Implant Strength Contributes to the Osseointegration Strength of Porous Metallic Materials.

Creating the optimal environment for effective and long term osseointegration is a heavily researched and sought-after design criteria for orthopedic implants. A validated multimaterial finite element (FE) model was developed to replicate and understand the results of an experimental in vivo push-out osseointegration model. The FE model results closely predicted global force (at 0.5 mm) and stiffness for the 50-90% porous implants with an r2 of 0.97 and 0.98, respectively. In addition, the FE global force at 0.5 mm showed a correlation to the maximum experimental forces with an r2 of 0.90. The highest porosity implants (80-90%) showed lower stiffnesses and more equitable load sharing but also failed at lower a global force level than the low porosity implants (50-70%). The lower strength of the high porosity implants caused premature plastic deformation of the implant itself during loading as well as significant deformations in the ingrown and surrounding bone, resulting in lower overall osseointegration strength, consistent with experimental measurements. The lower porosity implants showed a balance of sufficient bony ingrowth to support osseointegration strength coupled with implant mechanical properties to circumvent significant implant plasticity and collapse under the loading conditions. Together, the experimental and finite element modeling results support an optimal porosity in the range of 60-70% for maximizing osseointegration with current structure and loading.

Lateral fenestration of lumbar intervertebral discs in rabbits: development and characterisation of an in vivo preclinical model with multi-modal endpoint analysis.

PURPOSE: To evaluate the biological and biomechanical effects of fenestration/microdiscectomy in an in vivo rabbit model, and in doing so, create a preclinical animal model of IVDD. METHODS: Lateral lumbar IVD fenestration was performed in vivo as single- (L3/4; n = 12) and multi-level (L2/3, L3/4, L4/5; n = 12) fenestration in skeletally mature 6-month-old New Zealand White rabbits. Radiographic, micro-CT, micro-MRI, non-destructive robotic range of motion, and histological evaluations were performed 6- and 12-weeks postoperatively. Independent t tests, one-way and two-way ANOVA and Kruskal-Wallis tests were used for parametric and nonparametric data, respectively. Statistical significance was set at P < 0.05. RESULTS: All rabbits recovered uneventfully from surgery and ambulated normally. Radiographs and micro-CT demonstrated marked reactive proliferative osseous changes and endplate sclerosis at fenestrated IVDs. Range of motion at the fenestrated disc space was significantly reduced compared to intact controls at 6- and 12-weeks postoperatively (P < 0.05). Mean disc height index percentage for fenestrated IVDs was significantly lower than adjacent, non-operated IVDs for both single and multi-level groups, at 6 and 12 weeks (P < 0.001). Pfirrmann MRI IVDD and histological grading scores were significantly higher for fenestrated IVDs compared to non-operated adjacent and age-matched control IVDs for single and multi-level groups at 6 and 12 weeks (P < 0.001). CONCLUSIONS: Fenestration, akin to microdiscectomy, demonstrated significant biological, and biomechanical effects in this in vivo rabbit model and warrants consideration by veterinary and human spine surgeons. This described model may be suitable for preclinical in vivo evaluation of therapeutic strategies for IVDD in veterinary and human patients.

Radiological and clinical outcomes of novel Ti/PEEK combined spinal fusion cages: a systematic review and preclinical evaluation.

PURPOSE: The primary objective of this paper was to provide a systematic review of the available clinical studies of Ti/PEEK combined cages in spinal interbody fusion surgeries, focusing on their radiological and clinical outcomes. A secondary aim was to provide a review and evaluation of the in vitro and preclinical studies reported on Ti/PEEK-coated implants. METHODS: A systematic search of the literature was performed in March 2015 via three databases: Medline, Embase and Cochrane library. The following key search terms were combined with synonyms to identify relevant articles: "spinal fusion," "PEEK," "titanium" and "cage." RESULTS: The novelty of this intervention translates into a paucity of clinical trials, albeit the results of the seven clinical studies that met the criteria for inclusion are promising. All studies reported rate of fusion as a primary outcome. Two studies reported slightly improved fusion in the experimental Ti/PEEK combination cohort, one study identical fusion (91.7 %) and three studies excellent fusion (96, 100 and 94 %) in the Ti/PEEK cohort, although no differences reached statistical significance. CONCLUSIONS: Clinical studies at this early stage demonstrate that Ti/PEEK implants are safe and efficacious, exhibiting similar fusion rates and clinical outcomes compared to the current standard PEEK. There is clinical evidence substantiating the improved radiographic fusion of Ti/PEEK, albeit the differences were not significant. This field is promising, gaining substantial popularity, and further clinical trials are needed in the future to establish Ti/PEEK cages as a mainstay of clinical practice.

