Intact Femur Research Articles

Comparative study of two materials for dynamic hip screw during fall and gait loading: titanium alloy and stainless steel

BackgroundInternal fixation with dynamic hip screw is a choice of treatment for hip fractures to stabilize a femoral fracture. Choosing the proper implant and its material has a great effect on the healing process and failure prevention. The purpose of this analysis was to assess biomechanical behavior of dynamic hip screw with two different materials implanted in the femur during fall and gait. MethodsA 3D finite element model of an intact femur and a 3D implant within the same femur were developed. A finite element analysis was carried out to establish the effect of load conditions and implant material properties on biomechanical behavior of the dynamic hip screw after internal fixation. Two load configurations are chosen: one simulating the stance phase of the normal gait cycle, and the other replicating a low-energy fall. The implanted femur was investigated with two different materials for the dynamic hip screw: stainless steel and titanium alloy. ResultsDuring stance, more stress is placed on the implanted femur compared with the intact femur. During a fall, the implanted femur is in a greater state of stress, which mostly occurs inside the dynamic hip screw. Titanium alloy decreases stress levels by an average of 40% compared with stainless steel. However, deformation is slightly reduced with a stainless steel dynamic hip screw during both load cases. ConclusionsAfter internal fixation, dynamic hip screw generates greater stresses within the implanted femur compared with the intact femur under the same loading conditions. A titanium alloy implant appears to undergo less stress from a low-energy fall compared with stainless steel and can be considered the preferred implant material. The critical parts of the dynamic hip screw are the forth distal screw and the plate.

Biomechanical Evaluation of Screw‐In Femoral Implant in Cementless Total Hip System

To compare (1) proximal femoral axial strains, (2) femoral head deflection, and (3) failure mechanical properties, between Helica head and neck prosthesis implanted femora and normal femora. In vitro study. Cadaveric canine femora (n = 5 pair). Femoral bone strains and head displacement during in vitro simulation of midstance of the gallop were evaluated using cadaveric femurs cyclically loaded in vitro. Strains and displacements were compared within femurs, before and after, prosthesis implantation; and throughout cycling to seek evidence of movement with cyclic loading. Subsequently, implanted femurs and contralateral, intact femurs were loaded to failure to compare failure mechanical properties and modes of failure. Proximal femoral axial strains were significantly different between intact and implanted femora on all 4 cortical surfaces (P < .05). Compressive strains were lower in the implanted femur on all cortical surfaces, except on the caudal surface which was higher. No difference was noted for femoral head angle under an axial load corresponding to gallop (P > .05). Vertical head displacement was ∼0.1 mm greater for implanted femora than intact femora (P < .05). Yield and failure loads and yield energy of implanted femora were 39-54% lower than those for intact femora (P < .05). Mode of failure for both the intact and implanted femora did not appear to be different. Helica femoral prosthesis alters strain distribution in the proximal aspect of the femur and exhibits initial micromotion. Failure load in axial compression of the Helica-implanted femur is less than that of the normal femur, but greater than that expected in vivo.

A Comparative Biomechanical Analysis of Fixation Devices for Unstable Femoral Neck Fractures: The Intertan Versus Cannulated Screws or a Dynamic Hip Screw

