Proposal of a New Treatment-Oriented Classification System for Spinal Deformity in Ankylosing Spondylitis

To describe and apply an optimal classification system for the management of ankylosing spondylitis (AS) that may be appropriate to make a preoperative surgical plan.

The treatment choices of ankylosing spondylitis kyphosis remain controversial. The lack of a widely accepted classification system contributes to the variation in surgical decision making.

The classification is mainly based on radiographic findings. The sagittal deformity of spine in ankylosing spondylitis is classified according to three criteria: the location of the apex, the lumbar modifier (A, lumbar lordosis <0°, and B, lumbar kyphosis >0°) and the thoracic/thoracolumbar kyphosis severity modifier (- or +).

The ankylosing spondylitis kyphosis can be divided into 4 types according to the location of the apex: Type I (lumbar), Type II (thoracolumbar), Type III (thoracic), Type IV (cervical or cervicothoracic junction). Either Type II or Type III is further divided into four subtypes based on the lumbar modifier and the thoracic/thoracolumbar kyphosis severity modifier: Type IIA-, Type IIA+, Type IIB-, Type IIB+, Type IIIA-, Type IIIA+, Type IIIB-, and Type IIIB+. Surgical decision making for AS kyphosis can be made according to the new classification.

This new classification system can be used effectively to classify AS kyphosis, which can be used to guide surgical decision making, including determining the site and the levels of osteotomies. Further research may be needed to validate the classification.