Thursday, January 21, 2010

ACUTE HEMATOGENOUS OSTEOMYELITIS

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ACUTE HEMATOGENOUS OSTEOMYELITIS
·    most common type of bone infection, usually in children, males in all age groups affected
·   caused by a bacteremia, which is a common occurrence in childhood. The causes of bacteremia are many. Bacteriological seeding of bone generally is associated with other factors such as localized trauma, chronic illness, malnutrition, or an inadequate immune system.
·   In children, generally metaphyses of rapidly growing long bones involved.

·   
Bacterial seeding inflammatory reaction  local ischemic necrosis of bone abscess formation intramedullary pressure increases cortical ischemiapurulent material escape through the cortex into the subperiosteal spaceA subperiosteal abscess (Fig. 16-1) If left untreatedextensive sequestra formation and chronic osteomyelitis.

·   age distribution : in children is bimodal, generally younger than 2 years and 8 to 12 years old.
·   In children ˂2 years, some blood vessels cross the physis and may allow the spread of infection into the epiphysis.
·   Infants are susceptible to limb shortening or angular deformity if the physis or epiphysis is damaged from the infection. Otherwise, the physis acts as a barrier that prevents the direct spread of a metaphyseal abscess into the epiphysis. The metaphysis has relatively fewer phagocytic cells than the physis or diaphysis, allowing infection to occur more easily in this area. A resulting abscess breaks through the thin metaphyseal cortex, forming a subperiosteal abscess. The diaphysis rarely is involved, and extensive sequestration occurs infrequently except in the most severe cases.
·    In children ˃2 years, the physis acts as a barrier to the spread of a metaphyseal abscess. Metaphyseal cortex in older children is thicker, however, the diaphysis is at greater risk in these patients. If the infection spreads into the diaphysis, the endosteal blood supply jeopardized. With a concurrent subperiosteal abscess, the periosteal blood supply is damaged and can result in extensive sequestration and chronic osteomyelitis if not properly treated.
                ·    After  physes are closed, acute hematogenous osteomyelitis is much less common. Hematogenous seeding of bone in adults usually is seen in a compromised host. Although it can occur anywhere and in any part of the bone, generally the vertebral bodies are affected. In these patients, abscesses spread slowly, and large sequestra rarely form. If localized destruction of cortical bone occurs, pathological fracture can result.
·   In children ˂2 years, the common blood supply of the metaphysis and epiphysis crosses the physis and can allow spread of a metaphyseal abscess into the epiphysis and eventually into the joint. The hip joint is the most commonly affected in young patients; however, the physes of the proximal humerus, radial neck, and distal fibula also are intraarticular, and infection in these areas can lead to septic arthritis as well. In severe infection, epiphyseal separation can occur in children younger than 2 years.

In older children, this common circulation is no longer present, and septic arthritis is rare. After physes are closed, infection can extend directly from the metaphysis into the epiphysis and involve the joint. Septic arthritis resulting from acute hematogenous osteomyelitis generally is seen only in infants and adults.                

