Overview
Knee bursitis is inflammation of a bursa located near your knee joint. A bursa is a small fluid-filled, pad-like sac that reduces friction and cushions pressure points between your bones and the tendons and muscles near your joints. Each of your knees has 11 bursae. While any of these bursae can become inflamed, knee bursitis most commonly occurs over the kneecap or on the inner side of your knee below the joint.
Causes
Overuse
Running
Incorrect training techniques
Tight hamstring muscles
Obesity
Out-turning of the knee or lower leg
Osteoarthritis in the knee
Medial meniscus tear
Frequent and sustained pressure
Infection of the bursa
Direct blow
Excessive kneeling
Symptoms
Vary depending on which bursa is affected and the cause of the inflammation
Feel warm to the touch
Appears swollen or feels squishy to the touch
Pain and tenderness with movement or when pressure is put on it
Diagnosis
Physical examination and medical history consultation
X-ray
MRI
Ultrasound
Aspiration (removal of fluid)
Treatment
Workout/activity modification
Rest
Application of ice
Anti-inflammatory medication
Injections
Physical therapy
Surgery
Source: http://orthoinfo.aaos.org/topic.cfm?topic=a00335 ; http://www.mayoclinic.com/health/knee-bursitis/DS00954