Osteomyelitis

• Osteomyelitis, an inflammatory condition of the bone, may occur at any age.
• It is most commonly observed in children aged 3-12 years, with a peak incidence during this period.
• Osteomyelitis tends to affect boys twice as frequently as girls, possibly due to differences in activity levels and injury patterns.
• A microbial etiology is confirmed in approximately three-fourths of osteomyelitis cases, with various bacteria being the predominant causative agents.
• In cases of septic joint, which can be a complication of osteomyelitis, microbial involvement is identified in approximately two-thirds of cases, emphasizing the infectious nature of these conditions.

• Acute Hematogenous Osteomyelitis: This type typically occurs as a result of the hematogenous (blood-borne) spread of bacteria to the bone. It often presents suddenly with symptoms such as fever, localized pain, and swelling.
• Subacute Osteomyelitis: Subacute osteomyelitis has a more gradual onset compared to the acute form. Symptoms may develop over a longer period, and it is characterized by milder pain and less pronounced systemic signs of infection.
• Chronic Osteomyelitis: Chronic osteomyelitis is a long-standing, persistent infection of the bone. It can result from inadequate treatment of acute or subacute osteomyelitis or from the spread of infection from nearby tissues. This form often requires prolonged and comprehensive medical management.

1. Hematogenous: Osteomyelitis often originates from hematogenous spread, where bacteria enter the bloodstream and disseminate to the bone tissue.
2. Direct Spread from a Contiguous Focus of Infection: In some cases, osteomyelitis can result from the direct extension of infection from adjacent tissues.

In children, osteomyelitis frequently arises due to bacteremia, the presence of bacteria in the bloodstream. Key points in the pathogenesis include:

• It primarily involves growing bones, particularly the metaphyses of long bones.
• The femur and tibia are equally affected, accounting for almost half of all cases. Common sites include the distal femur, proximal tibia, distal humerus, and distal radius.
• Bacteria tend to lodge in the nutrient arteries that supply the growth plates of bones.
• Blood in the large sinusoidal veins within bones flows slowly, which may contribute to the establishment of infection.
• Phagocytic cells are notably absent in this area, making it challenging for the immune system to clear the infection.
• Obstruction of blood flow by bacterial microemboli can lead to the formation of small areas of avascular necrosis and metaphyseal abscess.

1. Bacteria Lodge in Nutrient Arteries: Bacteria have a propensity to lodge in the nutrient arteries that supply the growth plates of bones.
2. Slow Blood Flow in Sinusoidal Veins: Within bones, blood in the large sinusoidal veins flows slowly, and this area lacks phagocytic cells, making it a suitable environment for bacterial colonization.
3. Obstruction Leads to Avascular Necrosis: Obstruction of blood flow by bacterial microemboli can result in the formation of small areas of avascular necrosis and metaphyseal abscess.

Additional details regarding the pathogenesis of osteomyelitis include:

• Trauma is often noted before the onset of osteomyelitis, occurring in about one-third of cases.
• In infants under 1 year of age, capillaries perforate the epiphyseal growth plate.
• The infection can spread across the epiphysis, leading to septic arthritis.
• Pyarthrosis, an infection involving a joint, is a common complication of osteomyelitis, particularly in joints where the joint capsule inserts proximal to the epiphyseal plate (e.g., hip, elbow, shoulder, knee).

Chronic Osteomyelitis

• Involucrum: Infected periosteum can calcify, forming a shell of new bone around the infected portion of the bone shaft.
• Brodie Abscess: This is a subacute intraosseous abscess that does not drain into the subperiosteal space. It is classically located in the distal tibia.
• Sequestrum: Portions of avascular bone that have separated from adjacent bone, frequently covered with a thickened sheath.

Contiguous Osteomyelitis

• Less common in children compared to other forms of osteomyelitis.
• Usually occurs after the spread of cellulitis as a result of an infected wound.
• Osteomyelitis may also result from the direct inoculation of a penetrating wound.
• Primary viral infections of bones or joints are rare.

