How Leg Lengths Are Measured?

There is no universal acceptance about how much of a length difference is clinically significant, nor is there universal acceptance about which body landmarks should be used when analyzing the legs 

Every method for measuring leg lengths comes with limitations and some degree of error.

Physical Measurements Using a Measuring Tape

There are problems with using direct measurement over the skin in the supine position. These include difficulty in locating bone landmarks, poor positioning of the tape measure, and incorrect positioning of the patient’s limbs. Repeated measurements can yield quite different results. As a result, Dr. Horowitz no longer uses this method.

The pelvis has a certain amount of rotation that occurs at the pubic bones and sacroiliac joints, and pelvic rotation is common. This could lead to an inaccurate measurement.

X-Ray Measurements

Historically, the “gold standard” method for determining if there is a structurally short leg is by using a full-length standing X-ray that allows visualization of the entire leg and pelvis. 

Using X-rays exposes you to ionizing radiation, the effects of which accumulate in body tissues. 

There are numerous factors that can affect accuracy and reliability of X-ray measurements taken. For example:

• Was the floor completely level?
• Was the patient standing with their feet completely together?
• Was the patient wearing shoes, slippers orthotics or other devices?
• What landmarks were compared from side to side?
• Is there any hip osteoarthritis and changes that make landmarks difficult to compare?
• If each hip or knee is replaced separately, additional X-rays would need to be repeated to remeasure.

An X-ray that was taken in the supine or non-weight bearing positions cannot accurately determine leg length differences.

Visual Inspection and Testing using Heel Lifts

Heel lifts can be placed under your feet when you stand with your feet together. Dr. Horowitz can then check to make sure that:

• Your leg bones are now level 
• You feel more balanced and comfortable with a given lift

While it is true that visual inspection also involves inherent bias, there is little downside and risk in doing so. Factors that need to be considered include:

• The need for custom orthotics in addition to a heel lift
• Other conditions such as osteoarthritis in the foot, leg, and knee
• Genu valgus and varum (both increase measured values)
• Balance difficulties
• Inability to stand on both legs due to pain shortly after surgery
• Fixed flexion contracture of 15 degrees or greater of hip or knee

A significant aspect of the variability in the differences found visually is due to how the legs are positioned. There will be a different reading when the feet are placed together vs when they are placed casually apart. Choosing a landmark that does not inherently move is also important.