6th lecture
Musculoskeletal infections / Osteomyelitis
Dr.Alaa Al-algawy
Musculoskeletal infections are common; they can affect all parts of the musculoskeletal system;
and they can be dangerous and even life threatening.
Bacteria can gain entry into the body from direct penetrating trauma, by hematogenous spread
from adjacent or remote sites of infection, or during surgical exposures.
Osteomyelitis
Osteomyelitis is defined as an inflammation of the bone caused by an infecting organism. The
infection may be limited to a single portion of the bone or may involve numerous regions, such
as the marrow, cortex, periosteum, and the surrounding soft tissue.
The infection generally is due to a single organism, but polymicrobial infections can occur,
especially in the diabetic foot.
Classification is most commonly based on the timing of onset:
Acute: occurs within 7 to 14 days of onset .Most often from hematogenous spread
The most common organism in neonates is Staphylococcus aureus, followed by
Streptococcus or Gram-negative organisms (Haemophilus influenzae).(5-50 %).
In older infants and children, it usually is S. aureus.
Adults may also develop acute hematogenous infections especially around
implanted metal prostheses and fixation hardware.
Sub acute: is between several weeks and three months , Accounts for 1/3
of primary bone infections, Is characterized by insidious onset, 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:
bone infection that has bee present
for more than three months.
S. aureus is the most common organism. Usually, these patients have sequestra
and multiple cavities that require curettage and occasionally bone grafting.
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Incidence:
The incidence is higher in children than in adults, with a peak occurring in the later years of the
1st decade
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
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
Lab Tests :
A white blood cell count (WBC) 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.
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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.
It begins to elevate at 48 to 72 hours and returns to normal after 2 to 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 to 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.
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
Pathological Findings :
stage 1 Bacteraemia, stage 2 pus formation, stage 3 bone necrosis, stage 4 new bone formation,
(In acute Osteomyelitis in children, the metaphysis is commonly involved. It is thought that the
end vessels of the nutrient artery empty into much larger sinusoidal veins, causing a slow and
turbulent flow of blood at this junction. These conditions predispose bacteria to migrate through
adjacent gaps in the endothelium and adhere to the matrix. Also, low oxygen tension in this
region may compromise phagocytic activity of white blood cells.
Thrombosis due to infection results in a region of avascular
necrosis that may lead to abscess formation .
As pus accumulates and pressurizes,
it can track through the cortex via the
Haversian system and Volkmann's
canals to collect beneath the
periosteum.
Subperiosteal abscesses may
stimulate the formation of a
periosteal involucrum.
Once out of the cortex, pus can also
track through soft tissues to the
surface of the skin, forming a
draining sinus.
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The physis and joint capsule act as barriers to the flow of pus. However, secondary septic
arthritis may occur if the infection begins in a region of bone within the confines of a joint
capsule. This is why the hip joint is particularly susceptible to secondary infection arising from a
spreading osteomyelitis of the femoral head or neck.
Additionally, pus may track through the transphyseal vessels found in infants up to 6 months of
age, causing secondary septic arthritis.
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 to 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 specific but helpful in diagnosing acute Osteomyelitis, 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.
Differential Diagnosis
Trauma
Septic arthritis
Cellulitis
Malignancy (leukemia or Ewing sarcoma)
Thrombophlebitis
Sickle cell crisis
Toxic synovitis
Osteoid osteoma
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Treatment
General Measures
Principles of treatment include 1- identification of the organism, 2- selection of an appropriate
antibiotic, 3- surgical debridement if necessary, and 4-sufficient duration of treatment to allow
complete resolution.
Surgery is not indicated if the condition is detected early and no devascularized bone is present.
1-admission to the hospital
2-supportive measures:
I.V fluid.
pain killer.
splintage .
3- Antibiotics according to the age
Medication
Antibiotic selection (guided by cultures and sensitivities)
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 to 6 weeks of oral therapy is indicated, provided an appropriate oral
antibiotic is available
The following are suitable empirical antibiotic regimens:
A/ Non high-risk patients:
High-dose, IV flucloxacillin plus benzylpenicillin (plus either fusidic acid or
rifampicin depending on the severity of infection).
B/ If the patient is in a high-risk group or Gram-negative organisms were identified on Gram
stain, treatment can be modified as follows:
High-dose, IV flucloxacillin plus either an aminoglycoside such as gentamicin or a
quinolone such as ciprofloxacin (plus either fusidic acid or rifampicin depending on
severity)
or
A second-generation cephalosporin such as cefuroxime (plus either fusidic acid or
rifampicin depending on severity).
In penicillin-allergic patients:
Clindamycin plus a quinolone such as ciprofloxacin
or
Vancomycin plus a quinolone such as ciprofloxacin
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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 to 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.
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.and in Chronic osteomyelitis to debride dead tissues and
remove the sequestra.
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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