First introduced in 2005, the "Intertan" (IT), an intramedullary nail with two cephalocervical screws, has become an increasingly popular option for treating intertrochanteric fractures. The purpose of this study was to identify the utility of this device for stabilization of unstable femoral neck fractures compared with cannulated screws (CS) and a dynamic hip screw (DHS). Twenty-four human cadaveric femurs were harvested and assigned to three groups that were matched with regard to bone mineral density (BMD). Standardized Pauwels-Type-III fractures were osteomized with a custom-made saw guide and fixated by an "IT," three CS, or a DHS. All constructs were biomechanically tested in a servohydraulic testing machine with a physiologic mechanical axis loading of the femoral head (700 N), cyclical compression to 1,400 N (10,000 cycles; 2 Hz), and loading to failure. All specimens were compared with respect to the number of survived cycles, mechanical strength, head displacement, load to failure, and failure mechanism. Regardless of the fixation, the mechanical strength of the stabilized femurs was significantly decreased to 71% compared with the intact femurs (100%). During cyclical testing 46% of the constructs (6 CS, 4 DHS, and 1 IT) failed. There was no difference between the mechanical strength of all survived constructs regarding the BMD, but the BMD of the failed specimens was significantly reduced compared with the surviving femurs (0.71 g/cm² ± 0.18 g/cm² vs. 1.07 g/cm² ± 0.33 g/cm²; p < 0.05). IT femurs survived significantly longer than CS specimens (IT, 9,063 cycles ± 2,480 cycles vs. CS, 3,325 cycles ± 3,885 cycles vs. DHS, 5,716 cycles ± 4,448 cycles; p < 0.01), endured higher failure loads (IT, 4,929 N ± 1,105 N vs. CS, 3,421 N ± 20 N vs. DHS, 3,505 N ± 905 N; p < 0.05), and presented a less inferior head displacement (IT, 8.5 mm ± 1.6 mm vs. CS, 16.4 mm ± 6.7 mm vs. DHS, 14.5 mm ± 6.4 mm; p < 0.05). Our results suggest that (1) none of the tested devices restore a comparable mechanical strength in the fractured specimens compared with the intact femurs, and (2) the "IT" possesses some biomechanical benefits for internal fixation of unstable femoral neck fractures compared with DHS and CS. Because the IT constructs failed with an inferior femoral neck fracture, complicating the mandatory anchorage of a prosthetic stem in a revision operation, more biomechanical experiments using the IT in the presence of a posterior comminution defect are required, along with clinical outcome studies.

Hematopoietic Stem Cells Survive Circulation Arrest and Reconstitute Hematopoiesis in Myeloablated Mice

Hematopoietic stem and progenitor cells (HSPC) for bone marrow transplantation are currently obtained directly from living voluntary donors or from cord blood units. However, a suitable donor is not always found. Because HSPC are known for their relative resistance to hypoxia, using an experimental murine model, we explored cadaveric bone marrow (BM) as their alternative source. After donor mice were sacrificed, BM was left in intact femurs at 37°C, 20°C, or 4°C under ischemic conditions, resulting in combined oxygen and metabolic substrate shortage and the accumulation of metabolic waste products. BM cells were harvested after a set time period ranging from 0 to 48 hours. To determine the impact of delayed harvesting on the transplantability of HSPC, a competitive repopulation assay using a murine Ly5.1/Ly5.2 congenic model in 2 different settings was used: after submyeloablative (6 Gy) or myeloablative (9 Gy) total-body irradiation, Ly5.2 hosts received cadaveric Ly5.1 cells or a mixture of cadaveric Ly5.1 cells and fresh Ly5.2 cells in a 1:1 ratio. Chimerism resulting from cadaveric donor cells, followed up to 6 months after transplantation, proved that the long-term repopulation ability of HSPC was fully preserved for 2 hours, 6 hours, and 12 hours at 37°C, 20°C, and 4°C of ischemia, respectively. A colony-forming unit-spleen (CFU-S) clonogenic assay revealed a higher sensitivity of proliferating hematopoietic progenitors to ischemia compared to repopulating cells (STRC and LTRC). Flow cytometry analysis of apoptosis in cadaveric BM demonstrated that the LSK (Lin(low)Sca-1(+)c-Kit(+)) subpopulation, enriched in HSPC, contained less apoptotic and dead cells than the BM as a whole. Furthermore, the number of LSK SLAM (CD150(+)CD48(-)) and LSK SP (side population) cells (fractions highly enriched in hematopoietic stem cells) decreased in parallel with BM transplantability. As well as cadaveric BM cells, we also tested the transplantability and survival of BM cells after storage in a suspension in vitro without specific hematopoietic growth factors. HSPC did not display any decrease in transplantability after 2 days of storage at 37°C or 4 days at 4°C. A higher sensitivity of progenitors to unfavorable conditions was observed again using CFU-S and granulocyte macrophage-colony forming cell (GM-CFC) assays, especially at 37°C. This paper shows that HSPC survive the cessation of circulation for a considerable time and maintain their engraftment potential. This time is significantly extended with in vitro storage compared to the cadaveric BM.

