Abstract
INTRODUCTION
Recently, as the number of total knee arthroplasty (TKA) is increasing, the number of revision TKA due to loosening or osteolysis is rapidly increasing. Large bone defect is one of the most critical issues during revision TKA. Therefore, early detection of bone loss around the TKA prosthesis before bone loss has been enlarged is very important. However, it is difficult to detect the loosening or ostolysis at the early stage around the femoral component even using fluoroscopically guided plain radiograph. A novel technique of tomography (Tomosynthesis; Shimazu Corporation, Kyoto, Japan) was introduced to detect the small bone loss. The purpose of this study was to examine, in a pig model of radiolucent line and osteolysis around TKA, the sensitivity and specificity of detection of radiolucent line and osteolysis using fluoroscopically guided plain radiographs and a novel technique of tomography.
METHODS
Six cemented femoral components (PFC Sigma; DePuy, Warsaw, IN, USA) were implanted in pig knees. Two components were implanted with standard cement technique (Standard model). Two components were implanted with 2 mm-thick defect between the cement and bone (Radiolucent line model). Two components were implanted with cystic defects (mean size = 0.7 cm3) in femoral condyles (Osteolysis model). The simulated bone lesions were filled with agarose to simulate granuloma tissue and to reduce the air artifact around the bone lesions, which can interfere with imaging techniques (Figure 1). Fluoroscopically guided plain radiographs (63 kV, 360 mA, 50 msec) were taken in 4 postures (antero-posterior, lateral, and +/−45 degrees oblique views) for each specimen (Figure 2). For Tomosynthesis, 74 frames were acquired in the rate 30 frames/sec with fixed X-ray condition (65 kV 1.25 mAs) and were reconstructed (Figure 3). Seven blinded assessors experienced in clinical radiographic analysis examined. The sensitivities, specificities and accuracy of the two imaging techniques were compared.
RESULTS
The mean sensitivity and specificity of Tomosynthesis were 85.4% and 87.2% (Table 1). Any bone defects (radiolucent lines or osteolysis) were not detected using fluoroscopically guided plain radiographs, because metal box for post-cam mechanism hinder the bone defect around the femoral condyles.
DISCUSSION
This study demonstrates the uselessness of fluoroscopically guided plain radiographs for small bone defect around the femoral component. Tomosynthesis, a novel technique of tomography, showed much higher efficacy comparing to conventional fluoroscopically guided plain radiographs. Although the size of bone defect in this study (0.7 cm3) was much smaller than previous report (1.4 cm3) using CT (Solomon L, et al., J Arthroplasty in press), sensitivity of this study was higher than that of previous study using CT (75%). Tomosynthesis will be useful method for early detection of small periprosthetic bone defects around femoral component of TKA.
