Table of Contents
Basics
Description
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Osteomyelitis is inflammation or infection of bone.
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Classification is most commonly based on the timing of onset:
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Acute: Most often from hematogenous spread:
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The most common organism in neonates is Staphylococcus aureus, followed by Streptococcus or Gram-negative organisms.
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In older infants and children, it usually is S. aureus.
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Subacute:
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Accounts for 1/3 of primary bone infections
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Is characterized by insidious onset, mild symptoms, longer duration of infection, and inconclusive laboratory data.
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The most common organism is Staphylococcus species.
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It usually requires longer duration of antibiotic treatment than the acute condition.
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Chronic:
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S. aureus is the most common organism.
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Usually, these patients have sequestra and multiple cavities that require curettage and occasionally bone grafting.
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Other classification schemes focus on factors such as patient age (neonatal, child, or adult), causative organism (pyogenic or granulomatous), or route of infection (hematogenous, direct inoculation, or contiguous spread).
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Synonym: Bone infection
Epidemiology
A seasonal variation in acute hematogenous osteomyelitis may occur, with more cases in late summer and early autumn.
Incidence
The incidence is higher in children than in adults, with a peak occurring in the later years of the 1st decade.
Prevalence
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A male predilection appears, which is not clearly understood.
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It affects <1% of children .
Risk Factors
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Deficient immune systems as a result of viral illness, trauma, anesthesia, or malnutrition also may play a role in the development of osteomyelitis.
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Children and adults may have a history of antecedent trauma.
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Sickle cell disease:
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In this population, hematogenous osteomyelitis is more common secondary to bone infarcts than to other causes.
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Although S. aureus is the most common organism, Salmonella infections may occur.
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Etiology
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Although the causes remain unknown, factors suspected of having an association with infection include trauma and an altered immune system (especially in adults).
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Most children who develop osteomyelitis are otherwise completely healthy.
Associated Conditions
Nearly 1/2 of these patients have a history of a recent or a concurrent infection such as a viral or upper respiratory infection.
Diagnosis
Signs and Symptoms
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Pain is the most common symptom, followed by swelling, erythema, warmth, and limited ROM of the adjacent joints.
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Fever is not always present.
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Because children may not be able to verbalize symptoms, refusal to bear weight, inability to walk or move a limb, and development of a limp all suggest infection.
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The index of suspicion must be highest in the neonate.
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Consider a firm diagnosis when 2 of these 4 criteria are present:
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Pus aspirated from bone
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Positive bone or blood culture
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Symptoms of pain, swelling, warmth, and decreased ROM
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Typical radiographic changes consistent with osteomyelitis
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Physical Exam
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The goal of the examination is to localize the area of involvement and to identify any possible source.
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The appearance of the child may vary from cranky to lethargic, depending on the extent and duration of infection.
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Before palpation, visually assess the amount of limb movement or usage.
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Tenderness to palpation may need to be elicited by the parent, with instructions to differentiate the cry of a frightened child from a cry of true pain.
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Tenderness, warmth, and erythema usually are present in the bone’s metaphyseal region.
Tests
Lab
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A white blood cell count is not a reliable indicator of infection, but if it is elevated, it is suggestive of infection.
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Blood cultures also should be obtained with the initial diagnostic blood sample.
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~1/2 of cases are positive.
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If a case is positive, it may eliminate the need to aspirate bone to obtain the organism.
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The ESR rate is a nonspecific acute-phase reactant that is elevated in many cases and is a reliable indicator of inflammation.
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It begins to elevate at 48-72 hours and returns to normal after 2-3 weeks if the infection has resolved.
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Because of the lag time of the ESR, it is not helpful in assessing resolution of infection.
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An elevated level of C-reactive protein resulting from inflammation also is useful.
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This test is more reliable than ESR in assessing infection because it not only peaks earlier (50 hours versus 3-5 days) but also returns to normal earlier (7 days).
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Aspiration of the site may be performed to identify the causative organism.
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The specimen should be sent for Gram stain, aerobic and anaerobic cultures, acid-fast bacilli, and tests for fungi.
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Bone cultures often are positive.
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Some clinicians suggest fine-needle biopsy with an 11-gauge bone biopsy (or bone marrow) needle for histologic examination.
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Heavy sedation usually is required to allow the patient to be comfortable and to obtain a specimen from the proper area reliably.
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The site of involvement usually is metaphyseal bone rather than hard cortical bone, so it is possible to penetrate the bone for a sample.
