Engineering approach to knee surgery using soft-tissue as blueprint achieving global acclaim

19th February 2021 By: Schalk Burger - Creamer Media Senior Contributing Editor

A knee-surgery technique developed by local orthopaedic surgeon Professor Ponky Firer that uses a patient’s soft tissues as a blueprint for surgery, is gaining world acclaim and has led to patient satisfaction rates that are higher than global averages while restoring mobility and quality of life for patients.

With his understanding of biomechanics and the science of knees informed by a background in engineering, Firer’s technique, first developed 13 years ago, focuses on patient-specific surgical placement methods that complement natural balance.

"It is conventionally believed that the soft tissues should be adjusted to ensure the prosthetic knee fits within a very narrow hypothetical ideal range of 0° to 3° in relation to the mechanical axis.

"This axis is an imaginary line extending from the centre of the hip to the centre of the ankle and should pass through the centre of the knee when surgery is performed in the traditional way – this is known as ‘neutral mechanical alignment’," he explains.

“However, when you look at the distribution of the typical healthy knee population, it doesn’t conform to these theoretical confines and may have as much as 6° or 7° variance from the point that was thought to be the ‘ideal’,” says Firer, who practises at the Linksfield Orthopaedic Sport Rehabilitation Centre at Netcare Linksfield Hospital and has more than 40 years’ experience in knee conditions.

Every person’s knees are unique and integral to the body’s overall balance. Instead of adjusting the soft tissues during total knee replacements, Firer's approach takes the patient’s own soft tissues as the blueprint to guide surgery, as this indicates their natural alignment before they developed a knee problem.

“We adjust the bone cuts during surgery to achieve balance rather than cutting the ligaments, as is usually done, because there is no need to damage healthy tissues. The person can therefore retain their body’s natural alignment, which involves a complex and interconnected system of levers and balance – from our feet all the way up to our heads – and the knees fulfil a particularly crucial function."

According to Firer, getting the balance of the ligaments right for each patient is essential to the success of knee replacements and about one-third of surgical revisions internationally are owing to soft tissue instability. Where the tissues are too tight this causes pain, and when tissues are not tight enough the knee joint becomes unstable.

“Interestingly, we found that the alignment distribution that we achieved with our patient-specific balanced technique mirrored in nature the pattern one would expect to find across the population of healthy knees,” he highlights.

Pain and instability are the major causes of knee replacement revision surgery internationally. Firer, who studied engineering before pursuing a career in medicine, developed his unique technique in an attempt to address the potential post-operative difficulties related to imbalance of the soft tissues of the knee, which produces pain and instability, and dissatisfaction.

“With more than 2 000 total knee replacements having been performed using this revolutionary technique to date, Firer’s work is building an impressive body of empirical evidence of excellent patient satisfaction rates and clinical outcomes in total knee replacement surgery,” says Netcare hospital division MD Jacques Du Plessis.