A recent study evaluated the use of computed tomography (CT) versus magnetic resonance imaging (MRI) to determine hip position in the spica cast after closed reduction of dislocated hips in infants with hip dysplasia.[1]
Thirty-nine patients less than 13 months of age with hip dislocations underwent hip reduction under anesthesia. After reduction and cast application, patients either had a CT or MRI of the hips. Hips were classified as dislocated, subluxated (mildly displaced), or reduced. The hips that were dislocated were reduced by surgical intervention, but the displaced hips were observed. Two thirds of the subluxated hips reduced spontaneously with continued treatment in the cast.
The authors determined that the CT or the MRI were both accurate to assess the position of the hip. Average cost of CT examination was less than that for MRI. Radiation dose was understandably higher with CT, but there was greater need for sedation in the MRI group.
Comments:
Post-reduction assessment of hip dysplasia with imaging techniques like CT and MRI is being increasingly used in various hip centers. Some centers even advocate using the same anesthesia to transfer the patient to an imaging suite for study right after the procedure. However, other centers prefer to let the infant awaken to make sure the hip stays in the socket without general anesthesia.
It should be noted that the reason for the MRI or CT after closed reduction is because closed reduction is not always successful even for the most experienced orthopedic surgeons. Reported failure of closed reduction occurs in 5%-20% of patients depending on the age of the child, severity of the dislocation and on other variables. One useful finding of this study is that most subluxations will improve spontaneously although one third did not improve and needed additional treatment. Failures following closed reductions are all well-described outcomes and known setbacks that do not necessarily suggest poor surgeon technique or sub-optimal care.
Definitions:
- Sensitivity: Defined as the probability that the test says a person has the disease when in fact they do have the disease.
- Specificity: Defined as the probability that the test says a person does not have the disease when in fact they are disease free.
- False Positive: A false positive occurs when the test reports a positive result for a person who is disease free.
- False Negative: A false negative occurs when the test reports a negative result for a person who actually has the disease.
