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The Bone & Joint Journal
Vol. 106-B, Issue 2 | Pages 151 - 157
1 Feb 2024
Dreyer L Bader C Flörkemeier T Wagner M

Aims

The risk of mechanical failure of modular revision hip stems is frequently mentioned in the literature, but little is currently known about the actual clinical failure rates of this type of prosthesis. The current retrospective long-term analysis examines the distal and modular failure patterns of the Prevision hip stem from 18 years of clinical use. A design improvement of the modular taper was introduced in 2008, and the data could also be used to compare the original and the current design of the modular connection.

Methods

We performed an analysis of the Prevision modular hip stem using the manufacturer’s vigilance database and investigated different mechanical failure patterns of the hip stem from January 2004 to December 2022.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_II | Pages 99 - 99
1 May 2011
Rittershaus D Gottschalk D Reifenrath J Aljuneidi W Flörkemeier T Besdo S Meyer-Lindenberg A
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Introduction: Rabbits are a well-established animal model for orthopaedic research

and the tibia is commonly used for investigations of fracture repair with different implant materials

Occurring forces in the animal model are of fundamental interest for the development of degradable bone implants to prevent implant failure.

Therefore, a new method for the direct measurement of forces in the rabbit tibia was developed. The aim of this study was to determine maximal forces during weight bearing in the rabbit for future implementation into FEM-simulation.

Animals and Methods: An external ring fixation was attached to the left tibiae of 5 rabbits and an ostectomy followed. Force sensors were included into the collateral rods to incur the emerging forces completely. On each side, a measurement amplifier was applied to transfer the collected data telemetrically. During the study, the animals were weighted and x-rays were taken regularly. Measurements started 8 days postoperatively and were repeated 8 times until day 50 post-op. The rabbits were placed in a run and animated to move while the forces were registered. Force peaks were filtered from the collected data of each measurement as absolute values and relative to the animals’ weight (force-weight ratio/FWR).

Results: All included animals tolerated the external fixa-tion well and no clinical intolerances occurred. Beginning of callus formation was detected radiographically about 3 weeks post-op and all fixations could be removed 12–14 weeks after application without any permanent detriments. The maximal force amounted to 6950 g and 172 % FWR in animal 4 during the first recording. Means of the 5 maximal values for each measurement were located between 55 % FWR and 152 % FWR for the first measurement, converged to approx. 80 % FWR during the second recording 3 days later and descended to 20–40 % FWR until the end of the experiment.

Discussion: Aim of this study was to determine maximal forces during weight bearing in a rabbit model. Our model for in-vivo monitoring of these forces was practicable and provided profound data. The highest values occurred during the first or second recording. That coincides with the radiographic detection of callus after 3 weeks. Therefore, reliable measurements have to be carried out during the first 2 weeks postoperatively. Detected values show that the rabbit tibia is strained with up to 170 % of the body weight, which is the compressive force an implant in a weight bearing bone has to be able to bear. Future research will focus on the in-vivo monitoring of bending and torsion forces and the implementation of these data into FEM-simulation.