Generality
The knee prosthesis is implanted when the joint, which joins the femur and tibia, is irreparably damaged. With its application, the aim is to restore a certain joint mobility and to alleviate the painful sensation that characterizes serious knee injuries.
Knee replacement surgery is invasive and requires appropriate rehabilitation, but the results are more than comforting. The patient, in fact, can return to lead a normal life, without particular limitations.
There are two models of knee prosthesis. The choice of the most suitable model, which is up to the surgeon, is based above all on the patient's age and general health.
Research in the field of medical technology has a triple objective: to extend the life of the prosthesis, improve implantation techniques and reduce the invasiveness of the intervention.
Short anatomical reference: the knee
The articulation, or articular capsule, of the knee is placed between the femur (located above), tibia (inferiorly) and patella (anteriorly) and is formed by different elements, all equally important in allowing movement and in supporting the weight of the human body .
When is it necessary to intervene?
Like any joint in the human body, even that of the knee can be damaged. The most common symptoms are: pain, swelling and poor joint mobility .
If the damage to the joint is minor, the severity of these symptoms is modest and with the appropriate conservative countermeasures, such as physiotherapy or the use of anti-inflammatories, excellent results can be achieved.
On the contrary, when the damage is so severe that any daily activity is impossible, the hypothesis of undergoing surgery should be considered. In fact, surgery offers several possibilities: the knee prosthesis is one of them. Through it, the old, no longer functional joint is replaced by an artificial one.
When to operate?
- Strong pain and swelling
- Articular stiffness and reduced mobility of the knee
- Difficulty performing the most common daily activities
- Quality of life compromised
THE MOST FREQUENT CAUSES OF ARTICULAR DAMAGE
The most common causes, which require the intervention of knee prostheses, are:
- Osteoarthritis . They are the most common arthrosis, characterized by the consumption (by continuous rubbing) of the articular cartilage. For this reason, they are also called "wear arthrosis". The patient, usually elderly, experiences pain and motor difficulties.
- Rheumatoid arthritis . It is an autoimmune disease, in which the immune system, instead of defending the body from infections, "turns" against it. Joints pay the consequences: they become stiff, painful and swollen.
- Hemophilia . The continual bleeding lesions (hemarthros) weaken the joints, which become stiff and painful. The most affected targets are the knees and ankles.
Osteoarthritis, rheumatoid arthritis and hemophilia lead to progressive joint damage. Initially, it is possible to opt for a conservative treatment, aimed at alleviating symptoms. Subsequently, this therapeutic approach is no longer sufficient.
Figure: this is how osteoarthritis consumes articular cartilage. From the site: oxbridgebiotech.com
OTHER CAUSES
Other pathological circumstances are also treated with prostheses, which, although less common, also cause progressive knee damage.
One of these is gout, which inflames the joints due to the accumulation of uric acid.
Another is avascular necrosis due to alcohol abuse.
Another is represented by repeated injuries to the ligaments and tendons of the knee.
Finally, there are bone dysplasias and knee deformities . They both determine an anomalous disposition of the articular bony elements, which gradually lose their mobility and integrity. They are congenital disorders, that is, present since birth, often with an invalidating outcome.
HOW IS THE ARTICULATION DAMAGED?
Osteoarthritis, as well as the other causes mentioned, lead to deterioration of the articular cartilage. Without this cartilage that protects them, the femur, tibia and patella "rub" each other and consume the (distal) ends involved in the joint.
Thus we can observe more or less serious damage to the cartilage; a young adult, for example, may have partial injuries. Therefore, each patient shows his own clinical picture, which must be carefully evaluated, before intervening with a prosthesis.
WHO DO YOU INTERVENT?
The individuals who undergo most knee surgery are the elderly between the ages of 60 and 80. These, on the other hand, are also the subjects most affected by osteoarthritis and rheumatoid arthritis.
The same intervention, on young adults with severe joint damage, is not the best choice. Other solutions are preferred, less invasive and more durable. As you will see, in fact, the knee prosthesis has a duration of 15-20 years; after which a second operation must be carried out, for replacement; substitution, which, however, is much more complicated than the first intervention.
WHAT ARE THE FINAL OBJECTIVES OF THE INTERVENTION?
The objectives, which are aimed at the intervention of knee prostheses, are:
- Pain reduction
- Improvement of joint mobility
- Improvement of the motor skills of the operated individual
- Significant improvement in the quality of life
The methods of intervention
You can choose between two types of knee prostheses:
- Total prosthesis
- Partial or unicompartmental prosthesis
Figure: the parts that make up a total knee prosthesis. From the site: permedica.it
The choice depends on the severity of the joint damage: if the bone lesions, ligaments, tendons, etc., are serious, total prosthesis is used; when, on the other hand, the knee still has healthy areas, partial (or unicompartmental ) prosthesis is used
TOTAL KNEE PROSTHESIS
Severe knee joint damage requires a full denture. In fact, in these situations, osteoarthritis (or any of the other causes mentioned above) has so thoroughly consumed the ends of the femur and tibia, both of which must be replaced by artificial metal structures.
