Evaluation of functional and structural leg length discrepancy in patients with adolescent idiopathic scoliosis using the EOS imaging system: a prospective comparative study

Abstract

BackgroundTo our knowledge, no studies have reported the exact structural leg length discrepancies (LLDs) in patients with adolescent idiopathic scoliosis (AIS). Therefore, this study aimed to evaluate the differences between functional and structural LLDs and to examine the correlations between LLDs and spinopelvic parameters in patients with AIS using an EOS imaging system, which permits the three-dimensional reconstruction of spinal and lower-limb bony structures.MethodsEighty-two consecutive patients with AIS underwent whole-body EOS radiography in a standing position between August 2014 and March 2016. Functional LLD, lumbar Cobb angle, thoracic curve Cobb angle, coronal balance, and pelvic obliquity were measured using two-dimensional EOS radiography. Structural LLDs were measured using three-dimensional EOS-reconstructed images. The comparison between LLDs was assessed using paired t test. Pearson’s correlation coefficient (r) was used to determine potential correlations between the LLDs and spinopelvic alignment parameters.ResultsFunctional LLDs were significantly larger than structural LLDs (5.6 ± 5.0 vs. 0.2 ± 3.6 mm, respectively; p < 0.001). Both functional and structural LLDs were significantly correlated with pelvic obliquity (r = 0.69 and r = 0.51, respectively; p < 0.001 for both). Functional LLD, but not structural LLD, was correlated with lumbar Cobb angle (r = 0.44, p < 0.001; r = 0.17, p = 0.12, respectively). In addition, functional and structural LLDs were not correlated with thoracic Cobb angle (r = 0.09 and r = − 0.05, respectively; p ≥ 0.68 for both).ConclusionsAlthough patients with AIS often have functional LLDs, structural LLDs tend to be smaller. The correlation between functional LLDs and the lumbar Cobb angle indicates that functional LLDs compensate for the lumbar curve. Thus, the difference between functional and structural LLDs indicates a compensatory mechanism involving extension and flexion of the lower limbs.

Indications of sole lift and foot orthoses in the management of mild idiopathic scoliosis—a review

“…The functional LLDs appeared to be correlated with lumbar Cobb angles but not thoracic Cobb angles 14) . This suggested that functional LLD is possibly compensatory to lumbar curves.…”

“…They found that structural LLDs were not common in AIS patients as opposed to functional LLDs. Of the cohort, none had structural LLD in excess of 10 mm, whereas 18 of them had functional LLD in excess of 10 mm 14) .…”

“…Concerning structural scoliosis and how it relates to pelvis disposition and the leg length: Sekiya et al 14) used EOS imaging system to evaluate 82 AIS patients, to determine if they had anatomical LLDs. They found that structural LLDs were not common in AIS patients as opposed to functional LLDs.…”

“…Several studies found that LLD is correlated with pelvic tilt in the coronal plane, also called pelvic obliquity 1,2,13,14,[16][17][18] . Some have studied the immediate effects of artificially induced LLDs, using different measuring techniques and showed that LLD affected the pelvic disposition creating pelvic obliquity.…”

“…In the presence of lumbar curvature, addition of a sole lift on the side of apparent short leg would induce or enlarge the compensatory lumbosacral hemi-curve 4) . Another study has shown that majority of the LLD in structural scoliosis is apparent, and not anatomical 14) , thus questioning the use of sole lift in the presence of structural scoliosis.…”