Limb Length Discrepancy and Epiphysiodesis

Limb length discrepancy is a difference in functional or anatomical length between the lower limbs. Mild asymmetry is common and often asymptomatic. The clinically important problem is not simply whether one leg is shorter, but whether the discrepancy affects gait, pelvis, spine, sport, pain, shoe wear, cosmesis, joints, family burden or long-term function.

The initial clinical distinction is between a true bony discrepancy and an apparent discrepancy caused by pelvic obliquity, spine deformity, contracture, foot height or compensation. Assessment then progresses from block testing and whole-limb examination to calibrated imaging, skeletal maturity assessment and prediction of the discrepancy at maturity.

Published reviews consistently make two important points. First, high-quality evidence for exact treatment thresholds is limited, so many thresholds are consensus-based. Second, treatment is usually elective. A child with a 2 cm discrepancy, a compensating pelvis and no symptoms is not the same clinical problem as a child with a 2 cm discrepancy, pain, a progressive physeal bar or a complex congenital deficiency.

Why it matters clinically

• LLD can increase energy cost and alter gait.
• The short limb may compensate with equinus, toe walking or pelvic drop.
• The long limb may compensate with hip and knee flexion during stance.
• Pelvic obliquity can create a functional scoliosis that improves when the pelvis is levelled.
• A congenital deficiency may involve length, foot rays, ankle stability, knee stability, hip morphology and prosthetic options.
• A post-traumatic physeal arrest may produce both shortening and angular deformity.

Common causes

The diagnosis determines the growth behaviour. A congenital proportional discrepancy behaves differently from a post-traumatic bar, a vascular overgrowth syndrome or a post-infective joint-damaging lesion.

• Congenital or developmental: congenital femoral deficiency, fibular hemimelia, tibial deficiency, hemihyperplasia, skeletal dysplasia, neurofibromatosis, vascular malformation and idiopathic asymmetrical growth.
• Post-traumatic: malunion with shortening, physeal arrest, growth stimulation after femoral shaft fracture, or partial bar formation.
• Infective or inflammatory: neonatal osteomyelitis, septic arthritis, juvenile inflammatory disease or physeal injury.
• Tumour-related: resection, radiation, chemotherapy effects, benign aggressive lesions or limb salvage reconstruction.
• Neuromuscular and functional: pelvic obliquity, scoliosis, hip contracture, knee flexion, equinus, foot deformity or muscle imbalance.

Treatment is elective in most cases. That matters: the indication is not the X-ray measurement alone. The indication is the predicted discrepancy plus symptoms, gait, maturity, treatment risk and the family's priorities.

Every limb length discrepancy assessment should answer four linked questions.

The goal is functional equalisation, not a mathematical promise of exactly equal limbs. A residual discrepancy of about 1 cm is often acceptable if gait, pelvis and symptoms are satisfactory. Conversely, a smaller discrepancy may still need treatment when it is progressive, symptomatic, associated with deformity or part of a congenital deficiency plan.

True anatomical discrepancy

True discrepancy means the bones or foot height are genuinely different. The femur may be short, the tibia may be short, the foot may contribute, or all three may contribute. Segmental localisation is essential because the operation must match the segment.

Examples:

• Congenital femoral deficiency produces a femoral-dominant discrepancy, often with hip and knee instability.
• Fibular hemimelia may combine tibial shortening, foot ray deficiency, ankle deformity and valgus instability.
• Post-infective proximal femoral damage may combine shortening, deformity and joint damage.
• Post-fracture overgrowth may make the injured limb longer, especially after paediatric femoral shaft fracture.
• Physeal arrest can produce both length inequality and angular deformity.

Apparent functional discrepancy

Apparent discrepancy is not a true bony inequality. It is caused by posture, contracture, deformity or pain. This is a common clinical trap.

Common drivers:

• Pelvic obliquity from scoliosis.
• Hip adduction contracture making the limb appear short.
• Hip abduction contracture making the limb appear long.
• Knee flexion contracture functionally shortening the limb.
• Equinus on the short side as compensation.
• Foot height difference from cavus, planovalgus, vertical talus or partial foot deficiency.
• Painful limp being mislabelled as LLD.

