Limb Length Discrepancy

Introduction

If you or your child has been told that one leg is longer than the other, you are now likely thinking about what to do next. Limb length discrepancy often shortened to LLD  is a measurable difference between the two limbs, most commonly the legs. Some differences are small and need only observation or a simple shoe lift. Others are large enough to affect walking, posture, and joint health, and may benefit from surgery.

This guide is written for patients and parents who already have a diagnosis or a strong clinical suspicion of limb length discrepancy and are planning the next stage of care. It explains what causes the difference, how doctors measure it, when treatment is usually advised, what the surgical and non-surgical options involve, and what recovery typically looks like. It also covers the special timing considerations that apply in growing children, where decisions are shaped by how much growth is left.

Throughout, the article describes the medical landscape. The right plan for any one patient is a decision for you and an experienced orthopaedic specialist, ideally one who treats limb length differences regularly.

What Is Limb Length Discrepancy?

Doctors usually group leg length differences into broad categories based on how much shorter one leg is than the other:

• Mild: less than 2 cm. Very common in the general population and often causes no symptoms.
• Moderate: roughly 2 to 5 cm. More likely to cause a visible limp and longer-term effects on the hips, knees, and back.
• Severe: more than 5 cm. Usually produces a clear limp and significant functional difficulty, and is more likely to need surgical correction.

There are also two different ways a leg can be “short.” A true (structural) discrepancy means the bones themselves are different lengths. A functional (apparent) discrepancy means the bones are equal in length but the leg looks or behaves shorter because of a tight hip, pelvic tilt, scoliosis, or muscle imbalance. The distinction matters because treatment is very different: structural differences may need a lift, growth modulation, or lengthening, while functional differences are usually managed by treating the underlying cause — for example, physiotherapy, postural correction, or treatment of hip or spine problems.

Causes and Risk Factors

Limb length discrepancy can be present from birth (congenital) or develop later in life (acquired). Understanding the cause is important because it influences how the difference behaves over time — some differences stay stable, while others increase steadily during growth.

Causes in Children

• Congenital limb differences such as fibular hemimelia, proximal focal femoral deficiency, hemihypertrophy (overgrowth of one side of the body), and hemiatrophy (undergrowth of one side).
• Growth plate (physeal) injury from a fracture near the end of a long bone, which can slow or stop growth in that limb.
• Infections of bone (osteomyelitis) that damage the growth plate.
• Neuromuscular conditions such as cerebral palsy or polio, where reduced use of one limb can lead to undergrowth.
• Bone diseases such as Ollier disease, multiple hereditary exostoses, or fibrous dysplasia.
• Tumours and their treatment, including surgery or radiation that affects a growth plate.
• Legg-Calvé-Perthes disease and other hip conditions that change the shape of the femoral head and effectively shorten the leg.

Causes in Adults

• Fractures that heal slightly short or with malalignment.
• Hip or knee replacement surgery, where small differences after surgery are common.
• Severe arthritis of the hip or knee that causes joint collapse on one side.
• Previous bone infection or tumour surgery.
• Scoliosis or pelvic tilt contributing to a functional rather than true difference.

In children, the most important question is not just “what is the cause?” but also “will the difference get bigger?” A growth plate that has been damaged often continues to fall behind, so a small early difference may grow into a much larger one by skeletal maturity. This is why follow-up over time matters so much in paediatric LLD.

How Limb Length Discrepancy Shows Itself

If you are reading this, the difference has likely already been noticed by you, a doctor, or a school screening. The following features are typical of leg length discrepancy and are worth being aware of, particularly as your or your child’s care unfolds:

• A limp or uneven walking pattern, sometimes more obvious when tired or after long walks.
• One hip sitting higher than the other when standing.
• The pelvis tilting, which can pull the spine into a curve (functional scoliosis).
• Toe-walking on the shorter side as the body tries to even out the difference.
• Bending of the knee on the longer side, or hip flexion to lower the pelvis.
• Lower back, hip, or knee pain, particularly in adults or older adolescents.
• Trousers fitting unevenly, or shoes wearing down differently.

