Abstract
Introduction
Standard image-free navigation systems have proven to improve the accuracy of components placement and reduce the proportion of outliers for lower limb mechanical axis in total knee arthroplasty (TKA). However, their disadvantages include a longer duration of surgery and pin-tract related complications. More recently, pinless navigation has been developed to address these shortcomings. This study aims to investigate the effectiveness of a new pinless navigation system (Zimmer® iAssist™ Knee) in TKA.
Methods
Power analysis was performed. To detect a significant difference in the proportion of outliers for lower limb mechanical axis at a power of 0.80, a sample size of 50 patients would be required. Between May 2013 and April 2014, 50 patients diagnosed with osteoarthritis of the knee were divided into two surgical technique arms: 1) iAssist™; 2) conventional TKA. One Adult Reconstruction surgeon performed all the surgeries. The patients were prospectively followed up and postoperative long leg radiographs were taken at one month post-surgery. Two reviewers blinded to the surgical method performed the measurements on radiographic films. Five radiographic measurements were measured: 1) Hip-Knee-Ankle Angle (HKA); 2) Coronal Femoral-Component Angle (CFA); 3) Coronal Tibia-Component Angle (CTA); 4) Sagittal Femoral-Component Angle (SFA); and 5) Sagittal Tibia-Component Angle (STA), The Mann-Whitney U test was used to compare the two groups for quantitative variables while the Fisher's exact test was used for categorical variables.
Results
There was no difference between the two groups for age, BMI, gender and side of operated knee (all p>0.05). There was also no difference in the duration of surgery, postoperative drop in haemoglobin level and transfusion incidence. The median HKA, CFA, CTA, SFA and STA were comparable between both groups [Fig. 1]. Similarly, there was no difference in the proportion of outliers for lower limb alignment (HKA) and components placement (CFA, CTA, SFA and STA) [Fig. 2].
Conclusion
This study does not show any statistical difference in the use of iAssist™ to reduce the proportion of outliers for lower limb alignment and component placement in TKA patients. However this is possibly contributed by the fact that all the surgeries were performed by a single experienced Adult Reconstruction surgeon instead of orthopaedic surgeons in general, thereby reducing the incidence of outliers with conventional technique.
In keeping with other studies on pinless navigational systems, this study also found no significant difference in postoperative drop of haemoglobin levels with the use of iAssist™, however this study also found no significant difference in operative time when using iAssist™.
