Patella fracture

Fractures of patella, despite its small size may lead to profound pain and impairment of the extensor mechanism of the lower extremity (1)

Patella fractures can be due to either:

• indirect force - typically results in transverse fractures
• direct force - results in comminution, articular injury, anterior soft tissue damage and thus open injury (1).

There are three different types of fracture of the patella that may occur:

• an undisplaced fracture of the patella - likely to be the result of a direct blow
• a 'stellate' (comminuted) fracture - likely to be due to a direct blow to the front of the knee or a fall
• transverse fracture with a gap between the fragments - may occur if there is forced, passive flexion of the knee joint whilst the patient has his quadriceps muscles - knee joint extenders - contracted.

In the first two types, the extensor mechanism of the knee is left intact. In the third type, injury the extensor mechanism is completely disrupted and active knee extension is impossible.

Note:

• combination of fracture patterns can be commonly seen as well e.g. - a direct impact which is accompanied by knee flexion and quadriceps contraction may result in marked fragment displacement and soft tissue injury (1).

Reference:

• (1) Scolaro J, Bernstein J, Ahn J. Patellar fractures. Clin Orthop Relat Res. 2011;469(4):1213-5.