Range of motion (ROM) refers to the amount of movement available at a joint, measured in degrees. This assessment is used in orthopedic and rehabilitation medicine, focusing on knee flexion (bending) and extension (straightening). Reliable measurement of knee ROM is necessary for tracking recovery, establishing baselines after injury or surgery, and providing objective data for prognosis and insurance justification. The universal documentation system ensures all healthcare providers can interpret the functional capabilities of the knee joint.
Preparation and Setup for Accurate Measurement
Accurate measurement requires a universal goniometer, which features a stationary arm, a moving arm, and a central fulcrum. The patient must be positioned consistently to ensure reliable data, typically supine (lying on the back) for both flexion and extension measurements. Stabilizing the hip and pelvis is necessary to prevent compensatory movements that could artificially inflate the measured range of motion.
Before moving the knee, the goniometer must be aligned with the joint’s anatomical landmarks. The fulcrum (center axis) is placed over the lateral femoral epicondyle (the bony prominence on the outside of the thigh bone). The stationary arm is aligned with the lateral midline of the femur, using the greater trochanter of the hip as a reference point.
The moving arm is aligned with the lateral midline of the fibula, using the lateral malleolus at the ankle as a reference. This alignment of the three points establishes the zero position and is necessary for obtaining a measurement that reflects true knee joint movement. Maintaining this consistent setup for both the starting and ending positions is the foundation of reliable goniometry.
Standardized Measurement Procedure
Measurement begins by assessing the starting point of knee extension. In the standardized 0-180 degree system, 0 degrees represents a fully straight leg. If the knee cannot fully straighten, this lack of extension (extension lag) is measured by the degrees short of zero. For example, if the knee stops 10 degrees before full extension, the starting point is recorded as 10 degrees.
Hyperextension occurs when the knee extends beyond the neutral 0-degree position and is measured as a value preceding zero. The patient is often placed prone (lying on the stomach) with the foot off the edge of the table to allow gravity to assist in finding maximal extension. The goniometer is aligned, and the reading is taken at the point of maximal extension, whether it indicates a lag, neutral zero, or hyperextension.
To measure knee flexion, the patient is typically supine, and the hip is slightly flexed to slacken the rectus femoris muscle, permitting maximum knee bending. The examiner guides the patient’s lower leg, first asking for Active Range of Motion (AROM), where the patient moves the joint themselves. The goniometer remains aligned with the landmarks, and the reading is taken at the terminal point of the active movement.
If indicated, Passive Range of Motion (PROM) is measured by the examiner gently pushing the knee further into flexion until a firm or soft end-feel is met. The terminal degree is then recorded. Normal knee flexion often ranges between 120 and 150 degrees, though values vary based on age and body type.
Correct Documentation Format
The universal notation system uses the 0-180 degree system, defining the anatomical neutral position as 0 degrees. Documentation must include the joint measured, the type of range assessed (AROM or PROM), and the specific notation of the starting and ending degrees of motion. This provides a complete functional picture of the joint’s capability.
The standard format uses the starting degree followed by the ending degree, separated by a hyphen. For a knee with normal motion, documentation is recorded as $0^\circ – 135^\circ$. This numerical expression communicates the full arc of movement, from 0 degrees of extension to 135 degrees of flexion.
When a limitation in extension exists, the starting point is a positive number, such as $10^\circ – 135^\circ$, indicating a 10-degree extension lag. If hyperextension is present, the notation includes the hyperextension degree, the neutral zero, and the flexion degree, such as $5^\circ – 0^\circ – 135^\circ$. Every entry must also be accompanied by the date, time, and the examiner’s initials to ensure accountability and track changes over time.