Abstract
INTRODUCTION
The alignment of components in total knee arthroplasty (TKA) is perceived to be one of the most influential factors in determining the long-term outcomes. A contemporary debate exists regarding the choice of the alignment method. As a vast majority of the surgeons support the basis of the mechanical alignment philosophy (MA), others believe in the concept of anatomical alignment theory (AA) to closely match the anatomy of the femur and the tibia of the native knee [1]. This study was intended to evaluate the accuracy of achieving a planned tibial resection target using either the MA or AA methods.
Materials and Methods
Five healthy cadaveric knees (tibia and foot only) were studied. Four surgeons were independently asked to position a tibial cutting block (without pinning) using conventional extramedullary mechanical instrumentation (Exactech LPI instrumentation, Gainesville, FL, USA). Surgeons were asked to target a predefined proximal tibial cut according to MA (Varus= 0°, posterior slope= 3°, resection level= 10 mm) or to AA (Varus= 3°, posterior slope= 6°, resection level= 9 mm). Once the surgeon expressed satisfaction with the achieved position of the tibial cutting block, the planned resection was recorded using an imageless guidance system (ExactechGPS®, Blue-Ortho, Grenoble, FR). Surgeons completed at least three positioning trial for each alignment method on each cadaver. The accuracy and outliers (deviated more than 2°/mm from the target [2]) of resection planning were compared between the MA and AA methods. Statistical significance was defined as p< 0.05.
Results
The signed deviations were significantly greater for the AA method than the MA method for both the varus/valgus and the posterior tibial slope parameters (Table 1). A significant increase of the percentage of outliers for the varus/valgus parameter was observed in the AA (43.6%) method compared to the MA (8.9%) method (Table 2).
Regardless the type of method, the surgeons tended to place the cutting block with less varus than expected per the plan.
Discussion
While only focusing on the tibial resection planning, the findings of this study coincide with previous studies reporting that conventional instruments can achieve satisfactory lower limb alignment (within ± 3° of varus/valgus relative to mechanical axis) in 60% to 80% of the cases [3–4]. This study also highlights the difficulty of reproducing resection parameters associated with the AA method using conventional instrumentation. Notably, it was observed that in more than 40% of the cases, the deviation from the targeted value in the coronal plane was higher than 2°; which may impact clinical outcomes. Based on these findings, advanced technologies, such as computer navigation, may be of particular use to proponents of the AA method to assist in reducing deviations from planned resections.
