You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Osteomyelitis, Acute PyogenicArticle Last Updated: Apr 12, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Ali Nawaz Khan, MBBS, LRCP, FRCS, FRCP, FRCR, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the USA, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Veerabhadram Garimella, MBBS; Sumaira Macdonald, MBChB, MRCP, FRCR, PhD, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute Editors: Amilcare Gentili, MD, Clinical Professor of Radiology, University of California at San Diego; Consulting Staff, Department of Radiology, Thornton Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Javier Beltran, MD, Chair, Department of Radiology, Maimonides Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, EdM, MBA, Professor, Department of Radiology, Section Head of Musculoskeletal Radiology, Vice Chairman for Radiology Informatics, University of Washington Author and Editor Disclosure Synonyms and related keywords: acute osteomyelitis, subacute osteomyelitis, chronic osteomyelitis, bone inflammation, hematogenous osteomyelitis, exogenous osteomyelitis INTRODUCTIONSection 2 of 11
  BackgroundAcute osteomyelitis is an inflammation of bone caused by an infecting organism. Staphylococcus aureus is the most common bacterium involved in the infection. On the basis of the route of infection, acute osteomyelitis can be classified as hematogenous or exogenous. Hematogenous osteomyelitis is predominantly seen in children and involves the highly vascular long bones, especially those of the lower limb. In adults, hematogenous spread is more common to the lumbar vertebral bodies than elsewhere. Before puberty, infection starts in the metaphyseal sinusoidal veins. Because bones are relatively rigid structures, focal edema accumulates under pressure and leads to local tissue necrosis, breakdown of the trabecular bone structure, and removal of bone matrix and calcium. Infection spreads along the haversian canals, through the marrow cavity, and beneath the periosteal layer of the bone. Subsequent vascular damage causes the ischemic death of osteocytes, leading to the formation of a sequestrum. Periosteal new-bone formation on top of the sequestrum is known as involucrum. Osteomyelitis may be acute, subacute, or chronic. With acute osteomyelitis, the presenting complaint is usually local pain, swelling, and warmth. These often occur with associated fever and malaise. PathophysiologyIn summary, the pathophysiology depends on the degree of soft-tissue damage and impairment of the blood supply, instability of the fracture fragments, inoculation of the bacterial flora, and the immune system of the host. Microbiology Causative organisms can be summarized by patient group, as follows:
S aureus is the causative agent in 70-90% of pediatric cases. Bacteria pass through nutrient vessels to the metaphyses, where they become lodged and proliferate. The physeal plate acts as barrier to epiphyseal extension of infection because it is avascular. Infection commonly spreads from the primary intramedullary focus via the haversian canals of the cortex to the subperiosteal space, forming a subperiosteal abscess. If this ruptures, the infection extends into the overlying soft tissues. Metaphyseal inflammation leads to exudation, increased intraosseous pressure, vascular stasis, thrombosis, bone necrosis, and bone resorption. Sometimes, infection can extend to the adjacent joint. Tubular bones have most rapid growth and largest metaphyses; therefore, they are common sites of infection. As many as 75% of children have infections in sites such as distal and proximal femur and tibia, distal humerus, and fibula. In older children, the infecting organism is usually S aureus, whereas in neonates and infants, group A beta-hemolytic Streptococcus organisms are common. Mycobacterium species, Gram-negative bacteria, syphilis, and fungal and viral agents are less common causes of osteomyelitis. Salmonella osteomyelitis may occur, particularly in children with sickle cell disease. Local trauma may reduce host resistance and predispose an individual to osteomyelitis. A Brodie abscess is a localized form of osteomyelitis that appears in a subacute stage without preceding acute symptoms. Histologic evaluation shows an intraosseous abscess cavity lined by granulation tissue. The infecting organism is usually S aureus. The condition typically presents with relatively mild pain, which recurs over several months or sometimes years. The most common sites are the tibial or femoral metaphysis or diaphysis. The infection may cross the growth plate. Local soft-tissue swelling is minimal, and no soft-tissue mass is present. Stages of disease The disease process involves 5 stages:
