Introduction: Templating of radiographs is part of pre-operative planning in Total Hip Replacement (THR). Digital radiograph technology allows the manipulation of images, altering magnification and therefore affecting accuracy and reproducibility in templating. We have performed a study to investigate templating for hybrid total hip arthroplasty comparing digital hard copies with three computer methods to scale for magnification, in order to assess whether on-screen images can be templated directly with existing acetate templates.

Methods: 20 patients undergoing hybrid THR had pre-operative radiographs taken with a 10 pence coin attached to the skin overlying their greater trochanter. On-screen computer images were manipulated using either the 10p coin as a marker to scale for magnification, or two digital line methods using computer software against external ruler scales. Templating were performed for acetabular size, femoral offset, stem offset and stem size by three grades of observer, and the on-screen images were compared with hard copy digital prints. Intraclass Correlation (ICC) analyses were performed to assess intra-observer and inter-observer variability for the four methods. Comparisons were also made between templated results and the sizes of the inserted prostheses.

Results: All methods showed good reproducibility with all ICC values for intra-observer variability greater than 0.7. Inter-observer variability was less consistent, and the two digital line methods were the least reliable, with accuracy of sizing compared with the inserted prostheses varying between −1.6% to +10.2%. The hard copy radiographs showed better reproducibility than the 10p method, but less accuracy with 3.7% under-sizing. The 10p method was most accurate, with no significant differences for offset or acetabulum compared with the inserted prostheses, and templated under-sizing of only 0.9%.

Discussion: On-screen templating of digital radiographs with standard acetate templates is accurate and reproducible if a radio-opaque marker such as a 10p coin is included when taking the original radiograph.