E1216. Cross Sectional Imaging of Articular and Peri-Articular Infection Involving the Knee
  1. Anupam Basu; Cook County Health
  2. Luke Kopulos; Cook County Health
  3. Anita Kelekar; Cook County Health
  4. Edwin Wang; Cook County Health
  5. Nancy Wilkins; Cook County Health
Each year the diagnosis of musculoskeletal infection is made in nearly 2 million patients in the emergency department. Timely diagnosis and treatment of these conditions is critical. Risk factors for presence of infection include IV drug use, HIV, diabetes, sickle cell anemia and peripheral vascular disease. While radiographs and exam provide an initial assessment, they have limited utility for soft tissue infections, and are of particularly limited utility in the pediatric population. It is estimated, for example, that radiographs are diagnostic in less than 20% of cases of acute staphylococcal osteomyelitis of childhood. MRI is considered the gold standard imaging modality. However, delayed diagnosis can lead to increased morbidity, therefore CT may be a more practical modality in the emergent setting. CT is superior to MRI in the diagnosis of bony sequestra associated with osteomyelitis and for detection of soft-tissue gas that can indicate necrotizing fasciitis. Therefore, CT also has an important role in select cases.

Educational Goals / Teaching Points
We aim to demonstrate the imaging features associated with infections in and around the knee with particular emphasis on CT and MRI. We plan to illustrate the role that advanced imaging can play in guiding expeditious management of these conditions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Establishing the location of an infection is crucial for appropriate management. Several anatomical planes can be involved in infections around the knee joint and may co-exist. We will use a case-based approach to illustrate pathologically proven infections, broadly categorizing the processes from superficial to deep as; a) soft tissue, b) intra-articular and c) osseous. We will demonstrate the cross-sectional imaging appearance of soft tissue abscess, thrombophlebitis, necrotizing fasciitis, while discussing differential diagnoses including cystic and solid soft tissue masses. We will demonstrate cross-sectional imaging examples of pyogenic and non-pyogenic septic arthritis, with MR features of rheumatoid arthritis presented as a primary differential consideration. Osseous infections presented will include subperiosteal abscess in a pediatric patient. In addition, we will demonstrate CT and MR features of acute osteomyelitis, Brodie's abscess and chronic osteomyelitis. The differential imaging presented in this section will include other marrow replacing lesions on MR imaging, including Ewing’s Sarcoma in the pediatric patient and primary lymphoma of the bone in an adult. The knee provides a relatively simple, large weight-bearing joint will serve as a springboard to understand infections in and around other joints throughout the body.

Cross-sectional imaging, particularly CT and MR imaging can provide crucial information as to the presence and location of infection in and around the knee. It can be crucial to leverage these modalities in select situations to guide definitive management.