Hematogenous osteomyelitis The spread of infection is usually hematogenous. Among children, the metaphysis of the long bones is the most common site, where blood flow slows in the sinusoids, allowing bacteria to adhere to the vascular membranes. Local trauma with skin penetration and seeding of organisms is another pathway. Localized trauma to the bone, which causes hematoma and vascular obstruction in the metaphyseal region, and transient bacteremia around the same time result in infection. Hematogenous disease involves the bones. In children and adults, the femur, humerus, and tibia are typically affected. In adults, the vertebral bodies can be affected as well. Risk factors for hematogenous osteomyelitis in adults include the following:
Hematogenous spread mainly extends to the vertebral bodies from the Batson plexus. Pus spreads anteriorly along the vertebral body to form a paravertebral abscess, or it spreads posteriorly to form and extradural abscess. Weakening of the body results in collapse of the vertebra. Exogenous osteomyelitis With exogenous disease, the spread of infection can be the result of (1) direct trauma and the inoculation of infectious material in compound fractures; (2) iatrogenic causes, such as surgical procedures (eg, internal fixation of fractures, joint replacement); and (3) contiguous spread from soft-tissue infections surrounding the bone, especially in individuals with diabetes. Complications of osteomyelitis Complications of osteomyelitis include sequestrum formation with recurrent relapses, skin sinus formation, damage to the growth plate causing tethering, physeal bar, and subsequent growth deformity. FrequencyUnited StatesThe prevalence in children younger than 1 year is 1 in 1000. The prevalence in older children is 1 in 5000. The incidence of acute osteomyelitis in adults with diabetes is 30-40%, after puncture wounds to the feet. The incidence is 0.1-1.8% in the healthy adult population. The incidence in sickle cell disease is 0.46%. InternationalNo figures are available to suggest that the incidence of acute osteomyelitis is different from that in the US. However, the incidence in young children may be higher in developing countries than elsewhere. Mortality/MorbidityIn the preantibiotic era, the mortality rate was as high as 25-40%. Antibiotics have reduced the rate to almost 0%, with complication rate of about 5%. Complications include the following: (1) chronic osteomyelitis due to the persistence of the infective organisms (5-25%), (2) metastatic infection, (3) septic arthritis in children younger than 2 years due to the transphyseal spread of the infection (In adults, it occurs in the joints where the epiphysis is enclosed in the joint capsule [eg, hip and elbow joints].), (4) angular deformity of bones due to arrest of bone growth, (5) pathologic fractures, (6) bacteremia and septicemia, (7) soft tissue infection and persistent sinuses, and (8) premature epiphyseal fusion. RaceOsteomyelitis associated with sickle cell disease has a higher incidence in people of African descent than in others. SexStudies show a male preponderance, with a male-to-female ratio of 1.5:1 to 2:1. AgePersons of any age can be involved, but this disease is more common in neonates than in others. AnatomyThe capillary ends of the nutrient artery for sharp, non-anastomosing loops, which enter the large venous sinusoids. This vasculature results in slowing of the circulation and reduced oxygen tension. The capillaries do not communicate because columns of calcified cartilage separate them from each other. Children younger than 2 years of have transphyseal vessels, which cross from metaphysis to epiphysis. This causes the spread of infection into the joint. In children older than 2 years, the transphyseal vessels are absent, and hence, the epiphyseal plate acts as a barrier to the spread of infection into the joint. Clinical DetailsOsteomyelitis may be acute, subacute, or chronic. With acute osteomyelitis, the presenting complaint is usually local pain, swelling, and warmth. These often occur with associated fever and malaise. Clinical examination reveals pyrexia, local erythema, and tenderness. Investigations typically show leukocytosis and an elevated C-reactive protein (CRP) level and erythrocyte sedimentation rate (ESR). Findings in infants include the following:
Findings in older children include the following:
Findings in those with sickle cell disease include the following:
Findings in adults include the following:
Involvement of the lumbar spine is more common than involvement of the thoracic or cervical spine. The incidence of paralysis is higher when thoracic or cervical spine is involved. Preferred ExaminationImaging plays an important role in the diagnosis of osteomyelitis, and it should always start with plain radiographs of the affected area. Current imaging recommendations include plain radiography followed by 3-phase bone scanning and/or MRI if available. Although conventional radiographs begin to show osseous changes only 5-7 days into the disease process, plain radiographs are useful in ruling out other causes of bone pain, such as stress fractures. Plain radiography and radionuclide bone scanning greatly aids early diagnosis in acute osteomyelitis by excluding other conditions and by revealing evidence of inflammation at the site of bone