Growth behaviour

Congenital discrepancies often behave proportionally: the difference grows as the child grows. This is the basis for multiplier-style prediction. Acquired discrepancies may not behave predictably. A complete physeal arrest, partial bar, fracture overgrowth, vascular malformation, infection or tumour treatment can change the trend, which is why serial measurement is more valuable than a single radiograph.

The knee physes are the usual epiphysiodesis targets because they provide most clinically useful remaining growth: the distal femur contributes approximately 9 mm per year and the proximal tibia approximately 6 mm per year. Together they provide roughly 15 mm per year, although individual growth depends on skeletal maturity, sex, puberty and pathology.

The proximal femur and distal tibia contribute to total limb length, but they are not routine simple LLD arrest targets. They matter in prediction, congenital deficiency planning, ankle-level deformity and complex reconstruction.

Why epiphysiodesis works

Epiphysiodesis slows or stops growth in the longer limb. The shorter limb does not lengthen faster. Equalisation occurs because the long limb stops gaining length while the short limb continues to grow. Therefore epiphysiodesis only works if:

• The child is skeletally immature.
• The physes that are stopped still have enough growth remaining.
• The predicted discrepancy is within the correction capacity of growth arrest.
• The segment treated matches the segment responsible.
• The timing is correct.

The operation is technically simple compared with lengthening, but the planning is not simple.

Why lengthening is different

Lengthening is distraction osteogenesis. A corticotomy or osteotomy creates a biologic regenerate that is gradually distracted. The bone can lengthen, but bone is rarely the only limit.

Children present in several different ways:

• Parent notices asymmetric gait, hip height or toe walking.
• Screening identifies pelvic tilt or functional scoliosis.
• The child reports fatigue, tripping, sport limitation or shoe-wear difficulty.
• Adolescent reports back pain, hip pain, knee pain or cosmetic concern.
• A known congenital deficiency is followed through growth.
• A post-traumatic or post-infective child develops progressive inequality.

Characteristic compensations

Short side compensation:

• Toe walking or equinus on the short limb.
• Pelvic drop on the short side.
• Increased energy cost.
• Vaulting or circumduction in severe cases.

Long side compensation:

• Knee flexion on the long limb.
• Hip and knee flexion during stance.
• Pelvic hiking.
• Shoe modification or altered foot posture.

History that matters

The history should identify the cause of discrepancy, its progression and whether treatment would improve the child's function:

• Onset: present from birth, noticed with walking, or acquired after fracture, infection or surgery.
• Progression: stable, increasing proportionally, or changing unpredictably.
• Function: walking distance, running, sport, falls, fatigue, pain and school participation.
• Symptoms: back, hip, knee, ankle, foot pain, callosities and shoe intolerance.
• Known diagnosis: congenital femoral deficiency, fibular hemimelia, Perthes disease, SCFE, tumour treatment, infection or skeletal dysplasia.
• Previous treatment: lifts, orthoses, physiotherapy, guided growth, reconstruction, lengthening or prosthetic discussion.
• Family goals: avoid limp, avoid large shoe lift, participate in sport, reduce pain, avoid repeated operations, or plan a congenital deficiency pathway.

Red flags

• Painful limp that does not improve with blocks.
• Night pain, systemic symptoms or tumour/infection features.
• Neurological signs, progressive weakness or abnormal reflexes.
• Rapidly changing discrepancy after physeal injury.
• Pelvic obliquity that does not correct when the limbs are levelled.
• Joint instability in a child being considered for lengthening.

Inspection standing

Observe the child barefoot from front, side and back:

• Shoulder and pelvic levels.
• Lumbar scoliosis or compensatory curve.
• Iliac crest height.
• Knee flexion on the long side.
• Toe standing on the short side.
• Hindfoot valgus or varus.
• Foot size and foot height.
• Calf and thigh girth.
• Skin scars from trauma, infection or previous reconstruction.

Gait

Look for:

• Antalgic component suggesting pain rather than LLD alone.
• Short-leg gait with pelvic drop.
• Toe walking on the short side.
• Knee flexion on the long side.
• Circumduction or vaulting.
• Trendelenburg pattern suggesting hip abductor weakness or dysplasia.
• Neuromuscular features such as spasticity, foot drop or crouch.