Resistance to Subsidence of an Uncemented Femoral Stem After Cerclage Wiring of a Fissure

To compare: (1) the force required to initiate subsidence, and (2) the relative subsidence, of femoral stems implanted into intact femora, and then into the same femora in which an induced fissure had been stabilized by cerclage. In vitro, mechanical study. Femora (n=9) from 9 dogs. Femora were prepared for implantation of an uncemented stem. Stems were implanted with continuous and impact loading. After axial loading until a fissure occurred, the stems were extracted, and the fissure stabilized with double-loop cerclage. Stems were reimplanted, and reloaded to failure. Mean±SD load to initiate subsidence in intact femora was 1706±584 N compared with 2379±657 N for cerclaged bones (P=.002). Mean relative subsidence of intact femora was 3.99±2.09 mm compared with 1.79±2.99 mm for cerclaged bones (P=.091). The load to initiate subsidence is increased in femora that have fissured, then have been stabilized with double-loop cerclage, when compared with intact femora. The relative subsidence is not different between intact and stabilized specimens.

Cadaveric bone marrow as potential source of hematopoietic stem cells for transplantation.

Every year, bone marrow transplantation saves many lives worldwide. Unfortunately, a suitable donor is not always available. Since organs are routinely harvested from cadaveric organ donors, we decided to assess such a possibility for bone marrow. We analyzed the functional properties and phenotypic markers of murine hematopoietic stem and progenitor cells (HSPC) from cadaveric bone marrow and during storage in vitro in a suspension. It was demonstrated that HSPC exposed to a warm or cold ischemia in intact femur did not lose their phenotype and maintained their repopulating ability for two to twelve hours depending on the temperature. Additionally, fresh bone marrow remained fully viable in cell suspension for two days or four days at 37°C or 4°C, respectively. Based on these findings, cadaveric bone marrow could be considered as an alternative source of hematopoietic stem cells for transplantation.

Cadaveric bone marrow as potential source of hematopoietic stem cells for transplantation

Every year, bone marrow transplantation saves many lives worldwide. Unfortunately, a suitable donor is not always available. Since organs are routinely harvested from cadaveric organ donors, we decided to assess such a possibility for bone marrow. We analyzed the functional properties and phenotypic markers of murine hematopoietic stem and progenitor cells (HSPC) from cadaveric bone marrow and during storage in vitro in a suspension. It was demonstrated that HSPC exposed to a warm or cold ischemia in intact femur did not lose their phenotype and maintained their repopulating ability for two to twelve hours depending on the temperature. Additionally, fresh bone marrow remained fully viable in cell suspension for two days or four days at 37°C or 4°C, respectively. Based on these findings, cadaveric bone marrow could be considered as an alternative source of hematopoietic stem cells for transplantation.

The effect of primary stability on load transfer and bone remodelling within the uncemented resurfaced femur

One of the major causes of aseptic loosening in an uncemented implant is the lack of any attachment between the implant and the bone. The implant's stability depends on a combination of primary stability (mechanical stability) and secondary stability (biological stability). The primary stability may affect the implant-bone interface condition and thus influence the load transfer and mechanical stimuli for bone remodelling in the resurfaced femur. This paper reports the results of a study into the affect of primary stability on load transfer and bone adaptation for an uncemented resurfaced femur. Three-dimensional finite element models were used to simulate the intact and resurfaced femurs and the bone remodelling. As a first step towards assessing the immediate post-operative condition, a debonded interfacial contact condition with varying levels of the friction coefficient (0.4, 0.5, and 0.6) was simulated at the implant-bone interface. Then, using a threshold value of micromotion of 50 microm, the implant-bone interfacial condition was varied along the implant-bone boundary to mechanically represent non-osseointegrated or osseointegrated regions of the interface. The considered applied loading conditions included normal walking and stair climbing. Resurfacing leads to strain shielding in the femoral head (20-75 per cent strain reductions). In immediate post-operative conditions, there was no occurrence of elevated strains in the cancellous bone around the proximal femoral neck-component junction resulting in a lower risk of neck fracture. Predominantly, the micromotions were observed to remain below 50 microm at the implant-bone interface, which represents 97-99 per cent of the interfacial surface area. The predicted micromotions at the implant-bone interface strongly suggest the likelihood of bone ingrowth onto the coated surface of the implant, thereby enhancing implant fixation. For the osseointegrated implant-bone interface, the effect of strain shielding was observed in a considerably greater bone volume in the femoral head as compared to the initial debonded interfacial condition. A 50-80 per cent peri-prosthetic bone density reduction was predicted as compared to the value of the intact femur, indicating bone resorption within the superior resurfaced head. Although primary fixation of the resurfacing component may be achieved, the presence of high strain shielding and peri-prosthetic bone resorption are a major concern.

