Purpose: The aim of this study was to outline a fully automatic tool capable of reliably predicting the most suitable total knee
replacement implant sizes for patients, using bi-planar X-ray images. By eliminating the need for manual templating or guiding
software tools via the adoption of convolutional neural networks, time and resource requirements for pre-operative assessment
and surgery could be reduced, the risk of human error minimized, and patients could see improved outcomes.
Methods: The tool utilizes a machine learning-based 2D – 3D pipeline to generate accurate predictions of subjects’ distal femur and
proximal tibia bones from X-ray images. It then virtually fits different implant models and sizes to the 3D predictions, calculates
the implant to bone root-mean-squared error and maximum over/under hang for each, and advises the best option for the
patient. The tool was tested on 78, predominantly White subjects (45 female/33 male), using generic femur component and tibia
plate designs scaled to sizes obtained for five commercially available products. The predictions were then compared to the ground
truth best options, determined using subjects’ MRI data.
Results: The tool achieved average femur component size prediction accuracies across the five implant models of 77.95% in terms
of global fit (root-mean-squared error), and 71.79% for minimizing over/underhang. These increased to 99.74% and 99.49% with ±1
size permitted. For tibia plates, the average prediction accuracies were 80.51% and 72.82% respectively. These increased to
99.74% and 98.98% for ±1 size. Better prediction accuracies were obtained for implant models with fewer size options, however
such models more frequently resulted in a poor fit.
Conclusion: A fully automatic tool was developed and found to enable higher prediction accuracies than generally reported for
manual templating techniques, as well as similar computational methods.