Ignoring digital templating leads to prosthetic overhang in total knee replacement

Published studies on the accuracy of digital templating in total knee replacement (TKR) have employed standard knee, but not hip-to-ankle radiographs. A retrospective study was conducted in our hospital on patients undergoing TKR due to osteoarthritis in a period of six consecutive months. Templating was performed using a calibrating 25 mm metallic ball and Agfa Orthopaedic Tools software by a surgeon not involved with the operation. The surgeon performing the templating was blinded to the size of the implants inserted. Postoperative knee anteroposterior and lateral radiographs were then checked for the presence of prosthetic overhang of ≥ 3 mm. In total, 132 Caucasian adults were included in the study. Femoral overhang occurred in 33%, whereas tibial overhang in only 6% of cases. The exclusion of prosthetic overhang cases significantly improved the accuracy of size detection; exact match for femur increased from 55% to 69%, and for tibia from 70% to 73%. All implants were predicted to within one size in all cases. Digital templating using a calibrating 25 mm metallic ball, Agfa Orthopaedic Tools software and hip-to-ankle and knee lateral radiographs is an accurate method of predicting the knee implant to within one size. Ignoring this procedure leads to prosthetic overhang.