Visual semiquantitative methods of vertebral fracture assessment

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The first standardized approach was introduced by Smith et al. [44] in 1960. They introduced a classification of vertebral deformities as diagnosed from lateral thoracolumbar radiographs for the purpose of diagnosing the severity of osteoporosis. This method grades only the most severely deformed vertebra on the radiograph. In 1968 Meunier [33] proposed an approach in which each vertebra is graded according to its shape or deformity. Grade 1 is assigned to a normal vertebra that has no deformity, grade 2 to a biconcave vertebra, and grade 4 to an endplate fracture or a wedged or crushed vertebra. Using this approach vertebral bodies T3 (or T7) to L4 are evaluated. A "radiological vertebral index" can be calculated as the sum of the grades of all vertebrae, or as the quotient of this sum and the number of the vertebrae.

Kleerkoper et al. [26] modified Meunier's radiological vertebral index and introduced the so-called "vertebral deformity score." In the vertebral deformity score each vertebra from T4 to L5 is assigned an individual score from 0 to 3 depending on the type of deformity. This grading scheme is based on the reduction in the anterior, middle, and posterior vertebral heights (ha,hm, and hp, respectively).

A vertebral deformity (graded 1-3) is present when ha, hm, or hp is reduced by at least 4mm or 15%. This score, as with Meunier's radiological vertebral index, still relies very much on the type of deformity, i.e., the vertebral shape, and there would have to be changes in vertebral shape in order to account for incident vertebral fractures on follow-up radiographs. Furthermore, the majority of vertebral fractures consist of a combination of wedge and endplate deformities, and less frequently posterior deformities. Therefore an examiner's distinction among these deformities is often quite subjective.

A vertebral deformity does not always represent a vertebral fracture, but a vertebral fracture is always a vertebral deformity. From a radiological prospective, there are many potential differential diagnoses for vertebral deformities - osteoporotic fracture, posttraumatic deformity, degenerative remodeling, Scheuermann's disease (juvenile kyphosis), congenital anomaly, neoplastic deformity, and Paget's disease - and the correct qualitative classification of vertebral deformities can be accomplished only by visual inspection and expert interpretation of the radiograph. This perspective on vertebral fracture diagnosis is perhaps reflected at its best in the semiquantitative fracture assessment method proposed by Genant et al. [12, 13, 14, 15] This method provides an insight into the severity of a

Fig. 1 Schematic diagram of semiquantitative grading scale for vertebral fractures. (From Genant et al. [13])

Fig. 1 Schematic diagram of semiquantitative grading scale for vertebral fractures. (From Genant et al. [13])

fracture which is assessed solely by visual estimation of the extent of a vertebral height reduction and morphological change, and vertebral fractures are differentiated from other, nonfracture deformities. In Genant's visual semiquantitative assessment (Fig. 1) each vertebra receives a severity grade based upon the visually apparent degree of vertebral height loss. Unlike the other approaches the type of the deformity (wedge, biconcavity, or compression) is no longer linked to the grading of a fracture in this approach.

Thoracic and lumbar vertebrae from T4 to L4 are graded on visual inspection and without direct vertebral measurement as normal (grade 0), mildly deformed (grade 1: reduction of 20-25% of height and 10-20% of projected vertebral area), moderately deformed (grade 2: reduction of 26-40% of height and 21-40% of projected vertebral area), and severely deformed (grade 3: reduction of >40% of height and projected vertebral area; Fig. 2). A grade 0.5 designates "borderline" vertebrae that show some defor-

mation but cannot be clearly assigned to grade 1 fractures is sometimes also utilized. In addition to height reductions, careful attention is given to alterations in the shape and configuration of the vertebrae relative to adjacent vertebrae and expected normal appearances. These features add a strong qualitative aspect to the interpretation. For example, vertebral deformities due to degenerative changes should be ruled out, whereas an endplate vertebral fracture can be identified without a 20% reduction in the vertebral height. Nevertheless, in experienced, highly trained hands, it makes the approach both sensitive and specific. A "spinal fracture index") can be calculated from this semiquantitative assessment as the sum of all grades assigned to the vertebrae divided by the number of the evaluated vertebrae.

An advantage of this semiquantitative approach over other standardized visual approaches is that the severity of the deformation as the reduction in vertebral height means can be assessed from serial films and is especially useful for the interpretation of incident fractures. It considers the continuous character of vertebral fractures and makes a meaningful interpretation of follow-up radiographs possible. Furthermore, inevitably arbitrary decisions regarding wedge, endplate, or crush deformities, as assessed in some grading schemes, are not necessary since most fractures

contain a combination of these features, influenced by the local biomechanics of the spinal level.

The Genant's semiquantitative method has been tested and applied in a number of clinical drug trials and epi-demiological studies [15, 20, 47, 50, 52]. The repro-ducibility of the method for the diagnosis of prevalent and incident vertebral fractures was found to be high, with in-traobserver agreement of 93-99% and interobserver agreement of 90-99%. This indicates that close agreement among readers can be reached using this standardized visual semiquantitative grading method, and that subjectivity in the readings can be reduced. This accounts for experienced and relatively inexperienced readers with reasonable results.

There are limitations of this semiquantitative grading scheme that may also apply to other standardized approaches. For example, from the morphometric data on normal subjects we know that vertebrae in the middle thoracic spine (especially in women) and thoracolumbar junction (especially in men) are slightly more wedged than in other regions (Fig. 3) [3, 30, 32, 40]. As a result these normal variations may be misinterpreted as mild vertebral deformities, thereby falsely increasing prevalence values for vertebral fractures. The same applies to a lesser extent to the middle to lower lumbar spine, where some degree of biconcavity is frequently observed [26, 45]. Accurate diagnosis of prevalent fractures which requires distinguishing between normal variations and the degenerative changes from true fractures still depends on the experience of the observer. It has been argued that the diagnosis of mild vertebral fractures (grade 0.5-1) in particular may be quite subjective, and that these fractures may be unrelated to osteoporosis [45]. However, mild fractures are also associated with a lower bone density and to a certain extend predict future vertebral fractures [1].

Other limitations may apply for the diagnosis of incident fractures. The reader may sometimes feel that even though a further height reduction is seen in a previous vertebral fracture, it may not be justified to assign a higher fracture grade on a serial radiograph, since some degree of settling or remodeling generally occurs. Therefore in general, serial radiographs including the baseline radiograph of a patient should be viewed together so that incident fractures can be readily identified as only those progressive changes that lead to a full increase in deformity grade or from a questionable deformity (grade 0.5) to a definite fracture.

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