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Updated: Nov 15 2022

Leg Length Discrepancy (LLD)

Images lenght discrepancy scanogram_moved.jpg chart.jpg
  • summary
    • Leg Length Discrepancy is a common condition that may be caused by a congenital defect, disruption of the physis, or a paralytic disorder and presents with limb length asymmetry of varying magnitude. 
    • Diagnosis is made with block testing and radiographic scanography.  CT studies can be used to calculate LLD in the presence of contractures. 
    • Treatment is observation with or without shoe lifts for differences < 2 cm at skeletal maturity. Surgical intervention is indicated for differences > 2 cm, with different techniques depending on the discrepancy magnitude and remaining skeletal growth.
  • Epidemiology
    • Incidence
      • 2cm LLD occurs in up to 2/3 of the population
  • Etiology
    • Common causes of LLD
      • congenital disorders
        • hemihypertrophy
        • dysplasias
        • PFFD
        • DDH
        • unilateral clubfoot
      • paralytic disorders
        • spasticity (cerebral palsy)
        • polio
      • physis disruption
        • infection
        • trauma
        • tumor
    • Associated conditions
      • back pain
        • increased prevalence of back pain
      • osteoarthritis
        • decreased coverage of femoral head on long leg side leads to osteoarthritis 84% of the time
      • functional scoliosis
      • inefficient gait
      • equinus contracture of ankle
  • Classification
    • Static
      • malunion of femur or tibia
    • Progressive
      • physeal growth arrest
      • congenital
        • absolute discrepancy increases
        • proportion stats the same
  • Presentation
    • Symptoms
      • usually asymptomatic
    • Physical exam
      • block testing
        • with the patient standing, add blocks under the short leg until the pelvis is level, then measure the blocks to determine the discrepancy
        • block testing is considered the best initial screening method
      • tape measurement
        • measure from the anterior superior iliac spine to the medial malleolus with a tape measure
      • evaluate for hip, knee and ankle contractures
        • affect apparent limb length
        • hip adduction contracture causes apparent shortening of adducted side
  • Imaging
    • Radiographs
      • teleoroentgenography (scanography)
        • measure discrepancy with single exposure from 2m away
      • bone age hand films
        • determine bone age with bone age xray (hand)
    • CT Scanography
      • CT scanography is the most accurate diagnostic test with contractures of the hip, knee, or ankle
  • LLD Projections
    • General assumptions
      • growth continues until 16 yrs in boys and until 14 yrs in girls
    • Methods to project LLD at maturity
      • Mosley graph
      • estimation technique
        • leg grows 23 mm/year, with most of that coming from the knee (15 mm/yr)
          • proximal femur - 3 mm / yr (1/8 in)
          • distal femur - 9 mm / yr (3/8 in)
          • proximal tibia - 6 mm / yr (1/4 in)
          • distal tibia - 5 mm / yr (3/16 in)
    • Can be tracked with
      • Green-Anderson tables
        • uses extremity length for a given age
      • Moseley straight line graph
        • improves on Green-Anderson method by reformatting data in a graph form
        • accounts for differences between skeletal and chronologic age
        • minimizes error
          • averages serial measurements
      • Multiplier method
        • prediction based on multiplying the current discrepancy by a sex and age specific factor
        • most accurate for congenital LLD
        • 1/2 of final leg length
          • girls at age 3
          • boys at age 4
  • Treatment
    • Nonoperative
      • shoe lift or observation only
        • indications
          • < 2 cm projected LLD at maturity
        • outcomes
          • not associated with scoliosis or back pain
    • Operative
      • shortening of long side via epiphysiodesis of femur, tibia, or both
        • indications
          • 2-5 cm projected LLD
      • limb lengthening of short side
        • indications
          • > 5 cm projected LLD
          • lengthening often combined with a shortening procedure (epiphysiodesis, ostectomy) on long side
      • physeal bar excision
        • indications
          • bony bridge involves <50% of physis
          • at least 2 years left of growth
      • amputation and prosthetic fitting
        • indications
          • non-reconstructable limb
          • > 20 cmprojected LLD
  • Techniques
    • Distraction osteogenesis (Ilizarov principles)
      • initiation
        • perform osteotomy and place fixator
        • metaphyseal corticotomy to preserve medullary canal and blood supply
      • distraction
        • wait 5-7 days then begin distraction
        • distract ~ 1 mm/day
        • following distraction keep fixator on for as many days as you lengthened
      • concurrent procedures
        • may lengthen over a nail so ex-fix can be removed sooner
        • lengthening often combined with a shortening procedure (epiphysiodesis, ostectomy) on long side
  • Complications
    • Incomplete arrest/ angular deformity
      • open technique
      • percutaneous technique
    • Pin site infections
    • Fracture
    • Delayed union
    • Premature cessation of lengthening
    • Persistent limb length discrepancy due to error in timing of surgery
    • Joint subluxation/dislocation
    • Mechanical axis deviation (MAD)
      • lengthening along the anatomical axis of the femur leads to lateral MAD
      • shortening along the anatomical axis of the femur leads to medial MAD
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