With the progression of AS, the two major pathological features (chronic inflammation and new bone formation) continue to occur in various segments of the spine, and the calcification of the vertebral and paraspinal ligaments will become more and more serious. In the later stage of the disease, the “bamboo-like spine” is going to form a long bone-like feature and this feature will make the spinal fracture unstable and easily affect all the three columns of spine [12], which is easy to cause spinal cord injury [13]. Patients with AS are often accompanied by osteoporosis in the later stages of the disease [14], and spinal fractures can occur without violence or with slight violence. Patients with AS are often accompanied by kyphosis, which make the patients’ center of gravity tilted forward, thus the patients’ balance ability will decrease, as a result, it will increase the risk of falls, and reduce the patients’ ability to self-protect during falls [1]. All these factors can increase the fracture risks in patients with AS. Some studies have reported [15], the incidence of osteoporosis in patients with AS for the past 10 years is 25%, and the incidence of spinal fracture is about 10%. The stress on the thoracolumbar spine is usually larger, and the incidence of fractures in the thoracolumbar segments is higher [16, 17]. Our study, through long-term follow-up of 3 patients with AS and thoracolumbar spine fractures, found that simple posterior internal pedicle screw fixation surgery has a good effect on such fractures. During the follow-up period, no obvious postoperative complications, such as pedicle screws retraction, broken nail, loosening, nonunion of fracture, were observed. All the three patients successfully recovered to the state of life before the injury.
Fractures are always difficult to be found in the early state in the patients with AS [18], especially those with no obvious trauma. Because the pain in the early stage of the fracture is difficult to distinguish from the inflammatory pain of AS, and patients always tend to choose to stay at home rather than go to hospital for an examination, especially when they have no obvious trauma. When going to a hospital, patients always take an X-ray first, but X-ray is a 2D picture and it may sometimes miss some fractures that have no obvious displacement. After ossification of spinal ligaments, the ossified ligaments can also be “fractured” [19], and this “fracture” is also one of the important causes of spinal instability and continuous back pain. X-ray is difficult for early fracture diagnosis while CT and MRI play a very important role in the diagnosis of fractures [20], and MRI can show the signal changes of the spinal cord and the volume of the spinal canal. The contents that MRI delivers will be an important indication to determine whether the laminar decompression is needed.
Surgical treatment should be performed as soon as the spinal fractures with AS is diagnosed [21]. Although surgical treatment also has certain risks of surgery related complications, the risk of non-surgical treatment will be greater [22], so unless the risk of surgery is unacceptably high, it is generally recommended to perform the surgery treatment as soon as possible. For patients with AS have poorer bone condition, the time that conservative treatment needs will be longer than normal people of the same age need, and the risk of the complication of bed rest is greater, so conservative treatment is not recommended. Some scholars have reported [23] that surgical treatment can significantly improve the survival rate of patients with spinal fractures in AS. Westerveld et al. [24] pointed out in their meta-analysis that timely surgical treatment can improve neurological function and reduce the incidence of overall complications.
Ankylosing spondylitis with spinal fractures can be performed with simple anterior approach, simple posterior approach, and anterior-posterior approach. Both simple anterior and simple posterior approaches are single-cortical fixations, similar to long bone fractures. Because of thoracic and abdominal organs and large vessels in front of the spine, anterior surgery is more difficult [25], and the holding force of the screw in the anterior approach is always insufficient, so the anterior approach is mostly used to restore the front column [26], especially when the front column of spine was severely collapsed and difficult to be restored by posterior approach. Anterior and posterior combined surgery has the advantages of the best reduction and the most powerful holding force, but it has a large trauma, a long operation time, and a high risk of complication for elderly patients with poor basic conditions, so the anterior and posterior combined surgery approach is not wildly used actually [27]. Young patients with good basic conditions and severe fractures in all the three columns can try the combined anterior and posterior surgery approach. Simple posterior surgery is the most widely used method currently [24]. Most people choose the simple posterior approach because this approach, by inserting pedicle screws, has a powerful holding force, a good effect on reduction and good postoperative stability. Most importantly, it has less trauma. Because kyphosis deformity is common in the late stage of AS, the posterior column is the tension side, and the anterior column is the pressure side. With reference to the experience of internal fixation of the extremity fracture, the internal fixation is more stable when placed on the tension side [25]. This is also one of the reasons why the simple posterior approach is accepted by more people. Bredin et al. [28] reported a percutaneous surgery that also achieved good clinic effect for patients with ankylosing spondylitis and spinal fractures, and this method further reduced surgical trauma. All the three patients included in our study were treated with pedicle screws internal fixation by simple posterior approach and the follow-up results showed this approach had a good clinical effect on spinal fractures with AS. Kurucan E et al. also found that the best surgical method for thoracolumbar fracture patients with AS is posterior internal fixation [4]. This is consistent with our conclusions from these three cases.
Due to the long-term chronic inflammation and the calcification of the surrounding ligaments, the elasticity of the vertebral may decrease, and even the anatomical structure may be somewhat different. Compared with the normal vertebral, it is more difficult to insert the pedicle screws in the vertebral of AS. When placing the pedicle screws, more attention should be paid to identify the anatomical structure and it’s best to successfully insert the pedicle screws the first time we try. In patients with AS and spinal fractures, the number of vertebral segments in which pedicle screws are placed is currently controversial. Kruger et al. [29] reported that only 1.8 segments above and below the injured vertebra need to be fixed and reconstructed on average, but Yeoh et al. [30] confirmed that three segments at least need to be fixed above and below the injured vertebra. Of all the 3 patients included in this study, 2 segments above and below the injured vertebra were fixed and it turned out it has a good clinic effect.
In summary, through these three patients, we believe that AS patients with thoracolumbar spine fractures should be operated as early as possible. We performed posterior pedicle screw fixation in all three patients, and fixed the two upper and lower segments of the fractured vertebral body. The follow-up proved that the effect was very good.
There are also some shortcomings in this report. The number of the reported cases is too small, and no statistical comparison have been conducted. The next study will further expand the number of cases and further compare the effects of all the surgical methods for spinal fractures with AS.