Improved stability with intramedullary stem after anterior femoral notching in total knee arthroplasty

It has been hypothesized that femoral notching in total knee arthroplasties weakens the cortex of the femur, which can predispose to femoral fractures in the postoperative period. Some authors suggest that patients who sustain inadvertent notching should have additional protection in the postoperative period, and consideration should be given to the use of prophylactic femoral stems. In this case, a question can be raised: Is the use of femoral stem in an anterior femoral notching an effective way to reduce the fracture risk? We hypothesized that for a larger notch, the use of a femoral stem does not decrease considerably the stress-riser at the notch edge, and the use of stem is not enough to reduce the risk of fracture. In the present in vitro study, twelve synthetic femurs were selected and used for the experiments under two load scenarios. Femoral components with and without femoral stems were implanted in femurs with different notch sizes to predict experimentally the strain levels at the notch edge with the use of fiber Bragg gratings and at notch region with strain gauges. Despite the global strain reduction in stemmed condition, at the notch edge, the strain behavior was dissimilar for the different notch depths. For notch depths lower than 5 mm, the use of stem reduces the strain level at the notch edge to values below the intact femur condition, while for depths greater or equal to 5 mm, the strain levels at the notch edge were higher than the intact femur condition with values ranging from +10 to +189%. The present study suggests the use of a prophylactic stem for notch depths greater than 5 mm. For notch depths below 5 mm, the fracture risk due to strain increase at the notch edge seems to be low in the stemless condition.

Influences of Prosthesis Stem Lengths in Cementless Total Hip Arthroplasty

Stress shielding phenomenon is an important issues in considering the primary stability of the cementless hip arthroplasty. Stress shielding occurs when there is a mismatch in the elastic modulus of two materials perfectly bonded to each other, such as the prosthesis stem and the bone. In this study, influences of different prosthesis stem lengths on stress distribution in cementless THA are examined using finite element method. The calculated stress distribution is discussed with respect to stress shielding and primary stability issues in THA femur cases. Results show that similar pattern in stress distribution for intact and THA femur but differs in magnitudes. The stress level increases from the neck to the middle region and peaks at locations coinciding with the tip of the prosthesis. The maximum stress for intact femur is 55.5 MPa, THA with short stem is defined up to 112 MPa, while with medium and long stem are 204 MPa and 278 MPa, respectively.

Assessment of femoral neck fracture risk for a novel proximal epiphyseal hip prosthesis

Background This study addresses the risk of femoral neck fracture associated with resurfacing hip prostheses. A novel cemented Proximal Epiphyseal Replacement (PER) featuring a short curved stem was investigated. Methods Seven pairs of femurs were in vitro tested. One femur of each pair was randomly assigned for PER implantation. The contralateral femur was tested intact. All femurs were loaded to failure in a validated, physiological configuration. High-speed videos (10,000–12,000 frames/s) were acquired to identify the location of fracture initiation. For comparison, data were included from Birmingham Hip Resurfacing previously tested in an identical fashion (N = 3). Findings Relative to the contralateral intact femurs, the failure load of the PER and Birmingham implants was 15.4% higher and 10.0% lower, respectively. In six of the seven PER implants, fracture initiation (neck or inter-trochanteric) was similar to the contralateral intact femurs, suggesting comparable stress distribution. Conversely, fracture initiation in the Birmingham implants occurred at the lateral prosthesis rim, which differed substantially from the intact femurs. No correlation existed between bone quality and strengthening/weakening effect of the PER (failure load of implant as a percentage of intact: R^2 = 0.067). Conversely, Birmingham implantation weakened the femurs with lower density (R^2 = 0.92). Therefore, unlike most resurfacing prostheses, the PER seems suitable also for osteoporotic subjects. Interpretation This study seems to confirm that resurfacing with a Birmingham Hip tends to reduce the strength of the proximal femur. The opposite seemed to happen with the PER, which slightly reduced the risk of neck fracture, also in low-quality bones.