Small differences (under 2 cm) often produce no symptoms at all and may never need treatment. The body compensates well. Larger differences are more likely to be visible and to cause secondary problems in the back and joints over years.

Diagnosis

Accurate measurement is the foundation of treatment. A difference that feels obvious to the eye is not always confirmed on imaging, and a difference that looks small may actually be structural and progressive. Diagnosis usually combines a clinical examination with imaging.

Clinical Examination

The orthopaedic specialist will typically:

• Watch you or your child walk to look for a limp, toe-walking, or pelvic tilt.
• Place wooden blocks of known thickness under the shorter leg while you stand, and see what height makes the pelvis level. This is a quick, surprisingly accurate way to estimate the difference.
• Examine the hips, knees, ankles, and spine.
• Check for joint contractures (tightness) that may be producing a functional rather than true difference.

Imaging

• Standing long-leg X-ray (scanogram or EOS imaging): the standard tool for measuring true bone length and identifying where the difference lies (femur, tibia, or both).
• CT scanogram: sometimes used for very precise measurement or complex deformities.
• MRI: useful when growth plate damage, infection, or soft-tissue causes are suspected.
• Bone age X-ray (usually of the left hand and wrist): important in growing children, because skeletal age — not just calendar age — is used to predict how much growth is left.

In children, the surgeon often uses these measurements over time to estimate how big the difference will be at the end of growth. This future discrepancy, not the current one, is what surgical planning is based on. Several mathematical methods exist (the Moseley straight-line graph, the Paley multiplier method, and the White-Menelaus method are commonly used) to forecast adult leg length difference.

Non-Surgical Treatment

Many people with limb length discrepancy — particularly differences under about 2 cm — do well without surgery. Non-surgical care focuses on balancing the body, supporting good walking patterns, and watching for change.

Shoe Lifts and Orthotics

A shoe lift is the most common treatment for mild and some moderate differences. Lifts can be placed:

• Inside the shoe for small differences (usually up to about 1 cm).
• On the outside of the sole for larger differences, where a built-up sole and heel are added by a cobbler or orthotist.

Lifts do not correct the underlying bone difference, but they level the pelvis and reduce strain on the back, hip, and knee. Many people use them long-term without any problem.

Physiotherapy

Physiotherapy is used to:

• Stretch tight muscles (hip flexors, hamstrings, calf) that may be contributing to a functional difference.
• Strengthen the muscles around the hip, pelvis, and core to improve walking.
• Address back pain and posture.
• Support recovery before and after surgery, where surgery is planned.

Observation

In a growing child with a small difference, the most appropriate plan may be simply to monitor — with clinical review and X-rays at intervals — and to make a treatment decision later, once it is clearer what the final difference will be. This watchful approach is a recognised and often advised path in paediatric orthopaedics.

When Surgery Is Considered

Surgical treatment is generally considered when the predicted difference at skeletal maturity is large enough to cause significant gait, joint, or back problems. In broad terms, orthopaedic surgeons often consider intervention along these lines, though every case is individual:

• Less than 2 cm: usually no surgery; shoe lift if helpful.
• 2 to 5 cm: growth modulation in children, or surgical lengthening or shortening in adults, depending on the patient’s symptoms, age, and preference.
• 5 cm or more: limb lengthening surgery is more commonly recommended, sometimes in stages.
• Very large differences from major congenital limb deficiencies may involve a different approach, including reconstruction over multiple surgeries or, in selected cases, prosthetic management.

Other factors influencing the surgical decision include pain, scoliosis caused by the discrepancy, the cause of the difference, joint health, the patient’s skeletal maturity, and the family’s readiness for what is often a long treatment journey. The decision is made in conversation with an experienced surgeon and is rarely urgent.

Surgical Treatment Options

There are three broad surgical strategies for limb length discrepancy: slowing the growth of the longer leg, lengthening the shorter leg, or shortening the longer leg. The choice depends on the size of the difference, the age of the patient, the cause, and the condition of the bones and soft tissues.

Growth Modulation (Epiphysiodesis)

Epiphysiodesis is a procedure used in growing children to slow or stop growth at one or more growth plates in the longer leg, allowing the shorter leg to catch up. It is most useful for predicted final differences of about 2 to 5 cm and depends on accurate timing relative to skeletal age.

