CT-Based 3D Reconstruction of Lower Limb Versus X-Ray-Based 3D Reconstruction: A Comparative Analysis and Application for a Safe and Cost-Effective Modality in TKA.

AIM: Patient Specific Instrumentation (PSI) with 3D bone models have been used to improve the outcomes of Total Knee Arthroplasty (TKA). The PSI, however, needs a CT (Computed tomography)/MRI scan to reproduce a bone-based model. However, CT is not a routine imaging method in the TKA and has challenges such as high radiation exposure and increased investigation cost. Any technology or software which could accurately recreate 3D bone models using X-ray would be a cheaper and safer tool. This study is based on one such technology (XrayTo3D®) using X-ray to 3D as an alternative to other image-based 3D bone models and PSI available in the market. This study compares the accuracy of XrayTo3D® versus a Conventional CT to 3D, in the reconstruction of lower limb bones (femur and tibia).
METHOD: In an analysis of 45 lower limbs, 11 anatomical parameters were measured [Medial Proximal Tibial Angle-MPTA, Tibial(T)-torsion, T-slope, T-length, Mechanical Lateral Distal Femoral Angle (mLDFA), F-version, F-length, Distal femoral Medio lateral width (F-ML), Distal Femoral Antero Posterior (F-AP), Proximal Tibia Antero Posterior (T-AP), Proximal Tibia Medio Lateral (T-ML) based on landmarks selected by three orthopaedic surgeons(numbers of the authors superscript), on two groups of 3D models, one reconstructed using XrayTo3D® and the other using CT. Mean and standard-deviation values were measured for all the parameters in both the groups. Statistical association between both the groups was measured by Pearson's correlation coefficient. Two-sided t tests of the mean values were calculated to compare the two measurement methods. The interobserver reproducibility within each group was measured by the intraclass correlation coefficient (ICC). Point-to-surface (P2S) error, in the distal femur and proximal tibia regions of the models reconstructed using XrayTo3D®, were also measured.
RESULTS: For all the 11 parameters, no statistically significant difference was found between the 2 groups (p > 0.05). Pearson's correlation coefficients for all the parameters were not significant. The interobserver reproducibility was ranging from 0.90 to 1.00 and 0.90 to 1.00 for the XrayTo3D® and CT groups, respectively. The mean P2S distance was 1.0 mm in distal femur and 1.1 mm in proximal tibia which was within the acceptable limits.
CONCLUSION: The reconstruction accuracy of the XrayTo3D® is an accurate, safe and cost effective as compared to a CT-based method. © Indian Orthopaedics Association 2021.