Orthopedic Templating

Using Standard Orthopedic Templates with PACS

There is no reason why traditional orthopaedic template transparencies cannot be used with PACS.

All that is required is to ensure that the image on the monitor is zoomed such that the joint in question has the same degree of magnification as the templates. Once that is achieved, overlaying the templates over the image of the joint on the PACS monitor should allow a near perfect match.

The templates I have seen are magnified by 10% (DePuy), 15% (Protek) and 17% (Genesis).

We have radiopaque calibration discs available. They measure exactly 32 mm in diameter.  They are placed on the patient by the radiographic technician at the same plane as the joint in question; ie over the lateral trochanter for an AP hip Xray, and over the mid patella for a lateral knee Xray etc.

 

 

To use the template transparencies, you need to:

• Ascertain the magnification factor written on the template transparency and use the table below to tell you how big the image of the calibration disc should be on the monitor (eg 35.2mm for a magnification of 10%).
• Zoom the image on the monitor until the largest diameter of the disc is the size selected in the table, as measured manually using a clear plastic ruler placed on the monitor.

Magnification Factor	Size of Calibration Disc
10%	35.2 mm
15%	36.8 mm
17%	37.4 mm

 

• After this, you can pan the image but if you change the zoom, you will need to re-check the measurement.
• We have designed a credit card size ruler to be used with the 32mm disc, and it makes this task much easier.
• Once the image is correctly zoomed, superimpose and match the template to the joint in question.

The idea behind this is to ensure that you have a failsafe method that works and that is available wherever you have PACS.   I am certain that the method is far more accurate than what occurred with film, where magnification varied with the geometry of the equipment and no attempt was made to calibrate for this.

Lastly, the electronic programs to achieve the same ends are expensive, difficult to use, and it is likely that availability of the templates will lag behind your use of novel prostheses.

 

Tony Young
tony.young@crg.co.nz
2007