FEMORAL LOOSENING OF THR DUE TO TROCHANTE RIC NON UNIONS

Purpose of the study This survey of 48 cases of trochanteric non-union in THR showed that this complication had not only functional conseque nces (one patient out of three complains of some instability and mild pain) but may also lead to stem loosening (3/48) through an original m echanism. 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 t he cement, which extends progressively to the distal iib of the stem. Material and Methods A continous series of 446 cemented Charnley type prostheses by the trans trochanteric approach showed 48 trochanteric n on 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 un ion were characterized by: - clinical patterns:they occurred only afte r 6 years, in active patients under 50, - radiological aspects:osteoly sis was initially limited to the lateral cortex (without any calcar re sorption or radio lucency around the cup) - analysis by electronic mic roscopy of the granuloma (harvested at revision) showed metallic debri s (under 1 mu) inside macrophages, with some cement particles (seconda ry 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 a round the femoral stem, which both occur only much later with the Char nley 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. Hyposollicitation 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 p atients with tight non unions, as the patient's activity and contact o f the surfaces increase rubbing and wear of metal wires. - Prevention of trochanteric non union. Despite attentive care to fixation of troch anter there is an unavoidable percentage of non union even in simple c ases (3 to 4 per cent according to Charnley). Therefore we advocate th is technique on ly when a large exposition is necessary (revisions, TH R for dislocation etc.). Conclusions Trochanteric non union may lead t o stem loosening after 6 years in active patients under 50. Therefore we recommend: - to restrict the use of the trochanteric approach to so me difficult THR: revisions, prostheses for dislocation, etc... - to r eoperate patients under 50 with a trochanteric non union: - if it is c linically symptomatic - if a progressive granuloma of the lateral cort ex, even though asymptomatic, appears.