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Updated: Aug 23, 2026
Athymic Rat Model for Evaluation of Engineered Anterior Cruciate Ligament Grafts
Published on: March 26, 2015
Initial tension and anterior load-displacement behavior of high-stiffness anterior cruciate ligament graft constructs
Ari Karchin1, M L Hull, S M Howell
1Biomedical Engineering Program, and Department of Mechanical Engineering, University of California, Davis, CA 95616, USA.
Background:
Because the tension that exists in an anterior cruciate ligament graft when the knee is unloaded (the initial tension) affects the surgical outcome and because high initial tension has a number of adverse consequences, the primary purpose of this study was to determine quantitatively how much less initial tension was required for a high-stiffness construct than for a low-stiffness construct. A secondary purpose was to determine how the stiffness of the graft construct affects the anterior load-displacement behavior of the knee from 0 degrees to 90 degrees of flexion.
Methods:
Anterior-posterior load-displacement was measured in each of ten intact cadaveric knee specimens, the anterior cruciate ligament was excised, and the anterior cruciate ligament was reconstructed with a double-loop bovine tendon graft. Graft constructs of different stiffness were created with use of six springs, ranging in stiffness from 25 to 275 N/mm to simulate the fixation stiffness. After adjusting the initial tension of the graft so that the anterior-posterior laxity of the reconstructed knee matched that of the intact knee, the 0-N posterior limit and the 225-N anterior limit were measured at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion.
Results:
The highest stiffness fixation (275 N/mm) required an average of 73 N of initial tension, which was more than three times less than the average of 242 N of initial tension required by the lowest stiffness fixation (25 N/mm). The 225-N anterior limit was overconstrained an average of 1.0 mm with the highest stiffness fixation (275 N/mm), which was 3.6 mm less than the overconstraint with the lowest stiffness fixation (25 N/mm). Likewise, the posterior limit was overconstrained an average of 2.6 mm with the highest stiffness fixation (275 N/mm), which was 3.8 mm less than the overconstraint with the lowest stiffness fixation (25 N/mm).
Conclusions:
The initial tension for a high-stiffness graft construct is more than three times less than that for a low-stiffness construct. The initial tension for a high-stiffness graft construct better restores both the 225-N anterior limit and the 0-N posterior limit to normal than the initial tension for a low-stiffness graft construct over the range of flexion from 0 degrees to 90 degrees.
