Influence of Patellar Geometry on Kinematics, Quadriceps Function, and Patient Outcome in Subjects With the Attune PS RP
Phase: NA
Conditions: Total Knee Arthroplasty
Sponsor: University of Denver

COVER PAGE 
 
 
Title:  Stereo Radiography of TKA Patella Mechanics 1 
 
NCT Number:  NCT02532933 2 
 
Date:  5/31/2019 
 
Protocol and Statistical Plan 

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Stereo Radiography of TKA Patella Mechanics 
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NCT02532933 
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Protocol and Statistical Plan 
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The purpose of this study was to determine patellar kinematics in TKA patients with medialized 
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dome and medialized anatomic patellae during a seated knee extension and a weight-bearing lunge activity 
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using high-speed stereo radiography (HSSR).  Flexion of the patella in the sagittal plane was reported 
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relative to the femur and with respect to the long axis of the tibia to enable comparison to prior reports that 
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utilize each of these anatomic references.  Based on prior computational evaluation, we hypothesized that 
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patients with anatomic patellar implants would exhibit greater patellar flexion relative to the femur and less 
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external rotation, greater knee extension strength, and improved patient-reported outcomes compared to 
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patients with dome patellar implants. 
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Twenty-seven subjects with posterior-stabilized, rotating-platform total knee arthroplasty 
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(ATTUNE Knee, DePuy Synthes Products, Warsaw, IN) were recruited for this study after the approval of 
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the Institutional Review Board of the University of Denver and registration on www.clinicialtrials.gov 
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(NCT02532933).  All subjects signed informed consents.  A power analysis (90%) using an effect size of 
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8 degrees resulted in a sample size of 16 subjects per group [10]. Subjects were required to be at least nine 
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months post-operation and with no reported concomitant orthopaedic conditions or neurologic disorders 
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that hindered normal movement.  All subjects were patients of the surgeon co-authors, Drs. Dennis and 
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Haas, and each surgeon contributed patients from both the dome and the anatomic groups.  Surgeons 
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performed TKA using a femur-first gap-balancing operative technique [12].  Patient selection criteria for 
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dome v. anatomic patellae was not considered, as the focus of this study was solely on differences due to 
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implant design.    
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Postoperatively, at the time of testing, subjects completed Part 2 – Function of the Knee Society 
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Score (KSS) questionnaire, the Knee injury and Osteoarthritis Outcome Score (KOOS), and the Patient’s 
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Knee Implant Performance (PKIP) Questionnaire [13–16].  Because the completion of specific activities of 
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daily living were required for this study, only participants scoring good or excellent (>69) on the KSS were 
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included in the study.  Height, weight, and leg dominance were recorded.  Maximum isometric flexor and 
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extensor strength were evaluated at 60° knee flexion and normalized to body weight. (Cybex, Medway, 
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MA). 
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Subjects performed a non-weight-bearing seated knee extension and a weight-bearing lunge 
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activity while conventional marker-based motion capture (Vicon Motion Systems, Ltd., Oxford, UK) 
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recorded whole-body motion and HSSR captured x-ray images of the knee joint in two planes (50 Hz, 
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Figure 1).  Femur, tibial tray, and patellar component CAD geometries for each subject were obtained from 
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the manufacturer.  The femoral and tibial tray geometries were used to track the motion of the respective 
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implants (Autoscoper, Brown University, Providence, RI) [17].  Accuracy of the HSSR is 0.2±0.1 mm in 
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translation and 0.4±0.3 degrees in rotation, comparable to those measured in other stereo radiography 
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systems [11,18,19].  Because the patellar component is radiolucent, it was not visible in the x-ray images.  
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Thus, images of four static poses of each subject’s patella were recorded with the HSSR and used to derive 
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the 3D patellar bone geometry of each subject using a previously-developed statistical shape model (SSM) 
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[20].  The resection plane of the implant was assessed based on the radiographic images and the patellar 
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component model fit on the posterior surface of the SSM developed for each subject (Figure 2). 
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Sagittal plane patellar flexion was reported with respect to a medial-lateral axis on the femur (PF 
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flexion), PF tilt was reported with respect to the inferior-superior axis of the patella, and medial-lateral 
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translation was described along the medial-lateral axis of the femur.  In addition, patellar sagittal plane 
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flexion was reported with respect to the long axis of the tibia (patellotibial (PT) flexion) [21] for comparison 
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to prior work that uses PT flexion as the convention.  In general, higher PF flexion is associated with lower 
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PT flexion.  The maximum knee flexion achieved during each activity was measured from marker-based 
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motion capture [22].  
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Unpaired, two-tailed Student’s t-tests (p<0.05) were used to compare kinematic measurements 
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between the dome and anatomic groups, and paired, two-tailed t-tests (p<0.05) were used to compare 
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kinematic measurements between the knee extension and lunge activities. Pearson’s correlation coefficients 
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between measurements were calculated.  
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