Psoas Bursitis is an uncommon painful disorder of the hip.  The psoas bursa lies between the hip and the psoas muscle.  It is the largest bursa in the human body.  This bursa can become injured or inflamed and cause pain.  Psoas bursitis is also associated with Rheumatoid Arthritis and is found more frequently in patients with that disorder.  The pain is located in the groin area and radiates down the leg.  The pain is worsened by activities involving hip flexion, such as walking up stairs.  The bursa can sometimes be felt as a mass in the groin area.  A Thomas test or modified Thomas test ( done during physical exam by a doctor) can be indicative of psoas bursitis.  Sometimes a snapping sensation can also be felt in front of the hip.  Testing involves X-rays to look for bony pathology such as fractures.  MRI scans are useful to detect tumors in the area.  Blood work is drawn to exclude autoimmune disease such as Rheumatoid Arthritis.  Diseases that may be confused with psoas bursitis include hip pathology,  lumbar radiculopathy from a herniated disc or an inguinal hernia.  Treatment includes bedrest, heat, ice, physical therapy and non-steroidal anti-inflammatory medications.  For those patients in whom conservative modalities are not effective, injection of the bursa with a local anesthetic and a steroid may be useful.