The apparent elastic modulus of the juxtarticular subchondral bone of the femoral head

An experiment was undertaken to obtain approximate values for the intrinsic elastic modulus of subchondral bone. Shallow spherical caps, with uniform and incrementally controlled thickness, were machined from subchondral bone in the weight-bearing regions of 11 fresh-frozen normal femoral head autopsy specimens. Under application of polar point loads, the measured deflections were compared with a corresponding analytical shell solution, thus allowing back-calculation of the apparent modulus. Analogous tests were performed on similarly shaped specimens of stock Plexiglas of known modulus in order to estimate the precision of the testing method. The aggregate results for subchondral bone showed that its intrinsic stiffness correlated inversely with nominal shell thickness, but even the thinnest (1.0 mm thick) of these shells had an apparent modulus (mean = 1.372 GN/m2, SD = 414 MN/m2) well below that generally accepted for "pure" cortical bone (about 14 GN/m2). This stiffness deficit was very likely due to the presence of histologically evident marrow spaces. However, the low apparent modulus values measured in this study may not be fully representative of complex in vivo behavior, because in the testing of excised shells there is no radial compressive stress transfer to underlying cancellous bone.     

Strain imparted during impaction grafting may contribute to bony incorporation: an in vitro study of the release of bmp-7 from allograft

In order to investigate the osteoinductive properties of allograft used in impaction grafting and the effect of strain during impaction on these properties, we designed an in vitro experiment to measure strain-related release of bone morphogenetic protein-7 (BMP-7) from fresh-frozen femoral head allograft. A total of 40 10 mm cubes of cancellous bone were cut from ten samples of fresh-frozen femoral head. The marrow was removed from the cubes and the baseline concentrations of BMP-7 were measured. Specimens from each femoral head were allocated to four groups and subjected to different compressive strains with a material testing machine, after which BMP-7 activity was reassessed. It was present in all groups. There was a linear increase of 102.1 pg/g (95% confidence interval 68.6 to 135.6) BMP-7 for each 10% increase in strain. At 80% strain the mean concentration of BMP-7 released (830.3 pg/g bone) was approximately four times that released at 20% strain. Activity of BMP-7 in fresh-frozen allograft has not previously been demonstrated. This study shows that the freezing and storage of femoral heads allows some maintenance of biological activity, and that impaction grafting provides a source of osteoinductive bone for remodelling. We have shown that BMP-7 is released from fresh-frozen femoral head cancellous bone in proportion to the strain applied to the bone. This suggests that the impaction process itself may contribute to the biological process of remodelling and bony incorporation.     

Neck fracture femoral heads for impaction bone grafting: evolution of stiffness and compactness during impaction of osteoarthrotic and neck-fracture femoral heads

BACKGROUND: The need for safe bone allografts is increasing and preservation of femoral heads from patients being operated on with hip arthroplasty should be encouraged. However, should we preserve femoral heads from patients operated on for neck fracture as tissue mechanical quality may not be satisfactory? MATERIAL AND METHODS: We compared the evolution of stiffness and compactness of fresh-frozen morselized bone obtained from osteoarthrotic femoral heads and those from neck fractures. Both materials were also compared after freeze-drying and irradiation. We used 6 osteoarthrotic and 6 neck-fracture femoral heads to prepare 4 batches of morselized bone. 18 samples from each batch were impacted in a contained cylinder. Frozen bone grafts were tested after thawing at room temperature for 2 hours and freeze-dried grafts were tested after 30 minutes of rehydration. RESULTS: The stiffness of fresh-frozen neck fracture bone was lower than that of fresh-frozen osteoarthrotic bone at 150 impactions. The stiffness of freeze-dried irradiated bone was higher than that of the fresh-frozen bone and did not differ between osteoarthrotic and neck-fracture bone. INTERPRETATION: Solvent-treated freeze-dried bone from femoral heads procured during arthroplasty for sub-capital hip fractures represents a valuable source of material for allografts, addressing concerns regarding serological testing, medical history and bone quality.     

