Assessment of axial bone rigidity in rats with metabolic diseases using CT-based structural rigidity analysis.

OBJECTIVES: This study aims to assess the correlation of CT-based structural rigidity analysis with mechanically determined axial rigidity in normal and metabolically diseased rat bone. METHODS: A total of 30 rats were divided equally into normal, ovariectomized, and partially nephrectomized groups. Cortical and trabecular bone segments from each animal underwent micro-CT to assess their average and minimum axial rigidities using structural rigidity analysis. Following imaging, all specimens were subjected to uniaxial compression and assessment of mechanically-derived axial rigidity. RESULTS: The average structural rigidity-based axial rigidity was well correlated with the average mechanically-derived axial rigidity results (R(2) = 0.74). This correlation improved significantly (p < 0.0001) when the CT-based Structural Rigidity Analysis (CTRA) minimum axial rigidity was correlated to the mechanically-derived minimum axial rigidity results (R(2) = 0.84). Tests of slopes in the mixed model regression analysis indicated a significantly steeper slope for the average axial rigidity compared with the minimum axial rigidity (p = 0.028) and a significant difference in the intercepts (p = 0.022). The CTRA average and minimum axial rigidities were correlated with the mechanically-derived average and minimum axial rigidities using paired t-test analysis (p = 0.37 and p = 0.18, respectively). CONCLUSIONS: In summary, the results of this study suggest that structural rigidity analysis of micro-CT data can be used to accurately and quantitatively measure the axial rigidity of bones with metabolic pathologies in an experimental rat model. It appears that minimum axial rigidity is a better model for measuring bone rigidity than average axial rigidity.

Design and manufacture of a novel system to simulate the biomechanics of basic and pitching shoulder motion.

OBJECTIVES: Cadaveric models of the shoulder evaluate discrete motion segments using the glenohumeral joint in isolation over a defined trajectory. The aim of this study was to design, manufacture and validate a robotic system to accurately create three-dimensional movement of the upper body and capture it using high-speed motion cameras. METHODS: In particular, we intended to use the robotic system to simulate the normal throwing motion in an intact cadaver. The robotic system consists of a lower frame (to move the torso) and an upper frame (to move an arm) using seven actuators. The actuators accurately reproduced planned trajectories. The marker setup used for motion capture was able to determine the six degrees of freedom of all involved joints during the planned motion of the end effector. RESULTS: The testing system demonstrated high precision and accuracy based on the expected versus observed displacements of individual axes. The maximum coefficient of variation for displacement of unloaded axes was less than 0.5% for all axes. The expected and observed actual displacements had a high level of correlation with coefficients of determination of 1.0 for all axes. CONCLUSIONS: Given that this system can accurately simulate and track simple and complex motion, there is a new opportunity to study kinematics of the shoulder under normal and pathological conditions in a cadaveric shoulder model.

Contrast agent electrostatic attraction rather than repulsion to glycosaminoglycans affords a greater contrast uptake ratio and improved quantitative CT imaging in cartilage.

