Component alignment during total knee arthroplasty with use of standard or custom instrumentation: a randomized clinical trial using computed tomography for postoperative alignment measurement.

Background: Patient-specific femoral and tibial cutting blocks produced with use of data from preoperative computed tomography (CT) or magnetic resonance imaging (MRI) scans have been employed recently to optimize component alignment in total knee arthroplasty. We report the results of a randomized controlled trial in which CT scans were used to compare postoperative component alignment between patients treated with custom instruments and those managed with traditional instruments.

Methods: The in-hospital data and early clinical outcomes, including Knee Society scores, were determined in a randomized clinical trial of forty-seven patients who had undergone a total of forty-eight primary total knee arthroplasties with patient-specific instruments (twenty-two knees) or standard instruments (twenty-six knees). Orientation of the implants was compared by using three-dimensional CT data.

Results: No significant differences were found between the study and control groups with respect to any clinical outcome after a minimum of six months of follow-up. The patient-specific tibial cutting block was abandoned in favor of a standard external alignment jig in seven of the twenty-two study knees because of possible malalignment. A detailed analysis of intent-to-treat and per-protocol groups of study and control knees did not show any significant improvement in component alignment, including femoral component rotation in the axial plane, in the patients treated with the custom instruments. The percentage of outliers--defined as less than -3° or more than 3° from the correct orientation of the tibial slope--was significantly higher in the group treated with use of patient-specific blocks than it was in the control group, in both the intent-to-treat (32% versus 8%, p = 0.032) and the per-protocol (47% versus 6%, p = 0.0008) analysis.

Conclusions: There were no significant improvements in clinical outcomes or knee component alignment in patients treated with patient-specific cutting blocks as compared with those treated with standard instruments. The group treated with patient-specific cutting blocks had a significantly higher prevalence of malalignment in terms of tibial component slope than the knees treated with standard instruments.