Range of Motion (ROM) testing measures the distance and direction a joint can move. This assessment provides a value, expressed in degrees, that quantifies a joint’s mobility. Health professionals, including physical therapists, occupational therapists, and physicians, rely on ROM tests to assess the health of a joint and surrounding soft tissues. The results establish a baseline for a person’s physical function, which is important following an injury, surgery, or a chronic condition. Understanding joint movement is the first step in diagnosing limitations and developing an effective treatment plan.
Understanding Active Versus Passive Movement
The assessment of joint mobility is separated into two primary categories: active and passive. Active Range of Motion (AROM) measures the movement a person can achieve using only their own muscle strength. AROM demonstrates the functional capacity of the muscles to contract, motor control, and the willingness to move without external assistance. A limitation found during AROM suggests an issue with muscle weakness, pain on contraction, or impaired motor control.
Passive Range of Motion (PROM) involves an external force, such as a clinician, moving the joint while the person remains completely relaxed. Since the muscles are not actively engaged, PROM assesses the structural integrity of the joint capsule, ligaments, and the extensibility of non-contractile soft tissues. PROM is typically slightly greater than AROM because the external force can gently push the joint past the point where the person’s own muscles would stop.
The comparison between AROM and PROM is key to pinpointing the source of a mobility restriction. If a person’s AROM is significantly restricted but their PROM is normal, the limitation is likely due to muscular weakness or a painful muscle contraction. Conversely, if both AROM and PROM are restricted to a similar degree, the problem is more likely structural, involving joint stiffness, capsular tightness, or a bony block. This differential assessment allows the clinician to determine whether the intervention should focus on strengthening and motor control or on joint mobilization and stretching of soft tissues.
Standardized Tools and Techniques for Measurement
The primary tool used to quantify joint movement is the goniometer. This device is a large protractor with two arms: a stationary arm, a movable arm, and a central axis point called the fulcrum. Measurements are taken in degrees, with the starting position of a joint, such as the anatomical position, generally defined as zero degrees.
The clinician first positions the person appropriately, often lying down or seated, to ensure stability of the body segment proximal to the joint being tested. The goniometer’s fulcrum is then carefully aligned over the estimated axis of rotation of the joint. Specific bony landmarks are used to align the stationary arm with the fixed bone segment and the movable arm with the moving bone segment.
The person is instructed to move the joint through the required motion, or the clinician moves it passively, until the end of the available range is reached. At this endpoint, the movable arm is realigned with the distal segment, and the angle is read directly from the protractor scale. The accuracy of the measurement depends on correct anatomical alignment and the stabilization of adjacent joints to isolate the desired movement.
While the goniometer is the standard, other tools offer specialized utility for measuring motion. For instance, an inclinometer, which uses gravity to determine angular position, is often preferred for measuring the range of motion in the spine. Digital goniometers and smartphone applications also exist, providing rapid, though sometimes less precise, readings. Adherence to standardized testing protocols is necessary to ensure reliable and repeatable results for comparison over time.
Interpreting Results and Clinical Significance
The measured angle is compared against established normative data, which represents the expected range of motion for a specific joint based on factors like age and gender. These normative values act as guidelines, offering a reference point to identify deviations from the typical range. However, a person’s movement is rarely judged solely against these norms, as their opposite, unaffected limb often serves as a more individualized and accurate comparison.
Restricted ROM, known as hypomobility, suggests a lack of joint excursion and indicates pathology or injury. This limitation can be caused by muscle guarding due to pain, inflammation within the joint, long-term immobilization leading to soft tissue contracture, or structural damage such as arthritis. Conversely, excessive ROM, or hypermobility, may indicate ligamentous laxity, which can predispose the joint to instability or injury.
The results of ROM testing inform the clinical decision-making process and treatment planning. If a significant deficit is found, it establishes measurable goals for recovery, such as increasing shoulder flexion by 20 degrees. The type of restriction identified—muscular versus structural—determines the intervention, leading to prescription of targeted strengthening exercises, passive stretching, or joint mobilization techniques. Reassessment of ROM provides objective evidence of the treatment’s effectiveness and monitors the person’s progress toward functional recovery.