A Case of Chronic Deep Infrapatellar Bursitis Complicated by Patellar Tendinopathy and its Evaluation With Musculoskeletal Ultrasound.

Knee pain is a very common complaint in routine physiatry and orthopedic practice. While bursitis is a well-known and common cause of knee pain, deep infrapatellar bursa (DIPB) involvement is relatively less common. Inflammation of DIPB occurs commonly due to either direct trauma or overuse, but other rare causes have also been reported in the literature including infection, juvenile idiopathic arthritis, gout, and juvenile ankylosing spondylitis. We report a case of chronic inflammation of DIPB caused by direct trauma and associated with patellar tendinopathy. Additionally, we describe the characteristic findings on musculoskeletal ultrasonography (MSK-USG). For ultrasound evaluation, the patient should lie supine with the knee slightly flexed. Deep infrapatellar bursitis can be seen as an anechoic fluid-filled structure immediately posterior to the distal patellar tendon and anterior to the tibial tuberosity. While MRI can confirm the diagnosis of bursitis, MSK-USG can be quick, highly sensitive, and is able to confirm the diagnosis as well as to detect dynamic changes in the patellar tendon and adjacent structures. USG can also help in the treatment by guiding corticosteroid injection into the bursa. Activity modification and eccentric exercises play an important role in the rehabilitation program in these cases.