This study aimed to evaluate the relationship between upper instrumented vertebra (UIV) level and cervical sagittal alignment (CSA) in Lenke 1 adolescent idiopathic scoliosis (AIS) patients, treated with posterior instrumentation. The hypothesis was that higher level of UIV would cause decreased cervical lordosis.

Sixty-three Lenke 1 AIS patients that underwent posterior fusion with pedicle screw instrumentation were retrospectively evaluated. Patients were divided into three groups according to UIV level (T2, T3, T4). Twenty patients without spinal deformity made up the control group. Patients were compared at two years follow-up according to radiographic changes in coronal and sagittal planes. Main sagittal parameters were C2-C7 cervical lordosis (CL), T1 slope, T1-T5 and T5-T12 kyphosis. Clinical outcomes were assessed using scoliosis research society (SRS)-22, short form (SF)-36 and neck disability index (NDI) questionnaires.

Preoperative sagittal plane values of AIS patients were similar to the control group. C2-C7 CL, T1-T5 kyphosis and T1 slope significantly decreased postoperatively in T2 and T3 groups (p<0.05). These parameters were not changed significantly in T4 group after the surgery. T5-T12 kyphosis did not change significantly in all groups. SRS-22 and SF-36 scores significantly improved (p<0.05), while NDI scores were not changed significantly after the surgery.

In Lenke 1 AIS, treated with segmental all pedicle screw instrumentation using precontoured rods and rod rotation maneuver, postoperative decreased CL is more likely to occur if the UIV is selected as T2 or T3. Decreased CL seems to be caused by reduced T1-T5 kyphosis and T1 slope. However, the decrease in CL did not affect clinical outcome scores, including NDI, adversely. Hence, extending the fusion to appropriate level for shoulder balance seems reasonable.

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