Does Perfusion MRI After Closed Reduction of Developmental Dysplasia of the Hip Reduce the Incidence of Avascular Necrosis?

Abstract

Background: Gadolinium-enhanced perfusion MRI (pMRI) after closed reduction/spica casting for developmental dysplasia of the hip (DDH) has been suggested as a potential means to identify and avoid avascular necrosis (AVN). To date, however, no study has evaluated the effectiveness of pMRI in clinical practice or compared it with other approaches (such as postreduction CT scan) to show a difference in the proportion of AVN.

Questions/purposes: (1) Can a pMRI-based protocol be used immediately post closed reduction to minimize the risk that AVN would develop? (2) What are the overall hip-related outcomes after closed reduction/spica casting using this protocol? (3) Do any patient-specific factors at the time of closed reduction predict future AVN?

Methods: This was a retrospective cohort study at a large tertiary care children's hospital. Between 2009 and 2013 we treated 43 patients with closed reduction/spica casting for DDH, of whom 33 (77%) received a postreduction pMRI. All patients were indicated for pMRI per treating surgeon preference. A convenience sample totaling 25 hips in 22 patients treated with pMRI was then established using the following exclusion criteria: DDH of neuromuscular/syndromic origin, failed initial closed reduction, less than 1 year of clinical and radiographic followup, and subsequent open reduction. Next, the 40 patients treated with closed reduction between 2004 and 2009 were screened until the chronologically most recent 25 hips (after applying the previously mentioned exclusion criteria) were identified in 21 of the first 34 patients (62%) screened. Although termed the CT group, specific postreduction imaging was not a defined inclusion criterion in this group with the majority (21 of 25 [84%]) receiving postreduction CT and the remainder (four of 25 [16%]) receiving only postreduction radiographs. All hips with globally decreased femoral head perfusion on postreduction pMRI were treated with immediate cast removal followed by repeat closed reduction or open reduction, as per surgeon preference, with two of 33 (6%) requiring such further interventions. Salter criteria were then used to determine the proportion of AVN on radiographs at 1-year and final followup. Secondary outcomes including residual dysplasia and the need for further corrective surgery were ascertained through radiographic and retrospective chart review.

Results: At 1-year followup there was no difference in the proportion of AVN in the historical CT group as compared with the pMRI group (six of 25 [24%] versus one of 25 [4%]; odds ratio [OR], 7.6; 95% confidence interval [CI], 0.8-363; p = 0.098). However, by final followup there was a statistically higher proportion of AVN in the CT group (seven of 25 [28%] versus one of 25 [4%]; OR, 9.3; 95% CI, 1.0-438; p = 0.049). No patient with normal perfusion on postreduction pMRI went on to develop AVN. In those pMRI patients in whom a successful reduction was initially obtained, two of 25 (8%) went on to require further corrective surgery and one of 25 (4%) had a redislocation event. With the numbers available, no patient-specific factors at the time of closed reduction were predictive of future AVN, including the patient's age/weight, the presence of an ossific nucleus, history of previous bracing treatment, or the abduction angle in spica cast.

Conclusions: A pMRI-based protocol immediately after closed reduction/spica casting may decrease the risk of AVN by helping the surgeon to evaluate femoral head vascularity. Although preliminary in nature, this study could serve to guide further investigation into the potential role of pMRI for the treatment of patients who require closed reduction/spica casting for DDH.

Level of evidence: Level III, therapeutic study.

Figures

Fig. 1A–B

This flowchart depicts evaluation, exclusion, enrollment, and outcomes in the pMRI group (A) and the CT group (B).

Fig. 2A–D

Representative perfusion-MRI findings in four patients. Images are T1 axial post-gadolinium subtraction sequences, all following closed hip reduction and spica casting. (A) Symmetric epiphyseal vascular channels after left hip reduction. (B) Asymmetric vascular enhancement of the right epiphysis compared to the left side (arrow). (C) Focal, central, epiphyseal non-enhancement of left hip (arrow). (D) Global decreased perfusion of the right epiphysis (arrow).

Fig. 3A–C

Representative images of some hips meeting Salter criteria for AVN. (A) Salter 3—broadening of the femoral neck/metaphysis within 1 year of procedure  (B) Salter 4—fragmentation of the femoral head. (C) Salter 5—residual head/neck deformity.

Fig. 4

The International Hip Dysplasia Institute (IHDI) criteria are a means of classifying DDH disease severity even when the ossification center is absent [22]. To start, Hilgenreiner’s line (H-line) is drawn through the top of the triradiate cartilages bilaterally. Next, Perkin’s line (P-line) is drawn at the superolateral margin of the acetabulum perpendicular to the H-line. A diagonal line is then drawn 45° inferolaterally from the junction of the H-line and P-line. Finally, based on the location of the midpoint of the superior margin of the ossified metaphysis, as shown here with a black oval, the residual deformity may be graded from 1 to 4. In this example, the patient has an IHDI grade of 1.

Fig. 5A–D

The following is a case example of a pMRI-altered treatment course. (A) A 9-month-old girl had right hip DDH as demonstrated on AP pelvis radiograph. She subsequently underwent arthrogram, closed reduction, and spica casting. (B) The immediate postoperative pMRI demonstrated globally decreased perfusion of her right femoral epiphysis (arrow). Her cast was immediately removed and she had a repeat arthrogram and closed reduction 1 week later, at which time she was casted into less abduction. (C) Postreduction pMRI following the second attempt demonstrated symmetric enhancement of the vascular canals throughout the entire epiphysis and of the secondary ossification center (arrow). (D) Most recent AP pelvis radiograph demonstrates excellent interval femoral head development without signs of AVN. Of note, this patient is not included in the reported pMRI cohort as she was treated after the study’s timeframe.