Knee replacement is the only possible therapy in the case of advanced degeneration of the joint.
It involves surgical replacement of the articular surfaces of the femur and tibia with artificial components capable of reproducing as faithfully as possible all the movements of the arthritic joint.
A total knee replacement comprises the following:
- the femoral component, which replaces the articular surface of the femur; it is inserted in direct contact with the bone after removal of the arthritic cartilage and reproduces the anatomical shape of the femoral condyles;
- the tibial component, which replaces the articular surface of the tibial plateau; this is fixed to the tibia after removal of the articular cartilage;
- the tibial insert, which is fixed to the tibial component and, being congruent with the femoral condyles, articulates with the femoral component;
- the patellar component, which is applied to the articular surface of the patella after removal of the articular cartilage.
Total knee replacement – an operation carried out everyday in specialist clinics – involves the removal of worn cartilage from the articular surfaces of the femur and tibia with techniques that prepare the bone to receive the components, and the positioning of the femoral and tibial component on the two surfaces so that they “line” the old surface. The insertion of the tibial insert renders the two surfaces congruent, thus enabling the new joint to move.
A total knee replacement is indicated in cases of diffuse arthrosis of the joint. If the arthrosis is only affecting one compartment (the medial compartment in the great majority of cases), a mono-compartment prosthesis is recommended; this replaces only the articular cartilages of the femoral condyle and of the corresponding tibial plateau affected by the arthrosis.
X-ray of a total knee replacement: the femoral component completely covers the surfaces of the femoral condyles. The tibial component is implanted after the articular cartilage at the tibial plateau has been removed. The polyethylene insert has been positioned over the tibial component. Being radiotransparent, this insert is not visible in X-rays but can be identified in the apparently “empty” space between the two components.
X-ray of a mono-compartment knee prosthesis: the femoral component only covers the surface of the medial femoral condyle. The tibial component replaces only the medial tibial plateau. The tibial component is made entirely of polyethylene, which, being radiotransparent and not visible in X-rays, can be identified in the apparently “empty” space beneath the femoral component.
Although knee replacement operations, if carried out by specialized surgeons, solve the problem of arthritic pain and in a large majority of cases have successful outcomes, they may involve complications, as in all surgical operations, and require continuation of therapy. Perioperative preventive antibiotics are administered as standard practice, so infections are very infrequent. Should they occur, however, therapies here too will have to be continued.
DURATION OF IMPLANT
The duration of an implant depends on a great many factors, including the patient’s age, weight, gender, bone quality and activity. Many studies have shown that most implants can last even up to 20 years from the first operation.
The main cause of long-term failure of knee endoprostheses is wear of the tibial insert. Wear (or debris) may compromise the functionality and durability of the implant, not just because it causes alteration of the articular surfaces but also because the worn away particles favour bone resorption, the main cause of aseptic mobilization.
Such mobilization consists of a loosening of the main components of the prosthesis (femoral and tibial), which provokes pain in the prosthesized knee.
Periodical clinical and radiographic control of the prosthesized knee is useful for picking up initial signs of mobilization and preventing the serious bone damage that a loosened prosthesis may cause by its movements.
In the event of mobilization of one or both components, they may be removed and replaced with a new prosthesis (prosthetic revision). For complex revision operations, orthopaedic surgeons are provided with special prosthesis models to remedy the shortage of bone preventing the implant of a traditional prosthesis.
An articular recovery and rehabilitation programme after the implanting of a total knee replacement must be agreed with the orthopaedic surgeon who carried out the operation on the basis of the type of prosthesis implanted and the technique used.
In general, if the patient’s condition and the type of prosthesis allow it, rehabilitation in the weeks following the operation is designed to achieve full extension and 90° flexion. The exercises indicated by the therapist are often accompanied by passive mobilization (CPM) using apparatus to guide the movement of the leg.
The following are tips of a general nature for the post-operative period. It is important in this delicate phase to comply with the doctor’s recommendations.
- Full loading of the operated limb may be done immediately with the help of a walker.
- Don’t bend the knees excessively.
- When taking a shower it’s advisable to use an anti-slip mat. Put a stool in the shower and use it with your back against the wall.
- If you don’t have a shower, use an appropriate bathtub seat. Sit on the edge of the seat, put the operated leg in the bath first, then the other one.
- In the period when crutches are used, it’s best to brush hair, shave and brush teeth in a sitting position.
- Use firmly stable chairs, preferably with armrests. On sitting down, open the legs out slightly and rest your hands on the armrests or on your thighs and sit down slowly keeping your knees wide apart and your feet parallel.
- To get up from a chair, slide forward to the edge of the chair and rise with the help of the armrests.
- Going upstairs: lead with the sound, non-operated leg, then the crutches and then the operated leg.
- Going downstairs: lead with operated leg and then the sound one.
- Wear closed shoes with anti-slip soles.
- To get into a car it’s advisable to put a cushion on the seat, sit down keeping the legs out of the car and then bring the operated leg inside first and then the sound one. To facilitate this movement, if the left leg is the operated one, it’s best to sit to the right of the driver; if the operated leg is the right one, sit behind the driver.
- It is only possible to start driving again when your specialist has given clearance.
The rehabilitation period may last around three months but may also be extended if necessary.
On completion of the rehabilitation programme patients can normally carry out most day-to-day activities. Patients may resume normal sexual activity, drive and do sport provided they take due precautions and follow their therapist’s instructions.
Detailed in the table below are the activities recommended in the long term following a total hip or knee replacement.
|Very good, highly recommended||Good, recommended||Requiring certain abilities, previous experience||With care, subject to doctor’s advice||Avoid|
|Golf||Speed walking||Ice skating||Tennis (doubles)||Softball|
|Sci da fermo||Table tennis||Stepper (with hip prosthesis, not knee)||Handball|
|Skiing (downhill)||Tennis (singles)|
From DeAndrade RJ: Activities after replacement of the hip or knee. Orthop Special Ed 2:8, 1993.
The information provided above does not constitute medical consulting in lieu of a doctor’s opinion. It may under no circumstances substitute the consulting, examination or diagnosis of a doctor.
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