An acute osteoarticular infection in a child is most often hematogenous. The infection manifests as osteomyelitis or septic arthritis. The most common causative organism is Staphylococcus aureus. Medical advice is usually sought within 2 to 6 days from the onset of symptoms. A child with an osteomyelitis in a lower extremity characteristically presents with limping with or without notable local tenderness, whereas acute septic arthritis is often readily visible because the joint is red, tender, and swollen. Early diagnosis and prompt treatment remain pivotal in avoiding complications in acute bacterial bone and joint infections.
Key points
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The treatment of childhood acute osteoarticular infections can be simplified.
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For the treatment of uncomplicated childhood osteoarticular infections, in which fever and symptoms resolve rapidly, 2 to 4 days of intravenous antibiotics can be followed by high-dose oral antibiotics, for a total antibiotic course of 3 weeks for osteomyelitis and 2 weeks for septic arthritis.
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Oral antibiotics should be well absorbed, provide good bone penetration, and be given in sufficiently high doses. Clindamycin or first-generation cephalosporins should be given 4 times a day.
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Serum C-reactive protein measurements are reliable and inexpensive in the diagnosis and follow-up of osteomyelitis and septic arthritis.
Introduction
In contrast to developing countries, acute ostearticular infections (AOI) of children, osteomyelitis (OM), septic arthritis (SA), and OM with adjacent SA (OM+SA), are rare diseases in high-income settings. The annual incidence of AOI varies regionally between 10 and 25 per 100,000 population, of which OM constitutes two-thirds. The incidence is increased in immunocompromised patients and those with sickle-cell disease. The infection is considered acute if the time from the onset of symptoms to the presentation to a hospital is less than 2 weeks. Most cases are hematogenous in origin, although direct inoculation from trauma or spread from an adjacent tissue occurs as well. Boys predominate girls with an approximate ratio of 2:1.
Cultures frequently fail to disclose the causative agent, but when tested positive, almost all cases show only a single organism. Overwhelmingly, the most common agent is Staphylococcus aureus , followed by respiratory pathogens Streptococcus pyogenes, Streptococcus pneumoniae (pneumococcus), and Haemophilus influenzae type b (Hib). Kingella kingae is a common cause of OM and SA in some areas and requires special culture techniques or real-time polymerase chain reaction for diagnosis. Current vaccinations have caused decreased incidence of Hib and pneumococcus in some countries. Salmonella spp are a common agent in the tropics and in children with sickle-cell disease, and neonates may be affected by bacteria such as Streptococcus agalactiae .
Introduction
In contrast to developing countries, acute ostearticular infections (AOI) of children, osteomyelitis (OM), septic arthritis (SA), and OM with adjacent SA (OM+SA), are rare diseases in high-income settings. The annual incidence of AOI varies regionally between 10 and 25 per 100,000 population, of which OM constitutes two-thirds. The incidence is increased in immunocompromised patients and those with sickle-cell disease. The infection is considered acute if the time from the onset of symptoms to the presentation to a hospital is less than 2 weeks. Most cases are hematogenous in origin, although direct inoculation from trauma or spread from an adjacent tissue occurs as well. Boys predominate girls with an approximate ratio of 2:1.
Cultures frequently fail to disclose the causative agent, but when tested positive, almost all cases show only a single organism. Overwhelmingly, the most common agent is Staphylococcus aureus , followed by respiratory pathogens Streptococcus pyogenes, Streptococcus pneumoniae (pneumococcus), and Haemophilus influenzae type b (Hib). Kingella kingae is a common cause of OM and SA in some areas and requires special culture techniques or real-time polymerase chain reaction for diagnosis. Current vaccinations have caused decreased incidence of Hib and pneumococcus in some countries. Salmonella spp are a common agent in the tropics and in children with sickle-cell disease, and neonates may be affected by bacteria such as Streptococcus agalactiae .
