Goniometry Basics
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Direct answer
Three landmarks anchor every goniometric measurement: the axis or fulcrum placed over the joint's centre of motion, the stationary arm fixed along the proximal segment and the moving arm aligned with the distal segment. A universal goniometer — a 180 or 360 degree protractor with two overlapping arms — quantifies the arc of motion objectively, so progress reads as numbers rather than as "slightly better". Measurement is performed in the same test position each time, at both active and passive end of range, and recorded as start and end angles, for example knee flexion 0–110 degrees. Intratester reliability beats intertester reliability, which is why one therapist should follow one joint throughout a programme.
What you must remember
- Parts of the universal goniometer: the body (protractor scale), the axis point and the two arms; sizes vary — a small 6-inch instrument for the wrist and hand, a large 12-inch one for the hip and knee, and this matching is a standard MCQ.
- Alternate instruments: gravity and digital inclinometers (preferred for the spine), hydrogoniometers, electrogoniometers for continuous recording.
- Procedure in fixed order: position and stabilise the proximal segment, palpate bony landmarks, move the joint through the arc, read at end range, and average at least two or three trials.
- Bony landmarks worth memorising: shoulder axis lateral to the acromion or greater tubercle, elbow axis over the lateral epicondyle, knee axis over the lateral femoral epicondyle, ankle axis below the lateral malleolus.
- Representative norms: shoulder abduction 0–180, elbow flexion 0–150, forearm pronation and supination about 0–80 to 90, hip flexion 0–120 with the knee bent, knee flexion 0–135, ankle dorsiflexion 0–20, cervical rotation about 0–80 each side.
- Record the convention correctly: active and passive values documented separately, hyperextension beyond zero written as such, and the uninvolved limb measured as the control whenever it exists.
- Visual estimation under-reads restriction; goniometry remains the department standard for documenting contractures, serial plasters and Medicolegal progress.
Measuring knee flexion properly
Begin supine, hip flexed and comfortable, because a tight rectus femoris will otherwise steal flexion from the knee and flatter your record. Expose the landmarks: lateral femoral epicondyle for the axis, greater trochanter for the stationary arm, lateral malleolus for the moving arm.
Ask for active flexion first — heel sliding toward the buttock — and read the arc at its active end; then passively follow to the passive end, feeling the end-feel as you read again. Say the patient reaches 0–95 against a normal of 0–135: the 40-degree deficit is the contracture you are treating, and the end-feel recorded beside the number tells you whether the limit is muscle, capsule or bone. Repeat twice more; discard a first reading taken while the patient was still learning the instruction.
Two errors corrupt most student readings. The axis drifts off the epicondyle as the knee bends, so realign the arms at end range before reading. And the pelvis is left unstabilised, allowing pelvic tilt and lumbar movement to masquerade as hip motion during related hip tests — the same principle applies here, since a rolling pelvis changes the knee's arc. Document as "knee flexion AROM 0–95, PROM 0–100, firm end-feel, right", with the date and the tester's name; whoever measures at review must replicate every element of that setup, including side-lying versus supine, or the numbers are not comparable.
Where students slip
The recurring confusions are which arm goes where — the stationary arm belongs to the proximal segment, always — and mixing active with passive records between sessions. Students also misread 360-degree instruments, recording 240 instead of 120 for knee flexion, and forget that goniometer size must match the joint. In viva, expect the landmark question ("Where is the axis for elbow flexion?") and the reliability question: intratester reliability exceeds intertester reliability, so continuity of therapist is the practical answer.
Frequently asked questions
Which goniometer arm is aligned with the moving segment?
The moving arm follows the distal segment; the stationary arm is fixed along the proximal segment.
Where is the axis placed for measuring knee flexion?
Over the lateral epicondyle of the femur, with arms along the femur (greater trochanter) and fibula (lateral malleolus).
What are the normal active ranges of elbow and knee flexion?
Elbow flexion 0–150 degrees and knee flexion 0–135 degrees are the standard textbook values.
Why must the pelvis be stabilised during hip measurements?
Unstabilised pelvic tilt and lumbar movement substitute for hip motion, falsely enlarging the measured range.
Which instrument is preferred for measuring spinal motion?
Inclinometers — gravity-based or digital — as recommended for the spine in standard measurement texts.