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

Abstract

Insufficient primary stability of acetabular hip cups is a complication resulting in early cup loosening. Available cup designs vary in terms of wall thickness, potentially affecting implant fixation. This study investigated the influence of different wall thicknesses on the implantation process and the resulting primary stability using excised human acetabula. Implantations were performed using a powered impaction device providing consistent energy with each stroke. Two different wall thicknesses were compared in terms of seating progress, polar gap remaining after implantation, bone‐to‐implant contact area, cup deflection, and lever out moment. Thin‐walled cups showed higher lever out resistance (p < 0.001) and smaller polar gaps (p < 0.001) with larger bone contact toward the dome of the cup (p < 0.001) compared to thick‐walled cups. Small seating steps at the end of the impaction process were observed if a high number of strokes were needed to seat the cup (p = 0.045). A high number of strokes led to a strain release of the cup during the final strokes (p = 0.003). This strain release is indicative for over‐impaction of the cup associated with bone damage and reduced primary stability. Adequate cup seating can be achieved with thin‐walled cups with lower energy input in comparison to thicker ones. Thin‐walled cups showed improved primary stability and enable implantation with lower energy input, reducing the risk of over‐impaction and bone damage. Additional strokes should be avoided as soon as no further seating progress has been observed.

Acetabular cup size trends in total hip arthroplasty

“…We also acknowledge that a lack of data regarding the components used limits our results. Cup design is known to influence cup seating in THA[ 12 ]. This may in turn influence the degree of reaming required for different components.…”

Vibratory insertion of press-fit acetabular components requires less force than a single blow technique

“…The polar distance between two hemispheres fitted to the component outer surface, and the reamed PU block surface was then calculated and is referred to as polar gap. 19 …”

“…The polar distance between two hemispheres fitted to the component outer surface, and the reamed PU block surface was then calculated and is referred to as polar gap. 19 Two different battery-powered tools were used for acetabular component insertion. One was a commercially available and clinically used automated impaction device (KINCISE; DePuy Synthes, USA), which generates 3.5 J per blow and is triggered manually at 1 Hz using a metronome.…”

“… 6 Studies have indicated that polar gaps of less than 2 mm are associated with adequate primary stability. 19 , 20 The influence of implant and bone characteristics such as component design, 19 - 21 implant surface characteristics, 22 acetabular component stiffness, 23 bone density, 24 , 25 and the interface between bone and implant 2 , 26 on the initial implant stability have been investigated thoroughly. The impaction process has recently gained attention, such as different combinations of mass and velocity for impaction 27 or different energy levels.…”

Dynamics of manual impaction instruments during total hip arthroplasty

“…Acetabular component fixation testing is often performed in drop tower test rigs or uniaxial testing rigs where the force application is perfectly linear. [14][15][16][17][18][19][20] However, this is not a perfect model of surgery. The action of swinging a hammer involves coordination of several joints and muscle groups, and may introduce uncontrolled rotational movement of the cup in addition to the desired linear translation.…”