Prostheses are artificial substitutes for parts of our body. Thus the hip prosthesis is the artificial substitute of the hip joint. The hip joint consists of 2 main parts: the first is a spherical cavity that is attached to the pelvis that is called acetabulum, acetabular cavity or acetabulum; the second is the head of the femur, which is also spherical and fits perfectly into the hole that the pelvis offers.
The replacement of the hip by a prosthesis is usually done when the hip itself suffers such damage that does not allow a normal life for uncontrollable pain despite the medication.
Hip prostheses have evolved over time especially in terms of shape and materials used, today there are numerous types of prostheses that are adapted to each patient and each personal situation.
The surgery consists of removing the injured parts and applying the components that make up the prosthesis. All the prostheses are subject to wear and tear; therefore, over time they will stop working normally and a new surgery will be required to replace the worn parts.
Components of the prosthesis
The femoral component: it is a stem that is introduced into the medullar canal previously carved; for this it will be necessary to remove the head of the femur.
Head or cephalic component: This is a sphere that attaches to the stem. In certain prostheses the stem and the head are the same piece.
Acetabular component: This is the one that replaces the part of the hip joint attached to the pelvis. It is a hollow sphere that adapts perfectly to the head or cephalic component.
The femoral component or shank will usually be made of a metallic material such as steel or titanium, it must be a particularly resistant material since it is in charge of transmitting all the weight of the body to the femur.
The head or cephalic component must be made of a material that allows to create a very smooth and wear-resistant surface. The smoother the surface of the head, the less friction it will offer to the movement, therefore the lesser the wear will be over time. The materials that are usually used are ceramics, steel and high density polyethylene (which is a kind of very hard plastic).
Acetabular component: This usually has two slopes, the part that is attached to the bone is usually metallic to offer a good resistance to the transmission of loads: steel, titanium, tantalum, etc … The part that is in contact with the head It should be smooth and offer minimal friction and wear resistance: it could be made of ceramic or polyethylene.
There are no important differences regarding the clinical result of the different materials used in the prosthesis, the choice of these should always be made by the surgeon based on the particular characteristics of each patient as well as their personal experience and preferences.
When is the best time to implant a hip prosthesis?
In general terms it can be said that the later the better, as long as the pain is not very disabling and / or controlled by conventional analgesics. The surgeon is in charge of detecting coxarthrosis or osteoarthritis of the hip and informing the patient that their disease can be solved by implanting a prosthesis and at that moment proposes that possibility. The patient will be the one who accepts or declines that possibility depending on the pain and the incapacity that this produces. Therefore the decision must always be made through a consensus between patient and surgeon. Hip prostheses usually last 10 to 20 years, after which it is usually necessary to replace them, replacement surgery of a hip prosthesis is very aggressive and results in much worse than primary prostheses (first time), because therefore, it is desirable that patients suffering from hip osteoarthritis be operated on only once. But the decision to be operated on must be made with common sense on the part of the patient, it is useless to be seated and incapacitated with 60 years waiting for the right moment to be intervened and thus be able to walk at 80.
We must consider part of the cases of hip fractures in which the surgeon decides that the best option for the patient is the implantation of a hip prosthesis, this should be done in the days following the fracture.
How often does a hip prosthesis last:
The prostheses are manufactured with inert components, that is to say that they are not alive and therefore they are not able to regenerate themselves like the different parts of our body. Constant use subjects them to wear as can happen with any other object that surrounds us. Therefore and depending on different factors such as the use they are given or the pressure they are subjected to, they may last from 10 to 20 years. After this period of time, the components, especially the head and the acetabular component (which are the two surfaces that are in constant motion), wear out, becoming less and less efficient and transmitting an ever greater tension to the bone that surrounds them. In addition to the result of friction particles are released that the nearby bone absorbs, favoring the destruction of this bone.