Dear Raju,
We have been using for so many year simple templates... The prediction rate at that time looked to me rather good and the sizes implanted were quite close to these expected before surgery. Since we've been using Ct-Scanner or MRI sizing it looks to me that the precision expected is rather hard to get. I guess that it depends on many factors such as the machine used, the radiologist's experience and the conditions of the examination itself. There are a lot of programs that can be used as well but except for angles the accuracy looks insufficient as well, at least for me... May be these insufficient results are possibly related to the Hospitals we're working in and maybe mine is not efficient enough in this matter, but talking with some Colleagues it looks like that I'm not the only one in this situation. Does that mean that you're facing the same difficulty? The problem is certainly related to the scale used that should be calibrated prior to any measure and for each patient... There are for sure lees difficulties for specific implants which are shaped after specific measures, in specific reproductible conditions with efficient calibers.
Not sure I've been of any help for this problem but from my own experience, the variation reaches sometimes 20% and is still unpredictable... So let me know what you think about it and if you have any issue for it...
Thank you Thierry. We have similar experience of using the CT technology. It can be inaccurate in about 1/4th of the cases and hence cannot be relied upon in its present form for component size prediction. CT seems to be a better technology than the MRI.
We studied eighty-eight knees in 58 patients underwent total knee arthroplasty (TKA) using computed tomography based patient-specific instruments between March 2015 to April 2016. All these patients were assessed for the preoperative femoral and tibial component sizes predicted by the CT-based pre-operative plan. These sizes were compared with the implanted sizes during surgery, and the results were assessed for any upsizing or downsizing of the components.
Approximately 72% predicted tibia sizes matched the final implanted sizes whereas 66% femoral implants matched their pre-operative predicted sizes. The difference in the tibial implant size was not statistically significant (p value >0.05). However, the difference in the femoral size was statistically significant (p value 0.009). Downsizing of the tibial component was needed in 14.8% knees whereas upsizing was required in 13.6% of the knees. At the femoral side, 22.7% components needed downsizing at the time of implantation as compared to 11.4% components wherein a bigger component was used.
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