Fluid Bubble Method for Measuring Range of Motion

Range of motion is a measure of how much a joint can bend from fully extended. Doctors and physical therapists test ranges of motion to assess people's ability to function after a loss of motion in a part of the body. Several devices are used to measure those angles precisely; the bubble goniometer, or inclinometer, is among the most commonly used devices. Its use is also known as the fluid bubble method.

Fluid Bubble Device

• Mosby's Medical Dictionary defines a bubble goniometer as "a device used for measuring joint angles, consisting of a spirit level and a pendulum." According to Nancy Berryman Reese and William D. Bandy in their book "Joint Range of Motion and Muscle Length Testing," the device, which has a bubble level mounted in a 360-degree circular scale, has been around since the 1950s.

  "Strapping the device to the segment being measured and moving the segment causes the scale to rotate while the bubble remains stationary, thereby indicating the {range of motion] in the scale," Reese and Bandy explain.

  The fluid bubble goniometer can be used to measure motion in a shoulder, elbow, knee, ankle and cervical spine. For instance, to measure the range of motion of a person's elbow, the therapist places the device on the back of the patient's forearm with the scale set at zero as the patient holds his arm fully extended. Then the patient bends his arm as far as he can, and the therapist reads the scale when the arm is fully flexed.

  In 1988, a team of researchers led by Michele Petherick, then a recent physical therapy graduate from University of Health Sciences/The Chicago Medical School, compared the reliability of the readings from universal and fluid-based goniometers. Her group found "a significant difference" between the standard goniometer and the fluid-based goniometer. In tests, the fluid device was rated as highly reliable, while the standard goniometer had a much lower reliability rating.

  In a "Journal of Chiropractic Medicine" article, R.K. Pringle, from the Kelsey-Seybold Medical Group in Houston, Texas, reported that while the electrical inclinometer was the best measuring instrument, the less costly bubble goniometer was "just as reliable as the more expensive device."