Abstract
Aim: To develop an accurate and reproducible validated digital technique for the two-dimensional measurement of longitudinal femoral stem migration on AP radiographs.
Method: Eight patients who underwent total hip replacement, under the care of the senior author, were randomly selected. In each case, three radio-opaque marker beads had been implanted into the greater trochanteric region at surgery. Using a standardised x-ray protocol, three consecutive AP standing hip x-rays were taken of each patient on the same day. The plain radiographs were digitised, and the vertical bead to stem tip distance measured by two orthopaedic trainees using Scion Image ‘freeware’ software package and standard computer equipment. Every patient had three different measurements on each of their three consecutive x-rays. The vertical bead to stem tip distance was averaged over the three beads.
Results: Statistical analysis was performed and the repeatability coefficient between x-rays was 0.61 (confidence interval 0.46 to 0.78). The limits of agreement for inter observer error for average bead to stem distance were −0.15 to 0.39.
Conclusion: Our results demonstrate the efficacy of our system for analysis of femoral stem migration in everyday clinical practice. This technique does require implantation of marker beads and a standardised protocol for patient positioning for radiographs.
Theses abstracts were prepared by Mr Peter Kay. Correspondence should be address to him at The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
