Subacute Osteomyelitis (Brodie Abscess) Treatment & Management

Treatment of subacute osteomyelitis depends on the diagnosis. Almost one third of cases (the group that was categorized by Ross and Cole as aggressive lesions^[21] ) are indistinguishable from primary malignant bone tumors. Biopsy and curettage are required for diagnosis in these cases.

Once the diagnosis is established, appropriate antibiotics (with the dose adjusted according to the patient's weight and age) based on Gram stain, culture, and sensitivity results should be initially started intravenously for 2-7 days, followed generally by 6 weeks of oral antibiotics. (Consultation with pediatric or adult infectious diseases specialists is recommended for the appropriate antibiotic dose, route, and duration.) Clinical and laboratory (ESR and CRP) monitoring of clinical improvement is appropriate. Ezra et al reported their criteria for changing from intravenous to oral antibiotics to be marked cessation of pain, subsidence of swelling, and functional improvement.^[22]

In cases in which clinical and imaging findings and laboratory results are characteristic (ie, the diagnosis is not uncertain), although controversial, treatment with antibiotics alone may be undertaken as suggested by Bogoch et al,^[24] Ross and Cole,^[21] Andrew and Porter,^[25] Martin,^[27] Hamdy et al,^[26] Ezra et al,^{[22, 23]} and Gonzalez-Lopez et al.^[3] In the literature, opinion differs as to whether treatment for these classic lesions should be surgical or medical.

Although most of the available pediatric orthopedic literature supports medical treatment, no literature regarding treatment in adults is available to support either medical or surgical treatment (apart from recommending biopsy); most orthopedic surgeons treating adults feel more comfortable with surgical treatment. Ross and Cole reported an 87% success rate and Ezra et al reported a 96% success rate with a single course of medical treatment.^{[21, 22]}

Hoffman et al found that medical treatment with only biopsy (no curettage) was successful in every case of diaphyseal subacute osteomyelitis they treated (biopsy was required to exclude malignancy).^[33] In another study, Ezra et al reported a 90% success rate in medically treating subacute osteomyelitis in tarsal bones.^[23] Failure of resolution of symptoms after a course of antibiotics of up to 6 weeks or worsening of the condition during treatment should lead to reevaluation and a definite tissue diagnosis, bacteriologic diagnosis, or both, followed by surgical treatment and appropriate antibiotics.

Other indications for surgery are impending sinus formation or drainage into a synovial joint. Clinical signs of subperiosteal pus or synovitis indicate that the subacute infection has transformed into an acute component, and it must be drained surgically. If treating empirically, use a broad-spectrum antibiotic that covers S aureus first and other pathogens secondarily. Coverage should be considered for H influenzae in young children who have not been immunized adequately.

Antibiotics administered orally for osteomyelitis must be given in doses that often are 2-3 times that of those recommended in the agents' package inserts. Patient (or parent) education is essential to maintain the compliance that is required for successful treatment. Absorption of the antibiotic to produce effective concentrations at the site of infection is documented by measuring the concentration of the antibiotic or the antibacterial activity in serum.

In case of the aggressive subacute osteomyelitis lesion which is indistinguishable from a tumor, open biopsy for culture and histology is indicated. Other lesions are incised and drained when indicated, the granulation tissue present in the lesion is curetted and cultured, and antibiotics are started immediately after biopsy.

In pediatric patients with typical cavities in the metaphysis, the epiphysis, or in both, surgery is undertaken only for specific indications. When clinical signs of subperiosteal pus are present, incision and drainage is performed. When clinical signs of synovitis are present, with a possibility of pus within a joint, arthrotomy is performed and synovium is sent for culture and histology studies. If metaphyseal or epiphyseal cavities communicate with the joint they are curetted. Curettage of cavities is also indicated if the symptoms and signs of infection persist during conservative treatment or if they recur. Curettage of metaphyseal cavities should be carried out carefully, and perforations in the growth plate should not be curetted, because curettage of the metaphyseal lesion usually decompresses the epiphyseal lesion.

Ross and Cole reported all epiphyseal cavities in their study healed with a single course of antibiotics and immobilization without operation.^[21] However, when drainage was indicated, the procedure was not performed through the growth plate. Green et al described curetting epiphyseal lesions after localization by inserting a needle into the epiphysis and obtaining 2 plane radiographs, then making a 2- to 3-mm drill hole to avoid the weight-bearing or the articulating portion of the epiphysis.^[34] In the proximal femoral epiphysis, the drill hole has to be intracapsular as far distally as possible to avoid the portion of the femoral head that articulates with the acetabulum while avoiding the growth plate. In the distal femoral epiphysis, the drill hole also has to be intraarticular but avoid the weight-bearing articular surface coming medially or laterally.

Diaphyseal lesions may be difficult to treat surgically. In patients with these lesions, the clinical picture is more likely to resemble a tumor, and a surgical biopsy is necessary for diagnosis, which should include adequate periosteum, cortical bone, and medullary tissue. These usually respond to adequate antibiotic therapy. In those cases with inadequate response to medical treatment, exposure of the whole length of the affected bone is indicated, with excision or exposure of all abscess cavities to remove dead bone. The wound is sutured primarily and antibiotics started.

