What normal knee range of motion is
The normal range of motion reference chart lists knee flexion of about 135 degrees and extension of 0 degrees, and records a deficit as a negative number (for example -10 degrees short of straight). Physiopedia lists comparable values (flexion up to about 150 degrees, extension 0) and describes how goniometry notes a starting angle when neutral cannot be reached.
Why full extension matters
A knee that fully straightens shares load efficiently and lets you walk without a compensatory limp. Losing the last few degrees of extension changes gait and can overload other structures, which is why clinicians prioritize restoring it after injury.
Common non-injury reasons a knee feels stiff
In a healthy knee, stiffness can come from inactivity, swelling after a hard session, or simply age-related change, since knee norms vary and decline with age. Gentle range work and strengthening usually help mild, non-painful stiffness.
When it points to an injury
How range is restored after injury or surgery
After an injury or surgery, restoring extension and flexion is guided by a clinician and progressed gradually. Forcing a stuck knee is not the answer, and pushing hard through a blocked joint can set recovery back.
Track knee range responsibly with ROMRx
For a healthy knee, ROMRx Base tracks your flexion and extension over time and compares sides, so you notice a meaningful change and know when to get something checked.
Frequently asked questions
What is a normal knee range of motion?
Roughly 0 degrees of extension (fully straight) to about 135 degrees of flexion, though some people reach up to about 150 degrees. Full, pain-free extension is the key marker.
Why won't my knee fully straighten?
In a healthy knee it can be stiffness or swelling. If it follows trauma or comes with locking, catching, or giving way, it may signal an injury and should be assessed by a clinician.
Is a locked knee an emergency?
A knee that is truly locked, cannot bear weight, or is significantly swollen should be evaluated promptly. Do not force it to move.
How is knee range restored after surgery?
Gradually and under clinician guidance, restoring extension and flexion with progressive exercises. Timelines and methods depend on the specific injury or procedure.
Can stiffness be normal in a healthy knee?
Mild, pain-free stiffness from inactivity or aging is common and often responds to gentle range work and strengthening. Painful stiffness, locking, or swelling is not something to push through.