Abstract
ABSTRACTPatellofemoral (PF) osteoarthritis (OA) is a prevalent and clinically important knee OA subgroup. Malalignment may be an important risk factor for PF OA. However, little is known about alignment in PF OA, particularly in an upright, weightbearing environment. Using a vertically‐oriented open‐bore MR scanner, we evaluated 3D knee alignment in 15 PF OA cases and 15 individually matched asymptomatic controls. We imaged one knee per participant while they stood two‐legged at four flexion angles (0°, 15°, 30°, 45°), and also while they stood one‐legged at 30° knee flexion. We calculated 3D patellofemoral and tibiofemoral alignment. Using mixed effects models, four of the five patellofemoral measures differed by group. For key measures, PF OA patellae were 6.6° [95%CI 5.0, 8.2] more laterally tilted, 2.4 mm [1.3, 3.5] more laterally translated, and at least 3.7 mm [0.2, 7.2] more proximally translated compared to controls (more with knees flexed). Alignment did not differ between two‐legged stance and one‐legged stance in either group. Statement of Clinical Significance: Our study demonstrated significant and clinically relevant differences in alignment between PF OA cases and controls in upright standing and squatting positions. Our findings were similar to those in previous studies of PF OA using traditional MR scanners in supine positions, supporting the clinical usefulness of existing methods aimed at identifying individuals who may benefit from interventions designed to correct malalignment. © 2019 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. 9999:1–9, 2019.
Highlights
Patellofemoral (PF) osteoarthritis (OA) is highly prevalent[1] and is associated with substantial pain, reduced function, and lower quality of life.[2–5] Knee OA often begins at the patellofemoral joint, preceding multicompartment disease.[6–8] An international consortium[9] in 2017 posited that knee malalignment may increase patellofemoral joint stress, leading to OA
The patella is generally positioned in more lateral tilt, lateral displacement, and proximal displacement compared to knees without PF OA-related structural features
We aimed to evaluate upright 3D knee alignment to test the following hypotheses: (i) the patella would be more laterally displaced and tilted, and more proximally translated, in PF OA compared to matched controls and (ii) lateral displacement and tilt, and proximal translation, would be greater in one-legged stance than in two-legged stance
Summary
Patellofemoral (PF) osteoarthritis (OA) is highly prevalent[1] and is associated with substantial pain, reduced function, and lower quality of life.[2–5] Knee OA often begins at the patellofemoral joint, preceding multicompartment disease.[6–8] An international consortium[9] in 2017 posited that knee malalignment (both patellofemoral and tibiofemoral) may increase patellofemoral joint stress, leading to OA. The patella is generally positioned in more lateral tilt, lateral displacement, and proximal displacement compared to knees without PF OA-related structural features. Studies recruiting individuals with PF OA to investigate these relationships were rare11,15—most often, the target population was knee OA or tibiofemoral OA.[14]. An asymptomatic non-OA comparison group was included in just one study,[11] rendering it challenging to determine effect sizes of malalignment in PF OA compared to asymptomatic knees. It is clinically important to investigate between-group differences in upright positions to determine how alignment behaves in functional positions. In the few upright MRI studies of patellofemoral pain or instability, alignment is worse compared to controls.[18–20]. It is unknown if similar findings exist in upright, weightbearing positions in PF OA In the few upright MRI studies of patellofemoral pain or instability, alignment is worse compared to controls.[18–20] It is unknown if similar findings exist in upright, weightbearing positions in PF OA
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