Digital templating without a calibration marker is accurate at predicting implant size for hip hemiarthroplasty.

INTRODUCTION: This study aims to assess the accuracy of digital templating for hip hemiarthroplasty using radiographs without calibration.

METHODS: Two independent, blinded observers retrospectively utilised digital software to template 50 consecutive patients who had hip hemiarthroplasty. The templated parameters (head size, offset and stem size) derived from pre-operative radiographs were compared to the actual prosthetic sizes used intra-operatively. Inter and intra-observer variabilities were calculated.

RESULTS: Both observers correctly templated the offset and head size (± 2 mm) used in 90% (n = 45) of cases. The femoral stem size (± 1 size) was correctly predicted by templating in over 84% of the cases (n = 42). Inter-observer agreement was excellent for femoral head size with an intra-class correlation coefficients (ICC) of 0.94, substantial for offset (k = 0.7) but only fair for stem size (k = 0.27). ICC values comparing the actual prostheses inserted with the template values were excellent for head size (ICC = 0.96), substantial to near perfect for offset (k = 0.78, 0.85) and fair to moderate (k = 0.24, 0.45) for stem size.

CONCLUSION: Digital templating of radiographs without calibration can be used to accurately and reliably predict femoral head size and offset at a set magnification of 120%. Femoral stem size, however, is more difficult to template adequately on pre-operative radiographs without calibration.