Choosing the Distal Fusion Levels in Lenke Type 1 Adolescent Idiopathic Scoliosis: How Do the Existing Classifications and Recommendations Guide Us?

Abstract

Study design: Retrospective cohort.

Objective: (a) To compare the recommendations of Lenke and Peking Union Medical College (PUMC) classifications in choosing distal fusion levels in Lenke 1 adolescent idiopathic scoliosis (AIS) curves and (b) to analyze whether the variability in distal fusion levels influences treatment outcomes.

Methods: Hospital records of Lenke 1 AIS patients operated for single stage, posterior-only deformity correction were analyzed. Distal fusion levels recommended by Lenke and PUMC classifications were calculated and were compared with the actual distal fusion levels. The study population was divided based on whether the actual distal fusion levels were in agreement, shorter or longer than those recommended by Lenke classification. Subgroup analysis of Lenke 1C curves was done. The groups were compared with regard to the following outcome measures: Cobb angle correction, postoperative sagittal vertical axis, postoperative C7 offset, and Scoliosis Research Society-22r (SRS-22r) score at 24 months.

Results: The distal fusion levels recommended by the 2 classifications were in agreement in 92 of 104 cases. In all the cases with disparity, Lenke classification recommended shorter fusions than the PUMC classification. No statistically significant difference was observed in the outcome measures-whether the actual distal fusion levels were in agreement, shorter, or longer than those recommended by the Lenke classification or whether or not the recommendations for selective fusion of any of these classifications were adhered to.

Conclusion: Lenke classification can save fusion levels without compromising on treatment outcomes when compared with PUMC classification. Variability in choice of distal fusion levels is not clinically significant at 24-month follow-up.

Keywords: Lenke classification; PUMC classification; adolescent idiopathic scoliosis; scoliosis; spinal deformity.

Figure 1.

(A) Anteroposterior (AP) and lateral radiograph of a patient having a Lenke type 1C curve. Lenke-recommended fusion level: L5 (nonselective fusion) as the MT:TL/L Cobbs’ ratio <1.2, AVT < 1.2. PUMC-recommended fusion level: L5 (subtype IIb2) as the TL/L Cobbs >45°, TL/L rotation = 2°. (B) Postoperative AP and lateral radiograph of the same patient shown in (A). Our actual distal fusion level = L2 (matches neither with the Lenke- nor with the PUMC-recommended levels). PUMC, Peking Union Medical College; MT, main thoracic; TL/L, thoracolumbar/lumbar; AVT, apical vertebral translation; AVR, apical vertebral rotation; SVA, sagittal vertical axis.

Figure 2.

(A) Anteroposterior (AP) and lateral radiograph of a patient having a Lenke type 1C curve. Lenke-recommended fusion level: L1 (selective fusion) as the MT:TL/L Cobbs’ ratio >1.2, AVT > 1.2, AVR > 1.2, positive flexibility index. PUMC-recommended fusion level: L5 (subtype IIb2) as the TL/L Cobbs >45°. (B) Postoperative AP and lateral radiograph of the same patient shown in (A). Our actual distal fusion level = L1 (matches with the Lenke recommended level but not with the PUMC recommended level). PUMC, Peking Union Medical College; MT, main thoracic; TL/L, thoracolumbar/lumbar; AVT, apical vertebral translation; AVR, apical vertebral rotation; SVA, sagittal vertical axis.