Abstract
Purpose
The complication of patellofemoral compartment was quite often in total knee arthroplasty. One of the impotant factors in these complications would be the femoral component rotation in TKA. To determine the rotation of the femoral component, the reference of the surgical epicondylar axis (SEA), posterior condylar axis (PCA), AP axis with three dimensional model achieved from computed tomography data were considered. There are some limitations with pre-oprerative CT-based planning such as radio exposure, cost, time and detection of the depth of cartilage. We evaluate the determination of the femoral component rotation with image-free registration method to compare with three-dimensional template system.
Material and Methods
Thirty six knees were evaluated to determine the femoral component rotation. The reference points were marked to measure the PCA (posterior condylar axis), SEA (surgical transepicondylar axis), and APA (anteroposterior axis, Whiteside line) intra-operatively and calculated the angle from PCA to SEA and PCA to APA with Image free navigation system (BrainLAB). Those knees were preoperatively evaluated the angle deviation from SEA to PCA with three dimensional template system. These angle deviations, which suggested the femoral component rotation obtained from preoperative template system, were statistically compared with the femoral rotation angle in clinical situation.
Results
The mean angle from PCA to SEA was external rotated 2.7 degrees (SD=1.8 degrees) with the template system. During image- free system in TKA, the mean angle from PCA to SEA was external rotated 2.2 degrees (SD=4.5 degrees), and the mean angle from APA to SEA was 0.5 degrees (SD=4.4 degrees).
Discussion
The preoperative 3 dimensional template system showed the small ranges and standard deviations in PCA and SEA even when the residual cartilage of the surface at the femur was not considered to evaluate. Meanwhile, the three reference axes obtained from image free navigation system showed the large amount of deviations and thus the variability in these references was difficult to decide the rotation of the femoral component. Now navigation system provided the appropriate gap balance during knee motion. This gap-navigation technique would be one of the keys to obtain the proper rotation of the component.
