Review Question - QID 216520

Radiographs reveal an acetabular component that is prominent anteriorly. This combined with the physical exam are indicative of iliopsoas impingement.

Patients with iliopsoas impingement following THA often complain of pain that is exacerbated with activities of hip flexion including stair climbing and getting in and out of a car. The iliopsoas muscle belly may become irritated from acetabular screws that are too long and penetrate the ilium. The most common cause of impingement, however, is a prominent acetabular component anteriorly. This may occur if the component is too large relative to the native acetabulum or placed in a retroverted or lateral position.

Dora et al review iliopsoas impingement following THA. They report on 30 patients with well-fixed, malpositioned or oversized acetabular components who developed iliopsoas impingement. They conclude that iliopsoas tenotomy and acetabular revision both successful surgical options for the treatment of this condition.

Malik et al review impingement following THA. They report that impingement may lead to instability, accelerated wear, and unexplained pain. They conclude that the operative techniques for preventing impingement include medialization of the cup and restoration of hip offset and length.

Trousdale et al review anterior iliopsoas impingement following THA. They report iliopsoas impingement may be the cause of a painful total hip especially with malpositioned metal acetabular components. They conclude that surgeons should closely evaluate the position of the acetabular component and keep iliopsoas impingement on the differential in the workup of a painful THA.

Figure A is the AP pelvis radiograph of a patient with a right THA in which the acetabular component was not appropriately medialized. Figure B is the cross table lateral demonstrating prominence of the acetabular component anteriorly.

Incorrect Answers:
Answer 1 and 2: Radiographs do not demonstrate loosening of the components. This combined with no start up pain during the history make this diagnosis unlikely.
Answer 4: Trunionosis occurs as a result of wear at the head-neck junction. In reviewing the patients radiographs, iliopsoas impingement is much more likely and matches the patients symptoms.
Answer 5: There is mild heterotopic ossification above the greater trochanter, but no evidence of a trochanteric fracture.