[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 .