Does PEEK/HA Enhance Bone Formation Compared With PEEK in a Sheep Cervical Fusion Model?

BACKGROUND: Polyetheretherketone (PEEK) has a wide range of clinical applications but does not directly bond to bone. Bulk incorporation of osteoconductive materials including hydroxyapatite (HA) into the PEEK matrix is a potential solution to address the formation of a fibrous tissue layer between PEEK and bone and has not been tested. QUESTIONS/PURPOSES: Using in vivo ovine animal models, we asked: (1) Does PEEK-HA improve cortical and cancellous bone ongrowth compared with PEEK? (2) Does PEEK-HA improve bone ongrowth and fusion outcome in a more challenging functional ovine cervical fusion model? METHODS: The in vivo responses of PEEK-HA Enhanced and PEEK-OPTIMA® Natural were evaluated for bone ongrowth in the form of dowels implanted in the cancellous and cortical bone of adult sheep and examined at 4 and 12 weeks as well as interbody cervical fusion at 6, 12, and 26 weeks. The bone-implant interface was evaluated with radiographic and histologic endpoints for a qualitative assessment of direct bone contact of an intervening fibrous tissue later. Gamma-irradiated cortical allograft cages were evaluated as well. RESULTS: Incorporating HA into the PEEK matrix resulted in more direct bone apposition as opposed to the fibrous tissue interface with PEEK alone in the bone ongrowth as well as interbody cervical fusions. No adverse reactions were found at the implant-bone interface for either material. Radiography and histology revealed resorption and fracture of the allograft devices in vivo. CONCLUSIONS: Incorporating HA into PEEK provides a more favorable environment than PEEK alone for bone ongrowth. Cervical fusion was improved with PEEK-HA compared with PEEK alone as well as allograft bone interbody devices. CLINICAL RELEVANCE: Improving the bone-implant interface with a PEEK device by incorporating HA may improve interbody fusion results and requires further clinical studies.

The design evolution of interbody cages in anterior cervical discectomy and fusion: a systematic review.

BACKGROUND: Anterior cervical discectomy with fusion is a common surgical procedure for patients experiencing pain and/or neurological deficits due to cervical spondylosis. Although iliac crest bone graft remains the gold standard today, the associated morbidity has inspired the search for alternatives, including allograft, synthetic and factor/cell-based grafts; and has further led to a focus on cage fusion technology. Compared to their graft counterparts, cage interbody implants have enhanced biomechanical properties, with designs constantly improving to maximise biocompatibility and osseointegration. We present a systematic review examining the historical progress of implant designs and performance, as well as an update on the currently available designs, and the potential future of cervical interbody implants. METHODS: We performed a systematic review using the keywords "cervical fusion implant design", with no limits on year of publication. Databases used were PubMed, Medline, Embase and Cochrane. In addition, the search was extended to the reference lists of selected articles. RESULTS: 180 articles were reviewed and 64 articles were eligible for inclusion. Exclusion criteria were based around study design, implant information and patient cohorts. The evolution of cage implant design has been shaped by improved understanding of ideal anatomy, progress in materials research and continuing experimentation of structural design. Originally, designs varied primarily in their choice of structure, however long-term studies have displayed the overall advantages of non-threaded, wedge shaped cages in complementing healthy anatomical profiles, and thus focus has shifted to refining material utilisation and streamlining anterior fixation. CONCLUSIONS: Evolution of design has been dramatic over the past decades; however an ideal cage design has yet to be realised. Current research is focusing on the promotion of osseointegration through bioactiviation of surface materials, as well as streamlining anterior fixation with the introduction of integrated screws and zero profile designs. Future designs will benefit from a combination of these advances in order to achieve ideal disc heights, cervical alignments and fusions.

