Leg Length Test – Assessment of Leg Length Discrepancy (LLD)

Leg Length Test is used to assess discrepancies in leg length, also known as Leg Length Discrepancy (LLD). This condition can be classified into two main categories:

• True LLD → A genuine bony asymmetry measured between the femoral head and the talocrural joint (ankle).

• Functional LLD → An apparent difference caused by altered biomechanics, pelvic tilt, spinal alignment, or lower limb asymmetries [1].

A correct assessment of leg length is essential, as LLD can affect gait, posture, and load distribution throughout the kinetic chain, leading to hip, knee, and spinal dysfunction.

Methods for Measuring Leg Length

1. Direct Method (Tape Measure Test)

The traditional method is performed with a measuring tape:

• Measurement from ASIS (Anterior Superior Iliac Spine) to the medial malleolus.

• Alternatively, from AIIS (Anterior Inferior Iliac Spine) to the lateral malleolus.

Sources of error:

• Asymmetrical pelvic alignment can mask or exaggerate discrepancies.

• Malalignment of the lower extremity (e.g., genu varum/valgum).

• Inter-examiner variability.To improve reliability, the measurement should be repeated several times [2][3].

2. Indirect Method (Visual Inspection and Palpation)

This method evaluates pelvic height by palpating iliac crests and ASIS landmarks.

Block correction technique:

• The patient stands with feet ~10 cm apart.

• Wooden blocks are placed under the shorter limb until the pelvis is level.

• The thickness of the blocks corresponds to the discrepancy.

Sources of error: pelvic rotation or improper foot placement may produce false results [4].

3. PALM Measurement (Palpation Meter)

The Palpation Meter (PALM) is a standardized device for measuring pelvic height differences.

Procedure:

• The patient walks a few steps and stands with feet parallel.

• PALM is placed on the iliac crests.

• The vertical difference and angular displacement are recorded.

Advantages:

• Less subjective than palpation alone.

• A cost-effective alternative to radiographic assessment [5].

4. Standing on Blocks Test

This clinical test provides high inter-rater reliability:

• The patient stands with feet 10 cm apart, weight evenly distributed.

• The clinician palpates ASIS and PSIS landmarks.

• Blocks are inserted under the shorter leg until pelvic leveling is achieved.

Sources of error: pelvic rotation, joint contractures, or scoliosis may affect accuracy [6].

5. Imaging (Gold Standard)

The most accurate assessment of LLD requires imaging techniques:

• X-ray (orthoroentgenogram, scanogram, teleoroentgenogram).

• Low-dose digital radiography (reduced radiation exposure).

• Ultrasound (for hip, knee, and ankle landmarks).

• CT scanogram, providing precise femoral and tibial length measurement.

• MRI, particularly T1-weighted images for evaluating femoral length and bony landmarks.

Imaging is the gold standard but is costly and not always readily available [6].

Interpretation of Results

Test	Advantages	Limitations
Tape Measure Test	Simple, quick, no equipment	Low accuracy, affected by pelvic tilt and malalignment
Palpation of ASIS/iliac crests	Fast, can be performed standing	Examiner dependent, influenced by pelvic rotation
Standing on Blocks Test	High inter-rater reliability	Requires precise alignment
PALM Measurement	Standardized, reliable, inexpensive	Requires special device
Radiography/CT/MRI	Most precise, detects other pathologies	Costly, radiation exposure (except MRI/US)

Clinical Relevance

• True LLD can lead to hip/knee/back pain, pelvic obliquity, or functional scoliosis.

• Functional LLD may arise from muscular imbalance, pelvic rotation, or compensatory posture.

Small discrepancies (<10 mm) are common and usually asymptomatic. Larger differences, however, can significantly alter biomechanics and may require correction (shoe lifts, orthotics, or surgery) [1].

Conclusion

Leg Length Test is a key clinical assessment for detecting differences in leg length. Among clinical tools, the Standing on Blocks Test provides the most reliable clinical estimate, while PALM offers standardized accuracy. Imaging remains the gold standard for precise measurement. Differentiating between true and functional LLD is crucial for proper management and treatment.

Sources:

1. Leg Length Discrepancy Assessment: Accuracy and Precision in Five Clinical Methods of Evaluation [Internet]. Jospt.org. 2022 [cited 30 June 2022].

2. Brady RJ, Dean JB, Skinner TM, Gross MT. Limb length inequality: clinical implications for assessment and intervention. J Orthop Sports Phys Ther. 2003 May;33(5):221-34. Accessed 24 June 2019.

3. Gross MT, Burns CB, Chapman SW, Hudson CJ, Curtis HS, Lehmann JR, Renner JB. Reliability and validity of rigid lift and pelvic leveling device method in assessing functional leg length inequality. J Orthop Sports Phys Ther. 1998 Apr;27(4):285-94. Accessed 24 June 2019.

4. Standing Exam: Leg Length Inequality/Pelvic Symmetry Viewed on 30/06/2022

5. Petrone MR, Guinn J, Reddin A, Sutlive TG, Flynn TW, Garber MP. The accuracy of the palpation meter (PALM) for measuring pelvic crest height difference and leg length discrepancy. Journal of orthopaedic & sports physical Therapy. 2003 Jun;33(6):319-25.

6. Sabharwal S, Kumar A. Methods for assessing leg length discrepancy. Clinical orthopaedics and related research. 2008 Dec;466(12):2910-22.

7. Limb Length Discrepancy Viewed on 30/06/2022

8.  Supine Exam: Leg Length Inequality Viewed on 30/06/2022

9. Leg length discrepancy- what you should know Viewed on 30/06/2022