Leg Length Test

Original Editor"' - Candace Goh Top Contributors - {{Special:Contributors/Leg Length Test}

Purpose

The purpose of this test is to assess leg length difference of leg length discrepancy (LLD).

Leg length discrepancies are usually classified into two groups: true and functional.

True LLD are those in which an actual bony asymmetry exists somewhere between the head of the femur and the mortise of the ankle.

Functional LLD are those which occur as a physiological response to altered mechanics along the kinetic chain anywhere from the foot to the lumbar spine giving the appearance of a short leg when a bony asymmetry in the length of bones might not actually exist.

Technique

Direct Method:

• Involves measuring limb length with a tape measure between 2 defined points, in the stand. Two common points are the anterior iliac spine and the medial malleolus or the anterior inferior iliac spine and lateral malleolus
• Be careful, however, because there is a great deal of criticism and debate surroundings the accuracy of tape measure methods. If you choose this method, keep the following topics and possible errors in mind:
  • Always use the mean of at least 2 or 3 measures
  • If possible, compare measures between 2 or more clinicians
  • Iliac asymmetries may mask or accentuate a limb length inequality
  • Unilateral deviations in the long axis of the lower limb (eg. Genu varum,…) may mask or accentuate a limb length inequality
  • Asymmetrical position of the umbilicus
  • Joint contractures

Indirect Method

• Palpation of bony landmarks, most commonly the iliac crests or anterior iliac spines, in standing. These methods consist of detecting if bony landmarks are at (the horizontal) level or if limb length inequality is present.
• Palpation and visual estimation of the iliac crest (or ASIS) in combination with the use of blocks or book pages of known thickness under the shorter limb to adjust the level of the iliac crests (or ASIS) appears to be the best (most accurate and precise) clinical method to asses limb inequality.
• You should keep in mind that asymmetric pelvic rotations in planes other than the frontal plane may be associated with limb length inequality. A review of the literature suggests, therefore, that the greater trochanter major and as many pelvic landmarks should be palpated and compared (left trochanter with right trochanter) when the block correction method is used.

The PALM (Palpation Meter)

• The PALM is a reliable and valid instrument for measuring pelvic height difference. It is convenient, cost-effective, and is a good alternative to radiographic measurement.
• Measurement Procedure: 2 tape strips were placed on the ground, 15cm apart. The tape strips mark the location on the floor where patients have to place their feet. The patients are asked to walk for 10 steps and align the medial borders of their feet with the outside of the tape strips. Patients have to stand fully erected (no knee or hip or spine bending). The PALM is placed on the most superior aspect of the iliac crest. The distance between caliper heads is measured to the nearest mm and the angle of inclination to the nearest half degree. The inclinometer ball is designed to move towards the side of the shorter limb.

Standing on Blocks

• The patient is standing with feet 10 cm apart, knees extended and equal weight on both feet.
• The clinician places his/her hands on a bilateral anatomical structure: Spina iliaca posterior superior, Spina iliaca anterior superior, or crista iliaca left and right. Now the clinician visually assesses if there is a length inequality, and if so, places a wooden board of 0,5 cm under the foot of the shorter side.
• Keep placing thicker planks under the shorter side until the equal length is reached, the thickness of the plank is equal to the leg length difference.
• Although reliability is highly dependent on the accurate measurements of the clinician, this method has shown excellent results in inter-examination results between highly trained clinicians and medical students. Confounding variables reported by literature are pelvic asymmetry, incorrect positioning of feet, obesity, joint contractures, scoliosis, and inaccurate measurement.

Imaging Method :

A wide range of imaging methods can be used, including :

• Plain Radiography:

1. Orthoroentogenogram
2. Scanogram
3. Teleoroentgenogram: a full-length standing AP radiograph of the lower extremity.

• Computed Radiography.
• Micro-dose Digital Radiography: another form of computer-aided imaging that substantially reduces the radiation exposure to patients in comparison with conventional radiographic techniques.
• Ultrasound: In this technique, the ultrasound transducer is used to identify the bony landmarks at the hip, knee, and ankle joints.
• CT Scanogram : anteroposterior (AP) scout view of the bilateral femurs and tibias are obtained.
• MRI Scan: MRI images were obtained using a T1 weighted spin echo sequence and the best coronal images were selected for standardized assessment of femoral length using the classic bony landmarks of the femoral head and medial femoral condyle.

Special Tests:

• Supine exam

Resources

• Methods for Assessing Leg Length Discrepancy

References

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