Radiologic Results of Selective Thoracic Fusion in Adolescent Idiopathic Scoliosis (AIS) Lenke Type 3 and 4.

BACKGROUND: Selective thoracic fusion (STF) in Lenke type 3 and 4 adolescent idiopathic scoliosis (AIS) remains controversial because the thoracolumbar/lumbar curve is structural and is traditionally included in the fusion. This study evaluated the early radiographic outcomes of STF in preference-selected patients with Lenke type 3 and 4 AIS.

METHODS: A retrospective review was performed of 22 patients with Lenke type 3 or 4 AIS who underwent posterior STF between 2016 and 2022. Standing radiographs were evaluated preoperatively, immediately postoperatively, and at 1-year follow-up. Thoracic and lumbar curve magnitude, coronal and sagittal balance, lumbar lordosis, and radiographic factors potentially associated with spontaneous lumbar correction were analyzed.

RESULTS: Seventeen patients had Lenke type 3, and 5 had Lenke type 4 curves. The thoracic curve improved from 68 degrees preoperatively to 28 degrees immediately postoperatively (P<0.001). The unfused lumbar curve improved from 49 degrees preoperatively to 29 degrees immediately postoperatively and measured 30 degrees at 1-year follow-up (P<0.001 compared with preoperative values). Coronal balance worsened transiently immediately after surgery but returned to approximately the preoperative position at 1 year. Lumbar lordosis decreased from 56 degrees preoperatively to 48 degrees immediately postoperatively and recovered to 60 degrees at 1 year. Greater thoracic correction was associated with greater immediate lumbar correction (Spearman ρ=0.521, P=0.014), but this association was not maintained at 1 year. Preoperative lumbar Cobb angle (P=0.082) demonstrated borderline significance as a predictor; otherwise, no significant predictors were identified. One patient (5%) required revision with distal extension of the fusion to L3.

CONCLUSIONS: In this preference-selected cohort of patients with Lenke type 3 and 4 AIS, STF was associated with spontaneous improvement of the unfused structural lumbar curve during the first postoperative year. Early postoperative coronal imbalance and loss of lumbar lordosis largely recovered by 1 year. STF may be considered in carefully counseled patients seeking preservation of lumbar motion segments; however, these findings do not establish general selection criteria or long-term durability.

LEVELS OF EVIDENCE: Level IV.