The effect of supercritical carbon dioxide sterilization on the anisotropy of bovine cortical bone.

Bone allografts are used to replace bone that has been removed or to augment bone tissue in a number of clinical scenarios. In order to minimize the risk of infection and immune response, the bone is delipidated and terminally sterilized prior to implantation. The optimal method for bone graft sterilization has been the topic of considerable research and debate. Recently, supercritical carbon dioxide (SCCO(2)) treatments have been shown to terminally sterilize bone against a range of bacteria and viruses. This study aimed to evaluate the effect of these SCCO(2) treatments on the anisotropic mechanical properties of cortical bone. Adult bovine cortical cubes were prepared and treated using SCCO(2) and a range of common processing additives (ethanol, peracetic acid and hydrogen peroxide). The bone was mechanically tested in uniaxial compression in the axial, radial and tangential orientations. Ultimate stress, strain, elastic modulus, energy and stiffness were evaluated. This study found that SCCO(2) treatment without additive did not alter the ultimate stress, stiffness or energy to failure depreciably in any orientation. The addition of sterilants peracetic acid and hydrogen peroxide also preserved mechanical function, with no deleterious effect on stress or stiffness. This study highlights the expediency of SCCO(2) treatment for bone allograft processing as terminal sterilization can be achieved while maintaining the intrinsic mechanical properties of the graft.

Corrosion resistance, surface evaluation, and geometric design comparison of five self-expanding nitinol stents used in clinical practice.

PURPOSE: To investigate the corrosion resistance properties of 5 commercially available nitinol stents used to treat peripheral artery disease and compare their surface quality, elemental composition, and geometrical design. METHODS: Samples of 5 different designs of nitinol peripheral stents [LifeStent (n=4), Philon (n=6), Epic (n=6), S.M.A.R.T. Control (n=7), and Complete SE (n=7)] were examined using stereomicroscopy, environmental scanning electron microscopy, and x-ray photoelectron spectroscopy. Corrosion resistance testing was performed in accordance with ASTM International Standard F2129-08. RESULTS: Thirteen (43%) of 30 stents corroded during this experiment. Stent fracture was observed in 12 (92%) of these corroded stents. Mean breakdown potentials ranged from 517 to 835 mV (vs. Ag/AgCl) for the Philon, Complete SE, S.M.A.R.T. Control, Epic, and LifeStent models from lowest to highest. A statistically significant difference in breakdown potential was observed between the LifeStent vs. Philon stents (835 vs. 517 mV, p=0.01) and Epic vs. Philon stents (833 vs. 517 mV, p=0.03). Stents with lower breakdown potential and relative breakdown potentials were associated with a higher fracture frequency (Spearman correlation coefficient -0.44, p=0.015 and -0.869, p<0.01, respectively). CONCLUSION: In this in vitro study, corrosion led independently to stent fracture. There is a significant association between lower mean breakdown/relative breakdown potentials and stent fracture.

Comparison of three methods for nucleus pulposus volume measurement in rabbit lumbar spines: a preclinical model for measurement of the effectiveness of prophylactic intervertebral disk fenestration in dogs.

OBJECTIVE: Compare 3 methods of nucleus pulposus (NP) volume measurement using the rabbit lumbar spines as a preclinical model to determine the effectiveness of prophylactic intervertebral disk fenestration in dogs. ANIMALS: Twelve 9-month-old, skeletally mature female entire New Zealand White rabbits weighing between 3.5 to 4.5 kg. METHODS: NP volume measurements of dissected rabbit lumber spines between L1 and L6 were made and compared using gross measurements, reconstructed MRI images, and water volumetry based on Archimedes' principle. Water volumetry was used as the true gold standard volume measurement in this study. RESULTS: The true volume (mean ± SD) of the nucleus pulposus NP as measured by water volumetry increased caudally from L1/L2 (16.26 ± 3.32 mm3) to L5/L6 (22.73 ± 6.09 mm3). Volume estimates made by MRI were significantly higher than those made using water volumetry at all sites (L1/L2 [P = .044], L2/L3 [P = .012], L3/L4 [P = .015], L4/L5 [P < .001], and L5/L6 [P < .001]). Gross measurements also significantly overestimated volume when compared to water volumetry at all sites; L1/L2 (P = .021), L2/L3 (P = .025), L3/L4 (P = .001), L4/L5 (P < .001), and L5/L6 (P < .001). MRI and gross volume estimates were significantly different at L4/L5 (P = .035) and L5/L6 (P = .030). CLINICAL RELEVANCE: The findings of this preclinical model might be relevant to veterinary surgeons who perform prophylactic fenestration for which there is no reliable method to determine the amount of NP to be removed. Preclinical ex vivo and in vivo fenestration studies with pre- and postoperative NP volume assessment are required.

