Leg length discrepancy: one leg longer than the other, what's normal and what helps

Small differences are normal

On accurate X-rays, about 9 in 10 people have legs of slightly different lengths, about 5 mm on average. The American Academy of Orthopaedic Surgeons says more than half of people have a subtle difference.

Sources 1, 2

Measure it properly

Hands and tape measures are rough guides: feeling the hip bones missed the true difference by about 4 to 5 mm. Blocks under the shorter foot are the most useful clinic test, and a standing X-ray of the whole leg is the reference.

Sources 3, 4

Usually not a cause of back pain

People with and without back pain have the same small differences. People who stand all day with a difference of 6 mm or more may be an exception.

Sources 1, 5, 6

A lift helps some people

In the best trial, insoles that corrected most of a measured difference eased back pain in people who stand at work, but the evidence overall is low quality. Most people with a small difference don't need one.

Sources 7, 8

After a hip replacement it often settles

About 1 in 3 people feel a difference after a hip replacement, but only about a third of them have one on X-ray, and most felt differences improve within a year.

Sources 9, 10, 11

Structural: the bones differ

The bones of one leg are shorter, and almost always one leg is short rather than the other long. In children, causes include conditions present from birth, nerve conditions such as cerebral palsy, and an injury, infection or tumour affecting a growth plate. In adults, a fracture that healed short or a joint replacement can do it.

Sources 12, 2, 13

Functional: the bones are equal

Something above or below makes one leg act shorter: a tilted pelvis, a curve in the spine, muscle tension, or a stiff hip or knee. After a hip replacement, about two thirds of the people who feel a difference have this kind.

Sources 14, 15, 16

What your body does with a difference

Standing evenly on both feet, the pelvis tips towards the shorter leg and the lower back bends sideways a little. On one leg, the hip muscles level the pelvis, and the authors of one review estimate most people spend only about half an hour a day standing evenly on both feet. Children with larger differences may tilt the pelvis, bend the knee of the longer leg or rise onto the toes of the shorter one.

Sources 12, 17, 2

About 9 in 10 peopleStrong evidence

In X-ray studies of 573 people, about 90% had a leg length difference, averaging 5.2 mm. The American Academy of Orthopaedic Surgeons says more than half of people have a subtle difference, and that these usually cause no problems.

Sources 1, 2

10 mm or more: about 15% to 20%Emerging evidence

In pooled X-ray studies, 15.5% of people without back pain had a difference of 10 mm or more, and 20.1% of a wider group that included people with back pain. A review gives a higher estimate of one in three, citing studies we couldn't check.

Sources 1, 12

Over 2 cm is uncommonEmerging evidence

A difference over 20 mm affects about 1 in 1,000 people, and in a French study about 1 in 1,000 had treatment for a difference over 2 cm.

Sources 1, 12

A slightly tilted pelvis is normal tooEmerging evidence

On X-rays of 134 healthy adults, the pelvis tilted about 2 degrees to one side on average, and up to 5.6 degrees fell within the normal range.

Source 18

The best testsStrong evidence

A review of 37 clinical and 15 imaging studies found blocks the most useful clinic test: you stand on blocks of known height under the shorter leg until your pelvis is level. A full-length standing X-ray was the most valid and reliable measure. Specialists also use a CT (computed tomography) scan of the legs, called a scanogram.

Sources 3, 19

Hands and tape measuresEmerging evidence

Feeling the hip bones and levelling them with books gave repeatable answers but missed the true difference by 3.8 to 5.1 mm on average in 34 people. A hand-held palpation meter measured pelvic height well and leg length less well. In clinics, leg length can be measured to about 1 cm either way.

Sources 4, 20, 12

Mirrors and home checks

A mirror or a friend's hands can't tell a short leg from a tilted pelvis or a curve in the spine, and the two halves of most pelvises are a little different in shape anyway. If a difference matters to you, have it measured.

Sources 21, 22

Small differences don't change how children walkEmerging evidence

In 475 children, differences under 1 cm didn't change how they walked; from 1 cm, walking became measurably uneven. In 51 children with differences up to 3 cm, the pelvis tilted more as the difference grew, and the longer leg did the adjusting.

Sources 23, 17

Babies

In babies, legs that look different lengths can be a sign of developmental dysplasia of the hip, a loose hip joint, along with a clicking hip, one leg moving differently or dragging a leg when crawling. It's often found at the newborn check, treatment usually works well, and a GP can arrange a check.

Source 24

How a difference changes with growthEmerging evidence

A child's difference can stay the same, grow steadily or change pace, depending on the cause. Specialists predict the difference at the end of growth from growth charts, with an uncertainty of about 2 cm.

Sources 25, 12

After a broken leg

After a broken thigh bone between ages 7 and 13, the leg grew about 1 cm longer. A break through a growth plate can slow growth on that side, so children are followed up for at least a year, and until growth ends after thigh and shin bone fractures.

