Does vibratory implant insertion show any benefit due to the viscoelastic characteristics of the bone?

Abstract-Text (inkl. Referenzen und Bildunterschriften)

Introduction: Press-fit implants are impacted into undersized bone cavities. Increased impaction frequency was shown to reduce the impaction forces [1] apparently due to the viscoelastic behavior of the bone [2].

Aim: Investigating the effect of vibratory implant insertion on the implantation process and the achieved primary stability in viscoelastic and non-viscoelastic human bone substitutes.

Materials and Methods: Acetabular cups (Pinnacle, DePuy Synthes, UK) were implanted into 1mm undersized cavities in PU foams (SYNBONE, CH) and in porcine acetabula using devices providing 60Hz (Behzadi Medical Device, USA) or 1Hz (KINCISETM, DePuy Synthes, USA) strokes. Impaction forces were measured (Fig. 1). Achieved cup positions and resulting polar gaps were determined by aligning pre- and post-implantation 3D laser scans. The cup lever-out moment was a measure of primary stability (Z010, Zwick Roell, DE).

Results: Impaction force was higher with 1Hz impaction compared to 60Hz (both p<0.001; Fig. 2) and the cup seated deeper (Polar gap mean±SD; bone: 2.0±0.2, PU foam: 2.2±0.8 vs. bone: 4.5±1.6, PU foam: 4.7±0.4). The lever-out moments were significantly higher for cups inserted with 1Hz (both p<0.001; Fig. 2).

Conclusion: PPF risk could possibly decline by increasing the impaction frequency, but this comes along with reduced primary stability, likely as a result of incomplete seating. The similarity of the results between the not-viscoelastic material and the viscoelastic material indicates that the implantation process is a matter of overcoming the friction between the implant coating and bone tissue. The differences could be due to additional microstructural bone damage in the interface due to the higher number of impacts (enlarging of the cavity).

The provision of implants and surgical instruments by DePuy Synthes is kindly acknowledged.

References: [1] Nakasone et al., J. Arth. 2012 [2] Ruhr et al., Bone Jt. J 2023