Akifumi Nishida

Contribution of trabecular and cortical components to the mechanical properties of bone and their regulating parameters

To evaluate the mechanical contributions of the spongiosa and cortex to the whole rat vertebra, we developed a finite element analysis (FEA) system linked to three-dimensional data from microcomputed tomography (micro-CT). Twenty-eight fifth lumbar vertebrae (L-5) were obtained from 10-month-old female rats, comprised of ovariectomized (ovx, n = 6), sham operated (n = 7), and alfacalcidol-treated after ovx (0.1 microg/kg [n = 8] and 0.2 microg/kg [n = 7]) groups. The trabecular microstructure of L-5 was measured by micro-CT. Yield strength at the tissue level (YS), defined as the value at which 0.034% of all elements reached yield stress, was calculated by the FEA. Then, the ultimate compressive load of each specimen was measured by mechanical testing. The YS of the whole bone (YSw) showed a significant correlation with ultimate load (r = 0.91, p < 0.0001). The YS values of the isolated spongiosa (YSs) and cortex (YSc) were calculated in models with varying amounts of trabecular or cortical bone mass. The mechanical contribution of the spongiosa showed a nonlinear relationship with bone mass, and ovx reduced the mean mechanical contribution of the spongiosa to the whole bone by 13% in comparison to the sham group. YSs had a strong relationship with trabecular microstructure, especially with trabecular bone pattern factor (TBPf) and structure model index (SMI), and YSc had a strong relationship with cortical bone volume. The structural parameters most strongly related to YSw were BV/TV and TBPf. Our micro-FEA system was validated to assess the mechanical properties of bone, including the individual properties of the spongiosa and cortex, in the osteoporotic rat model. We found that the mechanical property of each component had a significant relationship with the respective bone mass, volume, or structure. Although trabecular microstructure has a significant relationship with bone strength, in ovx bone with deteriorated trabecular microstructure, the strength depended mainly on the cortical component.

Differences of three-dimensional trabecular microstructure in osteopenic rat models caused by ovariectomy and neurectomy

We investigated the differences in three-dimensional microstructure of bone in cases of osteopenia caused by two different procedures: ovariectomy (ovx) and sciatic neurectomy (nx). Thirty-nine 8-week-old female Lewis rats were divided into two groups: (1) ovx and sham operation; and (2) nx and sham operation. At 12 weeks of age these rats were killed to sample the right tibiae. The samples were scanned using microcomputed tomography to obtain metric parameters such as bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), and nonmetric parameters such as structure model index (SMI), trabecular bone pattern factor (TBPf), and degree of anisotropy (DA). The changes in all microstructural parameters were significant in both the ovx and nx groups, with those of BV/TV, Tb.Th, Tb.Sp, and SMI more significant in the ovx group than in the nx group, in comparison to their respective controls. The significantly higher coefficient of variance for Tb.Th across the entire analyzed area of the individual samples indicated that the trabecular thinning occurred heterogenously and that the microstructural deterioration induced by ovx and nx appeared to be locally accelerated, so as to induce perforation and disappearance of trabeculae. The DA increased significantly in the ovx rats, whereas it decreased in the nx rats. The appearance of microstructural deterioration differed between the two osteopenic models. The three-dimensional (3D) images from the nx rats showed flake-like trabeculae, whereas the ovx rats exhibited a diffuse disappearance of trabeculae, especially in the central part of the tibia, but with a preservation of shape for those trabeculae that were retained. The reduction in cortical area was more significant in the nx group. nx and ovx resulted in significant changes in bone microstructure, showing perforation and removal of trabeculae due to locally accelerated bone resorption. The 3D microcomputed tomography images demonstrated the different microstructural changes that occurred in the ovx and nx groups. Loading during bone resorption increased the anisotropy, whereas immobilization increased the isotropy. In addition, immobilization had a more significant effect on the cortical area.

Bone structure and mineralization demonstrated using synchrotron radiation computed tomography (SR-CT) in animal models: preliminary findings.

We investigated the ability of synchrotron radiation computed tomography (SR-CT) to demonstrate trabecular microstructure, detail of trabecular surfaces, and mineralization of bones. Eight rat vertebrae, six rat tibiae, and eight minipig vertebrae were scanned using SR-CT at the synchrotron radiation facility Super Photon ring-8GeV (SPring-8). Images obtained using conventional micro-CT, scanning electron microscopy (SEM), and contact microradiography (CMR) were compared with the SR-CT images. SR-CT showed high image quality without visible partial volume effect. Three-dimensional SR-CT revealed shallow concavities in the bone surface, which were considered to correspond to osteoclastic resorption areas, as well as the connectivity, anisotropy, and shape (rod- or platelike) of trabeculae. Two-dimensional SR-CT showed different density along the surface of the trabecular bone, indicating the degree of bone mineralization. In conclusion, SR-CT seems to be a useful tool for delineating trabecular surfaces, evaluating bone mineralization, and revealing precise trabecular structure.

