Retroperitoneal hematoma: an unusual cause of pain after total hip arthroplasty.

Pain following total hip arthroplasty due to impingement of the iliopsoas is a recognized complication of the procedure with a reported incidence as high as 4.3%. The pain is most often due to direct mechanical irritation of the iliopsoas due to a malpositioned or oversized acetabular cup. Definitive treatment of iliopsoas impingement often requires surgical revision or iliopsoas tenotomy, although many cases remain undiagnosed or are managed conservatively. We present an unusual case of pain after total hip arthroplasty due to a large retroperitoneal hematoma secondary to acetabular cup irritation of the iliopsoas tendon. This case represents a potentially important complication of undiagnosed or conservatively managed iliopsoas impingement, particularly in patients taking anticoagulants or antiplatelet medications.