17 year old previously healthy male presented to the ED with R knee swelling after he caught and hyperextended his leg while doing motocross the night before. He was unable to bear weight. Physical exam showed large medial R knee effusion with tenderness and limited passive range of motion.
Bedside ultrasound demonstrated large effusion with blood layering out to the bottom of the joint, as seen. Radiographs of the joint were concerning for tibial spine fracture, that is an ACL avulsion fracture due to hyperextension more common in pediatric populations. CT was obtained and patient was placed in knee immobilizer and discharged for ortho follow up the next week. He will likely require surgery.
Traumatic hemarthosis occurs when bone is fractured, spilling blood and lipids from the marrow. Joint aspiration is not required in patients with a clear history of trauma, and a suggestive ultrasound makes this procedure even less necessary. Mainstay treatment includes immobilization, ice, and addressing the underlying disorder. Therapeutic athrocentesis may be helpful for pain in large effusions, but is generally not recommended.