Leg Length Test: How to Check for Leg Length Discrepancy

The Leg Length Test is a standard clinical measurement used to assess for a leg length discrepancy (LLD). It is crucial for differentiating between a 'True' (structural) and 'Apparent' (functional) difference.

1. Purpose

The primary purpose is to measure and differentiate between a "True" and "Apparent" leg length discrepancy (LLD).

• True LLD: An actual difference in the bone length of the femur or tibia.
• Apparent LLD: The legs appear to be different lengths due to functional issues like a pelvic tilt, scoliosis, or muscle contractures, even though the bones are the same length.

2. How to Perform

1. The patient is positioned in supine (lying on their back) and as straight as possible. The examiner should ensure the pelvis is level.

True Leg Length Measurement

1. Use a tape measure.
2. Measure from the Anterior Superior Iliac Spine (ASIS) to the Medial Malleolus (inner ankle bone).
3. Compare the measurement to the other side.

Apparent (Functional) Leg Length Measurement

1. Use a tape measure.
2. Measure from the Umbilicus (navel) to the Medial Malleolus.
3. Compare the measurement to the other side.

3. Positive & Negative Sign

A "positive" sign indicates a discrepancy (a difference between the two legs).

• Positive for True Leg Length Discrepancy: There is a difference (e.g., > 1-1.5 cm) in the "True" measurement (ASIS to medial malleolus).
• Positive for Apparent Leg Length Discrepancy: The "True" measurement is equal, but the "Apparent" measurement (umbilicus to medial malleolus) is different. This indicates a functional issue, like a pelvic tilt.

Negative Sign (Test is NEGATIVE):
A negative test is when both "True" and "Apparent" measurements are equal or have no significant difference.