Anthropometric method for estimating component sizes in total hip arthroplasty.

Background: Preoperative templating is essential in total hip arthroplasty (THA) as it not only helps to facilitate the correct implant type and size but also determines the post-operative biomechanics. Templating is also increasingly important from a medico-legal perspective and recommended in the British Orthopaedic Association Guide to Good Practice. Although templating has become increasingly digitised, there are no simple anthropometric models to predict implant sizes in the absence of digital methods.

Aim: To assess the accuracy of using an easily obtainable measurement (shoe size) to predict component sizes in THA compared with digital templating.

Methods: Digital radiographs from a cohort of 102 patients (40 male, 62 female) who had undergone uncemented or hybrid THA at a single centre were retrospectively templated to desired cup and stem sizes using TraumaCad . We compared the templated size to the actual size of the implant and assessed if there was any correlation with the patient's shoe size.

Results: Statistically significant positive correlations were observed between: shoe size and templated cup size (ρ = 0.92, < 0.001); shoe size with implanted cup size (ρ = 0.71, < 0.001); shoe size and templated stem size (ρ = 0.87, < 0.001); and shoe size with implanted stem size (ρ = 0.57, < 0.001). Templated and implanted acetabular cup sizes were positively correlated (ρ = 0.76, < 0.001) and were exact in 43.1% cases; 80.4% of implanted cup sizes were within 1 size (+/- 2 mm) of the template and 100% within 2 sizes (+/- 4 mm). Positive correlation was also demonstrated between templated and implanted femoral stem sizes (ρ = 0.69, < 0.001) and were exact in 52.6% cases; 92.6% were within 1 size of the template and 98% within 2 sizes.

Conclusion: This study has shown there to be a significant positive correlation between shoe size and templated size. Anthropometric measurements are easily obtainable and can be used to predict uncemented component sizes in the absence of digital methods.