The most common reason for disorders of the knee joint is cartilage wear (arthrosis), mainly caused by a malalignment of the leg axes (in-knee or out-knee). In addition, gonarthrosis also occurs as the consequence of injuries, rheumatic and metabolic disorders as well as deformities.
The loss of cartilage results in increasing stiffening and deformation of the joint. Bony spurs (osteophytes) form, which sometimes can be palpated from the outside. At the same time, pains occurs, first associated with initial movement after periods of inactivity and with stress, later also at night and at rest, resulting in an increasing limitation of the walking range and ultimately in a reduction in quality of life.
The arthrosis can be shown in the normal X-ray image; the narrowing of the joint cavity between the femur and the tibia can be seen as an indirect indication of the loss of cartilage. The surfaces of the joint are often destroyed and no longer fit together well "running on the rim").
Severe medial gonarthrosis after resurfacing including correction of axis alignment.
Replacement knee joint: material - fixation - durability
If conserving the joint is not an option for technical reasons or because of the age of the patient, and all other conservative and surgical options (physiotherapy, painkillers, joint irrigation etc.) have been exhausted, a total knee endoprosthesis is carried out.
The main aim of the operation is to achieve freedom from pain and mobility including restoration of the natural leg axis. Continuous improvement in both surgical techniques and quality of implants has made this procedure one of the most common and most successful routine operations in orthopaedic surgery, with a total of about 140,000 operations a year in Europe alone.
Modern knee endoprostheses as fitted these days are classified as resurfacing implants, as only the worn cartilage surfaces are replaced, while preserving the patient's own knee ligament structure if possible. Basically, knee prostheses are divided into the following types:
- Single endoprosthesis (unicondylar or mono-sledge):
requirements for the isolated replacement of the inner - or less frequently the outer - section of the knee joint include just slight changes to cartilage in the other sections, and intact knee ligament structures. - Total endoprosthesis (bicondylar):
- Non-constrained: The surfaces of the joint are replaced while largely preserving the patient's own ligament structures. There is no mechanical connection between the thigh and the shin section of the joint.
- Constrained: A cone-shaped connection stabilizes the joint whose ligament structures could not be fully preserved.
A model of bicondylar resurfacing
Minor bone resection and preservation of ligament structures ensure long durability.
The individual prosthesis types are available in different sizes. The pre-operative planning sketch is used to specify the model size and fixation of the prosthesis, with full consideration of individual requirements (age, gender, shape of bone, body weight, etc. ).
Three different fixation techniques are used in the implantation:
- Cement-free total knee endoprosthesis: With the "press-fit" technique, the implants are accurately fitted in place and the bone regrows to the prosthesis.
- Cemented total knee endoprosthesis: An antibiotic cement is used to fix the implants to the bone.
- Hybrid total knee endoprosthesis: The femoral component is fitted cement-free, the tibial component is cemented to the bone.
Depending on the fixation method, the components are either made from titanium or a chrome-cobalt alloy. A polyethylene inlay is inserted between the replaced surfaces to aid gliding. Latest developments have made it possible to allow sliding and rotational movements of this inlay commensurate with the natural pattern of movement ("mobile bearing" principle). Abrasion behaviour has been optimized in such a way that many years of use can be tolerated with almost no abrasion to the material.
Durability promises to be further improved by the use of navigation systems; similar to a GPS in vehicle navigation, these will allow steps in the operation and bone resections to be checked on the computer to ensure an optimal fit of the parts of the prosthesis, axis-accurate alignment and optimization of tendon tension. First studies have shown extended durability, which is a result that we can confirm from our extensive experience with navigation systems.
Implantation of knee joint prostheses
Navigation systems similar to a GPS permit the optimal implantation of replacement knee joints, thus extending the durability of the prosthesis.
For this reason, durability of 12-15 years is ensured in most cases, irrespective of the fixation method used. If the implant should become loose, it can be replaced in a further operation, provided the patient is in sufficiently good general health.
Treatment prior to knee surgery and the operation itself
The operation is preceded by an extensive patient consultation, clinical and radiological examinations and accurate planning. In addition, the patient will undergo medical/anaesthetic checks, including an ECG, pulmogram and blood tests. The operation is conducted using a tourniquet, thus generally ruling out the need for autologous or donor blood. As a general rule, the patient is admitted as an in-patient on the day before the operation.
Depending on the individual arrangement, the operation is conducted under general anaesthesia or spinal anaesthesia. Access to the affected joint is through an incision (about 15 cm) at the front of the knee. Removal of the destroyed joint surfaces using precision instruments is followed by fixing of the prosthesis components to the femur and the tibia. In line with the general research opinion and confirmed by our own experience, a replacement of the posterior surface of the patella is only considered if it is is severely damaged by arthrosis. The mobility of the artificial joint is tested, then the wound is closed layer by layer with the insertion of drainage tubes. After the operation, a control X-ray is taken.
Aftercare
All endoprosthetic operations are exclusively performed on an in-patient basis. In order to ensure the best possible outcome of the operation, our patients are mobilized early with the help of physiotherapists; depending on the implantation technique used, patients can soon put weight on the treated leg. For cemented prostheses and normal wound healing, the treated leg can soon bear full weight. Partly cemented and cement-free implanted prosthesis can, for the first two weeks, only be exposed to loads of 10 - 20 kg; after that, progression to full load can be swift.
For most patients, a 10-14 day in-patient stay is followed by two weeks in a rehabilitation clinic. The progress of patients is documented through regular out-patient check-ups at close intervals; if necessary, mobilization therapy will be continued on an out-patient basis.
Joint replacement and sporting activities
Severe arthrosis of the knee comes with a significant limitation to sporting activities. The freedom from earlier complaints raises the desire in many patients to resume a certain level of sporting activities. There is international consensus that "low impact" activities such as cycling, swimming, sailing, diving, golf and bowling can be supported. Sports such as tennis, basketball and skiing are possible or advisable within limits, while contact sports such as football or rugby should be avoided unconditionally.