With the rapid development of spinal surgery, various internal fixation materials and methods have been introduced one after another, and spinal osteotomy has been promoted from simple correction of posterior convexity to lateral convexity, which has become increasingly difficult and extensive, raising new issues for surgical treatment methods aimed at correcting deformities. Surgery should not only be performed to correct spinal deformities, but also to consider how to minimize serious complications of surgery, such as spinal cord injury (even paralysis), nerve root injury, large vessel injury, and slippage due to spinal instability, in order to improve the patient’s quality of life. This means that the ideal surgical approach is to correct kyphosis to the maximum extent and effectively with safety in mind. This requires the surgeon to select the appropriate surgical plan based on factors such as the patient’s different types of kyphosis and spinal mobility.
Hunchback deformity due to ankylosing spondylitis (AS) is a relatively common spinal disorder for which surgical orthopedics is the only effective treatment. The development of surgical methods reflects the state of the treatment level. The current surgical approaches to kyphosis correction at home and abroad are mainly divided into: simple accessory osteotomy; arch vertebral body osteotomy. The current evaluation of multiplanar arch vertebral body osteotomy is higher. However, we found that this procedure involves two adjacent vertebral bodies, including the intervertebral discs, and the problems of bleeding, serious nerve root injury, and osteotomy angle and osteotomy distance are often based on experience are not solved in clinical application. Summarized mainly as.
① What is the safest osteotomy distance and angle?
② How to osteotomy less bleeding?
③ Can aortic calcification be absolutely inoperable?
④ How to operate on the complication of hip stiffness?
⑤ How to operate to reduce recurrence?
The potential risk of serious complications and their occurrence is still large, which limits the application of surgery. For this reason, the authors conducted a review to improve and refine the new surgery for problems that are prone to occur, with a view to minimizing the current complications of vertebral arch osteotomy and their chances of occurrence.
I. Characteristics of humpback in ankylosing spondylitis:
The treatment of ankylosing spondylitis humpback has the following characteristics:The cause of ankylosing spondylitis is currently unknown, but it is immunogenetically related, so there is no effective etiologic treatment, only symptomatic and combined chemotherapy to stabilize the disease. In most patients with stiff and severe spine, surgical orthopedics is an effective approach. This type of hunchback is a large round back deformity, which provides a greater option for surgical osteotomy orthopedics, and the disease provides a better pathological basis for multisegmental osteotomy. This means that a single osteotomy is not as effective as a multi-segment dispersed osteotomy for orthopedic purposes.
Ankylosing spondylitis has extensive lesions involving the cervical spine. In some of these cases, it is difficult to use general anesthesia during surgery and requires a high level of anesthesia. The spine has bamboo-like changes, sclerosis of the ligaments, and calcification of the aorta. If epidural anesthesia is chosen, puncture is difficult and local anesthetic infiltration is not effective. Therefore, the choice of anesthesia is more important than other types of hunchback. In addition, the spinal sclerosis requires more vigorous efforts in the correction process to correct the deformity. Ankylosing spinal bone is thickened, and brittle, poor toughness, easy to fracture, internal fixation is more difficult, the spinal joint is blurred after calcification, such as the upper arch dowel, according to the normal positioning method, inaccurate positioning during surgery, which may lead to nerve damage or dowel penetration arch fixation instability. Such patients have different degrees of hip flexion stiffness, which directly affects the orthopedic effect of the hunchback. It is required to properly deal with hip flexion deformity before hunchback orthopedics. Patients with poor general condition, long-term hunchback deformity, compression of the heart, lungs, abdomen and other organs, often accompanied by varying degrees of anemia, heart block and decreased lung capacity, tolerate anesthesia surgery less well than the general population. And the surgery of hunchback correction is more traumatic, so the preoperative preparation should be carried out fully for their disease characteristics.
