Bipartite patella

A bipartite patella (two-part patella) is a patella with an unfused accessory ossification center at the superolateral aspect.

Epidemiology

The superolateral accessory ossification center of the patella is usually present by 12 years of age and may persist into adult life. Prevalence of a bipartite patella occurs in approximately 2% of the population. It occurs bilaterally in about 43% of cases.

It is nine times more common in males than in females ².

Clinical presentation

A bipartite patella is usually discovered incidentally in asymptomatic individuals. Only 2% of patients with bipartite patella experience symptoms. It may cause anterior knee pain, especially after trauma, sports injury, or overuse.

Classification

One method of classification according to H Saupe is as:

• type I: inferior pole ~1%
• type II: lateral margin ~20-25%
• type III: superolateral portion ~75% 

Treatment and prognosis

In the majority of cases, a symptomatic bipartite patella improves without surgery. Surgical excision of the small fragment is recommended if conservative management fails and has been reported to give good results ³.

Differential diagnosis

May be radiographically confused with a patellar fracture, but the superolateral accessory ossification center is characteristic of a bipartite patella. With a multipartite patella, the volume of the true patella plus that of the smaller ossification centres is greater than that expected of a normal patella. With a patellar fracture, the volume of the fractured components is equivalent to that of a normal patella.