X-Ray Limitations for Hidden Bone Problems after Total Hip ReplacementWilhelm Conrad Roentgen discovered the use of X-rays in 1895. He was working as a professor of physics in Germany. He called the unknown radiation "X-rays," since "X" frequently stands for an unknown amount in math. His discovery changed the world of medicine. For the first time doctors could "see" inside their patients.
Today X-rays are still useful, but they have their limits. One of these limits is seeing areas of osteolysis in the pelvis after total hip replacement. Osteolysis is the breakdown of bone. It's a problem that can occur when hip implants are put in without cement. Areas around the hip implant can be hidden on X-ray. The shadow of the implant itself causes this problem. Doctors need to know how many and how large the areas of bone breakdown are when planning surgery to revise the joint replacement.
Researchers at the Anderson Orthopaedic Research Institute in Virginia measured the accuracy of X-rays in finding osteolysis. They used cadavers (human bodies saved for research). They put cementless hip implants in eight cadaver hips. Hip X-rays were taken. The implants were taken out and holes were made in the pelvic area of each hip. The size and shape of each hole was measured. The implants were put back in and more X-rays were taken.
The holes were redrilled two more times. The size of the holes was measured and X-rays taken each time. The scientists found that X-rays showed osteolysis just over 40 percent of the time. This means more than half the time the patient has unseen osteolysis. The authors report that larger lesions are more likely to be seen. Even so, the extent of osteolysis was underestimated using X-rays. When an experienced radiologist looked at multiple views, the rate increased to 73.6 percent. That still means that more than one-fourth of the osteolysis was missed.
X-ray can't show osteolysis, the authors conclude, unless the defect is large and in just the right place. They advise using multiple X-ray views when looking for osteolysis. Even with these steps, the doctor should be prepared to miss more than half of all lesions along the back side of the hip socket.
Alexandra M. Claus, MD, PhD, et al. Radiographic Definition of Pelvic Osteolysis Following Total Hip Arthroplasty. In The Journal of Bone and Joint Surgery. August 2003. Vol. 85-A. No. 8. Pp. 1519-1526.
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