Effects of screw eccentricity on the initial stability of the acetabular cup

Abstract

One of the major failure modes of cementless acetabular components is the loosening of the acetabular cup, which is mostly attributable to insufficient initial stability. A hemispherical cup with a porous coating which is inserted with press-fit fixation and secured with several screws is one of the most widely used approaches. Many studies have found that bone screws are very helpful aids for cup fixation, but the optimal surgical technique for inserting screws has not been clearly reported. In this study, hemispherical cups were fixed into blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity (a 1-mm offset and angular eccentricities of 15°and 25°) on the initial stability of the acetabular cup were evaluated. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing (i.e., with no eccentricity). An angular eccentricity of 15°did not affect the cup stability for fixation with one or two screws. However, the presence of 25°of angular eccentricity significantly reduced the stability of the cup, while 1 mm of offset eccentricity produced an even greater impact. Résumé Les modes les plus fréquents d'échecs des prothèses sans ciment sont le descellement de la cupule acétabulaire. Ce descellement est souvent en relation avec une stabilité initiale insuffisante. La cupule hémisphérique avec revêtement mis en place en press-fit avec vis additionnelles est un des modes opératoires les plus utilisés. De nombreuses études ont montré que l'utilisation de vis permettait de sécuriser la fixation. Pour cette étude, nous avons fixé des cupules hémisphériques dans un bloc d'os artificiel avec 0 à trois vis. Les effets de trois types de vissage ont permis d'évaluer la stabilité initiale de la cupule. Cette étude expérimentale montre que plus les vis sont nombreuses, meilleure est la stabilité. Une fixation excentrique de la cupule à 15°, stabilisée par une à deux vis n'a pas de conséquences néfastes, cependant une excentricité de 25°diminue de façon significative la stabilité de la cupule, de même, en ce qui concerne l'offset avec excentration de 1 mm.

Effect of screw fixation on acetabular component alignment change in total hip arthroplasty

“…Hsu et al [12,13] showed the number of screws applied does not appear to have a significant effect on peak micromotion or the patterns of micromotion distribution from finite element analyses. Kwong et al [14] experimentally investigated the use of one to four screws to fix the acetabular cup, and concluded that addition of supplemental screws did not significantly enhance stability of the implant under pressfit conditions.…”

Possible Vascular Injury Due to Screw Eccentricity in Minimally Invasive Total Hip Arthroplasty

“…Apart from this, Hsu et al . had studied the mechanical effect of press fit cup on the offset and angular eccentric screw in different experimental as well as the computational environment which is not directly associated with these findings 2324. Thus, we sought to determine the effect of the eccentric screw for two angular rotations (17° and 34°), along with different configurations [Table 1].…”

Evaluation of the effect of custom burr holes on a surgeon's sense of screw fixation in revision porous metal cups

“…It is not known, however, how these holes affect both the fixation of our shell or how they affect the surgeon's ability to distinguish good fixation. Previous studies have looked at screw insertion for acetabular shell fixation using Sawbones material [5][6][7] ; however, in our study, we set out to examine the biomechanics of screw insertion through custom burr holes in revision TM shells.…”

“…There have, however, been studies performed to validate the use of this material as a substitute for cancellous bone, [8][9][10][11] and many studies have used Sawbones as a substitute for biomechanical testing. [5][6][7]12,13 Its reproducibility during testing is favored for more accurate results. Our study was also limited by the blindfolding of the test subjects.…”