Ahi Sema Issever

High-Resolution Peripheral Quantitative Computed Tomographic Imaging of Cortical and Trabecular Bone Microarchitecture in Patients with Type 2 Diabetes Mellitus

CONTEXT Cross-sectional epidemiological studies have found that patients with type 2 diabetes mellitus (T2DM) have a higher incidence of certain fragility fractures despite normal or elevated bone mineral density (BMD). OBJECTIVE In this study, high-resolution peripheral quantitative computed tomography was applied to characterize cortical and trabecular microarchitecture and biomechanics in the peripheral skeleton of female patients with T2DM. DESIGN AND SETTING A cross-sectional study was conducted in patients with T2DM recruited from a diabetic outpatient clinic. PARTICIPANTS Elderly female patients (age, 62.9 ± 7.7 yr) with a history of T2DM (n = 19) and age- and height-matched controls (n = 19) were recruited. OUTCOME MEASURES Subjects were imaged using high-resolution peripheral quantitative computed tomography at the distal radius and tibia. Quantitative measures of volumetric (BMD), cross-sectional geometry, trabecular and cortical microarchitecture were calculated. Additionally, compressive mechanical properties were determined by micro-finite element analysis. RESULTS Compared to the controls, the T2DM cohort had 10% higher trabecular volumetric BMD (P < 0.05) adjacent to the cortex and higher trabecular thickness in the tibia (13.8%; P < 0.05). Cortical porosity differences alone were consistent with impaired bone strength and were significant in the radius (>+50%; P < 0.05), whereas pore volume approached significance in the tibia (+118%; P = 0.1). CONCLUSION The results of this pilot investigation provide a potential explanation for the inability of standard BMD measures to explain the elevated fracture incidence in patients with T2DM. The findings suggest that T2DM may be associated with impaired resistance to bending loads due to inefficient redistribution of bone mass, characterized by loss of intracortical bone offset by an elevation in trabecular bone density.

MR imaging of patellar instability: injury patterns and assessment of risk factors.

First-time patellar dislocation typically occurs with twisting knee motions, during which the medial ligamentous stabilizers rupture, and the patella strikes against the lateral femoral condyle. The typical injury pattern is a tear of the medial patellofemoral ligament (MPFL) and bone bruises of the patella and the lateral femoral condyle. Additionally, complex injuries to bone, cartilage, and ligaments may occur. The ensuing loss of medial restraint favors future patellar dislocations, especially if additional risk factors are present. Recurrent patellar dislocations usually occur in individuals with anatomic variants of the patellar stabilizers, such as trochlear dysplasia, patella alta, and lateralization of the tibial tuberosity. Magnetic resonance (MR) imaging is reliable in identifying risk factors for chronic patellar instability and in assessing knee joint damage associated with patellar dislocation. MR imaging can thus provide important information for individually tailored treatment. Patients with primary patellar dislocation without severe internal derangement who lack major risk factors can be treated conservatively. Patients with pronounced ligamentous tears or large osteochondral lesions require prompt surgery. In addition, surgical correction of anatomic variants will help reduce the potential for chronic instability. The most common procedures, in addition to MPFL reconstruction, include trochleoplasty, medialization of the tibial tuberosity, and medial capsular plication. For comprehensive assessment of patellar dislocation, a radiologist should be able to identify typical injury patterns, know standard methods to assess risk factors for patellar instability, and be familiar with surgical options.