Which bone densitometry and which skeletal site are clinically useful for monitoring bone mass

Long-term precision, as well as reproducibility, is important for monitoring bone mineral density (BMD) alteration in response to aging or therapy. In order to investigate which bone densitometry and which skeletal site are clinically useful for monitoring bone mass, we examined the standardized long-term precision of several bone density measurements in 83 healthy Japanese women. Annual BMD measurements were performed for 5 or 6 years using dual X-ray absorptiometry (DXA) on the lumbar spine, radius (EXP5000) and calcaneus (HeelScan); peripheral quantitative computed tomography (pQCT) on the radius (Densiscan1000); and quantitative ultrasound (QUS) on the calcaneus (Achilles+). The long-term precision error for the individual subject was given by the standard error of estimate (SEE), and the standardized long-term precision was defined as the percentage coefficient of variation (CV%) divided by the percentage ratio of the annual bone-loss rate. Based on the CV% of spinal DXA, speed of sound (SOS) and diaphyseal pQCT showed significantly higher precision than others, while radial ultradistal (UD) DXA and heel DXA showed significantly lower precision. The long-term precision errors of other measurements were statistically the same as that of the spinal DXA. The spinal DXA, the radial DXA, and pQCT at both the distal metaphysis and diaphysis showed high rates of annual bone loss. The radial trabecular BMD (pQCT) was significantly higher than that of spinal DXA. The annual rates of bone loss of QUS and of heel DXA were significantly lower than that of spinal DXA. Taken together, standardized long-term precision was obtained in the spinal DXA and radial pQCT. In conclusion, spinal DXA and radial pQCT were considered the most useful monitoring method for osteoporosis, while QUS was considered less useful.

Age-related changes in bone density, geometry and biomechanical properties of the proximal femur: CT-based 3D hip structure analysis in normal postmenopausal women.

The geometry as well as bone mineral density (BMD) of the proximal femur contributes to fracture risk. How and the extent to which they change due to natural aging is not fully understood. We assessed BMD and geometry in the femoral neck and shaft separately, in 59 normal Japanese postmenopausal women aged 54-84 years, using clinical computed tomography (CT) and commercially available software, at baseline and 2-year follow-up. This system detected significant reductions over the 2-year interval in total BMD (%change/year = -0.900 ± 0.257, p < 0.0005), cortical cross-sectional area (CSA) (-0.800 ± 0.423%/year, p < 0.05) and cortical thickness (-1.120 ± 0.453%/year, p < 0.01) in the femoral neck. In the femoral shaft, cortical BMD decreased significantly (-0.642 ± 0.188%/year, p < 0.005). Regarding biomechanical parameters in the femoral neck, the cross-sectional moment of inertia (CSMI) and section modulus (SM) decreased (-1.38 ± 3.65%/year, p < 0.01 and -1.37 ± 2.96%/year, p < 0.005) and the buckling ratio (BR) increased significantly (1.48 ± 4.81%/year, p < 0.05), whereas no changes were found in the femoral shaft. The distinct patterns of age-related changes in the geometry and biomechanical properties in the femoral neck and shaft suggest that improved geometric measures are possible with the current non-invasive method using clinical CT.

Human parathyroid hormone (1-34) increases mass and structure of the cortical shell, with resultant increase in lumbar bone strength, in ovariectomized rats

Estrogen deficiency causes reduction of bone mass and abnormal bone microarchitecture, consequently reducing bone strength. Human parathyroid hormone (hPTH) (1-34) increases bone mass and strength. To clarify the factors that determine the recovery of bone strength in the lumbar vertebrae of ovariectomized rats by intermittent hPTH administration, we analyzed the relationship between skeletal measurements and bone strength. Human PTH (1-34) administration resulted in recovery of cortical bone mineral content (BMC) and cortical bone area to sham the levels, but in resulted in a less pronounced recovery of trabecular BMC and no increase in the total cross-sectional area of the vertebral body. Of the three-dimensional (3D) trabecular bone parameters, hPTH (1-34) increased trabecular thickness (Tb.Th). The cortical shell area of L4, determined by histomorphometry, was also increased. In hPTH-treated rats, the only determinant of the compressive load of L5 was the cortical shell BMC, in the early recovery period (days 42–84). Our data suggest that increased cortical bone mass contributes more than trabecular bone mass and structure to the recovery of bone strength in response to hPTH therapy in the rat lumbar vertebral body after ovariectomy.

