In the paper the new approach for cognitive modeling of some medical structures, using picture grammar have been presented. Especially was discussed the method of artificial intelligence dedicated to the syntactic-based semantic inference of selected RTG visualizations with particular attention to the leg bones. The presented methodology makes possible to describe for each biological structure, its semantic characteristics, and allow to formulate a semantic meaning of pathological deformation. Presented approach proofed that cognitive informatics based on semantic formalisms can be used to develop a new classes of intelligent Computer-Aided Diagnosis systems. Such systems authors called UBIAS- Understanding Based Image Analysis Systems.