Rotational alignment in patient-specific instrumentation in TKA: MRI or CT?

Purpose: To compare CT-guided and MRI-guided patient-specific instrumentation in total knee arthroplasty (TKA). Methods: Forty-four patients underwent primary TKA using either CT-guided or MR-guided Signature™ patient-specific instrumentation. They were prospectively assigned into two groups: 23 patients into the MR-guided instrumentation (group A) and 21 patients into the CT-guided patient-specific instrumentation (group B). All patients underwent computed tomography of the operated knee in the first week after the surgery to measure the components rotation. Results: The femoral component rotation was 0.0° (0.0, 1.0) in group A and 0.0° (−2.0, 1.0) in group B. The tibial component rotation was −16.0° (−19.0, −14.0) in group A and −15.0° (−18.0, −8.0) in group B. In both components, there were no significant differences between the two groups. The difference between the tibial component rotation and the neutral tibial rotation was similar in both groups [2.0° (−1.4, 4.0) in group A and 3.0° (−0.5, 5.0) in group B], but the dispersion around the median was different between the two groups, with the amplitude of the difference between tibial rotation and neutral position 9° (−3.0, 6.0) in group A and 27° (−9.0, 18.0) in group B. Conclusions: MRI may be more accurate than CT using the Signature™ system when planning the surgical guides for TKA, with fewer patients with malrotation of the tibial component. Level of evidence: II.