pain, respectively. Nuclear medicine bone scans are a highly sensitive (>90%) modality in the diagnosis of osteomyelitis. This procedure is done in 3 parts. Technetium Tc 99m is used to create images to determine areas of infection and bone remodeling dependent on local blood flow. The sensitivity of bone scans is often helpful when the exact site and extent of the infection is not known. CT scanning allows for 3-dimensional (3D) examination of bone and surrounding soft tissue. CT scanning is an excellent modality for depicting periosteal new-bone formation, cortical bone destruction, and any sequestration or involucrum if present. Contrast-enhanced CT may show a ring-enhancing soft-tissue abscess. MRI if available is another useful modality for imaging acute osteomyelitis. Findings on MRI accurately illustrate the extent and structure of the area involved in the pathologic process. Sensitivity has been reported to be 88-100%, with a specificity of 75-100%. Fat-suppression sequences allow for better detection of bone marrow edema; however, infection and inflammation cannot be differentiated. MRI may be the imaging modality of choice in infections involving the spine, pelvis, or limbs because of its ability to provide fine details of the osseous changes and soft-tissue extension in these areas. Additional imaging can be performed with indium In 111–labeled leukocytes; gallium is used as needed. Gallium seems especially valuable in monitoring the efficacy of treatment. Urso and associates evaluated 40 pediatric patients (aged 2-16 y) with osteomyelitis to investigate the role of various imaging modalities, including conventional radiology, bone scanning with 99mTc methylene diphosphonate (MDP), scintigraphy with 99mTc hexamethylenepropyleneamineoxime (HMPAO)–labeled leukocytes, CT, and MRI. The modalities were used to detect lesions, to make a differential diagnosis, and to assess disease stages. As for acute osteomyelitis (6 patients), conventional radiography showed a lytic lesion and periosteal new-bone formation and soft tissue swelling (4 of 6 patients). (No abnormalities were demonstrated in the other 2.) Bone scanning, CT, and MRI depicted bone involvement. CT and MRI also showed involvement and the spread of an inflammatory lesion to surrounding soft tissue. 99mTc-HMPAO scintigraphy was not performed to assess acute osteomyelitis, because of technical difficulties in performing the study promptly; thus, early analysis of the nature of the lesion was made with bone biopsy. As for subacute osteomyelitis, 99mTc-HMPAO scintigraphy was performed in 8 of 23 patients and proved to be highly sensitive, showing cell clusters and confirming the diagnosis of an inflammatory lesion. T1-weighted MRIs showed a focal area of intermediate-to-low signal intensity. These MRIs also showed small, focal, intralesional areas of low intensity; a low-signal perifocal rim; and diffusely low signal intensity of the surrounding bone marrow. T2-weighted images showed high signal intensity in both the abscess lesion and in the bone marrow; the latter was probably due to edema. In 5 patients, a paramagnetic contrast agent (gadopentetate dimeglumine) was administered during MRI and resulted in inhomogeneous enhancement of both the inflammatory lesion and the surrounding bone marrow. Regarding chronic osteomyelitis (7 patients), MRI was performed in 5. In 4 patients, the lesion appeared as a hypointense area on T1-weighted images, whereas T2-weighted images showed an inhomogeneous hyperintense area. In the same patients, 99mTc-HMPAO scintigraphy was always positive. In patient 5, the lesion was represented by a hypointense area on both T1- and T2-weighted images, whereas 99mTc-HMPAO scans were negative. Therefore, in chronic osteomyelitis, both MRI and 99mTc-HMPAO were useful in detecting spinal and peripheral bone involvement, which was asymptomatic at first observation in some cases. Conventional radiography, CT (3 of 4 patients) and MRI (4 of 4 patients) findings of extra-axial localizations were similar to those in the subacute-chronic forms. Limitations of TechniquesPlain radiographs are often normal for at least a weak following infection, and they findings are nonspecific. MRI has limited availability and is relatively expensive. MRI is also contraindicated in patients with certain implant devices and metallic clips, and it is not tolerated by all patients because of claustrophobia or morbid obesity. In addition, young children may requiring sedation, Good MRI require patient cooperation because patient motion can degrade the images. CT is quick and inexpensive, but exposes the patient to ionizing radiation. The risk of a reaction to radio-iodinated contrast material is low, though the detection of bone destruction or a paraspinal mass does not require the use of contrast material. Although radionuclide studies are sensitive, they can be time-consuming, and they have lower spatial resolution. The incidence of false-negative scans is low in neonates and in elderly patients with osteomyelitis. DIFFERENTIALSSection 3 of 11