Fabric-mechanical property relationships of trabecular bone allografts are altered by supercritical CO₂ treatment and gamma sterilization

Tissue grafts are implanted in orthopedic surgery every day. In order to minimize infection risk, bone allografts are often delipidated with supercritical CO₂ and sterilized prior to implantation. This treatment may, however, impair the mechanical behavior of the bone graft tissue. The goal of this study was to determine clinically relevant mechanical properties of treated/sterilized human trabecular bone grafts, e.g. the apparent modulus, strength, and the ability to absorb energy during compaction. They were compared with results of identical experiments performed previously on untreated/fresh frozen human trabecular bone from the same anatomical site (Charlebois, 2008). We tested the hypothesis that the morphology–mechanical property relationships of treated cancellous allografts are similar to those of fresh untreated bone. The morphology of the allografts was determined by μCT. Subsequently, cylindrical samples were tested in unconfined and confined compression. To account for various morphologies, the experimental data was fitted to phenomenological mechanical models for elasticity, strength, and dissipated energy density based on bone volume fraction (BV/TV) and the fabric tensor determined by MIL. The treatment/sterilization process does not appear to influence bone graft stiffness. However, strength and energy dissipation of the bone grafts were found to be significantly reduced by 36% to 47% and 66% to 81%, respectively, for a broad range of volume fraction (0.14 < BV/TV < 0.39) and degree of anisotropy (1.24 < DA < 2.18). Since the latter properties are strongly dominated by BV/TV, the clinical consequences of this reduction can be compensated by using grafts with lower porosity. The data of this study suggests that an increase of 5–10% in BV/TV is sufficient to compensate for the reduced post-yield mechanical properties of treated/sterilized bone in monotonic compression. In applications where graft stiffness needs to be matched and strength is not a concern, treated allograft with the same BV/TV as an appropriate fresh bone graft may be used.     

Lipid oxidation may reduce the quality of a fresh-frozen bone allograft. Is the approved storage temperature too high?

Background?International standards indicate that bone allografts for human use should be stored in a –40°C or colder environment and the storage time should be up to 5 years. Bone allografts contain lipids which oxidate and become toxic with time.

Material and methods?We determined lipid oxidation in femoral head bone allografts by headspace gas chromatography at different storage temperatures and storage times.

Results?We found that lipid oxidation in fresh-frozen bone allograft was influenced by storage temperature and storage time. Lipid oxidation was significantly more rapid at –30°C than at –70°C. Even at –70°C, however, some oxidation occurred but it was quite minimal after 3 years.

Interpretation?Because of the negative effects of lipid oxidation, we recommend a storage temperature of –70°C or lower for bone allografts.     

Osteochondritis Dissecans Capituli Humeri) (Untersuchungen an 168 Fällen)

We examined the subchondral bone architecture of the femoral head in relation to trabecular microfracture. Three groups of femoral head specimens were studied. Twenty-eight specimens taken during hip replacement had grade III or IV arthrosis (70 × 8 years). From autopsy, 40 femoral heads were obtained, 18 in a group greater than 50 years of age (72 × 10 years) and 22 in a group less than 50 years of age (25 × 11 years). None of these 40 heads had worse than grade II arthrosis. Coronal slices of the femoral heads were macerated and examined under a dissecting microscope to count trabecular microfractures. For bone histomorphometry, blocks were taken from the subchondral principal compressive and tensile trabeculae. The bone volume, trabecular thickness, and marrow space were quantified. In the subchondral principal compressive region, the arthrotic group had more bone volume, thicker trabeculae, similar trabecular space, and trabecular microfractures when compared with the group greater than 50 years old. In the tensile region, there were no differences except for decreased trabecular microfracture number in the arthrotic group. With the thinnest trabeculae in the compressive region occurring in the greater than 50 years old group, the trabeculae of the younger age group have thinned with age, but with the onset of arthrosis, the thinning is overtaken by pathologic thickening of trabeculae.     

