ACCURACY OF MIGRATION ANALYSIS IN HIP-ARTHROPLASTY - DIGITIZED AND CONVENTIONAL RADIOGRAPHY, COMPARED TO RADIOSTEREOMETRY IN 51 PATIENTS

We assessed the accuracy of migration measurements on conventional and digitized radiographs of total hip arthroplasties by comparing the re sults with radiostereometry (RSA). 4 stem and 3 acetabular designs wer e studied. 2 of the stem designs and 1 cup design were uncemented. 180 manual and 202 digitized measurements were done on 120 conventional r adiographic examinations. The readings on digitized radiographs did no t differ from the manual measurements on the same radiographs. A compa rison of the measurements from plain radiographs and with RSA of the f emoral stems revealed an accuracy (absolute mean + 2 SD) of between 3. 9 and 12.3 mm, depending on the choice of landmarks. The greatest accu racy was obtained by using tantalum markers inserted into the greater or the lesser trochanter and the shoulder of the stem. The most medial point of the lesser trochanter proved to be the best bony landmark Me asurements, including both the center of the femoral head and the grea ter trochanter, were associated with poor accuracy. The accuracy as re gards horizontal cup migration varied from 4.4 to 6.5 mm and the accur acy as regards vertical migration varied between 4.4 and 6.3 mm. The i ntraobserver error (2 SD) ranged from 1.6 mm to 5.6 mm, The correspond ing figures for the interobserver error were 2.6 mm and 6.6 mm, respec tively. One of the cemented cup designs was associated with inferior a ccuracy. Stem design did not affect the accuracy.