Restoration of constitutional lower-limb coronal alignment (or hip-knee-ankle angle, HKA) is believed to improve reported patient satisfaction after total knee arthroplasty (TKA) (Howell et al. 2014). Long-term implant data suggests that deviation from neutral HKA would incur increased risk of prosthesis failure (van Hamersveld et al. 2019; Vanderkerckhove et al. 2017). Knee phenotype is a function of HKA and joint line obliquity (JLO). Sappey-Marinier et al. (2022) recently demonstrated study that JLO may not significantly affect clinical outcomes post TKA. Little is known about the independent effects of HKA versus JLO on bicompartmental knee loads during gait of TKA patients. We hypothesized that varus HKA concomitant with apex distal JLO would result in increased compressive medial knee loads. We also hypothesized that JLO would affect medial compressive load, independent of HKA effect.
Nine TKA patients were recruited and underwent gait analysis around 2 years post TKA Kinematics, force-plate and muscle electromyography data were recorded simultaneously for each walking trial during the stance phase of gait involving the TKA limb. Calculation of lower-limb muscle forces was based on musculoskeletal model which incorporated subject-specific implant contacts and alignment information (Lerner et al. 2015). Lower-limb muscle forces were determined using inverse dynamics and static optimization. Joint reaction analysis was used to determine the resultant contact forces and moments at each compartment (Steele et al. 2012).
The 9 patients had HKA and JLO of 1.6±2.1° and 177.6±2.6°, respectively. These two variables were independent of each other (r=0.069, p>0.05). The patients walked at a walking speed 1.09±0.1 m/s. Computational pipeline investigated the individual contribution of HKA and JLO on the compressive joint load within the medial and lateral knee compartments. Varus HKA loaded the medial compartment more than apex distal JLO during the early stance (HKA, ? = 0.19BW/deg, r=0.86, p<0.05; JLO, ? = 0.13BW/deg, r=0.73, p<0.05). Varus HKA unloaded the lateral compartment more than apex distal JLO during the both halves of stance (Early stance: HKA, ? =-0.16BW/deg, r=0.79, p<0.05; JLO, ? = -0.075BW/deg, r=0.59, p<0.05. Late stance: HKA, ? =-0.15BW/deg, r=0.67, p<0.05; JLO, ? = -0.074BW/deg, r=0.49, p<0.05).
Varus HKA concomitant with apex distal JLO resulted in highest compressive medial knee loads given achieved combinations of HKA and JLOs. Both HKA and JLO could individually and differently affect the medial and lateral compartments of the tibiofemoral joint. HKA had approximately twice the effect of JLO on affecting the two compartments within the tibiofemoral joint during gait. These findings may contribute data to the ongoing literature debate on long-term component wear risk with kinematic versus mechanical alignment, and inform future knee arthroplasty component placement (Parker, 2019; Parker, 2019b; Riviere C et al. 2019).