Bone Cylinders Research Articles

“Evaluation of a method to measure the friction coefficient between vital mandibular bone and biomedical materials”

PurposeThe aim of this study is to evaluate a developed experimental set-up to measure the coefficient of friction between fresh mandibular bone and biomaterials used in oral and maxillofacial surgery including a standardized routine for specimen preparation. Material and methodsFor this purpose, we developed a specialized routine for harvesting and preparation of cortical bone specimen from cadaveric porcine mandibles and modified a ball-plate tribometer. These harvested bone specimen were kept moist all the time. A total of 24 bone cylinders with 8 repetitions per material were examined for their coefficient of friction against stainless steel (1.4404), a titanium alloy (Ti6Al4V) and a cobalt‑chromium‑molybdenum alloy (Biosil F®) and subsequently analyzed by laser-scanning and scanning electron microscopy. ResultsThe lowest coefficients of friction between vital cortical bone and the investigated implant materials were found for Biosil F®, while the highest coefficients of friction were found for the titanium alloy Ti6Al4V. Significant differences for the initial coefficient of friction with p < 0.05 have been proven. Stick-slip effects occurred during the measurement and a layer of debris formed on the metallic samples. EDX analysis of the abrasion marks revealed that this layer consisted of elements contained in hydroxyapatites and carbon. ConclusionThe experimental set-up is suitable to perform reproducible comparative measurements of the coefficient of friction of different material combinations. A significant advantage of the methodology is the flexibility and scalability of harvesting and preparation of the bone specimen, which allows the simulation of realistic situations while measuring the coefficient of friction.

A Method for the Evaluation of Early Osseointegration of Implant Materials Ex Vivo: Human Bone Organ Model.

In the present work, an ex vivo organ model using human bone (explant) was developed for the evaluation of the initial osseointegration behavior of implant materials. The model was tested with additive manufactured Ti6Al4V test substrates with different 3D geometries. Explants were obtained from patients who underwent total knee replacement surgery. The tibial plateaus were used within 24 h after surgery to harvest bone cylinders (BC) from the anterior side using hollow burrs. The BCs were brought into contact with the test substrate and inserted into an agarose mold, then covered with cell culture media and subjected to the external load of 500 g. Incubation was performed for 28 days. After 28d the test substrate was removed for further analysis. Cells grown out BC onto substrate were immunostained with DAPI and with an antibody against Collagen-I and alkaline phosphatase (ALP) for visualization and cell counting. We show that cells stayed alive for up to 28d in our organ model. The geometry of test substrates influences the number of cells grown onto substrate from BCs. The model presented here can be used for testing implant materials as an alternative for in vitro tests and animal models.

Mechanical Effects of Lag Screw Retightening in a Simulated Hindfoot Arthrodesis Model.

Background:Nonunion following hindfoot arthrodesis may be caused by failure to maintain compression at the arthrodesis site. The ability of lag screws, commonly used in arthrodesis, to maintain compression in hindfoot bones has not been well characterized. The aim of this work was to quantify the stress relaxation response of hindfoot bone with initial and repeated compression with a lag screw.Methods:Ten sets of 25-mm-diameter bone cylinders were cut from the talus and calcaneus in fresh-thawed cadaveric feet. A load cell was compressed between cylinders with an 8.0-mm partially threaded cannulated lag screw simulating arthrodesis. For 7 sets, screws were tightened by 3 quarter-turns, rested for 3 minutes, retightened 1 quarter-turn, and rested for 30 minutes. Three sets served as controls in which screws were not retightened.Results:Maximum compression after initial screw tightening and retightening averaged 275 and 337 N (P = .07), respectively. Compression 3 minutes after initial screw tightening and retightening averaged 199 and 278 N (P = .027), respectively. The compression recorded 3 minutes after screw retightening was an average of 40% higher than that recorded 3 minutes after initial tightening. The average compression 30 minutes after screw retightening was 255 N, a compression loss of 25% from the average maximum compression after retightening. Eighty percent of this compression loss happened in an average of 5.5 minutes.Conclusion:Hindfoot bones exhibit compression loss over time during simulated arthrodesis. Compression maintenance in bone is improved with screw retightening. Further work is needed to understand the mechanism of action and determine optimum time for recompression.Clinical Relevance:Retightening lag screws before wound closure may improve compression at the arthrodesis site and thereby decrease the chance of nonunion.Level of Evidence:N/A, laboratory experiment.

