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]. 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.Introduction
Methods
Patellar resurfacing affects patellofemoral (PF) kinematics, contact mechanics, and loading on the patellar bone. Patients with total knee arthroplasty (TKA) often exhibit adaptations in movement patterns that may be linked to quadriceps deficiency and the mechanics of the reconstructed knee [1]. Previous comparisons of PF kinematics between dome and anatomic resurfacing have revealed differences in patellar sagittal plane flexion [2], but further investigation of PF joint mechanics is required to understand how these differences influence performance. The purpose of this study was to compare PF mechanics between medialized dome and medialized anatomic implants using subject-specific computational models. A high-speed stereo radiography (HSSR) system was used to capture 3D sub-mm measurement of bone and implant motion [3]. HSSR images were collected for 10 TKA patients with Attune® (DePuy Synthes, Warsaw, IN) posterior-stabilized, rotating-platform components, 5 with medialized dome and 5 with medialized anatomic patellar components (3M/7F, 62.5±6.6 years, 2.2±0.6 years post-surgery, BMI: 26.2±3.5 kg/m2), performing two activities of daily living: knee extension and lunge (Figure 1). Relative motions were tracked using Autoscoper (Brown University, Providence, RI) for implant geometries obtained from the manufacturer. A statistical shape model was used to predict the patella and track motions [4]. Subject-specific finite element models of the experiment were developed for all subjects and activities [5]. The model included implant components, patella, quadriceps, patellar tendon, and medial and lateral PF ligaments (Figure 2a). While tibiofemoral kinematics were prescribed based on experimental data, the PF joint was unconstrained. A constant 1000N quadriceps load was distributed among four muscle groups. Soft tissue attachments and pre-strain in PF ligaments were calibrated to match experimental kinematics [5]. Model outputs included PF kinematics, patellar and contact force ratios, patellar tendon angle, and moment arm.Introduction
Methods