Two main techniques are used:

• Permanent epiphysiodesis: the growth plate is destroyed using small drill holes or curettage. Growth stops at that plate permanently.
• Guided growth with tension-band plates or screws (for example, eight-plates or PETS — percutaneous epiphysiodesis using transphyseal screws): small implants temporarily tether the growth plate. These can sometimes be removed if needed.

Epiphysiodesis is technically a smaller operation than limb lengthening, with shorter recovery and lower complication rates. Its main limitation is that it works only while a child is still growing, and it slightly reduces the patient’s final adult height. Timing is critical: do it too early and the leg overcorrects; do it too late and the difference is not fully corrected. Bone-age X-rays guide this decision.

Limb Lengthening Surgery

Limb lengthening uses the body’s natural ability to form new bone in a controlled gap. The bone is cut surgically (an osteotomy), and the two ends are then gradually pulled apart by about 1 mm per day. As they separate, new bone forms in the gap — a process called distraction osteogenesis. Lengthening can be done in the femur, the tibia, or both, and is suitable for larger differences (typically more than 4–5 cm) and in adults or older adolescents.

Two main devices are used to achieve and control the lengthening:

External Fixation (Ilizarov and Related Frames)

Advantages:

• Allows correction of bone bowing or rotation at the same time as lengthening.
• Suitable for very large lengthenings and for complex congenital deformities.
• Useful when the bone is too narrow for an internal device, particularly in younger children.

Considerations:

• The frame is worn for many months, both during lengthening and while the new bone hardens.
• Pin sites need daily cleaning and can become infected.
• It is bulky and visible, which can be socially and emotionally demanding, especially in adolescents.

Internal Lengthening Nails (Motorised Intramedullary Nails)

An internal lengthening nail is a metal rod placed inside the cavity of the bone, with a motorised mechanism that allows the bone to be gradually lengthened. The most widely used current devices are activated externally through the skin by a magnetic or remote control unit (the PRECICE and STRYDE families are well-known examples; availability of specific models varies by region and over time).

Advantages:

• Nothing protrudes through the skin during lengthening, which reduces pin-site infection risk.
• More comfortable and cosmetically easier than an external frame.
• Allows more normal daily activities during treatment in many patients.

Considerations:

• The bone canal must be wide enough to accept the nail, so younger children may not be candidates.
• The nail is usually removed in a second operation after the bone has fully hardened.
• The device cannot correct large angular or rotational deformities as flexibly as a frame can.

The Limb Lengthening and Reconstruction Society and major paediatric orthopaedic centres now describe motorised internal nails as a major advance for suitable patients, with external fixators remaining important for complex cases and for younger or smaller patients.

Acute Shortening of the Longer Leg

In adults with mild to moderate differences (typically up to about 5 cm) who have finished growing, the longer leg can be shortened by removing a small segment of bone, usually from the femur, and fixing the bone with an internal rod or plate. Shortening is a shorter overall treatment than lengthening and has fewer complications, but it slightly reduces total height and can weaken the thigh muscle for a period.

Combined and Staged Approaches

For very large differences, surgeons sometimes combine approaches — for example, an epiphysiodesis of the longer leg in childhood, followed later by a single lengthening of the shorter leg, or two separate lengthenings in different bones at different stages. These long-term plans are mapped out with the family from early on.

Preparing for Surgery

If surgery is planned, the preparation phase typically includes:

• Detailed imaging with standing X-rays of both legs, and sometimes CT or MRI.
• Bone age assessment in children, to confirm timing.
• Surgical planning, including measurement of how much lengthening or shortening is needed and choice of device.
• Pre-operative physiotherapy to build strength and flexibility, which makes the post-operative phase easier.
• General health checks, blood tests, and an anaesthetic review.
• Discussion of expectations — what the daily routine will look like, how long treatment will take, what hospital follow-up is needed, and what activities will be restricted.

For lengthening procedures in particular, families are encouraged to think carefully about the time commitment. The active lengthening phase alone often runs for two to three months, with several more months of consolidation and rehabilitation before normal activities resume.

