No abstract

Several factors can cause bone loss and fixation failure following total hip arthroplasty (THA), including polyethylene wear debris, implant micromotion and stress shielding. Various techniques have been used in an effort to detect bone density loss in vivo, all with varying success. Quantitative computed tomography (qCT)-assisted osteodensitometry has been shown to be useful in assessing the in vivo structural bone changes after THA. It has a high resolution, accuracy and reproducibility, thereby making it a useful tool for research purposes, and it is able to differentiate between cortical and cancellous bone structures and assess the bone/implant interface. This technique also provides valuable information about the pattern of stress shielding which occurs around the prosthesis and can show early bony changes, which may prove informative about the quality of implant fixation and surrounding bone adaptation. In conjunction with finite-element analysis, qCT is able to generate accurate patient-specific meshes on which to model implants and their effect on bone remodelling. This technology can be useful to predict bone remodelling and the quality of implant fixation using prostheses with different design and/or biomaterials. In the future, this tool could be used for pre-clinical validation of new implants before their introduction in the market-place.Résumé Plusieurs facteurs peuvent causer une perte osseuse et la faillite de la fixation après une arthroplastie totale de la hanche. Ils incluent les débris de polyéthylène, la micromobilité des implants et le transfert de contraintes. Plusieurs techniques ont été utilisées pour détecter la perte de densité osseuse, avec des succés variés. L'ostéodensitométrie quantitative par scanner s'est montrée utile dans l'étude in vivo des modifications structurales osseuses après arthroplastie totale de la hanche. Elle a une haute résolution, une précision et une reproductibilité qui en font un outil approprié pour la recherche. L'ostéodensitométrie quantitative peut différen-cier l'os cortical et l'os spongieux, étudier l'interface osimplant et donner des informations sur le modèle de déviation des contraintes qui surviennent autour d'une prothèse. Elle peut montrer précocement des modifications osseuses, ce qui renseigne sur la qualité de la fixation des implants et l'adaptation de l'os voisin. En conjonction avec l'analyse par éléments finis elle peut générer un maillage précis spécifique du patient permettant l'étude de modèles d'implants et leur effet sur le remodelage osseux. Cette technologie peut être utile pour prévoir le remodelage osseux et la qualité de la fixation pour des prothèses de différentes formes et/ou matériaux. Dans le future cet outil pourra être utilisé pour la validation pré-clinique de nouveaux implants avant leur introduction sur le marché.

Sustained lidocaine release via a thermoresponsive poloxamer-based in situ gelling system has the potential to alleviate pain following knee arthroplasty. A previously developed formulation showed a promising drug release profile in synthetic phosphate-buffered saline (PBS). To support the translation of this formulation, ex vivo characterisation was warranted. This study therefore aimed (1) to modify the previously developed formulation to reduce the burst release, (2) to compare the release behaviour into ex vivo human intra-articular fluid (IAF) and PBS and (3) to determine the formulation spread in an ex vivo human knee using magnetic resonance imaging (MRI). All formulations provided sustained release out to 72 h; polyvinyl pyrrolidone was the most effective additive yielding a small yet significant decrease (p < 0.05) in the burst release. Release of lidocaine from the formulation occurred significantly faster into IAF compared to PBS (1.4 times greater release in the first 24 h), correlating with faster rates of gel erosion in IAF. Injection was easily achieved through a 21-gauge (G) needle into the synovial space of a human cadaveric knee, and MRI scans revealed effective spreading of the formulation throughout the joint cavity. The pattern of spread is promising for the drug to reach the widespread nerve endings in the joint capsule; the effect of this spread on release in an in vivo setting will be the subject of future studies. The demonstrated properties indicate that the in situ gelling formulation has the potential to be used clinically to treat post-operative pain following knee arthroplasty.

Quantitative CT-osteodensitometry is a reproducible method to measure bone mineral density changes about the knee and shows little variation between observers.

Background: Locking plate fixation is widely used in large long bone fixation and is now available for small “long” bones in the hand. Potential advantages of unicortical locked fixation are reduced risk of over-drilling and therefore reduced risk of damage to surrounding structures and reduced risk of irritation from proud screws. Furthermore, unicortical fixation may be used where bicortical fixation is technically impossible. Our aim was to compare fixation strength of unicortical locked plate fixation with bicortical non-locked fixation in a human cadaveric model, by assessing strength under cyclical loading conditions and load to failure (LTF). Methods: 16 matched pairs of embalmed and refrigerated human cadaveric metacarpals were randomly allocated to either unicortical locked or bicortical non-locked plate and screw fixation. A transverse osteotomy was made. Fractures were stabilized with 2.0 mm self-tapping locking or cortical screws. Each metacarpal was then loaded with a 3-point cantilever testing using a 100 N cell on an Instron materials testing device, cyclically loading them at 1,000 repetitions of 30 N and 50 N. If there was no visible failure of the fixation from cyclical loading they were then loaded to failure with a 1 kN cell. Results: There was a significant difference of average LTF between the bicortical non-locking and unicortical locking of 38.07–59.95 N (p < 0.01). However, both groups showed no statistically significant difference when comparing their performance under cyclical loading. Conclusions: The authors regard unicortical locked fixation as a useful adjunct to standard plating technique.