Effect of pathology type and severity on the distribution of MRI signal intensities within the degenerated nucleus pulposus: application to idiopathic scoliosis and spondylolisthesis

<p>Abstract</p> <p>Background</p> <p>Disc degeneration is characterized by a loss of cellularity, degradation of the extracellular matrix, and, as a result, morphological changes and biomechanical alterations. We hypothesized that the distribution of the MR signal intensity within the nucleus zone of the intervertebral disc was modified according to the pathology and the severity of the pathology. The objective of this study was to propose new parameters characterizing the distribution of the signal intensity within the nucleus zone of lumbar intervertebral discs, and to quantify these changes in patients suffering from spondylolisthesis or idiopathic scoliosis.</p> <p>Methods</p> <p>A retrospective study had been performed on T2-weighted MR images of twenty nine patients suffering from spondylolisthesis and/or scoliosis. The high intensity zone of the nucleus pulposus was semi-automatically detected. The distance "DX" between the center weighted by the signal intensity and the geometrical center was quantified. The sum of the signal intensity on the axis perpendicular to the longitudinal axis of the disc was plotted for each position of the longitudinal axis allowing defining the maximum sum "SM" and its position "PSM".</p> <p>Results</p> <p>"SM" was clearly higher and "PSM" was more shifted for scoliosis than for spondylolisthesis. A two-way analysis of variance showed that the differences observed on "DX" were not attributed to the pathology nor its severity, the differences observed on "SM" were attributed to the pathology but not to its severity, and the differences observed on "PSM" were attributed to both the pathology and its severity.</p> <p>Conclusions</p> <p>The technique proposed in this study showed significant differences in the distribution of the MR signal intensity within the nucleus zone of intervertebral discs due to the pathology and its severity. The dependence of the "PSM" parameter to the severity of the pathology suggests this parameter as a predictive factor of the pathology progression. This new technique should be useful for the early diagnosis of intervertebral disc pathologies as it highlights abnormal patterns in the MRI signal for low severity of the pathology.</p

Cutaneous lesions of the nose

Skin diseases on the nose are seen in a variety of medical disciplines. Dermatologists, otorhinolaryngologists, general practitioners and general plastic and dermatologic surgeons are regularly consulted regarding cutaneous lesions on the nose. This article is the second part of a review series dealing with cutaneous lesions on the head and face, which are frequently seen in daily practice by a dermatologic surgeon. In this review, we focus on those skin diseases on the nose where surgery or laser therapy is considered a possible treatment option or that can be surgically evaluated

A 1D elastic plastic damage constitutive law for bone tissue

Motivated by applications in orthopaedic and maxillo-facial surgery, the mechanical behaviour of cortical bone in cyclic overloads at physiological strain rates is investigated. To this end, a new one-dimensional rate-independent constitutive model for compact bone is proposed to simulate the damage accumulation occurring during tensile or compressive overloading. We adopted a macroscopic and phenomenological description of the mechanics of cortical bone. The mathematical formulation of the model is established within the framework of generalized standard materials and is based on the definition of three internal state variables: a tensile and a compressive damage variable that represent the microcrack density and a residual strain variable that represents the permanent strain associated with the sliding behaviour of these microcracks. Distinct damage threshold stresses are used in tension and compression. As the macroscopic mechanical behaviour of bovine cortical bone is very similar to that of human cortical bone and of much easier access, we first achieved the validation and identification of the material constants of the constitutive laws in tension using new uniaxial experimental results of bovine compact bone of our own. With adequate original hardening rules, the constitutive model is able to reproduce the main features of cortical bone behaviour under arbitrary cyclic tensile and compressive loadings. The proposed algorithm applies for the first time three distinct projections based on the relationship between the three internal variables and criteria. The predicted stress-strain curves exhibit a damaged reloading which is collinear with the origin as many cyclic overloading experiments on cortical bone have shown. Note that as our model was identified for physiological strain rates, it hardly can be applied in high strain rate situations like the ones involved in impact studies