The biomechanical assessment of fixation methods in periprosthetic femur fractures

The aim of our study was to compare the biomechanical properties of different fixation methods used in periprosthetic femur fractures. We created sawbone models with Mallory Type 2 periprosthetic femur fractures. The periprosthetic fractures were fixed with cables, cables and strut graft, or cables and plates. The biomechanical properties of these three different fixation methods were compared with the intact femur, the intact femur with prosthesis and the femur with periprosthetic fracture without fixation. The periprosthetic fracture without fixation had a significantly lower yield point value than the periprosthetic fractures with fixation (p<0.05). There was no significant difference between the three different fixation methods of the periprosthetic fractures. The intact femur with a prosthesis showed statistically higher values than all three fixation methods of perioprosthetic fractures. Mallory Type 2 periprosthetic fractures should be fixed. There is no difference among the fixation methods used in the study and none of them provide a stability equivalent to that of an intact femur with prosthesis.

Estimates of cortical thickness from the superior femoral neck are a risk marker for hip fracture in women from Cambridge and Prague

Event Abstract Back to Event Estimates of cortical thickness from the superior femoral neck are a risk marker for hip fracture in women from Cambridge and Prague KE Poole1*, PM Mayhew1, M Horak2, J Reeve1 and JJ Stepan2 1 University of Cambridge, NIHR Biomedical Research Centre, United Kingdom 2 Charles University, Czechia Introduction. Ageing is associated with progressive loss of bone in the superior femoral neck. Older individuals with better preservation of the superior cortex might be more resistant to hip fracture during falls, stumbles and trips. Among healthy elderly Icelandic men and women, a superior cortex thicker than 0.5mm (estimated with computed tomography (CT)) conferred significant protection against subsequent hip fracture (Johannesdottir ECTS 2010). With the present study, we investigated whether similar CT estimates of cortical thickness were a risk marker for hip fracture in women from Prague (Hip Joint in Trauma Study) and Cambridge (FEMCO study). {BR}Methods. Female volunteers awaiting surgery for an acute hip fracture (n62) and matched controls without fracture (n62) consented to a multi-detector clinical CT scan of both hips (52 age-matched pairs from Prague and 10 pairs from Cambridge, median age 79 IQR 74-85, n32 cervical and n30 trochanteric fractures). Scans were performed lying on a calibration phantom. During CT image processing, the intact contra-lateral proximal femur was extracted from soft tissue. Mid femoral neck estimates of cortical thickness were made in four anatomical quadrants as described previously (Poole JBMR 2010). Using the Bone Investigational Toolkit (BIT2, Mindways software), estimates from 6 cross-sections (1mm apart) were combined into a single mean estimate for each quadrant (Superoanterior-SAQ, Inferoanterior-IAQ, Inferoposterior-IPQ and Superoposterior-SPQ). Exclusion criteria were malignancy, severe hip osteoarthritis and Paget's, osteomyelitis or metalwork in either hip. Differences between cases and controls were analysed by repeated measures MANOVA. {BR}Results. Cortical bone in the superior quadrants appeared nearly twice as thick in controls compared with cases (e.g. median case SPQ 0.4mm IQR 0.3-0.6mm vs control 0.8mm IQR 0.4-1.3mm), but there were no significant differences in the inferior quadrants (whole model p=0.0068, between-quadrant contrast, p=0.008). Using Mindways reference data, only 12/62 fracture cases and 3 controls had an areal BMD T score <-2.5 at the femoral neck. Johannesdottir's proposed cortical threshold of 0.5mm in SAQ would identify 26/62 fracture cases and 9 controls.{BR}Conclusion. In agreement with Johannesdottirs' study and using similar clinical CT technology, these results confirm the association of reduced superior cortical thickness with hip fracture. Keywords: Bones, Bone Research Conference: 2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society, Cambridge, United Kingdom, 27 Jun - 29 Jun, 2011. Presentation Type: Poster Topic: Abstracts Citation: Poole K, Mayhew P, Horak M, Reeve J and Stepan J (2011). Estimates of cortical thickness from the superior femoral neck are a risk marker for hip fracture in women from Cambridge and Prague. Front. Endocrinol. Conference Abstract: 2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society. doi: 10.3389/conf.fendo.2011.02.00052 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Sep 2011; Published Online: 30 Sep 2011. * Correspondence: Dr. KE Poole, University of Cambridge, NIHR Biomedical Research Centre, Cambridge, United Kingdom, kp254@nhs.net Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers KE Poole PM Mayhew M Horak J Reeve JJ Stepan Google KE Poole PM Mayhew M Horak J Reeve JJ Stepan Google Scholar KE Poole PM Mayhew M Horak J Reeve JJ Stepan PubMed KE Poole PM Mayhew M Horak J Reeve JJ Stepan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Three-dimensional design optimisation of patient-specific femoral plates as a means of bone remodelling reduction

