Evolution without standing genetic variation: change in transgenerational plastic response under persistent predation pressure.

Transgenerational phenotypic plasticity is a fast non-genetic response to environmental modifications that can buffer the effects of environmental stresses on populations. However, little is known about the evolution of plasticity in the absence of standing genetic variation although several non-genetic inheritance mechanisms have now been identified. Here we monitored the pea aphid transgenerational phenotypic response to ladybird predators (production of winged offspring) during 27 generations of experimental evolution in the absence of initial genetic variation (clonal multiplication starting from a single individual). We found that the frequency of winged aphids first increased rapidly in response to predators and then remained stable over 25 generations, implying a stable phenotypic reconstruction at each generation. We also found that the high frequency of winged aphids persisted for one generation after removing predators. Winged aphid frequency then entered a refractory phase during which it dropped below the level of control lines for at least two generations before returning to it. Interestingly, the persistence of the winged phenotype decreased and the refractory phase lasted longer with the increasing number of generations of exposure to predators. Finally, we found that aphids continuously exposed to predators for 22 generations evolved a significantly weaker plastic response than aphids never exposed to predators, which, in turn, increased their fitness in presence of predators. Our findings therefore showcased an example of experimental evolution of plasticity in the absence of initial genetic variation and highlight the importance of integrating several components of non-genetic inheritance to detect evolutionary responses to environmental changes.

Interaction rewiring and the rapid turnover of plant-pollinator networks.

Whether species interactions are static or change over time has wide-reaching ecological and evolutionary consequences. However, species interaction networks are typically constructed from temporally aggregated interaction data, thereby implicitly assuming that interactions are fixed. This approach has advanced our understanding of communities, but it obscures the timescale at which interactions form (or dissolve) and the drivers and consequences of such dynamics. We address this knowledge gap by quantifying the within-season turnover of plant-pollinator interactions from weekly censuses across 3 years in a subalpine ecosystem. Week-to-week turnover of interactions (1) was high, (2) followed a consistent seasonal progression in all years of study and (3) was dominated by interaction rewiring (the reassembly of interactions among species). Simulation models revealed that species' phenologies and relative abundances constrained both total interaction turnover and rewiring. Our findings reveal the diversity of species interactions that may be missed when the temporal dynamics of networks are ignored.

Investigation of cancellous bone architecture using structural optimisation.

The optimality of bone's internal architecture and its remodelling is investigated by applying topological optimisation. The os-calcis (heel bone) which is subject to a relatively simple loading environment was used as the test problem. The solution is compared with X-ray and CT images of the os-calcis and is demonstrated to agree favourably with the bone's typical trabecular orientation in the coronal plane. The optimality of bone remodelling is further investigated by applying a perturbation during optimisation which leads to a different optimum topology. This is compared with in-vivo experimental results from a model in which the same perturbation was applied. The findings indicate that there may exist more than one optimum state for the same mechanical condition and that structural optimisation is able to find these multiple states. It is therefore suggested that structural optimisation can be used to investigate the mechanisms of bone remodelling.

Ultrasound transmission loss across transverse and oblique bone fractures: an in vitro study.

An axial transmission technique has been used to investigate the changes in the first arrival time and signal amplitude of 200 kHz ultrasonic waves travelling across different fracture geometries. Results taken from intact bovine femora were compared with those produced when a transverse and an oblique fracture were simulated. The arrival time and signal amplitude displayed a different variation with receiver position for the two geometries and a given fracture gap width. A comparison between this work and a previous study suggested that the marrow does not play a significant role in the mechanisms causing the change in arrival time and signal amplitude. Numerical modelling revealed that an oblique fracture caused a reduction in the extra time delay of the propagating wave compared with the transverse case, but a decrease in the corresponding signal amplitude, i.e., greater signal loss. The angle of the oblique fracture was investigated and results suggested that decreasing the fracture angle relative to the wave propagation direction caused a decrease in the extra time delay and an increase in signal loss. These findings are important for determining the sensitivity of systems for monitoring fracture healing using ultrasound arrival time and signal amplitude. (E-mail: spd@inorbit.com).

