You are in: eMedicine Specialties > Orthopedic Surgery > KNEE Subacute Osteomyelitis (Brodie Abscess)Article Last Updated: Jul 18, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Khalid Khoshhal, MBBS, FRCS Ed, ABOS, Vice Dean, College of Medicine; Assistant Professor, Pediatric Orthopedic Surgery, Department of Orthopedics, Taibah University, Saudi Arabia Coauthor(s): Robert Mervyn Letts, MD, FRCS(C), FACS, Former Chief, Department of Surgery, Division of Pediatric Orthopedics, Children's Hospital of Eastern Ontario, University of Ottawa; Consultant Pediatric Orthopedic Surgeon, Sheikh Khalifa Medical City, UAE Editors: Charles T Mehlman, DO, MPH, Director, Musculoskeletal Outcomes Research, Associate Professor, Division of Pediatric Orthopedic Surgery, Cincinnati Children's Hospital Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Thomas M DeBerardino, MD, Director, John A Feagin, Jr, Sports Medicine Fellowship at West Point, Associate Professor of Orthopedic Surgery, Uniformed Services University of the Health Sciences and Keller Army Community Hospital; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Carlos J Lavernia, MD, FAAOS, Adjunct Clinical Professor, Department of Orthopedic Surgery, University of Miami School of Medicine; Medical Director, Orthopedic Institute at Mercy Hospital Author and Editor Disclosure Synonyms and related keywords: subacute osteomyelitis, subacute osteomyelitis prognosis, subacute osteomyelitis diagnosis, subacute osteomyelitis treatment, Brodie abscess, Brodie abscess prognosis, Brodie abscess diagnosis, Brodie abscess treatment, Brodie's abscess, osteogenic sarcoma, osteosarcoma, bone infection, bone inflammation, primary subacute osteomyelitis, chronic osteomyelitis, hematogenous osteomyelitis, Ewing sarcoma, multifocal subacute osteomyelitis, punched-out radiolucency, punched-out lesion, serpentine sign, penumbra sign INTRODUCTIONSection 2 of 12
  Subacute osteomyelitis is a distinct form of osteomyelitis, and Brodie abscess is one type of subacute osteomyelitis. Subacute osteomyelitis is difficult to diagnose because the characteristic signs and symptoms of the acute form of the disease are absent.1, 2, 3 The disease has an insidious onset, mild symptoms, and lacks a systemic reaction, and supportive laboratory data are inconsistent. Subacute osteomyelitis may mimic various benign and malignant conditions, resulting in delayed diagnosis and treatment. The most frequently made incorrect diagnosis is that of tumor.1, 4, 5 In noncontemporary literature, Brodie abscess was referred to as a chronic form of osteomyelitis; however, in almost all contemporary literature references, Brodie abscess is referred to as the most common type of the subacute form of osteomyelitis. History of the ProcedureSir Benjamin Brodie, a surgeon in St. George's Hospital, London, United Kingdom, first described subacute osteomyelitis in 1832.6 He amputated the leg of a man who had intractable pain for a number of years. On examination of the amputated limb, Brodie found a cavity the size of a walnut filled with dark-colored pus. The bone immediately surrounding the cavity was whiter and harder than the surrounding bone. The inner surface of the cavity appeared to be highly vascular.6 Since then, low-grade pyogenic abscesses of the bone have frequently been referred to as Brodie abscesses. In 1951, Wiles referred to Brodie abscesses as a particular form of chronic osteomyelitis that follows an acute attack, when the virulence of the organism and the resistance of the patient are evenly balanced.7 Little discussion exists in the literature again until Harris and Kirkaldy-Willis described primary subacute osteomyelitis8; they were the first to publish a radiograph that demonstrated an abscess of subacute osteomyelitis crossing the epiphyseal plate of the distal tibia. Based on their experience in East Africa, Harris and Kirkaldy-Willis classified primary subacute osteomyelitis, into 2 types, depending on whether a bone abscess is present or not, with the first type being metaphyseal and the second type diaphyseal. Subsequently in 1973, Gledhill proposed a radiologic classification for primary subacute osteomyelitis that consisted of 4 types based on his review of 8 patients, as follows9:
In 1982, Roberts et al modified and expanded Gledhill's classification to 6 forms based on morphology, location, and similarity to neoplasms, as follows10 (see Image 22):
This classification system is the most widely used in the literature, and several reports advocate modifying the classification system to include flat bone involvement, tarsal bones, and lesions affecting both the metaphysis and the epiphysis. Some authors have modified the Roberts's classification system (see Introduction, Clinical, below). In all reported series of primary subacute osteomyelitis, the classic Brodie abscess (central metaphyseal lesion with well-defined sclerotic margins, type Ia according to the authors' new classification system) has comprised the largest number of cases. ProblemSubacute osteomyelitis is characterized by mild to moderate pain, usually described as a persistent ache; intermittent symptoms; insidious onset; and, often, a long delay between the onset of pain (the most common presenting symptom) and the diagnosis. Usually, symptoms are present for 2 weeks or longer. The course is generally marked by few or no constitutional symptoms and no known previous acute disease. FrequencyThe incidence of subacute osteomyelitis has increased since antibiotics have been used to treat osteomyelitis. The disease reportedly accounts for 8.8%,11 35%,12 and 42%13 of primary bone infections, although a report by Blyth et al indicates a mild decline in the incidence of both acute and subacute osteomyelitis, with greater decline in the acute form than in the subacute form.14 In East Africa, subacute osteomyelitis is the most common form of osteomyelitis. Onset of subacute osteomyelitis tends to occur in slightly older children than the onset of acute osteomyelitis. Subacute osteomyelitis