Abstract
Introduction
Accurate measurement of knee motion is necessary for assessment of natural joint function and in the diagnosis of pathology. In particular, precise knowledge of natural knee mechanics provides useful metrics for comparison to knee function following total knee arthroplasty (TKA). Reported measurements of natural knee kinematics during activities of daily living are rare, and often do not include both tibiofemoral (TF) and patellofemoral (PF) articulations. What's more, most studies record knee motion of younger subjects that are not necessarily representative of the age range associated with degenerative changes and TKA. The purpose of this study was to measure TF and PF kinematics of healthy older adults as they performed activities of daily living, including tasks considered more demanding for the knee [1].
Methods
High speed stereo radiography (HSSR) was used to measure the kinematics of the PF and TF joints. HSSR utilizes two views of the knee to capture 3D sub-mm measurements accurate to within ±0.15 mm in translation and ±0.41° in rotation [2]. Eight healthy subjects (4M/4F, 64.4±8.2 years, BMI: 27.6±4.8 kg/m2) performed six activities of daily living: seated knee extension, lunge, chair rise, gait, pivot and step down (Figure 1). The 3D geometry of the femur, tibia, and patella of each subject was reconstructed from CT and used to track bone motions using Autoscoper (Brown University, Providence RI). Motion of the tibia and patella were reported relative to a coordinate system centered in the posterior condyles of the femur [3]. Average range of motion (ROM) for each DOF was calculated as the difference between the maximum and the minimum value and averaged across the subjects for each activity.
Results and Discussion
Average patella ROM during the lunge and chair-rise activities was within the ROM of the knee extension, demonstrating consistent tracking of the patella during the loaded deep flexion activities. Tibia motion relative to the femur was consistent in trend during the knee extension, lunge, and chair rise, with the exceptions of increased internal rotation and anterior translation during weight bearing (Figure 2a). In agreement with in vitro studies [4], tibial and patellar internal rotation increased with knee flexion consistently across the high knee flexion activities (Figure 2a). Tibial and patellar external rotation increased as the subjects approached heel-off as they executed a pivot (Figure 3a). Higher-demand tasks, pivot and step down, presented larger ROM than gait with notable increase in tibial external rotation and patellar flexion, respectively (Figure 3b). The decreasing congruence of the patella and trochlea as the knee extends likely explains the greater variability in patella ROM in gait, pivot, and step down activities [5]. In conclusion, evaluating natural kinematics of the tibia and patella and their interaction during a variety of activities of daily living provides a standard for the evaluation of knee pathology and treatment.
