# Shoes size can predict implant sizes for primary total knee arthroplasty in a quick, reliable and costless manner

## TL;DR

This study shows that a patient's shoe size can accurately predict the implant sizes needed for knee replacement surgery, offering a quick and costless method.

## Contribution

The study introduces a validated method using European shoe sizes to predict implant sizes for primary total knee arthroplasty.

## Key findings

- Strong correlation between European shoe size and tibial/femoral implant sizes (Spearman rho of 0.84 and 0.81, respectively).
- 92-97% accuracy in predicting implant sizes within ±1 size after adjusting for sex and BMI.
- A weak correlation was found between shoe size and PE insert size (Spearman rho of 0.15).

## Abstract

Knowing the component sizes needed for a specific patient before total knee arthroplasty (TKA) surgery could help to optimise the logistics of medical device availability. Previous studies have correlated component size with patient age, sex, height, weight, and shoe size, but none have validated this method using the European shoe sizing system. The primary objective of this study was to determine the correlation between a patient's European shoe size at the time of surgery and the size of the tibial and femoral components used during primary TKA. The secondary objective was to evaluate the accuracy within ±1 size between the European shoe size and the component size.

This was a retrospective observational, single‐centre, single‐surgeon study of 227 primary TKA procedures done with the Score II implant (AMPLITUDE®, Valence, France) between 1 April 2022 and 1 July 2023. Data on the patient's shoe size was determined before the surgery. This information was retrospectively correlated with the size of the components used in the TKA surgery that was recorded in the operative report.

The correlation between a patient's shoe size and the component size was very strong: Spearman rho of 0.8095 for femur, 0.8400 for tibia and 0.6393 for patella (p < 0.001). The correlation between a patient's shoe size and the size of the PE insert was weak: Spearman rho 0.1532 (p = 0.0210). After adjusting for sex, the femoral component was predicted accurately within ±1 size in 92% (210/227) of procedures and the tibial component in 94% (213/227). After adjusting for sex and BMI, the patellar implant was predicted accurately within ±1 size in 97% (220/227) of procedures.

Our model provides a cost‐effective, assignable and easily implementable method for predicting tibial and femoral component sizes using European shoe size, demonstrating high accuracy (≥92%).

Level IV, retrospective observational study.