Block test

Place measured blocks under the short limb until the pelvis is level. This is the key clinical test.

The block test tells you:

• The functional correction needed to level the pelvis.
• Whether gait improves with correction.
• Whether spinal or pelvic obliquity is flexible.
• Whether the patient tolerates correction.
• Whether symptoms are likely related to the discrepancy.

Do not assume the block height equals the final surgical target. It is a clinical correction estimate, not a complete maturity prediction.

Length measurement

Clinical tape measurement is useful but not definitive.

• Apparent length: umbilicus to medial malleolus.
• True length: anterior superior iliac spine to medial malleolus.
• Segment lengths: compare femur and tibia clinically, then confirm radiographically.
• Foot contribution: compare plantar foot height, foot length and deformity.

Joint and spine examination

Assess:

• Spine: scoliosis, pelvic obliquity and flexibility.
• Hip: abduction, adduction contracture, flexion contracture, rotation, Trendelenburg and stability.
• Knee: flexion contracture, recurvatum, valgus or varus, instability and patellar height.
• Ankle and foot: equinus, calcaneus, cavus, planovalgus, subtalar stiffness and braceability.
• Neurology: tone, reflexes, power, sensation and selective motor control when indicated.

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Use prediction in practice by measuring current segmental discrepancy, determining skeletal age, estimating final discrepancy formally, repeating the estimate when possible, then choosing the less than 2 cm, 2 to 5 cm, or more than 5 cm pathway. A residual discrepancy of about 1 cm is often acceptable; perfect equality is not guaranteed.

Prediction workflow in clinic

1. Measure the current total discrepancy and segmental discrepancy.
2. Decide whether the short limb is truly short, the long limb is overgrown, or both are contributing.
3. Determine skeletal maturity using bone age or a validated knee maturity method where appropriate.
4. Estimate predicted discrepancy at maturity using a recognised method.
5. Check the estimate against prior measurements. A single radiograph is weaker than a trend.
6. Calculate whether the chosen physis has enough remaining growth to close the gap.
7. Counsel the family that prediction error can leave residual discrepancy or overcorrection.

Menelaus-style mental check

This is not a substitute for formal prediction, but it is useful for sense-checking the plan.

• Approximate skeletal maturity: girls around 14 years, boys around 16 years, adjusted for bone age and puberty.
• Approximate growth remaining around the knee: distal femur about 9 mm per year, proximal tibia about 6 mm per year.
• Distal femoral epiphysiodesis alone therefore corrects less than combined distal femoral and proximal tibial epiphysiodesis over the same time.
• If predicted correction required exceeds the remaining growth capacity, epiphysiodesis alone cannot solve the problem.

The differential is about avoiding a false diagnosis of bony LLD. The key discriminators are the response to the standing block test, whether the inequality is in the bone or the soft tissue/posture, and whether one limb is genuinely short or the other is overgrown.

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Management principles

The management decision is made in this order:

1. Confirm true versus apparent discrepancy.
2. Measure current discrepancy clinically and radiographically.
3. Localise femur, tibia, foot and axis contributions.
4. Estimate maturity discrepancy.
5. Place the child into a treatment threshold.
6. Check whether contracture, angular deformity, joint instability or foot deficiency changes the plan.
7. Choose the least burdensome treatment that achieves a functional goal.
8. Explain prediction error, residual inequality and treatment burden.

Timed epiphysiodesis: what the surgeon must know

Epiphysiodesis is not one operation; it is a family of techniques that slow or stop growth in the longer limb. The operative method matters, but timing matters more.

Preoperative checklist

• Confirm current LLD, predicted maturity LLD and acceptable residual inequality.
• Confirm bone age and growth remaining.
• Confirm long limb, long segment and exact physis.
• Review femoral and tibial lengths, mechanical axis and joint status.
• Decide whether distal femur, proximal tibia, both, fibula, or an associated angular correction is needed.
• Mark the operative side carefully because wrong-side surgery is a catastrophic error.
• Explain that equalisation occurs gradually during remaining growth, not immediately.

Which physis to stop

The physis chosen should match the measured segmental discrepancy and the predicted correction required.

