For the treatment of CSOTF, the following two classifications for Kümmell’s disease are currently recognized by most scholars.9,14 Li et al9 divided Kümmell′s disease into 3 stages based on the degeneration of the adjacent intervertebral disc, the degree of vertebral height loss and its combination with spinal cord compression. However, the study by Li et al described the natural course of Kümmell′s disease. This type of staging of Kümmell′s disease is easy to understand and memorize, but it does not cover all of the fracture patterns found. Additionally, the type of Kümmell′s disease was classified based on the height of the vertebral body and the degeneration of the adjacent intervertebral disc. However, the correlation between these two factors and the classification and treatment of Kümmell’s disease had not been proved in current literature. The recommended treatment is limited to percutaneous vertebroplasty or open internal fixation, and it is less practical in guiding treatment. In 2013, Patil et al14 grouped Kümmell’s disease patients based on the morphological patterns of fracture and proposed surgical options for each group. The morphological feature of kyphosis deformity was first used as a basis for classification. Kyphosis deformity greater than 30° on standing lateral radiography is classified as an independent type and treated using pedicle subtraction osteotomy (PSO) and posterior spinal instrumentation. However, in consideration of the possible dynamic instability of injured vertebral body in some cases, the kyphosis can be reduced or disappeared with changes in body position; and a large invasive treatment, such as PSO, may not necessary for these patients. Therefore, this classification system incompletely evaluates the kyphosis deformity. Additionally, in his classification system, axial instability of type I was not established due to the integrity of the posterior longitudinal ligament complex and the intervertebral joints. This classification system was also based only on 40 patients, which suggests that it is not comprehensive to cover all type injury.
This novel classification system is primarily based on 3 morphological features of dynamic instability of injured vertebra, spinal stenosis and kyphosis deformity. Many scholars have described dynamic instability as a unique phenomenon of Kümmell’s disease,1,8,10,11 but an accurate evaluation method for dynamic instability was lacking. Dynamic lateral radiography (flexion-extension radiograph) is a classic method for evaluating spinal stability, but it is not feasible for some patients with aggravated back pain during activity.15 A supine midsagittal CT scan can be a replacement for extension lateral radiography in these patients. In consideration of the collapse of the vertebral endplate in patients of CSOTF, it is not feasible to draw a line on the collapsed end plate for the VKA measurement. Therefore, we modified the measuring method of VKA. Different from VKA that applied to evaluate the stability of fractured vertebral body, CKA reflect the degree of segment kyphosis between the upper and lower adjacent vertebraes, which was significant for assessing the necessity of correcting kyphosis. The degree of kyphosis in some patients with kyphosis deformity due to the dynamic instability of the injured vertebra may be reduced or disappear in the supine position. Different from the previous study14, we defined kyphotic deformity type that the CKA is greater than 30° on dynamic lateral radiography not only the standing lateral radiography, which is valuable to screen out patients who really need correction operations.
Different fracture patterns determine the patient's symptoms, which determines the corresponding surgical strategy. In this system, type I is the basic type of CSOTF, and more than half of the 368 patients exhibited this type (56%). The injured vertebra is relatively stable. Mild activity of the IVC may be the primary source of back pain. Therefore, we recommend vertebroplasty, which is performed via the injection of bone cement to eliminate the slight motion at the IVC, to relieve pain for this type (Fig. 4).
Type II is typical with dynamic instability of the injured vertebra. The apparent activity of the pseudarthrosis formed at the fracture region causes back pain. Previous studies have ignored the instability of the injured vertebrae, and patients with this type were treated using vertebroplasty. However, vertebroplasty alone is not suitable for this type. The fibrous tissue and hardened necrotic bone of the inner surface of the IVC obstruct the crosslinking of bone cement with the surrounding cancellous bone, which reduces the bond strength of the cement with the injured vertebra. Therefore, the instability of the vertebra will greatly increase the risk of bone cement displacement. Tsai et al16 reported one case of Kümmell’s disease in T12. Preoperative imaging revealed instability of the injured vertebrae, and bone cement displacement occurred 1 month after vertebroplasty. Therefore, vertebroplasty alone is not sufficient to stabilize the unstable segments. Additional posterior instrumentation and posterolateral fusion are safer surgeries (Fig. 5).
Type III is characterized by spinal stenosis. Patients experience symptoms of back pain usually accompanied by varying degrees of neurological deficits, especially intermittent claudication, which are caused by bone fragment compression of the spinal cord. The purpose of surgical treatment is to immediately relieve the compression and stabilize the injured segment. Therefore, decompression internal fixation and posterolateral fusion are recommended (Fig. 6). Li et al9 and Zhang et al10 reported that posterior decompression, short segmental pedicle screw fixation and posterolateral fusion combined with vertebroplasty achieved satisfactory results for the treatment of Kümmell’s disease with neurological defict.
Type IV is characterized by kyphosis deformity. The local kyphosis is greater than 30°, even in the extension position. Muscle tension of the back triggered by the kyphosis deformity causes persistent back pain, disuse and atrophy of muscle. They may in turn affect the structure of the posterior tension bands that further aggravate kyphosis. For the patients only with the spasm of thoracolumbar muscles, the muscle relaxation under general anesthesia and nonunion of the vertebral body facilitate the correction of the kyphosis using the hyperextension position. Thus, a intraoperative examination should be performed firstly to verify whether the kyphosis can be corrected in an over-extending position under general anesthesia (Fig. 7). If the CKA is less than 30°after a hyperextension reduction under general anesthesia, a simple fixation and posterolateral fusion is adequate. Otherwise, different grades of osteotomy can be considered to achieve the correction based on the degree of kyphosis deformity.17
Type V is a mixed type that includes 2 or 3 morphological changes. This type includes "dynamic instability and spinal stenosis", "dynamic instability and kyphosis deformity", "spinal stenosis and kyphosis deformity" and "dynamic instability, spinal stenosis and kyphosis deformity". Among the morphological changes, it is usually that 1 or 2 pathology is the main reason to induce clinical symptom. The corresponding surgical strategies should take both the improvement of morphological changes and symptoms into consideration (Fig. 8).
Our treatment recommendations are based on the characteristics of each type and our experience, which need to be verified by the further clinical study. Large-sample prospective clinical trials are required to confirm the effectiveness of the system to guide clinical treatment, especially balancing the benefit and complications when introducing the internal implant into the osteoporosis patients.