Abstract
Introduction: The aims of this paper are to compare the results of measuring migration rates on radiographs manually and by computer assisted analysis of digitised images.
Methods: Standardised anteroposterior standing hip radiographs taken post operatively and then yearly following hip replacement were used. The radiographs were then scanned at 150 dpi (gray scale) and saved as tif files. The migration was measured manually by drawing a line along the long axis of the femoral component connecting the distal tip, to the notch which is used to impact the stem proximally. This gives us the length of the hip replacement and an axis along which migration can be measured. The tip of the greater trochanter was selected as a bony landmark. On the plain radiographs two sets of readings were made by one observer. The digitised images were then analysed in the same way using a software package (designed in house at the University of Dundee). Two sets of readings were performed by observer one and a second set by an independent observer.
Statistics: Inter and Intra observer rates were calculated using a paired sample t test.
Results: For the manual readings intra observer mean difference was 0.53 mm (CI 0.31–0.74 mm). Comparing manual vs computer readings for observer one there was a correlation of 0.89. For the computer readings intra observer mean difference was 0.36 mm (CI 0.64–0.8 mm) and inter observer mean difference 0.16 mm. Both non significant differences. This evidence shows that the readings made manually and by computer were not significantly different and that there was no significant inter and intra observer variation. The advantage of computer storage and reading being the faster analysis, the ability to store and access large numbers of radiographs. The disadvantages being the need to scan the radiographs to allow measurement.
The abstracts were prepared by Peter Kay. Correspondence should be addressed to him at Centre for Hip Surgery, Wrightington Hospital, Appley Bridge, Wigan WN6 9EP.
