What are the causes of leg length discrepancy?

Causes of Leg Length Discrepancy

Leg length discrepancy arises from congenital/developmental abnormalities, acquired conditions affecting bone growth, neurological disorders, metabolic bone diseases, and apparent discrepancies from spinal or pelvic pathology. 1

Congenital and Developmental Causes

Skeletal dysplasias represent a major category of congenital causes:

• Achondroplasia, osteogenesis imperfecta, and enchondromatoses cause disproportionate limb shortening with characteristic radiographic patterns 1
• Hemihypertrophy/hemiatrophy syndromes produce unilateral limb length differences from asymmetric growth 1
• Congenital femoral deficiency or fibular hemimelia result in significant shortening of affected bones 1
• Enchondromatoses (Ollier disease and Maffucci syndrome) cause bone shortening with leg length discrepancy due to multiple enchondromas affecting long bones, typically presenting in early childhood 1

Developmental dysplasia of the hip (DDH) is an important acquired-congenital cause:

• Unrecognized and untreated subluxation/dislocation inevitably leads to early degenerative joint disease 2
• DDH causes up to one-third of all total hip arthroplasties in patients under 60 years of age 2
• Complications of DDH treatment itself can cause leg length discrepancy, including avascular necrosis, femoral shortening, varus deformity at reduction, and septic arthritis 3

Acquired Causes

Tumor and tumor-like lesions affecting bone growth:

• Enchondromas can transform to chondrosarcoma in approximately 30% of enchondromatosis patients 1
• Any bone tumor affecting the growth plate can result in limb length discrepancy 1

Neurological conditions cause undergrowth of affected limbs:

• Poliomyelitis or cerebral palsy may cause undergrowth of affected limbs 1
• Muscle spasticity in cerebral palsy leads to joint contractures and apparent shortening 1

Trauma and infection:

• Growth arrest from physeal injury is a common acquired cause 4
• Septic arthritis complicating hip treatment can contribute to leg length discrepancy 3

Metabolic and Systemic Causes

Metabolic bone diseases affect bone growth and limb development:

• X-linked hypophosphatemia causes severe leg bowing and growth abnormalities with characteristic biochemical findings 1
• Vitamin D deficiency and rickets affect bone growth and can contribute to limb deformities 1

Apparent Leg Length Discrepancy (Not True Bone Length Difference)

Spinal and pelvic pathology creates the illusion of leg length discrepancy:

• Pelvic obliquity from scoliosis creates apparent shortening without true bone length difference 1
• Tethered cord syndrome can cause progressive scoliosis and exaggerated lumbosacral lordosis, leading to apparent leg length discrepancy 2, 1
• Patients with tethered cord may have a history of previously repaired orthopedic deformities or leg length discrepancies dating back to early childhood 2

Joint contractures from various causes:

• Muscle spasticity in conditions like cerebral palsy leads to joint contractures and apparent shortening 1

Iatrogenic Causes

Chorionic villus sampling (CVS) has been associated with limb deficiencies:

• CVS performed before 68 days' gestation is associated with more severe limb deficiencies and oromandibular-limb hypogenesis 2
• Approximately 74% of infants exposed to CVS at ≥70 days' gestation who developed limb deficiencies had digital deficiencies without proximal involvement 2
• The severity of outcome is associated with the specific timing of CVS exposure 2

Critical Diagnostic Pitfalls to Avoid

Distinguish true from apparent leg length discrepancy:

• Evaluate spine alignment for scoliosis or lordosis that might cause pelvic obliquity 1
• Standing radiographs provide accurate measurement of true leg length and are superior to supine films for clinical decision-making 1

Screen for systemic conditions:

• Check for disproportionate body habitus by measuring upper-to-lower segment ratios and arm span 1
• Skeletal survey is mandatory when disproportionate short stature or skeletal dysplasia is suspected 1
• Spinal MRI should be obtained when tethered cord syndrome is suspected based on cutaneous markers, neurological findings, or unexplained leg length discrepancy with back pain 1

Obtain appropriate laboratory evaluation:

• Metabolic workup including serum phosphate, alkaline phosphatase, vitamin D, PTH, calcium, and magnesium is necessary when metabolic bone disease is suspected 1
• FGF23 levels should be measured if X-linked hypophosphatemia is considered 1
• Genetic testing may be indicated for suspected skeletal dysplasias 1