Selection of the Lowest Instrumented Vertebra in Lenke-5 AIS: A Case Study With at Least 5-Year Follow-Up

The selection of the lowest instrumented vertebra (LIV) is crucial in the surgical treatment of adolescent idiopathic scoliosis (AIS), particularly for thoracolumbar/lumbar curves. While traditional LIV selection strategies primarily rely on weight-bearing radiographs, the utility of supine imaging remains unclear. This study aimed to evaluate the feasibility of using the last touched vertebra identified in the supine position (LTV-supine) as the LIV for Lenke-5 AIS.

We conducted a retrospective review of Lenke-5 AIS patients who underwent posterior spinal fusion at Peking Union Medical College Hospital from 2010 to 2017, with a minimum 5-year follow-up. All patients underwent distal fusion to the LTV-supine. Radiographic parameters, including coronal and sagittal alignments and LIV-related measurements (LIV tilt, translation, rotation, and the subjacent disc angle), as well as the Scoliosis Research Society-22 (SRS-22) scores were compared across preoperative, postoperative, and final follow-up time points using the paired t-tests. Based on the positional relationship between the LTV-supine (the selected LIV) and the LTV-upright, patients were categorized into two groups: the short-fusion group (LIV at the first vertebra proximal to the LTV-upright) and the non-short-fusion group (LIV at LTV-upright). Radiographic parameters, SRS-22 scores, and the incidence of radiographic complications were compared between groups using independent t-test.

Forty-five consecutive patients were included. Radiographic outcomes demonstrated significant improvements: the thoracolumbar/lumbar curve Cobb angle was corrected from 49.2° ± 10.8° preoperatively to 8.3° ± 5.6° at final follow-up (correction rate: 83.4% ± 10.9%; p < 0.05), and the coronal balance decreased from 20.3 ± 10.0 mm to 11.2 ± 6.9 mm (p < 0.05). All LIV-related parameters showed significant improvement at the final follow-up compared to preoperative values (p < 0.05). SRS-22 scores showed notable enhancements in self-image/appearance and mental health domains at final follow-up (p < 0.05). Fusion to LTV-supine saved 0.3 ± 0.5 distal vertebrae compared to the LTV-upright strategy (p < 0.05), resulting in shorter fusions in one-third of the patients (15/45). No significant differences were observed between the short-fusion (n = 15) and non-short-fusion (n = 30) groups in the final follow-up Cobb angle, correction rate, SRS-22 domain scores, nor in the incidence of adverse radiographic outcomes, such as sloped LIV, subjacent disc wedging, or coronal imbalance.

Supine imaging serves as a valuable adjunct for LIV selection in AIS. For Lenke-5 AIS, adopting the LTV-supine can yield comparable radiographic outcomes while potentially sparing additional distal segments in a subset of patients compared to the conventional upright radiograph-based approach.