Is the Gothic Arch a reliable radiographic landmark for migration percentage in children with cerebral palsy?

Abstract

Introduction: Reimers migration percentage (MP) is the gold standard for measuring hip displacement in children with cerebral palsy (CP). Hip surveillance registries proposed using the top of the Gothic arch (GA) as a modification in patients with acetabular dysplasia because the classical method (CM) described by Reimers may underestimate hip migration. The aim of this study is to assess the inter- and intra-observer reliability of the modified method (MM) versus the CM and identify their effect on the MP.

Methods: We performed a retrospective review of 50 children with CP, who had a hip radiograph at our institution between 1st April 2014 and 28th February 2018. All hip radiographs were carefully selected to show the presence of a GA. Four observers measured the MP using the CM and MM for each patient. Interclass coefficient was used to estimate inter- and intra-observer reliability.

Results: Inter-observer reliability was excellent for the CM with ICC 0.96 (95% CI 0.94 to 0.97) and good for the MM, ICC 0.78 (95% CI 0.51 to 0.89) p < 0.001. Intra-observer reliability was excellent for both methods raging from ICC 0.94 to 0.99 for the CM and ICC 0.89 to 0.95 for the MM. The mean MP was 19% for the CM and 28% for the MM (p < 0.001).

Conclusion: The CM is more reliable than the MM to measure hip migration in children with CP. If the CM is used and acetabular dysplasia with a GA are present on the hip radiograph, then a 9% hip migration underestimation should be considered on decisions for both referral and surgical management.

Level of evidence: II.

Keywords: Gothic arch; Reimer’s migration percentage; cerebral palsy; hip displacement; hip migration.

Fig. 1.

Graphical depiction of Reimers migration percentage.8 Hilgenreiner’s line (H) is a horizontal line that enables orientation of the pelvis in the horizontal plane. Perkins line (P) is a line which runs from the lateral edge of the roof of the acetabulum. The migration percentage is the part of the femoral head that extends beyond this line.

Fig. 2.

(a)Bombelli’s description of a Gothic arch as a characteristic feature of a normal AP hip radiograph. The base of the Gothic arch is formed by the sourcil, while the medial side of the arch represents an arc of dense cancellous bone extending from the quadrilateral plate towards the anterior superior and anterior inferior iliac spines, while the trabeculae forming the lateral side of the arch extend from the lateral acetabular ridge toward the sacroiliac joint. (b) In a normal hip, the apex of the Gothic arch lies directly above the centre of the femoral head on an AP pelvis radiograph. (c) Picture of Gothic arch obtained from personal photo.

Fig. 3.

Graphical representation of the MM for calculating the migration percentage utilized the top of the ‘Gothic arch’ in case of a dysplastic acetabulum (B) and the P (Perkins) line will therefore run more medial than the CM on the right (A). H represents Hilgenreiner’s line

Fig. 4.

The red arrow shows the top of Gothic arch, where the apex of acetabulum is located in case of dysplasia in children with CP.

Fig. 5.

Hip radiograph in patient with CP with the datum points and lines (shown in green) using the TraumaCad software. The Amber line represents Hilgenreiner’s line.

Fig. 6.

This is a hip radiograph of a child with CP, found to have a left dislocated hip and a right migrated hip. This is an example where decision making for surgical treatment will be influenced by the method chosen to measure Reimer’s migration as the MM shows a right hip migration of 48% while the CM shows a right hip migration of 39% (underestimation of 9%). Some surgeons would not choose to operate on the right hip unless there is migration over 40%. Green: Hilgenreiner’s line; red: Perkin’s line; blue: inner and outer margins of ossific nucleus; yellow: Gothic arch.

Fig. 7.

This is an example where decision making for referral to a specialist centre for further management will be determined by the method chosen to measure Reimer’s migration. The MM shows of a right hip migration of 37% while the CM a right hip migration of only 28% (9% migration underestimation), which means that using the CM in this case could cause delay to referral and appropriate management. Green: Hilgenreiner’s line; red: Perkin’s line; blue: inner and outer margins of ossific nucleus; yellow: Gothic arch.