Is the Contralateral Knee a Valid Reference When Quantitatively Assessing Secondary Knee Kinematics?
1University of Wisconsin, Madison, WI, USA, 2University of Wisconsin, Madison, WI, USA, 3University of Wisconsin, Madison, WI, USA
Introduction: It is common to use the contralateral limb as a reference when evaluating the effects of pathology and treatment on knee function (1-3; 5). Previous imaging studies have shown that the contralateral knee is a good morphological reference, with normal individuals exhibiting substantial bilateral symmetry in skeletal geometry, cartilage volume and ligament insertion points (2; 3). However, morphological symmetry does not imply functional symmetry, since inter-limb variations in tissue properties and neuromuscular coordination will influence joint behavior during voluntary movement. The objective of this study was to directly evaluate bilateral symmetry in tibiofemoral motion. To do this, we used new advances in dynamic magnetic resonance imaging (MRI) to precisely measure in vivo 3D skeletal kinematics during voluntary motion.
Methods: The dominant and non-dominant knees of 10 healthy subjects (5F, 5M, 24.6±3.2y; 65.1±5.0kg) were tested after obtaining informed consent according to an IRB-approved protocol. Subjects performed a knee flexion-extension task at 0.5 Hz against an inertial load that induced quadriceps loading with knee flexion, as occurs during load acceptance phase of gait. The 5 min task was performed in a 3T clinical MRI scanner while a vastly under-sampled isotropic projections (VIPR) sequence continuously recorded volumetric image data. Images were binned based on position to create 60 frames over a 2 s cycle. High resolution models of the tibia and femur, derived from a high resolution static MRI sequence, were optimally registered to each dynamic image frame (4). This process resulted in a reconstruction of the 3D femur and tibia kinematic trajectories throughout the flexion-extension cycle, which were then used to ascertain 3D translations and rotations at the tibiofemoral joint. Inter-limb differences in tibiofemoral angles and translations were determined at 5 deg increments of knee flexion, with all values referenced to corresponding measures in an extended knee. Inter-subject variations in knee kinematics were obtained by determining differences between an individual's limb measure and all other subjects’ dominance-matched limb. Inter-limb and inter-subject differences were compared at each flexion angle using an independent t-test with statistical significance set at p ≤ 0.5.
Results: Dynamic MRI measures of tibiofemoral kinematics exhibited characteristic posterior tibia translation and internal tibia rotation with knee flexion. Subjects showed significantly lower inter-limb differences than inter-subject differences in secondary tibiofemoral kinematic measures at every flexion angle (p < 0.05), with the most marked difference being in internal tibia rotation (Fig. 1).
Discussion: This represents the first study to use dynamic 3D volumetric MRI to measure in vivo knee kinematic behavior. This exciting new technology enables direct measures of knee joint behavior under in vivo conditions, which could be used to assess knee mechanics following injury, surgery or rehabilitation. This initial study on control subjects demonstrates that the contralateral knee seems to serve as a more valid reference of in vivo knee behavior than measures obtained from other subjects. This was particular true for internal tibia rotation which exhibited much greater variation between subjects than between limbs.
Significance: Individuals with ACL-deficient or reconstructed knees have been shown to exhibit bilateral asymmetries in internal tibia rotation during both walking (6) and running (7). This initial study shows that healthy control subjects exhibit substantial bilateral symmetry in this key measure, suggesting that bilateral differences likely reflect variations in knee behavior due to injury or treatment factors.
Acknowledgements: NIH AR062733-01, NSF 0966535
References:  Andriacchi, TP, et al. 2009. J Bone Joint Surg Am 91 Suppl 1: 95-101.  Dargel, Jet al. 2009. Knee Surg Sports Traumatol Arthrosc 17: 1368-1376.  Eckstein, F. 2002. OA and Cartilage 10: 914-921.  Kaiser, J et al. 2012. MRM.  Kozanek, M et al. 2008. Am J Sports Med 36: 2151-2157.  Scanlan, S et al. 2010. J Biomech 43: 1817-1822.  Tashman, S et al. 2004. Am J Sports Med 32: 975-983.