Mechanical Characterization of Human Trabecular and Formed Granulate Bone Cylinders Processed by High Hydrostatic Pressure.

One main disadvantage of commercially available allogenic bone substitute materials is the altered mechanical behavior due to applied material processing, including sterilization methods like thermal processing or gamma irradiation. The use of high hydrostatic pressure (HHP) might be a gentle alternative to avoid mechanical alteration. Therefore, we compressed ground trabecular human bone to granules and, afterwards, treated them with 250 and 300 MPa for 20 and 30 min respectively. We characterized the formed bone granule cylinders (BGC) with respect to their biomechanical properties by evaluating stiffness and stress at 15% strain. Furthermore, the stiffness and yield strength of HHP-treated and native human trabecular bone cylinders (TBC) as control were evaluated. The mechanical properties of native vs. HHP-treated TBCs as well as HHP-treated vs. untreated BGCs did not differ, independent of the applied HHP magnitude and duration. Our study suggests HHP treatment as a suitable alternative to current processing techniques for allogenic bone substitutes since no negative effects on mechanical properties occurred.

Platelet-rich plasma and stromal vascular fraction cells for the engineering of axially vascularized osteogenic grafts.

Avascular necrosis of bone (AVN) leads to sclerosis and collapse of bone and joints. We have previously shown that axially vascularized osteogenic constructs, engineered by combining human stromal vascular fraction (SVF) cells and a ceramic scaffold, can revitalize necrotic bone of clinically relevant size in a rat model of AVN. For a clinical translation, the fetal bovine serum (FBS) used to generate such grafts should be substituted by a nonxenogeneic culture supplement. Human thrombin-activated platelet-rich plasma (tPRP) was evaluated in this context. SVF cells were cultured inside porous hydroxyapatite scaffolds with a perfusion-based bioreactor system for 5 days. The culture medium was supplemented with either 10% FBS or 10% tPRP. The resulting constructs were inserted into devitalized bovine bone cylinders to mimic the treatment of a necrotic bone. A ligated vascular bundle was inserted into the constructs upon subcutaneous implantation in the groin of nude rats. After 1 and 8 weeks, constructs were harvested, and vascularization, host cell recruitment, and bone formation were analyzed. After 1 week in vivo, constructs were densely vascularized, with no difference between tPRP- and FBS-based ones. After 8 weeks, bone formation and vascularization was found in both tPRP- and FBS-precultured constructs. However, the amount of bone and the vessel density were respectively 2.2- and 1.8-fold higher in the tPRP group. Interestingly, the density of M2, proregenerative macrophages was also significantly higher (6.9-fold) following graft preparation with tPRP than with FBS. Our findings indicate that tPRP is a suitable substitute for FBS to generate vascularized, osteogenic grafts from SVF cells and could thus be implemented in protocols for clinical translation of this strategy towards the treatment of bone loss and AVN.

Does Lag Screw Retightening Improve Compression in Hindfoot Arthrodesis?

