Abstract
Introduction and Aims: Late degeneration of the ACL injured knee may be in part due to repeat injury, but also due to aberrant kinematics altering the wear pattern at the chondral surface. The aim of this study was to use tibio-femoral contact mapping by MRI to examine kinematic changes due to chronic ACL deficiency.
Method: Twenty subjects with a recent unilateral ACL deficiency (mean 13 months since injury) and 23 subjects with a chronic ACL deficiency (mean 18 years since injury) were recruited. Passive ligament laxity was quantified using a KT1000® device. Subjects performed a closed-chain leg press, relaxed and against a 15 kg weight. MRI recorded the tibio-femoral contact position at 15-degree intervals from zero to 90 degrees of knee flexion. Tibio-femoral contact points were measured at each position. Damage to the knee was recorded for all subjects by MRI, and at arthroscopy.
Results: The tibio-femoral contact pattern of the ACL injured knee was different from the healthy contralateral knee (p = 0.001). The contact pattern of the recently injured knees was different to the chronic ACL deficient knees (p = 0.034). In the recently injured knees the lateral compartment of the knee showed a posterior pattern of femoral contact, and in the chronic ACL deficient knees the medial compartment showed a posterior femoral contact pattern, particularly at zero and 15 degrees of knee flexion (p < 0.01), with the femur two millimetres (mean, SD 3.2mm) posterior on the tibial plateau. There was no difference in passive laxity between the recent and chronic injured knees (side-to-side difference: 5.8mm±2.4 for the recently injured knees, and 4.6±2.8mm for the chronic ACL-deficient knees). Nine of 20 recently injured knees had associated joint damage: three medial and three lateral meniscal tears, two with medial femoral condyle and two with patello-femoral damage. Eleven of 23 chronic ACL deficient subjects had associated joint damage: 15 medial and 16 lateral meniscus tears, 16 with medial and 12 with lateral compartment chondral damage. Greater kinematic changes in the chronic ACL deficient knees were associated with more severe chondral damage in the medial compartment.
Conclusion: ACL injury shifts the axis of rotation of the knee medially. In chronic ACL deficiency the tibio-femoral contact pattern is altered in the medial compartment, where it is associated with joint damage. These findings describe the relationship between aberrant kinematics and wear in the ACL deficient knee.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
