Table 3.

Criteria to classify adult scoliosis regarding type of lateral access fusion strategy

Type of deformity	Criteria	Surgical Strategy
Type I: localized nerve entrapment in adult scoliosis	Spinal stenosis at 1–2 levels and Two discs remaining between the upper level to be included in decompression/fusion and the apex of the curve and No severe degeneration or instability (including laterolisthesis) in the disc over the level to be decompressed or fused and sagittally balanced	Selective decompression or Selective decompression and fusion if instability is present or surgery will create instability
Type II: limited disc disease within the curve	Painful discs within the curve (i.e., Modic I changes in some of the discs, laterolisthesis at one or two discs, vacuum phenomenon in discs with severe collapse) and Mostly sagittally balanced. (Lumbar lordosis > pelvic incidence) and Coronal imbalance < 4 cm and Nonprogressive curve and Less severe curve (<30°) Ideally, painful discs around (over and below) the apex of the lumbar curve	Selective fusion with partial correction (do not correct over adjacent curve correction in bending films to avoid decompensation) Consider anterior XLIF alone (when little or no correction is needed) or XLIF and posterior instrumentation to improve and maintain correction, to improve sagittal balance or to restore coronal balance after anterior procedure
Type III: severe coronal deformity	Pain all over the curve or Progressive curve or More severe curve (>30°) or Coronal deformity with moderate sagittal imbalance or sagittally compensating	Fusion of the entire curve (as dictated by coronal and sagittal plane deformity): XLIF at all levels or at the more rigid segment plus posterior instrumentation. Eventually posterior correction of coronal imbalance if present after XLIF If discs in the extremes of the curve are preserved and mobile in lateral bending, consider XLIF at the apex (2 discs if apex is a vertebra, 3 discs if apex is a disc) with derotation of the apex through posterior instrumentation and compression in the convexity
Type IV: sagittal imbalance	No or minor coronal deformity Sagittally imbalanced or  Sagittally compensating with severe back pain or  Sagittally compensating with stenosis	Posterior instrumentation and fusion with osteotomies as needed. Consider adding XLIF (same day or staged) to increase stiffness around PSO or in open discs after SPO In case of severe sagittal deformity with large deformity coronal, consider XLIF at all levels or a the more rigid segment and at the levels of planned posterior osteotomy (see below) plus posterior instrumentation and fusion with osteotomies as needed In selected cases requiring less than 30° of sagittal correction, consider XLIF complete release and lengthening with hyperlordotic cage, followed by posterior instrumentation (currently under evaluation)