Osteomyelitis

By admin Last updated Feb 16, 2024

Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.

Title: 5-Minute Orthopaedic Consult, 2nd Edition

> Table of Contents > Osteomyelitis

Osteomyelitis

Frank J. Frassica MD

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 isS. 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 (1).

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.

P.299

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 débridement 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 36–48 hours of antibiotic treatment
Surgical treatment consists of opening the periosteum, drilling the cortex, and débriding 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.

References

1. McCarthy
EF, Frassica FJ. Infections of bones and joints. In: Pathology of Bone
and Joint Disorders: With Clinical and Radiographic Correlation.
Philadelphia: WB Saunders, 1998:153–164.

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.