Patient history
The classical presentation of AOI is a locally swollen, warm limb or joint combined with high fever with no prior history of trauma. In a high-income setting the time from onset of symptoms is 2 to 5 days, and rarely more than a week. Focal symptoms are not always remarkable, especially in OM, and fever of unknown origin may be the only remarkable sign present in an OM patient visiting the emergency department. Prior trauma is documented in one-third of the cases.
Physical examination
The limb or joint may be too painful to allow thorough palpation or testing of joint motion, but plenty of useful information may be obtained from the disease history and mere observation of the patient. The child may be limping or refuse to use an extremity. Newborns may be irritable and may present as pseudoparalytic, whereas older children show more clear signs such as focal tenderness. Fever may be absent or high, up to 40°C. Generally, children with SA are clinically more ill than those with OM, which has a more insidious onset. Mild reddish color with no swelling may be the only visible focal sign in OM. Gonococcal arthritis, previously more common than today in the western settings, may present in the newborn only with unspecific irritability and poor feeding.
Focal symptoms and signs vary according to localization, causative organism, and the age of the child ( Table 1 ). S aureus causes clear focal symptoms compared with the insidious onset of K kingae , and culture-negative cases tend to present milder symptoms. Spinal osteomyelitis may manifest as unspecific back pain. The diagnosis of pelvic osteomyelitis is difficult; the mean diagnostic delay in 1 study was 12 days. OM in a long bone of a child beyond the neonatal age might show local pinpoint tenderness, which can be provoked by percussing the bone away from the affected area. Calcaneal osteomyelitis is characterized by slowly developing symptoms, and thus, late presentation. Sacroilitis may present as pain in the sacrum or lower back, provoked by digital dorsal compression in rectal examination. The swelling in hip arthritis of a neonate may pass detection unless the child has sought a characteristic position, with the affected hip flexed and externally rotated. Pain is elicited by compression of the head of the femur into the acetabulum.
| OM | SA | |
|---|---|---|
| Fever >38.5°C | Suggestive if present | Suggestive |
| Malaise | Usually | Usually |
| Swollen joint/limited motion | Not unless concurrent arthritis | Nearly always |
| Edema overlying bone | Often | Absent |
| Back pain | Suggestive of spinal OM | Rare |
| Difficulty weight-bearing | Lower limb affected | Lower limb affected |
| S aureus | K kingae | |
|---|---|---|
| Age | Any age group | Often <4 y |
| Fever | >38°C | Afebrile on admission |
| CRP | Elevated | May be normal |
| WBC | Elevated | May be normal |
| Neonates | Children and Adolescents | |
|---|---|---|
| Systemic effects | Poor feeding/irritability | Malaise and fever |
| Pain | Nonspecific limp/pseudoparalysis | Often focal |
| Joint involvement | Common | Possible |
Diagnostic evaluation
Further evaluation is warranted whenever an acute AOI is suspected. Box 1 summarizes the commonly performed tests, and Box 2 lists some of the examinations to be considered in the differential diagnosis. Blood tests are used to assess the extent of inflammation. Blood leukocyte count (white blood cell count) is unspecific and elevated only in 20% of cases. Erythrocyte sedimentation rate with a cutoff of 20 mm/h is sensitive in the diagnostics, but is inferior to C-reactive protein (CRP) measurements in monitoring the course of the illness because of slow normalization. Procalcitonin is more useful in OM than SA, but is considerably more costly than CRP and does not offer more information. CRP with a cutoff of 20 mg/L is sensitive in the diagnosis of OM and SA. The levels of CRP not only increase rapidly (doubling time is 6 hours) but also descend quickly enough (the level is halved in 24 hours if the recovery is uneventful) to be useful later in the monitoring of the patient. CRP is especially high in OM complicated by SA, but because of considerable overlapping, OM, SA, and OM+SA cannot be distinguished from each other with CRP alone.
