A knee prosthesis is the replacement of a damaged joint with an artificial joint consisting of a femoral part, a tibial part and an intermediate part between the two.
Knee replacement is probably the most frequently performed arthroplasty after hip replacement (40,000 operations/year in France). Associated procedures on the bones or ligaments may be necessary for correct implantation of a knee prosthesis. These may vary widely depending on the case.
In the case of a total prosthesis, it may be more or less "constrained" (the maximum constraint being the hinged prosthesis), the choice being made according to bone and ligament wear.
There is therefore a specific type of prosthesis for each knee. Classically, there are :
These have only one degree of freedom in flexion and extension. Historically, these were the first knee prostheses to be fitted, with a short lifespan given the stresses imposed on the implants (loosening). At present, these prostheses are only used for limited indications: tumour surgery, major deviations of the limb with failure of the ligament system.
These are currently the most widely used. They provide the quality and reliability of current results. These are more or less constrained implants (prostheses preserving the two cruciate ligaments, prostheses preserving the posterior cruciate ligament, postero-stabilised prostheses sacrificing the two cruciates), the main characteristic of which is the absence of a fixed means of union between the femoral and tibial parts, stability being ensured by the design of the prosthesis and the assistance of the remaining ligaments.
It should be noted that in order to benefit from these advantages, a number of requirements must be met (type of wear, state of the ligaments, degree of deformity of the knee, weight). This type of implant is also less 'tolerant' than a total prosthesis: it cannot withstand a poor indication or technical imperfection.
The materials used are metal for the femur and tibia components, and polyethylene for both the intermediate surface used to replace the menisci and for resurfacing the patella.
Knee prostheses are usually fixed to the bone using surgical cement. Sometimes the cement is replaced by a material covering the implant. In this case, there is no immediate stabilisation but a secondary stabilisation induced by bone regrowth around the prosthesis. This is known as a cementless prosthesis.
In most cases, this operation can be carried out minimally invasively, thanks to modern surgical instruments and advances in implantation techniques. It can also be carried out under computer control (this is known as "computer navigated" surgery).
However, the long-term benefits of these new implantation techniques have yet to be clearly established, even though they are currently attracting considerable enthusiasm. In any case, the triptych good clinical examination - good indication for prosthesis - good implantation of the prosthesis remains the guarantee of the best functional result in knee prosthesis.
The choice of implanting a prosthesis will depend on a number of parameters:
To ensure that the operation runs smoothly:
Arrive the day before and prepare the skin.
Tell the nurse about any recent fever, even if it's minor, or any local problem that could be a potential source of infection (sore, pimple, scab, etc.): this could cancel the operation.
Don't forget all your documents
(especially X-rays)
Respect the instructions specific to any anaesthetic
(food, drink, smoking).
Generally, a pre-medication is prescribed
(a mild sedative, but above all a relaxant).
Antibiotic prophylaxis, started just before the operation and continued for 48 hours.
After the operation, you must be transferred to the recovery room. You will be monitored by a separate team from that in the operating theatre, which is responsible only for "waking up" and post-anaesthetic monitoring of patients. These staff are specially adapted to the immediate post-surgical stage. They work in collaboration with and under the supervision of your anaesthetist and surgeon.
When the anaesthetist considers that you can return to your room, you will be taken back to the surgical ward. Your limb is immobilised in a removable knee splint.
You are allowed to get up for the first time between the 1st and 3rd day, depending on the case. It must be done in the presence of the physiotherapist, who will be able to assist and guide you in complete safety.
Your surgeon, in conjunction with the physiotherapist, will decide whether or not to allow you to return to weight-bearing and support yourself with walking sticks (depending on the patient, the type of operation, the quality of the bone and the primary solidity of the attachment of the implants to the bone). Knee re-education generally begins the day after the operation: you will be encouraged to move your knee as soon as possible using an arthro-motor (a device that automatically moves your knee in flexion-extension, without causing pain). The aim is twofold: to avoid muscle wasting and to recover joint mobility (which is often rapid, the aim being to maintain 90° of flexion and above all to avoid the appearance of flessum).
