Abstract
Radiographs historically have not been standardized according to magnification. Depending upon the size of a patient, a film will either magnify a bone and joint (of large patients with more soft tissue) or minify (in the case of thin patients). An orthopedic surgeon must guess at the degree of over or under magnification to select an implant that is neither too large nor too small. The surgeon may be aided by the incorporation of a marker of known size. By calculating the difference between the size of the marker displayed on the film and the actual size of the marker, the orthopedic surgeon can identify the degree of magnification/minimization and compensate accordingly when selecting a prosthetic template.
This activity takes time and also is subject to mathematical error. Digital pre-op planning allows for an image to be displayed electronically, and with the use of a known sized marker, automatically calculate the magnification and recalibrate the image so that it is sized at 100% from the perspective of the user.
Digital pre-op planning incorporates a library of electronic templates of prostheses, which can be standardized to exactly match the size of diagnostic image being displayed. Traditionally, an orthopedic surgeon places an acetate template enlarged to be 110% to 120% over an X-ray film magnified to be110% to 130%. When there is a significant variation in magnification between the template and the procedure, this can contribute to surgical error. This type of error will be virtually eliminated with digital templating that has the capability to identically scale electronic templates to the X-ray image being displayed. Digital pre-op planning enables surgeons to select from a library of templates and electronically overlay them on an image as well as perform the necessary measurements critical to the templating procedure which not only speeds up this process but, as will be shown, has the potential of delivering unprecedented accuracy.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
