[Femoral loosening of total hip prosthesis caused by pseudarthrosis resulting from trochanterotomy]. / Descellements fémoraux de PTH par pseudarthrose de trochantérotomies.

ABSTRACT

PURPOSE OF THE STUDY This survey of 48 cases of trochanteric non-union in THR showed that this complication had not only functional consequences (one patient out of three complains of some instability and mild pain) but may also lead to stem loosening (3/48) through an original mechanism. The movements of the trochanter produce wear debris, mainly from the broken metal wires fixing the trochanter (and from rubbing of the cement on the femoral side of the osteotomy). These debris create an osteolytic granuloma between the proximal lateral endocortex and the cement, which extends progressively to the distal tip of the stem. MATERIAL AND METHODS: A continuous series of 446 cemented Charnley type prostheses by the trans trochanteric approach showed 48 trochanteric non unions (11 per cent) which were examined at an average follow up of 6.5 years. Six patients were reoperated for important hip instability. Ten who suffered only from moderate instability were not reoperated on. 32 were asymptomatic and therefore where not reoperated, but 3 of them suffered from severe femoral loosening after 6 years and required revision. RESULTS: These cases of loosening due to trochanteric non union were characterized by clinical patterns they occurred only after 6 years, in active patients under 50; radiological aspects osteolysis was initially limited to the lateral cortex (without any calcar resorption or radio lucency around the cup) analysis by electronic microscopy of the granuloma (harvested at revision) showed metallic debris (under 1 mu) inside macrophages, with some cement particles (secondary to the loosening). DISCUSSION: Mechanism of loosening These cases of loosening differ from those due to granuloma caused by wear debris of PE and from granulomas resulting from deterioration of the cement around the femoral stem, which both occur only much later with the Charnley prostheses. In our consecutive series of 32 cases of Charnley THR in young active patients with an average follow up of 9.5 years, the only cases of femoral loosening observed were related to trochanteric non unions. Hyposolicitation by trochanteric non union does not lead either to bone resorption or to stem loosening, as we could notice in a series of moderately active patients over 60 with loose non unions. Loosening due to trochanteric non unions was only observed in active patients with tight non unions, as the patient's activity and contact of the surfaces increase rubbing and wear of metal wires. Prevention of trochanteric non union. Despite attentive care to fixation of trochanter there is an unavoidable percentage of non union even in simple cases (3 to 4 per cent according to Charnley). Therefore we advocate this technique only when a large exposition is necessary (revisions, THR for dislocation etc..) CONCLUSIONS: Trochanteric non union may lead to stem loosening after 6 years in active patients under 50. Therefore we recommend to restrict the use of the trochanteric approach to some difficult THR revisions, prostheses for dislocation, etc... to reoperate patients under 50 with a trochanteric non union if it is clinically symptomatic if a progressive granuloma of the lateral cortex, even though asymptomatic, appears.