Fig 1.
Lateral radiograph showing placement of the magnification marker stand with the 100 mm magnification marker placed on the 20 mm step. A 25 mm ball marker (round white object) is adjacent to the MMS for a relative comparison. Note that the left femur diameter is magnified compared to the right side. This is because the right downside was closer to the receiver. The right proximal femur is near center beam to minimize the parallax effect.
Fig 2.
Example ventrodorsal radiograph.
Ventrodorsal radiograph with the magnification marker stand and the 100 mm magnification marker placed on the 60 mm step, with a portion of the marker stand cropped out. The radiography software (eFilm 3.3, a Sound-Eklin VCA Antech Company, Carlsbad, CA) was used to recalibrate for magnification to 10.0 cm and to superimpose the implant cup and stem templates with their identity tags. A 25 mm diameter ball marker (round dark object) was sitting tabletop near the end of the MMS with the 100 mm MM for comparison. The 100 mm distance reflects the distance as measured from the center of one ball bearing to the center of the other. Likewise, the distance is 100 mm from ball bearing edge to corresponding edge because both ball bearings are the same size.
Fig 3.
Magnification marker on magnification marker stand device.
A. The magnification marker stand device with the 100 mm magnification marker adjacent to the 60 mm step. The MMS has a 20, 40, 60, and an 80 mm step for the MM to rest atop. The numbers are metallic so the height of the MM can be confirmed on the radiographs. B. A radiograph of a magnification marker stand shows the 100 mm magnification marker on the 60 mm step when the image was captured. Use of the MMS provides a permanent record of the MM height when an image is captured.
Table 1.
Demographic information, implant size predictions, and magnification marker stand height used for dogs in this study.
Table 2.
Information when the templating process failed to predict an implant.
Fig 4.
Example total hip replacement case.
This case demonstrates that implant size primary prediction is not always the same as the implant selection used (secondary prediction in this case). The images are corrected for 12% magnification using the 100 mm magnification marker set on the 40 mm height above the radiology table. The cup and the stem were both in between 2 sizes in the presence of advanced osteoarthritis. Implants predicted to be used (primary plan) included a 26 mm cup and a #8 stem (A). Implants selected during surgery were a 24 mm cup and a #9 stem (secondary plan) (B). A 22 mm cup was a tertiary prediction for the worst-case scenario in anticipation of extensive acetabular filling with fibrotic tissue and bone plus extensive dorsal acetabular rim wear and flattening. If extensive intramedullary proximal femoral sclerosis would have been radiographically evident, a #7 femoral stem would have been available out of an abundance of caution.