The use of magnetic resonance imaging to predict ACL graft structural properties.

Magnetic resonance imaging (MRI) could potentially be used to non-invasively predict the strength of an ACL graft after ACL reconstruction. We hypothesized that the volume and T2 relaxation parameters of the ACL graft measured with MRI will predict the graft structural properties and anteroposterior (AP) laxity of the reconstructed knee. Nine goats underwent ACL reconstruction using a patellar tendon autograft augmented with a collagen or collagen-platelet composite. After 6 weeks of healing, the animals were euthanized, and the reconstructed knees were retrieved and imaged on a 3T scanner. AP laxity was measured prior to dissecting out the femur-graft-tibia constructs which were then tested to tensile failure to determine the structural properties. Regression analysis indicated a statistically significant relationship between the graft volume and the failure load (r(2)=0.502; p=0.049). When graft volume was normalized to the T2 relaxation time, the relationship was even greater (r(2)=0.687; p=0.011). There was a significant correlation between the graft volume and the linear stiffness (r(2)=0.847; p<0.001), which remained significant with T2 normalization (r(2)=0.764; p=0.002). For AP laxity at 30° flexion, there was not a significant correlation with graft volume, but there was a significant correlation with volume normalized by the T2 relaxation time (r(2)=0.512; p=0.046). These results suggest that MRI volumetric measures combined with graft T2 properties may be useful in predicting the structural properties of ACL grafts.