Hip Replacement Considerations

Thigh Pain

A primary goal of hip replacement is to reduce pain. Though most patients experience some pain during recovery from surgery, they find that the long-term relief is a welcome liberation from the pain caused by diseased hip joints.

However, hip replacement patients can experience pain if their implants are too rigid, “pinching” against the more flexible bone that supports them. Zimmer hip stems have several design features to minimize pain and stiffness.

Leg Length

Zimmer offers a variety of sizes and options to help surgeons match each patient’s natural leg length as closely as possible. Each hip system comes in a range of sizes, measured in precise millimeters.

Most patients’ hip joints have an approximate 130° neck angle. However, for those patients with slightly different anatomies, Zimmer offers both “offset” and “short neck” hip stems to adjust for unique anatomies.

Bone Preservation

Bone is living tissue and like most living things, needs stimulation to stay healthy.

A challenge in hip implant design is not to let the implant do all the work. If the implant overly shields the bone from stress (“stress-shielding”), bone can be resorbed or broken down by the body, resulting in bone loss for the patient.

On the other hand, if the bone is required to take on too much stress, abnormal growth can occur – called “adaptive remodeling.” 

Zimmer implants are designed to provide a balance between stable fit and natural stress loading.

Bone Loss (Osteolysis)

In addition to inadequate stress loading, bone can also be lost through a process known as osteolysis.

Here’s what happens: 

As the hip stem’s hard metal head rubs against the softer polyethylene cup in the hip socket, the friction can degrade the polyethylene over time, causing small wear particles to break off in the body. The body’s immune system rejects this foreign debris, attacking it much like it would attack an infection. 

Unfortunately, since the polyethylene debris typically settles around the site of the implant, the immune system may start attacking the surrounding bone tissue. This is known as osteolysis – literally, "eating away" of the bone. As the patient loses bone tissue in his or her hip, the implant may become loose and no longer function properly. Many orthopedic surgeons identify osteolysis as the number one cause of hip implant failure.

Zimmer implants have several design features that specifically address the issue of osteolysis: 

  • Build-up in the upper (proximal) area of the hip stem to effectively fill the bone and reduce potential tracks for debris.
  • Oxygenless packaging of implants, introduced in 1994, virtually eliminates all oxygen from the package during sterilization so oxidation (and possible subsequent aging) cannot occur. The absorber continues to remove oxygen from the package during its shelf life. These features lead to reduced debris degeneration.

Stability

Zimmer hip implant designs are the result of detailed analyses of hundreds of patient x-rays for maximum stability and optimal bone/implant fit. The goal is to maximize the patient’s range of motion while at the same time minimizing the possibility for dislocation.

Lifetime of Implant

The longevity of a prosthetic hip (how long it will last) varies from patient to patient. It depends on many factors, such as a patient's physical condition and activity level, body weight and the surgical technique. A prosthetic joint is not as strong or durable as a natural, healthy joint, and there is no guarantee that a prosthetic joint will last the rest of a patient's life. All prosthetic hips may need to be revised (replaced) at some point.

Revision Surgery

Some patients require a second revision implant due to loosening, trauma, infection or chronic dislocation. 

A common challenge with revision patients is the loss of bone due to too much stress shielding of the implant or osteolysis caused by wear of the polyethylene insert. 

Zimmer offers a full line of revision hip implants designed to preserve as much remaining bone as possible and minimize the need for yet another surgery.



View Hip Replacement Frequently Asked Questions