Abstract

Background: Acetabular index (AI) is the most commonly utilized radiographic measure for developmental dysplasia of the hip (DDH). However, there is variability in measurement of AI, thus impairing reproducibility. Frog-leg lateral (FL) positioning allows more consistent visualization of the acetabular sourcil compared with anteroposterior (AP). The purpose of this study is to determine if there is any difference in AI measurements on AP versus FL radiographs and if there is less measurement variability on FL than AP radiographs.

Methods: An IRB approved, retrospective study was performed on 274 hips that underwent screening AP and FL radiography for DDH. Radiographs were reviewed using a standard measurement technique. Interobserver measurement differences and the differences between measurements made on AP and FL radiographs were calculated.

Results: 233 (85%) were normal, and 41 (15%) had DDH. The average AI on AP vs FL was not significantly different (24.13 and 23.66 degrees, respectively; P = 0.147). There was a significant difference in measurement in variability for the interobserver difference for AI on AP (0.48 degrees; P = 0.001), whereas there was no significant difference for AI on the FL (0.18 degrees; P = 0.114).

Conclusion: AI had less variability on the FL view than the AP view, likely due to a more orthogonal projection of the sourcil creating a single sclerotic line with which to perform measurements. We recommend using the FL radiograph as a supplement to the AP radiograph for measuring AI for following up patients diagnosed with DDH.

Level of Evidence: Level III.

Keywords: Developmental Dysplasia of the Hip (DDH); Acetabular Index; Frog Lateral

