Leg Length Discrepancy

Shortening of a leg length is called leg length discrepancy.

The common types are; anatomical, functional, and combined (anatomical and functional).

  • Anatomical (structural) in which there is an actual shortening of the limb. This shortening can lead to pelvis tilting and compensatory spinal curves such as scoliosis.
  • Functional or Unloaded leg-length alignment asymmetry is secondary to the abnormal position of the foot, sacroiliac joint, pelvis, hip, and muscle spasm.

Is it structural or functional limb length?

Observe for a presence of scoliosis with the patient in a standing position. Then, observe the disappearance of scoliosis when the patient sits down. You can assume a functional shortening if patient’s scoliosis disappears during sitting down.

In structural discrepancy, anterior and posterior portions of the pelvis is usually low on the short leg side.

Causes

Typically, causes associated with leg length asymmetry included but not limited are the flat foot,
genu valgum, coxa vara, poor standing posture, or asymmetry in bone growth (Kisner 716).

Also, weakness of gluteus medius, over-lengthening of the limb during surgery, malpositioning of
prosthetic component (usually acetabular component), recurrent postoperative dislocation, and
total hip arthroplasty (Kisner 727) and open reduction and internal fixation (Kisner 739).

Common features associated with short Vs. long Leg

Unilateral Short Leg Unilateral Long Leg
Same side Pelvic drop
Side bend the trunk (lumbar) to the opposite side Side bending toward the same side
Rotation of the lumbar spine to the same side (Ref) Lumbar rotation to the opposite side
Convexity of the lumbar spine to the same side
Flexion and distraction of the lumbar facets Extension and compression of the lumbar facets
Coxa Vara Coxa Valga
Genu Valgum Genu Varum
Anteversion Retroversion
Pes Planus
Lowered ilium Elevated ilium
Hip Abduction Hip Adduction
Vertical Sacroiliac joint
Increased compression stress on SI Joint/hip joint Increased shear stress on SI joint/hip joint
Tight hip abductors Tight hip adductors
Stretched or weak hip adductors Stretched or weak hip abductors
Distracts IV disc Compresses IV disc
Narrowing of IV foramina
Degenerative changes of the hip/spine is more frequent
Stenosis
Flexion contractures at hip and knee Abduction contractures at hip (2)
Equinus deformity at the ankle

When it needs treatment?

  • Limb length discrepancy of less than ¾ inch usually need no correction.
  • Limb length discrepancy of equal or more of 1/8 inch with symptoms of imbalance needs correction.
  • Asymmetries of ¾-1½ need heel lift or foot correction.

Greater than 1½ inches need a prosthetic shoe, and major discrepancy may require surgery.

How to measure?

Accurate measurement of the leg length is essential to provide best possible treatment. The tape measure, standing on blocks, and imaging procedures are commonly used to measure the leg length symmetry. All of these methods are not error-free due to various reasons such as positioning of the patient, differences in leg circumferences, angular deformities, contractures, difficulty palpating bony
prominences, rater reliability, and bias.

Tape Measure

Tape measure is used to measure functional shortening. Researchers recommend calculating averages of two tape measurements (direct) to increase validity and reliability.

Direct – A tape measure is used to measure the length from anterior superior iliac spine to medial malleolus.

Apparent – A tape measurement from umbilicus to medial malleolus.

Standing Blocks (Indirect method)

The investigator palpates the posterior superior iliac spines with the patient in a standing position. Then, add 1/16 inch of calibrated blocks under the short leg until the spines are level. However, we use this method typically for measuring anatomical limb length discrepancies.

Other Methods

Various professionals in the medical field used the following methods for measuring leg length discrepancy, but these methods need more research to support their use and effects.

  • ASIS to the Lateral malleolus
  • Prone leg exam
  • Visual postural analysis
  • Handheld instruments to check the pelvic tilt

References will be provided soon.

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