Abstract
Increasingly hospitals are moving away from hard copy xrays to digital films. These offer advantages in terms of cost, film availability and decreased radiation dosage but concerns have been raised about the accuracy of these images for preoperative templating.
We reviewed the pre and post operative films in 20 patients with subcapital fractured necks of femur. Each film was reviewed by 3 different observers on 3 separate occasions. The sizes of the femoral head and the hemi-arthroplasty were measured using the PACS digital system. These were then compared with the known size of the implant.
A total of 360 measurements were taken. Intra and inter observer errors were low with intra class correlations of in excess of 0.98 and 0.99 respectively. The average magnification on the pre-op film was 117.6% (t=18.96, p< 0.0001) and on the post-op film 121.5% (t=22.18, p< 0.0001) with a range of 109.3% to 128.2%. The overall magnification was 119.6%.
We conclude that measurements made on PACS have a high repeatability and reproducibility but that PACS has a significant and wide variation in magnification errors. PACS should therefore not be used for templating until a way of standardising magnification has been found.
Correspondence should be addressed to Major S A Adams, Orthopaedic Department, Royal Infirmary of Edinburgh, 51 Little France Crescent, Edinburgh EH16 4SA.