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Parameters of inflammation/infection: C-reactive protein, procalcitonin, erythrocyte sedimentation rate, white blood cell count
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Plain X ray
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Ultrasound
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Scintigram
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Magnetic resonance imaging
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Blood cultures
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Synovial fluid cytology
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Synovial fluid/bone sample; Gram-staining, culture
Osteomyelitis
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Traumatic fracture
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Septicemia
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Rheumatic fever
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Cellulitis
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Thrombophlebitis
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Pyomyositis
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Leukemia
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Benign/malignant tumors
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Child abuse
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Scurvy
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Stress fracture
Septic arthritis
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Transient synovitis
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Viral arthritis
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Tuberculosis
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Henoch-Schönlein purpura
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Perthes disease
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Septic bursitis
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Slipped capital femoral epiphysis
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Reactive arthritis
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Juvenile rheumatoid arthritis
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Sickle cell anemia
In OM, plain radiographs are notoriously normal on admission in most cases because the characteristic “rat bites” appear only in 2 to 3 weeks in long bones and even after 6 weeks in flat bones. Traditional radiographs are still of value in ruling out other pathologic abnormalities, such as a fracture, Perthes disease, or slipped capital femoral epiphysis.
In SA, radiographs are of lesser importance and may at most show an enlarged joint space. Instead, ultrasound (US) may find joint effusion, but, conditions permitting, magnetic resonance imaging (MRI) is the most accurate diagnostic tool especially useful in OM. Contrast enhancement does not improve sensitivity or specificity of MRI in OM, but increases reader confidence if bone or soft tissue edema is found on unenhanced images. Computed tomography is another valuable option, along with technetium 99 bone scintigraphy (bone scan), which is still useful, especially in major long bones, or if the symptoms are poorly localized.
The symptoms, signs, routine blood tests, and vaccination history against Hib or pneumococcus may give a hint toward the possible causative organism. S aureus OM or SA often develops in a short time and causes high fever, which is not typical of K kingae infection (see Table 1 ). These generalizations may be valuable in the primary evaluation, but bacterial culture or other identification (polymerase chain reaction) remains pivotal in terms of the choice of treatment and for an antibiogram. In SA, the aspirated synovial fluid sample before treatment is essential for bacteriology. Spontaneous clotting, high white blood cell count, and low glucose concentration suggest SA, but values overlap with other types of arthritides causing problems with interpretation.
Joint puncture is always recommended in SA, although even 70% of synovial cultures may remain culture-negative. In OM the need for a bone sample is more contentious because the diagnosis by MRI is reliable. The authors strive to identify the agent also in OM and emphasize the importance of blood cultures, which yield bacteria in one-third of the cases. A sample for bacteriology is obtainable by needle aspiration of soft tissue in neonates, subperiosteal aspiration in infants, or drilling in older children.
Treatment
Choosing the Antibiotic
The major role of S aureus among the agents causing AOIs influences the choice of the initial antibiotic, provided the local resistance pattern is known. Table 2 summarizes some current recommendations for methicillin-sensitive S aureus and methicillin-resistant S aureus (MRSA). S pyogenes and pneumococcus do not pose a similar challenge, because both are sensitive to first-generation cephalosporins and clindamycin. The authors prefer to use clindamycin for staphylococcal infection, but anti-staphylococcal penicillins are also widely used. Of note, K kingae is resistant to clindamycin and vancomycin, but sensitive to cephalosporins and penicillins. In countries where Hib is still common in SA (Hib rarely causes OM), an unvaccinated child should receive concomitant ampicillin or amoxicillin (200 mg/kg/d divided in 4 equal doses) until the agent is identified. Gonococcal arthritis can be treated with ceftriaxone or cefotaxime. These agents are also appropriate for salmonella AOIs. In developing countries one may have to resort to cheaper agents such as chloramphenicol or possibly trimethoprim-sulfamethoxazole. An antibiogram would be of paramount importance in these situations.