Effect of gamma irradiation and supercritical carbon dioxide sterilization with Novakill™ or ethanol on the fracture toughness of cortical bone.

Sterilization of structural bone allografts is a critical process prior to their clinical use in large cortical bone defects. Gamma irradiation protocols are known to affect tissue integrity in a dose dependent manner. Alternative sterilization treatments, such as supercritical carbon dioxide (SCCO2 ), are gaining popularity due to advantages such as minimal exposure to denaturants, the lack of toxic residues, superior tissue penetration, and minor impacts on mechanical properties including strength and stiffness. The impact of SCCO2 on the fracture toughness of bone tissue, however, remains unknown. Here, we evaluate crack initiation and growth toughness after 2, 6, and 24 h SCCO2 -treatment using Novakill™ and ethanol as additives on ~11 samples per group obtained from a pair of femur diaphyses of a canine. All mechanical testing was performed at ambient air after 24 h soaking in Hanks' balanced salt solution (HBSS). Results show no statistically significant difference in the failure characteristics of the Novakill™-treated groups whereas crack growth toughness after 6 and 24 h of treatment with ethanol significantly increases by 37% (p = .010) and 34% (p = .038), respectively, compared to an untreated control group. In contrast, standard 25 kGy gamma irradiation causes significantly reduced crack growth resistance by 40% (p = .007) compared to untreated bone. FTIR vibrational spectroscopy, conducted after testing, reveals a consistent trend of statistically significant differences (p < .001) with fracture toughness. These trends align with variations in the ratios of enzymatic mature to immature crosslinks in the collagen structure, suggesting a potential association with fracture toughness. Additional Raman spectroscopy after testing shows a similar trend with statistically significant differences (p < .005), which further supports that collagen structural changes occur in the SCF-treated groups with ethanol after 6 and 24 h. Our work reveals the benefits of SCCO2 sterilization compared to gamma irradiation.

The effects of low-intensity pulsed ultrasound on tendon-bone healing in a transosseous-equivalent sheep rotator cuff model.

PURPOSE: The purpose of this study was to examine the effects Low-intensity Pulsed Ultrasound has on initial tendon-bone healing in a clinically relevant extra-articular transosseous-equivalent ovine rotator cuff model. METHODS: Eight skeletally mature wethers, randomly allocated to either control group (n = 4) or treatment group (n = 4), underwent rotator cuff surgery following injury to the infraspinatus tendon. All animals were killed 28 days post surgery to allow examination of early effects of Low-intensity Pulsed Ultrasound treatment. RESULTS: General improvement in histological appearance of tendon-bone integration was noted in the treatment group. Newly formed woven bone with increased osteoblast activity along the bone surface was evident. A continuum was observed between the tendon and bone in an interdigitated fashion with Sharpey's fibres noted in the treatment group. Low-intensity Pulsed Ultrasound treatment also increased bone mineral density at the tendon-bone interface (p < 0.01), while immunohistochemistry results revealed an increase in the protein expression patterns of VEGF (p = 0.038), RUNX2 (p = 0.02) and Smad4 (p = 0.05). CONCLUSIONS: The results of this study indicate that Low-intensity Pulsed Ultrasound may aid in the initial phase of tendon-bone healing process in patients who have undergone rotator cuff repair. This treatment may also be beneficial following other types of reconstructive surgeries involving the tendon-bone interface.

