Pain at the front of the knee has many causes — patellofemoral pain, patellar tendonitis, fat pad impingement, or plica syndrome. One less common cause is swelling around an accessory bone of the kneecap — a bipartite patella. So what is a bipartite patella, how does it cause pain, and what should we do about it?
What does a bipartite patella look like?
A bipartite kneecap forms when the patella develops from two bones instead of one. When these two bones fail to fuse during childhood, they remain separate, joined by cartilage. Most commonly, the smaller second bone sits at the upper and outer part of the patella.
About 2–3% of people have a bipartite patella, and most never know it.
Bipartite kneecap symptoms
Most bipartite kneecaps cause no symptoms. Only a small proportion becomes painful. The two bones are joined by fibrous tissue, called a synchondrosis, and the kneecap usually becomes painful after direct trauma or repetitive strain at this junction.
Typical symptoms of a painful bipartite patella include pain at the kneecap, pain when loading the patella (such as deep squats), and tenderness at the upper part of the patella.
Bipartite patella radiology
Both X-ray and MRI confirm a bipartite patella. MRI is generally more helpful, as it shows fluid around the synchondrosis — the sign that the bipartite patella is the painful culprit. An MRI also rules out other common causes of knee pain, such as a cartilage tear behind the kneecap.
Treatment options for a bipartite patella
Most cases need no treatment unless they’re painful.
A painful bony bump usually reflects swelling around the synchondrosis, so we start with anti-inflammatory measures:
- Ice — regular ice packs reduce inflammation and pain
- Ibuprofen — an anti-inflammatory tablet, calms the inflammation in the kneecap
- Patellar compression brace — a knee brace compresses the patella, reducing pain and allowing more movement
- Activity modification — avoid activities that aggravate the kneecap, such as weighted squats and contact sports
If these don’t settle it, an ultrasound-guided cortisone injection into the synchondrosis can reduce swelling and pain (covered below).
Surgery to remove the accessory bone is the next option if all conservative measures fail. Surgeons perform it either arthroscopically or open. But success isn’t guaranteed, and surgery carries risks including infection and persistent pain — so it’s a last resort.
More about the cortisone injection for a bipartite kneecap
We use a cortisone injection to reduce inflammation and pain. For a bipartite kneecap, cortisone is injected into the synchondrosis to reduce swelling between the two bones. Risks include infection, a cortisone flare, and skin changes such as depigmentation.
We recommend ultrasound guidance to direct the needle accurately to the target — ultrasound improves both the accuracy and the effectiveness of the injection.
Frequently asked questions about the bipartite patella
How do you tell a bipartite kneecap from a patella fracture?
Both can follow trauma such as a fall. But a bipartite kneecap separates at the upper and outer part of the patella, with wider, rounded edges. A patellar fracture usually occurs in the mid-portion, with well-defined, sharper borders. Imaging confirms the difference.
Does an MRI show whether a bipartite patella is painful?
Yes. In cases of pain, the MRI shows swelling around the synchondrosis between the two bones. If there’s no swelling there, another cause of the knee pain is more likely.
Does a bipartite kneecap always hurt?
No. Most bipartite kneecaps are painless. Only a small minority become painful, usually after trauma or repetitive strain to the patella.
Can you exercise with a bipartite patella?
Usually, yes, if it’s painless. If it’s painful, modify activity — avoid deep weighted squats and contact sports while it settles — and work with a physiotherapist on a graded return. A compression brace can help during loading.
Is a bipartite patella the same as a fractured kneecap from childhood?
No. A bipartite patella is a normal developmental variant — the kneecap formed from two bones that never fused. It isn’t an old fracture, though it can be mistaken for one on an X-ray, which is why the rounded, upper-outer location is a useful clue.
Final word from Sport Doctor London about the bipartite patella
Always consider a bipartite patella when there’s pain at the front of the knee. We confirm a painful bipartite kneecap through clinical examination, supported by MRI findings — then treat it with simple measures first, an ultrasound-guided cortisone injection next, and surgery only as a last resort.
To book a one-stop knee assessment with Dr Masci in London, contact the team here or call +44 (0) 203 488 0350.
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