Effect of ACL reconstruction graft size on simulated Lachman testing: a finite element analysis

ACL reconstructions are frequently performed following ACL injury. The most common treatment is single bundle reconstruction. While ACL reconstructions have been studied clinically and experimentally, quantitative information regarding the local biomechanics the knee following ACL reconstruction is generally lacking. Specifically, the role of graft size on joint stability and soft tissue injury propensity is currently unknown.

Therefore, a non-linear contact finite element model was developed to systematically evaluate the relationship between ACL graft size and knee joint biomechanics following ACL reconstruction. A simulated Lachman maneuver was utilized to assess knee joint laxity, meniscal stress, in situ graft loading, and peak articular cartilage contact pressure for ACL graft sizes between 5 and 9 mm, as well as an ACL-deficient knee. The model was validated by corroboration with previously published experimental (cadaveric) data on ACL reconstruction.

The 5 mm graft resulted in 30% greater relative AP translation compared to the 9 mm graft; the ACL deficient knee resulted in 2.56-times greater AP translation than the average graft reconstruction. Contact pressure and peak meniscal stresses decreased monotonically for increased values of ACL graft diameter. For all graft diameters, soft tissue stress and articular contact pressure was reduced versus the ACL-deficient knee.

ACL reconstruction dramatically affects the local biomechanics of the knee. Stresses occurring in the soft tissues, as well as contact pressure at the articular surfaces, were found to be highly sensitive to ACL graft size. Larger grafts were associated with lower meniscal stress, decreased joint laxity, and less articular cartilage contact stress. Therefore, the current data suggests that increased graft size confers a biomechanical advantage in the ACL reconstructed knee.