Traumatic knee pain in a child

A 12 year old boy presented to the emergency department with his parents after falling from a motocross bike. The child was unable to describe the precise history of the event or injury mechanism, but he described experiencing immediate and progressive pain in the left knee and was unable to fully extend the knee or bear weight on that side after the injury. He sustained no other injuries and was haemodynamically stable. On examination, a large effusion in the joint was noticed. Flexion was limited to between 20° and 90°, but the collateral knee ligaments were stable in extension and in 30° of flexion. Anterior drawer and Lachman test suggested grade 1 instability. The pivot shift test was not possible because of patient apprehension. The limb was neurovascularly intact and the boy’s calves were soft and non-tender. Radiographs of the knee were taken (figs 1, 2). Fig 1 Anteroposterior plain radiograph of the child’s knee taken shortly after arrival in the emergency department Fig 2 Lateral plain radiograph of the left knee ### What is the diagnosis? The plain radiographs show a fracture of the tibial spine (aka intercondylar eminence) (figs 3, 4). These are bony avulsion fractures of the anterior cruciate ligament (ACL) along with part of its attachment to the intercondylar eminence of the tibia. Fig 3 Anteroposterior radiographs of the child’s knee, with arrow pointing …