References

1. Lehmann HP., et al. “Developmental dysplasia of the hip practice guideline: technical report. Committee on Quality Improvement, and Subcommittee on Developmental Dysplasia of the Hip”. Pediatrics4 (2000): E57.
2. Patel H. “Canadian Task Force on Preventive Health C. Preventive health care, 2001 update: screening and management of developmental dysplasia of the hip in newborns”. Canadian Medical Association Journal12 (2001): 1669-1677.
3. Clinical practice guideline: early detection of developmental dysplasia of the hip. Committee on Quality Improvement, Subcommittee on Developmental Dysplasia of the Hip. American Academy of Pediatrics”. Pediatrics4-1 (2000): 896-905.
4. Karmazyn BK., et al. “ACR Appropriateness Criteria on developmental dysplasia of the hip-child”. Journal of the American College of Radiology8 (2009): 551-557.
5. Aronsson DD., et al. “Developmental dysplasia of the hip”. Pediatrics2-1 (1994): 201-208.
6. Dezateux C and Rosendahl K. “Developmental dysplasia of the hip”. Lancet9572 (2007): 1541-1552.
7. Bertol P., et al. “Radiographic features of neonatal congenital dislocation of the hip”. The Journal of Bone and Joint Surgery British2 (1982): 176-179.
8. Barrera CA., et al. “Imaging of developmental dysplasia of the hip: ultrasound, radiography and magnetic resonance imaging”. Pediatric Radiology12 (2019): 1652-1668.
9. Garvey M., et al. “Radiographic screening at four months of infants at risk for congenital hip dislocation”. The Journal of Bone and Joint Surgery British5 (1992): 704-707.
10. Keller MS and Nijs EL. “The role of radiographs and US in developmental dysplasia of the hip: how good are they?” Pediatric Radiology2 (2009): S211-215.
11. Donaldson JS and Feinstein KA. “Imaging of developmental dysplasia of the hip”. Pediatric Clinics of North America3 (1997): 591-614.
12. Von Rosen S. “Early diagnosis and treatment of congenital dislocation of the hip joint”. Acta Orthopaedica Scandinavica2 (1956): 136-155.
13. Hauk L. “Developmental Dysplasia of the Hip in Infants: A Clinical Report from the AAP on Evaluation and Referral”. American Family Physician3 (2017): 196-197.
14. Gerscovich EO. “A radiologist's guide to the imaging in the diagnosis and treatment of developmental dysplasia of the hip. II. Ultrasonography: anatomy, technique, acetabular angle measurements, acetabular coverage of femoral head, acetabular cartilage thickness, three-dimensional technique, screening of newborns, study of older children”. Skeletal Radiology8 (1997): 447-456.
15. Grissom L., et al. “Imaging in the surgical management of developmental dislocation of the hip”. Clinical Orthopaedics and Related Research4 (2008): 791-801.
16. Vaquero-Picado A., et al. “Developmental dysplasia of the hip: update of management”. EFORT Open Reviews9 (2019): 548-556.
17. Laurenson RD. “The anatomic relationships of the bifurcation of the trachea”. Surgery, Gynecology and Obstetrics1 (1959): 103-104.
18. Tonnis D. “Normal values of the hip joint for the evaluation of X-rays in children and adults”. Clinical Orthopaedics and Related Research 119 (1976): 39-47.
19. Mladenov K., et al. “Natural history of hips with borderline acetabular index and acetabular dysplasia in infants”. Journal of Pediatric Orthopaedics5 (2002): 607-612.
20. Pirpiris M., et al. “The assessment of acetabular index: is there still a place for plain radiography?” Journal of Pediatric Orthopaedics3 (2006): 310-315.
21. Spatz DK., et al. “Measurement of acetabular index intraobserver and interobserver variation”. Journal of Pediatric Orthopaedics2 (1997): 174-175.
22. Caffey J., et al. “Contradiction of the congenital dysplasia-predislocation hypothesis of congenital dislocation of the hip through a study of the normal variation in acetabular angles at successive periods in infancy”. Pediatrics5 (1956): 632-641.
23. Yang S., et al. “Developmental Dysplasia of the Hip”. Pediatrics1 (2019).
24. Boniforti FG., et al. “The reliability of measurements of pelvic radiographs in infants”. The Journal of Bone and Joint Surgery British4 (1997): 570-575.
25. Broughton NS., et al. “Reliability of radiological measurements in the assessment of the child's hip”. The Journal of Bone and Joint Surgery British1 (1989): 6-8.
26. Kay RM., et al. “Variability in the assessment of acetabular index”. Journal of Pediatric Orthopaedics2 (1997): 170-173.
27. Portinaro NM., et al. “Errors in measurement of acetabular index”. Journal of Pediatric Orthopaedics6 (1995): 780-784.
28. Skaggs DL., et al. “Variability in measurement of acetabular index in normal and dysplastic hips, before and after reduction”. Journal of Pediatric Orthopaedics6 (1998): 799-801.
29. Van Der Bom MJ., et al. “Pelvic rotation and tilt can cause misinterpretation of the acetabular index measured on radiographs”. Clinical Orthopaedics and Related Research6 (2011): 1743-1749.
30. Tannast M., et al. “Estimation of pelvic tilt on anteroposterior X-rays--a comparison of six parameters”. Skeletal Radiology3 (2006): 149-155.
31. Fan M., et al. “Anteroposterior pelvic radiograph is not sufficient to confirm hip reduction after conservative treatment of developmental dysplasia of the hip”. Journal of Pediatric Orthopaedics B (2022).
32. Shin CH., et al. “Which Acetabular Landmarks are the Most Useful for Measuring the Acetabular Index and Center-edge Angle in Developmental Dysplasia of the Hip? A Comparison of Two Methods”. Clinical Orthopaedics and Related Research9 (2020): 2120-2131.
33. Kim HT., et al. “Diagnosing childhood acetabular dysplasia using the lateral margin of the sourcil”. Journal of Pediatric Orthopaedics6 (2000): 709-717.
34. Imrie M., et al. “Is ultrasound screening for DDH in babies born breech sufficient?” Journal of Children's Orthopaedics1 (2010): 3-8.
35. Konan S., et al. “Is the frog lateral plain radiograph a reliable predictor of the alpha angle in femoroacetabular impingement?” The Journal of Bone and Joint Surgery British1 (2010): 47-50.
36. Agus H., et al. “How should the acetabular angle of Sharp be measured on a pelvic radiograph?” Journal of Pediatric Orthopaedics2 (2002): 228-231.
37. Hudak KE., et al. “Variations in AP and frog-leg pelvic radiographs in a pediatric population”. Journal of Pediatric Orthopaedics2 (2013): 212-215.
38. Stubbs AJ., et al. “Classic measures of hip dysplasia do not correlate with three-dimensional computer tomographic measures and indices”. HIP International5 (2011): 549-558.