Ewing Sarcoma Osteomyelitis, Chronic Septic Arthritis Stress Fracture Other Problems to Be ConsideredOsteosarcoma
RADIOGRAPHSection 4 of 11
FindingsRadiographs can vary in appearance. Radiographs performed early in the course of disease may show subtle swelling of the deep soft tissue or edematous subcutaneous soft tissues, but radiographs are often normal in the first 7-10 days. By 10-14 days, a focal area of bone opacity develops in the metaphysis. This progresses to lytic destruction with an associated focal periosteal reaction. Radiographs typically show a well-defined, longitudinally orientated, ovoid lucency with surrounding sclerotic margin but little or no periosteal new-bone formation. Radiographs can be normal, particularly early in the course of disease. Alternatively, they may demonstrate soft-tissue swelling, periosteal reaction, subperiosteal bone resorption, and erosions and sequestra. The extension of infection through the metaphyseal cortex can lead to periosteal new-bone formation. If untreated, this may completely encircle the bone, becoming an involucrum, which can envelope the nonviable infected bone; the result is called a sequestrum. Degree of ConfidencePlain radiography is an inexpensive and noninvasive technique that is readily available worldwide. Radiography has a reasonable sensitivity. Plain radiographs may help in differentiating between varieties of bone lesions that may mimic osteomyelitis clinically. However, radiographs are the least sensitive method of diagnosis. Lipman at al reported a sensitivity of 67%, a specificity of 40%, and an accuracy of 50%. On plain images, soft-tissue swelling can be seen at 1-3 days after infection. Destructive bone changes do not appear on plain images until 10-14 days after the infection starts. Initially, the bone may have a lucent, moth-eaten appearance. False Positives/NegativesRadiographs are often normal in the first 7-10 days after infection. Radiographic mimics of osteomyelitis include septic arthritis, Ewing sarcoma, osteosarcoma, juvenile arthritis, sickle cell crisis, Gaucher disease, stress fractures, and other bone lesions that may mimic osteomyelitis clinically. CT SCANSection 5 of 11
FindingsCT is the modality of choice for revealing sequestra and cortical erosions in chronic osteomyelitis. Chandnani et al investigated acute experimental osteomyelitis and abscesses that were induced in the proximal tibia and surrounding soft tissues, respectively, in 67 New Zealand white rabbits. Fifty-three rabbits were injected with a solution containing S aureus, and 26 were injected with sterile sodium chloride solution in the tibial medullae and/or surrounding soft tissues. Contrast-enhanced CT and MRI were performed 7 days after inoculation. MRI was more sensitive than CT in the detection of osteomyelitis (94% vs 66%, P < .025) and abscesses (97% vs 52%). MRI was equally specific to CT in the exclusion of osteomyelitis (93% vs 97%) but less specific than CT in the exclusion of abscesses (77% vs 100%). The overall accuracy of MRI was somewhat, although not significantly, greater than that of CT in the detection of both osteomyelitis (93% vs 80%) and abscesses (87% vs 75%). Piazza et al evaluated the role of CT in acute orbital infections in 15 patients (13 men, 2 women; mean age, 23 y) with orbital cellulitis secondary to frontoethmoidal sinusitis (10 cases), maxillary sinusitis (4 cases), or craniofacial trauma (1 case). After describing the CT patterns of cellulitis and its possible complications, the authors emphasize the role of CT as the method of choice for confirming the clinical diagnosis and for demonstrate the site, extent, and complications of acute orbital cellulitis. Hald and Sudmann studied the role of CT in the early diagnosis in acute hematogenous osteomyelitis. Increased medullary CT attenuation values were invariably recorded in affected regions in 7 patients with osteomyelitis. The results indicate that CT can depict bone marrow involvement can be detected in patients with osteomyelitis before bony changes appear on routine radiographs. Azouz evaluated 14 patients with proven septic arthritis, osteomyelitis, or spondylitis, as determined by both CT and conventional examinations. CT was performed only when specific problems of diagnosis were unsolved after plain radiography, standard tomography, or isotopic bone scanning was used. In these select cases, CT was of definite value for studying the entire articular surface of the bone and periarticular soft tissues; for delineating the extent of medullary and soft-tissue involvement; and for demonstrating cavities, serpiginous tracts, sequestra, or cloacae in osteomyelitis. CT sometimes showed soft-tissue edema or bone destruction not seen on plain radiographs. Degree of ConfidenceCT scanning allows for 3D examination of the bone and surrounding soft tissue. CT is an excellent for depicting periosteal new-bone formation, cortical bone destruction, and sequestration or involucrum if present. CT is the modality of choice