I'm not well versed in all classifications. I put some examples in there to give you an idea. It could be maformations, deformations, rotational displacements, abnormal length ratio's of bones etc. You can select the option 'Other' and may address the abnormaility in the comment section if you like to do so. Maximum votes are 3, if you, for example, got one of the examples shown and some other skeletal/bone abnormaility.