Endoprosthetics is the surgical replacement of pathologically changed and damaged joints (‘wear and tear’) with artificial joints. It is also often called hip replacement surgery. The damaged and pain causing surface of the joint is removed and replaced by the articial joint.
The natural hip joint is approximately globular and comprises a head and a socket, whose surfaces are covered in cartilage. The socket of the pelvic bone is called acetabulum. The globular part is the femoral head, which is connected to the thigh bone over the femoral neck.
A hip replacement is a total hip endoprosthesis (hip TEP) in most cases. It is also called an implant, a hip implant or total hip replacement. It does completely substitute both bony parts of the worn out joint, the femoral head and the hip socket. The prosthetic head is anchored with a shaft into the thigh bone. Often hip endoprosthesis consist of 4 parts (acetabular shell, acetabular liner, femoral head, femoral hip stem). Normally, they are built modularly, so that the surgeon can adjust the artificial hip joint to the original shape of the hip.
The most important part of the hip replacement is the so-called tribological pairing that forms the joint and comprises two parts. The femoral head mounted on the femoral hip stem consists of metal or ceramics. It moves in a half-shell acetabular liner, which is anchored in the acetabular shell. Its inlay is made of synthetics (polyethylene), ceramics or metal.
After the bony acetabulum (hip socket) and the inner of the thigh bone have been prepared by fraising and/or rasping, the artificial acetabulum (acetabular shell and acetabular liner) are anchored with bone cement. 3 different anchoring techniques are differentiated:
During the cementless hip replacement surgery, the artificial acetabulum and the femoral hip stem are pressed into the prepared bone bed (so-called Press-Fit technology), or the acetabulum is screwed. In addition to that, bone screws can be used. The rough surfaces make it possible that the bone grows into or onto the material. A requirement is a good bone quality. This method is particularly suitable for young patients.
During cemented hip replacement surgery, the artificial acetabulum, which is made of polyethylene, and the femoral hip stem are anchored with the so-called bone cement into the bone. Bone cement is a synthetic substance that intermeshes with the trabeculae and fixes the artificial hip replacement immediately and safely. It is not necessary that the bone grows into or onto this material, so that this method is also suitable for elderly patients, proven by very good long-term results.
During hybrid hip replacement surgery, both aforementioned surgery techniques (cementless hip replacement and cemented hip replacement) are combined. In most cases, the artificial acetabulum is implanted cementlessly, but the femoral hip stem is cemented. This has advantages in the area of the femoral hip stem, especially if the bone quality is not very good. The hip stem has to be fixed much alike a wedge in a pipe. The artificial acetabulum can be fixed cementlessly and safely, even in case of bad bone quality, because shear stress does not occur.
The total hip replacement surgery is the most frequent and successful orthopedic surgery. According to huge so-called retrospective cohort study, we know that elderly patients from 65 years on have a chance of 90% to lead a life that is free or almost free from medical complaints and actively take part in daily life. Even 16 years after surgery, the hip replacements works smoothly in 80% of all patients. Due to its outstanding treatment results, the artificial hip replacement is also used to treat younger patients who want to remain active and mobile despite their irreversible hip damage.
The right choice of suitable total endoprosthesis and the anchoring method depends on the cause of the disease, age, gender, bone quality and the individual needs of the patient. An alternative to the classic total endoprosthesis of the hip for younger patients is a short femoral stem hip prosthesis. The health condition and the expectations of the patients determine the individually adequate implant option.
The early phase after hip replacement surgery is accompanied by an optimal pain therapy: state-of-the-art catheters and PCA pumps (PCA – patient controlled anesthesia) as well as well-tolerated drugs. You will touch your hip replacement the first time one day after surgery.
Subject to the chosen surgical access, excessive movements should be avoided in the first 4-6 weeks because the joint capsule surrounding the hip joint has to grow as well as (as far as it was necessary to detach them) detached muscles. Hip joint dislocation with a removal of the prosthetic head from the prosthetic socket has to be prevented. (The anchorage of the prosthesis in the bone is not affected.)
The hip joint is stabilized due to recovery progress and muscle growth over time. A hip dislocation is then very rare, e. g., as a result of an accident. But certain movements and postures are not permitted in the early recovery stage. However, a gentle full load of the joint should occur soon. It is accomplished in the first weeks by using crutches.
Sleeping on the operated hip is permitted early after the surgical wound has healed. Sleeping on the opposite side should be supported by a pillow between the knees within the first 4-6 weeks.