Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Osteomyelitis

Basics
Description
  • Osteomyelitis is inflammation or infection of bone.
  • Classification is most commonly based on the timing of onset:
    • Acute: Most often from hematogenous spread:
      • The most common organism in neonates is Staphylococcus aureus, followed by Streptococcus or Gram-negative organisms.
      • In older infants and children, it usually is S. aureus.
    • Subacute:
      • Accounts for 1/3 of primary bone infections
      • Is characterized by insidious onset, mild symptoms, longer duration of infection, and inconclusive laboratory data.
      • The most common organism is Staphylococcus species.
      • It usually requires longer duration of antibiotic treatment than the acute condition.
    • Chronic:
      • S. aureus is the most common organism.
      • Usually, these patients have sequestra and multiple cavities that require curettage and occasionally bone grafting.
    • 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).
  • 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
  • A male predilection appears, which is not clearly understood.
  • It affects <1% of children .
Risk Factors
  • Deficient immune systems as a result of viral illness, trauma, anesthesia, or malnutrition also may play a role in the development of osteomyelitis.
  • Children and adults may have a history of antecedent trauma.
  • Sickle cell disease:
    • In this population, hematogenous osteomyelitis is more common secondary to bone infarcts than to other causes.
    • Although S. aureus is the most common organism, Salmonella infections may occur.
Etiology
  • Although the causes remain unknown, factors suspected of having an association with infection include trauma and an altered immune system (especially in adults).
  • 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
  • Pain is the most common symptom, followed by swelling, erythema, warmth, and limited ROM of the adjacent joints.
  • Fever is not always present.
  • 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.
  • The index of suspicion must be highest in the neonate.
  • Consider a firm diagnosis when 2 of these 4 criteria are present:
    • Pus aspirated from bone
    • Positive bone or blood culture
    • Symptoms of pain, swelling, warmth, and decreased ROM
    • Typical radiographic changes consistent with osteomyelitis
Physical Exam
  • The goal of the examination is to localize the area of involvement and to identify any possible source.
  • The appearance of the child may vary from cranky to lethargic, depending on the extent and duration of infection.
  • Before palpation, visually assess the amount of limb movement or usage.
  • 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.
  • Tenderness, warmth, and erythema usually are present in the bone’s metaphyseal region.
Tests
Lab
  • A white blood cell count is not a reliable indicator of infection, but if it is elevated, it is suggestive of infection.
  • Blood cultures also should be obtained with the initial diagnostic blood sample.
    • ~1/2 of cases are positive.
    • If a case is positive, it may eliminate the need to aspirate bone to obtain the organism.
  • The ESR rate is a nonspecific acute-phase reactant that is elevated in many cases and is a reliable indicator of inflammation.
    • It begins to elevate at 48-72 hours and returns to normal after 2-3 weeks if the infection has resolved.
    • Because of the lag time of the ESR, it is not helpful in assessing resolution of infection.
  • An elevated level of C-reactive protein resulting from inflammation also is useful.
    • 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).
  • Aspiration of the site may be performed to identify the causative organism.
    • The specimen should be sent for Gram stain, aerobic and anaerobic cultures, acid-fast bacilli, and tests for fungi.
    • Bone cultures often are positive.
    • Some clinicians suggest fine-needle biopsy with an 11-gauge bone biopsy (or bone marrow) needle for histologic examination.
      • Heavy sedation usually is required to allow the patient to be comfortable and to obtain a specimen from the proper area reliably.
      • The site of involvement usually is metaphyseal bone rather than hard cortical bone, so it is possible to penetrate the bone for a sample.
      • If the site of involvement is not clear, it should be localized via bone scanning or MRI.
  • All cultures and laboratory tests should be obtained before starting antibiotic treatment.
Imaging
  • Radiography:
    • Soft-tissue swelling is the earliest radiographic change.
    • Classic radiographic bony changes, such as osteopenia, bone resorption, and new periosteal bone formation, may not occur until 14-21 days after symptom onset.
  • Bone scan:
    • May be used to localize the area of involvement
    • Results may be falsely negative in the 1st month of life.
    • Bone aspiration will not affect bone scan results if the scan is performed within 48 hours of aspiration.
    • A bone scan is not needed if the area of involvement is already known.
  • CT:
    • Not useful in diagnosing acute osteomyelitis, but it may assist in differentiating other lucent lesions such as osteoid osteoma or chondroblastoma.
  • MRI:
    • Excellent sensitivity and specificity
    • T1-weighted images give excellent anatomic detail of the site of infection.
    • T2-weighted images show high signal in areas of inflammation and periosteal reaction.
  • 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
  • Infection begins in the sinusoids of the metaphysis, usually near the end of a long bone.
  • As the infection spreads, the medullary vessels thrombose and cause a mechanical blockage of inflammatory cells.
    • Results in inflammatory cell migration into the medullary cavity, with consequent intraosseous pressure buildup and development of pus
    • The pus then takes the path of least resistance and exits through the metaphyseal cortex, thereby elevating the periosteum.
    • A subperiosteal abscess subsequently forms under the elevated periosteum.
  • The elevated periosteum manifests ~10-14 days later as a periosteal reaction.
Differential Diagnosis
  • Trauma
  • Septic arthritis
  • Cellulitis
  • Malignancy (leukemia or Ewing sarcoma)
  • Thrombophlebitis
  • Sickle cell crisis
  • Toxic synovitis
  • EOG
  • Osteoid osteoma
Treatment
General Measures
  • 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.
  • Surgery is not indicated if the condition is detected early and no devascularized bone is present.
Medication
  • Antibiotic selection (guided by cultures and sensitivities):
    • Oxacillin in combination with cefotaxime or gentamicin in neonates and oxacillin alone in infants and children
    • Cefazolin is recommended for patients allergic to penicillin.
    • Clindamycin or vancomycin is recommended for patients allergic to both penicillin and cephalosporin.
  • The duration of antibiotic treatment is debatable.
    • It typically involves intravenous antibiotics for 5 days until symptoms resolve and antibiotic sensitivities are identified.
    • Thereafter, a regimen of 4-6 weeks of oral therapy is indicated, provided an appropriate oral antibiotic is available.
Surgery
  • Indications for surgery are controversial but usually include the following:
    • Aspiration of frank pus initially
    • Presence of substantial bone resorption
    • Failure of symptom resolution after 3-48 hours of antibiotic treatment
  • Surgical treatment consists of opening the periosteum, drilling the cortex, and debriding any devascularized bone.
Follow-up
Prognosis
  • Most children do extremely well with appropriate treatment, and they suffer no long-term effects.
  • Problems arise usually when infection is not recognized or treated in a timely manner, with the possible development of chronic osteomyelitis.
Complications
  • Growth plate arrest may occur, if the infection crosses the growth plate.
  • A pathologic fracture may develop if the bone is excessively loaded before healing and remodeling.
Miscellaneous
Codes
ICD9-CM
  • 730.0 Acute or subacute osteomyelitis
  • 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.

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