Among patients with AS, SCI is a major complication regardless of spinal fracture occurrence. Our results revealed that the SCI rate after spinal trauma in patients with AS was 57.1% (60/105) and the SCI rate in cases also involving spinal fractures was 52.1% (49/94), which are similar to the rates in Europe and North America, which range from 19.7% to 67.2% [3, 4, 11, 13, 14, 18]. Variation in the rate of SCI after spinal fractures in patients with AS may be due to differences in medical referral standards, severity of trauma, and severity of AS.
Diagnoses of fractures in patients with AS are frequently delayed at a rate of 17.1% to 65.4%[2, 4, 11, 14] due to the frequent presence of chronic pain in patients with AS, even in the absence of trauma. Therefore, aggravating pain following minor trauma may be overlooked. Due to alterations in bone density resulting from AS, radiological assessment of fracture in patients with AS can be difficult, with fractures difficult to identify and easily misinterpreted, especially in cases involving fractures at the thoracic spine and thoracolumbar junction. In our study, the rate of delayed diagnosis of spinal fracture was 31.4% (33/105), with 69.7% (23/33) of those cases involving fractures between the T8 and L1 vertebrae. Delay in 6 of the 33 cases was attributed to oversight by a doctor, and delay in the remaining cases was due to patients delaying visits. Oversight may put patients with AS at higher risk of delayed SCI. In our study, one-third of the 33 patients with a delayed diagnosis of spinal fracture developed delayed SCI. Within the initial posttrauma period, 90.9% of these patients had axial pain, such as neck or back pain, and 33.3% had limb numbness. Attending physicians should remain aware of the consequences of delayed diagnosis in patients with AS, even in cases of low-energy trauma. We suggest routine radiographic examination for all patients with AS after trauma and additional computed tomography imaging if axial pain progresses. Magnetic resonance imaging is a viable option for assessing spinal cord injuries and for detecting potential occult fractures [12, 29,30,31].
Bamboo spine is a radiographic feature in AS that occurs as a result of vertebral body fusion by marginal syndesmophytes. The resulting radiographic appearance is of radiopaque spicules that completely bridge the adjoining vertebral bodies. In our study, 74.3% (78/105) of patients with AS exhibited this feature. We also observed that the patients with bamboo spine had a higher rate of spinal fracture than those without bamboo spine (P = 0.006; Table 4). However, the results revealed no significant correlation between bamboo spine and SCI (P = 0.367; Table 4). This contradicted our finding that AS with spinal fracture was significantly related to SCI (P < 0.001). To clarify this discrepancy, we analyzed the relationship between bamboo spine and spinal fracture in the 60 patients with SCI. Four of the 11 patients who had SCI without spinal fracture presented with bamboo spine, and 43 of the 49 patients with both SCI and spinal fracture had bamboo spine. A comparison of these 2 groups revealed a significant difference (P = 0.001; Table 2). Patients with noncomplex compression fractures with intact posterior ligamentous complex (PLC) (AOSpine—Spine Trauma Classification System type A) [32] had a lower rate of SCI than those with complex fractures, which include tension band injuries in cervical spine, and distraction injuries in thoracolumbar spine (type B), or translation injuries (type C) (P < 0.001). Subluxation or dislocation was also a risk factor for patients with AS developing SCI (P < 0.001). The severity of disruption to the spinal structure is, thus, predictive of SCI in patients with AS. In cases involving a complex fracture, SCI is not only caused by the damage from direct impact but also by further compression from bone fragments, hematoma, or disk material [33]. Therefore, we hypothesize that patients with AS with bamboo spine have a high probability of experiencing spinal fracture. Mild fractures, however, do not necessarily cause SCI in patients with AS.
No universal guidelines have been developed for the management of spinal trauma in patients with AS [31]. Nonoperative treatment, including bed rest, skeletal traction, bracing, or immobilization with a halo-vest, has long been recommended for nondisplaced or minimally displaced fractures of ankylosed spines [31, 34, 35]. However, the inherent instability of these fractures and their high potential for acute displacement may cause severe damage [36]. Therefore, surgical fixation with long segmental instrumentation combined with fusion is recommended [36]. Furthermore, the compression of neurological elements often requires surgical evacuation. Recent studies have demonstrated a trend of higher complication rates in nonoperative patients—for instance, finding higher rates of pulmonary complications and a risk of neurological deterioration [3, 4, 35]. Surgical stabilization usually includes anterior, posterior, or combined fixation, often accompanied by decompression with laminectomy and several osteotomy techniques for deformity correction [37, 38]. In our study, 3 patients with an initial AIS grade A received closed reduction and halo-jacket fixation, and all 3 patients (100%) experienced complications: 1 patient experienced screw loosening and 2 developed pneumonia. By contrast, 7 of 9 patients (77.8%) with an initial AIS grade A experienced complications after surgery, suggesting a trend of lower complication rates in severe SCI.
All 14 patients with SEH developed SCI; SCI thus became a key predictive factor for SCI (P = 0.003). SEH occurred in 13.3% of the patients with AS, which is a much higher rate than that of the general population (range: 0.5% to 7.5%) [39, 40]. Compared with fractures that cause SCI immediately, SEH may lead to subacute SCI hours after trauma. The mechanisms underpinning cervical SEH formation are not fully understood; disruption of the posterior longitudinal ligament and spinal epidural vessel rupture, however, may play a vital role [25, 40]. Symptomatic SEH is generally considered a neurosurgical emergency. In the general population, better long-term neurological recovery has been noted after early surgical intervention. However, no major case study has reported the effects of early surgical intervention in patients with AS. In our study, the patients with SCI received surgical treatment 1.8 ± 3.2 days after trauma. Several of these patients had delayed surgical treatment due to delayed diagnosis, old age, comorbidity, or polytrauma that required additional treatments.
None of the patients who had complete SCI at admission exhibited improvement in AIS grade after 2 years. By contrast, 58.3% (35/60) of patients in the incomplete SCI group demonstrated improvement. Overall, patients with AS with incomplete SCI had better long-term neurological recovery. Complication rates were significantly higher (P = 0.001) in patients with SCI. The 4 patients who died within 1 year were significantly older (with an average age of 69.2 years). This echoes previous findings of higher mortality in older patients with AS after spinal fracture [11, 13]. Of the patients with AS with different complexities of fracture and varying degrees of SCI in our study, more than 53% of patients achieved long-term neurological recovery after surgical treatment.
Limitation
This is a single-center study thus obviating patient selection bias. Besides, most subjects achieved long-term follow-up. Meanwhile, this study was limited for its retrospective design, as well as the non-feasibility of analysis on cervical, thoracic and lumbar cohorts separately due to insufficient case number. Thus, further well-designed prospective randomized studies are needed.