Structural and functional imaging of normal bone marrow and evaluation of its age-related changes

Sensitivity of tissue differentiation and bone healing predictions to tissue properties

Computational models are employed as tools to investigate possible mechano-regulation pathways for tissue differentiation and bone healing. However, current models do not account for the uncertainty in input parameters, and often include assumptions about parameter values that are not yet established. The aim was to clarify the importance of the assumed tissue material properties in a computational model of tissue differentiation during bone healing. An established mechano-biological model was employed together with a statistical approach. The model included an adaptive 2D finite element model of a fractured long bone. Four outcome criteria were quantified: (1) ability to predict sequential healing events, (2) amount of bone formation at specific time points, (3) total time until healing, and (4) mechanical stability at specific time points. Statistical analysis based on fractional factorial designs first involved a screening experiment to identify the most significant tissue material properties. These seven properties were studied further with response surface methodology in a three-level Box-Behnken design. Generally, the sequential events were not significantly influenced by any properties, whereas rate-dependent outcome criteria and mechanical stability were significantly influenced by Young's modulus and permeability. Poisson's ratio and porosity had minor effects. The amount of bone formation at early, mid and late phases of healing, the time until complete healing and the mechanical stability were all mostly dependent on three material properties; permeability of granulation tissue, Young's modulus of cartilage and permeability of immature bone. The consistency between effects of the most influential parameters was high. To increase accuracy and predictive capacity of computational models of bone healing, the most influential tissue mechanical properties should be accurately quantified.

Cord Compression due to Extramedullary Hematopoiesis in an Adolescent with Known Beta Thalassemia Major

We describe a 16 year-old male with β thalassemia major and gait disturbances that had not been given blood transfusions due to a severe childhood transfusion reaction. Thoracic spine MRI demonstrated hematopoietic marrow throughout the spine and epidural masses causing cord compression consistent with extramedullary hematopoiesis (EMH). After treatment with steroids, radiotherapy and monitored blood transfusions, the patient demonstrated significant improvement of his paraspinal lesions and near complete resolution of his neurological symptoms. While EMH causing cord compression in adolescents is rare in the current era of bone marrow transplantation or chronic transfusions, it should be considered when thalassemia major patients present with neurological deficits. The well defined imaging features of EMH can play a central role in its diagnosis and management, especially because surgical and / or radiotherapeutic intervention are often considered in cases of failed medical treatment.