for revealing sequestra and cortical erosions in chronic osteomyelitis. The accuracy, sensitivity, and specificity of CT in assessing chronic osteomyelitis are reportedly 96.7%, 99.1, and 80.0%, respectively. Hald and Sudmann found that medullary CT attenuation values were invariably increased in their study of 7 patients with acute osteomyelitis. Thus, CT may show the bone-marrow involvement of osteomyelitis before bony changes appear on plain radiographs. High-tech procedures such as CT and MRI should be reserved for situations in which the diagnosis cannot be made by using simpler methods, as in cases of osteomyelitis of the spine or pelvis or in cases when the anatomic detail provided by MRI is required for surgical planning. Most children with uncomplicated osteomyelitis probably do not need to undergo CT or MRI. CT diagnosis appears particularly good when osteomyelitis secondary to sinus infection is suspected. False Positives/NegativesTheoretically, confusion may arise from other conditions associated with periosteal new-bone formation and destructive bone processes, as in primary or metastatic bone tumors. MRISection 6 of 11
FindingsOn T1-weighted MRIs, osteomyelitis typically has low signal intensity, and on T2-weighted and short-tau inversion recovery (STIR) images, it has high marrow signal intensity. MRI shows marrow edema and the extent of subperiosteal abscess collection. T1-weighted sequences with intravenous gadolinium enhancement allow the differentiation of enhancing, hyperemic inflammatory tissue from central pockets of nonenhancing pus. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently 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. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. The disease is generally milder in infants than in older children, subperiosteal abscess formation is more frequent and rapid, and rupture into the soft tissues is more common. In neonates, vascular channels penetrate the cartilaginous epiphysis and allow infection to spread from the metaphysis into the joint, causing adjacent septic arthritis. These changes are demonstrable on sonograms or MRIs. Degree of ConfidenceMRI is considered to be the most sensitive modality. The sensitivity is relatively high at about 85%. MRI offers improved soft tissue resolution and multiplanar abilities, and it provides guidance for tissue sampling. False Positives/NegativesIn their prospective and retrospective study, Erdman and associates compared 0.35-T MRI interpretations with final diagnoses in 110 patients with suspected osteomyelitis. The diagnostic criteria of dark marrow on T1-weighted images and bright marrow on STIR images yielded a prospective sensitivity of 98% and a prospective specificity of 75%. About 60% of uncomplicated septic joint effusions demonstrated abnormal marrow signal intensity that was mistaken for that of osteomyelitis. Their retrospective review revealed that overall specificity could be improved to 82% without a loss of sensitivity if increased marrow signal intensity on T2-weighted images was included as an additional criterion. Specificity could be increased further by using of knowledge of the morphologic patterns that distinguish various forms of osteomyelitis. Ten patients (9%) were given potential pitfall diagnoses (eg, fracture, infarction, healed infection) that mimic osteomyelitis. MRI can be sensitive and specific for osteomyelitis if characteristic appearances and pitfall diagnoses are incorporated into the diagnostic criteria. ULTRASOUNDSection 7 of 11
FindingsThe physical properties of bone do not usually lend themselves to ultrasonographic investigation, because of the reflection of sound waves at a soft tissue–bone interface. However, the periosteum, early new-bone formation, and soft-tissue changes alongside dense bone may be imaged. Ultrasonography is useful in the acute phase and shows the presence and extent of any subperiosteal abscess collection (for which aspiration or drainage is required). Thus, can be helpful in planning surgery. Taneja and associates performed a prospective study to evaluate the role of ultrasonography in early detection of bone infections.1 A hypoechoic collection adjacent to bone was considered to be highly suggestive of osteomyelitis, whereas a hypoechoic collection away from the bone implied a soft-tissue abscess. Cellulitis appeared as increased subcutaneous thickness. Of the 31 cases of clinically suspected osteomyelitis and studied with sonography, 25 were proven to be osteomyelitis with surgical or at subsequent radiologic findings. Four involved soft-tissue abscesses, and 2 involved cellulitis. Coexistent hip joint effusion was seen in 2 patients. The investigators believed that ultrasonography is a simple and noninvasive investigation that could be used to detect bone and soft-tissue infections. Abernethy and associates performed ultrasonography in 9 children with late-presenting acute osteomyelitis, in 4 children with typical superficial cellulitis, and in 4 with a soft-tissue abscess.2 Sonographic