Effect of alignment strategy on lower limb kinematics during stair descent after robot-assisted total knee arthroplasty.

Purpose: Total knee arthroplasty (TKA) effectively treats end-stage osteoarthritis; however, many patients still struggle with gait and functional movements such as stair descent. This study investigates how two surgical alignment techniques, inverse kinematic alignment (iKA) and adjusted mechanical alignment (aMA), affect lower limb kinematics during stair descent compared to healthy controls.

Methods: Forty-five participants (15 per group: iKA, aMA, controls) performed low (165 mm) and high (280 mm) stair descent tasks. Sagittal hip, knee, and ankle movements were recorded with 3D motion capture and analysed using Statistical Parametric Mapping (SPM).

Results: The aMA group exhibited significantly longer descent times for both low (p = 0.038) and high stairs (p = 0.003). Additionally, the aMA group demonstrated a reduction in trailing knee range of motion (ROM) during low stair descent (80.65°) compared to the control group (92.87°, p = 0.023). The mean joint angle of the trailing hip during low stair descent also differed significantly between the aMA group and healthy controls. Although no significant differences were observed in the trailing hip joint angle during low stair descent between the iKA and healthy control groups, substantial deviations were noted during high stair descent (p = 0.011). Furthermore, the ROM of the leading knee in the iKA group differed significantly from that of the healthy control group during both low and high stair descents.

Conclusions: The iKA group exhibited movement patterns that were slightly more similar to those of healthy controls during low stair descent but showed deviations during the more demanding high stair descent. These findings underscore the need for further research into the mechanisms underlying these adaptations to optimise rehabilitation and surgical strategies aimed at restoring more natural movement patterns in TKA patients.

Level of evidence: Level III.