MRI-based or CT-based patient-specific instrumentation in Total knee Arthroplasty: How do the two systems compare?

Patient-specific instrumentation (PSI) has been introduced into total knee arthroplasty (TKA) to improve accuracy in restoration of alignment. PSI in TKA refers to custom-made cutting jigs manufactured according to anatomic configuration of the patient's bone based on preoperative magnetic resonance imaging (MRI) or computed tomography (CT) scans. The purpose of this study was to compare the MRI- or CT-based PSI to see if they could reproduce accurate bone resection and postoperative outcomes.

Seventy-one patients who received elective TKA using a PSI system for primary osteoarthritis with varus deformity were prospectively enrolled for this study. We randomly allocated those patients to MRI-based PSI group (36 patients) and CT-based PSI group (35 patients). The actual resection thickness and planned resection thickness by preoperative PSI electronic program were compared between the two groups. Radiographic findings of the postoperative limb alignment, three-dimensional position of the implants, and related complications were also evaluated. Clinical evaluation was also performed before and 2 years after the surgery.

There were no significant differences in the resection thickness in femur and tibia between actual resection and planned resection in both groups. Furthermore, there were no significant differences between two groups in terms of coronal, sagittal and rotational alignment of the components. All clinical assessments revealed no differences between two groups 2 years after the operation. No specific complication related to PSI was observed.

Although MRI allows for visualization of cartilage, MRI-based PSI system did not show better accuracy in predicting the thickness of bone resection than CT-based PSI. Moreover, there were no differences in radiographic and clinical outcomes between the two groups.