MRI in idiopathic, stable, slipped capital femoral epiphysis: evaluation of contralateral pre-slip

Abstract

Purpose: Early diagnosis and treatment of slipped capital femoral epiphysis (SCFE) is important to prevent slip progression and avoid complications. We sought to determine if MRI findings in patients with unilateral SCFE could indicate 'pre-slip' or predict future SCFE in the contralateral hip.

Methods: A prospective study evaluated patients with unilateral SCFE over a two-year period. MRI of the asymptomatic hip was performed within the perioperative period. Patients were followed with radiographs until a contralateral slip occurred or until physeal closure. Demographics, clinical stability, severity, posterior slope angle (PSA), modified Oxford Bone Score (mOBS) and patency of the triradiate cartilage were recorded and statistical analysis performed.

Results: In all, 33 of 54 patients with unilateral SCFE were enrolled into the study. In all, 29 (87.8%) had complete follow-up. Five of the enrolled patients (15.2%) developed a sequential slip requiring in situ pinning. Six of 33 (18.2%) patients had positive MRI findings: four of which proceeded to sequential SCFE and two which did not. One sequential slip had a negative MRI. PSA predicted 1/11 sequential slips (sensitivity 9.09%, specificity 81.4%, positive predictive value (PPV) 11.1%, negative predictive value (NPV) 77.8%) and mOBS predicted 5/11 sequential slips (sensitivity 45.5%, specificity 93%, PPV 62.5%, NPV 87%). An open triradiate cartilage was present in 8/11 patients with sequential slips (sensitivity 72.7%, specificity 81.4%, PPV 50%, NPV 92.1%).

Conclusion: MRI findings consistent with 'pre-slip' were present in 66.7% of patients who developed a sequential SCFE. Further study on the utility/sensitivity of MRI in predicting sequential SCFE is warranted.

Level of evidence: II, diagnostic.

Keywords: MRI; asymptomatic hip; modified Oxford Bone Score; posterior slope angle; slipped capital femoral epiphysis.

Fig. 1

Axial diffusion weighted images. Physis is clearly increased in signal (a) on the diffusion image (white arrow). Radial oblique Proton Density Fat Saturated image (b). This image is obtained by obtaining six radial images perpendicular to the femoral physis. This technique will assure a good image with both the proximal femoral physis (PFP) and greater trochanteric physis (GTP) on the same image. Note that the PFP (blue) is brighter than the GTP (red), representing a ‘pre-slip’. The dark line is an artifact of the 392 technique (green).

Fig. 2

Preoperative anteroposterior/lateral radiographs (a,b) revealing mild, stable SCFE on left hip; normal radiograph on asymptomatic right hip; positive MRI on radial oblique image consistent with bilateral disease (c).

Fig. 3

Approximately four months postoperative; patient presents with pain; x-ray changes (a–c) consistent with sequential SCFE requiring in situ fixation.