CASE 69

By: Dr. Amna Kashgari MD,SSC-Rad

HISTORY: 2-year-old boy presented to the emergency room with fever, left knee swelling and limitation of movement.

What are your findings?

What is your differential diagnosis?

What is your most likely diagnosis?

Mention 3 complication of this entity?

FINDINGS:

Frontal and lateral radiographs (A) of the left knee demonstrate soft tissue swelling around the knee with loss of fat planes. There is suprapatellar effusion. The joint space is widened. No focal bone lesion is noted.

Sagittal T2-weighted image with fat saturation (B) demonstrates joint effusion with subcutaneous fat stranding and extensive inflammation involving the vastus lateralis muscle. Sagittal T1-fat sat weighted image with contrast (C) demonstrates thickened enhancing synovium. The bone marrow signal intensity is preserve.

DIFFERENTIAL DIAGNOSIS:

• Septic arthritis.

• Reactive arthritis – post viral infection.

• Juvenile idiopathic arthritis.

• Hemophilia.

DIAGNOSIS:

Pediatric Septic arthritis.

Complications:

Osteomyelitis.

Joint destruction (mechanical).

Leg length discrepancy secondary to early closure of the growth plate.

PEARLS AND DISCUSSION:

Septic arthritis is a destructive arthropathy caused by an intra-articular infection. It is considered a surgical emergency to prevent permanent joint damage.

It is more common in children below 3 years of age with boys twice affected than girls.

The mode of infection is usually haematogenous spread to the synovium. Less common mode of entry is direct penetration or from adjacent osteomyelitis.

Causative organisms:

Neonates: Most common cause is Staphylococcus aureus. Then, Escherichia coli, group B streptococci, and other gram-negative bacilli also cause the disease.

Children (2 months to 5 years): The most common organism is S. aureus. Second most common cause H influenzae type B. Other etiologies include group A streptococci and Streptococcus pneumoniae.

Adolescents: Neisseria gonorrhoeae, Group A streptococcus, and Salmonella in individuals with sickle cell anemia.

Clinical presentation: The patient is febrile with local pain.

Radiological diagnosis:

X-rays may be:

• Normal.

• Joint effusion may be seen.

• Juxta-articular osteoporosis due to hyperaemia.

Ultrasound:

• Shows joint effusion with echogenic debris.

• Color Doppler may show increased peri-synovial vascularity.

MRI:

Sensitive and more specific for early cartilaginous damage.

T1: Low signal within subchondral bone.

T2: Perisynovial oedema.

C+ (Gd): Synovial enhancement.

It is important to know that in neonate and young children below 2 years blood vessels that connect the metaphysis and epiphysis serve as a conduit for spread of the infection and the bony cortex is thin, and the periosteum is loose. They often have coexisting septic arthritis and osteomyelitis.

FURTHER READING:

1. Johanna Monsalve . J. Herman Kan et al. Septic Arthritis in Children: Frequency of Coexisting Unsuspected Osteomyelitis and Implications on Imaging Work-Up and Management. AJR 2015; 204:1289–1295.

2. Johan G Blickman, Bruce R Parker, Patrick D Barnes. Pediatric Radiology: The Requisites, 3e. ISBN-10: 0323031250