ConditionBones, joints & muscles
Leg Length Discrepancy
Leg length discrepancy is a difference in the length of the legs. Differences under about 2 cm (3/4 inch) are common and usually harmless. Larger ones can cause limping, a tilted pelvis and back, hip or knee pain. A structural discrepancy means the bones differ in length, from a fracture, growth plate injury or congenital condition. A functional one means the bones are equal but the pelvis, spine or tight muscles make the legs seem uneven. Treatment ranges from a shoe lift to limb-lengthening surgery.
Also called: Leg length inequality, limb length discrepancy, anisomelia, uneven leg length
At a glance
- What it is
- One leg is shorter or longer than the other.
- Types
- Structural (true bone length difference) or functional (apparent difference from pelvis, spine or soft tissue).
- How common
- Small differences (under 1 cm) are present in most people.
- Symptoms
- Limping, back, hip or knee pain; often none with small differences.
- Treatment
- Observation, shoe lifts, growth modulation in children, limb lengthening or shortening surgery.
When to get help
See a doctor within a day or two
- A child who suddenly starts limping or refuses to walk, especially with hip or knee pain or fever
- New leg shortening with hip pain after a fall in an older adult (possible hip fracture)
Book a routine appointment
- A noticeable limp, or one leg looking shorter or longer
- A child with uneven hip creases, a waddle, or walking on the toes of one foot
- Back, hip or knee pain with a feeling of uneven legs
- A known leg length difference in a growing child, to monitor
Structural vs functional discrepancy
| Structural (true) | Functional (apparent) | |
|---|---|---|
| What differs | Actual length of the thigh bone, shin bone or both | Bones equal; legs appear uneven |
| Causes | Fractures, growth plate injury, congenital conditions, infections, tumors, hip conditions | Pelvic tilt, scoliosis, hip or knee contractures, flat foot on one side, muscle tightness |
| Treatment focus | Equalizing length | Treating the underlying cause (stretching, physical therapy, orthotics) |
Causes of structural leg length discrepancy
Congenital
- congenital femoral deficiency or fibular hemimelia (underdeveloped bones)
- hemihypertrophy (one side of the body grows more)
- developmental hip dysplasia that leads to dislocation
Acquired
- fractures: a bone that heals short or overlapped, or a childhood fracture that stimulates extra growth. See fracture of the leg
- growth plate injuries from fractures or infections, which can slow or stop growth
- bone infection (osteomyelitis) in childhood
- Perthes disease and slipped capital femoral epiphysis in the hip
- neuromuscular conditions such as cerebral palsy and polio
- tumors and their treatment
- juvenile arthritis, which can increase growth on the affected side
- hip or knee replacement, which can change leg length slightly
Symptoms
Differences under about 2 cm often cause no symptoms. Larger differences may cause:
- limping or walking on the toes of the shorter leg
- pelvic tilt and uneven shoulders
- low back pain
- hip and knee pain on the longer side
- tiredness from the extra effort of walking
- a functional scoliosis (curve that corrects when the difference is evened out)
Diagnosis
- physical exam: comparing heights of the pelvis, knees and ankles; placing blocks under the short leg until the pelvis is level
- tape measure from the hip bone to the ankle, though this is not precise
- standing X-rays of the whole legs (scanogram or full-length standing film): the most accurate measurement
- EOS or CT scanogram in some centers, with lower radiation
- bone age X-ray of the hand in children, to predict how much the difference will grow by maturity
In growing children, serial measurements every 6 to 12 months track whether the difference is stable or increasing.
Treatment
Choice depends on the size of the difference (predicted at skeletal maturity for children), the cause and symptoms.
| Predicted difference | Usual approach |
|---|---|
| Under 2 cm | Observation, or a heel insert if symptomatic |
| 2 to 5 cm | Shoe lift, or growth modulation (epiphysiodesis) of the longer leg in a growing child |
| Over 5 cm | Limb lengthening, sometimes combined with other procedures |
Shoe lifts
A lift inside the shoe (up to about 1 cm) or built onto the sole (for larger amounts) levels the pelvis. Lifts often relieve back and hip pain.
Epiphysiodesis
In children, a small procedure slows or stops growth at the growth plate of the longer leg at a carefully timed age, allowing the shorter leg to catch up. Guided growth plates (tension band plates) can be removed later.
Limb lengthening
The bone is cut and slowly pulled apart (about 1 mm per day) using an external frame or an internal motorized nail, allowing new bone to form in the gap. The process takes several months and requires intensive physical therapy. Complications can include joint stiffness, infection and nerve problems.
Shortening
The longer leg can be shortened surgically in adults when the difference is moderate.
Functional discrepancy
Stretching, strengthening, treating a hip or knee contracture, and orthotics for flat feet.
Frequently asked questions
Is it normal to have one leg longer than the other?
Yes. Most people have a small difference, usually under 1 cm, which causes no problems. Differences over about 2 cm are more likely to cause a limp or pain and may need treatment.
Can leg length discrepancy cause back pain?
It can. A larger difference tilts the pelvis and can strain the lower back, hips and knees. A shoe lift often helps. Small differences are rarely the main cause of back pain.
How is leg length discrepancy measured?
A doctor can estimate it by examination and by placing blocks under the shorter leg until the pelvis is level. Standing X-rays of both legs give the most accurate measurement.
How is leg length discrepancy treated?
Small differences may need nothing or a shoe insert. Moderate differences are treated with a shoe lift or, in children, by slowing growth of the longer leg. Large differences may need limb-lengthening surgery.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Orthopaedic Surgeons (OrthoInfo): Limb length discrepancy
- Pediatric Orthopaedic Society of North America: Leg length discrepancy
- MedlinePlus: Leg length discrepancy
- Boston Children's Hospital: Limb length discrepancy