Painful Bipartite Patella

Coronal T1W MR image of the right knee in a patient with anterior knee pain shows a bipartite patella. Note cartilage lining of the synchondrosis (red arrowheads).

Axial fat-suppressed T2W image shows bone marrow edema within the bipartite segment (arrow) with small joint fluid (yellow arrowhead).

Facts: Bipartite Patella

• Developmental variation of an unfused accessory ossification center
• Typical location at superolateral aspect of the patella, at insertion of vastus lateralis
• This ossification center begins to ossify at age 3-5, and fuse by age 12; if unfused - it is called bipartite patella
• Almost always bilateral, male much more common than female
• Prevalence about 2% of population
• Most discovered incidentally

Painful Bipartite Patella

• Unrecognized cause of anterior knee pain
• It is postulated that synchondrosis of bipartite patella becomes disrupted due to overuse or acute injury, allowing abnormal motion, friction and subsequent edema
• "Rather than discounting it as a normal variant, a detailed search should be undertaken for signs of edema both within the bipartite fragment and along the margins of the synchondrosis or pseudarthrosis, especially in patients presenting with anterior knee pain." -- quoted from Kavanagh EC, et al (paper referenced below)
• In one study of 53 patients with bipartite patella, almost half of them had findings consistent with marrow edema in the bipartite segment (which probably responsible for pain)

Reference

Kavanagh EC, et al. MRI findings in bipartite patella. Skeletal Radiol 2007;36:209-214.