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 .
A prospective randomised controlled study of patient-specific cutting guides compared with conventional instrumentation in total knee replacement.
Patient-specific cutting guides ( PSCGs ) are design ed to improve the accuracy of alignment of total knee replacement ( TKR ) . We compared the accuracy of limb alignment and component positioning after  TKR  performed using PSCGs or conventional instrumentation . A total of 80 patients were r and omised to undergo TKR with either of the different forms of instrumentation , and radiological outcomes and peri-operative factors such as operating time were assessed . No significant difference was observed between the groups in terms of tibiofemoral angle or femoral component alignment . Although the tibial component in the PSCGs group was measurably closer to neutral alignment than in the conventional group , the size of the difference was very small ( 89.8 ° ( sd 1.2 ) vs 90.5 ° ( sd 1.6 ) ; p = 0.030 ) . This new technology slightly shortened the bone-cutting time by a mean of 3.6 minutes ( p < 0.001 ) and the operating time by a mean 5.1 minutes ( p = 0.019 ) , without tangible differences in post-operative blood loss ( p = 0.528 ) or need for blood transfusion ( p = 0.789 ) . This study demonstrated that both PSCGs and conventional instrumentation  restore limb alignment and place the components with the similar accuracy . The minimal advantages of PSCGs in terms of consistency of alignment or operative time are unlikely to be clinical ly relevant
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 .