PURPOSE: The purpose of this study is to evaluate the effect of contrast agent charge on the contrast agent uptake ratio (CUR) in cartilage and to image the naturally occurring variations in glycosaminoglycan (GAG) content present in bovine articular cartilage. METHODS: In an ex vivo bovine osteochondral plug model, we utilized three charged contrast agents (Gadopentetate/Magnevist [-2], Ioxaglate/Hexabrix [-1], and CA4+ [+4]) and µCT to image cartilage. The X-ray attenuation of the cartilage tissue after equilibration in each contrast agent was also related to the initial X-ray attenuation of each contrast agent in solution to compute the uptake of the respective contrast agent (i.e., the CUR). RESULTS: Use of the cationic contrast agent resulted in significantly higher equilibrium X-ray attenuations in cartilage ECM than either of the anionic contrast agents (Gadopentetate [-2] and Ioxaglate [-1]). The CUR (Mean±SD) as computed in this study was 2.38 (±0.26) for the cationic contrast agent indicating a 2.38 fold increase in computed tomography (CT) attenuation of the cartilage. For the anionic contrast agents, the CUR was 0.62 (±0.26) for Ioxaglate [-1] and 0.52 (±0.17) for Gadopentetate [-2], indicating exclusion of 38% Ioxaglate and 48% Gadopentetate from the cartilage extracellular matrix. The cationic contrast agent exhibited significant correlations between CT attenuation and GAG content whereas Ioxaglate and Gadopentetate did not (R(2)=0.83 for CA4+, R(2)=0.20 for Ioxaglate, and R(2)=0.22 for Gadopentetate). CONCLUSION: Electrostatic attraction of CA4+ allowed effective imaging of the GAG components of articular cartilage at 50% lower molar concentration than Ioxaglate and 20-fold lower molar concentration than Gadopentetate. The CA4+ contrast agent exhibited a significant correlation between CT attenuation and GAG content in ex vivo bovine osteochondral plugs.

Contrast enhanced computed tomography can predict the glycosaminoglycan content and biomechanical properties of articular cartilage.

OBJECTIVE: An early hallmark of osteoarthritis (OA) is the progressive loss of glycosaminoglycans (GAGs), the extracellular matrix (ECM) component of articular cartilage that confers it with compressive stiffness. Our aim in this work is to establish the feasibility of using Contrast Enhanced Computed Tomography (CECT) with an anionic iodinated contrast agent - Cysto Conray II - as a minimally invasive tool to measure the changes in the GAG content as well as the compressive stiffness of articular cartilage. METHODS: The GAG content of mated osteochondral plugs excised from bovine patello-femoral joints was progressively degraded using chondroitinase ABC. The mated plugs were then immersed in an anionic, tri-iodinated contrast agent, imaged using peripheral quantitative computed tomography (pQCT), subjected to an unconfined compressive stress relaxation test and the GAG content measured using 1,9-dimethylmethylene blue (DMMB) assay. Partial correlation analysis was performed to compare the variation in X-ray attenuation measured by pQCT to the variation in GAG content and in equilibrium compressive modulus. RESULTS: The X-ray attenuation of cartilage exposed to an anionic, tri-iodinated, contrast agent measured by quantitative computed tomography (QCT) accounted for 83% of the variation in GAG content (r(2)=0.83, P<0.0001) and 93% of the variation in the equilibrium compressive modulus (r(2)=0.93, P<0.0001). CONCLUSION: Using a mated osteochondral plug model to evaluate the biochemical composition and biomechanical properties of cartilage, this study demonstrates the interrelationships between X-ray attenuation, GAG content, and equilibrium compressive modulus, and that CECT can be used to monitor and quantify changes in the GAG content and biomechanical properties of articular cartilage.

Chronic refractory idiopathic thrombocytopenic purpura (ITP) and anti-CD20 monoclonal antibody: a case report.

Idiopathic thrombocytopenic purpura (ITP) is an immune-mediated disorder characterized by accelerated and premature destruction of platelets by reticuloendothelial system. CD20, a trans-membrane B-cell-specific antigen, is a potential target for treatment of certain malignant and nonmalignant plasma cell disorders including refractory ITP. Rituximab is a genetically engineered human anti-CD20 monoclonal antibody, which is approved for the treatment of low-grade non-Hodgkin's lymphoma. Recent clinical reports suggest that rituximab may be useful in treating certain patients with chronic refractory ITP. A 59-year-old woman with refractory ITP was placed on rituximab (four weekly doses of 375 mg/m(2)) and her condition and platelet count were observed for 18 months. There was a gradual increase in platelet count and she was symptom free in this period and no side effects of the drug were reported. Anti-CD20 antibodies are likely to be used in the treatment of refractory ITP cases, but further studies about treatment schedule and criteria for patient selection should be done.