Previous investigations into the optimisation of internal plates have mostly focused on the material properties of the implant. In this work, we optimise the shape, size and placement of the plate for successfully minimising bone remodelling around the implant. A design optimisation algorithm based on strain energy density criterion, combined with the finite element analysis, has been used in this study. The main optimisation goal was to reduce this change and keep it close to the conditions of an intact femur. The results suggest that the anterolateral side of the bone would be the optimum location for the plate, as for the geometry, the optimum moves towards having a thick, wide and short plate. These important results could be directly applicable to orthopaedic surgeons treating a femur fracture with internal plates. Since the optimisation algorithm remains the same for any patient, this advancement provides the surgeon with a tool to minimise the post surgery remodelling by trying to maintain the natural structure of the bone.

Hematopoietic Stem Cells Survive Warm Ischemia and the Bone Marrow Upregulates a Significant Number of Genes

AbstractAbstract 4694 Background:Quiescent hematopoietic stem cells (HSCs) located in stem cell niches are characterized by a relative resistance to hypoxia. This study is focused primarily on maintainance of the repopulating ability of HSCs in structurally intact BM exposed to anoxia, lack of metabolic substrates and accumulation of metabolic waste products during a period of ischemia at three different temperatures. In the case of a warm ischemia at 37°C, changes in gene expression profile in the whole bone marrow has been also examined. Methods:Murine congenic model C57Bl/6 Ly5.1/Ly5.2 was used in the experiments. Normal mice or mice recovering from a bone marrow damage induced either by cyclophosphamide or a sublethal irradiation were sacrified. Their BM was maintained in intact femurs at 37°C for different time periods up to 6 hours. For normal bone marrow, exposure to ischemia at 20°C and 4°C was also used for up to 20 and 48 hours, respectively. Afterwards, bone marrow cells were harvested and cells corresponding to a half of the femur were transplanted to sublethally (6 Gy) irradiated recipients in a competitive repopulation assay. Resulting chimerism was examined up to 6 months after transplantation to test for STRCs and LTRCs (Short and Long Term Repopulating Cells). Subpopulations of erythropoietic (Ter119+), B-lymphopoietic (B220+), granulo- and monocytopoietic (Gr-1/Mac+), and LSK (Lin-Sca-1+c-Kit+) bone marrow cells were analyzed for dead cells and apoptosis. Total RNA was isolated from bone marrow exposed to warm ischemia ranging 0 to 4 hours and dynamics of changes in its gene expression profile was determined by Illumina MouseRef8 BeadChip. Results:Repopulating ability of ischemic BM was fully preserved for 2 hour of the warm (37°C) ischemia and for 6 hours and 8 hours of 20°C and 4°C ischemia, respectively. There was no difference between STRCs and LTRCs in survival. STRCs and LTRCs from the bone marrow collected 2 days or 5 days after a single dose of cyclophosphamide exposed to warm ischemia showed decreased repopulating ability in comparison with those of normal mice. STRCs significantly prevailed over LTRCs in bone marrow collected 20 days after a sublethal irradiation and showed increased sensitivity to warm ischemia. B220+ cells were the most sensitive cells of the bone marrow to warm ischemia, LSK and Ter119 cells being the most resistant ones. Gene expression profile in bone marrow exposed to warm ischemia changed progressively over time. Despite the highly unfavorable metabolic conditions, hypoxia and lack of energy, a set of overexpressed genes equaled in number the one inhibited. Conclusions:HSCs exposed to warm or cold ischemia maintain their repopulating ability for a considerable time. Bone marrow ischemia activates specific gene expression in paralel with supression of others. Supported by projects LC06044, MSM 0021620806 and the grant SVV-2010-254260507. Disclosures:No relevant conflicts of interest to declare.