Sources 26, 27

Treatment depends on the expected differenceStrong evidence

Under 2 cm, specialists usually watch, or suggest a shoe lift. For 2 to 5 cm expected when growth ends, a small operation slows growth in the longer leg so the shorter one catches up, and over 5 cm the shorter leg can be lengthened. Growth usually stops at about 14 in girls and 16 in boys.

Sources 13, 2

Feeling a difference is commonEmerging evidence

Five to 8 years after a hip replacement, 30% of 1,114 people felt their legs were different lengths, but only 36% of them had a difference on X-ray. A review puts measured differences after the operation at 3% to 30% of cases, and says people tend to notice more than 10 mm.

Sources 9, 16

It usually settlesEmerging evidence

In two cohorts, 63% of 22 people and 73% of 62 people who felt a difference had improved or resolved within a year, and most of those who still felt one were satisfied with their hip.

Sources 10, 11

What surgeons aim forEmerging evidence

Less than 10 mm is broadly accepted, and lengthening causes more problems than shortening; in registry comparisons, both went with more limping and lower satisfaction. Most mild cases do well without more surgery, and an operation to correct it is a last resort that helps about half of the people who have it.

Sources 28, 29, 16

What the NHS says

The replaced leg can end up slightly longer than the other. Often the difference is too small to notice, and sometimes a raised heel on the other side is needed.

Source 30

After a knee replacementEmerging evidence

Straightening the knee usually makes the leg a little longer: about 6 mm on average across 5 studies, 7 mm in 100 knees and 10 mm in 237 knees, and more in knock-kneed knees. People noticed changes from about 6.6 mm, and a difference of 10 mm or more went with worse function.

Sources 31, 32, 33

Back painStrong evidence

Across X-ray studies, the average difference was the same in people with and without back pain (5.1 and 5.2 mm). In 247 working-age adults it was 5.5 mm in those who'd never had back pain and 5.3 mm in those with disabling back pain, and neither a case-control study nor a study of 600 adults found a link.

Sources 1, 5, 34, 35

Standing work may be differentEmerging evidence

In 148 workers, a difference of 6 mm or more went with more intense back pain in those who stood to work, but not in those who sat.

Source 6

Knee arthritisStrong evidence

In 3,026 adults aged 50 to 79, a difference of 1 cm or more went with knee arthritis in the shorter leg (53% against 36%) and with new painful arthritis in both legs. In a community study, a difference of 2 cm or more went with knee arthritis, and over about 6 years with knee arthritis getting worse.

Sources 36, 37, 38

Hip arthritisMixed evidence

In 4,593 adults, a difference of 2 cm or more went with new hip arthritis in the shorter leg, though only 1% had a difference that large and the estimate was uncertain. A community study found no clear link with hip arthritis, and in 220 people over 65, hip arthritis was worse on the shorter side.

Sources 39, 37, 40

Links, not proof

These studies show links, not cause, and no trial has tested whether a lift prevents arthritis. A review called the link with back pain questionable and a slightly higher rate of knee arthritis likely.

Sources 36, 12

ScoliosisStrong evidence

A difference can make the lower spine curve sideways when you stand, and that curve straightens when the pelvis is levelled. The Scoliosis Research Society says scoliosis doesn't come from a minor leg length difference, and a review found too little evidence to say a difference makes adolescent scoliosis worse. For people who have scoliosis, another review suggests a lift only when the hips, sacrum and pelvis all tilt the same way, which is a specialist's call.

Sources 41, 42, 43, 44, 45, 46

Most differences need nothing

Small differences are normal and don't change how people walk. There's no guideline on when to treat, so treatment is a choice, not a must.

Sources 1, 23, 12

Shoe lifts and insolesMixed evidence

In 42 meat cutters with back pain and a difference of 5 mm or more, insoles correcting 70% of it reduced pain by 2.6 points out of 10 more than plain insoles, with fewer days off sick. In 33 people with differences of 10 mm or less, correcting inserts eased pain and disability over about 10 weeks, and 12 people fitted with lifts improved too, without a comparison group. A review of 10 studies, only 1 of them randomised, called the evidence low quality and found no agreed threshold for when a lift is worth it.

Sources 7, 47, 48, 8, 49

How much to lift

Have the difference measured first. Full equalisation isn't the aim: the best trial corrected 70%, and for larger differences specialists accept about 1 cm left over in growing children and 2 cm in adults. A heel insole can correct up to about 2 cm and a raised sole up to about 5 cm. Lifts are cheap and easy to stop if they don't help.

Sources 12, 7, 2

Insoles for back pain in general

For low back pain in general, NICE (the National Institute for Health and Care Excellence) advises against foot orthotics. It doesn't cover a measured leg length difference, which is one more reason to have it measured before you buy a lift (our editorial reading).

