LONG TERM RADIOGRAPHIC ANALYSIS OF AN HYDROXYAPATITE-COATED ANATOMICAL STEM HIP PROSTHESIS

Abstract

The ABG stem (Anatomique Benoist Girard, How-medica) was realized of titanium alloy (TA6V) and it was designed to provide anchoring only at the femour’s metaphyseal portion. The long-term stability is achived by osteointegration of the implant at the metaphyseal region, which is coated with hydroxyapatite (HA) crystals. The plasma-sprayed HA coating has a tickness of 60 μm for the stem.

The current study presents radiographic outcomes of more than one hundred primary uncemented HA stems with a long-term follow-up. One hundred and eleven ABG hip arthroplasties were evaluated with a mean follow-up of 9.8 years. The radiographical findings have been classified observing Engh’s stability criteria according to Gruen’s subdivision of the periprosthetic femoral zones.

Dividing the hips into two different groups (in the first one the prosthesis implanted 11, 12 or 13 years ago and in the second one the prosthesis with a maximum age of 10 years) it’s possible to see as in the first group the radiolucent lines are quite reduced. Among the older prosthesis the percentage of radiolucent lines is 3.1% in zones 3 and 5 and 18.8% in zone 4. For what concerns the younger ones the percentage are 10.1% (zone 3), 21.5% (zone 4) and 15.2% (zone 5).

We believe that there is a load transfer from the metaphyseal to the metadiaphyseal portion of the femur without a worsening of the clinical outcomes. The absence of reactive lines and lucencies around the proximal HA-coated portion of the stem supports an excellent circumferential bony ingrowth in the metaphyseal area of the proximal femur. According to these percentages we can say that there’s less presence of radiolucency in the oldest prosthesis and it could be possible to argue that radiolucent lines tend to reduce along the time. This is probably due to the increase of the strength of the stem anchorage.