This paper presents a segmentation method that outlines fractured bones in an X-ray image of a patient?s arm within casting materials, and displays the alignment between the fractured bones. This segmentation task is often difficult because the casting materials cause a low contrast and high noise ratio in the X-ray images. A geodesic active contour model with global constraints is applied to this task. A prior shape is collected and used as a global constraint of our model. A maximum-likelihood function is derived to provide feedback for each evolving process. Experimental results show that the method produces the outlines of the fractured bones on the low contrast X-ray images robustly and accurately.