Noticeable swelling in front of the kneecap usually makes prepatellar bursitis easy to recognize. However, an accurate diagnosis requires ruling out other possible problems, such as rheumatoid arthritis, gout, and pseudogout (CPPD disease).
It is also important to identify whether or not the bursitis is caused by an infection. Infectious bursitis, called septic bursitis, can be serious and even life-threatening if it goes untreated.
Knee Bursitis Diagnostic Process
During a medical office visit, a health care provider will talk to the patient and conduct a physical exam. Depending on the circumstances, lab testing or medical imaging may be recommended.
The patient will be asked to describe when symptoms began, the pattern of knee pain and swelling, and how symptoms affect everyday activities. A patient may also be asked about his or her general medical history, work, and lifestyle.
A patient’s reported symptoms and medical history are important for diagnosis and treatment.
A doctor will examine the knee joint and compare it to the unaffected knee, taking note of swelling, tenderness, pain points, and range of motion.
Bursal aspiration and lab tests
If septic knee bursitis is suspected, a doctor may remove fluid from the bursa with a needle and syringe. This procedure is called a bursal aspiration. It is an outpatient procedure done with a local anesthetic.
The aspirated fluid and/or a blood sample may undergo lab testing. A doctor may order a:
- Gram stain of the aspirated fluid to determine if certain troublesome bacteria are present. Not all bacteria can be identified with a Gram stain, so even if the test result comes back negative, septic bursitis cannot be completely ruled out.
- White blood cell count of the aspirated fluid to check for an elevated number of white blood cells, which indicates an infection.
- Glucose level test of a blood sample to check for a lower-than-normal glucose level, which may indicate infection.
Occasionally, all lab test results come back negative even when an infection is present.1-3 Therefore, a doctor who strongly suspects septic bursitis may prescribe antibiotics without positive lab tests.
Bursal aspiration can relieve uncomfortable pressure in the knee and may also be recommended for treatment.
Imaging tests, such as x-rays, MRIs, and ultrasounds
While medical imaging is not usually needed to diagnose knee bursitis, it may be recommended to rule out another condition.
For example, when bursitis occurs after an injury, an x-ray may be ordered to rule out a broken bone. Similarly, an MRI or diagnostic ultrasound may be ordered to rule out excess fluid in the knee joint capsule.
Getting an accurate diagnosis is the first step in the treatment and prevention of knee bursitis.