If surgery is undertaken for subacute osteomyelitis lesions that measure more than 3 cm or in cases in which bone is weak and subject to fracture, the cavity could be filled with bone graft or bone graft substitutes (either primary bone grafting,^[35] if the surgeon was happy about the total excision of the abscess cavity to eliminate the dead space, or, more appropriately, delaying bone grafting until the antibiotic treatment is completed and the infection is believed to have been eradicated based on clinical and laboratory results).

Other options include the temporary use of antibiotic cement beads and the use of other alternatives to autologous bone graft, such as antibiotic-laden bone graft substitutes. A drain is generally indicated to avoid hematoma or seroma accumulation, which can lead to recurrent abscess.

In epiphyseal lesions especially, protection of the joints, either with traction or with splinting, and starting protected motion early is a consideration (with intermittent removal of the splint or traction for early range-of- motion exercises). Due to the proximity of the cavity to the articular surface and the risk of collapse, limitation of weight bearing is indicated until evidence of partial healing of the defect is seen on radiographs.

Follow-up in cases of subacute of osteomyelitis should continue for at least 2 years. In the first week, closely monitor for signs of response to treatment (clinical and laboratory). Monitor for compliance with antibiotic therapy for 6 weeks. Clinical response is usually within a few days of initiation of treatment. In the first 6 months, monitor for signs of recurrence. Most recurrences occur within 6 months, but recurrence after up to 18 months has been reported.

Radiologic healing is slower than clinical healing and usually occurs within 3-12 months. Metaphyseal and epiphyseal cavities usually disappear or heal, leaving either a small area of sclerosis or a small, indistinct lucency in the cortex. The purpose of follow-up after a year is mainly for assessment of bone growth and alignment, although physeal growth is very rarely affected.

In pediatric cases of subacute osteomyelitis, 24% of infants younger than 1 year experience complications, compared with 8.5% of older children.^[13] In epiphyseal or epiphyseal-metaphyseal lesions, due to the proximity of the cavity to the articular surface, risk of collapse exists, as does risk of pus discharge into the joint; Ross and Cole reported 2 such cases, one of the hip and one of the ankle joint.^[21] Effusions into the hip joint were also reported by Ross and Cole in 2 patients who had closed cavities in the femoral neck.^[21] Injury to the growth plate during surgical (curettage) treatment is also a possibility. In large lesions, especially the diaphyseal lesions, the involved bone might become weak and prone to fracture after surgical treatment.

Ross and Cole reported recurrence in 3 of 32 patients.^[21] Ezra et al reported recurrence in 1 of 21 patients treated with antibiotics only^[22] ; all of their patients responded to curettage and antibiotics. Stephens and MacAuley reported that the age and sex of the patient, size of the abscess, and length of intravenous therapy did not influence the rate of recurrence, but they noted more recurrences in patients who were given a shorter course of antibiotics (2-3 wk) and in patients with an initial high ESR level (mean of 30 mm/h in the recurrence group compared with a mean of 8 mm/h in the group without recurrences).^[35]

Although frequently located adjacent to the epiphyseal plate, subacute osteomyelitis rarely results in retardation or stimulation of growth, with Gonzalez-Lopez et al reporting a single case of 15-mm growth stimulation (these lesions are quiescent lesions and hyperemia is minimal)^[3] and Ross and Cole reporting a single case in a child with a metaphyseal and epiphyseal lesion of the proximal femur that resulted in growth retardation.^[21]

Despite evidence of penetration of the physis by the abscess, growth impairment is extremely rare. Subacute abscesses that traverse the epiphyseal plate do so in only one small cross-sectional area, which may explain the absence of bony bridging. Growth disturbance, thus, seems unlikely based on all the recorded experience with this condition. That stated, Lindenbaum and Alexander reported a case with varus recurvatum deformity of the knee (a metaphyseal-epiphyseal lesion that was present for more than 3 years before treatment).^[5] Stephens and MacAuley reported coxa vara in 1 patient, mild shortening (7 mm and 15 mm) in 2 patients, and growth stimulation in 2 patients (7 mm and 10 mm).^[35]

Subacute osteomyelitis is difficult to diagnose, but, once diagnosed, it is a curable disease with a 100% cure rate. Hamdy et al reported their results in treating 44 patients^[26] of which 24 were treated with antibiotics only, and 20 had surgical debridement followed by antibiotics. With the exception of 1 patient who received inadequate antibiotic therapy, all patients responded well, regardless of whether treatment was conservative or surgical. At an average follow-up of 18 months, no recurrences and no damage to the physis were reported.^{[26, 36]}

No good outcome studies have been reported as of yet, but from the available literature (apart from the previously mentioned rare complications), the outcome of subacute osteomyelitis is excellent, and full recovery is the rule in most cases.

Subacute osteomyelitis treatment remains controversial. Some investigators agree that a conservative course of antibiotic therapy is preferred. In lesions with an aggressive character in which a tumor cannot be excluded, surgery is indicated to establish the diagnosis. Diagnostic experience and awareness of the condition significantly reduce the indications for surgery from an approach in which biopsies are taken of all lesions, to an approach in which biopsies are taken of only selected lesions.

Development of molecular assays for the direct detection of microorganisms has been an actively growing specialty. Amplification techniques such as those using polymerase chain reaction (PCR) should provide increased sensitivity because of the extensive amplification of target nucleic acid to identify the RNA or DNA of viruses, bacteria, and other microorganisms in patients' blood. At present, however, these techniques are not widely available.