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