Primary stability of a press‐fit cup in combination with impaction grafting in an acetabular defect model

Abstract

The objectives of this study were to (a) assess primary stability of a press-fit cup in a simplified acetabular defect model, filled with compacted cancellous bone chips, and (b) to compare the results with primary stability of a press-fit cup combined with two different types of bone graft substitute in the same defect model. A previously developed acetabular test model made of polyurethane foam was used, in which a mainly medial contained defect was implemented. Three test groups (N = 6 each) were prepared: Cancellous bone chips (bone chips), tricalciumphosphate tetrapods + collagen matrix (tetrapods + coll), bioactive glass S53P4 + polyethylene glycolglycerol matrix (b.a.glass + PEG). Each material was compacted into the acetabulum and a press-fit cup was implanted. The specimens were loaded dynamically in the direction of the maximum resultant force during level walking. Relative motion between cup and test model was assessed with an optical measurement system. At the last load step (3000 N), inducible displacement was highest for bone chips with median [25th percentile; 75th percentile] value of 113 [110; 114] µm and lowest for b.a.glass + PEG with 91 [89; 93] µm. Migration at this load step was highest for b.a.glass + PEG with 868 [845; 936] µm and lowest for tetrapods + coll with 491 [487;497] µm. The results show a comparable behavior under load of tetrapods + coll and bone chips and suggest that tetrapods + coll could be an attractive alternative to bone chips. However, so far, this was found for one specific defect type and primary stability should be further investigated in additional/more severe defects.

Primary Stability of Revision Acetabular Reconstructions Using an Innovative Bone Graft Substitute: A Comparative Biomechanical Study on Cadaveric Pelvises

“…To replicate consistent defects in each hemipelvis, a standardized protocol for defect implementation, based on statistical shape modeling and quantitative defect analysis, was adopted [ 18 , 21 ]. Critical, contained defects were replicated representing mostly medial defects with rim damage of approximately one third of the circumference, located at the inferior-posterior area of the rim ( Figure 1 ).…”

“…Recently, a bone graft substitute made of TCP tetrapods has been shown to grant adequate mechanical load capacity in a simplified bone defect model [ 17 ]. In a previous study, the use of a bone graft substitute made of molded bodies within a matrix material was proven to grant implant stability, when used to restore bone defects with a standardized geometry implemented in a foam model [ 18 ]. In both the above-mentioned studies, synthetic acetabular models were used.…”