Review Question - QID 6401

The patient has the clinical picture of a child with acute hematogenous osteomyelitis about the knee. The next most appropriate step in workup is MRI of the knee.

Fever and unexplained bone pain suggest osteomyelitis until proven otherwise. Physical examination shows tenderness to direct palpation over the distal femur and a radiograph shows swelling of the deep soft tissues over the medial aspect of the left distal femoral metaphysis. MRI is the next best step to confirm the anatomic boundaries of the infection, identify the presence of abscess, and help guide treatment.

Dormans et. al. review pediatric hematogenous osteomyelitis. They emphasize that the clinical picture is the most important factor in making the diagnosis, and that MRI studies are highly sensitive and specific for osteomyelitis. MRI can identify bone edema, abscess formation, sequestra, and developing sinus tracts.

Copley et. al. discuss a multi-disciplinary approach to diagnosis and management of pediatric osteomyelitis. Their protocol includes obtaining an MRI with and without gadolinium contrast within 24 hours of admission, and prior to performing any invasive tests or procedures.

Figure A demonstrates an AP radiograph of bilateral knees in a skeletally immature patient. There is no suggestion of periosteal reaction or abscess formation. There is some suggestion of soft tissue edema in the peri-metaphyseal tissues of the left knee.

Illustration A is a workflow for management of pediatric osteomyelitis obtained from the Copley et. al. reference.

Incorrect Answers:
2. Antibiotics are the mainstay of treatment for hematogenous osteomyelitis without abscess formation, however they should not be administered until after an attempt is made to obtain specimen for culture.
3. Bone scans are not indicated in all cases of osteomyelitis, and frequently return as false negative studies during the first 24 hours of onset of infection. They are also non-specific, and may be positive in the setting of trauma or neoplasm as well.
4. In a patient with high suspicion for osteoarticular infection, application of a long leg cast is not appropriate and should not be performed without further workup.
5. Aspiration of bone is considered a valuable test in that it can obtain bacteriologic diagnosis and determine the presence of an abscess. However, given the ready availability of MRI it is not universally the next best step in management.