Category:Hindfoot; Ankle; Ankle ArthritisIntroduction/Purpose:Non-union and delayed union are common complications following hindfoot arthrodesis. The failure to obtain and maintain compression at the arthrodesis site may be a causative factor. Partially threaded cannulated ‘lag’ screws are commonly used for fixation in hindfoot arthrodesis; however, the ability of these screws to maintain compression in the hindfoot bones has not been well-characterized. The goals of this work were to: 1) quantify the stress relaxation response of hindfoot bones when compressed with a lag screw, particularly compression change upon screw retightening, and 2) compare the results to prior studies on stress relaxation in direct bone compression.Methods:12 pairs of calcaneus, talus and tibia bone cylinders, 25mm in diameter, were cut with a keyhole saw from fresh thawed cadaveric feet. The bone cylinders were prepared for simulated arthrodesis by removing the cartilage and flattening the subchondral surface with an oscillating saw. A Futek LTH 300 donut load cell and two metal washers were sandwiched between the two bone cylinders. An 8.0mm partially threaded cannulated lag screw (Smith and Nephew) was placed from the posterior- inferior aspect of the calcaneus cylinder to the anterior-superior aspect of the talus cylinder to simulate subtalar arthrodesis, or from the superior aspect of the tibia cylinder to the inferior aspect of the talus cylinder. Compression was recorded continuously as the screws were tightened by three-quarters of a turn and left untouched for 3 minutes. Recording continued as the screws were retightened one quarter-turn and then left untouched for 30 additional minutes.Results:Both initial and subsequent compression with a lag screw demonstrated a stress relaxation pattern, with increased maximum compression and slowed decay upon retightening. Maximum compression after three quarter-turns and retightening averaged 284 N and 351 N, respectively (n=12; t=-2.55; p=0.0136). Time to decay to 80% of maximum compression after three quarter-turns and retightening averaged 34 and 528 (n=9; t=-2.59; p=0.0159) seconds, respectively, compared to 21 seconds for direct compression. Compression loss 30 minutes after retightening averaged 25.5% (SD=8.8%), compared to 34.3% for direct compression.Conclusion:The maximum compression attained following retightening was significantly greater than the maximum compression attained after initial tightening. The time required to reach 80% of maximum compression was significantly longer after subsequent compared to initial maximum compression. These findings suggest that screw retightening before surgical wound closure may slow compression loss, which could increase the likelihood of successful arthrodesis. Lag screw compression resulted in a lower percent compression loss and loss rate compared to direct compression, which was previously used to describe bone viscoelasticity.

Why Cervical Vertebrae Do Not Fracture – A Biomechanical Approach Using Loading Tests on Human Vertebrae of A 79-Year-Old Body Donor.

Abstract Purpose: Bone structure alters with increasing age. Material and structural properties are both important for bone strength. Despite having an ageing society, there is a paucity of data from elderly subjects in terms of these parameters. The aim of the present study was to conduct comparative examinations of the structure and material properties of the cervical spine (CS), the thoracic spine (TS) and the lumbar spine (LS), in order to identify both structural and biomechanical differences between the segments of the spine. Methods: We examined central bone cylinders of vertebral bodies C1 to L5 from a 79-year-old body donor in regards to their bone volume fraction (BVF), trabecular thickness (Tb.Th.), separation (Tb.Sp.), trabecular orientation (SMI) and degree of anisotropy (DA). Samples were obtained from all vertebrae with a Jamshidi needle®, and were prepared with a damp cloth in an Eppendorf reaction vessel (1.5 ml). The investigations were performed with a micro-CT device (SKYSCAN 1172, RJL Micro &amp; Analytic GmbH, Germany). Existing deformities and fractures were registered with quantitative computed tomography (QCT). The load tests of the vertebral bodies C1 to L5 were performed on a servo-hydraulic testing machine (MTS 858, MTS Systems Cooperation, Eden Prairie, USA). Results: Regarding BVF (p=0.003), Tb.Th. (p=0.041) and SMI (p=0.012) statistically significant differences were found in the different spinal column sections. The force per area was significantly higher in the CS than in the TS and LS (CS vs. TS, p=0.022; CS vs. LS, p&lt;0.001; TS vs. LS, p=0.012). Conclusion: Due to their unique microarchitecture cervical vertebrae are less prone to fractures than thoracic and lumbar vertebrae. Among the reasons are the higher BVF and Tb.Th. of the cervical vertebrae compared to other vertebrae. Furthermore, the SMI of the CS has more plates than rods. Thus, the CS is characterized by specific features, whose causes must be determined in further investigations.

Evaluation of metal artefacts for two CBCT devices with a new dental arch phantom.

