Clinical results and surgery tactics of spinal osteotomy for ankylosing spondylitis kyphosis: experience of 428 patients

First, the clinical results and surgical tactics of spinal osteotomy for ankylosing spondylitis (AS) kyphosis were detailed.

Second, efficacy and safety of one-level osteotomy and two-level osteotomy are systematically compared.

Third, a novel spinal osteotomy technique, vertebral column decancellation (VCD), was introduced for patients with AS with severe kyphotic deformities.

Fourth, key points of the VCD osteotomy technique were detailed.

Ankylosing spondylitis (AS) is a chronic spondyloarthropathy that primarily involves the spine and sacroiliac joints [1‐3]. At advanced stages of AS, many cases result in spinal deformities, such as the loss of lumbar lordosis or an increase in thoracic kyphosis, which can lead to structural and functional impairments and a decrease in the quality of life [3]. Additionally, AS may be associated with severe sagittal imbalance, trunk collapse, and flexion-contracture deformities of the spine in the later stages, which may cause back pain, horizontal vision loss, or neurological deficits [4, 5]. Complications, such as walking difficulties, abdominal viscera compression, or lung dysfunction, may occur in patients with AS severe kyphotic deformities [6‐8].

Surgical correction of kyphosis is necessary for many patients with AS deformities to restore sagittal balance and the ability to see straight ahead [1, 9]. However, the most effective and safe surgical procedure for AS-related symptomatic kyphotic deformities is still controversial [2, 8], and the planning processes, which have been explored to determine the ideal site and to calculate the exact angle required for an osteotomy, carry some limitations as well [10].

The purposes of this study were to report the radiographic and clinical results of spinal osteotomy for AS kyphosis patients in our single spine center and to evaluate and compare the efficacy and feasibility of a one-level osteotomy and a two-level osteotomy for correcting kyphosis secondary to AS. In addition, the surgical tactics, including the corrective angle, surgical site, and number of osteotomies, are also described.

All patients could walk with horizontal vision and lie on their backs postoperatively. A one-level osteotomy was performed in 339 patients, and a two-level osteotomy was performed in the remaining 89 patients (Table 1). No mortalities or any major neurologic complications occurred during the follow-up period; however, 32 patients suffered one or two complications, including CSF leaks (n = 21, 9 in the two-level group and 12 in the one-level group), transient neurological deficits (n = 3, in the two-level group), vascular laceration bleeding (n = 1, in the two-level group), infections (n = 2, 1 in the two-level group and 1 in the one-level group), postoperative low back pain (n = 5, 2 in the two-level group and 3 in the one-level group), spinal rod broken (n = 3, 2 in the two-level group and 1 in the one-level group), distally pedicle screws pull out (n = 4, 2 in the two-level group and 2 in the one-level group), and non-fusion at the osteotomy site (n = 4, 3 patients associated with Andersson’s lesion preoperatively), as shown in Table 2, and there were significant differences between two groups in complications of CSF leaks and neurologic deficit (p < 0.05).

The preoperative, postoperative, and final follow-up radiological and clinical outcomes of the 428 patients are shown in Table 3. All patients demonstrated changes in the pre- and postoperative radiological parameters and the CBVA, while no significant differences were demonstrated in these parameters between the postoperative and final follow-up. The pre- and postoperative average GK angles were 82.6° and 12.7° (p < 0.05), respectively, in the two-level group and 55.8° and 9.6° (p < 0.05), respectively, in the one-level group. The CBVA improved from 68.3 to 8.2° (p < 0.05) in the two-level group and from 46.2 to 4.2° (p < 0.05) in the one-level group. The mean SVA improved from 29.4 to 8 cm (p < 0.05) in the two-level group and from 18.0 to 4.3 cm (p < 0.05) in the one-level group. All of these parameter changes demonstrated significant differences between the one- and two-level osteotomy groups (p < 0.001). The operative time, blood loss, and complication rate data are shown in Table 3. The average operative time was 253 min for the one-level group and 331 min for the two-level group, the average operation-related blood loss was 537 ml in the one-level group and 1132 ml in the two-level group, and the complication rate was 6.5% in the one-level group (22 of 339 patients) and 23.6% in the two-level group (21 of 89 patients). The results demonstrated that the operative time, blood loss, and frequency of complications were significantly higher in patients who underwent the two-level osteotomy than in patients who underwent the one-level osteotomy (p < 0.001; Table 3).

Surgical correction, such as a spinal osteotomy, may be the appropriate option for the treatment of AS patients with a severe kyphosis deformity [8, 9, 23]. As proven by our research group, spinal osteotomies not only corrected the sagittal deformity but also significantly increased pulmonary function [24, 25], digestive function by relieving abdominal viscera compression [19, 26], cardiac function [27], and sexual activity [28] of patients with AS.

Adequate preoperative planning of the surgery is critical for sagittal plane corrective osteotomies of the spine in AS patients. Suk [22] and Van Royen [29] used the CBVA and biomechanical and mathematical methods for planning the correction angle and the osteotomy site, but these methods carry some limitations [10, 30]. Thus, we have explored a new osteotomy angle calculation method according to an analysis of the CG of the trunk [10, 15]. Based on our extensive clinical experience, we found that the hilus pulmonis (HP) is located over the HA in normal subjects, so we chose the HP as the reference point for the center of CG of the trunk. Thus, if we shifted the HP over the hip axis, the exact angle required for a spinal osteotomy in patients with AS kyphosis can be calculated [10].

