# A shape completion model for corrective osteotomy of distal radius malunion

## TL;DR

This study develops a 3D shape completion model to help plan corrective surgeries for wrist bone malunions when the healthy opposite wrist is not usable.

## Contribution

A novel shape completion model is introduced to reconstruct healthy radius models from malunited bones for 3D surgical planning.

## Key findings

- The model achieved rotational errors of 2.6° to 3.6° and translational errors of 0.7 to 1.7 mm in 3D reconstructions.
- The model is viable for patients without a healthy contralateral radius but not recommended for routine use in those with a healthy opposite wrist.
- Length mismatch errors can be corrected during 3D planning if the ipsilateral ulna is intact.

## Abstract

When performing 3D planning for osteotomies in patients with distal radius malunion, the contralateral radius is commonly used as a template for reconstruction. However, in approximately 10% of the cases, the contralateral radius is not suitable for use. A shape completion model may provide an alternative by generating a healthy radius model based on the proximal part of the malunited bone. The aim of this study is to develop and clinically evaluate such a shape completion model.

A total of 100 segmented CT scans of healthy radii were used, with 80 scans used to train a statistical shape model (SSM). This SSM formed the base for a shape completion model capable of predicting the distal 12% based on the proximal 88%. Hyperparameters were optimized using 10 segmented 3D models, and the remaining 10 models were reserved for testing the performance of the shape completion model.

The shape completion model consistently produced clinically viable 3D reconstructions. The mean absolute errors between the predicted and corresponding reference models in the rotational errors were 2.6 ± 1.7° for radial inclination, 3.6 ± 2.2° for volar tilt, and 2.6 ± 2.8° for axial rotation. Translational errors were 0.7 ± 0.6 mm in dorsal shift, 0.8 ± 0.5 mm in radial shift, and 1.7 ± 1.1 mm in lengthening.

This study successfully developed a shape completion model capable of reconstructing healthy 3D radius models based on the proximal bone. The observed errors indicate that the model is viable for use in 3D planning for patients lacking a healthy contralateral radius. However, routine use in patients with a healthy contralateral radius is not yet advised, as error margins exceed bilateral differences observed in healthy populations. The most clinically relevant error found in the model, length mismatch, can be easily corrected during 3D planning if the ipsilateral ulna remains intact.