MicroCT evaluation of normal and osteoarthritic bone structure in human knee specimens

Although trabecular bone structure has been evaluated, variation with knee compartment and depth from joint surface is not completely understood. Cadaver knees were evaluated with microcomputed tomography analysis for these variations. Objective differences were compared between: medial vs. lateral compartments; femoral vs. tibial bone; and normal vs. arthritic knees. Depth dependent changes in the parameters were observed for the first 6 mm of the cores in normal knees: BV/TV, Tb.N and Conn.D gradually decrease, while Tb.Sp and SMI increase. In the first 6 mm of the normal tibia BV/TV, Tb.N, and Tb.Th are greater than in the femur on both the medial and lateral compartments while Tb.Sp, SMI, and Conn.D are lower. The medial compartment values for BV/TV, Tb.N, Tb.Th and Conn.D are generally greater than for the lateral in both the femur and tibia while Tb.Sp and SMI are lower. In comparison of normal vs. arthritic knees significant differences are observed in the first 6 mm of the medial tibia. With arthritis BV/TV and Tb.Th are lower, while SMI and Tb.Sp are higher. Tb.N and Conn.D show no statistically significant difference. The bone structure variations are, thus, most prominent in the first 6 mm of depth and medial compartment bone is generally more structurally sound than lateral. Severely arthritic bone changes are most prominent in the medial compartment of the tibia and bone structure is less sound in severe arthritis.

Local Differences in the Trabecular Bone Structure of the Proximal Femur Depicted with High-Spatial-Resolution MR Imaging and Multisection CT

RATIONALE AND OBJECTIVES The authors performed this study to investigate structural variations in the trabecular bone of the proximal femur at high-resolution magnetic resonance (MR) imaging and high-resolution multisection computed tomography (CT). MATERIALS AND METHODS Bone mineral density (BMD) was measured in 36 proximal human femur specimens by using dual x-ray absorptiometry. High-resolution MR imaging was performed at 1.5 T with an in-plane spatial resolution of 0.195 x 0.195 mm and a section thickness of 0.3 and 0.9 mm. Multisection CT was performed with an ultra-high-resolution protocol; images were obtained with an in-plane spatial resolution of 0.25 mm and a section thickness of 1 mm. In a subset of these specimens, micro CT was performed with an isotropic spatial resolution of 30 microm. Identical regions of interest (ROIs) were used to analyze images obtained with MR imaging, multisection CT, and micro CT. Trabecular bone structural parameters were obtained, and the parameters from the individual imaging modalities and BMD were correlated. RESULTS Significant differences concerning the trabecular microarchitecture between the individual ROIs were demonstrated with multisection CT and MR imaging. A number of the correlations between structural parameters derived with multisection CT, MR imaging, micro CT, and BMD measurements were significant. For MR imaging, threshold technique and section thickness had an effect on structural parameters. CONCLUSION Structural parameters obtained in the proximal femur with multisection CT and high-resolution MR imaging show regional differences. These techniques may be useful for depicting the trabecular architecture in the diagnosis of osteoporosis.

Assessment of trabecular bone structure of the calcaneus using multi-detector CT: correlation with microCT and biomechanical testing.

The prediction of bone strength can be improved when determining bone mineral density (BMD) in combination with measures of trabecular microarchitecture. The goal of this study was to assess parameters of trabecular bone structure and texture of the calcaneus by clinical multi-detector row computed tomography (MDCT) in an experimental in situ setup and to correlate these parameters with microCT (microCT) and biomechanical testing. Thirty calcanei in 15 intact cadavers were scanned using three different protocols on a 64-slice MDCT scanner with an in-plane pixel size of 208 microm and 500 microm slice thickness. Bone cores were harvested from each specimen and microCT images with a voxel size of 16 microm were obtained. After image coregistration, trabecular bone structure and texture were evaluated in identical regions on the MDCT images. After data acquisition, uniaxial compression testing was performed. Significant correlations between MDCT- and microCT-derived measures of bone volume fraction (BV/TV), trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) were found (range, R(2)=0.19-0.65, p<0.01 or 0.05). The MDCT-derived parameters of volumetric BMD, app. BV/TV, app. Tb.Th and app. Tb.Sp were capable of predicting 60%, 63%, 53% and 25% of the variation in bone strength (p<0.01). When combining those measures with one additional texture index (either GLCM, TOGLCM or MF.euler), prediction of mechanical competence was significantly improved to 86%, 85%, 71% and 63% (p<0.01). In conclusion, this study showed the feasibility of trabecular microarchitecture assessment using MDCT in an experimental setup simulating the clinical situation. Multivariate models of BMD or structural parameters combined with texture indices improved prediction of bone strength significantly and might provide more reliable estimates of fracture risk in patients.

