There were no significant differences regarding the biomechanical axis or frontal femoral and individual tibial component alignment .
Conclusion This systematic review and meta- analysis demonstrate that alignment with MRI-based PSI is at least as good as , if not better than , that with CT-based PSI .
Purpose Patient-specific instruments ( PSIs ) are already in relatively common use , and their post-operative radiographic results are equal to those for total knee arthroplasty ( TKA ) with conventional instrumentation .
PSI use requires a preoperative MRI scan , CT scan , or a combination of MRI and a long-leg st and ing radiograph .
However , there is no consensus as to which of these modalities , MRI or CT , is the preferred imaging modality when performing TKA with PSIs .
Inter-observer reliability of measurements performed on digital long-leg standing radiographs and assessment of validity compared to 3D CT-scan.
BACKGROUND Long-leg radiographs ( LLR ) are often used in orthopaedics to assess limb alignment in patients undergoing total knee arthroplasty ( TKA ) . However , there are still concerns about the adequacy of measurements performed on LLR . We assessed the reliability and validity of measurements on LLR using three-dimensional computed tomography ( 3D CT)-scan as a gold st and ard . METHODS Six different surgeons measured the mechanical axis and position of the femoral and tibial components individually on 24 LLR .  Intraclass correlation coefficients ( ICC ) were calculated to obtain reliability and Bl and -Altman plots were constructed to assess agreement between measurements on LLR and measurements on 3D CT-scan . RESULTS ICC agreement for the six observer measurements on LLR was 0.70 for the femoral component and 0.80 for the tibial component . The mean difference between measurements performed on LLR and 3D CT-scan was 0.3 ° for the femoral component and -1.1 ° for the tibial component . Variation of the difference between LLR and 3D CT-scan for the femoral component was 1.1 ° and 0.9 ° for the tibial component . 95 % of the differences between measurements performed on LLR and 3D CT-scan were between -1.9 and 2.4 ° ( femoral component ) and between -2.9 and 0.7 ( tibial component ) . CONCLUSION Measurements on LLR show moderate to good reliability and , when compared to 3D CT-scan , show good validity . CLINICAL TRIAL REGISTRATION NUMBER institutional review board Atrium-Orbis-Zuyd , number : 11-T-15 . LEVEL OF EVIDENCE Prospect i ve cohort study , Level II
There were no significant differences regarding the biomechanical axis or frontal femoral and individual tibial component alignment .
Conclusion This systematic review and meta- analysis demonstrate that alignment with MRI-based PSI is at least as good as , if not better than , that with CT-based PSI .
Purpose Patient-specific instruments ( PSIs ) are already in relatively common use , and their post-operative radiographic results are equal to those for total knee arthroplasty ( TKA ) with conventional instrumentation .
PSI use requires a preoperative MRI scan , CT scan , or a combination of MRI and a long-leg st and ing radiograph .
However , there is no consensus as to which of these modalities , MRI or CT , is the preferred imaging modality when performing TKA with PSIs .