LEFT KNEE INJURY
A 22-year-old woman is brought to the emergency department by ambulance. Her friend says that they had been out drinking and that she had fallen off a 4-foot wall landing directly on her left knee. Her knee swelled up immediately and she has not attempted to walk since the injury. She is normally fit and healthy. She takes the combined oral contraceptive pill, smokes 10–20 cigarettes a day and works in a supermarket.
Her observations are normal. There is no evidence of a head injury. Her left knee is diffusely swollen and there is evidence of bruising. The skin is intact. The medial and lateral joint lines are not tender. The patient is unable to actively extend the knee. The knee feels otherwise stable. The hip and ankle joints are unremarkable, and the pedal pulses
and foot sensation are normal.
This type of fracture typically occurs with direct trauma to the knee. It is possible, however, to sustain a similar injury by an indirect mechanism, such as by vigorous jumping which leads to rapid flexion of the knee against a fully contracted quadriceps muscle. An indirect injury tends to result in less displacement and comminution of the fracture.
The patella is a large sesamoid bone. The upper border is connected to the quadriceps tendon and the lower pole is connected to the patella tendon, which inserts into the tibial tuberosity. In order to actively extend the knee, the whole unit must remain in continuity.It is, therefore, very important when examining knee injuries to ensure the extensor
mechanism is intact by feeling for any palpable gap and by getting the patient to actively
extend the knee.
Patella fractures can be managed conservatively or operatively. If the extensor mechanism is disrupted and/or there is a greater than 3 mm gap in the fracture site, surgical fixation is necessary. If the extensor mechanism is intact and there is a small gap in the fracture site, more common with the indirect injuries, then a cylinder plaster of Paris cast is more
appropriate.It is worth noting that a bipartite patella occurs in 1 per cent of the population, and it is not uncommon for patients to be misdiagnosed with a patella fracture. The diagnosis of a patella fracture is supported if there is a plausible mechanism of injury and the appropriate examination findings are present.
• Bipartite patella occurs in 1 per cent of the population, and can be mistaken for a patella fracture