• Hip and knee surgery

The number of total hip replacements is increasing, with the highest increase among people aged 50-59 years. Unfortunately, the failure rates for young patients are also among the highest. An improvement in implant longevity is needed. Studies using radiostereometrical analysis (RSA) have shown that early prosthetic migration is associated with increased risk of aseptic loosening. One way to increase implant longevity could be an improvement of early implant stability. A potential way to enhance early implant fixation could be with the use of bisphosphonates. These drugs are strong inhibitors of osteoclastic bone resorption. They are currently used against osteoporosis and osteolytic tumors. Several clinical and experimental studies have investigated the use of bisphosphonates as adjuvants in total joint replacements. The results are promising. The bisphosphonate used in the present studies was alendronate. The aim of the studies in this PhD thesis was to improve implant fixation of experimental implants using alendronate as a local adjuvant. Implant fixation was defined in term of biomechanical stability and osseointegration. Study I investigated the effect of local alendronate treatment on implant fixation of porous-coated titanium implants inserted with the use of bone compaction. Implants were inserted with the use of bone compaction into undersized cavities that had been radial enlarged, thus transforming the surrounding bone into a zone compacted autograft. Implants were inserted bilaterally into the proximal part of tibia in ten canines. Alendronate was applied on one of the sides and saline on the other side. The observation period was 12 weeks. Push-out testing showed that alendronate increased the biomechanical fixation twofold. Histomorphometrical analysis showed that alendronate increased the amount of bone around and in contact with the implants. Study II investigated the effect of soaking morselized allograft in alendronate before impacting it around a porous-coated titanium implant. In 10 canines, a pair of implants surrounded by a 2.5-mm gap was inserted into the proximal part of humerus during two surgeries separated by time. The gap was filled with allograft soaked in either alendronate or saline. The two implant pairs were observed for 4 and 12 weeks respectively. Push-out testing showed that alendronate dramatically decreased biomechanical implant fixation, and histomorphometrical analysis showed that alendronate almost blocked new bone formation and preserved the allograft. Study III investigated the effect of local alendronate treatment on implant fixation of hydroxyapatite-coated implants inserted with the use of bone compaction. Study III had a similar design as used in study I. Push-out testing showed that local alendronate treatment was able to increase the biomechanical implant fixation. Histomorphometrical analysis showed that alendronate could increase the amount of both woven and lamellar bone around the implant, but not in contact with them. The studies in this PhD thesis demonstrate that alendronate can increase fixation of implants inserted with the use of bone compaction. However, they also indicate that caution should be taken when using bisphosphonate as an adjuvant in allografted implants. The results warrant further preclinical investigation.

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