March 7, 2013

Leg length difference

Leg length difference is a common occurrence. Most people do not have legs that are in fact exactly the same length – we are not perfect mirror opposites between left and right. For a number of reasons, leg length can be significantly different between the left and right sides, these include;

  • a congenital defect that has affected the growth of the bones of the leg
  • an angular deformity which affects the overall functional length in weight bearing (eg ‘bowed’ legs)
  • certain medical conditions which can affect bone growth (eg Rickets)
  • trauma, fractures and previous surgery
  • significant arthritic damage causing joint narrowing

In most instances, patients can discover they have a leg length difference of 5mm or more, and be completely unaware of it. It may not be until they undertake strenuous weight bearing acitivity (eg marathon running) until this small difference creates pain or discomfort in certain areas of the foot, ankle, knee, hip or lower back. Usually, differences of at least 10-15mm are required before they become symptomatic with normal daily activities.

CT scanogram for leg length difference

CT scan to assess leg length difference following knee replacement

Any difference beyond that point is almost certain to cause symptoms – either in the foot, leg or lower back.

Leg length difference can be difficult to assess clinically, especially if the difference is small or there is some degree of obesity present. In these situations, a CT scout scan (scanogram) (see above) is performed to provide the most accurate measurements of the tibia and femur bones. However, this is a non weight-bearing assessment, and does not fully take into account any other functional changes or compensations that occur once the legs are loaded, or rotational issues around the pelvis or lower back.

Leg length difference is particularly common after a hip or knee replacement, especially if the procedure was done as a revision for a previous replacement. Considerable bone loss can occur during the fitting of the artificial joint, leading to obvious changes post-operatively.

Treatment of pain related to true leg length difference is usually quite simple. A sole raise made for either inside (for small differences) or external to the shoe is the most preferred option, as the entire foot is raised to compensate for the inequality. Smaller differences may simply be managed with a heel lift in the back of the shoe – though this less desirable from a clinical perspective, it is a far simpler and more practical option for most patients.

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