Effect of introduction of digital radiographic techniques on pre-operative templating in orthopaedic practice.

AIM: To assess whether the introduction of digital radiographic acquisition has altered the magnification of pelvic radiographs compared to standard acquisition techniques, and whether this influences preoperative implant templating for total hip arthroplasty.
SETTING: District general hospital orthopaedic out-patient department. PATIENTS AND METHODS: 51 sets of patient radiographs were studied, where digital and standard radiographic techniques had been used for each patient. Key bony landmarks were measured, the scaled ruler analysed and the femur templated to gauge the most appropriate implant size of implant.
RESULTS: Introduction of digital techniques has resulted in a mean magnification of 97%, whereas most manufacturers' templates assume a magnification of 115-120%. For the Exeter femoral component, the templated size showed only moderate correlation with that templated from a standard radiograph (kappa index 0.46), although the offset templated showed good correlation (kappa index 0.89).
CONCLUSIONS: Surgeons should be aware that introduction of digital techniques of radiograph acquisition may reduce the magnification of the film and, therefore, reduce the accuracy of pre-operative templates supplied by the manufacturers of implants, resulting in incorrect selection of implants.