BONE PRESERVATION WITH A CONSERVATIVE METAPHYSEAL LOADING IMPLANT

Abstract

Introduction Significant cortical bone mass has been demonstrated at the proximo-lateral flare of the femur (Fetto et al). Experiments have shown that if a femoral stem has a medial and lateral flare proximally, the loads are transferred to the proximal femur and stress protection in this area is avoided. Furthermore, the results suggested that a stem below the lesser trochanter was unnecessary (Walker et al).

Methodology This paper reports on two cohorts of ten patients that had either a short stemmed fully coated implant (Group I) or an unstemmed metaphyseal implant on which all but the polished tip was coated (Group II). All implants were customised based on pre-operative CT data. All hips had serial post-operative AP and lateral radiographs and bone densitometry was assessed with DEXA scanning.

Results The most recent post-operative radiographs of all patients in Group I revealed buttressing in zone IV with trabeculae streaming from the cortices onto the tip of the stem. Qualitatively there appeared to be osteope-nia in Gruen zones I and VII. The x-rays of the Group II patients revealed good condensation of bone along the textured surface in zone I and VII with preservation of bone density in these regions. These findings were confirmed by the DEXA results which showed a reduction of the BMD in zones I and VII in Group I, while Group II revealed preservation of the BMD in these zones.

Conclusion A conservative prosthesis without a stem which effectively loads both medial and lateral proximal femoral flares not only removes less bone at the index operation but preserves proximal bone stock in the longer term.