The Journal of Bone and Joint Surgery (American). 2007;89:2723-2731.
© 2007 The Journal of Bone and Joint Surgery, Inc.
Relationship Between Varus-Valgus Alignment and Patellar Kinematics in Individuals with Knee Osteoarthritis
Emily J. McWalter, MASc1, Jolanda Cibere, MD, PhD2, Norma J. MacIntyre, PhD3, Savvas Nicolaou, MD4, Michael Schulzer, PhD1 and David R. Wilson, DPhil5
1 Department of Mechanical Engineering (E.J.McW), Centre for Clinical Epidemiology and Evaluation (M.S.), University of British Columbia and Vancouver Coastal Health Research Institute, 828 West 10th Avenue, Vancouver, BC V5Z 1L8, Canada
2 Division of Rheumatology, Department of Medicine, University of British Columbia and Arthritis Research Centre of Canada, 895 West 10th Avenue, Vancouver, BC V5Z 1L7, Canada
3 School of Rehabilitation Science, McMaster University, Institute for Applied Health Sciences, Room 432, 1400 Main Street West, Hamilton, ON L8S 1C9, Canada
4 Department of Radiology, University of British Columbia and Vancouver Hospital for Health Sciences Centre, Room 3350, 950 West 10th Avenue, Vancouver, BC V5Z 4E3, Canada
5 Department of Orthopaedics, University of British Columbia and Vancouver Coastal Health Research Institute, Room 3114, 910 West 10th Avenue, Vancouver, BC V5Z 4E3, Canada
Investigation performed at the University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, British Columbia, Canada
Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the Canadian Arthritis Network Trainee Fellowship (PhD level) and the Canadian Institutes of Health Research. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Background: Abnormal varus-valgus alignment is a risk factor for patellofemoral osteoarthritis, but tibiofemoral alignment alone does not explain compartmental patellofemoral osteoarthritis progression. Other mechanical factors, such as patellar kinematics, probably play a role in the initiation and progression of the disease. The objective of this study was to determine which three-dimensional patellar kinematic parameters (patellar flexion, spin, and tilt and patellar proximal, lateral, and anterior translation) are associated with varus and valgus alignment in subjects with osteoarthritis.
Methods: Ten individuals with knee osteoarthritis and varus (five subjects) or valgus (five subjects) knee alignment underwent assessment of three-dimensional patellar kinematics. We used a validated magnetic resonance imaging-based method to measure three-dimensional patellar kinematics in knee flexion while the subjects pushed against a pedal with constant load (80 N). A linear random-effects model was used to test the null hypothesis that there was no difference in the relationship between tibiofemoral flexion and patellar kinematics between the varus and valgus groups.
Results: Patellar spin was significantly different between groups (p = 0.0096), with the varus group having 2° of constant internal spin and the valgus group having 4.5° of constant external spin. In the varus group, the patellae tracked with a constant medial tilt of 9.6° with flexion, which was significantly different (p = 0.0056) from the increasing medial tilt (at a rate of 1.8° per 10° of increasing knee flexion) in the valgus group. The patellae of the valgus group were 7.5° more extended (p = 0.0093) and positioned 8.8 mm more proximally (p = 0.0155) than the varus group through the range of flexion that was studied. The pattern of anterior translation differed between the groups (p = 0.0011).
Conclusions: Our results suggest that authors of future large-scale studies of the relationships between knee mechanics and patellofemoral osteoarthritis should not rely solely on measurements of tibiofemoral alignment and should assess three-dimensional patellar kinematics directly.
Clinical Relevance: Direct measurements of patellar kinematics should be used to investigate links between patellofemoral joint mechanics and the development of patellofemoral osteoarthritis.
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