Recovery and Rehabilitation

Recovery looks very different depending on which procedure has been performed.

After Epiphysiodesis

Epiphysiodesis is usually a short hospital stay, sometimes a day-case procedure. Most children walk with crutches for a few weeks and return to normal school activities within four to six weeks. Sports are usually restricted for two to three months. Effects on growth then unfold gradually over months and years, with regular X-ray follow-up.

After Limb Lengthening

Lengthening unfolds in stages:

• Latency phase (about 5–10 days after surgery): the bone is cut but not yet lengthened. The patient begins gentle physiotherapy.
• Distraction phase (often 1–3 months): the bone is lengthened by approximately 1 mm per day, in small steps throughout the day. Physiotherapy is intensive during this phase to keep the muscles and joints supple as they stretch.
• Consolidation phase (often 2–4 months, sometimes longer): lengthening stops, and the new bone hardens. The frame stays on, or the internal nail remains in place. Weight-bearing is increased gradually.
• Device removal: the external frame is removed once X-rays show solid new bone. Internal nails are typically removed in a separate procedure, often around a year after the original surgery.

Throughout this period, physiotherapy is one of the most important parts of treatment. Without daily stretching and strengthening, the muscles and tendons cannot keep up with the lengthening bone, and joints become stiff. Most centres expect physiotherapy several times a week, with daily home exercises.

After Shortening Surgery

Recovery from shortening is generally faster than lengthening — usually a few days in hospital, several weeks on crutches, and a return to most activities by three to six months, depending on the size of the shortening and the strength of bone healing.

Risks and Complications

All limb length surgery carries some risk. Risks vary by procedure and are part of the careful conversation with a surgeon before treatment. The more important ones include:

• Infection, especially at pin sites with external fixators, and rarely deeper bone infection.
• Slow or incomplete bone healing (delayed union or non-union), which may need additional surgery or bone grafting.
• Joint stiffness and contractures, particularly of the knee and ankle during femoral or tibial lengthening.
• Nerve irritation or injury, sometimes causing numbness, tingling, or temporary weakness; less commonly, lasting nerve injury.
• Blood vessel injury, which is uncommon but serious.
• Deep vein thrombosis (blood clots in the leg), particularly in adults.
• Premature growth plate fusion or angular deformity in growing bones.
• Overcorrection or undercorrection of the final length.
• Mechanical problems with implants, including breakage or movement of pins, wires, or nails.
• Pain and psychological strain of a long treatment, which is particularly important to plan for in adolescents.

Centres that perform a high volume of these procedures, with a coordinated team of surgeons, physiotherapists, and nurses experienced in limb reconstruction, tend to manage and prevent these complications more effectively. When evaluating a surgeon and centre, it is reasonable to ask about their experience with the specific technique proposed, how often they treat similar cases, and how complications are handled if they arise.

Limb Length Discrepancy in Children

Most limb length discrepancy is diagnosed and treated in childhood, and several considerations apply specifically to growing patients.

Why Timing Matters

Because children are still growing, a small discrepancy now may become a large one by adulthood — or stay the same — depending on what is happening at the growth plates. Predicting the final adult difference is therefore central to planning. Treatment decisions are based on:

• The cause of the discrepancy and how it has behaved over time.
• The bone age, not just calendar age.
• How much growth remains at each relevant growth plate.
• How the child is functioning now and what is likely later.

Many paediatric centres see children every 6 to 12 months for growth follow-up. Treatment may be delayed for years while monitoring continues, and that delay is often the right choice.

Choosing Between Approaches in Children

Broadly, when the predicted final difference is in the 2–5 cm range and the child has enough growth left, paediatric orthopaedic surgeons frequently favour growth modulation (epiphysiodesis), because it is a smaller operation with shorter recovery. For larger predicted differences, or when growth is already complete, lengthening surgery becomes more relevant. The exact threshold and timing varies between surgeons and families, and is influenced by the cause of the difference, the height the child is expected to reach, and the child’s and family’s preferences.