Bone texture analysis is correlated with three-dimensional microarchitecture and mechanical properties of trabecular bone in osteoporotic femurs

Fracture of the proximal femur is a major public health problem in elderly persons. It has recently been suggested that combining texture analysis and bone mineral density measurement improves the failure load prediction in human femurs. In this study, we aimed to compare bone texture analysis with three-dimensional (3D) microarchitecture and mechanical properties of trabecular bone in osteoporotic femurs. Eight femoral heads from osteoporotic patients who fractured their femoral neck provided 31 bone cores. Bone samples were studied using a new high-resolution digital X-ray device (BMA?, D3A Medical Systems) allowing for texture analysis with fractal parameter H _mean, and were examined using micro-computed tomography (microCT) for 3D microarchitecture. Finally, uniaxial compression tests to failure were performed to estimate failure load and apparent modulus of bone samples. The fractal parameter H _mean was strongly correlated with bone volume fraction (BV/TV) (r = 0.84) and trabecular thickness (Tb.Th) (r = 0.91) (p < 0.01). H _mean was also markedly correlated with failure load (r = 0.84) and apparent modulus (r = 0.71) of core samples (p < 0.01). Bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) demonstrated significant correlations with failure load (r = 0.85 and 0.72, respectively) and apparent modulus (r = 0.72 and 0.64, respectively) (p < 0.01). Overall, the best predictors of failure load were H _mean, bone volume fraction, and trabecular thickness, with r ² coefficients of 0.83, 0.76, and 0.80 respectively. This study shows that the fractal parameter H _mean is correlated with 3D microCT parameters and mechanical properties of femoral head bone samples, which suggests that radiographic texture analysis is a suitable approach for trabecular bone microarchitecture assessment in osteoporotic femurs.     

Revision hip arthroplasty using strut allografts and fully porous-coated stems

At a minimum of 10 years after surgery, we prospectively evaluated the clinical and radiographic outcomes of revision total hip arthroplasties using cortical strut allografts and fully porous-coated cementless revision femoral components in patients with massive femoral bone deficiency. There were 21 men and 33 women (54 hips) in the series, with patients' mean age at the time of index revision being 54.6 years (range, 36 to 65 years). All femurs had 2 or 3 fresh-frozen femoral strut allografts. The Harris hip score improved from a mean of 21 points before revision surgery to a mean of 83 points at the latest case review. Two femoral stems (4%) had aseptic loosening and were revised. All allografts were predictably united to the host femur. On the basis of favorable results at a mean follow-up of 10.5 years, we recommend, as a salvage procedure, the use of fully porous-coated cementless femoral stems and strut allografts in revision surgery of the hip for massive femoral bone loss.     

Mechanical Properties and Density of Bone in a Case of Severe Endemic Fluorosis

Mechanical properties of 25 standardized specimens of compact bone from a 45-year-old man with extreme endemic fluorosis were compared with similar specimens of nonfluorotic bone. Data from dry and wet tested specimens were compared. Tensile strength, strain, energy absorbed to failure, and modulus of elasticity were reduced in fluorotic specimens while compressive strength, strain and energy were increased in both wet and dry specimens. Compressive properties exceeded tensile properties. Drying increased tensile and compressive strength and modulus but decreased tensile and compressive strength and energy absorbed. Dry specimens tended to follow Hooke's Law but wet specimens exhibited visco-elastic behavior. Wet fluorotic specimens had lower tensile properties but higher compressive properties and were more dense than fresh human compact bone.     