Permanent percutaneous epiphysiodesis

The aim is controlled physeal ablation.

Technique principles:

• General anaesthesia or appropriate paediatric anaesthesia.
• Supine positioning with fluoroscopy.
• AP and lateral image confirmation of the physis.
• Small medial and lateral incisions or percutaneous access depending technique.
• Drill, burr or curette the physis sufficiently to create a physeal bridge.
• Confirm physeal ablation radiographically.
• Avoid asymmetric ablation that may cause varus, valgus, procurvatum or recurvatum.
• Close wounds and allow protected or early mobilisation according to local protocol.

Pitfalls:

• Wrong side.
• Wrong physis.
• Insufficient ablation causing continued growth.
• Asymmetric ablation causing angular deformity.
• Injury to joint, neurovascular structures or proximal tibial tubercle region.

Practical details:

• Ablate both medial and lateral sides symmetrically when the aim is pure length arrest.
• Maintain awareness of the joint line and avoid intra-articular penetration.
• In the proximal tibia, respect the tibial tubercle apophysis and the lateral neurovascular anatomy.
• Document fluoroscopic confirmation of level, side and implant or ablation position.
• Continue radiographic surveillance because growth arrest is a biologic response, not just a completed operation.

Percutaneous transphyseal screws

PETS uses screws crossing the physis to slow growth. It is minimally invasive and commonly permits rapid mobilisation. It is attractive around the distal femur and proximal tibia, but it still needs accurate timing, careful screw placement and follow-up.

Advantages:

• Small incisions.
• Short operative time.
• Early mobilisation.
• Hardware can sometimes be removed if clinically required.

Problems:

• Hardware irritation.
• Incomplete arrest.
• Rebound or continued growth after removal.
• Angular deformity if screw placement or physeal response is asymmetric.
• Proximal tibial screw trajectory requires attention to deep peroneal nerve proximity.

Temporary tension-band plates or staples

Temporary implants may slow growth and later be removed. They are more commonly used for guided growth angular correction, but can be considered in selected length problems.

Advantages:

• Potentially reversible.
• Useful if angular correction is also required.
• Avoids complete physeal destruction.

Problems:

• Slower and less predictable for pure length correction.
• Requires removal.
• Rebound growth may occur.
• Hardware irritation or migration can occur.

For pure LLD, temporary tethering should not be presented as automatically equivalent to definitive epiphysiodesis. It can work, but some series report lower efficiency and revision burden, especially when used where a predictable definitive arrest is needed.

Lengthening operations

Lengthening requires the surgeon to manage bone, soft tissue and joints together.

External fixation options:

• Monolateral fixator for simple lengthening.
• Circular frame for lengthening with stability needs, small bone segments or deformity.
• Hexapod frame for multiplanar deformity correction and lengthening.

Internal lengthening options:

• Motorised intramedullary nail in appropriate older children and adolescents.
• Requires adequate bone size, open growth-plate considerations, joint protection and implant availability.
• Avoid when canal size, age, deformity, infection risk or joint instability makes the nail unsafe.

Lengthening-specific technical priorities:

• Prevent hip, knee and ankle contracture.
• Use physiotherapy from the start.
• Monitor regenerate density and shape.
• Slow or pause distraction if regenerate is poor or nerves/joints become symptomatic.
• Consider prophylactic joint spanning or soft-tissue release in high-risk congenital deficiency.

Physeal bar resection principles

Bar resection is a reconstruction of growth, not a standard length-equalisation operation.

The operation is particularly unforgiving because incomplete bar removal may fail, and excessive resection can damage remaining growth potential.

Segment selection

Segment selection should match the measured discrepancy:

• Long femur: distal femoral epiphysiodesis.
• Long tibia: proximal tibial epiphysiodesis.
• Both femur and tibia: combined around-knee epiphysiodesis.
• Foot height difference: epiphysiodesis will not correct the foot component.
• Angular deformity: may need guided growth or osteotomy in addition to length management.
• Proximal femur and distal tibia: include them in prediction, but do not choose them automatically for routine LLD arrest.

Prediction complications

• Residual discrepancy at maturity.
• Undercorrection if surgery is too late.
• Overcorrection if surgery is too early.
• Wrong segment treated.
• Failure to account for bone age or pubertal timing.
• Failure to update prediction with serial data.

