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Leg Length Measurement

 Leg Length Measurement


Leg Length measurement tests assesses actual and functional leg length differences.

Measurement of an actual difference in leg length is performed with the patient standing by placing shims of varying thickness (0.5, 1, 2 cm ) underneath the shorter leg until the pelvic obliquity is fully compensated.

Compensation of the pelvic obliquity is usually readily apparent, especially when the patient bends forward from a standing position.

With the pelvis horizontal, the leg length difference corresponds to the total height of the shims placed beneath the foot. Evaluating leg length difference by palpating the iliac crests from behind the patient is often imprecise. Often the iliac wings (iliac crests) will not be at the same level although radiographic findings confirm identical leg length and a normal vertical spine. Asymmetric iliac wings are frequently encountered in conditions such as hip dysplasia. The iliac wing on the dysplastic side is usually smaller. Often only a pelvic radiograph obtained with the patient standing and showing the sacrum and lower lumbar spine will allow one to draw reliable conclusions about the type and severity of the leg length difference.

Actual shortening of the leg
Actual shortening of the leg: (a) The legs appear equally long with the patient standing. Shortening of the left leg is compensated for by pelvic obliquity and scoliotic posture. (b) The pelvic obliquity and scoliotic posture can be eliminated by placing shims under the leg.

Where placement of shims cannot compensate the pelvic obliquity, the patient has a fixed deformity of one or more joints or a fixed scoliosis leading to a functional leg length difference. This functional difference occurs as a result of a flexion or adduction contracture in the hip. The pelvis dips toward the normal side; the normal leg appears lengthened and the affected leg shortened.

Functional shortening of the leg
Functional shortening of the leg: (e) Adduction contracture on the right side. (f) The affected leg appears shortened and the normal leg lengthened

An abduction contracture in the hip causes a functional leg length difference. The pelvis dips toward the affected side; the normal leg appears shortened and the affected leg lengthened. An actual leg length difference is best evaluated and measured with the patient standing, a functional difference with the patient supine.

Functional lengthening of the leg
Functional lengthening of the leg: (c) Abduction contracture on the right side. (d) The pelvis dips toward the affected side. The normal leg appears shortened and the affected leg lengthened.

Leg Length Discrepancy Measurement Methods

Leg Length Discrepancy can be measured by one of the following methods:

Block Method

The block method of determining a leg-length difference. Blocks of a known thickness are placed under the shorter extremity.

Patient is standing on a firm surface with the feet shoulder-width apart and the weight evenly distributed while the examiner is standing in front of the patient. The starting levels of the iliac crests are noted. If heights are determined to be unequal, blocks of known height (measured in millimeters) are placed under the shorter leg until the iliac crests are of equal height. The leg-length difference is calculated by adding the heights of the individual blocks.

Positive Test if a leg-length difference of 10–20 mm is frequently cited as the level at which gait is affected. Patients who acquire the LLD at an early age may tolerate more difference. Patients who are athletic or must stand for much of the day may tolerate less.

When the iliac crests are level, palpate the heights of the anterior superior iliac spine (ASIS). If these are not an equal height, then the patient has asymmetrical innominate bones.

See Also: Coleman Block Test

Apparent Length Measurement

With patient in supine position and limbs kept in line with the trunk, measure the distance from the patient’s umbilicus or xiphisternum to the tip of each medial malleolus. Compare both.

Causes for the difference in the apparent length measurements include:

  1. pelvic obliquity,
  2. pelvic deformity,
  3. flexion deformity of hip or knee in one limb and a true leg length discrepancy.
leg Length Measurement
A: True Length Measurement. B: Apparent Length Measurement

True Length Measurement

Squaring up the pelvis is a necessary prerequisite for true length measurement. The affected hip is manipulated such that both ASIS are in same level.

The distance between the ASIS and the distal tip of medial malleolus is measured with the measuring tape on the affected side. The same is repeated on the opposite normal side keeping the limb in identical position as the affected limb. Both the distances are compared.

