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

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

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.

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.

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.