Patella fracture

• The patella is largest sesamoid bone in the body.
• It forms part of the extensor mechanism of the knee and is held in place by the patellar tendon, quadriceps tendon and the adjacent retinaculae.
• Patella fracture is classified according to site and appearance – longitudinal, transverse, stellate, marginal, polar or osteochondral fractures. All except small rim avulsions are thought of as intracapsular.
• The commonest fracture is the transverse type resulting from a powerful muscular contraction transmitted to the patella. This type is commonly displaced.
• AP and lateral views are essential. In some cases a skyline view is helpful but often difficult to obtain in the acute stage as knee flexion is required.
• The fracture is usually obvious. Look for associated lipohaemarthrosis on the horizontal beam lateral.
• The congenital bi-partite and multi-partite patella; usually occur at the superolateral aspect of the patella. In these the fragments tend to be rounded and corticated as compared to the sharp non-sclerotic margins in a fracture. MRI is useful in subtle cases.

Displaced horizontal patella fracture.