Relationship of the tibial tuberosity (TT) position, tibial tuberositytrochlear groove (TT-TG) distance, and internal and external rotation of the knee under weight-bearing conditions

Abstract

An important factor which influences the clinical outcome of total knee arthroplasty (TKA) is the internal/external rotational alignment of the femoral and tibial components. A rotational error of few degrees has been found to be clinically important and linked to anterior knee pain [1] and patellofemoral problems [2]. A commonly used reference to align the tibial component rotationally is the tibial tuberosity (TT). However, Howell et al. [3] showed that the medial/lateral TT position varies strongly between patients and represents an unreliable landmark during (passive) kinematic component alignment. Thereby, passive kinematics differs from active kinematics [4,5]. For example, under weight-bearing conditions the magnitude of internal/external rotation is greater and occurs earlier [6]. In the active situation, a relative internal rotation of the tibial component increases the Q-angle with a change in the force vector of the extensor mechanism.An established radiographic measure to quantify the relative rotational alignment of the femur and tibia in extension is the tibial tuberosity-trochlear groove (TT-TG) distance. It has been measured recently at different flexion angles under non-weight-bearing conditions [7]. However, Izadpanah et al. [8] reported that it also depends on weight-bearing. Hence, the complex function of the extensor mechanism in terms of the relationship between TT position, TT-TG distance, and internal/external rotation under weight-bearing conditions is still unknown and accordingly component rotational alignment targets.The aim of the study was to investigate the relationship between TT position, TT-TG distance, and internal/external rotation of the knee in the active (weight-bearing) situation.