered healthy for one patient might not be the same for another.”

Van der Merwe pointed out that there is often a mismatch between current standardized sizes of commercially available implants and the shape and form of an individual patient’s knee. This generally requires the surgeon to make the patient fit the implant, and sometimes even deviate from the ideal intended implant placement based on experience and current best practices to achieve good outcomes.

By Orthopedic Design & TechnologyStellenbosch University

Image Credit: Dr. Johan van der Merwe / Stellenbosch University

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