To create a new phantom design to evaluate the real impact of artefacts caused by titanium on bone structures in cone beam CT images considering different positions and quantity of metals in the dental arch, with and without metal artefact reduction (MAR). A three cylindrical polymethyl methacrylate (PMMA) plate phantom was designed containing eight perforations arranged to simulate the lower dental arch in the intermediate plate. Three titanium cylinders were positioned in different locations and quantities to test different clinical conditions and to quantify the impact of the metal artefact around five bone cylinders. Scans were carried out in seven different protocols (Control, A-F) in two cone beam CT devices (OP300 Maxio and Picasso Trio). Eight regions of interest around each cortical and trabecular bone were used to measure the grey value standard deviation corresponding the artefact expression in the Image J software. Both the artefact expression and the MAR effect were assessed using the Wilcoxon, Friedman (Dunn) and Kruskal-Wallis tests (significance level of 5%). For both devices, MAR was statistically efficient only for the protocols E, and F. Protocol F (three metals on the adjacent area of the analysis region) showed higher artefact expression when compared to the others. In conclusion, the new phantom design allowed the quantification of the metal artefact expression caused by titanium. The metal artefact expression is higher when more metal objects are positioned in the adjacent bone structures. MAR may not be effective to reduce artefact expression on the adjacencies of those objects for the devices studied.

Temporospatial distribution of osteogenic and osteoclastic cells during development of the tarsometatarsal skeleton in the chick embryo (Gallus gallus).

The morphogenesis of long bones is a multistep process that generates a variety of genetically defined forms. The tarsometatarsal (TMT) long bone morphology in birds develops through lateral fusion of three initially independent periosteal bone cylinders (BCs). Previous studies have clarified the histological details and chronology of the changes occurring during development. The present study investigated the temporospatial distribution of osteogenic and osteoclastic cells in the embryonic chicken using histochemistry for alkaline phosphatase and tartrate-resistant acid phosphatase, with particular reference to the radial growth of BCs and their subsequent fusion process. Osteogenic cells were localized preferentially in the periosteum of radially growing BCs, leaving open cancellous spaces in the BC wall. Osteoclasts observed later than embryonic day 10 were localized preferentially in the endosteal surface, and therefore the radial growth of BCs resulting from osteoblast activity was accompanied by endosteal resorption by osteoclasts, with progressive enlargement of the bone marrow spaces. During BC fusion, trabecular bridges were formed by periosteal osteogenic cells, with removal of the bone septum by endosteal osteoclasts. These findings suggest that fusion of BCs in the embryonic chicken is mediated by cellular events constituting ordinary long bone development, and not through a defined mechanism specific for fusion.

