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A radiological technique for the assessment of wear in prosthetic knee replacements
I G Hide1, A J Grainger, I W Wallace
1Department of Radiology, North Tees and Hartlepool NHS Trust, c/o Hartlepool General Hospital, Cleveland, UK.
Objective:
Wear of the polyethylene insert is a well-recognised cause of implant failure in total knee replacements. The purpose of this study was to evaluate a simple, digital fluoroscopic technique for the assessment of wear in knee prostheses.
Design:
Fluoroscopic images of knee prostheses were produced both of a phantom and in a patient group. Joint space thickness was measured by reference to a known diameter. Measurements were made to assess repeatability of positioning, inter-and intra-observer variance and the effect of angulation.
Results:
Standard phantom images showed small variation between measurements, high inter-reader correlation (Pearson's correlation coefficient, r=0.98, P<0.001; coefficient of variation=0.53%) and low intra-reader variation (coefficient of variation=0.57%). Inter- and intra-imager variation were low (coefficient of variation=1.05% and 0.88%, respectively). In the patient group, the range of joint space measurements was 1.9-8.9 mm. The coefficient of variation in insert measurements on repeated images was 2.0%. Repeatability of measurements was 0.2 mm with 99% confidence interval.
Conclusions:
This technique allows repeatable, precise measurement of insert thickness. The technique may be adapted to any implant where a reliable calibrating distance is present.