Protocol for MRI of the hips after spica cast placement.
BACKGROUND
In reduction of hip displacement in developmental dysplasia, concentric placement of the femoral head within the acetabulum is key. Magnetic resonance imaging (MRI) is an effective modality to assess the adequacy of the reduction, but sedation may be required due to the length of the examination. MRI is also more expensive than other imaging modalities. Our goal was to provide an MRI protocol that does not require sedation and can be performed in <15 minutes.


METHODS
We retrospectively reviewed 34 consecutive MRI studies performed without sedation after spica cast placement in 24 developmental hip dysplasia patients. The MRI examinations were performed with a variety of techniques. Sequences used were evaluated for contrast, resolution, and motion artifact.


RESULTS
Ninety-seven percent of studies were diagnostic, although 18% of examinations had significant motion artifact. Seven sequences were analyzed. T2-weighted fast spin echo sequences had the best overall scores and were performed in <3 minutes. T1 and fat-suppressed T2-weighted fast spin echo sequences did not score as well, and also required <3 minutes. Single-shot fast spin echo sequences scored poorly due to decreased contrast and resolution, despite shorter acquisition times of 20 to 40 seconds. Three-dimensional (3D) gradient recovery imaging scored poorly due to lower contrast and increased motion due to longer acquisition times of approximately 4 minutes. Both coronally and axially oriented sequences satisfactorily assessed femoral head position within the acetabulum.


CONCLUSIONS
MRI is a useful tool in evaluating the hips without radiation exposure and without sedation in infants and toddlers after spica cast placement. Both axial and coronal T2 fast spin echo MRI sequences provided excellent anatomic definition and required ≤3 minutes per sequence. Orthopaedic surgeons can request these 2 sequences for accurate assessment of concentric reduction with a potential study time of 15 minutes, obviating the need for sedation.


METHODS
Level II.
Department of Medical Imaging, Alfred I. duPont Hospital for Children, Wilmington, DE 19899, USA. sgould@nemours.org
Sharon W
SW
Gould
Leslie E
LE
Grissom
Anastasia
A
Niedzielski
Heidi H
HH
Kecskemethy
J Richard
JR
Bowen
H Theodore
HT
Harcke
D000077:Acetabulum; D002370:Casts, Surgical; D005260:Female; D005270:Femur Head / Q000473:pathology*; D006618:Hip Dislocation, Congenital / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007223:Infant; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012189:Retrospective Studies; D013997:Time Factors