Hindfoot Bone Viscoelasticity and Stress Relaxation

Category:Ankle, Ankle Arthritis, Basic Sciences/Biologics, HindfootIntroduction/Purpose:Hindfoot arthrodeses have a non-union rate as high as 40%. Compression at the arthrodesis site plays a key role in stimulating bone growth leading to successful fusion. The ability to obtain and maintain compression depends not only on the surgical technique and the hardware which develop the compressive force but also on the response of the bone to compression. Bone, like other musculoskeletal tissues, is viscoelastic meaning that it has properties of both fluids and solids.Because bone is viscoelastic, it experiences stress relaxation (decrease in compressive force over time). The rate and magnitude of such stress relaxation is unknown. Our primary objective was to quantify stress relaxation of the hindfoot bones when subjected to a fixed compression displacement as would be done during arthrodesis.Methods:10 human cadaveric bone cylinders measuring 10 mm in both diameter and height were cut from the articular surfaces of the talus, calcaneus, and distal tibia using a disposable cylindrical osteochondral harvester (OATS, Arthrex inc, Naples, FL).Each bone cylinder sample included subchondral and trabecular bone, and articular cartilage was removed during preparation. Each sample was scanned with a micro-computed tomography (uCT) scanner (Biomedical Micro CT Scanner, Scanco Medical, Switzerland) to quantify bone volume/total volume ratio (BV/TV), trabecular thickness, trabecular separation, trabecular number, and connectivity density. Each specimen was submerged in a saline bath and compressed by 1 mm at a strain rate of 1mm/sec using a material testing machine (System 810, MTS Systems, Eden Prairie, MN), and load data was gathered by an Interface load cell. Displacement was held constant for 3 hours, after which each sample was removed from the test machine and immediately rescanned with the uCT scanner.Results:The ensemble load curve of the ten samples displayed uniform exponential decay. After the initial load was placed on the bone, a steep, negative load velocity was apparent. Rapid decay occurred within the first 3 minutes, after which the load plateaued, holding constant over the subsequent 3 hours of compression. The average peak load was 515.53 N (SD: 254.58 N). The average percent load loss was 65.77% over 30 minutes (SD: 20.95%). Discrete time periods (B1, B2, B3, B4) were established corresponding to 0-3 min, 3-10 min, 10-20 min, and 20-30 min, respectively. Time periods B1, B2, B3, and B4 demonstrated an average percent load loss per time period of 43.35% (SD: 10.09%), 13.80% (SD: 14.77%), 18.65% (SD: 24.97%) and 7.95% (SD: 13.37%), respectively.Conclusion:Our data suggest that a significant percentage of compressive load placed across a bone is lost within the first 3 minutes as compared to any subsequent time period. Moreover, approximately 65.77% of the compressive load is lost over the first 30 minutes. These data suggest that when performing arthrodesis with compressive hardware, the majority of the initially applied compressive load may dissipate over the first 3-30 minutes, which may contribute to nonunion. Thus, a re-tightening of screws after 5-30 minutes or the use of a continuous compressive device may help to maintain compression at the arthrodesis site throughout healing.

The influence of mini-fragment plates on the mechanical properties of long-bone plate fixation.

Objective:Mini-fragment plates (MFPs) are increasingly used in fracture surgery to provide provisional fixation. After definitive fixation, the surgeon decides whether to remove the plates or leave them in place as additional fixation, based on the perceived biomechanical influence of the MFP. However, there are no current biomechanical studies to guide this decision. Therefore, the purpose of this study was to evaluate the influence of MFPs on the four-point bending and torsional stiffness of long bone transverse and simple wedge fracture fixation constructs.Methods:Fourth-generation composite bone cylinders were cut to produce transverse (AO-OTA classification 12-A3) and simple wedge (AO-OTA classification 12-B2) fracture models. The specimens were fixed using a low-contact dynamic compression plate (LC-DCP) and MFPs. Specimens were tested in four-point bending and torsion utilizing 3 different MFP orientations.Results:No statistically significant differences in bending stiffness were found between control and MFP groups for transverse fracture constructs. MFPs significantly increased the bending stiffness for wedge fracture constructs under certain loading conditions. This increase was observed when MFPs were positioned both orthogonal (85.1% increase, P = .034) and opposite (848.2% increase, P < .001) to the LC-DCP. MFPs significantly increased the torsional stiffness for both transverse and wedge fracture constructs when MFPs were positioned both orthogonal (transverse: 27.7% increase, wedge: 16.7% increase) and opposite (transverse: 28.4%, wedge: 24.2% increase) to the LC-DCP.Conclusions:Our results indicate that including MFPs in definitive fixation can increase the bending and torsional stiffness of a long-bone fracture fixation construct. This suggests that the biomechanical influence of MFPs should be considered. However, clinical studies will be required to test the applicability of these findings to the clinical setting.

Bone cylinder plug and coil technique for accurate pedicle localization in thoracic spine surgery: A technical note.

