Functional alignment in total knee arthroplasty is an umbrella term-A call for better definition and reporting quality!

Abstract

Functional alignment (FA) aims to achieve a symmetric, rectangular extension gap and a rectangular or trapezoidal flexion gap, positioning the components in a manner that reduces the compromises to the soft tissue envelope. Because the FA surgeon can accomplish this goal with a multitude of adjustments to the components' position or soft tissue balance, the purpose of the present study was to analyze the possible paths for achieving FA. Ten knees undergoing robotic total knee arthroplasty (TKA) were analyzed. Based on the intraoperatively acquired data, a macro was created to perform a post hoc analysis of the 10 possible paths to align a TKA functionally: (1) starting from mechanical alignment (MA) or kinematic alignment (KA), (2) preserving either the position of the femoral or tibial component and (3) with equal, 1 mm gaps or with increased 90° lateral flexion laxity. Ten different knee phenotypes were analyzed (Var-Neu-Neu 2x; Neu-Neu-Val; Val-Val-Val; Neu-Val-Neu; Var-Neu-Var 3x; Var-Var-Var; Var-Var-Val). On average, 3.5 different paths resulted in FA for each TKA (range: 0-8). Two TKAs (Val-Val-Val; Var-Var-Val) could not be functionally aligned using any of the ten evaluated paths. One TKA could be functionally aligned using eight different paths. Functionally aligning a TKA can be achieved through multiple adjustments, resulting in various implant positions and soft tissue balances. To better understand the different combinations behind FA, a more detailed nomenclature is needed, including which initial alignment (MA or KA) was utilized, which component's position (femoral or tibial) was preserved, and whether a rectangular or trapezoidal flexion space was targeted. Level IV, therapeutic study.