Review Question - QID 218784

This febrile pediatric patient who presents with ankle pain, swelling, and erythema as well as an enhancing bony foci on MRI most likely has osteomyelitis of the distal tibia. The most common location of osteomyelitis in children is the metaphysis of long bones.

Osteomyelitis is a deep infection of the bones that can occur through hematogenous spread, contiguous infection, or direct inoculation of bone with microorganisms. Hematogenous spread happens most commonly in children and are located primarily in the metaphysis of long bones. The reason for bacterial deposition in these regions is that they feature slow-moving vascular sinusoids as blood vessels approach the physis. Bacteria can exit the vascular channels in these areas and cause osteomyelitis. Contiguous infection occurs more commonly in adults where an unrelated infection in a local area (for example, a soft tissue infection of the foot in a diabetic patient) leads to seeding of the underlying bone. Finally, direct inoculation happens in trauma such as in an open fracture. The most common organism causing osteomyelitis is Staphylococcus aureus, which can be treated with intravenous antibiotics such as ampicillin/sulbactam or vancomycin depending on antibiotic sensitivities.

Yildirim et al. studied the results of using an internal fixator technique to treat pathologic fractures. They found that this technique was successful in all cases though some patients developed shortening. They recommended considering this technique in patients with osteomyelitis causing pathologic fractures.

Incorrect Answers:
Answer 1: The diaphysis is a common location for osteomyelitis in patients with untreated open fractures as these regions are directly inoculated when they come through the skin.

Answer 2: The epiphysis is not a common location for infections because it has its own blood supply that is distinct from the vascular sinusoids of the metaphysis. The epiphysis is a common location for some neoplastic lesions such as chondroblastomas and giant cell tumors.

Answer 4: The periosteum often reacts in patients who have underlying osteomyelitis by forming new bone. This involucrum bone helps to contain a necrotic bone sequestrum. The bone is a more common site of infection than the surrounding periosteum.

Answer 5: The physis does not often become directly infected because it is essentially avascular. Physeal growth arrest may occur due to inflammation from a surrounding infection.

Bullet Summary:
The metaphysis is the most common site of infection in pediatric hematogenous osteomyelitis due to slow-flowing sinusoids that increase the risk of bacterial seeding.