[Iliopsoas impingement in 12 patients with a total hip arthroplasty].

PURPOSE OF THE STUDY: We report 12 cases of iliopsoas impingement, an under-recognized cause of hip pain in total hip arthroplasty patients.
MATERIAL AND METHODS: Between January 1998 and October 2000, we diagnosed 12 cases of iliopsoas impingement among 280 total hip arthroplasty patients with hip pain (4.3%). Our population was composed of 9 women and 3 men aged 62 to 80 years (mean 72 years). Nine patients had a first intention arthroplasty and 3 had a revision prosthesis. Delay from implantation to diagnosis of impingement ranged from 6 months to 5 years. Common cases of pain after hip arthroplasty, infection, loosening, were ruled out in all cases. A standard x-ray series including an AP view of the pelvis, an AP view of the hip and a surgical false-lateral view of the hip as well as a CT scan were obtained when iliopsoas impingement was suspected. The CT series extended from the lower part of the acetabulum through the fixation screws.
RESULTS: Pain had been observed immediately after implantation in 10 cases (83%) and in 2 cases (17%) 3 to 5 years later. These patients did not have to use crutches when pain started to develop. Pain projected anteriorly and was always exaggerated when moving from the sitting position to the upright position and when going up stairs. In one patient, palpation revealed a mass in the groin that corresponded to a massive iliopsoas bursitis. Two non-pathognomonic physical signs were found in all cases: groin pain induced by active flexion against force in the lateral reclining position and at hip extension, and pain in the dorsal reclining position at deflexion of the hip, starting at 45 degrees. The standard AP views showed evidence of defective anteversion of 4 press fit cups, 1 off-centered screwed cup and 3 oversized cups. The CT scan demonstrated that the impingement involved the anterior border of the cup applied against the iliopsoas tendon in 8 cases either due to anterior uncovering in a dysplasic hip or anterior cup overhang. In 4 cases the cup fixation screws protruded anteriorly in front of the ilion and came in contact with the posterior aspect of the iliopsoas muscle. A bursitis had developed in 50% of the cases. DISCUSSION: When infection and loosening have been ruled out, hip pain after total hip arthroplasty would suggest a possible impingement of the acetebular component on the iliopsoas muscle due to defective anteversion or centering, the use of oversized cups, and/or the use of fixation screws. We emphasize the importance of a correct position for the cup to avoid an overhanging anterior border and discuss the use of screwed cups for primary total hip arthroplasty and of oversized cups for revision procedures.