Implant infection is an increasing problem in orthopedic surgery, especially due to progressive antibiotic resistance and an aging population with rising numbers of implantations. As a consequence, new strategies for infection prevention are necessary. In the previous study it was hypothesized that laser-structured implant surfaces favor cellular adhesion while hindering bacterial ongrowth and therewith contribute to reduce implant infections. Cuboid titanium implants (0.8 × 0.8 × 12 mm. 3. , n=34) were used. Seventeen were laser-structured by ultra-short pulsed laser ablation to create a spike structure; the others were polished and served as controls. In general anesthesia, implants were inserted in rat tibiae and infected with a S. aureus suspension. During a 21 day postoperative follow-up, daily clinical control was performed. Radiographs were taken at day 14 and day 21. After euthanasia, bacterial load and biofilm formation on the implant surface was evaluated semi quantitatively by confocal laser scanning microscopy and computational acquisition of bacteria and cells by Imaris®-software. Additionally, histology of the surrounding bone was performed. Clinically, no differences were observed between the groups. However, contrary to our hypothesis, bacterial load was increased in the laser-structured implant group although cellular adhesion was even more pronounced. Radiographical and histological evaluations showed increased bone alterations in the group with laser-structured implants compared to the control group. These findings did not confirm prior in vitro studies, where a reduction of bacterial load was found for similar surfaces and demonstrate the necessity of in vivo trials prior to the clinical use of new materials

To date there has been no material for endoprosthetics providing excellent resistance to abrasion and corrosion combined with great tensile strength, fracture toughness, and bending strength, as well as adequate biocompatibility. Carbon-fiber-reinforced silicon carbide (C/SiC, C/C-SiC or C/SiSiC) is as a ceramic compound a potentially novel biomaterial offering higher ductility and durability than comparable oxide ceramics. Aim of this investigation was to test the suitability of C/SiC ceramics as a new material for bearing couples in endoprosthetics. One essential quality that any new material must possess is biocompatibility. For this project the in-vitro biocompatibility was investigated by using cuboid like scaffolds made of CMC. To determine whether the material is suited as a lubricant partner in endoprosthetics, we measured its abrasion coefficient and wear tolerance against various antibodies. The C/SiC samples tested were produced via the Liquid Silicon Infiltration (LSI) of pyrolized porous fiber preforms made by warm-flow pressing free-flowing granulates on a hydraulic downstroking press with a heated die of the type HPS-S, 1000 kN. After preparation of the composites, the tribological characteristics are determined. Flexural strength was determined at room temperature according to DIN685-3 with an universal testing machine Z100 and the Young”s -modulus was carried out via resonant frequency-damping analysis RFDA. The samples”surface as well as cell adhesion and cell morphology were assessed via ESEM. The human osteoblast-like cell line MG-63 and human ostoeblast were used for cel culture ecperiments (WST, Live/dead, Cytotoxicity, cell morphology). Based on the raw data the mean value and the standard deviation were calculated. The Mann-Whitney-U-Test was used to evaluate the differences between experiment and control samples. The flexural strength at room temperature is approx. 180 MPa, while the elongation at break is about 0.13%. The Young”s modulus is detected between 120 and 150 GPa. The density lies between 2.5 and 3.0 g/cm. 3. We noted a friction coefficient µ between 0.31. The cell lines exhibited no morphological alterations, and adhered well to the C/SiC samples. Vitality was not impaired by contact with the ceramic composite. Cell growth was observed evenly distributed over a 21-day period. In the future, investigators aiming to apply this composite in endoprosthetics will have to focus on its efficacy in conjunction with sudden, strong demands, and long-term performance in bodily fluids within joint simulators, etc. In conclusion: C/SiC can definitely be considered a new material with genuine potential for use in endoprosthetics

