Which element provides sagittal stability in KAFOs?

• A. An infrapatellar band
• B. Pretibial strap
• C. Straps providing posteriorly directed force
• D. Frontal plastic shell

Answer: (C)

Sagittal stability in a KAFO is about controlling movement in the knee’s flexion and extension. To keep the knee from bending too much or buckling during walking, you need a force that acts behind the knee to resist forward tibial movement relative to the femur. Straps that provide a posteriorly directed force accomplish this by creating a counter-moment at the knee, helping maintain alignment in the sagittal plane during stance and swing.

In contrast, an infrapatellar band mainly helps with patellar tracking and kneecap alignment rather than overall knee motion in the sagittal plane. A pretibial strap is on the front of the leg and influences anterior aspects of stability, not the sagittal knee mechanics, while a frontal plastic shell stabilizes the knee mostly in the coronal (side-to-side) plane rather than front-to-back movement.