Case of the Week
EDITED BY CLAIRE GERMAIN AND CARLEY BOWMAN-BURNS
Case 67: Boys, bikes and knees
Author: Dr Ian Stell
These two boys both had similar injuries. In the first, a 12 year old was doing ‘a wheelie’, (riding his bike with the front wheel off the ground). He stood on his pedals and felt a sudden pain in his knee, he could not weight-bear afterwards, and the knee swelled rapidly. On examination he had gross swelling, and very limited movement.
His x-ray is below (left).
In the second a 16 year old fell while performing a ‘jump’ on his BMX bike. He was also unable to weight bear, with a knee which swelled rapidly. On examination he had a moderate swelling and movement between 30 and 80 degrees from straight only. His x-rays are the middle and right.
1. What is the injury?
Avulsion of the tibial spine.
2. What is the mechanism?
The anterior cruciate ligament (ACL) attaches to the anterior tibial spine. Excessive tension in this ligament causes an avulsion fracture. This can arise from a hyperextension injury. It can also arise in the same way as an ACL tear, from a twisting force on the knee when bent.
3. Is this injury commoner at a certain age?
Yes, this injury is nearly always seen in the 8-16 age range. It can be considered an equivalent to an ACL tear in an adult. It is particularly associated with boys and bikes!