Hip replacement surgeries are increasingly common these days. The rising popularity of this surgery has not only increased the sophistication of its procedure, but also made us realize its shortcomings. Over a period of few years, a once good artificial hip joint, can turn into a nightmare. This surgery may be a necessity for some patients, like those suffering from femoral neck fracture or avascular necrosis. But many elderly people are opting for this surgery, just to continue an active lifestyle. The following discussion aims at making a person realize some of the disastrous consequences of a hip replacement.

Dislocation Problems after Hip Replacement

Normally, an artificial joint is highly stable and supports many types of movements like sitting, standing, walking, running, and so on. But there are certain movements like squatting, sitting cross-legged, or sitting on ground, which are to be avoided after a hip replacement. This is the most important cause of dislocation in a person with an artificial hip joint. An artificial joint can only provide a limited range of motion. When this limit is exceeded, the joint gets dislocated. A dislocation is felt as an inability to move the concerned joint, along with pain and swelling around the joint. After dislocation, it is very important to have it corrected immediately to prevent the problem of recurrent dislocations. A dislocated hip replacement should be preferably treated by the same surgeon, who performed the replacement surgery, as he knows the orientation of the joint better. However, it has to be done in an emergency !

Picture 1: Dislocated Hip Replacement
(source: Wikimedia)

The second reason for dislocation of an artificial joint, is improper alignment of the parts during the surgery. This can be easily recognized by a feeling of looseness in the hip joint after the surgery. Normally, muscles around the hip joint hold it in position and prevent it from dislocation. If the measurements  of the artificial joint (including angular orientation), are not similar to the original hip joint, the muscles around it are not able to contract and become lax. This paves the way for a dislocation after trivial trauma or sometimes even during sleep. Thus, any such feeling of a loose hip joint must be promptly conveyed to the surgeon, who can then take appropriate steps to correct the problem.

Wear and Tear

An artificial joint can be considered like a machine. Just as over the years a machine undergos wear and tear, so do the parts of an artificial joint. The surfaces of an artificial joint are made from a range of materials like polyethylene (plastic), or ceramics, and so on. These materials undergo wear and tear due to the constant motion between them. Normally, these surgeries are done in the elderly for whom the lifespan of the joint is mostly greater than their own lifespan. But due to increasing popularity the surgery now-a-days is being performed at a much younger age. This group of patients are the ones who also lead a more active life, leading to earlier wear and tear of the joint.

On an average, an artificial joint has a life span of 7 years after which it has to be replaced. Thus, it is natural for a person to undergo a repeat surgery for the same. The re-replacement of the hip is a simple procedure and may involve the replacement of only a plastic or ceramic components. This is possible only if one had chosen a modular artificial joint at the time of the surgery. Modular joints have separate parts which are interlocked together. Thus, only the problematic parts can be removed and the rest continue to remain in place. Hence, while considering various options of types of artificial joints at the time of surgery, it is important to choose a modular joint.

Joint Loosening

The metallic parts of an artificial joint are fixed firmly to the hip and the thigh bone at the time of the surgery. Over a period of years these bones undergo changes because of aging. Moreover the plastic or ceramic particles generated from the wear and tear of the joint cause an allergic response. This causes release of destructive enzymes near the bones, which erodes the bones to some extent. All these processes cause the firmly fixed parts to become loose. Joint loosening can occur anytime between 3-5 years after joint replacement or may not occur at all. Once it does occur, it leads to further problems like pain, frequent dislocations, or even fractures. Similar to a worn out joint, a loose joint has to be re-replaced. Even here a modular artificial joint is of help as only the loosened parts can be removed keeping the rest in place.

Heterotopic Ossification

Heterotopic ossification is formation of bones in tissues where bone is normally not present (like muscles). Certain regions of the body show this feature in response to repeated trauma in the form of friction. This is helpful in a way that it prevents the tissue from destruction, but it hampers mobility of the part as it looses its flexibility.

Picture 2: Heterotopic Ossification
(source: Wikimedia)

The surgical stress, along with continuous friction of muscle tissue with the artificial joint, leads to formation of bone within the hip muscles. This inturn leads to stiffness and decreased movements at the hip joint along with pain. A simple x-ray of the hip shows the newly formed bone. This can be prevented with a simple 10 day course of Indomethacin, or it can be treated with radiation therapy. This is followed by physical therapy, which improves the mobility of the joint in a gradual manner.

Thus, one has to properly understand the fate of an artificial hip joint, before going to the knife to sacrifice one’s own.

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Article reviewed by Dr. Greg. Last updated on February 16, 2010