CASE 12652 Published on 19.04.2015

Stress reaction of the femoral neck complicating contralateral transient synovitis


Paediatric radiology

Case Type

Clinical Cases


Vermaelen M1, Vanhoenacker FM1,2,3 Mulier E4.

1. Department of Radiology, AZ Sint-Maarten, Mechelen-Duffel, Belgium
2. Department of Radiology, University Hospital Ghent, Ghent, Belgium
3. Department of Radiology, University Hospital Antwerp, Edegem, Belgium
4. Department of Paediatric orthopaedics, AZ Sint-Maarten, Mechelen-Duffel, Belgium

7 years, male

Area of Interest Musculoskeletal joint, Paediatric, Musculoskeletal bone ; Imaging Technique Ultrasound, MR
Clinical History
A 7-year-old boy presented with right knee pain and limping. Ultrasound (US) revealed an effusion in the right hip. Plain radiography was normal. After initial successful treatment with weight-bearing restriction and nonsteroidal anti-inflammatory drugs (NSAID) the patient presented with recurrent limping and fluid effusion in both hips on US.
Imaging Findings
Initial US (Fig. 1) showed an effusion within the right hip with increased distance between the anterior joint capsule and the femoral neck.

Repeated US after recurrence of symptoms revealed a subtle fluid effusion within both hips. Persistent synovitis warranted MRI 9 weeks after initial presentation.

MRI of the pelvis confirmed a subtle bilateral effusion. There were no arguments for Perthes disease or slipped capital femoral epiphysis (SCFE). MRI (Fig. 2), however, revealed bone marrow oedema within the medial aspect of the left femoral neck in keeping with a grade 3 stress reaction according to Fredericson. [1] Repeated questioning revealed excessive antalgic hopping on the left leg while the right leg was submitted to weight-bearing restriction. Clinical examination at the time of MRI showed left hip pain on palpation and mobilisation.

Follow-up MRI after 6 weeks (Fig. 3) without any weight bearing showed near complete resolution of the bone marrow oedema.
Transient synovitis of the hip is a frequent, usually self-limiting joint inflammation. Aetiology is unclear, but viral, allergic and traumatic causes have been proposed. [2]

It typically occurs in children aged 3 to 8. [3] Symptoms include limited range of motion (ROM) and unwillingness to bear weight. [4] Septic arthritis may be differentiated from TS by analysis of additional parameters such as severity of symptoms, presence of fever or toxic appearance and laboratory analysis. [2]

Although radiography is the first step in the diagnostic algorithm of hip pain, they are negative in TS. US is the preferred technique for identifying a joint effusion and for follow-up. MRI does not have an established place in the acute setting, but may become necessary when symptoms persist. [4, 5]

Therapy with NSAID may shorten the duration of symptoms. [6] In the event of protracted course or recurrence, subsequent MRI to exclude Perthes disease is warranted. [3] To the best of our knowledge a contralateral stress reaction of the femoral neck, complicating an antalgic gait has not yet been described.

Paediatric femoral neck stress fractures are rare. There are two types: the compression-sided at the medial aspect of the femoral neck and the tension-sided at the superolateral aspect, which has a worse prognosis. They commonly present with hip pain or limping. Increased or repetitive activity is not always evident in the clinical history. A fracture line on plain films might not be present at the onset of symptoms and signs of bone healing only become apparent after 3 to 4 weeks. MRI is much more sensitive for early detection. Stress reactions on MRI can be classified into 4 grades according to Fredericson. A grade 1 reaction shows mild to moderate periosteal oedema on fat suppressed (FS) T2-weighted images (WI). Grade 2 corresponds to marked periosteal oedema combined with bone marrow oedema on FS T2-WI. In grade 3 there is bone marrow oedema on both pulse sequences. When a fracture line is present, it is considered grade 4. Grading is prognostic for expected time to recovery. Bone scintigraphy has an equal sensitivity but is far less specific. [1, 7]

Treatment options include conservative therapy with restriction of weight bearing until ROM is pain-free for compression-sided fractures. For refractory compression-sided or tension-sided fractures, reduction and internal fixation is the therapy of choice. [7]
Differential Diagnosis List
Femoral neck stress reaction grade 3
Perthes disease
Septic arthritis
Final Diagnosis
Femoral neck stress reaction grade 3
Case information
DOI: 10.1594/EURORAD/CASE.12652
ISSN: 1563-4086