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Abstract
Excessive wear in total knee arthroplasty is detected by measuring the minimum joint
space width (mJSW) in anterioposterior radiographs. The accuracy of conventional measurement
methods is limited and can be improved using model-based techniques. In this study,
the model-based wear measurement (MBWM) is introduced. Its accuracy and reproducibility
are assessed and compared to the conventional measurement. Forty anterioposterior
radiographs were obtained of a knee prosthesis using a phantom setup. Both measurement
methods were applied and the accuracy and precision were compared. The reproducibility
was calculated with inter- and intra-observer experiments. Three observers measured
the mJSW in 30 clinical radiographs with both the conventional measurement and the
MBWM and repeated this after 6 weeks. The experiments were conducted with a NexGen
mobile bearing and fixed bearing prostheses. In the phantom experiment, the accuracy
(mean of the absolute error) was significantly higher (t-test, p<0.01) for the MBWM
as for the conventional measurement (0.15 mm versus 0.43 mm, 0.14 mm versus 0.35 mm
for the mobile and fixed bearing, respectively). The standard deviation of the measurements
is the smallest for the MBWM measurement for both prosthesis types (0.16 mm versus
0.47 mm, Levene's test, p<0.01). In the reproducibility experiment, both the intra-
and inter-observer agreements were higher for the MBWM than for the conventional method.
The results show that the MBWM is superior to the conventional measurement in both
accuracy and reproducibility. Although the use of a phantom experiment poses some
limitations in conveying the findings to clinical practice, this improved mJSW measurement
can lead to better wear detection for surgery decisions and research purposes.