Immediate functional loading of single-tooth TIO2 grit-blasted implant restorations: a controlled prospective study in a porcine model. Part I: Clinical outcome.

BACKGROUND: Although favorable integration occurs with immediately loaded implants, the relationship between implant outcome, levels of occlusion, and diet requires optimization. PURPOSE: Pertubating load on single implant restorations immediately after placement by a hard food diet will increase the strains at the bone-implant interface, increasing the risk for failure. MATERIALS AND METHODS: Forty-eight implants replaced the first and third mandibular premolars in 12 pigs, allocated into two groups based on soft- and hard-diet feeding. Cylindrical and tapered implants replaced the first and third premolars, respectively. Each animal received at random four different masticatory loading conditions (group 1 control]: implant with either a cover screw or a healing abutment, and group 2 test]: implant with a crown either with or without occlusal contacts). RESULTS: Thirteen implants out of 44 failed in 11 animals (one with a cover screw, one with a healing abutment, three with nonocclusal, and eight with occlusal restorations). The failure rate of restored implants (either in occlusion or not) was significantly higher in the third premolar sites (p=.007), although diet had no significant effect (p=.421). CONCLUSIONS: While diet had no effect on the failure pattern of immediately loaded single implants, the position and type of load under the masticatory mode were significant. Immediately loaded implants both in and out of occlusion were less successful than the controls, and this is probably attributed to detrimental strain induced on the bone-implant interface.

Immediate functional loading of single-tooth TiO2 grit-blasted implant restoration. A controlled prospective study in a porcine model. Part II: Histology and histomorphometry.

BACKGROUND: Evidently, there is a fast-moving shift from delayed to immediate implant loading. The hypothesis to be tested was that bone reactions adjacent to single TiO2-microthreaded implants exposed to immediate masticatory loading for 10 weeks after placement would modulate osseointegration. MATERIALS AND METHODS: Cylindrical- and tapered-designed implants (Astra Tech AB, Mölndal, Sweden) replaced first and third mandibular premolars respectively in 12 pigs. The animals were allocated into two groups based on soft and hard diet feeding. Each animal received, at random positions, four different masticatory loading conditions: implant with either (1) a cover screw only, (2) a healing abutment, (3) an implant with a crown without occlusal contact, or (4) an implant with a crown in contact with the antagonistic teeth. RESULTS: Histomorphometry showed that there were no statistically significant differences in bone-implant contact (BIC), bone mass inside/outside of the threads and soft tissue ingrowth ratio for all the implants at 10 weeks after placement irrespective of masticatory loading condition. Bone loss showed a trend of progressive increase for implants with a healing abutment toward implants with occlusal contact. CONCLUSIONS: The results of this study rejected the hypothesis and could be explained by the fact that grit-blasted acid-etched implants were already placed in dense bone.

A brief history of total ankle replacement and a review of the current status.

Total ankle replacement (TAR) was first attempted in the early 1970s, but poor early results lead to it being abandoned in favour of arthrodesis. Arthrodesis is not totally satisfactory, often causing further hindfoot arthritis and this has lead to a resurgence of interest in joint replacement. New designs which more closely approximated the natural anatomy of the ankle and associated biomechanics have produced more encouraging results and led to renewed interest in total ankle replacement. Three prostheses dominate the market: Agility, Buechel-Pappas and STAR, and improving clinical results with these devices have led to more designs appearing on the market. Modern designs of prosthetic ankles almost exclusively consist of three part prostheses with a mobile bearing component, similar to the Buechel-Pappas and STAR. Clinical results of these newer designs are limited and short-term and have often been carried out by the designers of the implants. This paper presents a brief history of the development of total ankle replacement and a review of the current status.

Non-invasive vibrometry-based diagnostic detection of acetabular cup loosening in total hip replacement (THR).

