What is Leg Length Discrepancy?

A Leg Length Inequality or Leg Length Discrepancy is exactly as it sounds. One or more bones (the Femur or thigh bone, the Tibia or shin bone, and/or the joint spacing within the knee) are unequal in total length when measured in comparison to the same structures on the opposite side. It is common for people to have one leg longer than the other. In fact, it is more typical to be asymmetrical than it is to be symmetrical!

There are two anatomical factors that contribute to the development of leg length discrepancy:

Congenital Leg Length Discrepancy

Congenital, or the way your bones grew and formed from the time you were born. Keeping in mind that most Leg Length Discrepancy is inherited from one or both parents.

Acquired Leg Length Discrepancy

Acquired means that a particular trauma may have stunted the growth on one side, as in a broken bone, or perhaps as the result of an accident or a surgery to various boney structures or joints.

Beyond the two anatomical factors that can contribute to leg length inequality, there are two types of leg length discrepancies – anatomical and functional.

Anatomical Leg Length Discrepancy

This is also known as anatomical leg length inequality, which is a result of the bones (Femur and Tibia) not growing symmetrically.

Functional Leg Length Discrepancy

This is also known as functional leg length inequality, which is caused by muscular tightness, weakness and imbalance.

Leg Length Discrepancy Pain

What types of pain does it cause? As the body is connected via a series of bones, ligaments, tendons, and muscles, being uneven on one side causes excessive wear. Thus, practically any joint from head to toe can be negatively affected.

It is a regular occurrence for patients to tell me that their right knee hurts because they run or that a doctor told them that their left foot hurts because they ran too much.  It does not matter if it is your right foot, right knee or hip.  If your body part truly hurts because you ran why would it not hurt on both your right and left sides?  You obviously ran on both feet and legs!

When I point out to patients that one of their legs may be longer than the other, thus causing them to put more pressure on one side they usually seem perplexed.  “Don’t most people have one leg longer than the other?” they ask.  “Yes, they do.  But most people don’t run as much as you or run at all” I have to point out.  In fact, most Americans are overweight and do not even exercise much less run 20-30-50 miles a week.

When you do a repetitive motion such as running, small anatomical and biomechanical discrepancies can cause big trouble.  Studies have revealed that IN RUNNERS “As little as 3mm may be a primary cause of one-sided foot, leg, knee, hip or lower back pain and can possibly result in joint damage and arthritis”. The point is if you are sedentary and a classic “couch potato” who cares if one of your legs is longer, you are not using them anyway!

Leg Length Discrepancy Diagnosis

The only way to decipher between anatomical and functional leg length inequalities (you can have both) is by a physical measurement and series of biomechanical tests.  It is actually a simple process and gets to the true cause of some runner’s chronic foot, knee, hip and back pain.  After the muscles are tested and the legs are measured it may be necessary to get a special X-ray that measures both of your thighs (Femurs) and legs (Tibias).  The X-ray is read by a medical radiologist who provides a report of the actual difference down to the micrometer leaving zero room for error. Once the difference in leg length is known, the solution becomes clear.

Leg Length Discrepancy Treatment

There are many ways that Leg Length Discrepancy can be treated. Some are more risky and less effective than others.

Custom Orthotics

A properly made foot orthotic can go a long way in substituting additional millimeters or centimeter on the deficient side. Additional full length inserts are added to the shorter side bringing the runner closer to symmetrical.  Heel lifts do not work in runners because when you run you may land on your heel but the rest of the time you are on your forefoot then your toes pushing off. The right custom-made, biomechanical orthotic can address the underlying cause of your pain. Abnormal joint position, overpronation or foot rigidity can be addressed and the biomechanics normalized. San Diego Running Institute orthotics are custom molded to your foot and are designed with your specific body weight, leg length discrepancy, and activity in mind. The restoration of correct mechanical function takes the abnormal stress from the uneven side and allows the body to heal naturally.


We are often told  that muscles are too tight on one side and need to be stretched or lengthened in order to correct the leg length discrepancy. The problem is they are not following a scientific, research based approach. If they were, they would know that stretching a muscle will never increase the length of a shorter bone, or increase joint spacing in the knee or hip.


For many, rest/inactivity is not a realistic option. We need to use our bpodies for work, home, exercise, and play. If we are constantly putting excessive force on one side more than the other, we are eventually going to feel the wear ande tear and the damage that is being done daily. This comes in the form of ankle, knee, hip, back, and even shoulder pain. Uneven wear often results in unilateral arthritis and other unpleasant results. If you are a runner, these unwanted outcomes are sped up considerably. If your foot hits the ground 1,500 times in a one mile run, jut think of the cumulative damage that is done just by training for a single marathon. Our body truly is a wonderful “machine”. If you rest it long enough it will typically heal itself. But how long does it take to grow more bone? If you are over 18 years of age, this is no longer an option. And quite frankly, how does one get their bones to grow only on the short side anyway?


Drugs such as Ibuprofen are anti-inflammatory agents, not healing agents. They actually impair the healing process and may allow the runner to injure themselves further. Studies have proven that these medications are harmful to your biody, cause ulcers, and strain your liver and kidneys. They are not a solution to the pain caused by leg length inequality.


Many people undergo surgery for various reasons – arthritis, knee replacement, hip replacement, even back surgery. However, the underlying cause of leg length inequality still remains. So after expensive and painful surgery, follow by time-consuming and painful rehab, the true culprit still remains. Resuming normal activities only continues to place undue stress on the already overloaded side. Sadly so, years down the road more surgeries are recommended for other joints that now endure the excessive forces.

Who Can Help With Leg Length Discrepancy?

When the “quick fixes” fail and you are at your wits end the San Diego Running Institute can refer you to Dr. Allen, D.C. To schedule an appoin