Intravasation of bone marrow content. Can its magnitude and effects be modulated by low pressure reaming in a porcine model?

Introduction Intramedullary orthopaedic procedures may increase the intramedullary pressure (IMP) and thereby cause intravasation of bone marrow contents. In recent studies by the authors the reamer-irrigator-aspirator (RIA) has been demonstrated to reduce IMP and coagulation-, fibrinolysis- and cytokine responses, but did not prove any significant difference in cardiopulmonary function parameters or numbers of emboli when compared to a traditional reaming (TR) system. The correlations between IMP increase, regardless type of reamer, and inflammatory- and coagulation responses, pulmonary embolization, and cardiopulmonary alterations have, however, not previously been analyzed in this material. Our hypothesis was that a lower IMP would result in reduced occurrence of pulmonary embolization, reduced inflammatory-and coagulation responses, as well as reduced cardiopulmonary alterations. Materials and Methods Twenty-eight young Norwegian landrace pigs were exposed to femoral intramedullary reaming, with either the TR (n=10) or the RIA (n=10) system, or used as controls (n = 8). IMP was recorded during reaming and nailing. Serial blood samples for demonstration of coagulation-, fibrinolysis-, and cytokine activation were withdrawn peroperatively and until 72 hours post nail insertion. Circulatory and pulmonary effects were monitored peroperatively and until two hours postoperatively. The animals were sacrificed 72 hours post nail insertion and lung tissue biopsies were harvested and examined for lung emboli. Results and Conclusions A strong correlation between increased IMP and increased coagulation-and cytokine responses was found. The number of emboli was not significantly correlated to IMP, but was strongly correlated to changes in the coagulation- and cytokine responses. No clinical relevant correlations were observed between increased IMP or numbers of lung emboli and changes in hemodynamic- or pulmonary function parameters. A correlation between coagulation activation and cytokine activation was observed. This study confirms the connection between increased IMP, increased coagulation activation and the magnitude of pulmonary emboli in a model evaluating the effects of intramedullary reaming of intact pig femora. In this model, the lowering of IMP during reaming, as obtained with RIA, reduced the magnitude of and the effects of bone marrow extravasation.

Biomechanical effects of harvesting bone graft with the Reamer/Irrigator/Aspirator on the adult femur: a cadaver study

Objectives Test the biomechanical properties of femurs that have undergone reaming with the Reamer Irrigator Aspirator (RIA) device with an aim to prove no difference in torsional strength between matched pairs. Methods Intact femurs were harvested from embalmed cadavers, representing 19 matched pairs. One femur from each pair was randomly selected to undergo reaming using the RIA to 15mm. The bones were then cut and potted using a uniform jig for testing. Each specimen was tested in torsion and torsional stiffness was calculated for each pair. Samples were loaded until fracture or 11 3 N·m of torque. Results Nine of the reamed specimens and 13 of the unreamed samples remained intact until the machine limit of 113 N·m was reached, representing approximately four times the peak torque of 30N·m seen with stair climbing [Garino J, Beredjiklian P. Core Knowledge in Orthopaedics: Adult Reconstruction and Arthroplasty. Chapter 1, page 33. Mosby, 2007]. Mean torsional stiffness for the reamed group was 532.1 N·m/rad (SD = 208.2), and the unreamed was 546.2 N·m/rad (SD=206). Torsional load capacity was calculated for all specimens and compared in groups in which both reamed and unreamed specimens failed. In these five groups, mean load capacity was 80.6 Nm (SD = 9.5) for the reamed group, and 85 Nm (SD = 16.1) for the unreamed group. Conclusions 17 of our reamed specimens and all of our unreamed specimens withstood normal physiologic load seen with stair climbing. In addition, 16 of 19 reamed specimens remained intact at twice this load. The specimen in the reamed group with the lowest torsional load capacity was eccentrically reamed in the distal anterior cortex highlighting potential complications. Given these findings, reaming the cortex of the femur with the RIA device for the purpose of harvesting bone graft does not appear to dramatically diminish the mechanical properties of the cortex or require postoperative weight bearing restrictions. However, careful attention must be paid to technique as eccentric reaming either proximally or distally may result in catastrophic failure. Careful attention must be paid to the use of irrigating fluid and post operative blood loss, and a thorough discussion of risk factors including postoperative fracture should be covered when obtaining informed consent.

