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The effect of graft position for a single bundle ACL reconstruction – FEA Study

Ravi Sundaramurthy (B.Eng Biomedical)Dr. David Parker (FRACS)

Dr. Qing Li (PhD, University of Sydney)

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Background- Graft Placement

IsometricIsometric Minimum strain of graftMinimum strain of graft Preserves the life of the graft longestPreserves the life of the graft longest Knee biomechanics not represented Knee biomechanics not represented

AnatomicalAnatomical Placed at footprint of original ACLPlaced at footprint of original ACL Approximates knee biomechanics betterApproximates knee biomechanics better Higher failure rates, stretching etcHigher failure rates, stretching etc

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Literature Review

Several FEA models on knee Donohue et al, 2002 etc

Very few studies on ACL reconstruction using FEA models

Pena E et al, 2005*

*Pena E et al, Influence of the tunnel angle in ACL reconstructions on the biomechanics of the knee joint, Clinical Biomechanics, 2006, p508-516

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Aims

Build an accurate FE model of the knee

Analyse effect of changing ACL graft position on

Biomechanics of the knee

Stress and strain on the graft and major ligaments

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Methods

Describe what was actually done

Created a FE Model of knee using what program? How many knees did you use?

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Assumptions in the Model

Meniscus and articular cartilage not modelled

Muscles (Passive and active) not modelled

Knee is modelled in Full Extension

Ligament is modelled as linear non-viscoelastic

Pre-tensioning of ligaments and grafts not considered

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Graft Positioning

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Result Anterior Tibial Loading

190.7 N Posterior Femoral Load

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Results External Tibial Rotation

5 N.m External Torque

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LCL Stresses and Strain

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Internal Tibial Rotation

5 N.m Internal Tibial Rotation

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Internal Tibial Rotation

No ACL Loading

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Conclusion

Several trends were observed in ligament stress, strain and knee kinematics with varying graft position

An alternative method to clinical studies was used to study effect of graft position

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Future Directions

Effect of Different Flexion Angles

Model ligaments as non-linear viscoelastic

Study effect of muscles, meniscus etc

Study Double Bundle technique

Study effect of more graft materials