School, Sport, and Daily Life

Children with mild differences usually take part in all normal activities. Those undergoing lengthening will need significant time away from sports and may need school adaptations during the active phase — help with stairs, modified physical education, support carrying bags. Most children return fully to normal activity once treatment is complete. Emotional support during a long treatment is important; many centres involve psychologists or counsellors as part of the team.

Long-Term Outlook and Follow-up

For most patients, well-managed limb length discrepancy has a good long-term outcome. Goals of treatment are:

• A leg length difference small enough that the body works comfortably (often within 1–2 cm of equal).
• A level pelvis and improved walking pattern.
• Reduced strain on the hips, knees, and back.
• Confidence and freedom in daily activity and sport.

Long-term follow-up depends on the treatment. After epiphysiodesis or lengthening in childhood, periodic review until skeletal maturity is standard. After lengthening in adults, follow-up focuses on bone healing and implant status; if an internal nail is in place, removal is often planned around 12–24 months after the lengthening, depending on the surgeon’s protocol and how the bone has healed.

Adults who have had a lengthening or shortening typically do not need lifelong specialist follow-up once healing is complete, but should mention the history at any future joint replacement or trauma consultation, because previous surgery affects planning.

Frequently Asked Questions

How small a difference is “normal”?

Differences of less than about 1 cm are very common and are often considered within the normal range. They rarely cause symptoms or require treatment.

Will my child grow out of it?

Sometimes, particularly when the difference is small and the cause is uncertain. In other situations — for example, after a growth plate injury — the difference may actually grow over time. Periodic measurement and bone-age X-rays help your surgeon predict what will happen and decide whether and when to act.

Is limb lengthening painful?

There is discomfort, particularly during the active lengthening phase and during physiotherapy, but pain is actively managed with medication, nerve blocks where appropriate, and a structured rehabilitation plan. Most patients describe it as manageable rather than severe, especially with modern internal lengthening nails. Honest preparation with the surgical team helps families know what to expect.

Can I walk during limb lengthening?

Yes, in most cases. Patients usually walk with crutches or a walker during the lengthening and early consolidation phases. The amount of weight allowed on the leg depends on the device and the surgeon’s instructions. Internal lengthening nails generally allow earlier and more comfortable weight-bearing than external frames.

How much can a leg be lengthened in one operation?

A single lengthening segment is often limited to about 5–8 cm to protect the nerves, blood vessels, and muscles. Larger discrepancies are sometimes treated by lengthening two bones (femur and tibia) or by staged lengthening in different operations.

Will the leg ever be exactly the same length?

The goal is to bring the legs close enough that the body works comfortably, but small residual differences (under 1–2 cm) are common after surgery and rarely cause problems. Perfect equality is not always necessary or achievable.

Are the implants permanent?

External fixators are removed at the end of treatment. Internal lengthening nails are usually removed in a second operation once the bone is solid. Plates and screws used in growth modulation are often removed as well, particularly in growing children, though some patients keep them.

Can adults have limb lengthening?

Yes. Adults can have limb lengthening for true structural differences after fracture, hip replacement, infection, or congenital causes. The principles are similar, although bone healing is somewhat slower than in children, and rehabilitation is just as important.

Does limb length discrepancy cause arthritis later in life?

Large, untreated differences increase the strain on the hip, knee, and lower back over years and are linked with a higher risk of pain and joint wear. Small differences (under 2 cm) have not been clearly shown to cause arthritis on their own.

Conclusion

Limb length discrepancy ranges from a small difference noticed only on careful measurement to a major difference that shapes walking, joint health, and daily life. The right plan depends on the size of the difference, the cause, the patient’s age and remaining growth, and the impact on function.

For many people, no surgical treatment is needed — a shoe lift, physiotherapy, and periodic follow-up are enough. For others, especially children with progressive differences or adults with significant structural shortening, modern orthopaedic options — growth modulation, internal lengthening nails, external frames, and selective shortening — allow careful, individualised correction with generally good long-term results. These are long treatments, and the journey is easier when the surgical team, the physiotherapist, the family, and the patient share clear expectations from the start.

The most important next step for any patient or parent reading this is a detailed conversation with an orthopaedic specialist experienced in limb reconstruction, who can measure the difference accurately, forecast how it will behave over time, and walk through the options that fit your situation.