Trabecular Bone Cores Research Articles

Proximal tibial fracture stability with intramedullary nail fixation using oblique interlocking screws.

The purpose of this study was to evaluate the mechanical stability of oblique interlocking screws in supplementing intramedullary nail fixation of high proximal tibial fractures. In vitro experimental testing. SETTING Orthopaedic biomechanics laboratory, Sunnybrook and Women's College Health Sciences Center. Ten paired fresh-frozen human cadaver tibiae. One tibia of each pair was randomized to be instrumented with an intramedullary nail (M/DN; Zimmer, Warsaw, Indiana), while the other was stabilized with a 13-hole stainless steel lateral tibial head plate (Synthes AO/ASIF). Specimens were tested in varus-valgus (v/v), flexion-extension (f/e) and torsion, before and after a 2-cm gap osteotomy was performed in the proximal segment. Testing of the nailed tibiae was performed with and without oblique proximal screws. Bone density was physically determined by removing a core of trabecular bone from the distal end of each tibia following testing. Biomechanical construct stability. The addition of the proximally placed oblique screws increased the stability of the nail construct in v/v by 50% (6.8 mm, P < 0.05), in f/e by 47% (7.2 mm, P < 0.05), and in torsion by 18% (3.0 degrees, P < 0.05). There was no significant difference observed between the stability of the intramedullary nail construct with oblique screws and the plated construct. Trabecular bone density had a significant effect in reducing stability (P < 0.05) in nail and plate fixation. The addition of oblique interlocking screws significantly improves the stability of a nailed proximal tibia fracture and provides comparable stability to a plate osteosynthesis.

Biomechanical consequences of an isolated overload on the human vertebral body.

The biomechanical consequences of an isolated overload to the vertebral body may play a role in the etiology of vertebral fracture. In this context, we quantified residual strains and reductions in stiffness and ultimate load when vertebral bodies were loaded to various levels beyond the elastic regimen and related these properties to the externally applied strain and bone density. Twenty-three vertebral bodies (T11-L4, from 23 cadavers aged 20-90 years) were loaded once in compression to a randomized nominal strain level between 0.37 and 4.5%, unloaded, and then reloaded to 10% strain. Residual strains of up to 1.36% developed on unloading and depended on the applied strain (r2=0.85) but not on density (p = 0.25). Percentage reductions in stiffness and ultimate load of up to 83.7 and 52.5%, respectively, depended on both applied strain (r2 = 0.90 and r2 = 0.32, respectively) and density (r2 = 0.23 and r2 = 0.22, respectively). Development of residual strains is indicative of permanent deformations, whereas percentage reductions in stiffness are direct measures of effective mechanical damage. These results therefore demonstrate that substantial mechanical damage-which is not visible from radiographs-can develop in the vertebral body after isolated overloads, as well as subtle but significant permanent deformations. This behavior is similar to that observed previously for cylindrical cores of trabecular bone. Taken together, these findings indicate that the damage behavior of the lumbar and lower thoracic vertebral body is dominated by the trabecular bone and may be an important factor in the etiology of vertebral fracture.

Magnetic resonance imaging measurements of bone density and cross-sectional geometry.

Magnetic resonance imaging (MRI) is commonly used in the assessment of the musculoskeletal system and associated pathology. The ability of MRI to measure the signals from water and lipid protons enables quantitative measurements of bone porosity. The goal of this investigation was to demonstrate that the density and cross-sectional geometry of whole bones can be noninvasively measured using MRI. Ten trabecular specimens cored from whale vertebrae were used to compare apparent bone density measured directly, and using a quantitative MRI algorithm. Bone density and several cross-sectional geometric properties were also measured using MRI in the distal tibia of 14 volunteers. The MRI measurements were compared with measurements made using quantitative-computed tomography (QCT). A proton density sequence was used for all MRI studies. A porosity phantom was included in the MRI examinations and used to convert the MRI signal intensity to bone volume fraction. Bone density and cross-sectional bone geometry were calculated from the bone volume fractions by assuming constant tissue properties. The apparent density of trabecular bone cores measured directly and using quantitative MRI were linearly related (r(2) = 0.959; P < 0. 01). A strong linear relation also existed between MRI and QCT measurements of ash density (r(2) = 0.923; P < 0.01) and cross-sectional geometric properties (r(2) = 0.976-0.992; P < 0.01). MRI data can be used to measure bone density and cross-sectional geometry of whole bones if a proton density sequence is used to homogenize differences in marrow composition and a porosity phantom is used for slice-specific volume fraction calibration.

