Vector analysis of porosity evidences bone loss at the epiphysis in the BTX rat model of disuse osteoporosis

International audience

<p>Introduction</p><p>Botulinum toxin (BTX) injected in a muscle causes paralysis with a subsequent bone loss. It represents a model of disuse osteoporosis. Although bone loss has been regularly evaluated at the metaphysis of long bones, little is known concerning the bone changes occurring in the epiphysis.</p><p>Animals and methods</p><p>Ten Copenhagen male rats received a single BTX injection in the Mus quadriceps femoris on the right side and unilateral paralysis developed in the following days. Animals were euthanized after 28 days; femur and tibia were harvested and analyzed by microCT. Vector analysis of porosity was applied to the 2D sections and produced a frontal image with mapping in pseudo-colors. This allows quantitative analysis at the epiphysis and metaphysis. “Hot spot” were evidenced and indicated bone loss. Quantitative analysis of these images was done by decomposition of the R, G and B planes and deriving the ratio of R + G pixels on the whole pixel number.</p><p>Results</p><p>At the metaphysis, this ratio was correlated with measurement of the bone volume obtained by microCT. At the epiphysis, which has a complex shape in 3D, the method easily identified the bone loss.</p><p>Discussion</p><p>Paralysis of a unilateral quadriceps induces bone loss at the metaphysis of the long bones. However, the epiphysis, having a reduced bone remodeling is also concerned by disuse. MicroCT analysis of this part of the bones is difficult due to its complex shape in 3D. Vector analysis is a new and robust method to quantify bone loss in such complex areas.</p>