For Surgeons

Scaling

As the scaling factor (magnification) is annotated directly on the image, all that is required is to type the scaling factor into the templating software. Orthoview, used as an example below, uses an edit box named oversize.

If radiographers follow the protocol the magnification factor can be found in the lower right corner in the form of xxx RT where xxx is the magnification in percent (e.g. 122 RT means 122% measured on the right hip).

Practically every templating software solution allows the user to enter the magnification directly during the x-ray calibration stage, without referencing a radio opaque object.

Accuracy

The use of calibration devices has caused concern regarding accuracy, excessive use of x-rays, infection  control and increased workload for the radiology department. Our study (download 1MB) compares XCalibR agains other scaling techniques. 

35 consecutive hip replacements had routine post operative AP pelvic x-rays. Magnification was calculated using a  Calibration Ruler, a Laser method and a calibration ball. 

These methods utilise the greater trochanter as an indirect measure of the height of the hip joint.  The three techniques were compared against “Real magnification”. Real Magnification could be calculated since the size of the  arthroplasty components was known. 

The Calibration Ruler and Laser methods were accurate to 0.8% (0 –3.0%) and 1.4% (0% –3.4%) respectively.  The Calibration Ball was accurate to 11.2% (0 –16.8%). The Calibration Ball was least popular with the patients  (94% men, 100%women). Both the Calibration Ruler and Laser methods are quick and easy to learn and acceptable to  patients and radiographers. The equipment, especially the calibrated ruler, is small, light, robust and inexpensive.