1 Content

A spine severity measure should be based on relevant diagnostic items that include pertinent anatomy biomechanics, and clinical status (face validity). The diagnostic items should make intuitive sense and should be agreed upon by experts as appropriate and important (content validity). Furthermore, the measure must be able to distinguish between various degrees of severity.

In this book we divide the content of a severity measure as it relates to conditions of the spine into three main categories: type, scale, and interpretation (Fig 3–1).

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  Type refers to whether the severity measure is a disease severity or trauma severity measure.

  
  
  
  
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    Disease severity measures include those that measure disability as a result of a spinal disease process such as cervical myelopathy degenerative disc disease, ankylosing spondylitis, or idiopathic scoliosis.

    
    
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    Trauma severity measures include fracture classification systems, spinal cord injury measures and general trauma severity scores such as the Injury Severity Score.

  
  
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  Scale can be thought of in terms of the items that make up the severity measure. Four components, each containing one or more items, are considered important in evaluating spine severity scores, what we call the ABCDs of severity scoring:

  
  
  
  
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     Anatomical component

     
     
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     Biomechanical component

     
     
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     Clinical component

     
     
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     Degree of severity component

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   The anatomical component specifies which important anatomical locations or structures are affected by the trauma or disease process. This is often stated in fracture classifications, which identifies the specific anatomic structures injured such as ligaments, discs, or bones as in the Oner Classification of Thoracolumbar Fractures [1]. An example of a nonfracture severity measure that includes an anatomical component is the Enthesis Index for ankylosing spondylitis [2]. The Enthesis Index measures the pain response to pressure at several anatomical locations such as the nuchal crest and posterior superior iliac spines.

   
   
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   The biomechanical component of a spine severity measure includes a description of the mechanism or pattern of injury or disease, or an assessment of the stability of the spinal segment(s). The biomechanical component is essential because both mechanism of injury and spinal stability provide important information with respect to treatment options. The Thoracolumbar Injury Severity Score (TLISS) classification of thoracolumbar fractures is an example of a trauma severity measure that considers spinal stability by assessing the integrity of the posterior ligamentous complex [3]. On the other hand, the Kaufer classification of thoracolumbar fractures is based on morphology without considering instability in the grading scheme [4].

   
   
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   Clinical status as a measure of spine severity is often predictive of the final outcome in patients with spine trauma or disease [5–7]. Yet this important component is often omitted in spine severity measures. Inclusion of clinical status occurs more frequently in nonfracture measures such as in the Nurick or JOA measures for cervical myelopathy. One fracture classification that incorporates a clinical component by including the patient’s neurological status is the TLISS classification of thoracolumbar fractures. How well the patient functions and his/her quality of life remain the most important outcomes following treatment for spinal trauma or disease onset. Therefore, clinical or functional status as a component of a severity measure is essential.

   
   
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   A severity measure by definition should distinguish between degrees or levels of severity. Generally those with greater disease severity have poorer prognosis compared with those possessing lesser disease severity. An example is the Frankel Spinal Cord Severity Measure [8] where a category “A” injury represents complete paralysis and a category “E” represents normal function. Clearly patients with a category “A” injury have a poorer prognosis compared with those in category “E”. Some severity measures do not order their categories by degree of severity; rather their classification is primarily descriptive. The Three Zone Classification of Sacral Fractures by Denis [9] is an example where the classification is based on the location of the fracture; Zone 1 in the region of the ala, Zone 2 in the region of the foramina, and Zone 3 in the region of the central sacral canal. While the location of these fractures may be associated with characteristic clinical symptoms, a fracture in one zone is not necessarily more severe than a fracture in another zone.

All severity measures attempt to describe the extent of disease or injury using one or more of these components. While not all of the components are applicable for each type of severity measure, we believe that a good severity measure should consider parameters from each of these components.

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  Interpretation informs the reader as to what the severity score or classification means. For example, are higher scores indicative of greater or lesser severity?