J Korean Neurosurg Soc.  2021 Sep;64(5):776-783. 10.3340/jkns.2020.0348.

Adolescent Idiopathic Scoliosis Treated by Posterior Spinal Segmental Instrumented Fusion : When Is Fusion to L3 Stable?

• Hyun SJ
• Lenke LG
• Kim Y
• Bridwell KH
• Cerpa M
• Blanke KM

• KMID: 2519704
• DOI: http://doi.org/10.3340/jkns.2020.0348

Abstract

Objective
: The purpose of this study was to identify risk factors for distal adding on (AO) or distal junctional kyphosis (DJK) in adolescent idiopathic scoliosis (AIS) treated by posterior spinal fusion (PSF) to L3 with a minimum 2-year follow-up.
Methods
: AIS patients undergoing PSF to L3 by two senior surgeons from 2000–2010 were analyzed. Distal AO and DJK were deemed poor radiographic results and defined as >3 cm of deviation from L3 to the center sacral vertical line (CSVL), or >10° angle at L3–4 on the posterior anterior- or lateral X-ray at ultimate follow-up. New stable vertebra (SV) and neutral vertebra (NV) scores were defined for this study. The total stability (TS) score was the sum of the SV and NV scores.
Results
: Ten of 76 patients (13.1%) were included in the poor radiographic outcome group. The other 66 patients were included in the good radiographic outcome group. Lower Risser grade, more SV-3 (CSVL doesn’t touch the lowest instrumented vertebra [LIV]) on standing and side bending films, lesser NV and TS score, rigid L3–4 disc, more rotation and deviation of L3 were identified risk factors for AO or DJK. Age, number of fused vertebrae, curve correction, preoperative coronal/sagittal L3–4 disc angle did not differ significantly between the two groups. Multiple logistic regression results indicated that preoperative Risser grade 0, 1 (odds ratio [OR], 1.8), SV-3 at L3 in standing and side benders (OR, 2.1 and 2.8, respectively), TS score -5, -6 at L3 (OR, 4.4), rigid disc at L3–4 (OR, 3.1), LIV rotation >15° (OR, 2.9), and LIV deviation >2 cm from CSVL (OR, 2.2) were independent predictive factors. Although there was significant improvement of the of Scoliosis Research Society-22 average scores only in the good radiographic outcome group, there was no significant difference in the scores between the groups.
Conclusion
: The prevalence of AO or DJK at ultimate follow-up for AIS with LIV at L3 was 13.1%. To prevent AO or DJK following fusion to L3, we recommend that the CSVL touch L3 in both standing and side bending, TS score is -4 or less, the L3/4 disc is flexible, L3 is neutral (<15°) and ≤2 cm from the midline and the patient is ≥ Risser 2.

Keyword

Adolescent idiopathic scoliosis; Posterior spinal fusion; Lowest instrumented vertebra; Adding-on; Distal junctional kyphosis

Figure

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  Fig. 1. An example of radiographic measurement for deviation of the center of the L3 from the center sacral vertical line, distal junctional discal angulation at L3–4 in the coronal or sagittal plane.

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  Fig. 2. An example of radiographic evaluation for gravity, rotational and total stability scoring system. SV : stable vertebra, NV : neutral vertebra, TS : total stability.

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  Fig. 3. Representative cases of good (A) and poor (B) radiographic outcomes. A : A 14-year-old girl having neutral (<15°) L3 touched by the center sacral vertical line (CSVL) and located within 2 cm from the midline shows good radiographic outcome. B : A 15-year-old girl having rotated (>15°) L3 not touched by the CSVL and deviated more than 2 cm from the midline demonstrates poor radiographic outcome with 13° distal junctional discal angulation at L3–4 in the coronal plane. po : postoperative.

Reference

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