Direct Measures of Trabecular Bone Architecture from MR Images

Osteoporosis is a bone disorder involving a decrease in bone mass and changes in the cancellous bone network leading to an increase in fracture risk. Until recently only bone mass and density were routinely assessed in patients, usually measured by dual-energy X-ray absorptiometry (DXA) or by quantitative computed tomography (QCT). Although bone mineral density (BMD) is an important determinant of bone strength, there is strong evidence that architecture of cancellous bone plays a significant role in bone strength and determines its biomechanical properties.1The importance of three-dimensional trabecular bone structure in osteoporosis increases when evaluating the response to therapy, as studies have reported that changes in fracture risk were not mainly attributable to BMD.2The measurement of both bone micro-architecture and BMD may improve the estimation of bone strength. However, the precise relationship between density, structure and mechanical properties is still under investigation.

Diffraction enhanced imaging of articular cartilage and comparison with micro-computed tomography of the underlying bone structure

The goal of this study was to explore the role of diffraction enhanced X-ray imaging (DEI) for assessing changes in osteoarthritic cartilage and correlating the findings with concurrent changes in the underlying bone imaged using micro-computed tomography (μCT). DEI was used to image femoral head specimens at various beam energies. DEI utilizes a monochromatic, highly collimated beam, with an analyzer crystal that selectively weights out photons according to the angle they have been deviated with respect to the original direction. This provides images of very high contrast, with the rejection of X-ray scatter. The underlying bone was imaged using μCT and measures quantifying the bone structure were derived. Confirmation of cartilage degeneration was obtained from histology and polarized light microscopy. DEI allowed the visualization of articular cartilage and reflected the fibrillations and fissures in tissues from degenerated joints. The trabecular bone underlying the most degenerated articular cartilage showed increased bone volume fraction and more plate-like characteristics, compared with that underlying normal appearing cartilage. The histology and polarized light microscopy images reflected the DEI based features of cartilage architecture. These data reflect the ability of X-ray based emerging technologies to depict cartilage–bone interactions in joint degeneration.

Trabecular Bone Structure Analysis in the Osteoporotic Spine Using a Clinical In Vivo Setup for 64‐Slice MDCT Imaging: Comparison to μCT Imaging and μFE Modeling

Assessment of trabecular microarchitecture may improve estimation of biomechanical strength, but visualization of trabecular bone structure in vivo is challenging. We tested the feasibility of assessing trabecular microarchitecture in the spine using multidetector CT (MDCT) on intact human cadavers in an experimental in vivo–like setup. BMD, bone structure (e.g., bone volume/total volume = BV/TV; trabecular thickness = Tb.Th; structure model index = SMI) and bone texture parameters were evaluated in 45 lumbar vertebral bodies using MDCT (mean in‐plane pixel size, 274 μm2; slice thickness, 500 μm). These measures were correlated with structure measures assessed with μCT at an isotropic spatial resolution of 16 μm and to microfinite element models (μFE) of apparent modulus and stiffness. MDCT‐derived BMD and structure measures showed significant correlations to the density and structure obtained by μCT (BMD, R2 = 0.86, p < 0.0001; BV/TV, R2 = 0.64, p < 0.0001; Tb.Th, R2 = 0.36, p < 0.01). When comparing μCT‐derived measures with μFE models, the following correlations (p < 0.001) were found for apparent modulus and stiffness, respectively: BMD (R2 = 0.58 and 0.66), BV/TV (R2 = 0.44 and 0.58), and SMI (R2 = 0.44 and 0.49). However, the overall highest correlation (p < 0.001) with μFE app. modulus (R2 = 0.75) and stiffness (R2 = 0.76) was achieved by the combination of QCT‐derived BMD with the bone texture measure Minkowski Dimension. In summary, although still limited by its spatial resolution, trabecular bone structure assessment using MDCT is overall feasible. However, when comparing with μFE‐derived bone properties, BMD is superior compared with single parameters for microarchitecture, and correlations further improve when combining with texture measures.

