Custom-made knee prosthesis: myth or reality?

Dr. Roland Gardon

FMH orthopaedic surgery, knee surgery, Clinique de Genolier

January 9, 2022

Our knees are one of the biggest and most complex joints in our bodies. They function as a transition joint between the hip and the foot subjecting them to constant work and stress. There are a lot of risk factors including age, obesity, heredity, infections, old traumas, and much more. We already have good ways of dealing with these issues and we keep getting better and better options. Technology in medicine has advanced so much that custom-made knee prostheses are not only a reality but are already in use!

Do you want to learn more? Check the article from Dr. Roland Gardon.

Total knee arthroplasty (KTP) is preferred for patients with disabling gonarthrosis (osteoarthritis of the knee joint). It is a reliable and reproducible operation that provides excellent long-term clinical results. According to several projection studies, the number of implanted prostheses will increase significantly in the coming years. This is mainly due to the ageing of the population, obesity and the fact that KTPs are being implanted in younger and younger people. Despite the very good results of this operation, according to the literature about 20% of patients are dissatisfied with their prosthesis. This figure is not insignificant and is taken very seriously by orthopaedic surgeons. Important changes are currently taking place in relation to the manufacture of the prostheses, the surgical procedure and the post-operative period in order to keep them to a minimum.

The knee is the largest and most complex joint in the human body. It is located between the thigh and calf and functions as a transition joint between the hip and foot; in the course of life it is subjected to a lot of stress. The thigh bone (femur), the shin bone (tibia) and the kneecap (patella) form the bony joint bodies. The joint surface is covered by hyaline cartilage. This is a strong and resistant but very sensitive tissue that has excellent mechanical and biomechanical properties to give the joint surfaces ideal sliding properties.

When the cartilage tissue decreases, wear occurs. The bones rub against each other and a progressive inflammatory process that affects the entire joint begins. This is called a degenerative disease of the knee joints or gonarthrosis. The latter manifests itself through movement pain, a functional restriction (especially stiffness) and the progressive deformation of the joint.

The risk factors are numerous and well known: Age, heredity, obesity, female gender, morphological deformities, infections and old traumas.

Diagnosis is made by interview, a clinical examination and conventional X-rays. Magnetic resonance imaging is rarely necessary.

Two treatment methods can be considered: conservative and surgical.

Non-surgical treatment includes activity modification, weight loss, anti-inflammatory medication, ice therapy and physiotherapy. Intra-articular viscosupplementation with hyaluronic acid or chondroitin sulphate derivatives in tablet form are other options. It should be noted that these treatments do not cure osteoarthritis itself, but can relieve the pain or – better still – delay the progression of the degenerative disease.

If the well-executed conservative therapy accompanied by a specialist fails, a total knee prosthesis (KTP) can be considered. The worn parts of the knee are replaced with metallic parts (chrome-cobalt) and plastic parts (polyethylene). In the case of radiologically confirmed osteoarthritis and daily pain that significantly affects the quality of life, the decision is made by the patient after a thorough discussion with the surgeon. The main goal of the surgery is to restore a pain-free, stable and mobile knee and to achieve good clinical and functional long-term results for the patient. This is to be achieved through greater longevity of the implant and the absence of complications (loosening of the implants, wear of the joint surfaces and, above all, pain).

The first experiments with knee prostheses were carried out in the 19th century on patients with massive joint destruction, mainly due to tuberculosis. The worn surfaces were removed and replaced by soft tissue layers (fascia or joint capsule). During the 20th century, the soft tissue was replaced by synthetic (cellophane, nylon) and metallic (vitallium and chrome-cobalt) implants.

The first “modern” total knee prosthesis was developed in the early 1970s at the Hospital for Special Surgery (HSS) by Dr John Insall’s team. Since then, this procedure has become one of the greatest successes in modern orthopedic surgery, with excellent clinical results and a good long-term implant survival rate.

However, the various studies conclude that a proportion of patients are dissatisfied with their CIP. According to the authors, the figures vary between 20 and 30 %, so they are not insignificant. This fact concerns the orthopedic community and great efforts are being made to reduce it to a minimum.

As a reminder, at the beginning of the modern age of prosthesis in the 1970s, there was only one prosthesis size for all patients and this was to change only after a decade. Later, in the 1980s and 1990s, surgeons already had prostheses available in different sizes. However, it was not until the 2000s that thinking began in connection with the major differences in knee morphology and the idea of developing an artificial knee that resembled the human knee as closely as possible emerged. The work related to bio mechanics and a better understanding of the natural movements of the knee led to significant advances in knee prostheses.

However, it was not until the 2000s that thinking began in connection with the major differences in knee morphology and the idea of developing an artificial knee that resembled the human knee as closely as possible emerged.

Until recently, the surgery was planned with simple X-rays and the bone cuts in the femur and tibia were performed with standard guides and instruments for all patients, which were positioned by the surgeon according to “eye measurement”. The latter always looked for a compromise between the optimal correction of the deformity of the operated leg, the balance of the ligaments and the shape and size of the implants.

A few years ago, implant manufacturers developed a system for three-dimensional preoperative planning based on a CT scan. They then combined it with customized, personalized incision guide blocks made by 3D printing (from polyamide powder by laser melting technique) based on planning data. The aim was to reduce the operation time and blood loss but above all to optimally correct the malposition of the lower limb, as the residual deviation correlates directly with the long-term clinical results. Today, the quality of these guiding blocks has been confirmed in terms of precision when inserting the prosthesis and the reproducibility of the preoperative 3D planning.

Recently, a fully customized (specific to each patient) KTP concept has been developed. The aim is to restore the anatomy of the healthy, arthritis-free knee as well as possible. An important element is also the integration of the correction of the malposition of the lower limb with adjusted implants, without compromising size and shape, which can be the cause of pain and instability with traditional implants. It is therefore a matter of making a completely individualized prosthesis whose components are unique to each patient. The prosthesis is planned in 3D on the basis of a CT scan of the complete leg to be operated on. The data from the scan are then transmitted electronically and securely to the manufacturer, who creates an initial design. The latter must be validated and possibly modified by the surgeon on an online platform. The instruments for inserting the prosthesis, including the customized single-use incision guide blocks, and the customised prosthesis itself are delivered to the operating theatre a few days before the procedure. The surgical procedure takes 1 to 2 hours, depending on the complexity of the case.

The theoretical advantages for the surgeon are a better understanding and imaging of the diseased knee in 3D, which increases visibility and minimizes the risk of unforeseen problems during surgery. The surgical procedure is easier and more reproducible, with fewer implantation instruments and material in the surgical area. The theoretical benefits for the patient are a reduction in operating time, a reduction in intra-operative blood loss and ultimately an artificial knee that resembles the human knee as closely as possible, increasing long-term patient satisfaction. The benefits for the hospital are a significant reduction in preoperative logistics with shorter installation and rotation times and simplified management of surgical materials (disposable instrumentation), with great potential for savings in logistics processes.

Postoperative rehabilitation begins immediately and promotes early mobilization. The patient has to get up already on the day of the operation and the operated knee is mobilized actively with support as well as passively immediately after the operation. Patients stay in hospital for a few days and continue rehabilitation at home. The focus is on self-performed rehabilitation with specific exercises.

Finally, the customized knee prosthesis gives hope for an improvement in clinical outcomes and a decrease in the number of dissatisfied patients. The short-term clinical results are encouraging, but one must remain cautious and wait for the medium- and long-term results and randomized trials to prove superiority over the standard prosthesis.

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