Tailor-made implants for high demands - this is what patient-specific knee prostheses stand for. PD Dr. med. Erhan Basad explains the possible applications and special features of the custom-made prosthesis from the 3D printer in a case study. Frequently asked questions about the surgical technique will also be answered.
Soccer, cycling, skiing - Peter Schneider, 58, has always been an active person. Since the age of 17, the banker from Frankfurt has suffered from various knee injuries.
Arthroscopic surgery brought improvement for many years. In recent years, however, he developed osteoarthritis of the knee(gonarthrosis) with pain that could no longer be controlled. The doctors now advised an artificial replacement of the knee joint (total knee endoprosthesis, or knee TEP).
However, the athletically active banker shied away from such an operation, as he feared poorer mobility and severe physical limitations after such an operation.
© artstudio_pro / Fotolia
Osteoarthritis occurs when the joint cartilage is damaged, causing the bones to rub against each other during movement and strain. "This is caused by previous injuries, high or incorrect loads, increased body weight or misalignment of the joints," explains PD Dr. Basad. Physiotherapy and joint-preserving operations help in the early stages.
Advanced knee osteoarthritis can be successfully treated with an artificial joint replacement (endoprosthesis). Artificial joint replacement is performed by cutting the joint surfaces and anchoring implants to the surfaces of the thigh and lower leg. This prevents the cartilage-free joint partners from rubbing together painfully.
The better the patient's general condition, the quicker quality of life and activity can be regained as a result of such an operation. One of the most difficult problems after a knee prosthesis operation is regaining muscle strength and mobility.
In the long term, the durability of a knee prosthesis depends on mechanical and biological factors. For example, if the implants do not fit exactly or if the patient is overweight, these are among the risks that can lead to the endoprosthesis loosening.
Quality of life can be regained with a knee prosthesis. In Peter Schneider's case, a patient-specific knee implant was the right solution.
"This implant is 'tailor-made' and restores the individual anatomy," explains Heidelberg knee expert PD Dr. Basad. "Conventional endoprostheses come in 'ready-made sizes', which are determined according to average shapes. Customized implants, on the other hand, are made to measure if required."
The size, shape and axes of the knee prostheses are already taken into account during production. This ensures that the implant and bone fit together perfectly.
Computer-assisted techniques help to plan joint implants and manufacture implants individually (personalized). Individual implants produced with the help of CAD/CAM reproduce the natural geometry of the knee joint and allow significantly better positioning. The system allows the treatment of knee arthrosis.
It is indicated for patients with particularly difficult anatomical conditions or high performance requirements.
© alexonline / Fotolia
For a customized knee implant, a virtual 3D impression is first made using computer tomography . Experts in Boston (USA) use special computer programs to determine the optimum shape.
The knee prosthesis, including the corresponding surgical instruments, is produced there for the respective patient using 3D printers.
"The instruments are milled in such a way that they fit the patient's bone exactly and the preparation of the bone is safe and error-free. Templates contain all the dimensions and axial corrections required for perfect implant insertion," says Dr. Basad, explaining the surgical technique.
Just a few days after the operation, Peter Schneider was able to walk independently and was already able to bend his knee 90 degrees.
"The feeling of walking after the operation was really familiar. Once the initial pain from the operation had subsided, I could trust my joint to do almost anything," says the enthusiastic sportsman and emphasizes: "I was already riding my bike and playing golf again some time after the operation."
According to the surgeon, it should be added that such rapid progress is of course only possible if the patient has already been active in sports beforehand. Dr. Basad also prefers to educate patients carefully: "It can take several months for the body to get used to the foreign material and the altered statics, as well as to regain muscle and movement deficits."
© elnariz / Fotolia
Which knee patients need an endoprosthesis?
In general, a knee prosthesis should only be used if joint-preserving measures are no longer sufficiently effective. In the early stages of osteoarthritis, these include axial correction (for bow and knock knees) or arthroscopy (for isolated mechanical symptoms caused by meniscus tears).
Before deciding on a joint replacement, it is important to consider whether a total or partial replacement should be performed. In the case of internal or external knee osteoarthritis, the more economical partial replacement with a sled prosthesis is possible.
A customized implant can take into account patient-specific characteristics and save bone. Every knee is as individual as the person. Therefore, every patient can benefit from a custom-made product.
It is not only the exact fit without overhang that is important. The implant also covers all bleeding bone surfaces.
With sled prostheses, there is a further advantage: the implant harmonizes with the skid shape of the preserved joint part. As a result, the joint runs in the same way as it used to when healthy.
In principle, the operation is similar to the implantation of a standard prosthesis. However, implants and instruments are specially manufactured for the patient and the operation has already been successfully simulated on a 3D model in the computer.
A surgical planning sketch is provided to support the surgical technique. This contains all the necessary steps with the respective resection heights and angles, so that the correct instrument and implant positioning is confirmed at every step during the operation.
With regard to the instruments, it is particularly worth mentioning that the individualized saw templates are precisely adapted to the bone on which they must rest, so that each resection requires individual control during the operation. Preoperative navigation and the alignment specified in the templates reduce intraoperative steps and simplify them technically.
At a glance:
The system presented here has been in use for more than 14 years and has been applied thousands of times worldwide with truly individualized prosthetics using patient-specific instruments and implants.
CAD (Computer Aided Design) technology enables preoperative navigation, which indicates anatomical problems and possible solutions at an early stage. The initial radiological and clinical results of various working groups have tested the functionality of the system in terms of accuracy of fit, blood loss, safety and cost-effectiveness.
Knee joint operations are usually performed by specialists in orthopaedics and trauma surgery. As a rule, these doctors specialize in a particular joint, such as the knee joint, and are highly experienced in diagnosing all possible diseases and carrying out the appropriate treatment. You should therefore make sure you speak to a proven specialist in knee surgery.
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