**6. Classification of Kümmel's disease**

In an attempt to classify the alterations associated with KD, morphological analyses regarding the type, degree of deformity and severity of vertebral collapse with questionable clinical relevance in acute processes was proposed [101]. Later, was proposed a multidimensional scheme for the classification of VCF suggesting that it could have application in the selection of surgical treatment and follow-up of patients. This included six dimensions fracture morphometry, chronicity, repair, dynamic stability, rupture of intravertebral bone trabeculae or clefts, and involvement of the posterior cortex [102]. However, this has been considered complicated and without any correlation with a natural history of KD.

Then, another specific classification proposal for this disease is raised, dependent on the progression and sequential clinical changes of the same. For this scale, Stage I corresponded to vertebrae intact or with a loss of height of the anterior portion of the vertebral body of less than 20% and without IVC in plain X-ray films, with a small cleft and fluid sign on T2-weighted

30 patients in the literature have been reported. A patient with sarcoidosis discarded the possibility of osteoporotic vertebral collapse due to the shape and narrowing of the intravertebral groove, the involvement of the body and the posterior elements of the vertebra and lack of

Radiographically, non-demonstrable evidence of a fracture in consecutive studies supports the diagnosis of KD [14]. However, it is important to perform the differential diagnosis between KD and nontraumatic or spontaneous vertebral ON associated with osteoporosis. Clinically, it should be emphasized that osteoporotic compression fractures are not associated with neurological symptomatology. On the other hand, chronic radiographic osteoporotic fractures are not associated with changes in signal intensity on MRI [35]. This contrasts with the variability in signal characteristics on MRI in KD [6, 98]. Usually, these appear with an increase in the signal on T1-weighted images and reduced signal on T2-weighted images. However, in both KD and spontaneous vertebral ON, a hyperintense linear area on MRI can be observed. This pattern of signal change has been referred "double line sign" and corresponds to the phenomenon of IVC. This describes the accumulation of gas in the vertebral body observed in X-ray studies (**Figure 1**). This sign has also been observed associated with malignancy and intraosseous disc herniation, so it should not be considered as pathogno-

Another radiological sign associated with ON is the intravertebral fluid of the vertebral body. This appears as a well-circumscribed area of low signal intensity on T1-weighted MRI and high signal intensity on T2-weighted images [39, 99]. This characteristic is known as a sign of fluid. In this regard, it was reported the coexistence of air and fluid in the same vertebral body in 21.5% of the cases. It was observed a more severe vertebral collapse in those cases with only

In an attempt to classify the alterations associated with KD, morphological analyses regarding the type, degree of deformity and severity of vertebral collapse with questionable clinical relevance in acute processes was proposed [101]. Later, was proposed a multidimensional scheme for the classification of VCF suggesting that it could have application in the selection of surgical treatment and follow-up of patients. This included six dimensions fracture morphometry, chronicity, repair, dynamic stability, rupture of intravertebral bone trabeculae or clefts, and involvement of the posterior cortex [102]. However, this has been

considered complicated and without any correlation with a natural history of KD.

Then, another specific classification proposal for this disease is raised, dependent on the progression and sequential clinical changes of the same. For this scale, Stage I corresponded to vertebrae intact or with a loss of height of the anterior portion of the vertebral body of less than 20% and without IVC in plain X-ray films, with a small cleft and fluid sign on T2-weighted

intravertebral air than in those with fluid with or without air [100].

**6. Classification of Kümmel's disease**

evidence of new bone formation in the collapsed body [19].

**5. Radiographic characteristics**

monic of ON.

26 Osteonecrosis

**Figure 1.** CT scan of the lumbar spine with compression fracture of L1 and intravertebral vacuum cleft (arrow). A Multiplanar reconstruction in sagittal, B volumetric reconstruction (3D), C axial plane.

MRI. In Stage II, loss of anterior body height would be more than 20% without an involvement of the posterior cortical, collapse of the vertebral body with dynamic mobility in the radiographs and presence of the cleft sign on MRI. Finally, in Stage III included the severe collapse of the vertebral body with dynamic mobility and rupture of the posterior cortical, as well as IVC with retropulsion of bone fragments and compression of the spinal cord. At this stage, the patients presented back pain, deformity and neurological deficit [103].

Also were reported three stages related to the pathogenesis of progression to delayed vertebral collapse. Stage 1 showed presence of intravertebral cleft, Stage 2 showed IVC plus intravertebral instability, and Stage 3 showed complete vertebral collapse [104]. We can summarize that the main application of these classification proposals has not only been to describe the evolution of osteoporotic CF, but also to evaluate the clinical efficacy and to determine the follow-up of different surgical procedures.