A deep and long-standing damage can also affect the kneecap; consequently, total prostheses have been developed which are also suitable for this eventuality.
The graft of a total knee prosthesis is, by far, the most practiced procedure.
PARTIAL PROSTHESIS (OR SINGLE-COMPARTMENTAL) AT THE KNEE
When there is only one damaged or worn bone end, a partial prosthesis is applied.
From the site: adrianorusso.it
Since this is an infrequent pathological circumstance (usually, the whole joint structure is involved), the partial prosthesis is rarely implanted (only one person out of four with osteoarthritis). Furthermore, it also has disadvantages, which will be discussed later.
THE DURATION OF A PROSTHESIS
A total prosthesis lasts about 15-20 years.
A partial prosthesis, on the other hand, has a shorter life: about 10-15 years.
The pre-operative period
The period preceding the operation can be fundamental to shorten post-operative recovery.
Walking, for example, is of great benefit, both to the muscles and to the ligaments.
Another very important recommendation is to perform some muscle stretching and tendon exercises, for the lower limbs, and muscle strengthening for the upper limbs. The latter, in fact, will be called to work hard when crutches are used.
THE INSTRUMENTAL EXAMINATIONS
During the pre-operative phase, the patient undergoes various radiological and electrocardiographic instrumental examinations.
The aim is to get to know the patient thoroughly, clarifying his general state of health, the precise anatomy of the knee (the prosthesis is made to measure) etc. Acquiring this information increases the success rate of the intervention.
How is the operation performed? The procedure
The operation is performed by a surgeon skilled in knee orthopedics, who uses the help of consultants and an anesthesiologist. It is of fundamental importance that the operating surgeon knows the patient's medical history and the exact anatomy of the knee on which he will implant the prosthesis. The prosthesis, in fact, to work properly, must be custom built.
ANESTHESIA
The knee prosthesis (both total and partial) is usually performed under general anesthesia . However, it is also possible to opt for an epidural anesthesia, in which only the lower part of the body is insensitive to pain. Whoever chooses this second option, however, is not conscious, since he must take strong sedatives.
THE TOTAL PROSTHESIS OPERATION
Once anesthesia has occurred, the actual operation begins. The procedure can last from one to three hours and involves three key moments:
- Incision at the patella
- Removal of worn bone ends of femur and tibia
- Replacement with artificial joint
The incision is made where the kneecap resides, which is moved to one side, to have free access to the entire joint implant of the knee. At this point, the worn ends of the tibia and femur are removed and replaced with metal plates.
The distal part of the femur is replaced by a curved plate; the proximal part of the tibia, instead, is replaced with a flat plate.
From the site: francescobove.com
In the middle of the two plates, which are glued to the bones with a substance called " cement ", a spacer element (or insert) is inserted in plastic. It plays the same role as articular cartilage, avoiding direct rubbing of the femur and tibia.
If the kneecap is also damaged, a metal plate is applied to the inner part of the latter.
At the end of the procedure, the incision is closed and the incision is sutured.
THE PARTIAL PROSTHESIS OPERATION
The operation involves a minor incision, compared to the previous intervention described, and the removal of a single bone portion, or of the femur or tibia.
THE TWO PROSTHESES IN COMPARISON
The partial prosthesis is less invasive than the total one. In fact, it requires shorter healing times, since the incision is less deep and the rehabilitation path is shorter.
However, it has significant disadvantages, which lead the surgeon to opt, in most cases, for the total prosthesis.
Disadvantages of partial dentures
- It lasts less than the total prosthesis. An intervention to replace the old prosthesis is very problematic, much more than the first operation. For example, the adhesive (or cement), used to fix the plates, is very resistant and it is very difficult to remove it.
- It offers less therapeutic benefits than a total prosthesis. The pain, in fact, can recur after some time, as joint degeneration is a progressive process, which consumes the bone portions not yet replaced by the prosthesis.
WHICH PROSTHESES TO CHOOSE? THE CRITERIA OF CHOICE
The choice of the type of prosthesis to be used is up to the surgeon, who bases his considerations on the following elements:
- Age of the patient
- Basic pathology
- Body weight
Due to its importance, the patient 's age deserves special attention.
For the elderly. If joint damage is limited, a partial prosthesis may also work, the graft of which is less debilitating and invasive. In fact, although this solution is less durable, the patient of advanced age is unlikely to undergo a second operation to replace the worn prosthesis.
For the young or middle-aged patient. If the joint damage is severe and it has been found that there are no equally effective remedies, the most suitable prosthesis is the total type. It is the only way to postpone the replacement intervention as much as possible.
CONTINUE: Knee prosthesis - Recovery after surgery, Risks and Benefits "
