Detection of bone defects around zirconium component after total knee arthroplasty

It is difficult to detect bone defects caused by loosening or osteolysis around the femoral component after total knee arthroplasty (TKA) because the thick metal hinders visualization of bone defects. Previous reports have shown that tomosynthesis, a novel tomographic technique, is advantageous over fluoroscopically guided plain radiography, computed tomography (CT) and magnetic resonance imaging (MRI) for the early detection of bone defects around a conventional cobalt-chromium alloy component. However, there have been no reports on a zirconium component. The purpose of this study was to examine the sensitivity and specificity of the detection of bone defects around a zirconium component using fluoroscopically guided plain radiography, tomosynthesis, CT and MRI.

Six zirconium femoral components were implanted in pig knees. Two were cemented without any bone defects. Two were cemented with cystic defects. Two were cemented with four-millimeter-thick defects between the bone cement and the bone. Defects were filled with agarose gel. Eight orthopedic surgeons examined the fluoroscopically guided plain radiography, tomosynthesis, CT and MRI images. Sensitivity and specificity of each method were analyzed.

No bone defects were detected with plain radiography. The sensitivity and specificity of tomosynthesis were 21.9% and 36.8%, respectively. The sensitivity and specificity of CT were 15.1% and 33.0%, respectively. The sensitivity and specificity of MRI were 84.4% and 86.6%, respectively.

For the detection of bone defects around a zirconium component after TKA, MRI is advantageous over fluoroscopically guided plain radiography, tomography and CT, in terms of sensitivity and specificity.