Biomechanical Effect of Coronal Alignment and Ligament Laxity in Total Knee Arthroplasty: A Simulation Study

Abstract

The purposes of this study were to develop a cruciate-retaining total knee arthroplasty musculoskeletal model, which enables the adjustment of ligament length and implant alignment; validate the model; and evaluate the effects of varus/valgus alignment adjustment and unbalanced medial/lateral ligament laxity during gait. A cruciate-retaining total knee arthroplasty musculoskeletal model was constructed and validated against the in vivo contact forces. This model was transformed to 2° varus/valgus alignment of femoral or tibial replacement models and 2° medial/lateral laxity models. The contact forces and ligament tensions of the adjusted models were calculated. The contact forces in the model showed good agreement with the in vivo contact forces. Valgus replacement alignment with balanced ligament models showed a lower contact force at the medial compartment than at the neutral alignment model, whereas the varus replacement alignment with balanced ligament models showed a greater contact force at the medial compartment and medial/posterior cruciate ligament tension. The medial laxity with neutral alignment model showed a similar contact force with decreased medial ligament tension compared to the balanced neutral alignment model, whereas the lateral laxity with the neutral alignment model showed a greater contact force and decreased lateral ligament tension. The cruciate-retaining total knee arthroplasty model was validated using in vivo contact forces (r = 0.939) Two degrees of valgus alignment adjustment with balanced ligament or neutral alignment with 2° of medial laxity can be safe without increasing contact force or ligament tension compared to neutral alignment with a balanced extension gap. However, 2° of varus alignment adjustment with balanced ligament or neutral alignment with 2° of lateral laxity may be unfavorable due to the overloading of the joints and knee ligaments.

Keywords: collateral ligament tension; contact force; coronal alignment; knee arthroplasty; model.

FIGURE 1

Musculoskeletal model developed in this study. Anterolateral and posterior–medial view of the TKA knee joint.

FIGURE 2

Schematic diagram of the ligament adjustment process. The balanced neutral alignment model (left). Ligament adjustment performed at 2° varus (center). Model G: Neutral alignment model with laxity at lateral ligaments with balanced medial ligaments (right). Black arrow indicates the rotation of tibia from varus to neutral alignment.

FIGURE 3

Diagram of varus/valgus, medial/lateral laxity, and tibial/femoral replacement model configurations. The neutral alignment model (model A) was transformed into six cases: the 2° tibial valgus (model B) and femoral valgus (model C) alignment models with no laxity; the 2° tibial varus (model E) and femoral varus (model F) alignment models with no laxity; and neutral alignment models with 2° medial (model D) and lateral (model G) laxity. Medial and lateral laxity in models D and G are illustrated by light blue lines.

FIGURE 4

TCF, MCF, and LCF calculated from the model, and the measured data were compared during a gait cycle. Pearson’s correlation coefficient (r) for TCF, MCF, and LCF were 0.939, 0.962, and 0.703, respectively.

FIGURE 5

TCF, MCF, and LCF calculated during a gait cycle in models A–G. The neutral alignment model (model A); the 2° tibial valgus (model B) and femoral valgus (model C) alignment models with no laxity; the 2° tibial varus (model E) and femoral varus (model F) alignment models with no laxity; and neutral alignment models with 2° medial (model D) and lateral (model G) laxity.

FIGURE 6

Peak TCF, MCF, and LCF and peak tension force of the ALL, LCL, MCL, and PCL in models A–G in Newton.

FIGURE 7

Activation/deactivation point and activation rate during the gait cycle of the ALL, LCL, MCL, and PCL in models A–G.

FIGURE 8

Rotational and translational knee kinematics in models A–G: (A) knee flexion angle, (B) femoral internal/external rotation, (C) knee varus/valgus angle, (D) femoral anterior/posterior translation, (E) superior/inferior translation (the initial value of superior–inferior translation indicates superior–inferior height difference between the tibial and femoral coordinate systems), and (F) femoral medial/lateral translation.