Knee ROM Guide

Knee Extension Range of Motion Measurement Guide

KneeExtensionSagittal planeCustom in appUpdated 2026-09-27

Measurement Snapshot

MovementExtension
PlaneSagittal plane
Primary MusclesQuadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius)

There is no single value that establishes normality for every person or method. Record the setup and compare measurements in clinical context.

Knee extension and extension deficit are closely tracked after ACL reconstruction and total knee arthroplasty because a lingering flexion contracture affects gait. Interpret with the surgical timeline.

Standardized Setup

Patient Position
Place the patient supine with a small support under the ankle so the knee is free to reach full extension, or use long sitting for a functional view.
Stabilization
Stabilize the femur and prevent hip rotation so the value reflects tibiofemoral extension rather than limb rotation.
Landmarks
Use the lateral femoral epicondyle as the axis, the greater trochanter as the proximal reference, and the lateral malleolus as the distal reference.

Step-by-Step Measurement

  1. Support the ankle so the knee can settle toward full extension.
  2. Calibrate the baseline and read the angle at the available end range.
  3. Document any extension deficit as a positive number of degrees from zero.
  4. Record active and passive extension separately when both are measured.

Common Measurement Errors

  • Failing to free the knee, which hides a real extension deficit.
  • Reading hyperextension as a deficit or vice versa.
  • Allowing hip rotation to change the apparent tibial alignment.

Custom Cobb Angle Pro Workflow

The app does not provide a named protocol for this movement. Use Custom as the body part, choose the movement, and apply your own clinical measurement method.

  1. In Range of Motion, choose Custom as the body part, then Extension as the movement. The app does not provide a named Knee Extension protocol.
  2. Choose Photo, Camera, or Phone Sensor and use your own measurement setup. Custom measurements have generic in-app guidance rather than a reviewed movement-specific protocol.
  3. Record Knee Extension, side, position, and method in the case label or notes so the saved Custom measurement can be interpreted later.

References

  1. Norkin CC, White DJ. Measurement of Joint Motion: A Guide to Goniometry. 5th ed. F.A. Davis Company; 2016.
  2. Petersson LE, Nilsson H. Reliability of knee joint range of motion measurements. Physiotherapy Res Int. 2002;7(2):87-95.

Frequently Asked Questions

How should knee extension measurements be interpreted?

Record the measured value with the side, patient position, method, and active or passive status. Compare repeat measurements made the same way and interpret them with the full clinical context; one value alone cannot establish normality or a diagnosis.

What is a knee extension deficit?

An extension deficit, or flexion contracture, is the number of degrees the knee falls short of full straightening. It is commonly tracked after knee surgery because it affects gait mechanics.

How do you measure extension without missing a deficit?

Support the ankle so the knee is free to settle into extension. Measuring on the table with the calf blocked can hide a real deficit.