Bilateral elastofibroma of the thighs with concomitant subscapular lesions

Abstract. We report a case of elastofibroma that occurred in both thighs and subscapular regions. The MR signal intensity of the lesions was typical for elastofibroma. Although bilateral involvement of the thighs is exceptional, the presence of concomitant characteristic bilateral subscapular lesions was helpful in making the diagnosis of elastofibroma.

Chronic Aortic Dissection Complicated by Disseminated Intravascular Coagulation: Successful Treatment with Endovascular Stent-Grafting

PURPOSE To report endovascular repair of a chronic aortic dissection complicated by disseminated intravascular coagulation (DIC). CASE REPORT A 61-year-old man developed DIC associated with a chronic Stanford type B aortic dissection that occurred during cardiac catheterization 12 years earlier. At the current admission, computed tomography showed a partially thrombosed false lumen extending from the aortic arch to the left common iliac artery. On angiography, entry and re-entry tears were identified at the right subclavian and left common iliac arteries, respectively. After stent-graft implantation at the entry and re-entry sites, not only was the false lumen completely thrombosed but the DIC also resolved. The patient is doing well with no complication at 16 months after treatment. CONCLUSIONS Endovascular stent-grafting is an acceptable alternative to surgical repair for aortic dissection accompanied by DIC.

Coil embolization of iliac artery aneurysms developing after abdominal aortic aneurysm repair with a conventional bifurcated graft.

PURPOSE To evaluate the efficacy of embolizing iliac artery aneurysms (IAAs) developing after abdominal aortic aneurysm (AAA) repair. METHODS The records of 6 patients (5 men; mean age 79 years, range 61-87) with unilateral (n=3) or bilateral (n=3) IAAs that had developed after AAA repair were reviewed. In all patients, the limbs of the bifurcated graft were anastomosed end-to-end or end-to-side with the external iliac arteries during AAA repair. Before embolization, superior mesenteric artery (SMA) arteriography was done in all patients to evaluate collateral pathways to the inferior mesenteric artery (IMA). RESULTS The unilateral IAAs were treated by proximal and distal embolization. In 2 patients with bilateral IAAs, SMA angiography showed sufficient collateral flow to the IMA, so the aneurysms were treated by proximal embolization and packing. In the other bilateral IAA case, the left 6-cm IAA was treated by proximal and distal embolization, while the contralateral 3-cm IAA was not embolized because angiography demonstrated inadequate collateral flow to the IMA, indicating a possible risk of colon ischemia if both IAAs were embolized. Immediate postprocedural angiography in all patients showed complete exclusion of the IAAs. Mild buttock claudication occurred in 1 patient. There were no episodes of rupture over a mean 46-month follow-up. CONCLUSIONS Embolization is a safe and effective alternative to open surgery for the treatment of IAAs that develop after AAA repair. However, before embolization, angiographic evaluation of collateral pathways to the IMA is essential to reduce the risk of colon ischemia.

Effect of etidronate on three-dimensional trabecular structure in ovariectomized or sciatic neurectomized rats

The purpose of this study was to evaluate the effect of etidronate (EHDP) on three-dimensional (3D) trabecular structure in ovariectomized (OVX) and sciatic neurectomized (NX) rats. Eight-week-old female Lewis rats received ovariectomy (n = 19) or sham operation (OVX-sham; n = 10). OVX rats received either vehicle (OVX-control; n = 9) or EHDP (OVX-EHDP; n = 10). Eight-week-old female Lewis rats received NX (n = 20) or sham operation (NX-sham; n = 10). NX rats received either vehicle (NX-control; n = 10) or EHDP (NX-EHDP; n = 10). EHDP at 5 mg/kg or vehicle was subcutaneously injected 5 days a week. The treatment was initiated 2 weeks after surgery and was continued for 2 weeks. At 12 weeks of age, the rats were killed, and we scanned the proximal metaphysis of the tibia; this was done using micro-CT; (μ CT20; SCANCO Medical). The recovery of structural parameters was not complete in NX rats compared to OVX rats. The 3D micro-CT images showed that the subcortical spongiosa, which was preserved in OVX rats, had marked loss in NX rats. Furthermore, these trabeculae were not restored after the EHDP treatment. In conclusion, the mechanical driving of the control of trabecular structure is inactive in NX, and EHDP treatment for 2 weeks does not restore this condition.