Most patients present to the ED with acute exacerbations of chronic low back pain. Risk factors for a serious condition are common, but rarely do they develop. Racial disparities and psychosocial factors had concerning relationships with clinical decision-making.

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Disclosures: M. Fredericson, Coolsystems, Inc, Consulting fees or other remuneration. Objective: To test the hypothesis that measures of patellar maltracking, tilt, and bisect offset, correlate with vastus medialis onset delays in patellofemoral pain (PFP) subjects classified as maltrackers. Design: Post hoc cohort study. Setting: Three-dimensional motion analysis laboratory, magnetic resonance (MR) imaging laboratory. Participants: 55 subjects: 15 healthy controls and 40 subjects with patellofemoral pain (PFP). Interventions: Not applicable. Main Outcome Measures: Correlations between electromyography (EMG) activation onset delay of vastus medialis (VM) muscle compared with vastus lateralis and patellar maltracking measures, tilt, and bisect offset. The subjects with PFP were classified into nonmaltrackers and maltrackers based on their tilt and bisect offset measurements. Anticipatory EMG activations during the swing phase of walking were analyzed. Tilt and bisect offset were measured from images acquired in an open-configuration MR scanner with a subject upright and the knee near full extension. Results: Subjects classified as maltrackers with both abnormal tilt and abnormal bisect offset demonstrated a significant relationship between VM onset delay and patellar tilt (R2ϭ0.89, PϽ.001). Approximately 38% of the PFP subjects (15 of 40) were classified as maltrackers, with 8 subjects having both abnormal tilt and abnormal bisect offset. Conclusions: The etiology of PFP is unclear. It has been theorized that delay in VM activity onset causes lateral maltracking of the patella, resulting in elevated stress and pain in the PF joint; however, evidence relating muscle onset delay to maltracking of the patella is sparse. The results of this study demonstrate a significant relationship between VM onset delay and patellar maltracking in subjects classified as maltrackers with both abnormal tilt and abnormal bisect offset. This implies that a clinical intervention such as VM retraining may be effective only in a subset of subjects with PFP, those with excessive tilt and excessive bisect offset measures.