Relationship between patellar tendon shortening and in vitro kinematics in the ovine stifle joint.

Post-operative patellar tendon shortening induces a distal positioning of the patella in the femoral trochlear groove, which has been associated with pain and impeded mobility. An idealized in vitro model was used to examine the effects of shortening on patellar kinematics. The PT length was progressively reduced by up to 5 mm (1-mm instalments) using a device secured onto the tendon in n = 9 ovine stifles. In vitro 6 degrees-of-freedom motion data for the patellofemoral and tibiofemoral joints under conditions of passively induced flexion-extension was acquired electromagnetically. Patellar motion was analysed as a function of both tibial and patellar flexion angles relative to the femoral co-ordinate frame. Linear regression with contrasts was used to compare kinematic changes for each shortening level, with significance set at P<0.01. A mean maximum percentage length reduction of 8.2% was achieved. Patellar flexion was linearly correlated with tibial flexion angle in the intact joint, and this correlation persisted after tendon shortening (R = 0.977, P < 0.01). Patellar kinematics expressed as a function of tibial flexion angle were significantly altered by a mean length decrease of 8.2%, while flexion and proximo-distal shift patterns were significantly affected at lesser shortening levels of 3.1% and 4.7%, respectively. Patellar kinematics expressed as a function of patellar flexion angle remained unchanged. These results suggest that patellar motion within the trochlear groove in the ovine stifle joint follows a repeatable three-dimensional path and that patellar tendon shortening advances the position of the patella along this path, without significantly altering it.

The effect of sterilization on the mechanical properties of intact rabbit humeri in three-point bending, four-point bending and torsion.

Load bearing bone allografts are used to replace the mechanical function of bone that has been removed or to augment bone that has been damaged in trauma. In order to minimize the risk of infection and immune response, the bone is delipidated and terminally sterilized prior to implantation. The optimal method for bone graft sterilization has been the topic of considerable research. Recently, supercritical carbon dioxide (SCCO(2)) treatments have been shown to terminally sterilize bone against a range of bacteria and viruses. This study aimed to evaluate the effect of SCCO(2) treatment compared with two doses of gamma irradiation, on the mechanical properties of whole bone. Paired rabbit humeri were dissected and randomly assigned into either SCCO(2) control, SCCO(2) additive or gamma irradiation at 10 or 25 kGy treatment groups. The bones were mechanically tested in three-point and four-point bending and torsion, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated. This study found that SCCO(2) treatment with or without additive did not alter maximum load, energy to failure or stiffness significantly under any loading modality. Gamma irradiation had a deleterious dose dependant effect, with statistically significant decreases in all mechanical tests at 25 kGy; while at 10 kGy there were reductions in all loading profiles, though only reaching statistical significance in torsion. This study highlights the expediency of SCCO(2) treatment for bone allograft processing as terminal sterilization can be achieved while maintaining the intrinsic mechanical properties of the graft.

Can platelet-rich plasma (PRP) improve bone healing? A comparison between the theory and experimental outcomes.

The increased concentration of platelets within platelet-rich plasma (PRP) provides a vehicle to deliver supra-physiologic concentrations of growth factors to an injury site, possibly accelerating or otherwise improving connective tissue regeneration. This potential benefit has led to the application of PRP in several applications; however, inconsistent results have limited widespread adoption in bone healing. This review provides a core understanding of the bone healing mechanisms, and corresponds this to the factors present in PRP. In addition, the current state of the art of PRP preparation, the key aspects that may influence its effectiveness, and treatment outcomes as they relate specifically to bone defect healing are presented. Although PRP does have a sound scientific basis, its use for bone healing appears only beneficial when used in combination with osteoconductive scaffolds; however, neither allograft nor autograft appear to be appropriate carriers. Aggressive processing techniques and very high concentrations of PRP may not improve healing outcomes. Moreover, many other variables exist in PRP preparation and use that influence its efficacy; the effect of these variables should be understood when considering PRP use. This review includes the essentials of what has been established, what is currently missing in the literature, and recommendations for future directions.

Preclinical in vivo animal models of intervertebral disc degeneration. Part 1: A systematic review.

