MID-TERM (SIX YEARS) BONE REMODELLING AROUND REVISION HIP PROSTHESIS STEMS: DUAL ENERGY X-RAY ABSORPTIOMETRY (DEXA)

Abstract

Purpose: Bone remodelling and osteolysis around total hip arthroplasty (THA) is a highly debated subject in the medical literature. Such bone behaviour is poorly understood around femoral stems used in revision THA. The main problem is to obtain an objective assessment of bone remodelling and bone reconstruction over time, reconstruction techniques being very variable. Conventional radiology is insufficient, but dual energy x-ray absorptiometry (DEXA) provides a means of following changes in the bone around first intention femoral stems.

Material and methods: We studied bone behaviour around revision femoral stems using the non-cemented “P.P. system”. This type of femoral stem is implanted after trochanter osteotomy to facilitate access and stimulate reconstruction. The series included 31 patients who underwent revision total hip arthroplasty. Follow-up examinations included standard radiographs and DEXA of the operated hips, the contralateral hip and the lumbar spine. Periprosthetic zones defined by Grüen were compared with the same zones in the contra-lateral femur. Mean follow-up was six years.

Results: The standard radiographs did not demonstrate any significant change in periprosthetic cortical thickness. The DEXA demonstrated a significant an average 19.97% reduction in bone density in zones 2, 3, 4, 5 and 6. There was no significant difference in zone 7 and an increase in zone 1 (torchanter osteotomy). These figures are to be compared with the variable thickness observed for first intention pros-theses even shortly after implantation.

Discussion: Our results are the first to our knowledge demonstrating the behaviour of bone around revision femoral stems.

Conclusion: Digastric trochanterotomy appears to be an effective means of stimulating reconstruction of the proximal femur. At equivalent follow-up, the quadrangular section of the revision P.P. stem is more favourable in terms of bone loss compared with first intention stems.