CASE 10770 Published on 22.03.2013

CT imaging of acetabular changes in Perthe\'s disease.

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

B Ashiq Zindha

Ramnad MRI and CT Scans, Ramnad, India; Email:dr_ashiqzindha@yahoo.co.in
Patient

9 years, male

Categories
Area of Interest Musculoskeletal bone ; Imaging Technique CT
Clinical History
A 9 year old male child presented with history of pain in the right hip region for the past 3 months associated with limping. No history of trauma was elicited.
Imaging Findings
The epiphysis of the right femoral head appeared thin and significantly fragmented in comparison to the left side.The right femoral neck appeared expanded with lucent areas in the metaphyseal region. A well-defined lucent/cystic lesion was also noted in the posteromedial aspect of the femoral metaphysis adjacent to the physeal plate. These features were highly suggestive of Perthe's disease involving the right femur.
The mediolateral thickness of the floor of the right acetabulum on axial CT images appeared less in comparison to the left side. A sharply demarcated step was seen on axial images at the interface of the posterior border of the acetabular fossa and the posterior lunate surface of the acetabulum. The left acetabular fossa showed a smooth posterior border. The mediolateral thickness of the triradiate cartilage at the level of the acetabular floor on coronal images appeared more on the right side in comparison to the left side.
Discussion
Legg Calve Perthe’s disease (LCPD) is a form of idiopathic osteonecrosis or osteochondrosis involving the proximal femoral epiphysis and is one of the commonest causes of hip pain involving preadolescent children. It affects approximately 5.1 to 15.6 in 100,000 children usually between the ages of 2 and 14 years, affecting boys 5 times more commonly. About 15% of cases may be bilateral involving both hips asymmetrically. Three stages namely the avascular, revascularization and reparative stages have been described and imaging features vary depending on the stage of disease [1].
Findings in the avascular phase include an asymmetrically small femoral epiphysis, joint effusion and presence of a subchondral fracture also termed the crescent sign [2]. MRI may show signal changes and lack of enhancement within the epiphysis before CT and conventional radiographs [2]. In the later stages fragmentation or irregularity of the epiphysis, widening and shortening of the femoral neck and metaphyseal radiolucent or cystic lesions may show. These metaphyseal cysts occur due to metaphyseal extension of the unossified physeal plate [1, 2]. Presence of epiphyseal fragmentation, femoral neck widening and a metaphyseal cyst confirmed the diagnosis of LCPD in our case.
Although most of the characteristic imaging features described in LCPD involve the femoral aspect of the hip joint, characteristic acetabular changes have been reported. The medial wall of the acetabulum normally consists of a depressed acetabular fossa and flat lunate surfaces anterior and posterior to this fossa. The floor of the acetabular fossa on the affected side was thinner in comparison to the normal side on axial CT images. Sharp demarcation of the posterior border of the acetabular fossa from the posterior lunate surface of the acetabulum was also seen on axial images on the affected side whereas this border zone was smooth on the normal side. Coronal reformatted images revealed mediolateral thickening of the triradiate cartilage on the affected side in comparison to the normal side[3].
Ischemic changes in the femoral epiphysis cause synovitis and this synovial inflammation is thought to trigger triradiate and lunate surface cartilage hypertrophy. The acetabular fossa is normally devoid of cartilage. Pressure effect from the surrounding swollen soft tissues causes deepening of the acetabular fossa resulting in thinning of the floor and sharp posterior demarcation[3]. All above-described acetabular changes were seen in our case further confirming the diagnosis. Some authors have postulated the presence of acetabular changes in LCPD to be a poor prognostic feature[4].
Differential Diagnosis List
Legg Calve Perthe's disease on the right side.
Slipped capital femoral epiphysis.
Septic arthritis.
Transient synovitis of hip.
Final Diagnosis
Legg Calve Perthe's disease on the right side.
Case information
URL: https://www.eurorad.org/case/10770
DOI: 10.1594/EURORAD/CASE.10770
ISSN: 1563-4086