Limb-Length Discrepancy

CHAPTER 60

Limb-Length Discrepancy

Introduction/Etiology/Epidemiology

• Incidence of limb-length inequality, or anisomelia, is unknown. Studies estimate up to 35% of adults have discrepancies between 0.5 and 1.5 cm.

• Underdiagnosis of small discrepancies is common.

• Misdiagnosis of discrepancies is also common.

• Discrepancies may be acquired, congenital, or idiopathic (very common) (Box 60-1).

• Clinically significant leg-length discrepancies usually have an identifiable cause.

• The behavior of a limb-length discrepancy depends on its etiology.

• Acquired leg-length discrepancy is most commonly caused by trauma or infection.

— Trauma to the growth plates: the potential resultant discrepancy depends on the affected bone, the amount of growth remaining, and the extent of injury to the growth plate.

■A Salter-Harris type II injury of the distal femoral physis has a reported rate of growth arrest as high as 37%.

■In contrast, a Salter-Harris type II injury of the distal radius may lead to growth arrest only 4% of the time.

■Different physes grow at different but consistent rates and close at different times. For example, a distal femoral physeal fracture in a boy with a skeletal age of 10 years with 6½ years of growth remaining could result in a 6-cm (0.9 cm/year × 6.5 years = 5.85 cm) discrepancy. The same fracture in the distal tibial physis would only result in a 2-cm (0.3 cm/year × 6.5 years = 1.95 cm) discrepancy that may not require any intervention.

■The diaphysis may be shortened by trauma or stimulated to overgrow after a fracture.

■The fractured femoral diaphysis in a child aged 2 to 10 years may cause overgrowth of the ipsilateral injured side by an average of 1 cm (range, 0.4–2.7 cm). Seventy-eight percent of the overgrowth occurs in the first 18 months after fracture.

— Osteomyelitis: bacterial enzymes and inflammation can injure the growth plate.

• Congenital leg-length discrepancies tend to worsen with time.

Box 60-1. Etiology of Limb-Length Discrepancy

Acquired

• Trauma

— Acute bone loss

— Physeal fracture

— Post-traumatic overgrowth

— Burns

— Irradiation

— Iatrogenic (surgical)

• Infection

— Osteomyelitis

— Septic arthritis

— Bacteremia

— Inflammation

— Juvenile idiopathic arthritis

— Hemophilia

— Pigmented villonodular synovitis

•Neurologic

— Closed head injury

— Poliomyelitis

— Cerebral palsy

— Myelomeningocele

• Vascular

— Congenital heart disease

— Thromboembolic

Congenital

• Developmental dysplasia of the hip

• Limb hypoplasia

• Proximal focal femoral deficiency

• Congenital short femur/tibia

• Hypoplastic femur

• Fibular hemimelia

• Tibial hemimelia

• Congenital pseudarthrosis of tibia

• Amniotic band syndrome

• Hemihypertrophy/atrophy

• Idiopathic

• Overgrowth syndromes

— Klippel-Trénauney syndrome

— Beckwith-Wiedemann syndrome

— Proteus syndrome

— Russell-Silver syndrome

— Neurofibromatosis-1

• Skeletal dysplasia

• Ollier disease

• Fibrous dysplasia

• Multiple hereditary exostoses

Signs and Symptoms

• The most common presenting symptoms are abnormal asymmetry of gait, toe walking, scoliosis, hip pain, and back pain.

Differential Diagnosis

• Leg-length discrepancies may be real or apparent (Figure 60-1).

• Muscle contractures or bony deformities around the hip may produce a pelvic tilt that causes an apparent leg-length discrepancy.

Diagnostic Considerations

• History may reveal one or more of the following causes or risk factors:

— History of trauma, infection, burn, or other injury to the limbs

— History of clubfoot, bowing of the tibia, café au lait spots (a sign of neurofibromatosis), and overgrowth/hemihypertrophy or “swelling” of the leg (Figure 60-2)

— Family history of skeletal dysplasia

• Physical examination should address the following:

— Lower extremity limb-length assessment can be simply and rapidly performed.

— Lower extremity limb lengths should be assessed at the annual well-child care visit and whenever a gait abnormality, hip pain, or spinal asymmetry is identified.

— Observe posture and gait from behind, focusing on the pelvis.

■Limp resulting from limb-length discrepancy is associated with a decreased stance time on the shorter side, decreased walking velocity, increased cadence, and decreased step length on the shorter side (may walk with ankle plantar flexion on short side and/or flexed knee posture on long side)

Figure 60-1. Real versus apparent leg-length discrepancy. A, normal; B, apparent; C, real. The apparent leg length is measured from the umbilicus to the tip of the medial malleolus. This will take into account pelvic obliquity due to muscle contracture around the pelvis. Real leg length may be measured from the anterior superior iliac spine to the tip of the medial malleolus.