Physical
Findings at physical examination may include the following:
·   Fever (present in only 50% of neonates)
·   Edema
·   Warmth
·   Fluctuance
·   Tenderness to palpation
·   Reduction in the use of the extremity (eg, reluctance to ambulate, if the lower extremity is involved or pseudoparalysis of limb in neonates)
·   Failure of a young child to sit up normally
·   Sinus tract drainage (usually a late finding or one that occurs with chronic infection)
Infecting organism: Staphylococcus aureus is the most common found in older children and , gram-negative bacteria cause an increasing number of vertebral body infections in adults. Pseudomonas is the most common infecting organism found in intravenous drug abusers with osteomyelitis. Fungal osteomyelitis is seen increasingly in chronically ill patients receiving long-term intravenous therapy or parenteral nutrition. Salmonella osteomyelitis has long been associated with SS or SC hemoglobinopathies. This infection tends to be diaphyseal rather than metaphyseal. 
In infants with acute hematogenous osteomyelitis, S. aureus is still a frequent isolate, but group B streptococcus and gram-negative coliforms also are commonly found. S. aureus or gram-negative organisms are the usual cause of orthopaedic infections found in premature infants undergoing treatment in the neonatal intensive care unit; more than 40% have multifocal involvement. Group B streptococcus is the most likely infecting organism found in otherwise healthy infants 2 to 4 weeks old. Haemophilus influenzae infections occur primarily in children 6 months to 4 years old. The incidence of this infection has been reduced dramatically because of routine immunizations against the organism.
·   Hematogenous long-bone osteomyelitis
o Abrupt onset of high fever (fever is present in only 50% of neonates with osteomyelitis)
o Fatigue
o Irritability
o Malaise
o Restriction of movement (pseudoparalysis of limb in neonates)
o Local edema, erythema, and tenderness
·   Hematogenous vertebral osteomyelitis
o Insidious onset
o History of an acute bacteremic episode
o May be associated with contiguous vascular insufficiency
o Local edema, erythema, and tenderness
o Failure of a young child to sit up normally2
·   Chronic osteomyelitis
o Nonhealing ulcer
o Sinus tract drainage
o Chronic fatigue
o Malaise
Diagnosis: Clinical: History
Hematogenous osteomyelitis usually presents with a slow insidious progression of symptoms. Direct osteomyelitis generally is more localized, with prominent signs and symptoms. General symptoms of osteomyelitis include the following:
Causes
Bacterial causes of acute and direct osteomyelitis:
·   Acute hematogenous osteomyelitis
o Newborns (younger than 4 mo): S aureusEnterobacter species, and group A and B Streptococcus species
o Children (aged 4 mo to 4 y): S aureus, group A Streptococcus species, Haemophilus influenzae, and Enterobacter species
o Children, adolescents (aged 4 y to adult): S aureus (80%), group A Streptococcus species, H influenzae, and Enterobacter species
o Adult - S aureus and occasionally Enterobacter or Streptococcus species
o Note increasing reports of other pathogens in bone and joint infections including community-associated methicillin-resistant Staphylococcus aureus (MRSA), Kingella kingae,and others.
·   Direct osteomyelitis
o Generally - S aureusEnterobacter species, and Pseudomonas species
o Puncture wound through an athletic shoe - S aureus and Pseudomonas species
o Sickle cell disease -S aureus and Salmonellae species

 Note that responsible pathogens may be isolated in only 35% to 40% of infections.



Fever and malaise may or may not be present in the early stages of the disease, although pain and local tenderness are common findings. Swelling may be significant, and compartment syndrome has been reported in children.

