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MR evaluation of hips following surgical reduction for developmental hip dysplasia: Are there quantitative and qualitative predictors of avascular necrosis?1Radiology, Children's Hospital of Philadelphia, Philadelphia, PA, United States, 2Radiology, Children's Hospital of Philadelphia, philadelphia, PA, United States
Synopsis
The purpose of our study is to investigate whether there are qualitative and quantitative imaging markers on the post reduction MR study that can predict the development of AVN using follow-up pelvic radiographs as reference standards. Post-reduction contrast-enhanced MR studies from thirty-seven infants with unilateral DDH were retrospectively reviewed which showed focally (27%) or globally decreased femoral head enhancement (22%). None of the clinical and imaging markers, including both qualitative and quantitative imaging factors present on the post reduction contrast-enhanced MR, can predict the future development of AVN, which sheds light on our incomplete understanding of the underlying pathophysiology.
Introduction
Untreated developmental dysplasia of the hip (DDH) is a risk factor for premature osteoarthritis. For cases that do not respond to conservation management, surgical reduction followed by spica cast immobilization is the standard of care with the goal to restore hip joint congruity. Globally decreased enhancement of the femoral head is a dreaded complication and has been linked to a 50% risk of avascular necrosis (AVN) in small study cohorts and using short-term radiographic follow-up (1). However, the true incidence for AVN at longer term follow-ups and the predictive values of various qualitative and quantitative imaging findings on post reduction contrast-enhanced MR studies remain indeterminate (2). Thus, the purpose of our study is to investigate whether there are qualitative and quantitative imaging markers on the post reduction MR study that can predict the development of AVN using follow-up pelvic radiographs as reference standards.Methods
This IRB-approved, HIPPA compliant study include all contrast-enhanced MR studies performed after hip reduction on patients with DDH between 2009 and 2017. Patients with neuromuscular disorders, congenital or syndromic musculoskeletal deformities, history or imaging findings of infection or trauma were excluded. Those without follow-up pelvic radiographs or with treated bilateral DDH were also excluded. For each patient, a pediatric radiologist retrospectively qualitatively assessed the MR study to determine the pattern of femoral head enhancement, categorized into globally decreased, focally decreased (Fig 1), or preserved enhancement (Fig 2), and the initial follow-up pelvic radiograph obtained after cast removal at around 1 year after reduction to identify features of AVN using the Salter classification. For patients with additional, longer radiographic follow-ups, the most recent pelvic radiograph was also assessed for interval femoral head growth, persistent, or new features of AVN. Quantitative assessment was performed by drawing regions of interest on the femoral head, greater trochanter (GT), and proximal femoral metaphysis of both normal and abnormal hips using the post-contrast images. Signal intensity enhancement ratios were calculated between the head and greater trochanter (head/GT) and between the head and proximal metaphysis (head/metaphysis). Hip abduction angles were also recorded. Descriptive information was presented as mean ± SD (range). Non-parametric tests and Chi-square were used with a p < 0.05 considered significant.Results
Thirty-seven infants with DDH (32 girls, 5 boys; mean age at surgery: 8.2 months ± 3.4, range 3 – 18) underwent either closed (n=33; 89%) or open (n=4; 11%) hip reductions. Post reduction MR studies showed preserved enhancement in 19 hips (51%), focally decreased enhancement in 10 hips (27%) and globally decreased enhancement in 8 hips (22%). Initial follow-up radiographs (mean months from surgery: 14.8 ± 3.5, range 11-24) showed features suggestive of AVN in 17 (46%). No significant association was identified between those with features of AVN and age at surgery (p=0.33), surgical approach (p=0.68), qualitative patterns of femoral head enhancement (p = 0.97), and hip abduction angle (p = 0.47), Table 1. The enhancement ratios were not significantly different between treated hips and the contralateral untreated hips (p=0.18) and between treated hips with and without features of AVN (p=0.84), Table 2. Twenty-five (68%) patients [NJC1] [BCCA2] had additional radiographic follow-ups (mean months from surgery: 46.7 ± 24.4, range 13-92). Of the 11 patients who had initial features of AVN, only 7 (55%) had persistent features of AVN.
Discussion
AVN of the femoral head is one of the most dreadful complications of treatment for DDH. Post reduction MR is becoming more routinely utilized to confirm adequate reduction and preserved femoral head perfusion. Although differences in prognosis between focal and diffusely decreased enhancement were previously demonstrated, our results failed to identify any relevant clinical or imaging markers that predict the development of AVN. This may be partially due to the fact that only 55% of abnormal hips with features of AVN on initial radiographs had persistent features at delayed radiographic follow-up, which questions diagnostic accuracy of the Salter classification to identify AVN a priori.
Conclusion
None of the clinical and imaging markers, including both qualitative and quantitative imaging factors present on the post reduction contrast-enhanced MR, can predict the future development of AVN, which sheds light on our incomplete understanding of the underlying pathophysiology and suggests additional undiscovered factors that influence the development of AVN.
Acknowledgements
No acknowledgement found.References
1. Tiderius C, Jaramillo D, Connolly S, Griffey M, Rodriguez DP, Kasser JR, et al. Post-closed Reduction Perfusion Magnetic Resonance Imaging as a Predictor of Avascular Necrosis in Developmental Hip Dysplasia. J Pediatr Orthop [Internet]. 2009 Jan [cited 2018 Nov 6];29(1):14–20. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19098638
2. Gornitzky AL, Georgiadis AG, Seeley MA, Horn BD, Sankar WN. Does Perfusion MRI After Closed Reduction of Developmental Dysplasia of the Hip Reduce the Incidence of Avascular Necrosis? Clin Orthop Relat Res [Internet]. 2016 May 20 [cited 2018 Nov 6];474(5):1153–65. Available from: http://www.ncbi.nlm.nih.gov/pubmed/26092677
Figures
Fig 2. Coronal post-contrast image from a 5 month-old girl after closed right hip reduction shows globally decreased enhancement of the right femoral head (arrow). Note the normally enhancing vascular channels within the contralateral left femoral head (arrowhead).
