Researchers become hip to prosthetic complication

A new application of a standard imaging technique promises to afford earlier detection of a common long-term complication in total hip replacement.

Periprosthetic osteolysis occurs when the body reacts to submicron polyethylene fragments from the hip prosthetic. The bone absorbs the material, causing the replacement to loosen, often asymptomatically. As the condition worsens, the patient's chances of a dangerous fall increase, as does the complexity of revision surgery.

Follow-up radiographs are the current standard for detecting osteolysis, though the disease often lacks visual radiographic evidence until the later stages, when treatment options are limited.

Researchers from the University of Chicago have applied radiographic texture analysis to follow-up images over time. The technique shows potential for detecting the disease at a more treatable stage. Essentially, a region of interest is chosen on follow-up hip replacement radiographs. A program calculates the content of the trabecular pattern, whose alignment breaks apart in disease.

Joel Wilkie, a graduate student in medical physics, and colleagues digitized 78 total hip replacement radiographs from the Anderson Orthopaedic Research Institute in Virginia. The team had sufficient follow-up images to evaluate years six and eight. An ROC analysis yielded Az values of 0.76 and 0.82, respectively, for the two years, to distinguish between osteolytic and normal cases. According to patient records, the average time for clinical detection was 9.5 years (spanning seven to 14 years).

Researchers are conducting further studies to evaluate the frequency of trabecular structure changes over time. They want to determine if a trend analysis will perform better than individual time points in detecting early disease. The preliminary data suggest it will.

"We're seeing evidence that changes in the texture are more important than actual texture values," Wilkie said. "Clinically, it means x-rays from multiple time points should be monitored to see if patients are trending toward osteolysis."

Researchers also want to compare the ability of orthopedic surgeons and radiologists to distinguish between the positive and negative patients by looking at the trabecular structure features on radiographs.

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