Acetabular revision with impacted freeze-dried cancellous bone chips and a cemented cup: a report of 7 cases at 5 to 9 years' follow-up

The long-term results of bone impaction grafting with fresh-frozen femoral head allografts and a cemented cup are favorable. Because of intermittent shortage of fresh-frozen femoral heads at our local bone bank, we used processed freeze-dried bone in 7 acetabular revisions operated between 1989 and 1994. All 7 consecutive patients were followed annually. At final review (March 2000), 1 patient had died after 8.5 years of follow-up of a cause not related to the surgery. In 1 hip, a rerevision was performed for septic loosening 5 years after the previous septic loosening. Radiographically the freeze-dried allografts seemed to incorporate in all cases but the reinfected one; progressive radiolucent lines were not seen, although 1 case had a stable line in 1 zone. The overall survival rate for the 7 acetabular reconstructions at an average follow-up of 7 years (range, 5-9 years) was 86%. At midterm follow-up, there was no aseptic loosening. In this limited case report, the results at midterm for freeze-dried allograft bone chips in acetabular reconstructions are acceptable.     

腰椎疲劳骨折后松质骨力学性质的变化

目的　了解人体腰椎疲劳骨折后椎体松质骨力学性质的变化。方法　取正常和疲劳实验后的腰椎标本从中取出松质骨制成 1.2 cm× 1.0 cm× 1.0 cm长方体 ,标本进行压力载荷实验 ,然后进行力学计算和分析。结果　疲劳骨折后松质骨标本的极限压力强度和弹性模量均低于正常标本 ,标本破坏时的应变大于 0 .8%比正常标本大。结论　腰椎疲劳骨折时松质骨力学性质改变较大。     

The concentration of antibiotic in fresh-frozen bone graft

We investigated the antibiotic concentration in fresh-frozen femoral head allografts harvested from two groups of living donors. Ten samples were collected from patients with osteoarthritis of the hip and ten from those with a fracture of the neck of the femur scheduled for primary arthroplasty. Cefazolin (1 g) was administered as a pre-operative prophylactic antibiotic. After storage at -80 degrees C for two weeks the pattern of release of cefazolin from morsellised femoral heads was evaluated by an in vitro broth elution assay using high-performance liquid chromatography. The bioactivity of the bone was further determined with an agar disc diffusion and standardised tube dilution bioassay. The results indicated that the fresh-frozen femoral heads contained cefazolin. The morsellised bone released cefazolin for up to four days. The concentration of cefazolin was significantly higher in the heads from patients with osteoarthritis of the hip than in those with a fracture.Also, in bioassays the bone showed inhibitory effects against bacteria.We concluded that allografts of morsellised bone from the femoral head harvested from patients undergoing arthroplasty of the hip contained cefazolin, which had been administered pre-operatively and they exhibited inhibitory effects against bacteria in vitro.     

Compressive mechanical properties of human cancellous bone after gamma irradiation.

The effect of gamma irradiation on the mechanical properties of human bone was examined. Specimens of cancellous bone were cut from the proximal epiphyseal region of fresh-frozen tibiae and divided into control and irradiated groups according to anatomical region. The irradiated groups were exposed to 10,000, 31,000, 51,000, or 60,000 gray (1.0, 3.1, 5.1, or 6.0 megarad). The specimens were tested in compression to failure to determine failure stress, strain to failure, and elastic modulus. Failure stress and elastic modulus were found to be proportional to the square of the density and were normalized with respect to this property. Significant differences in normalized failure stress (p less than 0.001) and normalized elastic modulus (p = 0.003), when compared with the values for matched control specimens, were found only for the specimens that had been irradiated with 60,000 gray (6.0 megarad).     

