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Measuring the Acetabular Index: An Accurate and Reliable Alternative Method of Measurement
Benjamin Sherman1,2, Francois D Lalonde1, John A Schlechter1,2
1Children's Hospital of Orange County, Orange, CA.
Insights
A new method for measuring the acetabular index in children improves accuracy and reliability for diagnosing developmental hip dysplasia. This alternative technique offers a more consistent assessment than the traditional method.
Area of Science:
- Pediatric Orthopedics
- Radiology
- Developmental Dysplasia of the Hip
Background:
- Radiographic acetabular index measurement is standard for assessing developmental hip dysplasia in children aged 4 months to 8 years.
- The traditional acetabular index method faces criticism due to variable reliability stemming from difficulties in identifying anatomical landmarks, particularly the triradiate cartilage.
Purpose of the Study:
- To evaluate the accuracy and reliability of a proposed alternative method for measuring the acetabular index.
- The alternative method utilizes the ischium as a reference point to mitigate landmark identification variability.
Main Methods:
- Children aged 4 months to 8 years undergoing evaluation for developmental hip dysplasia were included.
- Two physicians independently measured acetabular indexes using both the traditional and alternative methods on pelvic radiographs.
- Accuracy was defined as a mean absolute error < 6°, and reliability was assessed using the intraclass correlation coefficient (ICC).
Main Results:
- The alternative method demonstrated a mean absolute error of 2.50°, significantly below the 6° threshold (p < 0.001).
- Intrarater reliability was very high for the alternative method (ICC = 0.92) compared to the traditional method (ICC = 0.81).
- Interrater reliability was also very high for the alternative method (ICC = 0.91) versus the traditional method (ICC = 0.89).
Conclusions:
- The alternative method for measuring the acetabular index exhibits very high accuracy.
- This novel approach demonstrates superior intrarater and interrater reliability compared to the traditional method.
- The proposed technique offers a more reliable radiographic assessment for developmental hip dysplasia in pediatric patients.
Abstract:
OBJECTIVE. In children (4 months to 8 years old), radiographic measurements of the acetabular index are the preferred method to assess developmental hip dysplasia. However, the acetabular index has been criticized as having variable reliability owing to difficulty identifying the correct anatomic landmarks. An alternative method of measuring the acetabular index using the ischium is being proposed to avoid the variability of the triradiate cartilage line as a reference point. With the alternative method, the acetabular index is derived by measuring the angle between a line connecting the ischial tuberosi-ties and a line connecting the inferomedial and superolateral edges of the acetabulum. The purpose of this study was to evaluate the accuracy and reliability of this alternative method of measuring the acetabular index compared with the traditional method. MATERIALS AND METHODS. Children 4 months to 8 years old who presented for evaluation of developmental dysplasia of the hip were included. Two physicians, each using both the traditional and the alternative method, measured acetabular indexes on all radiographs. Accuracy was defined as mean absolute error less than 6°. Reliability was calculated by means of intraclass correlation coefficient (ICC). RESULTS. Pelvic radiographs of 40 children (324 hips) were included. The mean age was 23.7 months (range, 4-96 months) and mean acetabular index was 24.2° (range, 8-50°). The alternative method was associated with mean absolute error of 2.50°, which is significantly below the threshold of 6° (t < 0.001). Intrarater reliability for the traditional method was high (ICC, 0.81) and for the alternative method was very high (ICC, 0.92). Interrater reliability for the traditional method was high (ICC, 0.89) and for the alternative method was very high (ICC, 0.91). CONCLUSION. Measuring the acetabular index using the alternative method has very high accuracy and intrarater and interrater reliability.
