Impaction technique influences implant stability in low-density bone model

Abstract

Aims Cementless acetabular components rely on press-fit fixation for initial stability. In certain cases, initial stability is more difficult to obtain (such as during revision). No current study evaluates how a surgeon’s impaction technique (mallet mass, mallet velocity, and number of strikes) may affect component fixation. This study seeks to answer the following research questions: 1) how does impaction technique affect a) bone strain generation and deterioration (and hence implant stability) and b) seating in different density bones?; and 2) can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular component? Methods A custom drop tower was used to simulate surgical strikes seating acetabular components into synthetic bone. Strike velocity and drop mass were varied. Synthetic bone strain was measured using strain gauges and stability was assessed via push-out tests. Polar gap was measured using optical trackers. Results A phenomenon of strain deterioration was identified if an excessive number of strikes was used to seat a component. This effect was most pronounced in low-density bone at high strike velocities. Polar gap was reduced with increasing strike mass and velocity. Conclusion A high mallet mass with low strike velocity resulted in satisfactory implant stability and polar gap, while minimizing the risk of losing stability due to over-striking. Extreme caution not to over-strike must be exercised when using high velocity strikes in low-density bone for any mallet mass. Cite this article: Bone Joint Res 2020;9(7):386–393.

WITHDRAWN: A Parametric Analysis of Femoral Stem Impaction

“…In this study seating of a press-t femoral stem by impaction was modelled. Dynamic seating of orthopaedic implants has been documented experimentally (13)(14)(15)(16)(18)(19)(20) but little modelling exists, although publications exist in other elds, such as pile driving (21,22). The aim was to nd parameters that decreased introducer stresses without compromising seating.…”

“…Despite recent interest in orthopaedic impaction (13)(14)(15)(16)(17) there remains little understanding of the mechanism and little evidence-based information for the surgeon or the designers regarding technique or tools.…”

Influence of acetabular cup thickness on seating and primary stability in total hip arthroplasty

“…The phenomenon of over-impaction to occur for a high number of strokes, resulting in reduced lever out moments, has also been reported by other authors. 26 A high number of strokes was associated with a small seating progress over many strokes toward the end of impaction associated with larger strain release pronounced for the thick-walled cup. It is speculated that the final strokes with small seating progress reduced primary stability due to increased bone damage at the interface without increasing press-fit.…”

“…It is speculated that the final strokes with small seating progress reduced primary stability due to increased bone damage at the interface without increasing press-fit. 26,37 Excessive or over-impaction is critical for primary stability and should be omitted. Thin-walled cups benefit from their faster converging seating progress.…”

“…Cavity preparation, cup orientation, and impaction forces have been shown to influence primary cup stability 16,22–24 . High impaction energies were shown to improve primary stability, while excessive impaction in terms of energy amount and number of strokes should be avoided 25,26 . An influence of the surrogate density on the impaction process has been demonstrated, 26 but the influence of the cup design has not yet been considered.…”