The effect of trabecular structure on DXA-based predictions of bovine bone failure.

The objective of this study was to determine the influence of structural organization on the relationship between clinically assessed bone mineral density (BMD) and strength of trabecular bone. Accurate assessment of bone strength or fracture risk is a critical need as the population ages and the incidence of fractures increases. While ex vivo tests have demonstrated that BMD measured with dual-energy X-ray absorptiometry (DXA) correlates with failure load of whole bones, it is also known that the strength of trabecular bone cannot be explained by density alone. Cylindrical cores of bovine trabecular bone, harvested in a variety of orientations, were scanned with DXA to determine density, assessed with micro-MRI (magnetic resonance imaging) to measure orientation, and then loaded them to failure in bending. Measures of trabecular architecture included the angle between the specimen longitudinal (Z) axis and the principal material axis, the maximum mean intercept length (MILmax), the mean intercept length in the specimen primary axis (MILz), the degree of anisotropy, and the ratio between MILz and the length of the principal material axis. MILz was strongly associated with failure stress (r2 = 0.85, P < 0.001). BMD was also moderately associated with failure stress (r2 = 0.44, P = 0.004). Using a stepwise linear multiple regression analysis, the strongest predictor of failure stress was a combination of BMD, angle, and MILz (R2 = 0.91). When only longitudinal specimens were analyzed, the strongest predictor of failure stress was a combination of BMD and angle (R2 = 0.95). Therefore, trabecular orientation plays a significant and important role in failure of trabecular bone. Accounting for this may improve the associations between DXA-based density measures and patient fractures.

Interspecies differences in bone composition, density, and quality: potential implications for in vivo bone research.

This study compares bone composition, density, and quality in bone samples derived from seven vertebrates that are commonly used in bone research: human, dog, pig, cow, sheep, chicken, and rat. Cortical femoral bone samples were analyzed for their content of ash, collagen, extractable proteins, and insulin-like growth factor-I. These parameters were also measured in bone powder fractions that were obtained after separation of bone particles according to their density. Large interspecies differences were observed in all analyses. Of all species included in the biochemical analyses, rat bone was most different, whereas canine bone best resembled human bone. In addition, bone density and mechanical testing analyses were performed on cylindrical trabecular bone cores. Both analyses demonstrated large interspecies variations. The lowest bone density and fracture stress values were found in the human samples; porcine and canine bone best resembled these samples. The relative contribution of bone density to bone mechanical competence was largely species-dependent. Together, the data reported here suggest that interspecies differences are likely to be found in other clinical and experimental bone parameters and should therefore be considered when choosing an appropriate animal model for bone research.

Material properties of bone from the femoral neck and calcar femorale of patients with osteoporosis or osteoarthritis.

Patients with osteoarthritis (OA) rarely fracture the neck of the femur whereas this is common in patients with osteoporosis (OP). The reasons for this are not clear. In this study, cores of trabecular bone and thin slices of bone from the calcar were obtained from the femoral neck of patients with OA or OP following hip arthroplasty and a normal group post mortem. The mechanical properties, densities and material composition were measured. The aim was to determine whether differences in these properties could explain why osteoarthritic patients did not suffer from fractured neck of femur. No difference was found in the density or stiffness of the calcar between the groups, though there appeared to be a small increase in mineralization in the OA bone compared with the OP. However, there was a 72% increase in the volume of trabecular bone in the OA group compared with a loss of about 20% in the OP group. This increased apparent density of the OA trabecular bone resulted in a greater stiffness, yield strength and energy absorbed to yield, whereas the same properties of OP bone were not significantly lower than normal. These marked changes in the OA bone could result in a redistribution of stresses due to loads caused by falling, thereby absorbing the energy of impact and preventing the formation of a fracture surface.

Assessment of bone quantity and ‘quality’ by ultrasound attenuation and velocity in the heel

Objective. To determine if ultrasound measurements in the heel are related to bone quality in addition to quantity. Design. In situ and in vitro experiments on cadaver heels. Background. It has been suggested, but not demonstrated, that clinical ultrasound—used to screen for osteoporosis in clinical trials — provides a measure of ‘bone quality’ as distinct from bone quantity. Methods. Ultrasound transmission velocity (UTV) and the slope of the linear dependence of broadband ultrasound attenuation on frequency (BUA) were measured in situ in 32 heels of 16 cadavers and in vitro in cores of calcaneal trabecular bone. Results. After adjusting for Young's modulus, in situ UTV explains 33% P = 0.03) and in situ BUA explains none of the remaining variance in density ( r 2 = 0.02, P = 0.60). After adjusting for density, in situ BUA explains 29% ( P = 0.04) and in situ UTV explains none of the remaining variance in Young's modulus ( r 2 = 0.01, P = 0.79). By comparison, in vitro BUA explains 58% ( P = 0.001) of the remaining variance in Young's modulus, after adjusting for density. Conclusions. In situ BUA reflects ‘bone quality’ independently of bone quantity, whereas in situ UTV reflects bone quantity independently of ‘bone quality’.