II. Surgical methods and improvement
The surgical correction of hunchback deformity in ankylosing spondylitis is a more effective method, but it has been a major concern for orthopedic surgeons because of the high surgical difficulty and risk. The most effective site for correction of kyphosis, the apex of the kyphosis, was attempted at that time, but because kyphosis occurs mostly in the thoracolumbar or lower thoracic segment, which is the spinal cord segment of the spine, Smith considered this area to be off-limits for osteotomy and chose to make a wedge-shaped osteotomy of the posterior attachment of the spine in the lumbar space below the spinal cord cone for 1-2 gaps, and then brought the osteotomy surfaces The anterior longitudinal ligament and fibrous ring rupture, forming an anterior opening of the vertebral body, increasing the anterior convexity of the lumbar spine, and compensating for the erect posterior convexity of the trunk, so that the original “C” type kyphosis of the spine becomes “3” type. The procedure is a pioneer in the surgical treatment of kyphosis, and it provides a solution to the patient’s pain. Because the basic principle is the compensatory correction of lumbar adnexal osteotomy, the osteotomy site and the number of osteotomies are not reasonable, which may cause a huge local pulling force on the large blood vessels in front of the lumbar spine, resulting in vascular tearing and life-threatening hemorrhage, and the intervertebral opening is unstable after spinal osteotomy, which may easily slip and cause spinal nerve injury. The orthopedic effect of this procedure is poor, with many complications and high mortality. Lichtblau [2] reported complications of up to 60% and mortality of up to 30%. In response to these surgical risks, many scholars [3-5] have made continuous improvements in the surgical approach. However, it was not until the 1980s that significant results were achieved. The main progresses of improvement are as follows:
1. improvement of the degree of osteotomy: one of the main advances in the correction of humpback in recent years is the improvement from accessory spinal osteotomy to combined vertebral arch osteotomy [6-8], and the scope of adaptation varies widely among different reported methods for combined vertebral arch osteotomy, which depends to some extent on the pathological characteristics of different types of humpback, and can be broadly divided into two categories: total spinal osteotomy and subtotal spinal osteotomy. The secondary total spinal osteotomy, i.e., accessory osteotomy plus posterior vertebral osteotomy, is characterized by a bottom-to-back wedge-shaped osteotomy at the posterior aspect of the spine, generally removing the posterior 1/2-2/3 of the vertebral body. This approach increases the bony contact surface and spinal stability after osteotomy. Thomasen [4] was the first to report a surgical approach to compress the posterior vertebral bone by scraping the cancellous bone of the vertebral body through the pedicle. Later, some scholars [5,6] reported a peri-arch vertebral body osteotomy via the pedicle and improved it to a multi-segmental osteotomy, which improved the surgical results to a large extent. The authors [7] analyzed the principles of multi-segmental vertebral arch osteotomy at the vertebral headquarters from a biomechanical perspective to reduce the chance of possible nerve root and spinal cord injury during surgery. Total spinal osteotomy: reported by Mcmaster M.J. [8] and Tian Huizhong [6], the scope of osteotomy includes the entire vertebral arch and vertebral body, forward to the anterior longitudinal ligament, and all the bone within the wedge needs to be removed, so that the spine is completely truncated and 1-3 vertebral bodies are affected up and down, so that the spinal nerve roots are free from the osteotomy surface. Closure of the osteotomy gap to correct the deformity and postoperative spinal stability are maintained by internal fixation devices. It is mainly applied to angular kyphosis and posterior scoliosis of the spine. Recurrence of kyphosis and posterior scoliosis after ankylosing spondylitis hump surgery is also indicated, but not for bowed hump due to ankylosing spondylitis. The advantages are wide range of single osteotomy and large correction angle, but the surgery is traumatic and has potential spinal cord injury.
2, osteotomy limits: based on animal tests [9, 10] and a review of the correction of kyphosis in ankylosing spondylitis [11], the authors conducted a prospective study of 118 patients with AS kyphosis with multisegmental osteotomy correction and spinal shortening to investigate the relationship between osteotomy correction limits and spinal cord function in ankylosing spondylitis kyphosis and to clarify the osteotomy limits of kyphosis in clinical practice. The spine was shortened by 12-24 mm, and the pre- and post-correction X-ray vertebral osteotomy volume was also analyzed; intraoperative osteotomy volume, spinal cord deformation and spinal canal relationship were measured; changes in spinal cord function were observed with the arousal test. The difference between the amount of spinal osteotomy and the amount of spinal cord laxity and its influencing factors were also analyzed. The results showed that spinal cord relaxation could also cause spinal cord dysfunction. There were significant site differences in the amount of single-segment osteotomy in this group of patients, and the amount of single osteotomy was in the range of 9-16 mm in the T10-L1 segment; it was safer in the range of 15-24 mm in the L2-4 segment. The limit of osteotomy is also limited by the stability of the spine, the distribution of spinal cord vessels, and the operation style [12]. It is suggested that too large an osteotomy can cause spinal cord dysfunction, and it is generally said to be safer within 25 mm, which is consistent with the results of animal experiments [9, 10].
3, the increase in the number of osteotomy segments (planes): the previous single-segment osteotomy, the angle of correction is limited, and the increase to a certain extent is prone to serious complications such as spinal slippage and overdistraction of the surrounding soft tissues. Wilson M.J. [3] proposed multi-segmental osteotomy, which was limited to accessory osteotomy and showed that only one osteotomy had an orthopedic effect after radiography. In recent years, many scholars have done two or three arch osteotomies to make multi-segmental osteotomies have significant orthopedic effect [5,7]. Three-segment osteotomies can correct posterior convexity above the COBB’S angle of 90b. The design of the computer application software makes multi-segment osteotomy fast and standardized [13 ].
4. Improvement of the osteotomy plane: The apex of the kyphosis in ankylosing spondylitis is mainly in the lumbar region, mostly in the thoracolumbar segment, and occasionally in the cervical and upper thoracic segments. The osteotomy site is generally best at the apex of the posterior convexity. In the past, it was thought that the spine above L1 was forbidden to be osteotomized, because the osteotomy was likely to cause paraplegia. In recent years, the operation style has been improved and above L1 is no longer a forbidden area, and the original lumbar osteotomy has been raised to the thoracic and cervical segments. In the selection of surgery, the vertebral arch osteotomy can be used for those whose posterior convex apex is below T10 [7]; for those whose posterior convex apex is above T10, because the thoracic contour affects the closure of the osteotomy surface, multi-segment attachment osteotomy is used above T10, combined with the vertebral arch osteotomy below T10, so that the surgical trauma is small, the orthopedic effect is good, and the thoracic contour can protect the upper thoracic spine from complications such as slippage. For cervical kyphosis, the vertebral artery stroke should be taken into account, and most scholars currently advocate the choice of cervical 7 osteotomy is safer.
