Magnetic resonance image of a healed patellar fracture.
A patella fracture is an injury that involves the bone located in front of the knee joint, also known as the knee cap. The patella is a sesmoid bone, which means it is located within a tendon. The function of the patella is to increase the leverage of the quadriceps muscle and it also protects the quadriceps and patellar tendons. A patella fracture usually is caused by a forceful direct blow to the knee, it can also be caused by an indirect injury such as a sudden contraction of the quadriceps muscle. When a patella fracture happens there is immediate intense knee pain, almost immediately the knee will become swollen and the patient is unlikely to be able to bend the affected knee. If the fracture is right across the knee cap it may be possible to feel a gap.
There are several classifications of a patella fracture. They are classified according to the pattern of the fractures.
Lower or upper pole fractures
Transverse - fracture occurs through the mid line dividing the bone into two parts upper and lower Longitudinal - the bone has a verticle split
Comminuted - multiple pieces
Osteochondral - involving the cartilage
Displaced - bone fragments are separated
Undisplaced - bone fragments are not separated
Treatment depends on the above factors. It can include the following methods: ankle to groin plaster casts, as well as surgery. Severely communited fractures may require a total patellectomy if they are unsalvageable.
The latest trend is to attempt to save as much of the patella as possible by gently holding the pieces in proper position and fixing them with flexible and stiff wires. It usually takes four to six weeks for the bone to unite and it can take eight months to a year to reach the pre-fracture level.
In most patients rediographs are the most useful imaging tool for the initial examination. Then x-ray is followed by CT scans, MRI imaging, and sometimes bone scans. Fractures of the patella are responsible for approximmately 1% of all skeletal injuries in both adults and children.