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If the site of involvement is not clear, it should be localized via bone scanning or MRI.
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All cultures and laboratory tests should be obtained before starting antibiotic treatment.
Imaging
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Radiography:
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Soft-tissue swelling is the earliest radiographic change.
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Classic radiographic bony changes, such as osteopenia, bone resorption, and new periosteal bone formation, may not occur until 14-21 days after symptom onset.
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Bone scan:
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May be used to localize the area of involvement
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Results may be falsely negative in the 1st month of life.
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Bone aspiration will not affect bone scan results if the scan is performed within 48 hours of aspiration.
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A bone scan is not needed if the area of involvement is already known.
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CT:
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Not useful in diagnosing acute osteomyelitis, but it may assist in differentiating other lucent lesions such as osteoid osteoma or chondroblastoma.
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MRI:
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Excellent sensitivity and specificity
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T1-weighted images give excellent anatomic detail of the site of infection.
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T2-weighted images show high signal in areas of inflammation and periosteal reaction.
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Ultrasound may help to identify a subperiosteal fluid collection, but because it does not penetrate bone well, it is not useful in assessing metaphyseal fluid collections.
Pathological Findings
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Infection begins in the sinusoids of the metaphysis, usually near the end of a long bone.
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As the infection spreads, the medullary vessels thrombose and cause a mechanical blockage of inflammatory cells.
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Results in inflammatory cell migration into the medullary cavity, with consequent intraosseous pressure buildup and development of pus
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The pus then takes the path of least resistance and exits through the metaphyseal cortex, thereby elevating the periosteum.
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A subperiosteal abscess subsequently forms under the elevated periosteum.
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The elevated periosteum manifests ~10-14 days later as a periosteal reaction.
Differential Diagnosis
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Trauma
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Septic arthritis
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Cellulitis
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Malignancy (leukemia or Ewing sarcoma)
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Thrombophlebitis
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Sickle cell crisis
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Toxic synovitis
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EOG
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Osteoid osteoma
Treatment for Osteomyelitis in Singapore
General Measures
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Principles of treatment include identification of the organism, selection of an appropriate antibiotic, surgical debridement if necessary, and sufficient duration of treatment to allow complete resolution.
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Surgery is not indicated if the condition is detected early and no devascularized bone is present.
Medication
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Antibiotic selection (guided by cultures and sensitivities):
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Oxacillin in combination with cefotaxime or gentamicin in neonates and oxacillin alone in infants and children
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Cefazolin is recommended for patients allergic to penicillin.
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Clindamycin or vancomycin is recommended for patients allergic to both penicillin and cephalosporin.
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The duration of antibiotic treatment is debatable.
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It typically involves intravenous antibiotics for 5 days until symptoms resolve and antibiotic sensitivities are identified.
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Thereafter, a regimen of 4-6 weeks of oral therapy is indicated, provided an appropriate oral antibiotic is available.
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Surgery
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Indications for surgery are controversial but usually include the following:
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Aspiration of frank pus initially
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Presence of substantial bone resorption
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Failure of symptom resolution after 3-48 hours of antibiotic treatment
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Surgical treatment consists of opening the periosteum, drilling the cortex, and debriding any devascularized bone.
Follow-up
Prognosis
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Most children do extremely well with appropriate treatment, and they suffer no long-term effects.
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Problems arise usually when infection is not recognized or treated in a timely manner, with the possible development of chronic osteomyelitis.
Complications
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Growth plate arrest may occur, if the infection crosses the growth plate.
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A pathologic fracture may develop if the bone is excessively loaded before healing and remodeling.
Miscellaneous
Codes
ICD9-CM
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730.0 Acute or subacute osteomyelitis
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730.1 Chronic osteomyelitis
FAQ
Q: When do patients with osteomyelitis need surgery?
A: Surgery often is necessary if there is lytic bone destruction or extension of the infection into the soft tissue with abscess formation.
Q: Can bone infection be confused with bone cancer?
A: Yes, it can. Ewing tumor and blood malignancies, such as lymphoma and leukemia, can be confused with osteomyelitis.
Appointment
If you would like an appointment / review with our osteomyelitis specialist in Singapore, the best way is to call +65 6664 8135 or click here to book an appointment at the clinic. If you would like to speak to one of our clinicians first about e.g. hematogenous vs contiguous spread, causative organism of osteomyelitis, hematogenous osteomyelitis etc, then please contact feedback2@bone.com.sg or SMS/WhatsApp to +65 6664 8135.
Rest assured that the best possible care will be provided for you.
