Psoas abscess masquerading as a prosthetic hip infection: A case report

Psoas abscess is an unusual condition and is defined as a collection of pus in the iliopsoas compartment. Due to the unique anatomy of psoas muscle it forms a conduit for spread of infection from upper part of body to hip joint in neglected cases.

A 67year old lady presented with left groin pain for three weeks. She underwent an uncemented unipolar hemiarthoplasty eight years back. Currently, she developed fever and was unable to do any active left hip range of motion. Passive motion of the left hip was restricted to 30° flexion, no internal rotation, 5° external rotation, and 10° abduction. Lab workup showed raised serum infective markers and radiographs of pelvis were normal with no evidence of any radiolucency. Ultrasound guided aspiration of left hip joint showed E coli. Arthrotomy revealed clear fluid in hip joint but pus was drained at psoas insertion. Later on, culture reported presence of E. coli and biopsy confirmed psoas abscess. Postoperatively CT scan abdomen showed pyelonephritis. Antibiotics were given for three months. Twenty months later, she remains asymptomatic without evidence of infection with normal gait.

Psoas abscess is a rare clinical entity that may mimic symptoms of a primary prosthetic hip infection. Treatment outcomes are directly related to early detection with adequate dissection of the psoas muscle up to sites of attachment and complete eradication of infection.

This case highlights importance of thorough initial clinical examination, lab workup and radiological assessment to rule out rare causes of hip joint pain.