265. BRODIE ABSCESS: A MISLEADING BONE INFECTION: 10 CASES

Abstract

Purpose of the study: Brodie abscess is a purulent collection in the centre of a bone separated in its typical form from soft tissue by an impermeable barrier of compact bone tissue. This “trapped” collection causes a clinical syndrome of pain and infection. Lat diagnosis is frequent after the symptoms have evolved over months or years. The purpose of our work was to illustrate the misleading features of this bone infection using a series of 11 periarticular localisations of Brodie abscess.

Material and methods: Our study included ten patients, mean age 18 years, who were treated over a period of six years. One patient had a double localisation. The main foci were the distal femur (n=4) and the upper tibia (n=4). There was one case involving the lower tibia, on in the olecranon and one in an iliac bone. The clinical course was greater than one year in three patients, and greater than one month in four others. The clinical presentation was a septic arthritis of the knee joint in three patients and of the hip in one, with rupture of the abscess into the soft tissues in three cases and a central intra-osseous collection in four. Biological features of infection were present in all patients. Imaging (x-ray, CT) showed a bone defect in the metaphyseal or metaphyseal epiphyseal region in all cases with condensed contours and a fistulous tract to a joint or soft tissue. Surgical treatment was proposed in all cases to treat the causal lesion by saucerisation and drainage of the intra-osseous abscess. The defect was filled with an autologous graft in one case and by cement in another. The germ identified in 70% of the cases was a Staphylococcus aureus. Adapted antibiotics were delivered for eight weeks on average.

Results: One patient had a secondary fistula which developed early after excision of a central abscess of the proximal tibia; dry drainage was achieved after cover with a medial gastrocnemian flap. At mean 27 months follow-up, all lesions have cured without recurrence; blood tests returned to normal. Radiographically, the defect exhibited bone remodelling visible in the absence of surgical filling. Regarding function, there was one stiff knee due to adherence on the extensor system.

Discussion: The Brodie abscess is a form of chronic osteomyelitis. It is a rare condition generally observed in young subjects since the majority of reported cases have occurred during the second decade of life. Clinically, the Brodie abscess can be “cold” with little or no overt expression, or more readily “hot” with a syndrome of acute infection and fistulisation to soft tissue. Fistulisation to a joint can mislead the diagnosis to septic arthritis as occurred in one of our patients who underwent two revisions for septic recurrent arthritis of the knee. Most Brodie abscesses are located in the metaphysic. A double metaphyseal and epiphyseal localisation through the growth plate is rare, resulting from an old septic process with inevitable joint collection as in one of our patients aged ten years. Discovery of a second concomitant localisation can be explained by an insufficient or inadequate treatment of the initial focus as we also observed in one case. The classical radiographic image of a Brodie abscess is observed in only two-thirds of the cases. Computed tomography is highly contributive demonstrating possible infra-radiographic fistulisation to a joint or soft tissue as occurred in most of our patients. The Brodie abscess can also simulate bone tuberculosis, hydatic cyst, or bone tumour. Surgically, we adopted to therapeutic strategies: excision of the infected bone associated or not with a cancellous graft and per primam closure for cold abscesses. We have considered that cold abscesses are generally cause by germs with weak virulence; this attitude enables avoiding superinfection. The second option is excision with dressing with or without secondary cancellous graft after budding used for hot abscesses, especially when complicated by a soft tissue complication. Search for germs in blood cultures and in the excision produce was only positive in half of our cases. Staphylococcus was identified in 90%. A histology examination of the excision specimen should be systematically requested to confirm the diagnosis. Finally, the outcome of a well-treated Brodie abscess is favourable.

Conclusion: Brodie abscess is a rare condition observed in young subjects generally due to Staphylococcus aureus. Cold and hot abscesses can be differentiated by their clinical and therapeutic features. Often misleading, clinical symptoms can be detailed with modern imaging, particularly important when the radiographic aspect is atypical. A biopsy is indispensable to confirm the diagnosis.