Abstract
Introduction
Proper alignment of the components and soft tissue balance are the two factors that determine the long term outcome of total knee arthroplasty (TKA). On the femoral side a distal cut made perpendicular to the MA will restore the MA of the leg. Different methods are commonly used to resect the femur perpendicular to its MA. In uncomplicated cases, most surgeons routinely use a fixed valgus cut angle (VCA) of 5° or 6°. Various studies have questioned the use of fixed valgus angle resection to restore the mechanical axis. The purpose of this prospective study is to analyze the variability in the valgus angle following computer assisted TKA.
Materials and methods
Twenty-three patients who underwent computer assisted TKA in our institution in 2009 were involved in the study. A total of 40 knees were available for analysis. All the knees underwent a CT scanogram postoperatively. Each scanogram was analyzed using the Amrita medvision(r) software. The angle subtended between the mechanical axis and the distal femoral anatomic axis is the valgus angle. Two independent observers calculated all the values and the interobserver reliability was calculated.
Results
The average age of the patients was 65.6 years. The kappa coefficient of agreement was 0.8, which shows good interobserver reliability.
The average angle formed by the femoral component with the mechanical axis was 91.60 and the average valgus angle calculated was 7.410. 14 knees out of 40 (35%) were lying within the range of 4 - 7 degrees. In 25 knees (65%) valgus angle was more than 7 degrees. In one case the valgus angle was less than 4 degrees.
Conclusions
Fixed valgus angle resection is not reliable in restoring mechanical axis in total knee arthroplasty. In the absence of facilities for surgical navigation, a pre operative planning with long leg films is extremely important to achieve long-term success.