Intervertebral disc degeneration (IVDD), a widely recognized cause of lower back pain, is the leading cause of disability worldwide. A myriad of preclinical in vivo animal models of IVDD have been described in the literature. There is a need for critical evaluation of these models to better inform researchers and clinicians to optimize study design and ultimately, enhance experimental outcomes. The purpose of this study was to conduct an extensive systematic literature review to report the variability of animal species, IVDD induction method, and experimental timepoints and endpoints used in in vivo IVDD preclinical research. A systematic literature review of peer-reviewed manuscripts featured on PubMed and EMBASE databases was conducted in accordance with PRISMA guidelines. Studies were included if they reported an in vivo animal model of IVDD and included details of the species used, how disc degeneration was induced, and the experimental endpoints used for analysis. Two-hundred and fifty-nine (259) studies were reviewed. The most common species, IVDD induction method and experimental endpoint used was rodents(140/259, 54.05%), surgery (168/259, 64.86%) and histology (217/259, 83.78%), respectively. Experimental timepoint varied greatly between studies, ranging from 1 week (dog and rodent models), to >104 weeks in dog, horse, monkey, rabbit, and sheep models. The two most common timepoints used across all species were 4 weeks (49 manuscripts) and 12 weeks (44 manuscripts). A comprehensive discussion of the species, methods of IVDD induction and experimental endpoints is presented. There was great variability across all categories: animal species, method of IVDD induction, timepoints and experimental endpoints. While no animal model can replicate the human scenario, the most appropriate model should be selected in line with the study objectives to optimize experimental design, outcomes and improve comparisons between studies.

'SMART' implantable devices for spinal implants: a systematic review on current and future trends.

Background: 'SMART' implants refer to modified orthopedic implants that combine the biomechanical safety and efficacy of traditional devices with the intelligence of data-logging sensors. This review aims to systematically assess the available literature on SMART spinal implants and present these findings in a clinically relevant manner. Methods: A search of PubMed, Scopus, and Google Scholar databases was conducted by two separate reviewers. Information including sensor type, intended application, and sample size, was extracted from included studies. Risk of bias assessment was conducted using the Office of Health Assessment and Translation (OHAT) risk of bias tool. Results: Eighteen studies were included for analysis. Eight studies involved SMART rods and ten studies used SMART vertebral body replacements (VBR). No more than 20 patients are reported to have received a SMART spinal implant. Including non-primary evidence, seven unique designs for SMART spinal implants were found. The majority of these used strain gauges with recent designs including thermometers and accelerometers. Discussion: At present, SMART spinal implants have primarily focused on utilising strain gauges to report loading on the implant itself. This is a logical first step as it allows quantification of real-world requirements of an implant, detection of catastrophic failure, while also allowing researchers and clinicians to estimate changes in load sharing between newly forming bone and the implant itself, providing real-time information on the progression of healing and fusion. Future work includes documenting the correlation between data provided by these SMART implants and clinical findings, including complications such as pedicle screw loosening and interbody cage subsidence.

Corrosion Resistance of 3D Printed Ti6Al4V Gyroid Lattices with Varying Porosity.

Corrosion of medical implants is a possible failure mode via induced local inflammatory effects, systemic deposition and corrosion related mechanical failure. Cyclic potentiodynamic polarisation (CPP) testing was utilized to evaluate the effect of increased porosity (60% and 80%) and decreased wall thickness in gyroid lattice structures on the electrochemical behaviour of LPBF Ti6Al4V structures. The use of CPP allowed for the landmarks of breakdown potential, resting potential and vertex potential to be analysed, as well as facilitating the construction of Tafel plots and qualitative Goldberg analysis. The results indicated that 60% gyroid samples were most susceptible to the onset of pitting corrosion when compared to 80% gyroid and solid samples. This was shown through decreased breakdown and vertex potentials and were found to correlate to increased lattice surface area to void volume ratio. Tafel plots indicated that despite the earlier onset of pitting corrosion, both gyroid test groups displayed lower rates of corrosion per year, indicating a lower severity of corrosion. This study highlighted inherent tradeoffs between lattice optimisation and corrosion behaviour with a potential parabolic link between void volume, surface area and corrosion being identified. This potential link is supported by 60% gyroid samples having the lowest breakdown potentials, but investigation into other porosity ranges is suggested to support the hypothesis. All 3D printed materials studied here showed breakdown potentials higher than ASTM F2129's suggestion of 800 mV for evaluation within the physiological environment, indicating that under static conditions pitting and crevice corrosion should not initiate within the body.

