ELECTROMAGNETIC NAVIGATION IN TOTAL KNEE ARTHROPLASTY

Abstract

Malalignment of more than three degrees in coronal plane was associated with poor outcome. Most of the alignment occurred in the tibial coronal plane alignment. Computer assisted surgery (CAS) in total knee arthroplasty (TKA) aimed to minimize malalignment. Most of the CAS-TKA results were using infrared tracking system. Electromagnetic navigation in total knee arthroplasty was developed in recent years. It aimed at high accuracy and easy signal detection. However, there was limited result being published.

From August, 2006 to March, 2008, 50 patients had TKA performed with Medtronic electromagnetic navigation (EM CAS-TKA). The results were compared with 50 matched patients who had TKA performed with conventional technique. The post-operative limb alignments were compared. More than three degrees deviation from neutral alignment was defined as outliers.

There was no significant difference in the age, sex distribution, pre-operative range of motion and pre-operative deformity between the two groups. EM-CAS TKA group had significantly less deviation from neutral in the tibial coronal plane (p < 0.001) and femoral sagittal plane (p = 0.006) plane than conventional group. There was no significant difference in femoral coronal plane and tibial sagittal plane alignment between the two groups (p = 0.069 and 0.185 respectively). There were significantly more outliers (> 3 malalignment) in tibial coronal plane (p = 0.004) and femoral sagittal plane (p = 0.049) in conventional group than EM-CAS TKA group. There was no significant difference in the outliers in femoral coronal plane, and tibial sagittal plane (p = 1 and 0.1 respectively). The mean tourniquet time of the EM-CAS TKA group, 95.7 minutes (range, 65 to 126 minutes), was significantly higher than the conventional group, mean 72.1 minutes (range, 45 to 120 minutes), p value < 0.001. There was no pin tract complication and infection in the electromagnetic navigation group.

Electromagnetic navigation had improved the tibial coronal plane and femoral sagittal plane alignment in total knee arthroplasty with less outlier. Better alignment may improve the survival of the prosthesis. The learning curve is short and it is easy to handle. Electromagnetic navigation has the potential application in minimally invasive total knee arthroplasty.