Background:Intraoperative identification of the correct level during thoracic spine surgery is essential to avoid wrong-level procedures. Despite technological progress, intraoperative imaging modalities for identifying the correct thoracic spine level remain unreliable and often lead to wrong-level surgery. To counter potential wrong-level operations, here, we have proposed a novel pedicle/bone cylinder marking technique for use in the thoracic spine utilizing biplanar fluoroscopy and confirmed with computed tomography (CT).Methods:First, under fluoroscopic guidance, a bone cylinder is removed from the correct thoracic pedicle. Next, endovascular coils are packed into the cancellous bone defect followed by reinsertion of the bony plug. The patient then undergoes a CT scan of the entire thoracolumbosacral spine to precisely identify the marked level before surgery.Results:We utilized this bone cylinder plug/coil technique to identify the T9-T10 level in a 56-year-old female with a soft thoracic disc herniation. The index thoracic pedicle was successfully localized before performing the unilateral minimally invasive laminectomy followed by the transpedicular thoracic disc excision.Conclusion:The bone cylinder plug/coil technique is a safe and effective method for marking the correct level in thoracic spine surgery, while also reducing the operative time.

Effect of different mixing modes of enoxaparin sodium on biomechanics of bone cement

Objective To observe the biomechanical effects of enoxaparin sodium added to bone in different mixing modes. Methods The enoxaparin sodium for injection was mixed with polymethylmethacrylate (PMMA) bone according to different dosages and different mixing methods. Group A was used as blank control group without enoxaparin sodium. Groups B (8 000 AxaIU), C (16 000 AxaIU) and D (24 000 AxaIU) served as control groups in a powder mixture. Groups E (8 000 AxaIU), F (16 000 AxaIU) and G (24 000 AxaIU) served as experimental groups. The enoxaparin sodium for injection was dissolved and added to the PMMA bone cement. Under the environment of sterility, temperature (23±1) ℃, relative humidity higher than 40% (operating room environment), according to the international standard ISO5833: 2002 Implants for surgery-Acrylic resin cement regulations, bone cylinder specimens and cuboid specimens were prepared. After measurement and X-ray irradiation, 5 specimens of each group were selected, and the compressive strength, flexural strength and flexural modulus were measured on an electronic material universal testing machine. Results The compressive strength, flexural strength and flexural modulus in groups E, F and G were significantly lower than those in the control groups (t=12.731, 41.646, 3.128, P<0.05). The lowest values were (57.17±1.15) MPa, (67.93± 0.55) MPa, and (19.2± 0.114) GPa respectively. Conclusion The addition of enoxaparin sodium to PMMA bone in a liquid mixture can significantly reduce the biomechanical properties of bone cement. Key words: Polymethylmethacrylate bone cement; Enoxaparin sodium; Biomechanics

Precision lattice parameter determination from transmission diffraction of thick specimens with irregular cross sections

Accurate determination of lattice parameters from X-ray diffraction requires that the diffraction angles be measured very precisely, and significant errors result if the sample–detector separation differs from that assumed. Transmission diffraction from bones, which have a complex cross section and must be left intact, is a situation where this separation is difficult to measure and it may differ from position to position across the specimen. This article describes a method for eliminating the effect of variable sample cross section. Diffraction patterns for each position on the specimen are collected before and after 180° rotation about an axis normal to the cross section of interest. This places the centroid of the diffracting mass at the center of rotation and provides the absolute lattice parameters from the average apparent lattice parameters at the two rotation angles. Diffraction patterns were collected across the cross section of three specimens: a 3D-printed elliptical cylinder of Hyperelastic Bone (HB), which is composed primarily of synthetic hydroxyapatite (hAp), a 3D-printed HB model of the second metacarpal bone (Mc2), and a modern human Mc2 containing nanocrystalline carbonated apatite (cAp). Rietveld refinement was used to determine precise unit-cell parameters a apparent and c apparent for each pattern of each scan, and these values determined the actual average 〈a〉 and 〈c〉 for each sample. The results indicate that the 0°/180° rotation method works well enough to uncover variations approaching 1 × 10−3 Å in cAp unit-cell parameters in intact bones with irregular cross sections.

