Bursitis of the knee typically occurs due to overuse, friction, or stress on the bursa. The cause often depends on which bursa is affected:

• Pes anserine bursitis is most common in athletes, particularly runners, and is caused by irritation of the bursa between the shinbone and three tendons on the inside of the knee. Contributing factors include improper training techniques (such as insufficient stretching, excessive hill running, or abrupt increases in activity levels), tight hamstring muscles, obesity, outward rotation of the knee or lower leg, osteoarthritis, and medial meniscus tears.
• Prepatellar bursitis is typically caused by direct, repeated pressure or trauma to the front of the knee, such as frequent kneeling on hard surfaces. It is common in tradespeople such as plumbers, roofers, and gardeners, as well as from a direct blow to the knee.
• Popliteal bursitis (Baker's cyst) usually develops as a consequence of another knee condition — such as osteoarthritis, rheumatoid arthritis, or a cartilage tear — that causes the knee joint to overproduce fluid, which then collects in the bursa behind the knee.

The primary symptoms of knee bursitis include pain, swelling, and tenderness over the affected bursa. The specific location of symptoms can help identify the type:

• Pes anserine bursitis causes pain and swelling on the inner side of the knee, just below the joint.
• Prepatellar bursitis causes swelling and tenderness directly over the kneecap, which may appear as a visible, squishy lump. The skin over the kneecap may feel warm to the touch.
• Popliteal bursitis (Baker's cyst) causes a feeling of tightness or a noticeable bulge behind the knee, which may worsen when you straighten your leg fully.

Across all types, pain may present as a dull ache that intensifies with movement or pressure. You might also experience stiffness in the joint, limiting your knee's range of motion. If the area becomes red and you develop a fever, it could indicate an infection, which requires immediate medical attention.

Modifying physical activity is essential to prevent recurrent inflammation. Additional treatments include:

• Rest: Temporarily stop activities that worsen the condition or switch to low-impact exercises.
• Ice: Apply ice three to four times daily for 20 minutes to reduce swelling and pain.
• Anti-inflammatory medications: Over-the-counter options, such as ibuprofen or Aleve, may relieve pain and inflammation.
• Injections: Your doctor may administer an anesthetic and steroid injection into the bursa for quick relief.
• Physical therapy: Specific stretching exercises, ice application, gait mechanics, and use of modality machines may be helpful to resolve symptoms. For popliteal bursitis, addressing the underlying knee condition is also a key part of treatment.

If your symptoms do not improve with conservative treatments, your doctor might recommend outpatient surgery. The appropriate procedure depends on the type of bursitis:

• Bursectomy: For cases that do not respond to conservative care, a surgeon can remove the inflamed bursa through a minimally invasive procedure performed under local or general anesthesia. A small incision is made over the affected joint to remove the damaged bursa sac.
• Incision and drainage (I&D): For septic (infected) prepatellar bursitis, surgery to drain and clean the infected bursa is typically recommended.
• Treatment of underlying conditions: For popliteal bursitis (Baker's cyst), surgery may be directed at correcting the underlying knee problem — such as repairing a cartilage tear — rather than removing the cyst itself, as the cyst often resolves once the root cause is addressed.

Post-surgery, you will likely need to use crutches for a short period to keep weight off the area. Most patients can expect a relatively quick recovery, gradually resuming their normal activities within about three weeks.