Pain at the front of the knee can be due to patellofemoral pain, patellar tendonitis, fat pad impingement, or plica syndrome. One less common cause is swelling around an accessory ossicle of the patella, also known as a bipartite patella, which can be painful. What is a bipartite patella, how does it cause pain, and what should we do?
What does a bipartite patella look like?
A bipartite kneecap occurs when the patella forms from two bones. Failure to fuse these two bones during childhood leads to two separate bones. These bones are joined by cartilage. Most commonly, the smaller second bone is located at the upper and outer part of the patella.
Generally, about 2-3 % of the population has a bipartite patella.
Bipartite kneecap symptoms
Most bipartite kneecaps don’t have symptoms. However, a small percentage of cases become painful. The two bones are joined by fibrous tissue, also known as a synchondrosis. Generally, the bipartite patella becomes painful after direct trauma or repetitive strain to the synchondrosis.
Usually, symptoms of a bipartite patella pain include:
- pain at the kneecap
- pain with loading the patella, including deep squats
- tenderness at the top part of the patella
Bipartite patella radiology
Both X-ray and MRI will determine whether the person has a bipartite patella. Generally, MRI is more helpful as it shows fluid around the synchondrosis. Additionally, an MRI rules out other common causes of knee pain, such as a cartilage tear behind the kneecap.
Treatment options
Generally, cases do not require treatment unless they are painful.
Often, a painful bony bump is related to swelling around the synchondrosis. In these cases, we suggest anti-inflammatory measures such as
- Ice: Regular ice packs will decrease inflammation and pain.
- Ibuprofen: Taking an anti-inflammatory medication, such as ibuprofen, helps calm the inflammation in the knee cap. In some cases, a cortisone injection into the synchondrosis can help.
- Patellar compression brace: Knee braces can help compress the patella, thereby reducing pain and allowing for increased movement.
- Activity modification: Avoid activities that aggravate the kneecap, such as weighted squats and contact sports.
In cases that fail conservative measures, an ultrasound-guided cortisone injection may help to reduce swelling and inflammation.
Surgery to excise the bipartite kneecap is the next option if all other conservative treatments fail. Usually, surgeons perform surgery either arthroscopically or through an open approach. However, you need to remember that surgery success is not guaranteed, and there are risks of surgery, including infection and persistent pain.
More about cortisone injection for a bipartite kneecap
Generally, we use cortisone injections to reduce inflammation and pain. In the case of a bipartite kneecap, cortisone is directed into the synchondrosis to reduce swelling between the two bones. Risks associated with a cortisone injection include infection, a cortisone flare, and skin changes, such as depigmentation.
We recommend using ultrasound guidance to accurately direct the needle to the target location. Generally, ultrasound enhances the accuracy and effectiveness of a cortisone injection.
Frequently asked questions on the bipartite patella.
How do we differentiate between a bipartite kneecap and a patella fracture?
Both conditions can occur with trauma to the patella, such as a fall. However, in a bipartite kneecap, the separation of the bones occurs in the outer upper aspects of the patella. Also, the edges of the bone separation are wider and rounded in the bipartite patella. On the other hand, patellar fractures usually occur in the mid-portion of the patella with well-defined, sharper borders.
Does an MRI scan give clues as to whether a bipartite patella is painful?
Yes. We see swelling surrounding the synchondrosis between the two bones in painful bipartite kneecaps. However, if there is no swelling between the two bones, then other causes of knee pain are likely.
Does a bipartite kneecap always hurt?
No. Most cases of bipartite kneecaps are not painful. However, we estimate about 2-3% of patients experience pain, usually due to trauma to the patella.
Final word from Sportdoctorlondon about bipartite patella
We need to think about a bipartite patella in cases of pain at the front of the knee. Generally, a diagnosis of a painful bipartite kneecap is confirmed through clinical examination, supported by MRI findings.
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