THE “ISCHIAL LIMB”, AN ULTRASONIC LANDMARK TO ASSESS REDUCTION IN DEVELOPMENTAL DYSPLASIA OF THE HIP.

Abstract

The standard plane imaging of Graf and the dynamic methods of Harcke are well established methods in assessing hip dysplasia but give limited information in the flexed-abducted treatment position used in the Pavlik harness. The femoral head may sit on the edge of the acetabulum in a flexed position and only reduce when the hips are abducted. This may mean that hips, which reduce when abducted in the Pavlik harness, appear subluxed when scanned in neutral abduction. Harness treatment may thereby be abandoned prematurely due to the failure to confirm reduction. This study identifies ultrasound landmarks on an anterior hip scan which could be used to confirm reduction of the hip in Pavlik Harness.

Hips of a newborn piglet were scanned, imaged with magnetic resonance and x-rayed both before and after anatomical dissection. Radiographic markers delineated the position of the tri-radiate cartilage and potential ultrasound landmarks identified to help confirm hip reduction in the flexed-abducted position. Porcine imaging was then compared with that of a human newborn.

The porcine model corresponded well to human imaging and we were able to establish a landmark, the “Ischial Limb”, which corresponds to the ossification front delineating the posterior ischial edge of the tri-radiate cartilage. This could clearly be seen on anterior hip ultrasound of both the porcine and human hip. This landmark can be used to confirm the hip is reduced by reference to the centre of the femoral head.

We would recommend anterior hip scanning using the “Ischial Limb” as a reference point to confirm hip reduction in Pavlik harness. This simple method is a useful adjunct to conventional ultrasound scanning in the harness treatment of hip instability.