Purpose: To determine if use of CAS in TKA improves postoperative mechanical axis alignment and component position as compared to use of standard surgical instrumentation.

Method: 200 patients were prospectively randomized to TKA utilizing CAS navigation vs. standard surgical technique. Two surgeons performed all procedures utilizing a subvastus approach, the BrainLab navigation system and posterior cruciate substituting implants. Postoperative mechanical axis alignment was measured on full length standing radiographs and component placement on CT (Perth protocol). Two independent raters measured radiographic angles. The variation in mechanical axis measures were compared between the two treatment groups using a two-sided permutation test.

Results: Surgery has been completed on all 200 patients with patient demographics similar among the two treatment groups. Median tourniquet time was increased in the navigation group (82 mins versus 57 mins, p < 0.001). Radiographic analysis of the first 100 patients showed the standard deviation of the post-operative mechanical axis measurements to be 22% lower in the navigation group than the standard surgical instrumentation group (2.4 vs. 3.0), marginally significant (p = 0.055). Optimal mechanical axis alignment (to within 3 degrees or less) was achieved in 75% of patients with navigation and in 68% of patients with standard surgical instrumentation. Analysis of all 200 pts will be completed shortly as well as results of component placement based on postoperative CT.

Conclusion: Based on analysis of the first 100 patients, use of CAS in TKA marginally statistically improved mechanical axis alignment precision compared to standard surgical technique.