Reliability of Radiographic Assessments of the Hip in Cerebral Palsy

Abstract

Introduction: Children with cerebral palsy are at risk for progressive hip displacement. Since surveillance for hip displacement uses specific radiographic measurements to guide decision making, it is important to establish the reliability of these measurements, which include Reimer’s migration percentage (MP), acetabular index or acetabular angle (AI or AA), and pelvic obliquity (PO). The purpose of this study was to determine the intraobserver and interobserver reliability of these radiographic measures among an international group of pediatric orthopaedic surgeons participating in the prospective international multicenter Cerebral Palsy Hip Outcomes Project (CHOP) currently underway to evaluate the outcomes of hip interventions in cerebral palsy. Methods: Two compact discs (CDs) containing the same 25 anteroposterior pelvis radiographs in Digital Imaging and Communications in Medicine (DICOM) format were provided to participating surgeons at least 2 weeks apart. To reduce the likelihood of recall or any effects of learning or fatigue, the order of the radiographs varied on the 2 CD versions, and participating surgeons received the 2 CDs in random order. The intraclass correlation coefficients (ICCs) were calculated to assess interobserver and intraobserver reliability. Mean absolute differences of hip measurements obtained at 2 time points were also calculated. Results: The MP had the highest reliability followed by PO, AI, and AA with a mean intrarater ICC (SD; range) of 0.95 (0.04; 0.84 to 0.98); 0.92 (0.03; 0.85 to 0.97); 0.84 (0.05; 0.75 to 0.92); and 0.82 (0.14; 0.51 to 0.98); respectively. The mean interrater ICC (SD; range) for MP, PO, AI, and AA were 0.94 (0.05; 0.78 to 0.99); 0.90 (0.04; 0.76 to 0.99); 0.79 (0.08; 0.52 to 0.93); and 0.69 (0.23; 0.42 to 0.98) for MP, PO, AI, and AA, respectively. The mean (SD; 95% confidence interval) for the absolute difference between the 2 measurements for the raters was 4.9% (2.9%; 3.4%-6.4%); 3. 8 degrees (1.2 degrees; 3.1-4.5 degrees); 2.6 degrees (1.5 degrees; 1.7-3.5 degrees); and 1.3 degrees (0.3 degrees; 1.29-1.31 degrees) for MP, AI, AA, and PO, respectively. Conclusions: MP is a reproducible measure with excellent intrarater and interrater reliability. However, differences in MP of <7% should be treated with caution as these might be a consequence of measurement error. Although we found a high level of intrarater and interrater reliability of the AI, AA, and PO, these measurements are more variable and not ideal for use as discrete outcome measures. Instead, these parameters might be useful for prognostication and decision making when consistent trends are observed longitudinally over time which might be better indications of true change.

Outcome of Femoral Varus Derotational Osteotomy for the Spastic Hip Displacement: Implication for the Indication of Concomitant Pelvic Osteotomy

“…The MP, AI, NSA, and HSA showed good to excellent intra-observer and inter-observer reliabilities (Table 1). These results were comparable to the values reported in the literature [36][37][38].…”

Inter-rater and Intrarater Reliabilities of the Identification of a “Gothic Arch” in the Acetabulum of Children With Cerebral Palsy

“…Previous reports have described the inter-rater and intrarater reliabilities of measuring MP in children with CP as good to excellent. 12 Most recently, Shore et al 25 reported high reliability in measuring MP among 15 international experts. However, they noted that MP exceeded a SD of 10% in 8 of 50 hips and the only factor that was associated with this variability was the presence of a gothic arch (6/8 hips).…”

The migration percentage measured on EOS® standing full-leg radiographs: equivalent and advantageous in ambulant children with cerebral palsy

“…Reimers estimated a standard measuring error of ± 10% due to the limited calcification of the femoral head in young children and difficulties in defining the lateral acetabular rim in larger children. Several authors already demonstrated a high inter- and intraobserver reproducibility and intraclass correlation coefficient when measuring the MP, these analyses were not performed as this was not the goal of this study [7–9, 16]. A recent study compared the classic MP with a modified MP using a vertical line at the lateral edge of the acetabular sourcil instead of the Perkin’s line.…”