results distinguished the superficial cellulitis, soft-tissue abscess, and subperiosteal abscess. The abscesses were confirmed at surgery, and a subperiosteal abscess was also detected in the child with deep periosseous cellulitis. Ultrasonography was particularly useful in confirming a subperiosteal abscess and in precisely localizing it in children with diffuse swelling and tenderness of a limb owing to late-acute osteomyelitis. Surgical drainage of pus can be avoided in patients without sonographic features of an abscess, and with sonography, surgery can be better planned in those who require it. Kang and associates examined 24 children with clinically suspected acute hematogenous osteomyelitis in an early stage by using sonography.3 Subperiosteal abscesses were sonographically detected in all patients at 4-14 days after onset. The mean length and anteroposterior distance of the subperiosteal abscesses were 86.4 and 10.7 mm, respectively. Of 24 cases of subperiosteal abscesses, aspiration performed under sonographic guidance revealed purulent fluid in all patients; 23 cases were verified surgically. The results indicate that sonography can be used to diagnose acute hematogenous osteomyelitis in the early stage. The earliest case was diagnosed by means of sonography 4 days after its onset. Mah and associates studied the sonographic features of acute osteomyelitis in children. Findings in 38 children with osteomyelitis of the limb bones were analyzed in 4 time-related groups on the basis of the interval between the onset of symptoms and sonography. Deep soft-tissue swelling was the earliest sign of acute osteomyelitis. In the next stage, there was periosteal elevation and a thin layer of subperiosteal fluid; in some cases, this progressed to form a subperiosteal abscess. The later stages were characterized by cortical erosion, which was common in those who had had symptoms for more than a week. Concurrent septic arthritis was revealed in 11 patients, most frequently in association with osteomyelitis of the proximal femur or distal humerus. Four weeks after clinical cure, sonography showed no abnormalities. The authors concluded that sonography is a useful additional method for diagnosing and assessing osteomyelitis and its complications. Chao and associates evaluated color Doppler sonography in the diagnosis of acute osteomyelitis in 12 children with clinically suspected acute osteomyelitis.4 The children were evaluated at admission and at regular intervals to observe the inflammatory process, determine the response to antibiotic therapy, and predict the need of surgery. At admission, color Doppler showed flow within or around the infected periosteum in patients with symptoms for 4 days or longer, whereas those with symptoms for less than 4 days had no such flow. During sonographic follow-up, 6 patients had increased color Doppler vascular flow within and around the affected periosteum, 2 of whom had periosteal abscess. They eventually required surgical treatment. Persistent or increased color Doppler flows during follow-up examination was correlated with elevated serum levels of CRP. This study indicated that color Doppler vascular flow within or around the infected periosteum was correlated with advanced acute osteomyelitis, and surgery usually was required in the patients. Thus, color Doppler sonography allowed the detection of advanced osteomyelitis and revealed the progression of inflammation during antibiotic therapy. The authors postulated that color Doppler ultrasonography may be valuable in determining the efficacy of antibiotic therapy and in justifying the need for an operation. Riebel and associates reviewed the imaging results of 24 infants and children (aged 2 wk to 13 y) with osteomyelitis (21, acute; 3 chronic) to determine the accuracy of ultrasonography.5 Sonograms and conventional radiographs were available in all patients. Additional skeletal scintigraphy had been performed in 13 patients, and MRI in, 3. Different sonographic findings and their onset in the course of disease were emphasized. Intra-articular fluid collections (15 cases) and/or subperiosteal abscess formation (12 cases) were the most frequent early sonographic findings and preceded radiographic changes by several days in 11 of these cases. With positive clinical signs of inflammation, the sonographic results were usually sufficient for correct diagnosis. In select cases, fluid or abscess puncture for immediate microscopic and later bacteriologic studies was performed under sonographic control. In addition, sonography was also able to depict superficial cortical erosion and even an intramedullary focus in a young patient. The authors concluded that ultrasonography is helpful for establishing the correct diagnosis in osteomyelitis and in reducing the frequency of additional imaging studies. Degree of ConfidenceUltrasonography is a noninvasive, simple, and inexpensive technique that uses nonionizing radiation; thus, it is an ideal modality for children. Ultrasonography is fairly reliable for