The majority of fractures occur from direct injuries to the patella, such as a fall or direct blow from an object. Dashboard injuries in motor vehicle accidents are also common. Indirect injuries can also occur, and these are usually secondary to soft tissue injuries resulting from twisting or jumping. An example is avulsion fracture secondary to pull of the quadriceps or patella tendon.

Pain, loss of motion, and inability to weight bear are the most common symptoms. Major signs are abrasion, swelling, or crepitus with inability to fully extend the knee from a flexed position (suggesting damage to the quadriceps or patella tendon). All lacerations should be checked to see if they communicate with the joint. (This can be checked by injecting saline in the joint to see if it extravasates from the wound.) If the test is positive, the knee joint requires surgical débridement as an emergency. If the knee x-ray shows air in the joint, the laceration goes into the knee.

Anteroposterior/lateral, sunrise, and tunnel views are used. Lateral views in 30 degrees flexion are used to assess patella baja or alta (indicative of quadriceps tendon or patella tendon injury, respectively) and to evaluate fracture displacement. These views show if the patella is dislocated or subluxed (Fig. 1). Do not confuse an anatomic variant, bipartite patella, with a fracture (Fig. 2). This patella is nontender. It is always in the upper outer quadrant.