has been reported in patients as young as 6 months and as old as 39 years, but the common age range is 2-15 years. Sex ratios vary, but in general, males are affected slightly more often than are females. EtiologySubacute osteomyelitis is one of the many clinical presentations of hematogenous osteomyelitis. The organisms reach the bone from a disrupted site elsewhere in the body that may pose little or no threat of its own accord (eg, skin pustule, furuncles, impetigo, infected blisters and burns). Infection has even been suggested to be the outcome of common events such as normally harmless daily teeth brushing. Factors that may influence the behavior of a septic process in bone may relate to host resistance, virulence of the infecting organism, and adequacy of antibiotic therapy. Moreover, subacute osteomyelitis appears to depend on the interplay between the infecting bacteria and the immune mechanism of the host. True primary subacute osteomyelitis represents a favorable host-pathogen response. In East Africa, where subacute osteomyelitis is the most common form of osteomyelitis, children in bare feet have frequent foot infections and develop a high resistance to staphylococcal infections (the most common causative organism), as pointed out by Harris and Kirkaldy-Willis.8 That trauma results in vascular injury and an area of hypoxia in the metaphyseal region of bone is an attractive theory, but it is difficult to prove as an inciting cause of subacute osteomyelitis. When the host resistance is insufficient to overwhelm the infection, it is conceivable that subacute osteomyelitis may develop. The pyogenic organisms' initial attack is presumed to be controlled by the host, and presumably, spread to large areas of cancellous tissue or to the subperiosteal region has not occurred. A central area of suppurative necrosis in the metaphyseal region becomes enclosed by a wall of fibrous tissue and granulations, the offending organisms are destroyed, and the pus is usually sterile. The circulation of the epiphysis predisposes to sluggish blood flow through the vascular loops. Possibly, the rich supply of the reticuloendothelial cells located in the epiphysis attenuates the osteomyelitis, leading to the subacute course in this region. The metaphyseal-equivalent regions are defined as the portion of a flat or irregular bone that borders cartilage (apophyseal growth plates, articular cartilage, or fibrocartilage), such as the pelvis, the vertebrae, the clavicle, and the small bones (tarsal bones).15 The vascular anatomy and the mechanism of seeding are analogous to those found in the metaphysis of long bones. PathophysiologySite of infection Subacute osteomyelitis occurs in a much wider variety of bones than does the acute type, and the disease occurs at various sites within the affected bones. The lower limb is affected much more often than the upper limb, and the tibia is affected relatively more often than is the femur. Subacute osteomyelitis may involve only the epiphysis, which is contrary to the belief that primary bone infection does not occur in the epiphysis (see Image 1). The diaphysis is occasionally affected (see Images 2-3), although this occurs more often in adults than in children; the most commonly affected site is the metaphysis (see Images 4-5). Communication of the lesion between the metaphysis and the epiphysis is also common (see Images 6-7). Other sites in which subacute osteomyelitis is frequently reported are metaphyseal-equivalent locations, such as the pelvis, the vertebrae, the calcaneum, the clavicle, and the talus. When subacute osteomyelitis occurs in tarsal bones, it usually occurs in the subchondral part or on the border of the apophysis of the calcaneus. Subacute lesions of the spine occur more often in adults than in children (see Image 8). When subacute osteomyelitis occurs in the long bones of adults, the diaphysis is involved as often as is the metaphysis. The patella is rarely involved. Multifocal subacute osteomyelitis is a rare form of subacute osteomyelitis that was reported by Season and Miller and by Rasool.16, 17 It is usually associated with a deficient immune system. Bacteriology The causative organism is usually coagulase-positive Staphylococcus (30-60%). Other organisms encountered are Streptococcus, Pseudomonas, Haemophilus influenzae (much less common after widespread vaccination), and coagulase-negative Staphylococcus. An increased prevalence of Kingella kingae, a gram-negative coccobacillus, was noted by Lundy and Kehl, mostly in children younger than 3 years as a cause of all types of osteoarticular infections, including subacute osteomyelitis.18 ClinicalPresenting symptoms of subacute osteomyelitis include mild to moderate localized pain. Pain is the most consistent complaint in most patients, and it may at times become more intense or remit and is frequently exacerbated following a period of unusual activity. Night pain that is relieved with aspirin is frequently reported. Minimal loss of function is another common symptom (eg, limping in a patient with a lower limb lesion), with no history of systemic toxicity. On clinical examination, localized tenderness may only occasionally be associated with warmth, redness, and soft-tissue swelling with the involvement of subcutaneous bone. This finding seems to increase and subside with activity. Pain may occur with movement of the adjacent joint, and some joint effusion may be present, but the pain and effusion are usually mild. The surrounding muscles may occasionally demonstrate some wasting. Ross and Cole categorized these lesions either as aggressive or as cavities in the area of the metaphysis and epiphysis.19 This categorization helps in the treatment plan, as aggressive lesions should be treated surgically for diagnosis. Gledhill classified subacute osteomyelitis according to radiologic appearance,9 and this classification scheme has since been modified by Roberts et al.10 The classification scheme is useful for reporting the results of treatment according to the site but is not a prognosis or treatment plan. The authors have modified the latter as follows (see Image 22):
