The "ischial limb": a landmark on anterior ultrasound scanning used to assess reduction in developmental dysplasia of the hip

Abstract

BACKGROUND: Early recognition of failure of reduction during abduction splinting in developmental dysplasia of the hip (DDH) is essential to avoid inappropriate prolonged damaging harness use. Graf ultrasound scanning (USS) is an accepted gold standard for assessing neonatal hip dysplasia but cannot verify reduction in the abducted position of a neonatal hip in a Pavlik harness. We describe a new anatomic landmark of the hip using anterior USS-the "ischial limb," correlate this to the position of the femoral head in reduced and dislocated positions, and assess the application of this in the assessment of DDH. METHODS: A porcine model was used to identify anatomic, radiologic, and ultrasonic features comparable to the human neonatal hip. A pilot clinical study was conducted of 50 neonates (11M:39F) treated for DDH in Pavlik harness, utilizing weekly anterior USS to determine the concentricity of femoral head reduction relative to the ischial limb and whether this could identify any failures to achieve reduction. RESULTS: The animal model identified an ultrasound landmark, termed the ischial limb that represents the ossification zone of the ischial contribution to the tri-radiate acetabular cartilage, and approximates to the center of the acetabulum. Anterior USS clearly demonstrated this ischial limb in clinical practice and its relation to the femoral head in all dysplastic hips (n=79). Immediate concentric reduction was observed in 11 patients, more gradual reduction over 3 weeks in 37 patients, and failure to achieve stable reduction was verified in 2 patients. The technique was reproducible in 100% of patients (n=50). Mean additional clinic time was 5 minutes per visit. CONCLUSIONS: The ischial limb, identified on anterior hip USS, delineates the position of the tri-radiate cartilage. This technique efficiently assesses hip reduction during Pavlik harness treatment and can differentiate between failure to achieve reduction or maintain a stable reduction at an earlier stage than conventional US methods. LEVEL OF EVIDENCE: Development of diagnostic criteria on basis of consecutive patients: level 2 evidence.