Introductions: Although magnetic resonance imaging (MRI) is useful for diagnosis of anterior cruciate ligament (ACL) injuries, it is difficult to assess joint kinematics under weight bearing condition with MRI. Recently, a 320-detector row upright computed tomography (CT) which enables scanning of whole leg in standing position has been available. We aimed to evaluate 3D joint kinematics of the whole leg under weight bearing condition in ACL injured knees using the upright CT. It was hypothesized that abnormal motion would be found on the affected side.
A total of 18 knee joints in 9 patients with unilateral ACL-deficient knees (4 females and 5 males with a mean age of 34.1 ± 12.6 yrs) were enrolled. Each participant had given a written informed consent and the study protocol was approved by our ethical committee (#20150293).
CT images were acquired from hip joint to whole foot using a 320-detector row upright CT scanner (TSX-401R, Canon Medical Systems, Otawara, Japan). Participants underwent CT imaging in two weight bearing conditions, each in a one-leg standing position (affected or unaffected side). Three-dimension surface data of the femur and the tibia were extracted from CT DICOM data using three-dimensional visualization software (AVIZO 6.3; Thermo Fisher Scientific, Tokyo, Japan). After matching the surface data of the femur, we used the iterative closest point algorithm based on the Visualization Toolkit 8.1.0 (Kitware Inc., NY, USA), for the surface matching technique in which point data on another surface by iterative steps to reach to the closest points. The triaxial positional and angular changes of the tibia relative to the femur were measured. Angular changes around each axis can be described by the Euler/Cardan angles representing three sequential rotations about the anatomical axis of the proximal bone.
Participants are divided into two groups based on fresh (within three months after injury) or chronic ACL injury, and the unaffected side was compared to the affected side in each group. The differences were compared statistically using two-tailed paired t-test, and the level of significance was set at p<0.05. For statistical analysis, SPSS software (IBM, Armonk, NY, USA) was used.
Four participants were classified as fresh injury and five as chronic. In fresh group, anterior translation of the tibia was significantly greater on the affected side than on the unaffected side under full weight bearing (18.1mm vs 15.1mm, p<0.05), while no significant differences were found for rotation. On the other hand, in chronic group, tibial external rotation was greater on the unaffected side than on the affected side (15.2° vs 7.8°, P<0.01).
According to previous literatures, anterior translation and internal rotation of the tibia have been reported to be greater in ACL-deficient knees compared to healthy knees using MRI. However, knee kinematics under weight bearing condition have been still unknown. To the best of our knowledge, this is the first study to assess knee kinematics under weight bearing condition using novel upright CT. Our findings suggest that chronic ACL injured knee will lead to rotational changes (decreased screw home movement) as well as anterior translation of the tibia.