Cementless implants have gained popularity in modern orthopaedic practice. The type implants and surface characteristics on fixation has been extensively investigated, however there is insufficient data on the effect of the host bone bed status on implant fixation. This study aims to determine if there is a correlation between the fixation strength of cementless press-fit implants and bone mineral density (BMD) of the host bone bed.

Implants coated with pure titanium, Hydroxyapatite (HA) with or without Hyaluronic Acid (HY) and implants coated with bone growth factors – Bone Morphogenetic Protein 2 (BMP-2) were inserted into tibiae and femora of 32 skeletally mature ewes (109 implants) for a period of 1, 2 and 4 weeks. Mechanical pull-out testing was performed after each time interval to evaluate the ultimate load of failure (Nmm⁻²). The BMD (gcm⁻³) surrounding the implant site was measured using a CT scanner.

The mean BMD (S.D.) was 1.515gcm⁻³ (0.147gcm⁻³). The mean (S.D.) mechanical pull-out strength at 1, 2 and 4 weeks was 0.37 (0.31), 3.14 (0.17) and 9.74 (2.31) Nmm⁻² respectively. The overall correlation co-efficient between BMD and pull out strength is 0.31.

Early fixation strength of implants is independent of BMD, however, the strength of fixation increases with time in a ‘normal’ sheep population. This suggests that the fixation of implants is dependent on the type of implant and surface coating used rather than the density of the host bone bed.