The influence of hip revision stem spline design on the torsional stability in the presence of major proximal bone defects

The study evaluates how hip revision stem design influences torsional stability in patients with significant bone loss. Specifically, it compares an established stem (Reclaim®) with a prototype featuring two sets of splines, one being less prominent. Five pairs of human femurs were used in the study, simulating large bone defects, common for revision surgeries. The prototype stem showed improved contact with the femoral cortex, resulting in 54% more cortical contact area and significantly higher torsional stability (35.2 Nm vs. 28.2 Nm). Although both stems demonstrated similar implantation characteristics, the prototype required slightly more force for proper seating. No significant differences in implant depth or angular misalignment during implantation were observed between the two designs. The study concluded that adding less prominent splines can enhance contact between the implant and bone, providing greater resistance to torsional loads and potentially improving the long-term success of hip revision surgeries.

Reference: Julius M. Boettcher ,Kay Sellenschloh,Gerd Huber,Benjamin Ondruschka,Michael M. Morlock https://doi.org/10.1371/journal.pone.0291599

Strength of the taper junction of modular revision hip stems

The study investigates the impact of contamination and improper assembly on the stability of modular hip stem connections in revision surgeries. Modular components offer flexibility in fitting implants to the patient's bone structure but are vulnerable to relative motion, which can cause fretting corrosion and implant failure. The research tested 48 neck-stem connections under various conditions of contamination (native, contaminated, cleaned) and assembly (secured, pre-tensioned). Results showed that contamination, particularly combined with improper assembly, significantly increased neck rotation (35.3° vs. 2.4°), micromotion (67.8 μm vs. 5.1 μm), and axial displacement (34.1 μm vs. 4.3 μm). A significant reduction in mechanical stability was observed in improperly secured connections. Proper cleaning with a new instrument and pre-tensioning of components reduced these adverse effects. The study highlights the importance of thorough cleaning and correct assembly to prevent early implant failure and potential complications.

Reference: Julius M. Boettcher, Kay Sellenschloh, Anna Strube, Gerd Huber & Michael M. Morlock https://doi.org/10.1007/s00132-023-04459-2

Post Mortem Retrievals

Rare and valuable feedback can be gained by studying retrieved post mortem specimens. This is possible on a large scale in Hamburg. Implanted specimens are analysed with the implant in situ, whereby sections are made either using histological techniques, or non-invasively using CT scanning (Titanium only) and documented for quality of implant anchorage. Mechanical tests are applied to measure implantation stability or strength (all histological sections to be displayed on this website in 2013).

Small design modifications can improve the primary stability of a fully coated tapered wedge hip stem

In this study small design modifications of a hip stem were experimentally compared to the established stem design (Emphasys™ vs. Corail®, DePuy Synthes, n = 6 per design) to identify whether they can increase the primary stability without increasing the periprosthetic fracture risk (PFF). The design modifications include a wider proximal section, smaller tip, and shorter length (Figure 1b). Additionally, new surgical equipment was introduced combining compaction and sharp extraction broaching (Figure 1a). Broaching and implantation were performed by an experienced surgeon followed by cyclic loading (1 Hz, 600 cycles @ 80 to 800 N, 600 cycles @ 80 to 1600 N) recorded with digital image correlation (Zeiss GOM). Broaching and implantation forces for the modified stem were up to 40% higher (p = 0.024), resulting in a 23% larger contact area between stem and bone (R2 = 0.694, p = 0.039). This led to a fourfold reduction in subsidence during loading (p = 0.028). The slight design modifications in this in-vitro study resulted in a higher primary stability, which suggests a reduced risk of loosening. While the higher forces during preparation and implantation might increase the PFF risk, there were no PFFs observed.

Reference: Katja Glismann ,Tobias Konow,Frank Lampe,Benjamin Ondruschka,Gerd Huber,Michael M. Morlock https://doi.org/10.1371/journal.pone.0300956

BoneStress

TUHH BoneStress is an interactive model demonstrating the effects of impaction and joint loading on bone stresses for different hip stem designs. It describes radial load transfer between implant and bone in uncemented press-fit femoral stem implantations.

This app provides a visual representation of the stress states between press-fit implant and bone directly post-operatively, and after bone ingrowth.

Stem design (stem and neck lengths, neck angle), impaction force, and joint loading can be varied to limit implant-bone separation while maintaining bone stresses within “normal” or “osteoporotic” limits. This will allow bone ingrowth and reduced stresses.

Its intuitive use makes TUHH BoneStress the perfect learning tool for surgeons and their patients by demonstrating the influence of stem design, implantation conditions, and patient activity, on the local stress situation, and its effect on successfull bone ingrowth.

It is noted that the simple model used cannot be directly transferred to an individual patient Situation

This App has been designed for the iPhone and for the iPad

Price: 0,89 €; Category: Medicine; Published: 21.10.2013; Version: 1.0; Size: 2.6 MB; Language: English;

Developer: Solutionline.de Agency for Online-Service GmbH; © TuTech innovation GmbH

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