differentiating acute hematogenous osteomyelitis from cellulites, soft-tissue abscesses, acute septic arthritis, and malignant bone tumors. However, the modality remains operator dependent, and a child with acute tenderness at the site of suspected infection may not be able to tolerate the ultrasonic probe touching the surface. Larcos and associates found that the sensitivity of ultrasound was 63% in 16 patients with acute osteomyelitis. False Positives/NegativesLarcos and associates determined the accuracy of ultrasonography in evaluating suspected acute osteomyelitis.6 They prospectively examined 19 patients with high-resolution sonography for subperiosteal fluid or cortical irregularity. The diagnosis was established at surgery (3 cases) or other tests and clinical follow-up. Sixteen patients were identified as having osteomyelitis, with positive sonographic results in 10 (sensitivity = 63%). Two studies were false positive; the diagnostic accuracy was 58%. Thus, ultrasonographic results may be potentially misleading, and the authors emphasized the importance of clinical judgment and other tests. NUCLEAR MEDICINESection 8 of 11
Findings99mTc diphosphonate bone scan is usually positive 24 hours after infection and demonstrates a well-defined focus of tracer activity 1-2 hours after injection. This finding is correlated with the presence of radiotracer in the same area on dynamic scans. Bone scintigraphy may show focal uptake at the affected site, and it is particularly valuable in looking for other sites of infection, because multifocal osteomyelitis may occur, especially in neonates. Three-phase bone scanning This technique uses the same radionuclide as in static bone scans. The 3 phases involve the following:
The sensitivity of the 3-phase bone scan in the diagnosis of acute osteomyelitis is higher than that of static bone scans. The sensitivity and specificity of 3-phase bone scans has been reported to be 85-92% and 54-87%, respectively. The uptake on 3-phase bone scans is related to blood flow and osteoblastic activity. In acute osteomyelitis, isotopic activity is increased in all 3 phases. Gallium scanning Mechanisms of gallium Ga 67 citrate uptake include the following: (1) direct leukocyte and bacterial uptake, (2) lactoferrin and transferring binding, (3) increased vascularity, and (4) increased bone turnover. Criteria for a positive gallium scan include uptake exceeding that of the bone scan and/or differing in distribution compared with that on bone scan. If patients with suspected acute osteomyelitis are currently untreated and if 99mTc diphosphonate and gallium scans show concordant pattern, the scans are interpreted as follows: If 99mTc diphosphonate uptake is less than gallium uptake, infection is suggested. If 99mTc diphosphonate is present, reactive bone is suggested. If 99mTc diphosphonate and gallium uptake are discordant and if uptake is truly in bone, the likely diagnosis is osteomyelitis. Johnson et al evaluated 22 diabetic patients with osteomyelitis by using gallium scans.7 The results yielded a sensitivity of 100%, a specificity of 40%, and an accuracy of 73%. In Schauwecker et al's review of the literature, the sensitivity was 81% with a specificity of 69%.8 Gallium has a proven role in the monitoring of treatment. 111In-labeled leukocyte scintigraphy 111In-labeled leukocytes become localized in infectious and inflammatory lesions by means of leukotaxis. 111In is regarded as the best available agent for acute infections. However, Tc-labeled leukocytes have largely replaced indium labeling, especially in studies of suspected osteomyelitis in the extremities. Images are obtained at 2-4 hours and at 24 hours. Drawbacks include the low count rate, the cost of the radiopharmaceutical preparation, the complexity of the labeling, and the lack of bony landmarks. Johnson et al showed a sensitivity of 100%, a specificity of 70%, and an accuracy of 86%. When combined with bone scanning, the specificity increased to 80%, and the accuracy increased to 91%. Neuropathic joint disease and osteomyelitis in diabetes Diabetes mellitus affects 5% of the US population. Twenty percent of adult hospitalized diabetic patients have foot disorders leading to significant disability. One third of patients have evidence of osteomyelitis. Contributing factors include angiopathy and peripheral neuropathy. Osteomyelitis in a diabetic setting presents a difficult clinical problem, and differentiating between cellulites, osteomyelitis, and neuropathic osteoarthropathy may be problematic. These conditions most often affect the feet, and neuropathic osteoarthropathy can cause a warm and swollen extremity even without concomitant infection. Plain radiographs of osteomyelitis may show destructive changes, osteosclerosis, and periosteal new-bone formation. Fractures can occur with minimal trauma in neuropathic osteoarthropathy and add another complicating factor. Plain radiographs of neuropathic osteoarthropathy may depict joint subluxation, fracture fragmentation, subchondral osteoporosis, sclerosis in adjacent bone, and periosteal new-bone formation. Differentiating these changes from an infection may difficult radiographically. Similarly, a bone scintigraphy may be positive in all the 3 conditions. 