Collagen and mineral deposition in rabbit cortical bone during maturation and growth: Effects on tissue properties

We characterized the composition and mechanical properties of cortical bone during maturation and growth and in adult life in the rabbit. We hypothesized that the collagen network develops earlier than the mineralized matrix. Growth was monitored, and the rabbits were euthanized at birth (newborn), and at 1, 3, 6, 9, and 18 months of age. The collagen network was assessed biochemically (collagen content, enzymatic and non-enzymatic cross-links) in specimens from the mid-diaphysis of the tibia and femur and biomechanically (tensile testing) from decalcified whole tibia specimens. The mineralized matrix was analyzed using pQCT and 3-point bend tests from intact femur specimens. The collagen content and the Young's modulus of the collagen matrix increased significantly until the rabbits were 3 months old, and thereafter remained stable. The amount of HP and LP collagen cross-links increased continuously from newborn to 18 months of age, whereas PEN cross-links increased after 6 months of age. Bone mineral density and the Young's modulus of the mineralized bone increased until the rabbits were at least 6 months old. We concluded that substantial changes take place during the normal process of development in both the biochemical and biomechanical properties of rabbit cortical bone. In cortical bone, the collagen network reaches its mature composition and mechanical strength prior to the mineralized matrix.

Cardiopulmonary Response to Reamed Intramedullary Nailing of the Femur Comparing Traditional Reaming With a One-Step Reamer-Irrigator-Aspirator Reaming System: An Experimental Study in Pigs

Intramedullary reaming and nailing increases intramedullary pressure. This may cause intravasation of bone marrow contents, leading to bone marrow embolization and altered cardiopulmonary function. Possible beneficial effects of attenuation of the intramedullary pressure increase by the use of a reamer-irrigator-aspirator (RIA) system were studied with the hypothesis that the RIA technique would cause lower numbers of pulmonary embolisms (PEs) and lesser cardiopulmonary affection than traditional reaming (TR). Intramedullary reaming and nailing was performed in intact femora of young Norwegian landrace pigs using either a standard intramedullary nailing technique (n = 8) or a RIA technique (n = 7). The hemodynamic and pulmonary effects were investigated during the reaming and nailing procedure and for 2 hours postoperatively. The animals were killed after 72 hours, and the lung/carcass weight ratio and the numbers of PEs were investigated. The pattern of the procedure-related hemodynamic and pulmonary effects did not differ significantly between the RIA and the TR groups. The RIA group had lower numbers (ns) of embolisms per square centimeter lung area than the TR group. After reaming with the TR device, two animals died of PEs, the first postoperative day. The patients with femoral shaft fracture and additional cardiopulmonary injury or preexisting reduced cardiopulmonary function, however, need special attention, and the use of RIA may, in these cases, represent a better operative alternative with a lesser operative burden.

Comparison of Femoral Morphology and Bone Mineral Density between Femoral Neck Fractures and Trochanteric Fractures

Many studies that analyzed bone mineral density (BMD) and skeletal factors of hip fractures were based on uncalibrated radiographs or dual-energy xray absorptiometry (DXA). Spatial accuracy in measuring BMD and morphologic features of the femur with DXA is limited. This study investigated differences in BMD and morphologic features of the femur between two types of hip fractures using quantitative computed tomography (QCT). Forty patients with hip fractures with normal contralateral hips were selected for this study between 2003 and 2007 (trochanteric fracture, n=18; femoral neck fracture, n=22). Each patient underwent QCT of the bilateral femora using a calibration phantom. Using images of the intact contralateral femur, BMD measurements were made at the point of minimum femoral-neck cross-sectional area, middle of the intertrochanteric region, and center of the femoral head. QCT images also were used to measure morphologic features of the hip, including hip axis length, femoral neck axis length, neck-shaft angle, neck width, head offset, anteversion of the femoral neck, and cortical index at the femoral isthmus. No significant differences were found in trabecular BMD between groups in those three regions. Patients with trochanteric fractures showed a smaller neck shaft angle and smaller cortical index at the femoral canal isthmus compared with patients with femoral neck fractures. We conclude that severe osteoporosis with thinner cortical bone of the femoral diaphysis is seen more often in patients with trochanteric fracture than in patients with femoral neck fracture. Level IV, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.