Leg length discrepancy

Leg Length Discrepancy: What Is It and Could It Be Causing Your Pain?

A leg length discrepancy means one leg is shorter than the other. It can be a real difference in bone length (structural). Or it can be an apparent difference caused by pelvic tilt or muscle imbalance (functional). Even a small difference can change how you stand and move. Over time, this can create pain in the hip, back or knee.

Key points

A leg length discrepancy can be structural (bone length) or functional (related to alignment and muscles).
Pain often appears in the hip, lower back or knee, rather than in the shorter leg itself.
Imaging done lying down can miss the difference, because gravity and relaxed muscles hide it.
A standing, full-body scan measures both legs while they carry your real body weight.
Accurate measurement is the first step, so that any management plan addresses the right cause.

What is the difference between structural and functional leg length discrepancy?

A structural leg length discrepancy is a measurable difference in actual bone length between the two sides. A functional discrepancy is when the bones are similar in length, but the legs look unequal. This is because of the way the pelvis, hips or muscles are positioned.

Structural means the thigh bone (femur) or shin bone (tibia) is truly shorter on one side. You may have been born with this. It can also result from a fracture that healed with some shortening, or from a joint replacement. A structural discrepancy does not change when you stretch or correct your posture.

Functional means the bones may be the same length, but a tilted pelvis, tight hip muscles or a scoliosis makes one leg look shorter. This type can sometimes improve with targeted exercises or manual therapy. This is because the underlying cause is muscular or postural, not skeletal.

Knowing which type you have matters. A shoe lift may help a structural discrepancy but could make a functional one worse. Accurate, weight-bearing imaging helps clinicians tell the difference.

What are the symptoms of a leg length discrepancy?

Many people with a small discrepancy feel nothing at all. When symptoms do appear, they usually show up away from the shorter leg itself, in the places that are compensating.

Lower back ache The spine curves to make up for the uneven pelvis, loading one side more than the other.

Hip pain on one side The hip joint of the longer leg carries extra load, especially when walking or standing for a long time.

Knee or ankle strain A change in the way you walk puts uneven stress through the knee or ankle on either side.

Uneven walk or limp You may notice you lean to one side, or others might comment on an uneven walk.

If you have sudden numbness, weakness in either leg, or any loss of bladder or bowel control, get urgent medical help from your doctor or the nearest emergency department. These are red-flag symptoms that need immediate assessment.

What causes one leg to be longer than the other?

There are several reasons one leg can end up shorter, or look shorter. Some are present from birth. Others develop over time.

Growth variation The bones on one side simply grew a little more or less during development.

Fracture or surgery A healed break, or a hip or knee replacement, can change the effective length of the leg.

Joint wear Arthritis in the hip can wear the joint down, which in effect shortens that side.

Pelvic tilt or scoliosis A tilted pelvis or a curve in the spine can make the legs look unequal, even when the bones match.

Your body is a connected chain from your feet to your head. When one link changes, the links above and below adjust to keep you balanced. That is why a short leg can lead to hip pain, a curved spine or a sore knee. The pain often appears well away from the original cause.

How is leg length discrepancy measured when you are standing up?

The most reliable way to assess a leg length discrepancy is to image the whole body while you stand on both feet. Your muscles and gravity then do what they normally do. Imaging done lying down relaxes the muscles and lets the pelvis settle into a neutral position. This can hide a functional discrepancy completely. It can also make a structural one harder to measure accurately.

Illustration of leg length discrepancy assessment at the ScanAlign clinic

An EOS scan captures both legs, the pelvis, spine and feet in a single standing image using about 90% less radiation than a standard X-ray, around ten times less. Because it images you upright, the picture shows how your body actually lines up under load. Your clinician can then see whether the discrepancy is structural, functional, or a mix of both.

Not sure whether a standing scan in London would help in your case?

Book a free video consultation

How is leg length discrepancy usually managed?

Management depends entirely on the type and size of the discrepancy, and on the symptoms you have. ScanAlign is a diagnostic imaging clinic, not a treatment provider. The role of the scan is to give you and your clinician accurate, weight-bearing measurements to guide the right next step.

In general terms, options that clinicians may consider include:

Observation. Small discrepancies with no symptoms may need no intervention at all.
Shoe lift or insole. For structural discrepancies, a heel lift can level the pelvis and reduce the strain of compensating. The correct height depends on accurate measurement.
Physiotherapy or exercise. Functional discrepancies caused by tight muscles or pelvic tilt may respond to targeted strengthening and stretching.
Surgical review. Larger structural discrepancies, or those linked to a previous fracture or replacement, may need assessment by an orthopaedic specialist.

Whatever the approach, it starts with knowing the exact situation. A standing, whole-body image gives clinicians the full picture of alignment, rather than a guess based on a tape measure or a lying-down scan.

So before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.

When MRI is the better tool. EOS shows bones, joints and alignment clearly. If your clinician suspects soft-tissue problems, nerve compression or disc issues, MRI is usually the better choice. The two scans work well together.

Frequently asked questions about leg length discrepancy

How do I know if I have a leg length discrepancy?+

Common clues include uneven wear on your shoes, a noticeable lean to one side, or persistent pain in the hip, back or knee on one side. A standing scan is the most reliable way to confirm and measure it.

Can a small leg length difference really cause pain?+

Yes. Even a small difference can tilt the pelvis, which forces the spine and joints to compensate. Over months or years, this extra strain can lead to pain in places well away from the shorter leg.

What is the difference between a functional and structural leg length discrepancy?+

Structural means the bones are truly different in length. Functional means the bones are similar, but muscle tightness, pelvic tilt or a curve in the spine makes one leg look shorter. Treatment differs for each type, so an accurate diagnosis matters.

Why is a standing scan better for measuring leg length?+

When you lie down, gravity and relaxed muscles let the pelvis settle into a neutral position. This hides the way your body truly lines up. Standing imaging captures both legs, the pelvis and spine while they carry your real body weight, giving a much more accurate measurement.

Is an EOS scan safe?+

Yes. An EOS scan uses about 90% less radiation than a standard X-ray, around ten times less. You can find more details on safety, preparation and what to expect on our FAQs page.

Do I need a referral from my doctor to get a scan at ScanAlign?+

No. ScanAlign is a private, self-pay clinic. You can refer yourself directly. We recommend starting with a free video consultation, so we can check that a standing scan is the right next step for you.

How much does a scan for leg length discrepancy cost?+

The price for patients travelling from abroad is confirmed during the free video consultation, and you can read more on our FAQs and cost page.

Will a shoe lift fix my leg length discrepancy?+

A shoe lift can help level the pelvis when the discrepancy is structural and has been accurately measured. If the discrepancy is functional, caused by muscle or alignment issues rather than bone length, a lift alone may not address the root cause. Accurate imaging helps your clinician decide what is appropriate.

Can leg length discrepancy cause hip or knee arthritis?+

Research suggests that a long-standing discrepancy can place uneven load on the hip and knee joints, which may contribute to wear over time. Finding it early and managing it properly can help reduce that uneven strain.

What happens during a free video consultation?+

You speak with a specialist diagnostic radiographer who reviews your symptoms and history. They will tell you whether a standing, whole-body scan is likely to add useful information in your case. There is no obligation to go ahead.

Find out what is really going on

A standing, whole-body scan shows your true alignment under load. Start with a free video consultation from home to see if a scan in London is right for you.