gms | German Medical Science

Objectives/Interrogation: To explore how engineering drawing analysis can be applied to understand xrays of complex fractures.

Engineering drawing is a technical and graphical language with its own rules. It is useful to apply the principles of engineering drawing to complex radiographs when the supplied views do not supply enough information to identify the bones or fracture fragments.

Methods: The engineering drawing principle that is important in the application to interpreting radiographs is that in an isometric projection, the shortest distance between a point and a plane will be equidistant in all planes that contain that line and are perpendicular to the first plane. This principle is clearest when presented in an example.(NOTE: the abstract program does not allow uploading of images, which are an essential part of this submission.)

In this isometric projection of a house, the red line in the left view, called a front elevation view, will be the same length in the side elevation view on the right. It will also be the same length in any view in which the image of the house is rotated on the line (the plane of view will contain that line).

In radiology terms, a front view is a PA view, and the side view is a lateral view. Importantly, any view involving only pronation or supination (the oblique views) will show all distances which are purely proximal-distal as true-length lines. There is a restriction, which is normally easily met: the magnification of the radiology views must be the same.

Results and Conclusions: This method is best explained with an example.

In this complex wrist radiograph, the PA looks almost normal, but the lateral looks seriously abnormal. The presentation will demonstrate how engineering drawing principles can sort it out.

This view appears to clearly show the lunate:

But an engineering analysis shows that it is not, a different shadow on the lateral is the lunate: Identify the lunate on the PA, and extend horizontal lines to the lateral. The margins of the lunate must lie on these lines. The lines identify a different shadow on the lateral as the lunate.

So what is the apparent "lunate"?

It is a proximal scaphoid,which is fractured.

An engineering drawing analysis can help to identify fragments and bone in the PA, any oblique, or lateral view, as long that the images are taken with rotation about a longitudinal line, which is the same as any degree of pronation and supination. This can be helpful in analyzing complex fractures or dislocations.