Stand up! Are normal weight-bearing forces sufficient for a 12/14 Morse taper locking in total hip arthroplasty?

BACKGROUND: The aim of this study was to investigate total hip arthroplasty (THA) Morse taper pull-off strengths after impaction prior to cyclical loading compared to cyclical loading alone. The practical relevance of the experiment is to provide a perspective on what may be clinically satisfactory taper assembly given the spectrum of head tapping patterns used by surgeons, as well as compare traditional impaction performed in standard THA with alternate methods of taper engagement such as 'in situ assembly' used in micro-invasive techniques. METHODS: 36 taper constructs utilising a combination of cobalt-chrome alloy and ceramic-titanium alloy junctions were investigated in vitro in wet and dry conditions with cyclical loading of the constructs. Taper disengagement strengths with and without impaction were compared. Secondary investigation of the surface roughness of the heads and tapers was also assessed. RESULTS: An impaction to a wet taper resulted in a greater pull off force compared to a dry taper with a CoCr head and taper combination. Impacting the head and dryness of the taper did not affect pull off forces of a ceramic femoral head on titanium taper. Pulling a head off a taper significantly alters the head surface roughness. CONCLUSION: Impaction of a taper does not provide any benefit over cyclical loading of a taper assembly alone for pull-off strength.

Vacuum-Sealed Hot Water Bath Immersion for the Preparation of Anatomical and Surgical Cadaveric Bone Models.

Bone models serve many purposes, including improving anatomical understanding, preoperative surgical planning, and intraoperative referencing. Several techniques for the maceration of soft tissues have been described, mainly for forensic analysis. For clinical research and medical use, these methods have been superseded by three-dimensional (3D) printed models, which require substantial equipment and expertise, and are costly. Here, cadaveric sheep vertebral bone was cleaned by vacuum sealing the specimen with commercial dishwashing detergent, immersing in a hot water bath, and subsequently manually removing the soft tissue. This eliminated the disadvantages of the previously existing maceration methods, such as the existence of foul odors, usage of hazardous chemicals, substantial equipment, and high costs. The described technique produced clean, dry samples while maintaining anatomical detail and structure to accurately model the osseous structures that can be useful for preoperative planning and intraoperative referencing. The method is simple, low-cost, and effective for bone model preparation for education and surgical planning in veterinary and human medicine.

Impact of test environment on the fracture resistance of cortical bone.

Water is a crucial component of bone, affecting the interplay of collagen and minerals and contributing to bone's high strength and ductility. Dehydration has been shown to significantly effect osseous mechanical properties; however, studies comparing the effects of various dehydrating environments on fracture toughness of bone are scarce. Accordingly, the crack resistance curve (R-curve) behavior of human and sheep cortical bone was characterized in a bio-bath, in ambient pressure air, and in scanning electron microscopes (SEMs) under three different environmental conditions (water vapor pressure, air pressure, and high-vacuum). The aim of this work was to better understand the impact of test environment on both intrinsic and extrinsic toughening and hence crack initiation toughness, K0 and crack growth resistance, dK/dΔa. Results show significantly lower K0 values for samples that were tested inside SEMs combined with pronounced extrinsic toughening through microcracking and crack path deflections out of the mode I plane. Importantly, all three SEM test environments gave similar results, and thus it does not matter which type of SEM is used. Ex situ testing of hydrated samples revealed similar K0 for both environments but elevated crack growth resistance for testing in ambient air relative to the bio-bath. Our data reveals the experimental difficulties to directly observe microscale crack propagation in cortical bone that resembles the in vivo situation. Ex situ testing immersed in Hanks' Balanced Salt Solution (HBSS) with subsequent crack path analysis, while tedious, is thought to presents the most realistic picture of the in vivo structure-fracture property relations in biological tissue.