Contact force between the tibial spine and medial femoral condyle: A biomechanical study

BackgroundContact between the tibial spine and medial femoral condyle with internal tibial rotation (ITR) has been proposed as a factor for the development of osteochondritis dissecans lesions. We hypothesized that tibial spine contact force (CF) would increase significantly with applied internal tibial torque (IT). MethodsA 20 mm diameter cylinder of bone encompassing the tibial spine was cored and attached to a load cell. The isolated bone cylinder included the tibial attachments of the anterior cruciate ligament (ACL) and anterior horn of the lateral meniscus (AHLM). Eleven human cadaveric knees were flexed from 0°–50° under 200 N of tibiofemoral compression (TFC), without and with 2 N-m IT. Tests were repeated with the AHLM cut, and again with both AHLM and ACL cut, where the load cell recorded CF alone without contributions from any ligamentous attachments. FindingsThere were no significant differences in CF, ITR, or valgus tibial rotation (VTR) after sectioning the AHLM, without or with applied IT. With no tibial torque, mean CFs were less than 20 N throughout the flexion range. Addition of IT significantly increased 1) mean CF by 44.4 N(SD 15.8 N) at 0°(+240%) and 27.2 N(SD 5.0 N) at 20°(+675%), 2), mean ITR by 10.2°(SD 0.8°) at 0° flexion and 18.6°(SD 2.0°) at 20° flexion, and 3) mean VTR by 1.3°(SD 0.4°) at 0° flexion and 4.4°(SD 0.8°) at 20° flexion. InterpretationOur hypothesis was confirmed only between 0° and 20° of knee flexion, where the intercondylar separation distance is relatively small and the possibility of tibial spine contact with ITR is greater.

Intramedullary pinning of a non-homogeneous adaptive elastic bone hollow cylinder: A theoretical implant–bone interface investigation

A metal rod forced into the medullary cavity of a bone, known as an intramedullary pinning, is considered as the quickest and cheapest form of oblique fracture repair available for use in the femur, tibia, metatarsal bones, humerus, ulna and metacarpal bones. Implants endurance as well as a good clinical tolerance depends on the recovery of a physiological stress/strain distribution within bone after implantation. What is well known is that the human femur, along the entire femoral diaphysis, exhibited statistically significant anatomic variation in elastic magnitude and anisotropy and the main question treated here is: does bone's inhomogeneity, expressed here by the proportionality to some power of the hollow bone cylinder radius r with respect to the elastic tensor components, affects substantially the implant–bone interfacial pressure as well as the implant–bone interfacial strains and stresses both immediately and a longtime after insertion?

One-stage revision anterior cruciate ligament reconstruction in cases with excessive tunnel osteolysis. Results of a new technique using impaction bone grafting

BackgroundThis level IV study describes a new one-stage procedure for revision ACL reconstruction in cases with extreme tunnel widening. MethodsEight consecutively treated subjects requiring ACL revision and presenting with excessive tunnel widening (87.5% to 250% tunnel enlargement) were included in this study. The graft-tunnel mismatch was resolved in this one-stage revision procedure by the use of custom-made eight to 10 mm cylindrical shaped bone allografts in a press-fit construct with the ACL-graft in combination with the usual fixation devices for ACL-reconstruction. All subjects were evaluated pre-operatively and at a minimum follow-up of one year by the IKDC objective and subjective scores, KOOS, and Tegner activity scale. ResultsMean improvement was 24.8 ± 16.1 on the KOOS evaluation (P-value 0,006) and 38.1 ± 16.8 on the IKDC subjective score (P-value 0,001). The objective IKDC scores improved significantly with an average of one grade (P-value 0,038). Anterior laxity as determined on the KT-1000 arthrometer improved with an average of 3.63 mm compared to the situation before primary reconstruction, and the Pivot-shift test was negative in all but one patient after the revision procedure while positive in all patients before primary reconstruction. ConclusionThis new surgical technique using eight to 10 mm allograft bone cylinders for the management of excessive tunnel enlargement at single stage revision ACL reconstruction delivers excellent results after minimum one year of follow-up. The results of this study have the potential to lower the threshold for one-stage surgery in ACL revision complicated by extreme tunnel widening.

Remodelling of human bone on the chorioallantoic membrane of the chicken egg: De novo bone formation and resorption.