Mechanical strength of cortical allografts with gamma radiation versus ethylene oxide sterilization

We investigated the effects of gamma irradiation versus ethylene oxide (ETO) sterilization on the mechanical strength of cortical bone grafts. Tibias were collected from cadavers of mature goats. Sixty test specimens were randomized into four groups: fresh (no processing), frozen (freezing at -70 degrees C), gamma-irradiated, and ETO-sterilized specimens. Torsion, three-point bending, and compression testing were separately performed with a material testing machine. Parameters studied included maximum stress, strain, deflection, extension, load, shear modulus, and E-modulus. Compared with findings for the fresh specimens, findings were as follows for gamma-irradiated specimens: maximal shear modulus, reduced by 48%; shear stress, by 55%; deflection, by 71%; bending stress, by 51%; bending strain, by 74%; extension, by 60%; and compression strain, by 50%. However, there were no reductions in those parameters for the frozen specimens or the ETO-sterilized specimens. These findings confirm that shear, bending, and compression strength of cortical allografts are weakened by gamma irradiation at room temperature. To maintain optimum mechanical properties, ETO sterilization of allografts is better than gamma sterilization, especially for cortical bone, because it is usually used in load-bearing settings.     

Supercharging allografts with mesenchymal stem cells in the operating room during hip revision

Purpose

Bone marrow derived mesenchymal stem cells (BM-MSCs) have been proposed to improve allografts used during hip revision. However, no study has reported the number of MSCs that could be associated with the allograft and the best technique to load MSCs in allografts. The optimal loading technique should combine methods to increase the initial cell density and create an appropriate environment to accelerate the efficiency of the cell-allograft constructs into clinically applicable grafts. We designed a study to evaluate the number of MSCs in an autograft femoral head considered as the gold standard and to determine the best operating room procedure for loading in allograft with MSCs to approach the same number as in an autograft femoral head. Therefore this study explored a potential of charging whole femoral head allografts with autologous MSCs from iliac crest aspirate for hip revision procedures.

Methods

First, the study evaluated the total number of mesenchymal stem cells (MSCs) in 1 cc of an average autograft femoral head; this number then serves as a target for loading allografts, in order to achieve the same density of MSCs. For the loading technique itself, several questions were asked and hence several options were investigated. For example, is it better to load the whole allograft or break it up into several fragments? Which way of injecting works best for the whole femoral head allograft (through cartilage or femoral neck)? How concentrated (in terms of MSCs) should the injected iliac crest marrow be? Bone marrow for injection in allografts was obtained from residual marrow from patients undergoing surgical procedures with concentrated bone marrow. With this bone marrow (with and without concentration) we tested different techniques (injection and soaking) to load stem cells in allografts of different sizes: bulk allografts, pieces or blocks (8 or 1 cm³ blocks) and morselized fragments (from 125 to 8 mm³) or particules (1 mm³). We also evaluated the release of MSCs from fragments of autografts and allografts loaded with MSCs in cultured medium.

Results

The femoral head autografts contained a lower concentration of MSCs than the iliac crests of the same patient. However, in absence of concentration, with bone marrow aspirated from the iliac crest, we were not able to load in the femoral head allograft the same number of MSCs as the number present in an autograft. The loaded volume of bone marrow (and the corresponding number of MSCs) depended on the technique (injecting, soaking) as well as on the volume and shape of the allografts. The seeding efficiency of loading MSCs in allografts increased with the concentration of MSCs in the bone marrow. With concentrated bone marrow, supercharging the allograft with MSCs (as compared with an autograft) was possible in the operating room, and the number of MSCs supercharged in allografts was predictable.

Conclusions

The loaded volume of bone marrow depended on the technique (injecting, soaking) as well as on the volume and shape of the allografts. With concentrated bone marrow, the allograft could be charged with a similar or higher number of MSCs than the number present in a femoral head autograft.     

Revision shoulder arthroplasty with a reverse shoulder prosthesis

Introduction

Revision shoulder arthroplasty presents many unique and complex challenges when glenoid bone loss is involved. A distorted and medialized anatomy prevents the proper mechanics of the reverse prosthesis with regard to deltoid tension and ultimate function. This paper highlights one surgeon’s experience using structural allograft for glenoid bone loss.