Total hip replacement is aimed at relieving pain and restoring function. Currently, imaging techniques are primarily used as a clinical diagnosis and follow-up method. However, these are unreliable for detecting early loosening, and this has led to the proposal of novel techniques such as vibrometry. The present study had two aims, namely, the validation of the outcomes of a previous work related to loosening detection, and the provision of a more realistic anatomical representation of the clinical scenario. The acetabular cup loosening conditions (secure, and 1 and 2 mm spherical loosening) considered were simulated using Sawbones composite bones. The excitation signal was introduced in the femoral lateral condyle region using a frequency range of 100-1500 Hz. Both the 1 and 2 mm spherical loosening conditions were successfully distinguished from the secure condition, with a favourable frequency range of 500-1500 Hz. The results of this study represent a key advance on previous research into vibrometric detection of acetabular loosening using geometrically realistic model, and demonstrate the clinical potential of this technique.

Role of hydroxyapatite coating in resisting wear particle migration and osteolysis around acetabular components.

The main problem facing the longevity of total joint replacements is wear particle-induced osteolysis, particularly around the acetabular component. Ovine Total Hip Replacement surgery was performed with roughened femoral heads in order to enhance wear debris generation in vivo. The resistance to aseptic loosening of acetabular components with different surface coatings was investigated. Implants remained in vivo for 1 year. Sheep were randomly assigned to one of six experimental groups where the acetabular cup was fixed utilising an: (a) cemented polyethylene acetabular cup, (b) metal backed grit blasted surface, (c) metal backed plasma sprayed titanium porous coating, (d) metal backed sintered beaded coating, (e) Hydroxyapatite (HA)-coated grit blasted surface (f) and HA-coated porous components. Ground Reaction Force (GRF) was used to asses the functional performance of the implants and data was collected pre-operatively and at 12, 24, 36 and 52 weeks post op. Wear debris generated was analysed and radiographs taken prior to preparation of thin sections. Fibrous tissue (FT) thickness and bone contact at 1 mm intervals along the acetabular bone-implant interface was calculated. GRF data demonstrated significant differences between experimental groups. In all groups there was an increase in the function of the hip after surgery and up to 24 weeks but thereafter the function of the group with the grit blasted surface reduced whereas the function of the other groups did not significantly change. Average wear particles generated were <1 microm in size. The cemented group demonstrated a significantly thicker average FT layer (2.69 mm) when compared with all other groups (p<0.05 in all cases) except the grit blasted group (1.56 mm). HA porous coated cups demonstrated significantly least fibrous tissue adjacent to its interface when compared with all other groups (cemented p<0.05, grit blasted p=0.029, porous p<0.05, sintered beads p<0.05 and HA grit blasted p<0.05). Significantly increased bone contact to HA-coated porous cups (73.33%) when compared with all groups was identified except HA-coated grit blasted cups where no significant difference was demonstrated. Radiographic signs of loosening were visible in all groups except the HA-coated porous group. Results demonstrated that HA porous coated acetabular components significantly enhanced bone ingrowth in the presence of wear particles, preventing their migration and reducing osteolysis. Non-HA-coated porous and sintered beaded components provided a more effective seal against the ingress of wear debris when compared with cemented cups.

Development of a non-invasive diagnostic technique for acetabular component loosening in total hip replacements.

Current techniques for diagnosing early loosening of a total hip replacement (THR) are ineffective, especially for the acetabular component. Accordingly, new, accurate, and quantifiable methods are required. The aim of this study was to investigate the viability of vibrational analysis for accurately detecting acetabular component loosening. A simplified acetabular model was constructed using a Sawbones(®) foam block. By placing a thin silicone layer between the acetabular component and the Sawbones block, 2- and 4-mm soft tissue membranes were simulated representing different loosening scenarios. A constant amplitude sinusoidal excitation with a sweep range of 100-1500 Hz was used. Output vibration from the model was measured using an accelerometer and an ultrasound probe. Loosening was determined from output signal features such as the number and relative strength of observed harmonic frequencies. Both measurement methods were sufficient to measure the output vibration. Vibrational analysis reliably detected loosening corresponding to both 2 and 4 mm tissue membranes at driving frequencies between 100 and 1000 Hz (p < 0.01) using the accelerometer. In contrast, ultrasound detected 2-mm loosening at a frequency range of 850-1050 Hz (p < 0.01) and 4-mm loosening at 500-950 Hz (p < 0.01).