Traditionally used as an angiogenic assay, the chorioallantoic membrane (CAM) assay of the chick embryo offers significant potential as an in vivo model for xenograft organ culture. Viable human bone can be cultivated on the CAM and increases in bone volume are evident; however, it remains unclear by what mechanism this change occurs and whether this reflects the physiological process of bone remodelling. In this study we tested the hypothesis that CAM-induced bone remodelling is a consequence of host and graft mediated processes. Bone cylinders harvested from femoral heads post surgery were placed on the CAM of green fluorescent protein (GFP)-chick embryos for 9days, followed by micro computed tomography (μCT) and histological analysis. Three-dimensional registration of consecutive μCT-scans showed newly mineralised tissue in CAM-implanted bone cylinders, as well as new osteoid deposition histologically. Immunohistochemistry demonstrated the presence of bone resorption and formation markers (Cathepsin K, SOX9 and RUNX2) co-localising with GFP staining, expressed by avian cells only. To investigate the role of the human cells in the process of bone formation, decellularised bone cylinders were implanted on the CAM and comparable increases in bone volume were observed, indicating that avian cells were responsible for the bone mineralisation process. Finally, CAM-implantation of acellular collagen sponges, containing bone morphogenetic protein 2, resulted in the deposition of extracellular matrix and tissue mineralisation. These studies indicate that the CAM can respond to osteogenic stimuli and support formation or resorption of implanted human bone, providing a humanised CAM model for regenerative medicine research and a novel short-term in vivo model for tissue engineering and biomaterial testing.

Abstract 10.55 PLATELET-RICH PLASMA VS. FETAL BOVINE SERUM IN ENGINEERING OF AXIALLY-VASCULARIZED OSTEOGENIC GRAFTS FROM HUMAN ADIPOSE-DERIVED CELLS TO TREAT AVASCULAR NECROSIS OF BONE

INTRODUCTION: Avascular necrosis of bone (AVN) leads to sclerosis and collapse of bone and joints. Engineered, axially vascularized, human adipose-derived stromal vascular fraction (SVF) cell based osteogenic constructs have been shown to revitalize necrotic bone of clinically-relevant size in a challenging rat model of AVN. To reduce regulatory difficulties towards clinical translation, fetal bovine serum (FBS) was substituted by thrombin-activated platelet-rich plasma (tPRP). METHODS: SVF cells from 5 lipoaspirate were isolated and cultured onto porous hydroxyapatite scaffolds within a perfusion-based bioreactor system for 5 days. The medium was supplemented either with 10% FBS or 10% tPRP. The resulting constructs were inserted into devitalized bone cylinders mimicking AVN-affected bone. A ligated vascular bundle was inserted upon subcutaneous implantation of constructs in nude rats. After 1 and 8 weeks, vascularization and bone formation were analyzed. RESULTS: After 1 week, neither maximal distance of vessels from the bundle nor vascular density was significantly different. However, FBS cultured grafts revealed significantly more human vessel (hCD34) and osteoclasts compared to tPRP cultured grafts. Overall macrophages and M2 macrophages were not different between FBS and tPRP cultured grafts. After 8 weeks in vivo, 3/5 samples from FBS culture and 1/5 sample from tPRP culture showed bone formation. Roughly 40% of the osteocytes were of human origin (36% from FBS and 42% from tPRP culture). DISCUSSION: Despite promising results in literature, replacement of FBS by tPRP resulted in a reduced capacity of bone formation in our series. Further studies are necessary to analyze and improve the low bone formation capacity, possibly caused by the heterogeneity of the SVF donors and tPRP samples.

Szabolcs-Szatmár-Bereg megye avar sírleletei V. Kora avar kori padmalyos temetkezés Tiszavasvári, Eszenyi-telekről

In 1960, an isolated grave – dated to the early Avar period – was found in Tiszavasvári, on the plot of Miklós eszenyi. According to the burial customs (the nee-sWW orientation of the deceased, the niche grave, the horse skin burial), this grave fits well into the type characteristic of the early Avar period the Trans-Tisza region. in this article, we examine two parts of the horse harness in detail, i.e. the bone cylinder for fastening the stirrup leather and the omega shaped iron object which was attached to the saddle for fixing the bridle.