EVALUATION OF ALTERNATE RADIOGRAPHS TO REDUCE HIP SURVEILLANCE IMAGING IN CHILDREN WITH CEREBRAL PALSY

While risk associated with plain radiographs is low, efforts to limit lifetime radiation exposure are warranted. To reduce radiation exposure, x-rays completed for other purposes may be utilized for hip surveillance when the hips and pelvis are visible. This study aimed to evaluate hip positioning in alternate x-rays and whether migration percentage (MP) measured from alternative images is consistent with MP measured on anteroposterior (AP) pelvis radiographs. Children enrolled in a province population-based hip surveillance program who 1) had an alternate x-ray, defined as a non-AP pelvis radiograph that showed the hips and pelvis, and 2) had an AP pelvis taken prior to or after the alternate x-ray. An alternate x-ray was defined as a non-AP pelvis radiograph that shows the hips and pelvis. All participant data up until Janaury 2021 were reviewed. Radiographic data, including type and date of x-ray, MP, and acceptability of the imaging, as measured by degree of hip adduction/abduction from neutral and interforaminal ratio (IFR), were exported from the hip surveillance program's database. The mean difference in MP and standard deviation (SD) of the difference were calculated; influence of Gross Motor Function Classification Score (GMFCS) level and time between images were evaluated. Agreement was measured using Bland-Altman plots and summarized with the average difference and corresponding 95% confidence interval (CI). In total, 50 alternate x-rays were reviewed: 34 abdominal x-rays, 8 standing hips to ankle x-rays, and 8 scoliosis images. Images were from children at GMFCS levels I to V (1, 7, 3, 11, 28) at a mean age of 9yrs, 0mo (SD 4.0, range 1yr1mo to 16yrs2 mo). There were 73 pairs identified for comparison. Hip abd/adduction was categorized as acceptable or borderline (≤ 12 degrees from neutral) in 49% of the alternate x-rays and 80% of the AP pelvis x-rays; it could not be assessed in 26% of alternate x-rays and 3% of AP pelvis x-rays. IFR was acceptable (0.5–2.0) in 80% of alternative x-rays and 97% of AP pelvis radiographs; IFR could not be measured in 12% of alternate x-rays and <1% AP pelvis x-rays. The overall mean difference for MPs measured on 146 hips was −0.26 (SD 7.27). Mean differences did not differ by GMFCS or time between images. Bland Altman analysis found a mean difference of −0.26% (95% CI = −1.4, 0.9) with lower and upper limits of agreement being −14.5% (−16.5, −12.5) and 14% (12, 16). Positioning of non-AP pelvis radiographs was acceptable less than 50% of the time but MP values were consistent between the x-rays. Limits of agreement suggest not all images provide accurate measures of MP. The use of alternate radiographs can be appropriate for monitoring hip displacement while reducing lifetime radiation exposure and its associated risks and decreasing caregiver burden associated with repeated imaging.