Hip & Pelvis

Bisphosphonates to stop the hip loosening?

There seems to be a slight trend back towards greater use of cemented acetabular components, especially in the older patient population. The evidence from registries suggests that they probably have a slightly better longevity, and come with less in the way of costs and intra-operative complications. The technique, however, is somewhat more demanding. Post-operative radiolucency around cemented cups is a recognised phenomenon, and although this is by no means pathognomonic of loosening, there is a recognised association with loosening and component migration. This Swedish paper from Linköping (Sweden) reports on the outcomes of an interesting potential intervention investigated in the form of a randomised controlled trial (RCT).¹ The investigators have examined the application of local bisphosphonate to plain saline-soaked gauze against the bone bed prior to cementation in cemented hip replacement. These investigators enrolled 60 participants in the randomised double-blinded controlled trial, with outcomes assessed using radiostereometric analysis at three, six, 12 and 24 months. The intervention was saline containing ibandronate. Other potential confounding variables (such as implant design and surgical approach) were appropriately standardised, and the randomisation was undertaken outside theatre to blind surgeons and theatre staff to which solution was used in each case. Perhaps surprisingly, once the RSA has been undertaken serially between three days and 24 months, in the intervention group component migration was roughly halved versus that in the bisphosphonate cohort. There were also substantial differences seen in the detection of radiolucent lines (over four times as likely with saline only). Although there was no difference in clinical outcomes at two-year follow-up, this would not be expected given the very low failure rate of the intervention. It could certainly be postulated that there may be longer-term implications to this finding. Bisphosphonates work both through inclusion in the hydroxyapatite crystal and as a direct effect on the osteoclasts through action on the FPPS pathway, affecting the ability of the osteoclasts to resorb bone. Happily, the half-life of bisphosphonates is in the order of years and so the effect could be expected to be long-lasting. Without a more firmly established correlation between early lucency and failure, extrapolation of these early results to long-term failure rate would be rash, however, it will undoubtedly be interesting to see the longer-term follow-up results from this cohort.