The increase in revision joint replacement surgery and fractures of bone around orthopaedic implants may be partly addressed by keeping bone healthy around orthopaedic implants by inserting implants with mechanical properties closer to the patient's bone properties. We do not currently have an accurate way of calculating a patient's bone mechanical properties. We are therefore investigating whether microindentation can accurately calculate bone stiffness. We received ethical approval to retrieve femoral heads and necks from patients undergoing hip replacement surgery for research. Cortical bone from the medial calcar region of the femoral neck was cut into 3×3×6mm cuboid specimens. Micro-indentation testing was performed in the direction of loading of the bone using a MicroMaterials indenter. The samples were kept hydrated and were not fixed or polished. From the unloading curve after indentation, the elastic modulus was calculated, using the Oliver- Pharr method. To assess which microindentation machine settings most precisely calculate the elastic modulus we varied the loading and unloading rates, load and indenter tip shape. The most precise results were obtained by using a spherical indenter tip (rather than Berkovich tip), high load (10N), a loading rate of 100 mN/s and unloading rate of 300 mN/s with a pause of 60 seconds at maximum load and multiple load cycles with constant loads. Using these settings the mean elastic modulus over 12 cycles of testing was 13.0 GPa (+/- 2.47). By using a spherical indenter tip and fast unloading it was possible to get precise apparent modulus values. By unloading as fast as possible the effects of bone viscoelastic properties are minimised. By using a spherical indenter tip, plastic deformation at the tip is minimised (compared to the Berkovich tip). We are performing further standard compression tests on the samples to verify the accuracy of the indentation tests

We present a case of a 14 year old who sustained an isolated injury to her foot while horse riding. X-rays demonstrated a medial and plantar dislocation at the level of the talo-navicular and calcaneo-cuboid joint, with associated fractures of the cuboid and navicular. This was treated initially with open reduction and fixation with kirschner wires as the injury was grossly unstable and reduction difficult to maintain with casting alone. CT scan was then performed prior which confirmed satisfactory reduction of the dislocation and fixation with the k wires so these were left in situ and the navicular fracture reduced and fixed with a barouk screw. The Chopart joint was first described by French surgeon Francois Chopart as the talo-navicular and calcaneo-cuboid joints were a practical level for amputation. Injury here is a rare but missed in 40% at presentation. Pure dislocation occurs in 10–25% with most having concomitant fractures. The Chopart joint has critical role in balance and stability in normal gait. Early recognition allows prompt reduction and fixation of these injuries which has been associated with a better outcome. However these are severe injuries and patients should be counselled on potential long term functional impairment even with optimal management

Summary. At the clinical CT image resolution level, there is no influence of the image voxel size on the derived finite element human cancellous bone models. Introduction. Computed tomography (CT)-based finite element (FE) models have been proved to provide a better prediction of vertebral strength than dual-energy x-ray absorptiometry [1]. FE models based on µCTs are able to provide the golden standard results [2], but due to the sample size restriction of the µCT and the XtremeCT machines, the clinical CT-based FE models is still the most promising tool for the in vivo prediction of vertebrae's strength. It has been found [3] that FE predicted Young's modulus of human cancellous bone increases as the image voxel size increases at the µCT resolution level [3]. However, it is still not clear whether the image voxel size in the clinical range has an impact on the predicted mechanical behavior of cancellous bone. This study is designed to answer this question. Methods. For this study, 6 thoracolumbar vertebrae (Th12) obtained from the female donors were scanned in the non-dissected cadavers under 2 different resolutions – group A: 120 kVp, 100 mAs, with a resolution of 0.29×0.29×1.3 mm. 3. ; group B: 120 kVp, 360 mAs, with a resolution of 0.18×0.18×0.6 mm. 3. A solid calibration phantom (QRM-BDC) was placed beneath the cadavers during the scans. Cuboids with the size of 12.3×12.3×14.3 mm. 3. were cropped from the center of each vertebral body. The FE model was created by converting each image voxel into hexahedron (C3D8). Inhomogeneous material property was defined for the cuboid [4], i.e. the image greyscale value were firstly calibrated into the bone mineral density (BMD), then the Young's modulus and yield stress were calculated from the BMD [5] for each element. Statistical analysis was performed to compare the FE predicted mechanical properties between the groups and the significance level was set to 95% (α=0.05). Results. The trabecular structure is more clearly mimicked in the models from group B than those from group A. The modulus (mean ± SE) in group A is 5.9% higher than that in group B (193.33 ± 31.67 MPa vs. 182.50 ± 27.07 MPa). The yield strength (mean ± SE) in group A is 6.4% higher than that in group B (0.99 ± 0.21MPa vs. 0.93 ± 0.17MPa). However, the paired t-test shows there is no significant difference of the mechanical properties in the two groups (p=0.109 for the modulus and p=0.234 for the yield strength). Discussion. This study shows that there is no influence of the voxel size on the clinical CT derived FE cancellous bone models. This finding can help choose a better, less invasive CT protocol for the patient when creating a clinical CT image based FE model. Acknowledgements. This study is financially supported by the Federal Ministry of Education and Research and the state of Hamburg, Germany

Objectives

Lengthening osteotomies of the calcaneus in children are in general grafted with bone from the iliac crest. Artificial bone grafts have been introduced, however, their structural and clinical durability has not been documented. Radiostereometric analysis (RSA) is a very accurate and precise method for measurements of rigid body movements including the evaluation of joint implant and fracture stability, however, RSA has not previously been used in clinical studies of calcaneal osteotomies. We assessed the precision of RSA as a measurement tool in a lateral calcaneal lengthening osteotomy (LCLO).

