Limb Length Discrepancy

Epidemiology

• Common to have small inequalities <2cm – asymptomatic

Aetiology

• Congenital or Acquired
  • Dwarfism, Neuromuscular, PFFD, CSF, etc.
  • Infection, Physeal trauma, Tumour, AVN
• True or Apparent
  • Always screen for:
    • Scoliosis
    • Hip, knee, ankle soft tissue contracture
  • Most common: Hip adductor contracture – apparent shortening
• Proportional or Disproportional
  • Proportional: 70% discrepancy remains consistent at maturity (congenital)
  • Disproportionate: Discrepancy varies with growth (acquired conditions)

Potential Problems from Limb Length Discrepancy

• Limp – main focus of intervention is to cure limp
• Psychologic distress
• Back pain – no evidence
• Early osteoarthritis (OA) – uncovered femoral head on long side & increased joint reaction forces (debatable)

Methods of Predicting Growth

Rule of Thumb Method

• Girls stop growing at 14 years, boys stop at 16 years
• Mean limb length (LL) at maturity:
  • Female: 80cm
  • Male: 85cm
• Growth predicted by mean yearly growth at each physis:
  • Distal Tibia: 3mm/year
  • Proximal Tibia: 6mm/year
  • Distal Femur: 9mm/year
  • Proximal Femur: 3mm/year
• Most applicable to the last 4 years of growth.

Predicted Height at Maturity

• TW3 formula: More applicable to boys.
• If predicted height is short, consider lengthening instead of epiphysiodesis.

Linear Growth Estimates

• Sufficient for most conditions, even disproportionate LLD.
• Common methods:
  • Green & Anderson Tables
  • Mosley Graphs
  • Paley Multiplier Method (accounts for gender)

Non-Linear Growth Estimates

• Eastwood Method
• Shapiro Method

Clinical Evaluation

Examination

• Pelvic tilt
• Limp
• Compensatory gait pattern – vaulting, toe walking, knee flexion
• Compensatory scoliosis

Block Test

• Examine from behind with knees extended.
• Stack blocks under the shorter limb until pelvis is level.
• As accurate as imaging measurements.

Supine Measurement

• Measure limb lengths supine (estimation only – less accurate).

Imaging

• Single long cassette X-ray of both lower limbs (Weight Bearing - WB)
• CT scanogram (Non-WB)
• X-ray scanogram (3 small cassettes stitched together - WB preferred)

Additional Tests

• All children with congenital LLD should undergo abdomen ultrasound.
  • 6% incidence of neuroectodermal tumours (e.g., Wilms tumour).

Management

General Principles of Lengthening

• Do not lengthen >15% of residual limb length in one sitting.
• Best done at metaphysis:
  • Less non-union
  • Easier access
• Rate: 1mm/day in 3-4 slots.
• Start lengthening 5-7 days after corticotomy.
• Leave fixator on for at least the same time as the lengthening period.
• For very long discrepancies (>15cm), amputation and prosthetic fitting may provide better outcomes.

Acute Shortening

• For discrepancies of 2-5cm, shortening is an option, especially in the upper limb.
• Most predictable when performed after skeletal maturity.

Epiphysiodesis

• Performed with a drill – no plating required.
• Predictable and easy to perform.

Physeal Bar Excision

• More reliable in post-traumatic than post-infection cases.
• Indicated if:
  • <50% of the physis is affected.
  • 2cm discrepancy or at least 2 years of growth left.
• Shortening or epiphysiodesis may be easier and more reliable.

Options Based on Limb Length Discrepancy