Measurements of permeability in human calcaneal trabecular bone

2.36 cm diameter cores of trabecular bone ( n = 22), oriented in the mediolateral direction, were obtained from fresh-frozen caleanei of 16 cadavers ranging in age from 32 to 89 yr. The cores were defatted and tested to determine values for permeability along the cylinder axis. Permeability values (0.4–11 × 10 −9 m 2) were found to be strongly correlated with specimen porosity (78–92%) through a linear relationship ( r 2 =0.91). These results provide essential information for the biphasie or poroclastic modeling of fluid-filled trabecular bone at this location.

Correlation of appendicular bone mineral density and arterial blood ph in chronic obstructive pulmonary disease

This study used both multi-slice pQCT and microCT to investigate regional changes in bone mineral density and structural parameters in the ultradistal tibia and in the mid-femoral neck under habitual gait loading. Twenty cadavers with 2 females and 18 males aged 70.8 ± 8.5 were used in this study. Seventy-two cylindrical bone cores with 5 mm in diameter and 10 mm in length from the anterior/posterior and superior/inferior regions were obtained from ultradistal tibia and mid-femur neck, respectively, so that their differences in terms of volumetric trabecular bone mineral density (tBMD) as well as micro-architectural parameters could be studied. The results showed that the mean volumetric tBMD at both the organ (including the bone marrow spaces) and tissue levels (excluding the bone marrow spaces) were a 49.2% and 28.3%, respectively, lower in the anterior bone cores than in the posterior bone cores from the ultradistal tibia (P < 0.01). MicroCT measurements on BV/TV, BS/TV, Tb.N, Tb.Th, and DA were found to be on average of 33.5%, 23.6%, 9.1%, 18.0%, and 14.6%, respectively, lower in the anterior trabecular bone cores (P < 0.001), while Tb.Sp and SMI were 12.5% and 29.3%, respectively, higher in the anterior trabecular bone cores (P < 0.01). No significant difference in micro-architectural parameters was found in the trabecular bone cores obtained from mid-femoral neck, except that the mean DA of the inferior bone cores was significantly higher by 30.1% than that of the superior bone cores (P = 0.01). A statistically significant linear relationship with the correlation coefficient, ranging from 0.37 to 0.94 and −0.62 to −0.85, respectively, was shown between the tBMD at the organ level and all of the micro-architectural parameters (P < 0.05). We suggest that dynamic loading changes during the striking of the heel in normal gait, as well as the peaks of the hip joint reaction force occur during the heel strike and before toe off positions in the lifetime of the subject may account for such regional differences in BMD and micro-architecture. The findings from the correlation study also suggest that, apart from BMD, the micro-architecture may exhibit adaptation in response to such excessive loading.

Calcium-restricted ovariectomized sinclair S-1 minipigs: An animal model of osteopenia and trabecular plate perforation

The ovariectomized rat model has now been generally accepted as a useful model for screening different therapeutic agents, but there is a major requirement to identify reliable large animal models for osteoporosis research. In this study, the calcium restricted, ovariectomized minipig has been thoroughly investigated in order to define a large animal model with trabecular and cortical bone remodeling which would be reliable for further testing of agents that had shown promise of efficacy during the screening procedure. Twenty six female, 4-month old minipigs were randomized into four groups and fed either normal diet (0.90% calcium (Ca.)) or diet with restricted calcium content (0.75%, 0.50%). At the age of ten months, 3 groups were ovariectomized (OVX) while one group on normal diet was shamoperated. The groups were followed for six months after the operation. At death, bone mass was determined by densitometry and by ashing. Additionally, biomechanical competence was assessed in trabecular bone cores from the vertebral bodies. Finally, histomorphometry (static and dynamic parameters) and structural analyses (star volume) were performed on the vertebral bodies. The study revealed an OVX-related decline of 6% in vertebral bone mineral density (BMD) and a decline of 15% in trabecular bone volume (BV/TV). In contrast, a 15% increase in mean trabecular plate separation (Tb.Sp.) and a small increase in marrow space star volume (Ma. Star V.) were detected. The structural changes became more pronounced when OVX was combined with mild Ca. restriction (0.75% Ca.) with an increase in Ma. Star V. to 164%. By using a higher degree of Ca., restriction (0.50%), all the described changes in bone mass and structure were blunted. The biomechanical data followed the same pattern with a progressive decrease from the .90% Ca. sham-operated through the 0.90% OVX and to the 0.75% Ca. OVX group and then an increase. It is concluded that the OVX minipig on a 0.75% calcium-restricted diet promises to be a useful large animal model for osteoporosis research.

