What is the optimal alignment of the tibial and femoral components in knee arthroplasty?

Abstract

Background: Surgeon-dependent factors such as optimal implant alignment are thought to play a significant role in outcome following primary total knee arthroplasty (TKA). Exact definitions and references for optimal alignment are, however, still being debated. This overview of the literature describes different definitions of component alignment following primary TKA for (1) tibiofemoral alignment in the AP plane, (2) tibial and femoral component placement in the AP plane, (3) tibial and femoral component placement in the sagittal plane, and (4) rotational alignment of tibial and femoral components and their role in outcome and implant survival.

Methods: We performed a literature search for original and review articles on implant positioning following primary TKA. Definitions for coronal, sagittal, and rotational placement of femoral and tibial components were summarized and the influence of positioning on survival and functional outcome was considered.

Results: Many definitions exist when evaluating placement of femoral and tibial components. Implant alignment plays a role in both survival and functional outcome following primary TKA, as component malalignment can lead to increased failure rates, maltracking, and knee pain.

Interpretation: Based on currently available evidence, surgeons should aim for optimal alignment of tibial and femoral components when performing TKA.

Figure 1.

Example of measurements of femoral and tibial TKA component placement in the coronal plane with respect to the femoral and tibial anatomical axes, respectively, according to Petersen and Engh (1988) and as used by e.g. Ritter et al. (2011). Placement of the femoral component is measured using the angle (α) between the line across the bottom of the femoral condyles and femoral shaft axis. α = 90 corresponds to neutral placement, α > 90 corresponds to valgus placement of the femoral component, and α < 90 corresponds to varus placement of the femoral component. Placement of the tibial component is measured using the angle (β) between the line across the base of the tibial plate and the tibial shaft axis. β = 90 corresponds to neutral placement, β > 90 corresponds to valgus placement of the tibial component, and β < 90 corresponds to varus placement of the tibial component. TFA stands for tibiofemoral axis, measured at the angle between the tibial and femoral shaft axes (TFA angle). TFA angle = 180 corresponds to neutral alignment, TFA angle > 180 correponds to TFA in valgus, and TFA angle < 180 corresponds to TFA in varus.

Figure 2.

Example of measurements of femoral and tibial TKA component placement in the sagittal plane with respect to the femoral and tibial anatomical axes, respectively, according to Petersen and Engh (1988) and as used by e.g. Ritter et al. (2011). Flexion of the femoral component is measured as the angle (FF) between the line across the bottom of the femoral implant and the femoral shaft axis. FF = 90 corresponds to neutral placement, FF > 90 corresponds to femoral component in extension, and FF < 90 corresponds to femoral component in flexion. Tibial slope* is measured as the angle (TS) between the line across the bottom of the tibial plate and the tibial shaft axis. TS = 90 correponds to neutral placement, TS > 90 corresponds to anterior tibial slope*, and TS < 90 corresponds to posterior tibial slope*. * Some component types have posterior slope built into the implant design.