Theoretically, an osteotomy at the apex vertebra should achieve a better corrective effect [27, 31, 32]. With the same correction angle, an osteotomy at the lower level vertebra can achieve greater safety [33]. Therefore, we prefer to perform osteotomy at the lumbar or thoracolumbar spinal regions. Usually, we do not perform an osteotomy at L4 or L5 because L4 and L5 are not the apex vertebrae of lumbar lordosis [10], and fusion to the sacrum with a short lever arm on the distal part of fusion will result in discomfort or an inability to sit on the floor [32]. In view of these abovementioned considerations, we suggest that most osteotomy sites are located at the second and third lumbar vertebrae because the third vertebra is the apex of the lumbar spine and the second vertebra is usually near the thoracolumbar kyphosis. In addition, the second and third vertebrae are usually located below the conus medullaris, which means an osteotomy can be performed more safely. For thoracic hyperkyphosis, the osteotomy site can also be T12 or L1 because T12 and L1 are near the apex vertebrae.

In our opinion, a two-level spinal osteotomy at the spinal cord region is not recommended. First, satisfactory reconstruction of lumbar lordosis is necessary because the loss of lumbar lordosis is usually co-existent with hyperkyphosis of the thoracolumbar and thoracic spine. Second, a spinal osteotomy in a non-spinal cord region is relatively safe, and an osteotomy in the lumbar region can allow a relatively large operating space and correction angle [23]. At the same time, a continuous two-level spinal osteotomy is not recommended because excessive shortening of the area may result in buckling of the dura and spinal cord, which is very dangerous [34]. Thus, for severe thoracolumbar kyphotic deformities, the ideal combination of osteotomy sites is L1 and L3. If the apex of the kyphosis is located above T12, we may choose T12 and L2 as the osteotomy sites [23].

Several spinal osteotomy techniques, including the Smith-Petersen osteotomy (SPO) [35], PSO [16], and VCD [13, 18], have been performed for the treatment of AS kyphotic deformities. However, the most effective and safe surgical procedure for an AS-related kyphosis deformity is still controversial [2, 9]. An SPO is more suitable for a flexible kyphosis and deformities without ossification of the anterior column of the spine [36, 37]. PSO is a technically demanding procedure with relatively severe surgical trauma and a high risk of complications [37]. VCD was first described in 2011 by our research group as an operative technique for the treatment of patients with a sharp angular spinal deformity [18]. Due to its many advantages as an osteotomy technique, VCD has been performed for and is an effective and excellent treatment option for kyphotic deformities in patients with AS [13, 14].

In the current study, the total complication rate was 10.1% (43 complications in 32 patients) for all 428 patients, and there were no major acute complications, such as death or complete paralysis. The patients were divided into two groups according to the number of osteotomy segments (one- and two-level osteotomy groups), and the complication rate was significantly higher in the two-level osteotomy group than in the one-level osteotomy group. Therefore, a two-level osteotomy can provide more extensive correction than a one-level osteotomy, but it has a higher complication rate.

In our experience, CSF leakage, which is the most common complication in the literature [13, 23], is difficult to avoid when the dura is extremely thin due to chronic inflammation adhering to the surroundings, especially to the ossified ligamentum flavum [1, 9]. If a dural tear occurs intraoperatively, prompt management of the leak with a gel sponge or muscle and myofascia should be made, a drainage tube should be left until the output rate falls below 50 ml/24 h, and the duration of drainage and bedrest should be prolonged if needed. There are three causes of vascular damage: the osteotomy procedure direct injury, the excessive elongation injury of the anterior column, and osteotomy stump stab. Therefore, gentle manipulation during surgery and a linear fracture at the anterior cortex of the osteotomized vertebrae are important in order to avoid vascular damage. In addition, avoiding excessive stretching of the anterior column also reduces the risk of thoracic and ventral aorta injury. To avoid neurological damage, it is safer to perform a creeping expansion laminectomy and to avoid excessive shortening of the spinal posterior column. Many investigators have reported that pseudarthrosis or rod breakage can occur when the osteotomy is performed through an area that is not previously fused at the time of osteotomy [36, 38]. Thus, we suggest that a sufficient bone graft must be achieved to facilitate better bony fusion and better stability in the corrected position during the osteotomy. For preventing infection, adhering to the principles of asepsis during and after surgery and sufficient wash of the operation area will help. There are some other complications that have been reported, such as paralytic ileus [39], which resolved after the insertion of a Levin tube and oral intake restriction, and blindness, possibly caused by local extrusion during the operation, which may be avoided if individuals such as non-operative personnel pay more attention to protecting the patient’s eyes [40]. Because of the high complication rate of spinal osteotomies, the indication should be carefully assessed, the surgery should be performed by an experienced spine surgeon who has mastered various types of deformity correction techniques, and the role of non-operative assistants is also of importance, especially when positioning patients and during reduction [23].

Based on the large number of AS-related kyphotic deformities treated by spinal osteotomies in our single spine center, we have many key recommendations to ensure the successful performance of several spinal osteotomy techniques:

In this study, we reported the results of two types of spinal osteotomies for a large number of patients with AS kyphosis, focusing on the surgical strategy, technical aspects, complications, and correction outcomes. In addition, we compared the results of the one-level osteotomy with the results of the two-level osteotomy. The results demonstrate that both PSO and VCD are effective osteotomies in correcting kyphotic deformities in AS patients. In addition, the one-level spinal osteotomy showed a lower complication rate, while the two-level spinal osteotomy was a relatively aggressive procedure that was more suitable in correcting severe AS kyphotic deformities.