In this study, 37 patients with AS combined with SCSF were successfully treated by the three approaches of bone grafting, fusion and ORIF. The purpose of the surgery was to decompress the compression symptoms of the spinal cord effectively, restore and stabilize the bone rupture, and promote bone union. Twenty-four cases were improved to grade E (64.8%), and 10 cases were improved to grade D (27%), according to ASIA classification. The incidence of complications was 8.1% (3/37).
In the patients with AS, extensive joint and ligament ossification usually affected the axial skeleton of the spine, such as ankylosis, kyphotic deformity, and osteoporosis [5, 6, 8]. In particular, the force line of the lower cervical may be destroyed by daily neck activities, which caused the vertebrae fracture. However, AS with SCSF is commonly misdiagnosed since the preexisting pain and kyphotic deformity [7, 9]. Besides, SCSF was caused by lower energy trauma, because the vertebral osteoporosis caused by AS reduced spinal flexibility. Via published articles , SCSF mostly neared the cervico-thoracic junction and involved three columns of the spine, which were so unstable to associate with vertebrae dislocation, nerve compression symptoms, and respiratory complications. Westerveld et al.  found that the incidence of spinal cord injury in patients with AS combined with spine fracture was significantly higher than in a patient without AS (four times). In this study, high-energy trauma was the main cause of SCSF (67.5%), which affected three-column of vertebrae in 14 cases. Besides, 34 patients were associated with neurological injury, and the longer the duration of AS, the more severe the nerve injury. Therefore, CT and MRI were recommended to be applied to diagnose AS with SCSF at the early stage, especially for patients with a history of high-energy trauma.
The primary treatment of AS with SCSF was to restore the fractured ends and stabilize the spinal sagittal balance [5, 7, 11]. Nonsurgical treatment was limited to simple fractures without involving the three columns of the vertebrae and displacement, such as fixation using a Halo brace for 10 to 16 weeks . Surgical treatment (ORIF) was necessary for patients with unstable fractures involving the three columns, spinal cord injury, vertebral disc incarceration, and the presence of sagittal or coronal imbalance [12–14]. Its advantage was to stabilize the lower cervical sequence to promote bone union and decompress the spinal cord compression symptoms.
The approach of surgery included anterior, posterior, and combined anterior and posterior. The clinical efficacy of the anterior surgery remained controversial, although its advantages of complete decompression and satisfactory bone union. Kouyoumdjian et al.  reported 19 patients with AS combined with SCSF were successfully treated by the anterior surgery and concluded that the lengthened internal titanium plates should be used in the anterior surgery to effectively resist abnormal stresses to receive satisfactory stabilization. However, Najib and Xiang et al. [16, 17]considered that the anterior surgery was only suitable for SCSF with anterior and middle columns affected, whereas it had a poor ability to resist torsion and bending. In this cohort, 11 patients were performed anterior surgery and received a good bone fusion. We concluded that it was difficult to intraoperatively place the prone position in patients with kyphosis, which easily led to the iatrogenic fracture of the vertebral body and aggravated spinal cord injury. Hence, the anterior surgery could be preferred for patients with severe kyphotic deformity. If completely reducing the fracture cannot be received, an additional posterior surgery was recommended to prevent the failure of ORIF caused by the anterior stress concentration. Based on the satisfactory results of the anterior surgery in our patients, it was an effective option for patients without severe anterior column injury, disc fragmentation, and deformity.
The posterior surgery had been certified its good biomechanical stability and reduction of the fracture, which was mainly suitable for fractures with the good axial load-bearing function of the anterior column, especially for fractures with dislocation and facet joint twist-lock [5, 16, 18]. Taggard et al.  reported 7 patients with AS combined SCSF were effectively managed by the posterior surgery, which improved the neurological compression symptoms at the final follow-up. Liang et al.  found that the posterior surgery using pedicle screw fixation and autologous bone grafting could play a critical role in stabilizing the spinal sagittal balance, correcting kyphosis, and relieving spinal cord compression. However, its shortcomings were mainly limited to dealing with anterior column fracture and compression, because the injured intervertebral disc was difficult to be removed . Thirteen patients in this study were conducted by posterior surgery and obtained good outcomes of spinal sagittal balance and neurological improvement. As far as we were considered, the posterior surgery could receive stronger stability than the anterior , since the strong pedicle screws belonged to three-column fixation. However, its decompression of spinal cord compression caused by anterior protrusion into the spinal canal was worse than the anterior surgery. Besides, it should be in consideration that AS combined with severe osteoporosis, which was recommended that the internal fixation included 2 to 3 upper and lower vertebral bodies around the affected vertebrae respectively to resist the stress concentration caused by ankylosing segment.
The combined anterior and posterior surgery was mainly indicated for patients with severe osteoporosis, three-column injury, dislocation, and spinal cord compression. Via published studies , satisfactory bone union with the improvement of spinal cord compression could be obtained by combined anterior and posterior surgery. For instance, Olerud and He et al. [8, 22] presented a total of 41 patients with AS combined with SCSF successfully treated by combined anterior and posterior surgery, and considered that this method was a practical tool to treat SCSF with significant vertebral collapse and lack of anterior column support. Einsiedel et al.  found that there were approximately half of patients with the secondary displacement of the fracture end after anterior surgery, and they proposed that combined anterior and posterior surgery was ought to effectively decompress the spinal cord compression, especially vertebrectomy. Besides, whether anterior or posterior side surgery was performed firstly was still controversial. Some scholars believed that fractures of the anterior column mostly affected the intervertebral disc, in which there was nucleus pulposus tissue to reduce the possibility of self-fusion [4, 7, 11, 23]. It was necessary to perform posterior surgery firstly to provide stability to complete anterior decompression and ORIF . Others pointed out that the order of combined surgery depended on the efficacy of skull traction . Anterior surgery could be performed firstly as a satisfactory reduction, but posterior surgery should be performed initially in case of the failure of reduction. In our cohort, 13 patients were effectively managed by a one-stage combined anterior and posterior surgery and improved their severe neurological deficits. In our opinion, the first step should be conducted on the side with a simple type of fracture and mild neurological symptoms. The affected anterior column of 10 patients was fixated firstly using a titanium plate to provide stability for resolving the injured intervertebral disc and fracture. And posterior surgery was performed firstly on 3 patients.
Surgery was just the beginning and not the end of the treatment. Postoperative management and strategies for complications were equally important. In this cohort, complications occurred in 3 patients after combined anterior and posterior ORIF, including intraoperative dural tear, delayed wound healing, and pulmonary infection. Fortunately, complications were resolved using antibiotics and dressing changes. It can be concluded that the risk of intraoperative trauma and complications were brought out by the combined surgery. Hence, orthopedics should pay more attention to the surgical indication for AS combined with SCSF, and choose a practical method according to the affected vertebrae column.
The limitations caused by the small-sample, single-medical-center, retrospective study existed in this study. Further, a comparison between the efficacy of different surgical approaches was not performed since the small number of cases.