Box   

-History and physical examination
-Laboratory tests: white blood cell count, erythrocyte sedimentation rate, C-reactive protein
-Plain radiographs
-Technetium-99m bone scan ± MRI
-Aspiration for suspected abscess
The WBC count often is normal, but the ESR and C-reactive protein level usually are elevated. The C-reactive protein is a measurement of the acute phase response and is especially useful in monitoring the course of treatment of acute osteomyelitis because it normalizes much sooner than the erythrocyte sedimentation rate. Standard radiographs generally are negative, but may show soft-tissue swelling. Skeletal changes, such as periosteal reaction or bony destruction, generally are not seen on plain films until 10 to 12 days into the infection. Technetium-99m bone scans can confirm the diagnosis 24 to 48 hours after onset in 90% to 95% of patients. Gallium scans and indium-111–labeled leukocyte scans also can aid in diagnosis when used in conjunction with technetium scanning. MRI can show early inflammatory changes in bone marrow and soft tissue.          
The causative organism can be identified in approximately 50% of patients through blood cultures. Bone aspiration usually gives an accurate bacteriological diagnosis and should be performed with a 16-gauge or 18-gauge needle in the area of maximal swelling and tenderness, usually the long bone metaphysis. The subperiosteal space should be aspirated first by inserting the needle to the level of the outer cortex. If no purulent material or fluid is encountered, the needle is placed through the cortex to obtain a marrow aspirate. Patients with suspected osteomyelitis of the hip or vertebra should have CT- or ultrasound-assisted aspiration. The sample is sent to the laboratory for Gram stain, culture, and sensitivities.
Treatment
Appropriate treatment shortly after onset of acute hematogenous osteomyelitis can significantly lower morbidity. Surgery and antibiotic treatment are complementary, and in some patients antibiotic treatment alone cures the disease; in others, prolonged antibiotic treatment is doomed to failure without surgical treatment. The choice of antibiotic is based on the highest bactericidal activity, the least toxicity, and the lowest cost.
It has been well established that sequestered abscesses demand surgical drainage. Areas of simple inflammation without abscess formation can be treated with antibiotics alone, however. In 1983, Nade proposed five principles for the treatment of acute hematogenous osteomyelitis that are still applicable today: (1) an appropriate antibiotic is effective before pus formation; (2) antibiotics do not sterilize avascular tissues or abscesses, and such areas require surgical removal; (3) if such removal is effective, antibiotics should prevent their reformation, and primary wound closure should be safe; (4) surgery should not damage further already ischemic bone and soft tissue; and (5) antibiotics should be continued after surgery.
The patient should receive general supportive care consisting of intravenous fluids, appropriate analgesics, and comfortable positioning of the affected limb. Frequent serial examinations should be done. If an abscess requiring surgical drainage is not found by subperiosteal or bone marrow aspirate, intravenous antibiotics based on the Gram stain should be started. Empirical antibiotic coverage for the most likely infecting organism should be started if Gram stain is negative, and the patient should be carefully monitored. The C-reactive protein should be checked every 2 to 3 days after the initiation of antibiotic therapy. If no appreciable clinical response to antibiotic treatment is noted within 24 to 48 hours, occult abscesses must be sought, and surgical drainage should be considered. The two main indications for surgery in acute hematogenous osteomyelitis are (1) the presence of an abscess requiring drainage and (2) failure of the patient to improve despite appropriate intravenous antibiotic treatment.
The objective of surgery is to drain any abscess cavity and remove all nonviable or necrotic tissue. When a subperiosteal abscess is found in an infant, several small holes should be drilled through the cortex into the medullary canal. If intramedullary pus is found, a small window of bone is removed. The skin is closed loosely over drains, and the limb is splinted. The limb is protected for several weeks to prevent pathological fracture. Intravenous antibiotics should be continued postoperatively. The duration of antibiotic therapy is controversial; however, the current trend is toward a shorter course of intravenous antibiotics, followed by oral antibiotics and monitoring of serum antibiotic levels. This schedule should be determined on an individual.
Drainage of Acute Hematogenous Osteomyelitis
The technique for draining acute osteomyelitis of the tibia is described. The technique and principles for drainage in other long bones are similar. 

TECHNIQUE 
·    Use a tourniquet whenever possible. Elevate the extremity for a few minutes before inflating the tourniquet. Do not exsanguinate the limb with an elastic bandage if infection is present.
·    Make an anteromedial incision 5 to 7.5 cm long over the affected part of the tibia.
·    Incise the periosteum longitudinally; it may be elevated from bone by a subperiosteal abscess, and if so, the compressed pus will escape.
·    If no abscess is found, gently elevate the periosteum 1.5 cm on each side. Try to strip as little periosteum as possible; the more periosteum that is stripped, the more an already compromised blood supply to bone is damaged.
·    Drill several holes 4 mm in diameter through the cortex into the medullary canal, regardless of whether a subperiosteal abscess is present. If pus escapes through these holes, use a drill to outline a cortical window 1.3 × 2.5 cm, and remove the cortex with an osteotome.
·    Evacuate the intramedullary pus, and gently remove any necrotic tissue.
·    Irrigate the cavity with at least 3 L of saline with a pulsatile lavage system. Antibiotics may be placed in the irrigation solution. Close the skin loosely over drains, but do not close the wound if this produces excessive tension on the skin.


AFTERTREATMENT

A long leg posterior plaster splint is applied with the foot in a neutral position, the ankle at 90 degrees, and the knee at 20 degrees of flexion. When the wound has healed, the splint is removed, and protected weight bearing with crutches is begun. The patient is placed on antibiotics based on culture sensitivities directed by an infectious disease specialist. Generally, a 6-week course of intravenous antibiotics is given. Orthopaedic and infectious disease follow-up is continued for at least 1 year.



TABLE. Comparison of Acute and Subacute Hematogenous Ostemyelitis
Acute
Subacute
WBC count
Frequently elevated
Frequently normal
ESR
Frequently elevated
Frequently elevated
Blood cultures
50% positive
Rarely positive
Bone cultures
90% positive
60% positive
Localization
Metaphysis
Diaphysis, metaphysis, epiphysis, cross physis
Pain
Severe
Mild to moderate
Systemic illness
Fever, malaise
No
Loss of function
Marked
No or minimal
Prior antibiotics
Occasional
30%-40%
Initial radiograph
Bone normal
Frequently abnormal