Comparative Study of Ultrasound vs. MRI in Diagnosing Pediatric Hip Dysplasia

Pediatric hip dysplasia is one of the musculoskeletal disorders that are the most prevalent during infancy and, when not treated, may cause gait anomalies, long-term pain, and early osteoarthritis. Identification at an early stage is hence very important and imaging has become a key central figure in the process of ruling out clinical suspicions. The use of ultrasound has long been the first method of diagnosis during the first few months of life as it allows visualization of the cartilaginous structures, non-radiation, and is easily applicable to the screening programs provided on a regular basis [1-3].

Although it has its benefits, ultrasound has known shortcomings. The precision of diagnostics can be affected by operator dependence, positioning and distinguishing mild dysplasia and physiological immaturity. MRI, however, offers a clear picture of the acetabular cartilage, labrum and the coverage of the femur head without overly depending on the position of the patient. Due to these reasons, MRI is also increasingly utilized as a test in cases of the borderline, incongruent ultrasound results and more detailed anatomical analysis is needed in determining treatment [4-6].

It is important to compare the strengths of both modalities in order to establish how they can be combined in the diagnostic pathways. There have been previous studies indicating variability in sensitivity and specificities and the extent of MRI changing clinical management is a significant factor of consideration [7-9]. This paper attempted to give a renewed comparison of ultrasound and MRI with a prospective cohort of infants and young children and not only compare their diagnostic performance but also their effects on decisions of treatment.

Eighty two children who had ultrasound and MRI assessment were studied and assessed to have suspected pediatric hip dysplasia. The proportion of instances detected as dysplasia by ultrasound was larger than that detected by MRI, but MRI offered greater degree of visualization of the acetabular cartilage and labral morphology. Demographic characteristics, findings of imaging and diagnostic performance are summarized in the following tables.

Early screening trends were evident with majority of children being below one year old. There was a female slight over preponderance which is in line with established epidemiology of hip dysplasia. A bilateral participation was found in almost 1/3 of the sample.

Table 1. Demographic Profile of Study Participants (n = 82)

Higher percentages of hips were deemed to be dysplastic according to α-angle and type of Graf by ultrasound. MRI, in its turn, proved to be better at visualizing labral abnormalities and femoral head coverage. There were statistically significant differences between detection of structural abnormalities (p < 0.05).

Table 2. Imaging Findings on Ultrasound and MRI

The reference standard of diagnostic accuracy comprised MRI. The ultrasound showed a sensitivity level of high with a moderate specificity showing a tendency to overcall mild dysplasia. The general diagnostic agreement was good ( 0.72).

Table 3. Diagnostic Accuracy of Ultrasound (Using MRI as Reference)

MRI results changed the course of treatment among some children that were initially mild or borderline on ultrasound. This was a statistically significant change that was clinically relevant. Further complicated intervention was to be used in case of more severe structural anomalies detected by MRI.

Table 4. Change in Clinical Management after MRI

Figure 1. Comparison of Ultrasound and MRI Findings in Pediatric Hip Dysplasia (n = 82).

Figure shows the occurrence of positive cases identified by ultrasound and MRI in three categories of diagnoses related to hip dysplasia, labral abnormalities, and subluxation/ dislocation. MRI found more labral abnormalities and cases of subluxation and ultrasound found slightly more hips dysplastic in general.

This comparative study compared the diagnostic capabilities of ultrasound and MRI in pediatric hip dysplasia within a period of one year and gained an insight into the complementary advantages of the two modalities. A higher percentage of the dysplastic hips was detected by ultrasound, which is sensitive to the initial cartilaginous changes, and which is the initial imaging method of a child. MRI was however found to be more proficient in describing more deep-lying structural abnormalities especially labral morphology and acetabular cartilage arrangement leading to more sophisticated severity evaluations [10-12].

The result that ultrasound had high sensitivity (95.5) with moderate specificity (75.7) is consistent with the literature that reported that early hip immaturity may be overdiagnosed as dysplasia particularly in borderline cases of Graf categories. As the reference standard, MRI reclassified a number of borderline and mild cases by detailing the coverage and status of the reduction of the femoral head. This is the reason why the percentage of cases (23.2) in which MRI results changed the clinical management plan is huge and particularly in infants who need to be escalated to bracing, closed reduction, or surgery [13-15].

The fact that MRI is better able to identify labral abnormalities (39% vs. 22% on ultrasound) highlights its usefulness in the evaluation of cases in which the results of ultrasound remain unclear or do not coincide with the clinical picture. As labral hypertrophy or inversion may affect stability and treatment choices, MRI can not be replaced since the symptoms may not disappear despite the normal or questionable ultrasound findings. Simultaneously, the non-invasive aspect, absence of radiations, portability and high accessibility of ultrasound render it as the best first line of investigation in large scale screening [16-18].

Although MRI provided more anatomical details, it is more expensive, time consuming to acquire and requires sedation in some cases, which reduces its clinical usage. Thus, a screening approach with ultrasound and a complex or treatment-resistant case with MRI seems to be the most suitable [19, 20]. This complementary nature is supported by the good correspondence between the two modalities ( 0.72) and this justifies the use of ultrasound as a primary diagnostic tool with MRI added to determine the severity and management as required.

Ultrasound still forms a very sensitive and useful first-line imaging method of diagnosing pediatric hip dysplasia and especially in infancy. Despite the less accessibility, MRI has the advantage of giving critical anatomy and enhancement of diagnostic assurance in cases of borderline, complex, or treatment-planning. The structured stepwise utilization of both modalities leads to better accuracy, confined misclassification, and aids in better clinical decision-making in the development of the hip in young children.

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