• S. aureus: Responsible for most infections in all age groups.
• Group B Streptococci (neonate) and other Streptococci (Group A), Pneumococcus: Among the causative bacteria, especially in neonates.
• Anaerobic Microorganisms and Gram-Negative Enteric Bacteria: Can also be responsible for osteomyelitis infections.
• Mycobacterium tuberculosis: In certain cases, such as tuberculous osteomyelitis.
• Underlying Conditions: Osteomyelitis can occur as a result of conditions like furunculosis, infected burns, varicella, trauma, drug abuse, and prolonged IV or central parenteral alimentation.
• Sickle Cell Anemia: May be associated with infections caused by Salmonella, Staphylococcus, and less commonly, Streptococcus pneumonia.
• Cat or Dog Bite: Infections may result from bites, with Pasteurella multocida being a common pathogen.
• Puncture Wounds, IV Drug Abuse: Pseudomonas infections are more common in cases involving puncture wounds or IV drug abuse.
• H. influenzae Type b: Accounts for more than half of all cases but is rarely seen in an immunized population due to vaccination efforts.

• Hematogenous Osteomyelitis: Typically involves a single bone.
• Common Presenting Complaints: Patients often present with complaints such as focal pain, exquisite point tenderness over the affected bone, warmth, erythema, swelling, and decreased use of the affected extremity.
• Systemic Symptoms: Symptoms may also include fever, anorexia, irritability, and lethargy in addition to the focal findings.
• Pseudoparalysis: Affected individuals may refuse weight-bearing and spontaneous or requested motion, a phenomenon known as pseudoparalysis.
• Hematogenous Vertebral Osteomyelitis: Typically presents with an insidious onset and may have little fever or systemic toxicity.
• Pelvic Osteomyelitis: Presents with symptoms such as limping, abdominal pain, hip pain, groin pain, and fever.

Age Group	Common Sites	Clinical Features	Common Pathogens
Neonates	40% multiple site	Local edema Reduced limb motion Joint effusion (60-70%)	GBS, E. coli, S. aureus
1 - 24 months	Long bones Joint involvement	Pseudoparalysis Fever Limp	S. aureus, GBS
2 - 20 years	Metaphysis of long bones Rarely vertebral or pelvic involvement	Focal pain + fever (90%) Focal tenderness (70%) Joint effusion (20%)	S. aureus (60-90%), Strep (10%)

• Marked Tenderness: Patients typically exhibit marked tenderness over the involved site.
• Lab Findings:
  • Leukocytosis may be present.
  • ESR (Erythrocyte Sedimentation Rate) is often elevated.
  • CRP (C-Reactive Protein) levels may be elevated as well.
• Blood Culture: Blood culture is performed, and it can be positive in approximately 60% of cases.
• Aspirated Cellulitis or Periosteal Space Cultures: Cultures are often obtained before antibiotic therapy, typically from aspirated cellulitis or the periosteal space.
• Radiography:
  • Early finding (around 9 days) of acute systemic osteomyelitis is the loss of the periosteal fat line.
  • Later findings include periosteal elevation and periosteal destruction.
• Technetium 99m Bone Scans: These scans may be utilized in the diagnostic process.
• MRI (Magnetic Resonance Imaging): MRI is particularly useful for assessing the extent of infection or when infection is a complication of trauma, surgery, or conditions like sickle cell anemia.

Treatment

• Initial IV Antibiotic Selection: The choice of the initial IV antibiotic should be based on the results of the Gram stain of bone aspiration, blood culture, and any age-associated disease factors.
• Coverage for S. aureus: The initial IV antibiotic should cover S. aureus, and options include oxacillin, nafcillin, methicillin, or clindamycin.
• Methicillin-Resistant Staph Consideration: The possibility of methicillin-resistant Staphylococcus aureus (MRSA) should be considered.
• Gram-Negative Organisms: If there is a history of wound contamination or IV drug abuse, consider covering Gram-negative organisms.
• Sickle Cell Anemia: For patients with sickle cell anemia, coverage for S. aureus and Salmonella is essential. Options include cefotaxime or ceftriaxone.
• Response to Antibiotics: A response to appropriate IV antibiotics usually occurs within 48 hours. Lack of improvement in fever and pain after this time may indicate the need for surgical drainage or the presence of an unusual pathogen.
• Indications for Surgical Drainage: Surgical drainage may be appropriate at an earlier time if sequestrum is present, the disease is chronic or atypical, the hip joint is involved, or there is spinal cord compression.
• Duration of Antibiotic Therapy: Standard therapy typically consists of antibiotics for 4-6 weeks.
• Transition to Home Therapy: After initial inpatient treatment and a good clinical response, including decreases in CRP or ESR, consideration may be given for home therapy with IV antibiotics or oral antibiotics.