Leg length discrepancy

Definition

Leg length discrepancy (LLD) is a difference in the lengths of the lower limbs. It may be true or apparent, and may be static or progressive.

Causes

Congenital

• proximal femoral focal deficiency
• hemihypertrophy or hemiatrophy
• congenital limb deficiency
• developmental dysplasia of the hip

Acquired

• physeal injury or infection
• malunion
• avascular necrosis
• tumour or tumour treatment
• neuromuscular disease

Clinical assessment

Block test

With the child standing, blocks are placed under the short limb until the pelvis is level. The total block height estimates the discrepancy and is the best simple screening test.

Tape measurement

True length is commonly measured from the ASIS to the medial malleolus. Apparent length is affected by pelvic obliquity and joint contractures.

Always assess:

• hip, knee and ankle contractures
• pelvic obliquity
• angular deformity
• gait

Imaging

• standing long-leg radiograph / scanogram
• teleoroentgenogram
• CT scanogram when contracture makes conventional radiographic measurement unreliable
• bone-age radiograph when growth prediction is required

Predicting discrepancy at maturity

Methods include:

• Green–Anderson growth-remaining charts
• Moseley straight-line graph
• Multiplier method

The multiplier method is particularly useful for congenital discrepancy. Prediction should use skeletal maturity rather than chronological age alone whenever possible.

Principles of treatment

Treatment is based on the predicted discrepancy at skeletal maturity, the cause, remaining growth and patient factors.

• < 2 cm — observation or shoe lift is usually sufficient
• > 2 cm — operative treatment may be considered depending on predicted final discrepancy and growth remaining
• epiphysiodesis is used to slow growth of the longer limb in a growing child
• limb lengthening is used for larger discrepancies when preservation of overall height and limb length is important
• shortening procedures may be considered in selected skeletally mature patients

Epiphysiodesis

Timing is critical. The procedure may involve:

• distal femur
• proximal tibia
• both distal femur and proximal tibia

Accurate prediction of remaining growth is essential to avoid under- or over-correction.

Lengthening

Distraction osteogenesis usually follows a latency period after corticotomy and gradual distraction of approximately 1 mm/day, adjusted according to regenerate quality and soft-tissue tolerance.

Complications of treatment

• residual discrepancy
• angular deformity
• joint stiffness or subluxation
• pin-site infection
• fracture
• delayed regenerate formation
• neurovascular or soft-tissue complications

References

1. Orthobullets. Leg Length Discrepancy (LLD).
2. Paley / multiplier-method literature for prediction of limb-length discrepancy at maturity.