Orthopaedic fracture fixation implants are increasingly being designed using accurate 3D models of long bones based on computer tomography (CT). Unlike CT, magnetic resonance imaging (MRI) does not involve ionising radiation and is therefore a desirable alternative to CT. This study aims to quantify the accuracy of MRI-based 3D models compared to CT-based 3D models of long bones. The femora of five intact cadaver ovine limbs were scanned using a 1.5 T MRI and a CT scanner. Image segmentation of CT and MRI data was performed using a multi-threshold segmentation method. Reference models were generated by digitising the bone surfaces free of soft tissue with a mechanical contact scanner. The MRI- and CT-derived models were validated against the reference models. The results demonstrated that the CT-based models contained an average error of 0.15 mm while the MRI-based models contained an average error of 0.23 mm. Statistical validation shows that there are no significant differences between 3D models based on CT and MRI data. These results indicate that the geometric accuracy of MRI based 3D models was comparable to that of CT-based models and therefore MRI is a potential alternative to CT for generation of 3D models with high geometric accuracy.

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Although for the 4 individual criteria plate fits of 43%-62% were achieved, a global/anatomic fit only occurred for 19% of the bone models. This outcome is likely a result of bone morphology variations, which exist in a random population sample combined with the effects of a nonoptimized plate shape. Recommendations for optimizing the fit of the plate are discussed.

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The developed comprehensive anatomical 3D measurement protocol could serve as standardised approach for anthropometric studies in the future. Our data suggest that the ROC of current nail designs should be reduced from between 1500 and 2000 to 1000 mm to achieve an improved fit for the investigated population.