[Anterior iliopsoas impingement after total hip arthroplasty: diagnosis and conservative treatment in 9 cases].

PURPOSE OF THE STUDY: Impingement of the iliopsoas muscle due to a protruding acetabular component is an uncommon cause of pain after total hip arthroplasty. Diagnostic signs may be misleading and therapeutic management has varied, leading to divergent findings reported in the literature. The purpose of this prospective work was to determine the frequency of groin pain due to iliopsoas impingement (with or without an identified causal mechanism) in patients with painful total hip arthroplasties and to identify diagnostic criteria that can be used to determine the appropriate therapeutic strategy.

MATERIAL AND METHODS: This prospective study was conducted between 1998 and 2000 and included 206 painful total hip arthroplasties. From this series, we excluded cases where pain was related to loosening (139 cases, 67%), infection (45 cases, 21.7%), bursitis on trochanteric sutures (2 cases, 1%), and aortic aneurysm with gluteal claudication and resulting from a lumbosacral disorder (10 cases, 4.8%). This left 9 cases (4.3%) with a clinical picture suggestive of iliopsoas impingement. These 9 patients (mean age 50 years, age range 38 - 65) had 8 uncemented press-fix cups and 1 cemented cup with an acetabular mesh. Mean delay to the development of pain after the arthroplasty procedure was 7.3 months (1 - 48 months). The most suggestive clinical sign was groin pain triggered by active flexion of the hip and flexion of the hip against force with a painful arc measuring 30 degrees to 70 degrees. None of these 9 patients had any sign of material loosening and puncture aspiration ruled out infection. The final diagnosis was confirmed by sedation of pain after extra-articular infiltration at the anterior border of the cup (overhanging cup in 6/9 cases) under computed tomographic guidance.

RESULTS: Infiltrations with xylocaine and long-release corticosteroids led to complete sedation of pain in 4 out of 9 patients and partial sedation in 1 other. Recurrent pain led to terminal tenotomy of the iliopsoas in 4 patients, that provided total sedation in 3 and partial sedation in 1. In all, successful pain relief was achieved in 7 out of 9 cases: 4 after infiltration (repeated in 1 cases) and 3 after tenotomy. At last follow-up physical examination has not identified any loss of flexion force.

DISCUSSION AND CONCLUSION: Irritation of the iliopsoas muscle can be the cause of pain in 4.3% of patients experiencing pain after total hip arthroplasty. The delay to symptom onset is variable but there appears to be a pain-free period after implantation. An anatomic element (anterior cup overhang) is not necessary for diagnosis since the infiltration test was positive in 1 out of 3 cases without any identified acetabular factor. The infiltration test is an important element for positive diagnosis and should be the first therapeutic measure taken. We achieved success in 4 out of 9 cases. Tenotomy is indicated in case of recurrence, providing complete cure in 3 out of 4 cases in our series. Cure may be achieved without changing the cup by simple infiltration or tenotomy of the iliopsoas that led to complete cure in 7 out of 9 cases in our series, even in patients with an overhanging cup (6 out of 9 cases). An elective procedure might be indicated if a specific anomaly is identified (overly long screw, cement leakage) or for a screwed cup. The infiltration test should however be performed beforehand to confirm the diagnosis.