Abstract
The purpose of this study was to identify imaging risk factors on contrast-enhanced hip MRI after closed reduction of developmental dysplasia of the hip (DDH) that could predict future development of avascular necrosis (AVN) of the femoral head. Fifty-eight infants (F: M = 53: 5, aged 3-18 months) who underwent immediate postoperative contrast-enhanced hip MRI after closed reduction of DDH were included in this study. Quality of reduction (concentric vs eccentric reduction with or without obstacles), abduction angle of the hip, presence of ossific nucleus, and pattern of contrast enhancement of the femoral head were retrospectively evaluated on MRI. Interobserver agreement of contrast enhancement pattern on MRI were evaluated by two radiologists. Development of AVN was determined through radiographic findings at 1 year after reduction. AVN of the femoral head developed in 13 (22%) of 58 patients. Excessive abduction of the hip joint (OR 4.65, [95% CI 1.20, 18.06] and global decreased enhancement of the femoral head (OR 71.66, [95% CI 10.54, 487.31]) exhibited statistically significant differences between the AVN and non-AVN groups (P < 0.05). Eccentric reduction (P = 0.320) did not show statistically significant difference between two groups and invisible ossific nucleus (P = 0.05) showed borderline significance. Multi-variable logistic regression indicated that global decreased enhancement of the femoral head was a significant risk factor of AVN (OR 27.92, 95% CI [4.17, 350.18]) (P = 0.0031). Interobserver agreement of contrast enhancement pattern analysis and diagnosis of AVN were good (0.66, 95% CI [0.52, 0.80]). Contrast-enhanced hip MRI provides accurate anatomical assessment of the hip after closed reduction of DDH. Global decreased enhancement of the femoral head could be used as a good predictor for future development of AVN after closed reduction of DDH.
Highlights
Closed reduction and spica casting under general anesthesia is a common treatment for infants with developmental dysplasia of the hip (DDH) who fail initial nonsurgical management or those who present late [1,2,3]
Excessive abduction of the hip joint (OR 4.65, [95% confidence interval (CI) 1.20, 18.06] and global decreased enhancement of the femoral head exhibited statistically significant differences between the avascular necrosis (AVN) and non-AVN groups (P < 0.05)
Global decreased enhancement of the femoral head could be used as a good predictor for future development of AVN after closed reduction of DDH
Summary
Closed reduction and spica casting under general anesthesia is a common treatment for infants with developmental dysplasia of the hip (DDH) who fail initial nonsurgical management or those who present late [1,2,3]. The reported incidence of AVN has varied widely from 6% to 47% [4,7,9] This may be attributed to the lack of consensus on the specific radiographic features that define AVN in DDH. The most widely-used classification of AVN is that from Salter et al [10] who defined five characteristic radiographic findings at 1 year after reduction. Several factors such as excessive hip abduction, intra-articular obstacles that block concentric reduction, absence of an ossific nucleus, and age at reduction have been postulated to associate with development of AVN [7,8,11,12]
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