On Measuring Implant Fixation Stability in ACL Reconstruction.

Emir Benca,Reinhard Windhager,Jan Caspar,Lena Hirtler,Kenneth Van Knegsel,Peter Varga,Boyko Gueorguiev,Harald Widhalm,Ivan Zderic

doi:10.3390/s21196632

Emir Benca, Reinhard Windhager + Show 7 more

Open Access

https://doi.org/10.3390/s21196632

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Abstract

Numerous methods and devices are available for implant fixation in anterior cruciate ligament (ACL) reconstruction. Biomechanical data indicate high variability in fixation stability across different devices. This study aims to provide a better insight into measuring the structural characteristics and mechanical behavior of ACL implant fixations. Fourteen human tibial specimens with reconstructed ACLs were subjected to progressively increasing dynamic loading until failure. The motions of the tibia, the proximal and distal graft ends, as well as the testing frame and actuator, were continuously recorded via a motion tracking system. Significantly higher displacements of the machine actuator (1.0 mm at graft slippage onset, and 12.2 mm at ultimate load) were measured compared to the displacements of the proximal (0.8 and 4.3 mm, respectively) and distal graft (0.1 and 3.4 mm, respectively) ends. The displacements measured at different sites showed significant correlations. The provided data suggest significant and systematic inaccuracies in the stiffness and slippage of the fixation when using machine displacement, as commonly reported in the literature. The assessment of the distal graft displacement excludes the artifactual graft elongation, and most accurately reflects the graft slippage onset indicating clinical failure. Considering the high displacement at the ultimate load, the ultimate load could be used as a standardized variable to compare different fixation methods. However, the ultimate load alone is not sufficient to qualitatively describe fixation stability.

Highlights

The rupture of the anterior cruciate ligament (ACL) is among the most common knee injuries
This study aimed to: (1) measure the isolated displacements and elasticities of single components in the experimental setup via motion tracking; (2) compare the magnitude of the measured machine displacement and the actual slippage of the ACL graft; and (3) investigate if stiffness and ultimate load can be valid parameters to quantify the primary stability of an ACL fixation
The data in the present study show, that this corresponds to less than one millimeter of actual graft slippage

Summary

Introduction

The rupture of the anterior cruciate ligament (ACL) is among the most common knee injuries. The assessed structural characteristics of the fixations included slippage onset, stiffness, yield, and ultimate load These measures can be used for direct performance comparisons between different devices and methods for ACL graft fixation. Yield load (in N) marks the limit of the elastic behavior and the onset of irreversible plastic deformation The latter results from either slippage or the mechanical damage of the graft. This study aimed to: (1) measure the isolated displacements and elasticities of single components in the experimental setup via motion tracking; (2) compare the magnitude of the measured machine displacement and the actual slippage of the ACL graft; and (3) investigate if stiffness and ultimate load can be valid parameters to quantify the primary stability of an ACL fixation

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