The relationship between knee radiographs and the timing of physical therapy in individuals with patellofemoral pain

Background: Routine knee radiographs are discouraged for individuals with nontraumatic knee pain, but they are often still ordered despite limited evidence of their value in guiding treatment choices. Radiograph utilization may delay the use of physical therapy, which has been associated with improved outcomes and lower long-term costs. Objective: To examine the relationship between obtaining knee radiographs for patients with patellofemoral pain (PFP) and the timing of physical therapy, and the association between ordering radiographs for patients who use physical therapy and the likelihood of knee pain recurrence. Study Design: Retrospective cohort. Setting: United States Military Health System civilian and military clinics. Patients: A total of 23,332 individuals ages 18 to 50 years who were diagnosed with PFP between 2010 and 2011 in the United States Military Health System and who received physical therapy. Interventions: Physical therapy provided to individuals with or without an initial radiograph. Main Outcome Measures: Timing of physical therapy and recurrence of knee pain were compared between groups (with and without initial radiographs). Results: If radiographs were obtained, the odds of initiating physical therapy (adjusted odds ratio [aOR] 0.78, 95% confidence interval [CI] 0.64–0.94) within 30 days of the initial diagnosis were significantly lower. The mean days from diagnosis to initiating physical therapy was 12.1 (95% CI 9.1–16.1) if patients had radiographs versus 6.9 (95% CI 5.2–9.1) without. The odds of knee pain recurrence were no greater if radiographs were used (aOR 1.01, 95% CI 0.83–1.22). Conclusions: Acquisition of knee radiographs as part of initial care for PFP was associated with delayed initiation of physical therapy, but there was no association between early knee radiographs and recurrence of knee pain. Routine use of radiographs for PFP is not warranted, and can potentially delay appropriate treatment.