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 .
Small Improvements in Mechanical Axis Alignment Achieved With MRI versus CT-based Patient-specific Instruments in TKA: A Randomized Clinical Trial
Background Patient-specific instrumentation in TKA has the proposed benefits of improving coronal and sagittal alignment and rotation of the components . In contrast , the literature is inconsistent if the use of patient-specific instrumentation improves alignment in comparison to conventional instrumentation . Depending on the manufacturer , patient-specific instrumentation is based on either MRI or CT scans . However , it is unknown whether one patient-specific instrumentation approach is more accurate than the other and if there is a potential benefit in terms of reduction of duration of surgery . Questions / purpose sWe compared the accuracy of MRI- and CT-based patient-specific instrumentation with conventional instrumentation and with each other in TKAs . The three approaches also were compared with respect to vali date d outcomes scores and duration of surgery . Methods A r and omized clinical trial was conducted in which 90 patients were enrolled and divided into three groups :  CT-based , MRI-based patient-specific instrumentation , and conventional instrumentation . The groups were not different regarding age , male/female sex distribution , and BMI . In all groups , coronal and sagittal alignments were measured on postoperative st and ing long-leg and lateral radiographs . Component rotation was measured on CT scans . Clinical outcomes ( Knee Society and WOMAC scores ) were evaluated preoperatively and at a mean of 3 months postoperatively and the duration of surgery was analyzed for each patient . MRI- and CT-based patient-specific instrumentation groups were first compared with conventional instrumentation , the patient-specific instrumentation groups were compared with each other , and all three approaches were compared for clinical outcome measures and duration of surgery . Results Compared with conventional instrumentation MRI- and CT-based patient-specific instrumentation showed higher accuracy regarding the coronal limb axis ( MRI versus conventional , 1.0 ° [ range , 0 ° –4 ° ] versus 4.5 ° [ range , 0 ° –8 ° ] , p < 0.001 ; CT versus conventional , 3.0 ° [ range , 0 ° –5 ° ] versus 4.5 ° [ range , 0 ° –8 ° ] , p = 0.02 ) , femoral rotation ( MRI versus conventional , 1.0 ° [ range , 0 ° –2 ° ] versus 4.0 ° [ range , 1 ° –7 ° ] , p < 0.001 ; CT versus conventional , 1.0 ° [ range , 0 ° –2 ° ] versus 4.0 ° [ range , 1 ° –7 ° ] , p < 0.001 ) , and tibial slope ( MRI versus conventional , 1.0 ° [ range , 0 ° –2 ° ] versus 3.5 ° [ range , 1 ° –7 ° ] , p < 0.001 ; CT versus conventional , 1.0 ° [ range , 0 ° –2 ° ] versus 3.5 ° [ range , 1 ° –7 ° ] , p < 0.001 ) , but the differences were small . Furthermore , MRI-based patient-specific instrumentation showed a smaller deviation in the postoperative coronal mechanical limb axis compared with CT-based patient-specific instrumentation ( MRI versus CT , 1.0 ° [ range , 0 ° –4 ° ] versus 3.0 ° [ range , 0 ° –5 ° ] , p = 0.03 ) , while there was no difference in femoral rotation or tibial slope . Although there was a significant reduction of the duration of surgery in both patient-specific instrumentation groups in comparison to conventional instrumentation ( MRI versus conventional , 58 minutes [ range , 53–67 minutes ] versus 76 minutes [ range , 57–83 minutes ] , p < 0.001 ; CT versus conventional , 63 minutes [ range , 59–69 minutes ] versus 76 minutes [ range , 57–83 minutes ] , p < .001 ) , there were no differences in the postoperative Knee Society pain and function and WOMAC scores among the groups . Conclusions Although this study supports that patient-specific instrumentation increased accuracy compared with conventional instrumentation and that MRI-based patient-specific instrumentation is more accurate compared with CT-based patient-specific instrumentation regarding coronal mechanical limb axis , differences are only subtle and of question able clinical relevance . Because there are no differences in the long-term clinical outcome or survivorship yet available , the widespread use of this technique can not be recommended . Level of Evidence Level I , therapeutic study . See the Instructions to Authors for a complete description of levels of evidence
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 .