Different calcaneal plates with locked screws were compared in an experimental model of a calcaneal fracture. Four plate models were tested, three with uniaxially-locked screws (Synthes, Newdeal, Darco), and one with polyaxially-locked screws (90° ± 15°) (Rimbus). Synthetic calcanei were osteotomised to create a fracture model and then fixed with the plates and screws. Seven specimens for each plate model were subjected to cyclic loading (preload 20 N, 1000 cycles at 800 N, 0.75 mm/s), and load to failure (0.75 mm/s).

During cyclic loading, the plate with polyaxially-locked screws (Rimbus) showed significantly lower displacement in the primary loading direction than the plates with uniaxially-locked screws (mean values of maximum displacement during cyclic loading: Rimbus, 3.13 mm (sd 0.68); Synthes, 3.46 mm (sd 1.25); Darco, 4.48 mm (sd 3.17); Newdeal, 5.02 mm (sd 3.79); one-way analysis of variance, p < 0.001).

The increased stability of a plate with polyaxially-locked screws demonstrated during cyclic loading compared with plates with uniaxially-locked screws may be beneficial for clinical use.

Compartment syndrome of the foot requires urgent surgical treatment. Currently, there is still no agreement on the number and location of the myofascial compartments of the foot. The aim of this cadaver study was to provide an anatomical basis for surgical decompression in the event of compartment syndrome. We found that there were three tough vertical fascial septae that extended from the hindfoot to the midfoot on the plantar aspect of the foot. These septae separated the posterior half of the foot into three compartments. The medial compartment containing the abductor hallucis was surrounded medially by skin and subcutaneous fat and laterally by the medial septum. The intermediate compartment, containing the flexor digitorum brevis and the quadratus plantae more deeply, was surrounded by the medial septum medially, the intermediate septum laterally and the main plantar aponeurosis on its plantar aspect. The lateral compartment containing the abductor digiti minimi was surrounded medially by the intermediate septum, laterally by the lateral septum and on its plantar aspect by the lateral band of the main plantar aponeurosis. No distinct myofascial compartments exist in the forefoot.

Based on our findings, in theory, fasciotomy of the hindfoot compartments through a modified medial incision would be sufficient to decompress the foot.

We performed a biomechanical study to compare the augmentation of isolated fractured vertebral bodies using two different bone tamps. Compression fractures were created in 21 vertebral bodies harvested from red deer after determining their initial strength and stiffness, which was then assessed after standardised bipedicular vertebral augmentation using a balloon or an expandable polymer bone tamp.

The median strength and stiffness of the balloon bone tamp group was 6.71 kN (sd 2.71) and 1.885 kN/mm (sd 0.340), respectively, versus 7.36 kN (sd 3.43) and 1.882 kN/mm (sd 0.868) in the polymer bone tamp group. The strength and stiffness tended to be greater in the polymer bone tamp group than in the balloon bone tamp group, but this difference was not statistically significant (strength p > 0.8, and stiffness p = 0.4).

The role of vacuum mixing on the reduction of porosity and on the clinical performance of cemented total hip replacements remains uncertain. We have used paired femoral constructs prepared with either hand-mixed or vacuum-mixed cement in a cadaver model which simulated intra-operative conditions during cementing of the femoral component. After the cement had cured, the distribution of its porosity was determined, as was the strength of the cement-stem and cement-bone interfaces.

The overall fraction of the pore area was similar for both hand-mixed and vacuum-mixed cement (hand 6%; vacuum 5.7%; paired t-test, p = 0.187). The linear pore fractions at the interfaces were also similar for the two techniques. The pore number-density was much higher for the hand-mixed cement (paired t-test, p = 0.0013). The strength of the cement-stem interface was greater with the hand-mixed cement (paired t-test, p = 0.0005), while the strength of the cement-bone interface was not affected by the conditions of mixing (paired t-test, p = 0.275). The reduction in porosity with vacuum mixing did not affect the porosity of the mantle, but the distribution of the porosity can be affected by the technique of mixing used.