Mechanical alignment tolerance of a cruciate-retaining knee prosthesis under gait loading-A finite element analysis

Abstract

Component alignment is one of the most crucial factors affecting total knee arthroplasty's clinical outcome and survival. This study aimed to investigate how coronal, sagittal, and transverse malalignment affects the mechanical behavior of the tibial insert and to determine a suitable alignment tolerance on the coronal, sagittal, and transverse planes. A finite element model of a cruciate-retaining knee prosthesis was assembled with different joint alignments (-10°, -7°, -5°, -3°, 0°, 3°, 5°, 7°, 10°) to assess the effect of malalignment under gait loading. The results showed that varus or valgus, extension, internal rotation, and excessive external rotation malalignments increased the maximum Von Mises stress and contact pressure on the tibial insert. The mechanical alignment tolerance of the studied prosthesis on the coronal, sagittal, and transverse planes was 3° varus to 3° valgus, 0°-10° flexion, and 0°-5° external rotation, respectively. This study suggests that each prosthesis should include a tolerance range for the joint alignment angle on the three planes, which may be used during surgical planning.

Keywords: alignment tolerance; contact pressure; finite element analysis; gait loading; knee prosthesis; stress.

FIGURE 1

3D model of the knee prosthesis (A): Definition of the femoral flexion center (FFC); (B) anteroposterior and medial-lateral axes of the tibial component; (C) the coordinate system of the model, TCC, tibial component center).

FIGURE 2

Input curves and loading conditions (A): flexion angle; (B) anteroposterior translation, (C) axial force, (D) tibial rotation, (E) schematic diagram of loading conditions).

FIGURE 3

Malalignment of the knee prosthesis and coordinate systems of loading conditions (A): coronal plane; (B) sagittal plane; (C) transverse plane).

FIGURE 4

Comparison between previous studies and the present study (A): contact pressure at different flexion angles; (B) contact area at different flexion angles; (C) maximum Von Mises stress during gait loading).

FIGURE 5

Maximum Von Mises stress and contact pressure with different coronal malalignments (VAR: varus malalignment; VAL: valgus malalignment; red line: yield stress = 20.2 MPa).

FIGURE 6

Distribution of maximum Von Mises stress on the liner with different coronal malalignments of the knee prosthesis (VAR: varus malalignment; VAL: valgus malalignment).

FIGURE 7

Maximum Von Mises stress and contact pressure with different sagittal malalignments of the knee prosthesis (E: extension malalignment; F: flexion malalignment; red line: yield stress = 20.2 MPa).

FIGURE 8

Distribution of maximum Von Mises stress on the liner with different sagittal malalignments of the knee prosthesis (E, extension malalignment; F, flexion malalignment).

FIGURE 9

Maximum Von Mises stress and contact pressure with different transverse malalignments (IR: internal rotation malalignment; ER: external rotation malalignment; red line: yield stress = 20.2 MPa).

FIGURE 10

Distribution of maximum Von Mises stress with different transverse malalignments of the knee prosthesis (IR: internal rotation malalignment; ER: external rotation malalignment).