Upright MRI in kinematic assessment of the ACL-deficient knee.

The ability to quantify in vivo femoro-tibial relations in the knee holds great advantage to further patient care. There is little consensus on the optimal weight-bearing environment and measurement method for MRI assessment of in vivo knee kinematics. This study set out to establish the optimal method of measuring femoro-tibial relations in an upright, weight-bearing environment in normal individuals and those with ACL deficiency. Upright, load bearing, MRI scans of both knees were evaluated by two methods, flexion facet centre (FFC) and femoro-tibial contact point (FTCP), in order to establish femoro-tibial relations in the sagittal plane throughout different angles of knee flexion. A group of healthy volunteers (n=5) and a group with unilateral ACL insufficiency (n=8) were studied. Abnormal femoro-tibial relations were found in all ACL-deficient knees (n=8): the lateral tibial plateau was anteriorly displaced in extension and early flexion and, coupled with smaller changes in the medical compartment, this constitutes internal rotation of the tibia relative to the femur in early flexion. This study found that the FFC measurement technique holds an advantage over the FTCP technique in terms of validity, repeatability and ease of measurements, allowing detection of kinematic changes such as tibial internal rotation in early flexion in ACL-deficient knees in an upright weight-bearing model. We propose that FFC measurement in an upright, weight-bearing position is a reliable and representative tool for the assessment of femoro-tibial movement.