Validation of three-dimensional models of the distal femur created from surgical navigation point cloud data for intraoperative and postoperative analysis of total knee arthroplasty
Despite the success of total knee arthroplasty, there continues to be a significant proportion of patients who are dissatisfied. One explanation may be a shape mismatch between pre- and postoperative distal femurs. The purpose of this study was to investigate methods suitable for matching a statistical shape model (SSM) to intraoperatively acquired point cloud data from a surgical navigation system and to validate these against the preoperative magnetic resonance imaging (MRI) data from the same patients.
A total of 10 patients who underwent navigated total knee arthroplasty also had an MRI scan <2 months preoperatively. The standard surgical protocol was followed which included partial digitization of the distal femur. Two different methods were employed to fit the SSM to the digitized point cloud data, based on (1) iterative closest points and (2) Gaussian mixture models. The available MRI data were manually segmented and the reconstructed three-dimensional surfaces used as ground truth against which the SSM fit was compared.
For both approaches, the difference between the SSM-generated femur and the surface generated from MRI segmentation averaged less than 1.7 mm, with maximum errors occurring in less clinically important areas.
The results demonstrated good correspondence with the distal femoral morphology even in cases of sparse datasets. Application of this technique will allow for measurement of mismatch between pre- and postoperative femurs retrospectively on any case done using the surgical navigation system and could be integrated into the surgical navigation unit to provide real-time feedback.
KeywordsNavigation Arthroplasty Statistical shape model Knee
The authors wish to thank the Capital District Health Authority and Alberta Innovates Technology Futures for financial assistance with this project. Parts of this work were also funded by the German Federal Ministry of Education and Research (BMBF), Grant Nos. 01EC1406E and 01EC1408B. The authors would like to thank Valentin Mocanu (Dalhousie University), Robert Joachimsky (ZIB), and Agnieszka Putyra (ZIB) for assisting with the manual segmentations on which this work is based. The authors would also like to thank the reviewers whose excellent comments and feedback resulted in a significantly improved paper.
Compliance with ethical standards
Funding for this study was obtained in part through grants from Capital District Health Authority, Alberta Innovates and the German Federal Ministry of Education and Research.
Conflict of interest
Dr. Dunbar has performed paid consultancy services with Stryker Orthopaedics International, the manufacturer of the navigation system used. None of the other authors have any conflicts of interest to disclose.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
All research undertaken in this study was approved by the institutional ethics board, and informed consent was obtained from all participants.
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