Duration of symptoms Because the symptoms of subacute osteomyelitis are vague, an accurate diagnosis is usually delayed. The bone lesion may also not be readily apparent on plain radiographs for some time. The average duration of symptoms before diagnosis is 1-6 months, but symptoms may be present longer before the diagnosis. Differential diagnosis Osteomyelitis is a known mimic of various diseases, and subacute osteomyelitis is no exception, having all of the presenting signs and symptoms of many bone tumors, both benign and malignant. The variety of radiographic presentations of subacute osteomyelitis has been emphasized by Gledhill.9 The classic solitary lesion located in the metaphysis surrounded by reactive new bone presents little difficulty in diagnosis. However, extensive erosions of cortical bone, periosteal new bone formation, or both may add a more ominous dimension. Patients with subacute osteomyelitis may occasionally be initially diagnosed with Ewing sarcoma or osteogenic sarcoma. From these observations, the following lesions must be considered among the differential diagnosis of subacute osteomyelitis:
Related Medscape topics: INDICATIONSSection 3 of 12
Subacute osteomyelitis treatment is controversial; however, in patients with characteristic clinical and imaging findings and laboratory results, treatment with antibiotics alone may be undertaken without biopsy, at least in the pediatric age group.3, 19, 21, 22, 23, 24, 25 In the literature, opinion differs as to whether treatment should be surgical or medical for these classic lesions. Failure of symptoms to resolve after an up to 6-week course of antibiotics or worsening of the condition during treatment should lead to reevaluation and a definite tissue and/or bacteriologic diagnosis, 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. RELEVANT ANATOMYSection 4 of 12
Interconnecting subacute osteomyelitis of the epiphysis and metaphysis is readily explainable in infants younger than 18 months, when one considers that vascular communication between the epiphysis and metaphysis is present until age 18 months, as described by Trueta.26 Epiphyseal lesions may also occur in older adolescents when the growth plate becomes attenuated and fails to provide a barrier to epiphyseal infection. Another interesting explanation for the localization of subacute osteomyelitis adjacent to the growth plate cartilage is the finding by Speers and Nade that S aureus has a certain affinity for physeal cartilage.27 The transgression of the epiphyseal plate from osteomyelitis foci has been well documented (see Images 6-7). A review of the literature indicates that despite localized transgression of the epiphyseal plate by subacute osteomyelitis, growth plate arrest, stimulation, or development of transepiphyseal bony bars is exceedingly rare. CONTRAINDICATIONSSection 5 of 12
Contraindications to medical treatment alone for subacute osteomyelitis include the following:
No literature exists to support medical treatment in adults, as subacute osteomyelitis mostly affects patients in the pediatric age group. Until medical treatment in adults is described, surgical treatment of subacute osteomyelitis is indicated. No true contraindications to surgical intervention exist, as medical treatment alone without biopsy or curettage is still controversial in the literature. WORKUPSection 6 of 12
Lab StudiesThe laboratory workup of subacute osteomyelitis includes the following:
Related Medscape topic: Imaging Studies
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], and gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. Diagnostic Procedures
Related Medscape topic: Histologic FindingsIn subacute osteomyelitis, the surrounding bone is usually sclerotic, but it is of variable thickness, most often thin rather than dense and thick. For most lesions, granulation tissue lines the abscess cavities, and the presence of fat, fibroblastic response (commonly, a fibrin layer separates bone from granulation tissue), remnant of necrotic bone, and new bone formation is seen. TREATMENTSection 7 of 12
Medical therapyTreatment of subacute osteomyelitis depends on the diagnosis. Almost one third of cases (the group that was categorized by Ross and Cole as aggressive lesions19) are indistinguishable from primary malignant bone tumors. Biopsy and curettage are required for diagnosis in these cases. 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,22 Ross and Cole,19 Andrew and Porter,23 Martin,25 Hamdy et al,24 Ezra et al,20, 21 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.19, 20 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. Surgical therapyIn 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.19 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.32 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. Intraoperative detailsIf 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,33 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). Postoperative detailsIn 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-upFollow-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. COMPLICATIONSSection 8 of 12
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.19 Effusions into the hip joint were also reported by Ross and Cole in 2 patients who had closed cavities in the femoral neck.19 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.19 Ezra et al reported recurrence in 1 of 21 patients treated with antibiotics only20; 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).33 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.19 OUTCOME AND PROGNOSISSection 9 of 12
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 patients24 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.24 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. FUTURE AND CONTROVERSIESSection 10 of 12
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. MULTIMEDIASection 11 of 12
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