Epiphysiodesis complications

• Continued growth from incomplete arrest.
• Angular deformity from asymmetric arrest.
• Hardware irritation or screw prominence.
• Knee pain or stiffness.
• Infection or wound problem.
• Reduced final height.
• Need for contralateral or revision procedure if prediction proves wrong.

Shortening complications

• Nonunion or delayed union.
• Hardware irritation.
• Malrotation.
• Weakness from excessive shortening.
• Loss of height.

Lengthening complications

• Pin-site infection or implant-related pain.
• Poor regenerate or delayed consolidation.
• Regenerate fracture.
• Joint stiffness.
• Hip, knee or ankle subluxation.
• Nerve stretch symptoms.
• Muscle contracture.
• Psychological fatigue and family burnout.
• Residual discrepancy or recurrent deformity.

Follow-up

Follow-up must continue beyond the operation:

• Recheck clinical block height.
• Repeat calibrated imaging.
• Monitor axis as well as length.
• Confirm the physis has responded.
• Adjust shoe lift during growth.
• Watch for overcorrection.
• Follow to skeletal maturity.

Common pitfalls

• Starting with "I would get a scanogram" before saying true versus apparent discrepancy.
• Forgetting the block test.
• Treating the current discrepancy instead of predicted maturity discrepancy.
• Using chronological age alone.
• Forgetting femur versus tibia contribution.
• Ignoring foot height.
• Ignoring angular deformity.
• Offering lengthening without joint stability assessment.
• Calling epiphysiodesis "simple" without discussing timing error.
• Assuming equal legs is always the goal.

Structured case presentation

Use this structure:

1. "This child has a suspected limb length discrepancy. I would first distinguish true from apparent discrepancy."
2. "I would observe gait and level the pelvis with blocks."
3. "I would examine spine, hips, knees, ankles, feet and neurology."
4. "I would measure femur, tibia and total limb length using calibrated imaging."
5. "I would assess bone age and predict discrepancy at maturity."
6. "I would decide whether observation, lift, epiphysiodesis, shortening, lengthening or reconstruction best matches the child."
7. "I would discuss prediction error and follow until maturity."

Concise epiphysiodesis summary

"Epiphysiodesis is timed growth arrest of the longer limb. I would only offer it after confirming true anatomical LLD, identifying the responsible segment, estimating bone age and predicted maturity discrepancy, and confirming enough growth remains. I would counsel about undercorrection, overcorrection, angular deformity, residual inequality and the need for follow-up to maturity."

Concise lengthening summary

"Lengthening is considered for larger discrepancies or congenital deficiency pathways, but it requires stable joints, correctable alignment, good range of motion, family commitment and prolonged rehabilitation. The risks include regenerate problems, stiffness, subluxation, nerve stretch, infection, pain and residual discrepancy."

There is no single high-level international guideline that dictates limb length discrepancy (LLD) thresholds. Practice is built on consensus, narrative reviews and registry-style cohorts rather than randomised trials, and the major bodies (AAOS, the British Society for Children's Orthopaedic Surgery, EFORT/EPOS in Europe, and the deformity-correction community around the AO and Paley schools) converge on a similar treatment ladder while differing in emphasis and the strength of the evidence they cite.

Global epidemiology

Mild anatomical inequality is near universal; it is the magnitude and the symptoms, not the mere presence of inequality, that define a clinical problem.

How guidance differs across regions

Registry and practice-variation evidence

There is no dedicated international LLD registry equivalent to arthroplasty registries. The best registry-style evidence comes from large single-centre and institutional cohorts that prospectively track lengthening and epiphysiodesis to maturity. A representative deformity-unit cohort treated 323 patients for LLD of 2 cm or more over roughly five years, of whom 55 percent were managed with motorised intramedullary nails, 27 percent with epiphysiodesis around the knee and 18 percent with external fixation, illustrating how method selection varies even within one expert centre (Frommer et al, Clin Orthop Relat Res 2022). Practice variation between centres and countries reflects implant availability, cost, family capacity for prolonged rehabilitation and surgeon training far more than disagreement about the underlying treatment ladder.