Lumbar and Thoracolumbar Curves Are Associated with Coronal Lower Limb Malalignment in Adolescent Idiopathic Scoliosis

Background: Adolescent idiopathic scoliosis (AIS) may influence pelvic orientation and lower limb alignment, but data after completion of spinal correction are limited . Methods: In this retrospective study, 70 consecutive AIS patients (61 females, 9 males; mean age 17.0 ± 3.2 years, range 13–30 years) treated surgically (n = 52) or with brace therapy (n = 18) between 2010 and 2020 were analyzed. Patients were grouped by main curve location as thoracic (n = 28), lumbar (n = 21) or thoracolumbar (n = 21). Pre treatment standing full spine radiographs were used to measure Cobb angles, coronal balance and pelvic coronal obliquity angle (PCOA). After completion of spinal correction, full length weight bearing lower limb radiographs were obtained to assess femoral and tibial lengths, mechanical axis deviation (MAD), femoral neck–shaft angle (NSA), and distal/proximal femoral mechanical and anatomical angles. Results: Mean PCOA for the whole cohort was 2.3 ± 1.9°, and mean MAD was −0.41 ± 10.2 mm on the right and −0.7 ± 8.0 mm on the left. PCOA, coronal balance, MAD, right anatomical lateral distal femoral angle (aLDFA) and right mechanical lateral distal femoral angle (mLDFA) differed significantly among the three groups (p<0.05). Thoracolumbar versus thoracic curves showed higher PCOA and greater coronal imbalance (p = 0.011 and p = 0.004). The lumbar group demonstrated bilateral valgus alignment with more negative MAD values than the thoracic group (right MAD −5.88 ± 8.8 mm, left MAD −3.5 ± 7.5 mm; p = 0.004 and p = 0.005). The thoracic group had higher right aLDFA and mLDFA than lumbar and thoracolumbar groups (all p<0.05). No between group differences were found in femoral or tibial lengths or NSA (p>0.05) Conclusions: After spinal correction, AIS patients show subtle but measurable differences in coronal lower limb alignment according to curve location. Pelvic obliquity and MAD are more pronounced in lumbar and thoracolumbar curves, whereas limb lengths and NSA remain comparable among groups. These small deviations may influence long term load distribution and should be considered in the clinical assessment of AIS, particularly in patients with distal curve patterns.