5, multi-directional osteotomy: mainly refers to osteotomy orthopedic in more than two planes such as sagittal plane and coronal plane, ankylosing spondylitis hunchback is mainly posterior convexity, some patients are accompanied by mild lateral convexity deformity, currently proposed vertebral osteotomy, the bottom edge of the wedge to the most convex direction, the tip of the wedge points to the concave side, but also retain a little bone to maintain the continuity of the spine and prevent spinal displacement. Better results can be achieved.
Third, ankylosing spondylitis humpback correction surgery often encountered problems and countermeasures:
1, surgical indications: ① surgery with hip ankylosis: hunchback and hip ankylosis, because the hip flexion deformity aggravates the upper part of the body, which has already shifted the center of gravity, so that the stress on the spine and hip joint is further increased. In order to effectively and accurately correct the hunchback, restore the normal force characteristics of the spine, and avoid complications such as excessive correction of kyphosis caused by the illusion of anterior tilt of the spine, insufficient correction of the angle of the hunchback, and recurrence due to anterior tilt of the spine after correction of the hunchback, it is necessary to perform orthopedic surgery on both parts. Since the longitudinal axis of the spine is tilted forward due to the ankylosis of the hip joint, the longitudinal axis of the spine must be made basically vertical in order to achieve more definite results in hunchback orthopedics. From the biomechanical point of view, it is reasonable to perform hip orthopedic surgery first and then correct the hunchback [14 ]. (2) Surgery for combined abdominal aortic calcification: Previously, abdominal aortic calcification was considered a contraindication to surgery because of the strong longitudinal pulling force during surgery, which could lead to large vessel injury. The current procedure has been improved to avoid excessive longitudinal strain during spinal orthopedics. The authors have operated on 41 patients with abdominal aortic calcification and no complications of large vessel rupture occurred [7, 15].
2. internal fixation selection: for ankylosing spondylitis with poor mobility and extensive calcification of the spine, there are three conditions.
① When calcification is severe, the structure is unclear, the accessory bone cortex is calcified, and the bone marrow is fatty and liquefied, and instability is not possible with or when pedicle screws and CDs are applied and are prone to instability. When the spine needs to be fixed extensively during multi-segmental osteotomy, and CD rods are difficult to fix and generally not firmly fixed. It is recommended to use multi-segmental spine root padding wire and Luque rod internal fixation, which is simpler and easier. Especially when the lack of X-ray equipment and the inconvenience of applying pedicle screws and CD, it is more advantageous. ②In cases of mild calcification, the small joints of the spine are still recognizable. It is more stable to apply the pedicle screw system. ③Between the two, the application of hook and nail combination technology is better.
3. Hemostasis: The bleeding during orthopedic spinal osteotomy is extensive and large, and there are no well-known vessels that can effectively stop the bleeding. Hemostasis is always present throughout the surgery, so the hemostasis method should be serial. Preoperative application of hemostatic drugs to improve the coagulation mechanism; patient prone position, the abdomen as much as possible suspended, so that the abdominal pressure to reduce wound bleeding; anesthesia, you can use controlled hypotension (systolic blood pressure of about 10Kpa) to reduce wound bleeding; osteotomy procedures, you can first retain the peridural bone cortex to prevent diffuse bleeding due to premature destruction of the epidural venous plexus [16 ].
4. Prevention of spinal cord injury: Spinal cord injury is one of the more serious complications during hunchback correction, which directly affects the operation. Therefore, many scholars are very concerned about how spinal cord injury can be avoided. However, it is mainly related to the way and method of osteotomy process. Exposure of the spinal cord: Some patients with hunchbacked ankylosing spondylitis have a long history of sclerosis and adhesions to the vertebrae, so when separating the dura mater, it is better to start from the posterior midline on both sides where adhesions are less likely to occur and less likely to damage the spinal cord. The process of osteotomy should be performed under direct vision with instruments to protect the spinal cord and avoid touching and overstretching the spinal cord, otherwise the dura mater is intact and the spinal cord may be damaged by touching or stretching. In multisegmental osteotomy, prophylactic fixation of the osteotomized segment is feasible. This can prevent the spinal cord from being damaged by sudden misalignment during osteotomy of other segments. The order of osteotomy: It is best to perform osteotomy in a circular fashion, from the outside to the inside, layer by layer. SEP and MEP monitoring: In recent years, the monitoring of SEP.MEP in the process of spinal orthopedics has a greater practical value for early detection and reduction of spinal cord injury occurrence [17], and combined with the arousal test can basically provide a reliable reference value for predicting and preventing spinal cord injury.