Relationship between biomechanical asymmetries during a step up and over task and stair climbing after total knee arthroplasty

Abstract

Background: Patients six months after total knee arthroplasty (TKA) demonstrate movement asymmetries and functional deficits, which may be related to poor functional performance. The aims of this study were to 1) compare biomechanical variables between subjects 6 months after TKA and an age-matched healthy control group during a step up and over task and 2) determine the relationship between quadriceps strength, movement patterns and stair climbing performance.

Methods: Twenty patients 6 months following unilateral TKA and twenty healthy controls were enrolled. Participants completed questionnaires, isometric quadriceps strength testing and performance based tests to quantify functional performance. Motion analysis was performed during a step up and over task. Functional and biomechanical variables were analyzed using a 2 × 2 ANOVA. The symmetry ratios (operated/non-operated limb*100) for biomechanical variables were analyzed using independent t-tests. Pearson correlations were performed to determine the relationships between biomechanical variables, strength and stair climbing performance.

Findings: In the TKA group, subjects had lower peak moments, power and sagittal plane excursion in the operated knee compared to the contralateral knee (P<0.05), while the hip on the operated side had greater power generation (P = 0.014). Compared to the control group, all symmetry ratios were significantly lower in the surgical group (P < 0.05). Stair climbing time was correlated with quadriceps strength of the operated limb (R = -0.762, P < 0.001).

Interpretation: Individuals 6 months after TKA had worse performance with respect to biomechanics, quadriceps strength, and performance-based tests. Biomechanical asymmetries after TKA reduce the demand on the operated knee and increase reliance on the contralateral limb and ipsilateral hip.

Keywords: Arthroplasty; Knee; Lower extremity; Orthopedics; Rehabilitation.

Figure 1

Representative subject performing the step up and over task. Subjects started behind the wooden box and stepped up and over the box on the investigator’s command. The limb on the box was referred to as the stepping limb and the limb that landed on the anterior side of the box was referred to as the landing limb. The propulsive phase started when the stepping limb contacted the wooden box and ended at 60% of the stance phase. At this point, the lowering phase started and lasted until toe-off of the stepping limb from the box. The weight acceptance phase stated at initial contact of the landing limb on the ground and ended at 25% of the stance phase for this limb.

Figure 2

Symmetry ratio (operated divided by the non-operated side) for peak sagittal knee moment and peak knee and hip powers during the propulsive and lowering phases in the stepping limb. Error bars represent standard deviation.