Compound patellar fracture

This patient suffered direct trauma to the front of his knee and presented to the ED with an extensive laceration. The AP view, left, shows a vertical fracture of the patella (yellow arrows). What tells us, radiographically, that this is a compound fracture is that a large amount of lucent gas (orange arrows) is visible in the joint on the lateral radiograph. Note how the fracture is not visible on this view, re-emphasising the requirement for orthogonal views in the setting of extremity trauma. The knee joint was washed out and the fracture fixed with transverse screws, right-hand intra-operative fluoroscopic image.