1) Description of Measurement

The Cincinnati / PUMC Classification System is an operative classification for adolescent idiopathic scoliosis (AIS) designed to improve reliability and to directly guide surgical fusion strategy. Unlike earlier systems, it incorporates not only coronal curve morphology, but also curve magnitude, flexibility, apical rotation, stable vertebra, and thoracolumbar sagittal alignment.

Curves are divided into three major types based on number of apices:

• Type I: Single curve

• Type II: Double curves

• Type III: Triple curves

These are subdivided into Ia, Ib, Ic, IIa, IIb, IIc, IId, IIIa, and IIIb, each with distinct morphologic patterns and fusion guidelines.

2) Instructions to Measure

For each patient obtain standing AP, lateral, and supine side-bending radiographs.

Record the following parameters:

1. Cobb Angle

• Measure Cobb angle for each curve.

• A curve is defined when Cobb angle >10°.

1. Flexibility (%):

Flexibility = Standing Cobb - Convex Bending CobbStanding Cobb100

1. Apical Vertebral Rotation

• Grade rotation using the Nash-Moe method (Grade 0-4)

1. Stable Vertebra

• Identify the most distal vertebra bisected by the Central Sacral Vertical Line (CSVL)

1. Thoracolumbar Kyphosis

• Measure sagittal Cobb angle between T12-L1

• Kyphosis is defined as angle > 0°

3) Normal vs. Pathologic Ranges

• Normal Cobb Angle: < 10°

• Pathologic Cobb Angle: ≥ 10° (defines scoliosis)

• Normal Curve dominance: Difference < 10° = equivalent

• Pathologic Curve dominance: Difference ≥ 10° = larger vs minor curve

• Normal Flexibility: > 70% 

• Pathologic Flexibility: < 50% (rigid)

• Normal Apical rotation (Nash-Moe): Grade 0-I

• Pathologic Apical rotation (Nash-Moe): ≥ Grade II (significant)

• Normal thoracolumbar kyphosis: 0°

• Pathologicc thoracolumbar kyphosis: > 0° indicates kyphotic TL junction

4) Important References

Qiu G, Zhang J, Wang Y, et al. A new operative classification of idiopathic scoliosis: a peking union medical college method. Spine (Phila Pa 1976). 2005 Jun 15;30(12):1419-26. doi: 10.1097/01.brs.0000166531.52232.0c.

Nash CL Jr, Moe JH. A study of vertebral rotation. J Bone Joint Surg Am. 1969 Mar;51(2):223-9.

Qiu G, Zhang J, Wang Y, et al. A new operative classification of idiopathic scoliosis: a peking union medical college method. Spine (Phila Pa 1976). 2005 Jun 15;30(12):1419-26. doi: 10.1097/01.brs.0000166531.52232.0c.

5) Other info....(Curve Types and Surgical Logic)

• Type Ia: Single thoracic (Apex T2-T11/12)

• Type Ib: Single thoracolumbar (TL/L) (Apex T12-L1)

• Type Ic: Single lumbar (Apex L1-L4/5)

• Type IIa: Double thoracic (Two thoracic apices)

• Type IIb: Thoracic + TL/L (thoracic ≥ 10° larger)

• Selective thoracic fusion if lumbar Cobb ≤ 45°, flexibility ≥70%, rotation ≤ Grade I

• Type IIc: Thoracic + TL/L (difference <10°)

• Fusion based on relative flexibility

• Type IId: Thoracic + TL/L (lumbar ≥10° larger)

• Selective lumbar if thoracic flexible

• Type IIIa: Triple curves – distal flexible

• Fuse proximal two curves

• Type IIIb: Triple curves – distal rigid

• Fuse all three curves