The internal brace (IB) technique is a promising treatment option for repairing the proximal rupture of the anterior cruciate ligament (ACL). This paper presents a biomechanical evaluation of the IB technique. Sixteen cadaveric sheep knees underwent monotonic tensile tests, cyclic loading, and passive flexion-extension testing. Data were compared in a series of eight control specimens with an intact ACL and eight repaired specimens where the ACL was cut and repaired using the IB. In parallel with the mechanical testing, finite element analysis (FEA) was performed to investigate the influence of IB loading on the femur-ACL-tibia complex (FATC). The 3D geometry of the FATC was reconstructed from CT scans of the sheep. The IB 3D model was integrated with the 3D FATC for FEA to obtain the femur-repaired ACL with IB - tibia complex (FRA-IB-TC) group. For the intact specimens, the mean (±SD) failure load in the tensile testing was 937 N (±192 N), while for the FRA-IB-TC specimens, it was 519 N (±52 N). The FRA-IB-TC remained biomechanically stable during the cyclic loading testing. The FEA demonstrated an increase in ACL stress to 24.59 MPa and displacement values of 0.391 mm. The IB construct exhibited shear and notch effects at the button-suture-bone fixation site. Testing on this sheep model allowed us a parametric analysis of the impact of the IB repair technique. However, the results will need to be confirmed in a human model. In conclusion, although the IB technique has biomechanical drawbacks, the mechanical properties of the technique are satisfactory.
Keywords: ACL repair; ACL tear; Experimental testing; FEM analysis.
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