SA Orthopaedic Journal
On-line version ISSN 2309-8309
BACKGROUND: Accurate calibration of digital radiographs in arthroplasty is essential for pre-operative planning. Our study was designed to evaluate the accuracy of using a 20 mm spherical radio-opaque calibration marker placed between the legs during an AP pelvis X-ray. The marker is then used to calibrate the size of the digital radiograph and measurements can be taken. Using an AP pelvis view including both hips is desirable as this allows the use of the contralateral hip for templating. We used a 20 mm ball bearing in a clear plastic tube as a marker positioned at the same depth as the greater trochanter, but between the patient's legs. Placing the marker between the patient's legs prevents the problem of the marker disappearing off the side of the image, as is seen when placing the marker at the side of the obese patient. METHOD: One-hundred-and-one selected post-operative radiographs were used. The radiographs were calibrated according to the known head size of the femoral prosthesis, which was obtained from the operation report. The marker between the legs was then measured to assess the accuracy for its use as a calibration tool. RESULTS: There was a mean difference of less than 0.1 mm between the measured size of the marker and actual size (20 mm), with a range of 1.9 mm. CONCLUSION: This is a cost-effective, accurate and repeatable method of calibrating the size of digital radiographs.
Keywords : calibration; arthroplasty; ball bearing; digital radiographs; picture archiving and communications systems (PACS).