CASE 18506 Published on 27.03.2024

Chronic osteomyelitis with bone sequestrum and cutaneous fistula in a previous femur fracture

Section

Musculoskeletal system

Case Type

Clinical Case

Authors

Ana Luísa Pinto 1, Alexandra Tavares Ferreira 2

1 Radiology Services, Hospital do Divino Espírito Santo, Ponta Delgada, Azores, Portugal

2 Radiology Services, Hospital Dona Estefânia, Centro Hospitalar Universitário de Lisboa Central, Lisbon, Portugal

Patient

15 years, male

Categories
Area of Interest Musculoskeletal bone, Paediatric ; Imaging Technique Conventional radiography, CT, MR
Clinical History

A 15-year-old boy born in West Africa with a left femur fracture 1 year ago, treated conservatively with casting immobilisation, is now admitted to the hospital with leg pain and purulent cutaneous drainage. Blood tests revealed high c-reactive protein and erythrocyte sedimentation rate, and exudate culture revealed meticillin-susceptible Staphylococcus aureus.

Imaging Findings

The initial imaging evaluation was done with plain radiography that revealed signs of a fracture with malalignment, marked cortical thickening and an endomedullar bone fragment, suspicious for chronic osteomyelitis with bone sequestrum (Figures 1a and 1b). A computed tomography was also performed and proved morphostructural changes of the diaphysis of the femur, with inadequate fracture consolidation, cortical sclerosis and multiple bone sequestra, the biggest one with 10cm (Figure 2).

The MRI results confirmed the suspicion of chronic osteomyelitis, revealing exuberant bone marrow oedema, intraosseous abscess and bone sequestra (Figure 3a). There are also areas of cortical bone disruption (cloacae), that allow communication of the intraosseous abscess with an intramuscular abscess along the inner part of vastus intermedius muscle, as well as the cutaneous surface through two fistulous tracts (Figures 3b, 3c and 3d). There is also significant muscle oedema of vastus intermedius and lateralis consistent with myositis (Figure 3b).

Discussion

Osteomyelitis is defined as bone infection, that usually results from haematogenous dissemination, continuous spread from soft tissues and joints or direct inoculation from open fractures or post-surgical procedures [1,2]. Staphylococcus aureus is the cause of 80% to 90% of infections, and in children, the inferior limbs are more commonly affected [3,4].

Clinical presentation is variable according to age, but local swelling, pain and movement reduction are the most common symptoms, especially in the acute phase [2].

Chronic osteomyelitis is a process that results from an inadequately treated bone infection, usually with more than 6 weeks from the onset, with consequent bone necrosis due to the disruption of intraosseous and periosteal blood supply at the acute stages, with the formation of sequestrum, that consists of an isolated fragment of necrotic bone. The isolation of this fragment from blood supply prevents the antibiotics from acting, originating a nidus of chronic infection [3]. An involucrum is a layer of living bone surrounding a sequestrum, that can become perforated by tracts, via an opening called cloaca. These tracts may dissect to the skin surface, originating sinuses or fistulas that drain the pus out of the bone [4]. A Brodie abscess is an intraosseous abscess and is also a common feature of chronic osteomyelitis [2].

Imaging workup is essential in a timely diagnosis and in assessing the extent of the infectious process. Plain radiography is normal in the first 10 to 20 days after the onset of the infection, but in chronic osteomyelitis, a bone sequestrum may be visible as a focal sclerotic lesion with a lucent rim, as in our case [3,5].

Computed tomography is more sensitive for osseous changes than radiography, and contrast enhancement is useful for abscesses detection.

MRI is the gold standard for a suspicion of osteomyelitis, with high sensitivity for bone marrow oedema and fluid collections – high signal on fluid-sensitive sequences such as T2w and STIR and low signal intensity on T1w images. Contrast administration is helpful for detecting abscesses, fistulas and epiphyseal involvement [3].

Treatment for osteomyelitis is done with long-lasting intravenous antibiotics, but in chronic cases, a surgical procedure may be needed [6]. In our case, a surgical debridement was performed, with cement application with gentamicin in the osseous defect, and later a graft of cancellous bone from the iliac crest, with internal fixation. The patient had a positive clinical recovery, without significant deficits and with fracture consolidation.

Written informed law tutor consent for publication has been obtained.

Differential Diagnosis List
Ewing sarcoma
Osteosarcoma
Bone lymphoma
Chronic osteomyelitis with bone sequestrum and cutaneous fistula
Langerhans cell histiocytosis
Chronic recurrent multifocal osteomyelitis (CRMO)
Final Diagnosis
Chronic osteomyelitis with bone sequestrum and cutaneous fistula
Case information
URL: https://eurorad.org/case/18506
DOI: 10.35100/eurorad/case.18506
ISSN: 1563-4086
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