Finite element stress analysis of simulated metastatic lesions in the lumbar vertebral body

A three-dimensional finite element model of a lumbar vertebral body was developed to study the effects of geometry, material properties and loading conditions on stresses in the presence of metastatic lesions. Parameters studied included location and size of the lesion, modulus of the cortical and trabecular bone within and near the lesion, generalized osteoporosis and load distribution. The results, expressed as ratios of peak values of displacement and stress, relative to a normal baseline case, indicated that the location of a defect which did not penetrate the cortex had a minor influence on the peak displacement and stresses, as did the presence of lesions occupying less than 40% of the volume of the vertebral centrum. A lesion occupying 40% of the centrum volume increased the endplate displacement by 2.9 times, the peak tensile stress in the cortical shell by 2.2 times, and the peak von Mises stress in the endplate by 2.8 times. When this lesion penetrated the cortex, these values increased to 3.8, 3.3 and 4.4 times, repsectively. The most severe case involved a defect penetrating the anterior cortex, osteoporotic bone properties and anteriorly eccentric loading. In this case, the peak values increased to 8.4, 3.4 and 5.9 times their baseline values, respectively. The results are consistent with a model of the vertebral body as a stiff frame of cortical bone surrounding a relatively compliant core of trabecular bone. Only variations in geometry and properties large enough to lessen significantly the structural stiffness affect the peak stresses and displacements. Such a case occurs when an osteoporotic vertebral body containing a lesion of approximately half its volume is subjected to an anterior eccentric load distribution, as occurs in forward flexion. Under these conditions, large increases in the stress magnitudes put the vertebral body at extreme risk of fracture.

Osteochondroma in laboratory rats: a report of 3 cases in a Fischer-344, a Sprague-Dawley, and a Wistar rat.

Three cases of osteochondroma in a male Sprague-Dawley (SD) rat, a female Fischer (F344) rat, and a male Wistar rat are described. The rats were aged between 26 and 30 months. All osteochondromas were considered to be of spontaneous origin. The Wistar rat had multiple osteochondromas on both hind legs, the skull base, and a lumbar vertebra, whereas each of the F344 and SD rats was affected by a solitary osteochondroma, also on a lumbar vertebra. The lumbar osteochondromas were similar in appearance in all rats and consisted of a central core of trabecular bone, interspersed with fatty marrow and covered by a cap of hyaline cartilage. The additional tumors in the Wistar rat represented different developmental stages of osteochondroma with or without endochondral activity. The osteochondromas in the rats were morphologically similar to those described in humans and some domestic animal species.

Mechanical properties of bone from iliac crest and relationship to L5 vertebral bone

Apparent density, yield stress and yield energy were measured in transiliac cores of trabecular bone from iliac crest and craniocaudal cores of L5 vertebra from 26 cadavers. In the iliac crest, bone from the anterior superior spine region had significantly greater apparent density and had greater yield energy than bone from the center of the crest. Yield stress was greater at the anterior superior spine than either the center or at the posterior spine. Lumbar vertebral bone was uniform in its characteristics. Apparent density was the property showing the best correlation between iliac crest and L5 ( r = 0.79), while yield energy was less well associated ( r = 0.67). In L5, mechanical properties decline more rapidly with age than apparent density. Between the ages of 25 and 75 years the rate of fall of yield stress was twice and yield energy 2.6 times compared with the rate of fall of apparent density. Iliac crest behaved similarly. Yield stress in iliac crest paired for density in subjects <40 years and >60 years was 40.7% lower in the older subjects ( p = 0.03), suggesting a specific mechanical defect in old age. The yield stress advantage accruing to orientated lumbar bone was more marked at lower values of yield stress in the iliac crest when cores from the same cadaver were matched for apparent density. Mechanical properties of iliac crest bone are very dependent upon site and at no one site in the iliac crest do the physical properties satisfactorily predict those in the lumbar spine.