Reliability of radiographic measurements for hip dysplasia using a reduced radiation technique

The purpose of this study was to examine whether measurement accuracy is impacted with a low radiation radiograph technique. Treatment decisions for hip dysplasia require serial radiographs to monitor acetabular anatomy. However, radiation use creates concern for future malignancy. Standard radiograph technique utilizes a grid to enhance clarity, but requires a larger X-ray dose. We hypothesized grid removal would lower radiation exposure without decreasing measurement accuracy. This is a retrospective cohort study of patients with idiopathic DDH and neuromuscular hip displacement at a single institution from 2019 to 2020 receiving surveillance radiographs. A cohort receiving modified technique radiographs (grid removed) was compared to an age-matched cohort receiving standard technique radiographs. Four examiners measured radiographs on two separate occasions, a minimum of 2 weeks apart. Migration percentage (MP) was measured for neuromuscular patients and acetabular index (AI) for idiopathic DDH. Intraclass correlation coefficient (ICC) with a 95% confidence interval (CI) was used to evaluate inter-observer and intra-observer agreement for measurements. Average radiation dose for both techniques. A total of 134 age-matched patients were included for measurement of MP. Thirty age-matched patients were included for AI measurements. Inter and intra-rater reliability of MP and AI were not different with or without use of the grid. There was a 50-75% decrease in radiation dose per radiograph following grid removal, dependent on patient size. The adjusted radiograph technique showed no significant difference in MP or AI reliability. A slight decrease in picture contrast did not jeopardize measurement reliability and decreased radiation exposure for the patient significantly. This simple technique can be useful for patients requiring multiple radiographs over time.