What is the AAOS normative range for knee extension?

• A. 0-135 degrees
• B. 0-20 degrees
• C. 0-30 degrees
• D. 0 is normal, but up to 10 degrees of hyperextension

Answer: (D)

Knee extension is normally neutral at 0 degrees, but many people can extend a little beyond that—up to about 10 degrees of hyperextension. That means the normal extension range isn’t just 0; it can include a small amount of hyperextension without being considered abnormal. The AAOS standard reflects this: 0 is normal, with up to around 10 degrees of hyperextension acceptable.

This contrasts with numbers like 0-135 or 0-30, which describe how far the knee can bend (flexion), not how straight it can be. In practice, if someone cannot reach 0 degrees of extension or shows excessive hyperextension beyond ~10 degrees, it may warrant further assessment for stiffness or ligamentous laxity.