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Research Papers

The Influence of Component Alignment and Ligament Properties on Tibiofemoral Contact Forces in Total Knee Replacement

[+] Author and Article Information
Colin R. Smith

Department of Mechanical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706
e-mail: crsmith25@wisc.edu

Michael F. Vignos

Department of Mechanical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706
e-mail: mvignos@wisc.edu

Rachel L. Lenhart

Department of Mechanical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706;
Department of Biomedical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706
e-mail: rlenhart@wisc.edu

Jarred Kaiser

Department of Mechanical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706
e-mail: jmkaiser2@wisc.edu

Darryl G. Thelen

Fellow ASME
Department of Mechanical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706;
Department of Biomedical Engineering,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706;
Department of Orthopedics and Rehabilitation,
University of Wisconsin-Madison,
1513 University Avenue,
Madison, WI 53706
e-mail: dgthelen@wisc.edu

1Corresponding author.

Manuscript received October 16, 2015; final manuscript received January 6, 2016; published online January 27, 2016. Editor: Beth A. Winkelstein.

J Biomech Eng 138(2), 021017 (Jan 27, 2016) (10 pages) Paper No: BIO-15-1520; doi: 10.1115/1.4032464 History: Received October 16, 2015; Revised January 06, 2016

The study objective was to investigate the influence of coronal plane alignment and ligament properties on total knee replacement (TKR) contact loads during walking. We created a subject-specific knee model of an 83-year-old male who had an instrumented TKR. The knee model was incorporated into a lower extremity musculoskeletal model and included deformable contact, ligamentous structures, and six degrees-of-freedom (DOF) tibiofemoral and patellofemoral joints. A novel numerical optimization technique was used to simultaneously predict muscle forces, secondary knee kinematics, ligament forces, and joint contact pressures from standard gait analysis data collected on the subject. The nominal knee model predictions of medial, lateral, and total contact forces during gait agreed well with TKR measures, with root-mean-square (rms) errors of 0.23, 0.22, and 0.33 body weight (BW), respectively. Coronal plane component alignment did not affect total knee contact loads, but did alter the medial–lateral load distribution, with 4 deg varus and 4 deg valgus rotations in component alignment inducing +17% and −23% changes in the first peak medial tibiofemoral contact forces, respectively. A Monte Carlo analysis showed that uncertainties in ligament stiffness and reference strains induce ±0.2 BW uncertainty in tibiofemoral force estimates over the gait cycle. Ligament properties had substantial influence on the TKR load distributions, with the medial collateral ligament and iliotibial band (ITB) properties having the largest effects on medial and lateral compartment loading, respectively. The computational framework provides a viable approach for virtually designing TKR components, considering parametric uncertainty and predicting the effects of joint alignment and soft tissue balancing procedures on TKR function during movement.

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References

Figures

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Fig. 1

The knee model used subject-specific bone and TKR component geometry and included an extensible PT and 11 ligament bundles. The knee model was integrated into a generic lower extremity model which included 44 muscle–tendon units acting about the hip, knee, and ankle. The coronal plane TKR component alignment in the nominal model was set to match the limb alignment measured for the subject in a standing radiograph.

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Fig. 2

A numerical optimization approach was used to simultaneously predict patellofemoral kinematics, secondary tibiofemoral kinematics, and muscle forces that, together with the induced ligament forces and contact pressures, generated the measured hip, knee, and ankle accelerations at each time step of a gait cycle. Muscle force distribution was determined by minimizing an objective function that consisted of a sum of volume weighted squared muscle activations and the knee joint contact energy.

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Fig. 3

Lower extremity posture, activated muscles (shown in red), and computed contact pressures on the femoral and tibial components throughout the smooth gait cycle (see online version for color)

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Fig. 4

Representative scatter plots showing the correlation between the second peak tibiofemoral contact forces and ligament reference strain. Each data point corresponds to 1 of the 2000 simulations run. The strength of the correlation between the predicted contact forces and the reference strain was evaluated using Pearson's correlation coefficients (R).

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Fig. 5

Comparison of the blinded and unblinded model predicted tibial component contact forces (in tibia superior direction) to measured contact forces throughout the smooth and bouncy gait cycles. Error metrics are given in Table 2.

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Fig. 6

Sensitivity of the joint contact forces to variations in coronal plane component alignment for smooth gait. Placing the components in a varus alignment relative to the nominal position shifted more of the total contact force to the medial compartment. The opposite relationship exists when placing the components in a valgus alignment, relative to nominal. Comparable results were found for bouncy gait.

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Fig. 7

Variability in ligament forces (shaded area represents the 95% confidence interval) throughout the smooth gait cycle due to uncertainty in ligament stiffness and reference strains. The dark center line is the mean of the Monte Carlo simulations, which is nearly identical to the force predicted by the nominal model.

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Fig. 8

Variability in predicted tibiofemoral joint contact forces (95% confience interval) throughout the smooth gait cycle due to uncertainty in the stiffness and reference strains assumed for ligaments

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Fig. 9

Correlations of tibiofemoral contact forces with ligament stiffness (solid bars) and reference strain (open bars) at the first and second peaks of tibiofemoral loading during stance

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