[Conflict between psoas and total hip prosthesis].

This conflict leads to a chronic irritation of the psoas by the antero-medial part of the cup, but it has been poorly described in the past. A study of six patients suffering from this trauma, and who were re-operated revealed that the muscle was worn thin in front of the prominent cup. In the case of 4 of the 6 patients pain had started to occur shortly after total hip replacement. The following symptoms were noted among all 6 patients: pain was suffered during flexion--extension movements--walking up stairs--arising from a chair. Pressure on the medial part of the groin was painful, especially during active elevation of the lower limb. Passive mobility was normal and painless. Psoas bursitis was observed in three cases. The main cause of this conflict is the protrusion of the cup beyond the antero-medial edge of the acetabulum; this protrusion may be either due to a bone graft or a bit of cement, but most often an acetabular insufficiency (congenital dysplasia) favors the formation of this anterior overhang. The spiral cup screwed into the bone can be especially aggressive when it protrudes. Treatment includes the resection of the overhang, but post-operative results will be uncertain unless the resection is really complete. In the case of 4 patients the results of such an intervention were only mild to poor. This problem can be avoided by proper care and preventive measures in the original replacement avoiding all projections beyond the anterior edge of the acetabulum--cup, bone graft, cement, especially if dysplasic.(ABSTRACT TRUNCATED AT 250 WORDS)