67Ga concentrates in inflammatory lesions and can add some diagnostic specificity. Its intense concentration is thought to indicate osteomyelitis. However, scans may show mildly increased uptake in diabetic neuropathic osteoarthropathy, but accumulation can occasionally be substantial, compounding the problem. 111In-labeled white blood cells are specific for acute osteomyelitis and helpful in the differentiation of nonseptic from septic osteoarthropathy in diabetic patients. Maurer et al performed a retrospective study of 13 diabetic patients in whom 111In-labeled leukocyte studies were performed to assess possible osteomyelitis. The patients also had radiographic evidence of neuropathic osteoarthropathy. Three-phase scintigraphy was performed in all patients and showed increased uptake in both septic and nonseptic osteoarthropathy with a sensitivity of 75% and a specificity of 56% for osteomyelitis. Leukocyte imaging had the same sensitivity but was most helpful for excluding infection, with a specificity of 89%. Schauwecker et al studied the use of bone imaging, leukocyte imaging, and gallium imaging in the setting of suspected osteomyelitis superimposed on other diseases and causing increased bone turnover.8 111In leukocyte imaging had a sensitivity of 100% in acute osteomyelitis and 60% in chronic osteomyelitis, with a specificity of 95%. 67Ga scanning was excellent for ruling out osteomyelitis when findings were normal or for ruling it in when scans showed hyperintense uptake compared with bone imaging or a different distribution from the bone images. This situation occurred in 28% of the patients studied. Splittgerber et al evaluated 6 diabetic patients with radiographic findings of osteomyelitis, osteoarthropathy, or both by using leukocyte and bone imaging. Three patients actually had osteomyelitis. Bone images showed increased uptake in all patients, while leukocyte imaging showed increased uptake only in the 3 patients with osteomyelitis. In conclusion, 111In-labeled leukocyte imaging may add further specificity in differentiating septic diabetic osteoarthropathy from nonseptic diabetic osteoarthropathy in patients with increased uptake shown on bone and/or gallium images. Degree of ConfidenceStatic 99mTc diphosphonate bone scans have a sensitivity of 83% but a 5-60% false-negative rate in neonates and children because of the masking effect from normal increase in activity in the epiphyseal plate. Another factor is the unusual spectrum of radioactivity in children with osteomyelitis. Initially, the lesion may appear photon deficient, but it eventually appearing as an area of enhanced activity. The 3-phase bone scan has a higher sensitivity and specificity, but it also has several limitations in some patients: in children; in those in posttraumatic and postoperative states; in diabetics with neuropathic osteoarthropathy; and in those with bone tumors, septic arthritis, healed osteomyelitis, Paget disease, or other non-inflammatory bone lesions. Confusions may also arise with cellulitis, although activity in cellulitis decreases with time. Gallium scans have 100% sensitivity, and increased uptake appears a day earlier than on 99mTc diphosphonate scans. However, labeled-leukocyte scanning has largely replaced gallium scanning in the context of acute osteomyelitis because of its improved photo flux and improved dosimetry, which allows faster scanning with better resolution. False Positives/NegativesBone scintigraphy with 99mTc diphosphonate is a highly sensitive technique for evaluating bone pathology, but it not specific. False-positive results can occur with fractures, primary and metastatic neoplasms, heterotopic ossification, arthritis, osteomyelitis, and neuropathic joints. False-negative bone scans may be seen if scanning performed early in the infection or in babies younger than 6 weeks. On scans, cold lesions can occur in the first hours to days of the infection due to increased pressure in the medullary space. Therefore, the lesion can be easily missed. INTERVENTIONSection 9 of 11
Fine-needle aspiration (FNA) or needle biopsy can be used under ultrasonographic, fluoroscopic, or CT guidance to obtain pus and/or tissue to establish a histologic diagnosis of acute osteomyelitis. The 3 basic components of acute bacterial osteomyelitis are acute inflammatory cell exudates of neutrophils, necrotic bone, and bacteria in cells. These components may be present in the FNA or needle-biopsy smears and cell blocks. Bacteria may be present on Gram stains of FNA or needle-biopsy smears and in cultures of part of the FNA or needle-biopsy specimen. Medical/Legal Pitfalls
Special Concerns
MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Osteomyelitis, Acute Pyogenic excerpt Article Last Updated: Apr 12, 2007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
