What distance does CORI use to size the femoral implant?

• A. The distance between the tidemark and intercondylar notch.
• B. The distance between the tidemark and the posterior femoral condyle.
• C. The distance between the most posterior point and the tidemark.
• D. The distance between the anterior eminence ridge and tidemark.

Answer: (C)

In CORI sizing, the key measurement is the posterior bone depth of the distal femur, taken from the tidemark—the cartilage-bone boundary—to the most posterior point of the distal femur. This distance reflects how much bone stock is available behind the cartilage at the back of the knee and is used to select a femoral implant size that fits the posterior aspect properly, ensuring full coverage without overhang. The other landmarks don’t provide the standard posterior depth used for sizing: the tidemark to the intercondylar notch isn’t the typical reference for posterior stock; tidemark to a posterior condyle point can be imprecise for overall depth; and measuring from an anterior ridge assesses front structure, not the posterior fit.