Patients and methods

In all, 20 patients for a total of 24 surgeries with a medialized glenoid and/or substantial glenoid bone loss of grade IIB or higher were evaluated in this retrospective study. The allograft surgeries were performed as a one-stage procedure except for three patients. Recombinant human bone morphogenetic protein-2 (BMP2) was added to supplement incorporation in all cases. Four patients had two separate allograft procedures. Eight of the allograft procedure were femoral shaft, eleven of the allografts were femoral neck/head, and five of the allograft procedures were from proximal humerus. A graft was considered a success if they had at least 12 months of clinical and radiographic follow-up without subsequent removal of the graft or radiographic failure. Patients with less than 12 months of follow-up were included if the graft was removed or had early failure.

Results

All femoral shaft allografts except one failed, and during revision surgery it was often noted that the graft was cracked where the peripheral screws had been drilled. In nine patients the graft was still in place at last follow-up, seven of these were femoral neck/head allografts. Five grafts were removed secondary to infection. Average follow-up was 24 months (range 5–45 months).

Conclusions

Femoral neck allografts are an option in patients with substantial bone loss. The authors do not recommend use of femoral shaft allografts.

     

The effect of trochlea tilting on patellofemoral contact patterns after total knee arthroplasty: an in vitro study

Introduction

Patellofemoral complications are one major concern after total knee arthroplasty (TKA). Anterior knee pain is one of these complications and to a high percentage responsible for unsatisfied patients after TKA. Malrotation of the femoral component can contribute to retropatellar peak pressure and consequently to anterior knee pain.

Materials and methods

Eight fresh frozen cadavers were tested in a force-controlled knee rig after TKA during isokinetic flexing of the knee from 20° to 120° under constant load. By tilting the trochlea in the material of the created femoral component replicas, a rotation of the femoral component by 3° internal, 0° (neutral), 3° and 6° external rotation to transepicondylar line was simulated without changing flexion or extension gap. Retropatellar pressure distribution was measured during flexion and extension of the knee while quadriceps muscles and hamstring forces were applied.

Results

Maximum peak pressure for internal rotation of the trochlea was 7.32 ± 2.31 MPa, in neutral position the pressure reduced slightly to 7.31 ± 2.12 MPa and during further external rotation of trochlea rotation a decrease from 3° with 7.18 ± 2.14 MPa to 6° with 6.22 ± 1.83 MPa was observed (p < 0.01). There was a tendency of lower quadriceps force with increasing external rotation of the trochlea (p = 0.08).

Conclusions

The implantation of the femoral component by 3° internal trochlea rotation to transepicondylar line resulted in a highly significant increase of the mean maximal retropatellar pressure compared to 6° external rotation of the trochlea of the femoral component (p < 0.01). A higher retropatellar pressure might lead to anterior knee pain after TKA. We recommend an external rotation of the femoral component between 3° and 6° to anatomical transepicondylar line to reduce the maximal retropatellar pressure, but only if adequate soft tissue balancing and stable knee kinematics are provided.     

Glutaraldehyde-Cross-linked Meniscal Allografts: Mechanical Properties

Removal of a severely damaged medial meniscus has been shown to lead to degradation of the articular cartilage and formation of degenerative arthritis. To counter this degenerative effect, meniscal prostheses, including glutaraldehyde-cross-linked allografts, have been evaluated in dogs. The purpose of this research was to quantify the mechanical properties of both fresh and glutaraldehyde-cross-linked canine medial menisci. Mechanical properties quantified were tensile strength, tensile modulus, and compressive stiffness. In addition, water content of compressive test samples was measured. Analysis of variance showed significantly lower tensile strength and tensile modulus and significantly higher compressive stiffness for the glutaraldehydecross-linked menisci, as compared to fresh specimens. Measurement of the weight percentage of water in fresh and cross-linked samples revealed no significant differences in water content. When implanted into a joint, the increased compressive stiffness could increase the peripheral tensile load. Due to the decreased tensile strength in this region, the prosthetic meniscus could be susceptible to peripheral tears