Capturing patient-reported area of knee pain: A concurrent validity study using digital technology in patients with patellofemoral pain

Background: Patellofemoral pain (PFP) is often reported as a diffuse pain at the front of the knee during knee-loading activities. A patient's description of pain location and distribution is commonly drawn on paper by clinicians, which is difficult to quantify, report and compare within and between patients. One way of overcoming these potential limitations is to have the patient draw their pain regions using digital platforms, such as personal computer tablets. Objective: To assess the validity of using computer tablets to acquire a patient's knee pain drawings as compared to paper-based records in patients with PFP. Methods: Patients (N = 35) completed knee pain drawings on identical images (size and colour) of the knee as displayed on paper and a computer tablet. Pain area expressed as pixel density, was calculated as a percentage of the total drawable area for paper and digital records. Bland-Altman plots, intraclass correlation coefficient (ICC), Pearson's correlation coefficients and one-sample tests were used in data analysis. Results: No significant difference in pain area was found between the paper and digital records of mapping pain area (p = 0.98), with the mean difference = 0.002% (95% CI [-0.159-0.157%]). A very high agreement in pain area between paper and digital pain drawings (ICC = 0.966 (95% CI [0.93-0.98], F = 28.834, df = 31, p < 0.001). A strong linear correlation (R² = 0.870) was found for pain area and the limits of agreement show less than ±1% difference between paper and digital drawings. Conclusion: Pain drawings as acquired using paper and computer tablet are equivalent in terms of total area of reported knee pain. The advantages of digital recording platforms, such as quantification and reporting of pain area, could be realized in both research and clinical settings.