Source 50

ExerciseEmerging evidence

Exercise can't change the length of your bones. In 48 people with back pain and a functional difference, 6 weeks of gluteal control training (10 holds of 10 seconds per exercise, 3 times a week) reduced the measured difference from 0.9 to 0.3 cm, and pain, more than trunk exercise. It's one small trial, measured by hand, with heat and traction given to both groups and no follow-up after 6 weeks.

Source 51

A starting programme

Side-hip and single-leg strength work 2 or 3 times a week, the same on both sides (our editorial starting point). The wall press at its move page's dose, 3 to 5 holds of 5 to 15 seconds each side, twice a day, and the lying belt press at its move page's dose, 3 to 5 holds of 5 to 10 seconds at a light effort, twice a day. Side-lying leg raises and band walks, starting with 2 sets of 10 and building to 3 sets of 15; single-leg bridges and step-ups, starting with 2 sets of 8; one-leg stands, 3 holds of 20 to 30 seconds; suitcase carries, 2 to 3 walks of 20 to 30 m each side (our editorial starting points, as on the lateral pelvic tilt guide).

Children

Children with a small difference don't need exercises for it; active play is what they need (our editorial advice). Specialists decide on lifts or surgery for larger differences.

Sources 13, 2

After a joint replacement

Give it time and keep up the exercises from your surgical team, ask them to measure it if it doesn't settle, and try a small lift if a true difference is confirmed. That order is our editorial reading of the studies above.

Sources 10, 11, 28, 30

Not a warning sign on its own

A small difference found at a check-up, or one trouser leg that needs taking up, isn't a warning sign.

Source 1

Babies

See a GP if you notice any of these:

• Their legs look different lengths.
• A clicking or popping sound when they move their hips.
• One leg moves differently from the other during play or nappy changes.
• They drag one leg when they crawl, or limp when they start walking.

Source 24

Children: call 999 or go to A&E

If your child:

• Gets sudden pain in the hip, knee or thigh.
• Can't put any weight on the leg.
• Has a leg that has changed shape or is pointing at an odd angle.
• Feels generally unwell with a high temperature, or feels hot, cold or shivery.
• Has severe pain in the lower part of the tummy, or symptoms that are getting worse.

Source 52

Children: see a GP

See a GP if your child has a limp and you're not sure why. Also get a difference checked if it seems to be growing, if your child walks on tiptoe on one side, or after a broken leg, a growth plate injury or a bone infection (our editorial reading of the specialist pages).

Sources 52, 2, 27

After a hip replacement

A hip replacement can dislocate, which is painful. Severe hip pain with a leg that suddenly looks shorter or is turned unusually far in or out can be a dislocation: our hip replacement guide says to go to A&E straight away without walking on it. The NHS says to call 999 for pain and swelling in your hip or leg with difficulty breathing or chest pain, which can be a blood clot in the lungs.

Source 30

Adults: see a GP

See a GP for a new difference after an injury, or for hip or back pain that is stopping your normal activities, getting worse, or not improving after a couple of weeks of looking after it at home.

Sources 53, 54

"Everyone with a leg length difference needs a shoe lift."Strong evidence

About 9 in 10 people have a small difference, under 1 cm doesn't change how people walk, and small differences aren't linked with back pain. Lifts helped some people with a measured difference and pain, on low-quality evidence.

Sources 1, 23, 5, 8

"A short leg causes back pain."Strong evidence

People with and without back pain have the same small differences. People who stand all day with 6 mm or more may be an exception.

Sources 1, 5, 34, 35, 6

"A therapist can measure it by feel, or on a treatment couch."Strong evidence

Feeling the hip bones missed the true difference by 3.8 to 5.1 mm, and a leg that looks short on a couch can reflect an uneven pelvis. Blocks and standing X-rays are the reliable methods.

Sources 4, 3, 21

"Stretching or exercise can lengthen a short leg."Strong evidence

Exercise can't change bone length. In one small trial, measured by hand, it reduced a functional difference, where the bones are equal, and it builds strength around the hips whatever your leg lengths.

Sources 12, 51

"A leg length difference causes scoliosis."Strong evidence

It can make the spine curve while you stand, and that curve straightens when the pelvis is levelled. Scoliosis doesn't come from a minor difference, and there's too little evidence that a difference makes it worse.

Sources 42, 41, 45

"If one leg feels longer after a hip replacement, the operation went wrong."Emerging evidence

About 1 in 3 people feel a difference, only about a third of them have one on X-ray, most felt differences settle within a year, and the NHS lists a small difference as a known possibility.

Sources 9, 10, 11, 30

"Children with a small difference need treatment."Strong evidence

Under 2 cm, specialists usually watch or suggest a lift, and under 1 cm didn't change how children walked.

Sources 13, 23