Abstract
Digital radiographs have taken over from conventional radiographs in most of the hospitals in New Zealand. This has created a challenge with respect to templating and pre-operative planning of total hip replacement surgeries. Digital templating has not, until recently, been available in our hospitals. Recently, a digital templating system (Cedara) has become available and has been installed and used at Middlemore Hospital and at Manukau Surgical Centre. This system allows computerised templating of digital radiographs. The aim of this study was to assess the accuracy of digital templating and to compare this method to the “compromised” conventional templating that has been performed at Middlemore hospital for the last 10 years.
In order to correct for magnification a fiducial stand has been created. This is a plastic stand and a pole with a movable 36mm metal ball. The ball is placed at the level of the greater trochanter and the stand is then placed between the patients legs. A standard templating “AP pelvis for hips” radiograph is then taken with the limbs internally rotated, such that the patellae are facing anteriorly. A traditional hard film was then created from this image for traditional acetate templating. Digital templating, with the Cedara system, was performed on the digital images after calibrating the image size using the fiducial image of known size. The results of the two methods were tabulated. The operation record was read and the component size and type was tabulated. The postoperative radiographs were assessed and the component positioning was evaluated and compared with the conventional and digital templates. A critical assessment of component size, with respect to under sizing and over sizing, was also performed on the postoperative radiographs and this was correlated with the digital and conventional templates.
This templating, and the evaluation of the postoperative radiographs, was performed by the authors of this paper (a consultant surgeon and a registrar). The accuracy of the two templating methods was assessed by comparison with the post operative radiographs and also with the aid of the knowledge of the actual components which were used at the time of surgery.
The templating images and radiographs of 100 patients were evaluated in the above stated manner and the results were analysed. The results from this analysis will be presented.
Correspondence should be addressed to: Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
