Introduction/Aims: Initial implant stability is crucial for long-term implant survival. A new surgical technique, compaction, has increased in vivo stability of implants inserted with pressþt. However, gaps often exist in total joint replacements between the implant bone bed and the implant. Therefore, we examined in a gap model whether the compaction technique would increase þxation of hydroxylapatite (HA) implants when compared with the conventional drilling technique. Methods: HA coated titanium implants (diameter 6 mm) were inserted bilaterally in the proximal humerus of 7 dogs for 2 weeks. The implant cavity was randomized to either drilling with an 8 mm drill or to compaction by radial enlarging an initial 5 mm drill hole to 8 mm. Implants were tested to failure by push-out test, and histomorphometry was performed. Data are presented as medians with interquartile range in brackets. The Wilcoxon Signed Ranked Test tested differences between compaction and drilling. P-values < 0.05 were considered signiþcant (*).

Conclusion: In this gap model, compaction signiþcantly increased mechanical and histological þxation of HA coated implants.