Variability in Femoral Preparation and Implantation Between Surgeons Using Manual and Powered Impaction in Total Hip Arthroplasty

Abstract

Background The influence of the surgical process on implant loosening and periprosthetic fractures (PPF) as major complications in uncemented total hip arthroplasty (THA) has rarely been studied because of the difficulty in quantification. Meanwhile, registry analyses have clearly shown a decrease in complications with increasing experience. The goal of this study was to determine the extent of variability in THA stem implantation between highly experienced surgeons with respect to implant size, position, press-fit, contact area, primary stability, and the effect of using a powered impaction tool. Methods Primary hip stems were implanted in 16 cadaveric femur pairs by three experienced surgeons using manual and powered impaction. Quantitative CTs were taken before and after each process step, and stem tilt, canal-fill-ratio, press-fit, and contact determined. Eleven femur pairs were additionally tested for primary stability under cyclic loading conditions. Results Manual impactions led to higher variations in press-fit and contact area between the surgeons than powered impactions. Stem tilt and implant sizing varied between surgeons but not between impaction methods. Larger stems exhibited less micromotion than smaller stems. Conclusions Larger implants may increase PPF risk, while smaller implants reduce primary stability. The reduced variation for powered impactions indicates that appropriate measures may promote a more standardized process. The variations between these experienced surgeons may represent an acceptable range for this specific stem design. Variability in the implantation process warrants further investigations since certain deviations, for example, a stem tilt toward varus, might increase bone stresses and PPF risk.

A parametric numerical analysis of femoral stem impaction

“…It is noted that the hammer tip stiffness increases with tip material stiffnesses at the impaction interface, and with increasing radius or contact area of the interface surfaces. These things could be achieved by powered impaction tools [32,33] with a predefined impaction interface geometry. The maximum effective tip stiffness tends to the magnitude of the lower of the stiffness of the bulk hammer or introducer materials.…”

“…It should be noted that the assumption of constant energy consecutive impactions presented in this study does not reflect the clinical situation, in which the surgeon tends to increase the impaction energy with consecutive impactions. Increasing energy will increase introducer stresses and more constant energy impaction may be preferable, for example, using powered impaction tools [32,33].…”

“…Such data is unavailable! Implant seating in bone can be measured quite easily, using non-invasive systems [33,36]. Stressing can be derived from surface strain measurements.…”

“…Stressing can be derived from surface strain measurements. Implant seating measurements have been published [33,36], but are not generally related to the input variables of interest in the current study. Many studies of impaction dynamics have been published, often addressing the prediction of sufficient and safe implant seating, by signal processing of impaction accelerations [23], forces [21,22,26] or acoustic measurements [24,25].…”

“…Of course, more complex models will be necessary to study load transfer in multiple degrees of freedom and detailed geometry will allow local stress concentrations and detailed failure modes of impaction devices to be studied. The current uni-axial model may be particularly relevant to contemporary linear implant insertion systems, and particularly those which employ an axially mounted impaction gun, offering optimal impaction [32,33].…”