As I sit here writing you, tears are streaming down my face. I have had three hip replacements -- on the same leg. And now the stem piece of this one (a modular type) has broken and needs replacing. I am overweight so that is always blamed as the reason. Other people who are fat don't break their implants. There must be some other reason besides my weight that this keeps happening to me. What do you think?
It doesn't happen very often but sometimes patients who have a total hip replacement end up having a second or (more) revision surgeries because of a failed implant. Even more rare is the occasional revision surgery that fails. And any number of failures (no matter how few) are unacceptable to the surgeon as well as to the patient.
Studies have shown that certain risk factors are linked with stem fracture. The most common of these factors are being overweight, high levels of physical activity, and malposition of the first implant. Implants have improved in design to help counter these problems but there are still a few now and then.
As you suspected, there are other possible risk factors to consider. For example, poor bone structure that cannot support the junction area of the stem might be an issue. Sometimes the problem is within the implant itself. With the modular implants, there are three separate pieces that fit together. The body, neck, and stem are held together with a modular connection and that connector has a taper junction and an engaged-fit junction.
Femoral stem fractures can occur as a result of a problem at these modular junctions. Implant manufacturers have worked with surgeons to find a design strong enough to withstand the forces at the intersection between two component parts.
When broken implants have been removed, they have found visible evidence of wear and tear on the implant stem near the junction. Fractures just above the body-stem junction (hidden under the main body of the stem) seem to be the most common. A force strong enough to bend the stem at that point contributes to fractures of this type.
The surgeon who removes your broken implant will be able to examine it carefully and see what might have caused the problem. The solution may be in choosing a different implant that will meet your specific needs.
Dror Lakstein, MD, et al. Fracture of Cementless Femoral Stems at the Mid-Stem Junction in Modular Revision Hip Arthroplasty Systems. In The Journal of Bone and Joint Surgery. January 5, 2011. Vol. 93(1):57-65.
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