Development of an optimal interface between bone and orthopaedic or dental implants has taken place for many years. In order to determine whether a newly developed implant material conforms to the requirements of biocompatibility, mechanical stability and safety, it must undergo rigorous testing both in vitro and in vivo. Results from in vitro studies can be difficult to extrapolate to the in vivo situation. For this reason the use of animal models is often an essential step in the testing of orthopaedic and dental implants prior to clinical use in humans. This review discusses some of the more commonly available and frequently used animal models such as the dog, sheep, goat, pig and rabbit models for the evaluation of bone-implant interactions. Factors for consideration when choosing an animal model and implant design are discussed. Various bone specific features are discussed including the usage of the species, bone macrostructure and microstructure and bone composition and remodelling, with emphasis being placed on the similarity between the animal model and the human clinical situation. While the rabbit was the most commonly used of the species discussed in this review, it is clear that this species shows the least similarities to human bone. There were only minor differences in bone composition between the various species and humans. The pig demonstrates a good likeness with human bone, however difficulties may be encountered in relation to their size and ease of handling. In this respect the dog and sheep/ goat show more promise as animal models for the testing of bone implant materials. While no species fulfils all of the requirements of an ideal model, an understanding of the differences in bone architecture and remodelling will assist in the selection of a suitable model for a defined research question.

Difficulty in removing implants used in trauma patients can be a complication, and increased bone-implant adhesion likely is a major contributing factor. In vitro studies have shown that surface morphology of implant materials has the ability to influence cellular responses, with polished surfaces decreasing the potential for mineralization. This study examined the effect of polishing commercially pure titanium (cpTi) and the titanium alloy TAN on the removal torque and percentage bone-implant contact in cortical and cancellous bone of sheep. Polishing had a significant effect on both removal torque and percentage bone-implant contact, with the polished implants demonstrating a lower removal torque in both cortical and cancellous bone. Polished cpTi and stainless steel were similar in terms of surface roughness and removal torque. However, polished TAN, which was not as smooth as polished cpTi, did not show the same low level for reducing removal torque. Improved polishing of TAN should reduce the removal torque further. The results of the study show that polishing is promising in improving the ease of implant removal after fracture fixation and repair. ß

Difficulties removing temporary fracture fixation devices due to excessive bony on-growth results in extended surgical time leading to excessive blood loss, debris contamination and potentially refracture. Commercially available locking plates and screws are manufactured for clinics with a micro-rough surface, which contributes to the excessive bony on-growth reported. We have applied polishing technology to commercially pure titanium locking compression plates (LCP) and titanium-6%aluminium-7%niobium (TAN) plates and screws to assess if it can alleviate problems with strong bony overgrowth. Samples were implanted for 6, 12 and 18 months in a bilateral sheep tibia non fracture model and assessed for screw removal torque, percentage of bone contact and tissue-material response. Both electropolishing (p=0.001) and paste polishing (p=0.010) of TAN screws significantly reduced the mean torque required for removal compared to their micro-rough counterparts. This was accompanied by a trend for a lower percentage of bone contact for polished screws. This difference in bone contact was significant for paste polished TAN screws (p<0.001) but not electropolished TAN screws (p=0.066). Ex vivo, soft tissue removal was much easier (~five minutes) for polished constructs, which was difficult and at least four times longer for standard micro-rough constructs. We suggest that polishing of locked plate/screw systems will improve ease of removal and reduce implant related removal complications encountered due to excessive strong bony on-growth while maintaining biocompatibility and implant stability. Future studies aim to assess the potential of this technology in the next level of complication, a fracture model.

BackgroundRecent studies using sheep critical sized defect models to test tissue engineered products report high morbidity and complications rates. This study evaluates a large bone defect model in the sheep tibia, stabilized with two, a novel Carbon fibre Poly-ether-ether-ketone (CF-PEEK) and a locking compression plate (LCP) which could sustain duration for up to 6 month with an acceptable low complication rate.MethodsA large bone defect of 3 cm was performed in the mid diaphysis of the right tibia in 33 sheep. The defect was stabilised with the CF - PEEK plate and an LCP. All sheep were supported with slings for 8 weeks after surgery. The study was carried out for 3 months in 6 and for 6 months in 27 animals.ResultsThe surgical procedure could easily be performed in all sheep and continuous in vivo radiographic evaluation of the defect was possible. This long bone critical sized defect model shows with 6.1% a low rate of complications compared with numbers mentioned in the literature.ConclusionsThis experimental animal model could serve as a standard model in comparative research. A well defined standard model would reduce the number of experimental animals needed in future studies and would therefore add to ethical considerations.

BackgroundAppalachian rural pediatric trauma has its unique incidence, presentation, and distribution due to the mechanisms of injury, geographic location, access to care, and social issues. PurposeTo review, analyze, and understand pediatric trauma in West Virginia during the period 2017-2019. Materials and methodsAfter institutional review board approval, the statewide trauma database was queried and analyzed in a retrospective cohort study for all pediatric trauma ages zero to 18 from 2017-2019 in the Appalachian regions one through four in West Virginia.The following were analyzed: gender, injury mechanism, Glasgow Coma Scale Score (GCS) at admission, injury severity score (ISS), toxicology screen results, hospital length of stay, duration of ventilatory support, number of procedures performed during admission, presence of non-accidental trauma, cardiac arrest, patient discharge disposition, and mortality. ResultsOne-thousand eighty-two (1182) patients between the ages of zero to 18 were admitted to the trauma center. An average of 37% was female and 63% male. In the 11-18 age group, 24% were female and 76% were male. Most injuries were due to blunt force (89%), followed by penetrating injuries (7.2%) and burns (1.4%). The majority had minor or moderate injuries with 95% receiving a Glasgow Coma Scale (GCS) >13 and 72% listed as minor on the injury severity score (ISS). Children in ages 0-2 years had the highest proportion of poor (0-8) GCS scores, high ISS (>14) scores, most hospital admission days, most days on a ventilator, highest mortality, most pre-hospital cardiac arrests, child abuse, burns, and placement with child protective services. An average of 31% of children tested, and 17% in the age group of 0-2 had a positive toxicology screen. There were 3670 procedures done in total and the most common procedure performed was an ultrasound of the abdomen. Procedures were performed in 90% of the patients. Conclusions and relevanceBased on our study, the zero to two-year-old pediatric trauma patients are most vulnerable to poor outcomes and may need targeted preventative interventions. Toxicology screens may need to be more widely implemented in pediatric trauma in the Appalachian region.Rural trauma in Appalachia has endemic issues related to substance abuse, poverty, and a lower degree of social support as compared to urban areas. Although the distribution of injury may follow a national distribution, mechanism, management, and outcomes can vary.