[Update: Just noticed that when describing the radial features I initially swapped the locations for the styloid process (lateral) and the interosseous crest (medial) for the anterior view of the radius. This is why you don’t assemble your powerpoint slides late at night. If you downloaded the pdf before Feb 2, I’ve since updated, so you can get the corrected version below!]

The radius is a double-edged sword.

No, no, that’s not what I meant. The radius is a double-edged sword because it’s one of the easiest bones to identify and side when it is complete, and one of the trickiest long bones to deal with when it is fragmentary. However, after a few years of dealing with fragmentary radii, I have some tips and tricks to help you with identification and siding, even if you’re not working with a complete bone.

First off, the radius is one of the smaller long bones in the human body; when fragmentary it’s only likely to be confused with the ulna or portions of the fibula. If you’re having trouble wading through the bones of the forearm and leg, I have a handy flow chart that you can use to determine which of the smaller long bones your fragment likely comes from:

If you’re dealing with a very small portion of the shaft, examining the cross-sectional shape of the bone can often provide some insight:

The radius also has a suite of distinct features that are easily recognizable with a little practice:

Finally, If you’re having trouble orienting a relatively complete bone, the easiest way to do it is to use your own hand and forearm. To wit:

I’ve condensed these three sheets into a pdf guide to siding the radius that’s easy to print out and bring along to the lab or field.

Bone Broke Guide to Identifying and Siding the Radius

Thanks to Kyle Waller (Mizzou) for originally teaching me the forearm siding trick!

References: As always, I relied heavily on White & Folkens (2005) Human Bone Manual to double-check my terminology when composing this post.

Image Credits: The unedited images of the radius, ulna and fibula were originally found here and here, and the image of a double-edged sword found here. Distressed pug was found here, while teardrop icon was found at this site. Guernica replica found here, crazy concave loaf pans found here. Johnny Bravo cartoon here, guitar pick here, and red cylinder here. The unedited image of the radius and ulna and SAP found here.