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Experimental analysis of insertion torques and forces of threaded and press-fit acetabular cups by means of ex vivo and in vivo measurements

Vogel D., Rathay A., Teufel S., Ellenrieder M., Zietz C., Sander M., Bader R.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 3

155--163

EN

In THA sufficient primary implant stability is the precondition for successful secondary stability. Industrial foams of different densities have been used for primary stability investigations. The aim of this study was to analyse and compare the insertion behaviour of threaded and press-fit cups in vivo and ex vivo using bone substitutes with various densities. Methods: Two threaded (Bicon Plus®, Trident® TC) and one press-fit cup (Trident PSL®) were inserted by orthopaedic surgeons (S1, S2) into 10, 20 and 31 pcf blocks using modified surgical instruments allowing measurements of the insertion forces and torques. Furthermore, the insertion behaviour of two cups were analysed intraoperatively. Results:Torques for the threaded cups increased while bone substitute density increased. Maximum insertion torques were observed for S2 with 102 Nm for the Bicon Plus® in 20 pcf blocks and 77 Nm for the Trident® TC in 31 pcf blocks which compares to the in vivo measurement (85 Nm). The average insertion forces for the press-fit cup varied from 5.2-6.8 kN (S1) and 7.2-11.5 kN (S2) ex vivo. Intraoperatively an average insertion force of 8.0 kN was determined. Conclusions: Implantation behaviour was influenced by acetabular cup design, bone substitute and experience of the surgeon. No specific density of bone substitute could be favoured for ex vivo investigations on the implantation behaviour of acetabular cups. The synthetic bone blocks of high density (31 pcf) led to problems regarding cup orientation and seating. Therefore, bone substitutes used should be critically scrutinized in terms of the comparability to the in vivo situation.

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Influence of cementless cup surface on stability and bone fixation 2 years after total hip arthroplasty

Urbański W., Krawczyk A., Dragan Sz.Ł., Kulej M., Dragan Sz.F.

Acta of Bioengineering and Biomechanics

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2012

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Vol. 14, no. 2

27-35

EN

Loss of fixation between bone and implant surface is one of the main treatment problems in total hip arthroplasty. It might lead to implant instability, bone loss and treatment failure resulting in revision surgery. Surface modification is a method for improving bone response to implant and increasing implant osseointegration. However, the currently applied modifications such as hydroxyapatite coatings do not meet expectation and do not provide good clinical result. The object of the study was to evaluate the influence of acetabular cup surface modification on fixation and bone remodelling in total hip arthroplasty. Clinical and radiological outcomes were evaluated in patients two years after cementless total hip replacement. Two groups were compared: patients with acetabular component with uncoated titanium surface and patients with hydroxyapatite-coated acetabular surface. Hips X-rays were analysed for early signs of losing stability of acetabular cups. Two years after surgery the analysis of X-rays did not reveal any statistical differences in stability, migration of acetabular components of endoprosthesis between both groups. No differences were also observed in bone remodelling around implants. Particularly high percentage of cups, i.e. 17.64%, were classified into the group with high risk of early implant loosening, i.e., the group with HA coatings. Hydroxyapatite coatings on titanium cementless acetabular cups implanted by press-fit technique have no influence on their stability, bone-implant fixation and the remodelling of bone surrounding an implant two years after surgery.

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Ceramic-ceramic coupling in total hip arthroplasty

Blömer W.

Acta of Bioengineering and Biomechanics

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1999

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Vol. 1, nr 2

85-91

EN

Based on positive clinical experience with the taper lock of ceramic heads in total hip replacement, the conical fixation was also chosen for modular cup inlay made of alumina ceramic and polyethylene. For a comparative assessment of inlay fixation, new ceramic and polyethylene inlays with a taper lock were biomachanically tested and compared with clinically proven system with a snap lock mechanism. With regard to the prevention of dislocation and relative movements the same level of safety was found. Measurements of the damping characteristic of the acetabulum replacement showed that there is no considerable shock-absorption for a metal backed polyethylene inlay and there are no differences in this respect between ceramic and polyethylene inlays.