Overview and Spinal Implications of Leg Length Discrepancy: Narrative Review.

Leg length discrepancy (LLD) is an underrecognized and prevalent condition among the U.S. population, with effects varying depending on the cause and size of the discrepancy. LLD occurs when the paired lower extremities are unequal in length and can be etiologically classified as functional or structural. Length differences are typically less than 10 mm and asymptomatic or easily compensated for by the patient through self-lengthening or shortening of the lower extremities. Literature review of the etiology, diagnostic modalities, clinical complications, and treatment option for patients with LLD. LLD can be assessed directly through tape measurements or indirectly through palpation of bony landmarks. Imaging modalities, specifically radiography, are more precise and help identify coexistent deformity. Once LLD has been diagnosed, evaluation for potential adverse complications is necessary. Discrepancies greater than 20 mm can alter biomechanics and loading patterns with resultant functional limitations and musculoskeletal disorders, such as functional scoliosis. Functional scoliosis is nonprogressive and involves a structurally normal spine with an apparent lateral curvature, which regresses fully or partially when the LLD is corrected. Long-standing LLD and functional scoliosis often result in permanent degenerative changes in the facet joints and intervertebral discs of the spine. Further understanding of the contribution of LLD in the development of scoliosis and degenerative spine disease will allow for more effective preventative treatment strategies and hasten return to function.