CT-Based Patient-Specific Modeling of Glenoid Rim Defects: A Feasibility Study

OBJECTIVE Reconstruction of glenoid bone defects requires accurate preoperative planning. The purpose of this study is to present a method for quantifying the defect size and generating a 3D model of the bone graft for augmentation by matching the fractured glenoid with the contralateral side. MATERIALS AND METHODS Ten paired shoulders from five cadavers (subjects: three women and two men; mean age, 85 years) and 60 paired shoulders in 30 patients (controls: nine women and 21 men; mean age, 21 years) were examined using CT to determine bilateral comparability by assessment of the maximum glenoid diameters, surface area, and volume. After creation of a glenoid rim defect in the study group, repeated CT scans were superimposed with the data from the contralateral side. The defect size was quantified and the missing fragment virtually reconstructed. Accuracy was evaluated by comparing the virtually repaired glenoid with the predefect CT scan. RESULTS There were no significant side-to-side differences in intact shoulders (p < 0.05). After creation of the glenoid defects, there was a mean decrease of 31% in the anteroposterior diameter, 34% in surface area, and 19% in volume. The virtually reconstructed glenoids did not differ significantly from the predefect CT scans. The averaged predefect-to-postdefect difference was 3% for the anteroposterior diameter (R(2) = 0.71), 6% for the surface area (R(2) = 0.82), and 4% for the volume (R(2) = 0.98). CONCLUSION A precise 3D model of the glenoid bony defect can be generated. The computer simulation provides a virtual model of the bone graft, which may potentially improve arthroscopic bone augmentation.

Prediction of bone strength by μCT and MDCT-based finite-element-models: How much spatial resolution is needed?

OBJECTIVES Finite-element-models (FEM) are a promising technology to predict bone strength and fracture risk. Usually, the highest spatial resolution technically available is used, but this requires excessive computation time and memory in numerical simulations of large volumes. Thus, FEM were compared at decreasing resolutions with respect to local strain distribution and prediction of failure load to (1) validate MDCT-based FEM and to (2) optimize spatial resolution to save computation time. MATERIALS AND METHODS 20 cylindrical trabecular bone specimens (diameter 12 mm, length 15-20mm) were harvested from elderly formalin-fixed human thoracic spines. All specimens were examined by micro-CT (isotropic resolution 30 μm) and whole-body multi-row-detector computed tomography (MDCT, 250 μm × 250 μm × 500 μm). The resolution of all datasets was lowered in eight steps to ~ 2,000 μm × 2000 μm × 500 μm and FEM were calculated at all resolutions. Failure load was determined by biomechanical testing. Probability density functions of local micro-strains were compared in all datasets and correlations between FEM-based and biomechanically measured failure loads were determined. RESULTS The distribution of local micro-strains was similar for micro-CT and MDCT at comparable resolutions and showed a shift toward higher average values with decreasing resolution, corresponding to the increasing apparent trabecular thickness. Small micro-strains (εeff<0.005) could be calculated down to 250 μm × 250 μm × 500 μm. Biomechanically determined failure load showed significant correlations with all FEM, up to r=0.85 and did not significantly change with lower resolution but decreased with high thresholds, due to loss of trabecular connectivity. CONCLUSION When choosing connectivity-preserving thresholds, both micro-CT- and MDCT-based finite-element-models well predicted failure load and still accurately revealed the distribution of local micro-strains in spatial resolutions, available in vivo (250 μm × 250 μm × 500 μm), that thus seemed to be the optimal compromise between high accuracy and low computation time.