Controlled induction of a pseudarthrosis: a study using a rodent model.

OBJECTIVES: This study aimed to test the hypothesis that under standardized mechanical and biologic conditions, the process of indirect bone repair in a rodent species could be manipulated to form a reproducible, atrophic, fibrous pseudarthrosis. DESIGN: The model used comprised a mid-diaphyseal, transverse osteotomy in the rat femur, stabilized via a precision miniature external fixator, a constant axial fixation stiffness being defined by a specific frame geometry. MAIN OUTCOME MEASUREMENTS: The repair process for both 0.5-mm and 3.0-mm gap osteotomies was characterized using radiography, dual-energy x-ray absorptiometry, histologic assessment of standardized longitudinal sections, and postmortem mechanical testing. RESULTS: Healing of the defect was highly reproducible, bone union being attained at around 5 weeks postoperatively with a 0.5-mm gap. Increasing the gap width to 3.0 mm resulted consistently in a pseudarthrosis. CONCLUSION: These two reproducible patterns of repair can now be used to elucidate the underlying molecular mechanisms controlling the extent and progression of connective tissue differentiation in indirect bone repair without the additional variable of a nonstandardized mechanical environment.

Investigation of an acoustic-mechanical method to detect implant loosening.

Precise diagnosis of loosening of endoprosthetic implants plays an important role in timely, adequate treatment. However, today's diagnostic tools, mainly radiological evaluation, do not yield satisfactory results. Therefore, a new approach based on the transmission of an internally generated combined acoustic and vibration signal, was investigated. For signal generation, a magnetic oscillator which impinges inside an implant component, can be used. The signal can be detected by an external accelerometer being positioned on the skin surface. Differences in the signal generated result from varying degrees of implant fixation. This principle was tested in seven porcine foreleg specimens with a custom implant. Influence of the measurement location at the porcine skin and different levels of fixation were investigated (pressfit, slight loosening, advanced loosening), with regard to the pull-out strength. Evaluation of different parameters, especially the frequency spectrum resulted in differences of up to 12% for the comparison between pressfit and slight loosening, and 30% between pressfit and advanced loosening. A significant correlation between the measured frequency and the pull-out strength for different levels of fixation was found. Thus, the novel diagnostic method shows potential for the precise detection of implant loosening. Further work is required to determine the sensitivity and specificity of the proposed system in animal experiments.

Mechanical characteristics of antibiotic-laden bone cement.

We studied the mechanical characteristics of cement-antibiotic combinations in vitro. Palacos R was tested without antibiotics, with gentamicin alone and with gentamicin plus vancomycin or flucloxacillin. Palacos LV was studied only with gentamicin added. CMW 1 was studied with gentamicin added, with gentamicin plus vancomycin, and with gentamicin plus flucloxacillin. We performed four-point bending tests on beams of cement to establish bending strength and modulus, and compared the values to ISO standards. Density was also assessed. Palacos R was the strongest of the cements (bending strength 80 MPa). Palacos formulations (apart from Palacos LV) had a higher density and bending modulus than CMW 1. Statistical comparison of various cements with plain Palacos R showed lower density in 4 of the mixtures, and lower bending strength and modulus in 6 of the mixtures. Palacos R/gentamicin plus vancomycin and CMW 1/gentamicin plus vancomycin had bending strength slightly above minimum ISO standards, suggesting that the addition of vancomycin during cement mixing may compromise the outcome in revision surgery for sepsis.