Pain is not an obstacle to active mobilisation of the operated knee, since the femoral catheter is left in place for a few days. In any event, you will be given appropriate instructions by your surgeon, physiotherapist and possibly your rehabilitation doctor if you subsequently go to a rehabilitation centre. The splint should only be removed if the quadriceps allow the knee to lock properly when weight-bearing. Discontinuation of the walking sticks will be subject to precise instructions depending on your progress, X-ray check-ups, muscle tone and the quality of your functional recovery.
Do not take any personal initiative.
Depending on your condition, the pathology you suffer from, the type of prosthesis fitted and the technique used, rehabilitation will vary considerably. In general, you will be encouraged to use the prosthesis to regain mobility and muscle function, but a number of precautions will need to be taken.
In all cases, you will need to :
The initial large dressing and drain are removed once the knee has been mobilised. The average length of hospitalisation is 3 to 7 days. A stay in a rehabilitation centre is strongly recommended before returning home in the case of total prostheses.
The results of this operation are reliable, with prolonged setbacks. The main benefit to be expected is the elimination of pain and an improvement in the mobility of the joint, making it possible to increase the walking perimeter.
For a large number of patients (75%), these figures reflect the transformation of pain that was considered permanent or significant into no, moderate or even occasional pain. For these patients, the average knee flexion is 110°, they can walk without a cane, they can climb stairs almost normally (although they often need to use a ramp to go downstairs), and their walking perimeter is around three kilometres. In some patients, the result is even better, allowing unlimited walking and light sporting activity or a return to work. As a general rule, patients can drive after 2 months.
Many patients experience muscle weakness after the operation (mainly in the quadriceps). This is linked to the operation itself, but also to the fact that a destroyed and painful joint sees its muscles weaken over time. Recovery takes several months, and the final result should not be judged for 6 months.
As with any operation, an anaesthetic accident is possible. It is currently extremely rare. Despite all the pre-operative precautions, there are risks associated with this type of operation. These potential surgical complications are varied but rare. Some are common to all operations on the lower limb, while others are more specific:
Indoors, do simple, gradual exercises: practise picking up objects from the floor by bending over your operated leg; the other leg lies backwards. Go up and down stairs using a cane on the side of the operated limb and the handrail on the other side. Learn to get up from a chair with less and less support from your arms. Outside, try to get out and walk every day. Don't take long strides, even to avoid an obstacle. At first, prefer even, flat ground. Don't carry heavy loads or bulky packages. DIY and housework should obey the same safety rules as before.
During the first few weeks, you should be aware that your prosthesis requires regular monitoring. A number of accidents may still occur. Prevention is the best way to avoid complications:
- Prosthesis wear is a normal process that must be monitored. Clinical and radiological checks should be carried out every 2 years.
- Osteoporosis can be grafted onto this knee and increase the risk of fracture and/or loosening. Have your knee checked regularly by a densitometry test and follow the suggested treatments to avoid these accidents. Above all, know how to prevent infection, because in 95% of cases, infection of a knee prosthesis occurs from a distant site. You therefore need to take a number of precautions: look after your feet; men, have your prostate checked every year. Ladies, retrain your bladder to avoid urinary incontinence, which can lead to infection. Every six months, have your teeth checked by a dentist. Finally, in the event of a feverish sensation or inflammation of the throat, bronchi or other areas, call your doctor and describe the prosthesis you are wearing, so that if necessary it can be protected by systematic antibiotic therapy.
Prosthetic knee surgery has caught up with hip surgery, even if the results are difficult to compare (lower functional results, but generally less demand from an older population). Developments in knee prosthesis design and improvements in fitting techniques have made it possible to achieve these results. However, the purpose of fitting a prosthesis is not to resume activities that place too much strain on the knee. Such activities are not recommended, to avoid compromising the future of the prosthesis. On the other hand, physical activity is recommended, and active people who maintain their muscles have better long-term results than non-active people.
Joint destruction and the state of the bone and ligament structures at the time of the operation but also after the prosthesis has been fitted, an unstable or badly positioned prosthesis leading to mechanical failure (pain, stiffness, loosening, premature wear).
(and not all the same results): this choice follows from the previous conclusions
And work with the physiotherapist immediately after the operation.
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