Knee Proprioception Test (Joint Position Sense): Protocol and Error Values

The knee proprioception test, or Joint Position Sense Test, assesses something that's often overlooked in assessments: the body's ability to "know" what angle a joint is at without looking at it. It's especially relevant for knees that have suffered a ligament injury, since proprioception often remains impaired even after strength and mobility have been restored.

If you work with athletes in advanced phases of knee rehabilitation, this test helps you detect a deficit that won't show up on an X-ray or a strength test.

What does this test measure?

The test measures joint repositioning error: the difference between a reference knee angle (which the subject memorizes with their eyes closed) and the angle the subject is able to actively reproduce, also with their eyes closed.

The larger the error in degrees, the worse that joint's proprioceptive ability to detect and reproduce its position.

Equipment needed

• A goniometer (or a smartphone goniometry app)
• A table or chair where the subject can sit with the leg hanging freely
• A blindfold (or simply ask them to close their eyes)

Execution protocol

1. The subject sits on the edge of a table, with the leg being assessed hanging freely and the knee flexed at 90°
2. Ask them to close their eyes
3. Passively move the subject's leg to a reference angle (for example, knee extension to 40° of flexion) and hold it for a few seconds, asking them to "memorize" that position
4. Return the leg to the starting position (90° of flexion)
5. Ask the subject to, actively and with eyes still closed, reproduce the memorized angle by extending or flexing the knee on their own
6. Measure the angle reached with the goniometer and calculate the difference in degrees from the reference angle (repositioning error)
7. Repeat 3-5 times per leg and calculate the average error

Common mistakes

• Not making sure the subject keeps their eyes closed throughout the entire process (if they open their eyes, the attempt is invalid)
• Moving the subject's leg too fast when positioning it (makes proprioceptive "memorization" harder)
• Not comparing with the healthy contralateral leg, which is the most useful reference in unilateral injuries

How to interpret the result

Repositioning error	Interpretation
< 3-5°	Normal proprioception
5-8°	Mild-to-moderate deficit, common in early phases of ACL rehabilitation
> 8-10°	Notable deficit — proprioception should be a priority goal of the program

The most practical reference is usually comparison with the healthy leg in unilateral injuries: a difference of several degrees between both legs indicates that the injured knee hasn't yet fully recovered its proprioceptive capacity, even if strength and mobility are already good.

Related tests

• Romberg test on an unstable surface — assesses proprioception more globally (whole body), while this test is knee-specific
• Y Balance Test — combines proprioception with dynamic functional control, useful as a next step once joint position sense has improved

Track a deficit that's invisible at first glance

A proprioceptive deficit is one of the hardest things to "sell" to an athlete, because it doesn't hurt or show up in daily life, but it's linked to a higher risk of re-injury. Having a number (the error in degrees) that improves session by session makes it much easier to justify why you keep including proprioceptive exercises in the program. In Movalytics you can record the repositioning error for each leg at every assessment and show your athlete how that number drops with training.

Frequently asked questions

Is a digital goniometer necessary? No, a standard manual goniometer is sufficient. What matters is consistency in how the goniometer arms are placed between measurements. When does it make the most sense to include this test? Especially in mid-to-advanced phases of rehabilitation after an anterior cruciate ligament (ACL) injury, meniscectomy, or any injury that required prolonged immobilization. Can proprioception be trained? Yes, and it actually improves fairly quickly with specific exercises (unstable surfaces, eyes-closed exercises, motor control work), which makes this test very useful for showing short-to-medium-term progress.