This gives the amount of true shortening or lengthening. If true lengths on both sides are equal and apparent lengths are different, functional or apparent leg length discrepancy is present.

leg length measurement with tape
Leg Length Measurement by using a Tape

Galeazzi Sign (Allis Test):

Galeazzi Test or Allis Test assesses leg length difference.

The patient is supine with the knees flexed 90° and the soles of the feet at on the examining table. The examiner assesses the position of both knees from the end of the table and from the side.

Normally both knees are at the same level. Where one knee is higher than the other, either the tibia of that side is longer or the contralateral tibia is shorter. Where one knee projects farther forward than the other, either that femur is longer or the contralateral femur is shorter.

The test for assessment of femur length is indicated as an additional test for evaluating hip dislocation. However, in such a case there is only an apparent difference in length; the femurs are the same length but one thigh appears shorter due to the hip dislocation.

Note that the Galeazzi test will yield a false-negative result in cases of bilateral hip dislocation.

Galeazzi sign
Galeazzi sign

Prone Test:

Chiropractors assess leg length with the patient prone. The comparative lengths of the legs are compared by observing the heels or the medial malleoli. If a discrepancy is noted, the knees are flexed to 90 degrees while maintaining neutral hip rotation, and the landmarks are reassessed to screen for a shortened tibia.

The patient is then positioned supine, and the leg lengths are reassessed using the same landmarks. Finally, the leg lengths are assessed using the long sit test.

Functional leg length inequality that is secondary to SI subluxation or dysfunction may reverse from the supine to sitting position, whereas anatomic leg length inequality or functional inequality secondary to dysfunction at other sites likely will not.

Functional Leg Length:

The patient stands with the feet shoulder-width apart. The clinician palpates the iliac crests, the ASISs, and the PSISs and compares the relative heights for asymmetry.

The patient is then positioned with the subtalar joints in neutral, the toes pointing forward, and the knees fully extended. The same landmarks are reassessed. If the second position corrects any asymmetry found in the first position, the test is positive for a functional leg length discrepancy and indicates that the leg is structurally normal but has abnormal joint mechanics.

Segmental Measurements

If a true leg length discrepancy is detected, next step is to determine whether it is at femoral level or at tibial level or both. Measure the distance from the ASIS to the medial joint line of the knee and the distance from the medial joint line of the knee to the distal tip of medial malleolus. Compare on both sides.

Notes

Some authors have claimed that a leg length discrepancy leads to mechanical and functional changes in gait and increased energy expenditure. Intervention has been advocated for limb-length discrepancies of less than 1 cm to discrepancies greater than 5 cm, but the rationale for these recommendations has not been well defined, and the literature contains little substantive information regarding the functional significance of these discrepancies.

For example, Gross found no noticeable functional or cosmetic problems in a study of 74 adults who had less than 2 cm of discrepancy and 35 marathon runners who had as much as 2.5 cm of Leg Length Discrepancy.

References

  1. Hanada E, Kirby RL, Mitchell M, Swuste JM. Measuring leg-length discrepancy by the “iliac crest palpation and book correction” method: reliability and validity. Arch Phys Med Rehabil. 2001 Jul;82(7):938-42. doi: 10.1053/apmr.2001.22622. PMID: 11441382.
  2. Bergmann TF, Peterson DH, Lawrence DJ: Chiropractic Technique: Principles and Procedures. New York, NY: Churchill Livingstone, 1993.
  3. Moseley CF: Leg-length discrepancy. In: Morrissy RT, ed. Lovell and Winter , s Pediatric Orthopaedics, 3rd ed. Philadelphia, PA: J. B. Lippincott, 1990:767–813.
  4. Song KM, Halliday SE, Little DG: The effect of limb-length discrepancy on gait. J Bone Joint Surg Am 79A:1690–1698, 1997.
  5. Gross RH: Leg length discrepancy: How much is too much? Orthopedics 1:307–310, 1978.
  6. Clinical Tests for the Musculoskeletal System 3rd Edition.
  7. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.

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