“We need a specific language for adult deformity”

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The Schwab Adult Spinal Deformity Classification was established to categorise adult spinal deformity and direct management. Last year, the classification system was revised to include pelvic parameters. Frank Schwab, clinical professor, Department of Orthopaedic Surgery, Center for Musculoskeletal Care, New York, USA, spoke to Spinal News International about the clinical relevance of the classification system.

What is the clinical role of classification systems? And why was it necessary to develop one specifically for adults with spinal deformity?

Classification systems are tremendously important in orthopaedics because they allow us to group patients into categories, and they also allow us to compare natural history with treatment strategies. We need a specific language for adult deformity and classification systems act as this language.

We cannot use classification systems that have been established for the paediatric population (eg. ones for adolescent idiopathic scoliosis) in the adult population because the main drivers for treatment are different. In children, the main drivers are cosmetic or the risk of progression. In adults, however, the main drivers for treatment are pain and disability—these factors are rare in children with spinal deformity. Therefore, a new classification system for adults was required.

It has taken us nearly 10 years to develop the Schwab Adult Spinal Deformity Classification system; it is not something that was quickly thought up—it is based on a lot of outcome data.

The system was recently revised to include pelvic parameters. Why was it important to include these parameters

The initial classification was built upon on a very large database of patients. However, at that point, the relevance of pelvic parameters was not well established because the data for pelvic parameters were limited. Now, as more data have emerged, we know that pelvic parameters play a substantial role in disability and pain in the setting of adult deformity. Therefore, we realised that pelvic parameters had to be added to the classification system.

What is the evidence base for this revised system?

The evidence now indicates that pelvic parameters are critical in determining the ideal alignment of the lumbar spine and that they are also critical for understanding the compensatory mechanisms that a patient may use to deal with their spinal deformity (particularly in the sagittal plane).

The other evidence that has emerged from our work related to the classification system is that not only does it help us to create distinct categories of patients according to one what sees radiographically, but it also helps us to create thresholds of disability. Furthermore, we can use the system to identify surgically modifiable factors and, therefore, understand what we need to surgically correct to reduce the patient’s deformity/disability.

How might the system be further revised?

Classification systems have to be balanced between something that is clinically valuable and something that is simple enough to use in everyday practice. I think we have that balance with this system, but I would like to add more surgical modifiers. For instance, the system could be enhanced in such a way that a surgeon could use it to define in more specific detail which levels need to be fused.

What is the clinical role of this classification system?

It is a global classification system, so can be used in all adults patients with deformity, and it can be used to give a much richer impression of the type of deformity that the patient has etc.

The system can also be used in a more academic setting. For example, it can be used to follow-up patients in a study to see how their deformity progresses or how they respond to treatment. Therefore, it has a pragmatic clinical role in an everyday sense but also a more far reaching scientific role.

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