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Background
The hip joint is one of the most mobile joints in the human body, which is made possible by intricate anatomy consisting of three trochanteric bursae and multiple tendon insertions. Bursae are fluid filled sacs lined by synovium, which prevent friction from occurring between tendons overlying the surface of the bone. Greater trochanter bursitis is a common condition characterized by hip pain that worsens with palpation, active abduction, and passive adduction. While the condition is self-limiting, it often impacts patient’s functionality. Treatment often consists of multimodal conservative therapy to improve symptoms, with corticosteroid injections being a primary treatment modality. The purpose of the exhibit is to educate radiologists on the greater trochanter anatomy and imaging findings of greater trochanteric bursitis.

Educational Goals / Teaching Points
The objective of this exhibit is to establish a foundation of the normal greater trochanter anatomy and providing the key features of abnormal bursae that may suggest greater trochanteric bursitis. Magnetic resonance imaging (MRI) is most frequently used to evaluate the bursae and tendon insertions given its ability to display great anatomic detail. Imaging features supporting bursitis can also be seen on Computed Tomography (CT) and ultrasound. If a radiologist is familiar with the normal anatomy and appearance of bursae, the diagnosis can be made with ease.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The three major greater trochanteric bursae are the trochanteric or subgluteus maximus bursa, subgluteus medius bursa, and subgluteus minimus bursa. The trochanteric bursa is the largest and lies over the posterior facet deep to the gluteus maximus muscle and iliotibial tract. This bursa is easily identified on MRI by its T2 hyperintense fluid signal and surrounding thin layer of fat. Enlargement of the bursa is supportive of bursitis and is often seen in conjunction with gluteal tendon tears. The sonographic appearance of a normal bursa is an anechoic fluid collection with hyperechoic synovial lining. Bursitis on ultrasound is identified when there is enlargement of the bursa, often with internal debris. Sonographic findings of bursitis are less consistent; however ultrasound is often integrated into the treatment plan through ultrasound guided corticosteroid injections. On CT, a normal bursa is rarely seen, and bursitis can be identified by the presence of a hypodense fluid collection overlying a joint. In cases of severe bursitis, rim enhancement and calcifications may be visualized.

Conclusion
Being able to recognize the clinical and imaging feature of greater trochanteric bursitis is essential to providing effective treatment to improve pain and restore mobility. MRI is frequently utilized to diagnosis bursitis; however it is necessary to be able identify suggestive features of bursitis across modalities.