Source: Jiangang Shi Associate Editor of Spine Major, Orthopedics Online
Author: Department of Spine II, Orthopedic Hospital, Changzheng Hospital, Naval Military Medical University, Yang Haisong, Shi Jiangang
Preface
"What are the treatment principles of cervical spine surgery?" This is a frequently mentioned issue in clinical work. Answers such as "complete stress reduction" and "restoration of cervical vertebrae" can already be blurted out. When we say these answers without thinking, do we really understand the deep meaning?
In the process of human evolution, the spine has gradually formed four physiological curvatures of cervical, thoracic, lumbar and sacral vertebrae. As we all know, the core function of the spinal axis bone is to protect the spinal cord and nerve roots in the spinal canal, so that it remains in a "normal" and "comfortable" physiological state, so as to perform normal functions. Once the spinal cord is out of this "physiological state", even the most perfect spine will lose its existence value. Therefore, in this sense, cervical spine surgery restores the physiological curvature of the cervical spine while achieving complete decompression, and its most essential core is to restore the physiological curvature of the cervical spinal cord, so that it is in a "comfortable" physiological preflex state as much as possible.
Physiological curvature of the cervical spine
When the human body is sitting upright or standing, the neck of the person appears to be straight from the side, but the cervical vertebrae wrapped around it are not straight, but have a forward projection curve in the middle. This forward curved bump is medically known as the "physiological curvature of the cervical spine." This is the physiological need of the human body, and it is also the need for the normal anatomy and physiology of important tissues such as the neck spinal cord, nerves, and blood vessels. The normal physiological curvature value of the cervical spine is about 10° to 40°, and the clinical measurement mainly includes the following three methods1 (Figure 1).
Fig. 1 Measurement method of physiological curvature of the cervical spine:
A. Cobb angle method; B. Jackson physiological stress curve method;
C. Harrison's trailing edge tangent method
Many scholars have done research on the relationship between the physiological curvature of the cervical spine and the postoperative efficacy of the cervical spine. Uchida K believes that the change in the physiological curvature of the cervical spine, resulting in the cervical spinal cord being compressed by the anterior disc, bone excess and ligaments, through anterior surgery to reduce the pressure while correcting the physiological curvature of the cervical spine, compared with the patients who only gave complete decompression and did not restore the physiological curvature of the cervical spine, the efficacy of the posterior spinal canal enlargement molding was significantly increased2. Lau D concluded by comparing the efficacy of posterior spinal enlargement with laminectomy bone graft fusion internal fixation in the treatment of multisectional cervical spondylosis that the physiological curvature of the cervical spine should be considered a very important factor in increasing postoperative efficacy3. Buell TJ also believes that straightening or even kyphosis of the cervical spine can increase longitudinal stretch stress of the spinal cord, increase intramedullary pressure, and reduce blood supply to spinal arteries, resulting in worsening symptoms or affecting postoperative efficacy4. But there are also many authors who take different views. Patel S proposes that the use of posterior cervical surgery for cervical spondylosis does not have a significant correlation between the change in Nurick score after surgery and the degree of correction of cervical curvature5. Shamji MF believes that improving physiological curvature during cervical spine surgery will increase postoperative efficacy is still unknown6.
In all these literatures, we found that the author only focused on the physiological curvature of the cervical spine, but ignored the spinal cord and nerve roots in the cervical spinal canal, rather than the cervical spine, ignoring the physiological curvature of the cervical spinal cord. Because we found in the clinic that the physiological curvature of the cervical spine does not fully represent the physiological curvature of the cervical spinal cord.
Physiological curvature of the cervical spinal cord
Under normal conditions, the physiological curvature of the cervical spinal cord is consistent with the physiological curvature of the cervical spine. However, in the clinic, it was found that although the physiological curvature of the cervical spine was normal in some patients, the physiological curvature of the cervical spinal cord disappeared, the kyphosis was even completely deformed. There are also some patients with mild kyphosis, but the physiological curvature of the cervical spinal cord is worse, and the phenomenon of "derailment" of the two has occurred (Figure 2). This condition is predominantly present in patients with multi-segment cervical spondylosis or ossification of the posterior longitudinal ligament of the cervical spine, where posterior surgery results in a backward drift of the spinal cord7, deviating from their "comfortable" physiological state of "convexity forward". Although complete decompression was achieved (MRI showed a good morphology of the spinal cord and no compression), clinically it was found that some patients did not have significant improvement in symptoms, and even worsened numbness in both upper extremities. Therefore, it is not that the greater the distance the spinal cord drifts backwards, the better the clinical effect obtained. The literature also reports that the degree of backward drift of the cervical spinal cord after posterior surgery is not significantly correlated with postoperative efficacy8,9. Excessive spinal cord drift leads to excessive anterior nerve root tone, affecting postoperative nerve recovery in patients1,10. This also explains why after posterior cervical surgery, cervical MRI shows no compression of the spinal cord, but many patients' symptoms, especially numbness in both upper extremities, have not improved significantly, and even some patients have worsened their symptoms because spinal cord drift has caused them to lose their normal physiological bulge.
Figure 2 "Derailment" of the physiological curvature of the cervical spinal cord and the physiological curvature of the cervical spine:
A. The physiological curvature of the cervical spine is normal, and the physiological curvature of the cervical spinal cord is straightened;
B. Normal physiological curvature of the cervical spine, partial kyphosis of the physiological curvature of the cervical spinal cord;
C. Kyphosis of the cervical spine, the physiological curvature of the cervical spinal cord is even more convex
The author evaluates the physiological curvature of the cervical spinal cord by connecting the arc of C2 to the center of the C7 spinal cord on the SAgittal surface of the cervical spine, which is roughly divided into six types: anterior convexity, straightening, kyphosis, S-shaped, inverse S-shaped, and locally convex (Figure 3). By comparing the relationship between the physiological curvature of the cervical spinal cord and the patient's postoperative JOA score, it was found that the JOA score was the highest after anterior convexity and straightening, followed by kyphosis and S-shaped, and the two types of INVERS-shaped and local bulge had the worst JOA scores. The physiological curvature of the cervical spine in the anterior convex and straightened groups was better than that of other types, and there was no significant difference in the physiological curvature of the cervical spine in the kyphosis and S-shaped and locally convex groups.
Figure 3 Physiological curvature of the cervical spinal cord:
A, anterior convexity; B, straightening; C, kyphosis;
D, S-shaped; E, inverse S-shaped; F, locally convex
ACAF technique with physiological curvature of the cervical spinal cord
How can surgery not only restore the physiological curvature of the cervical spine, but also make the physiological curvature of the cervical spinal cord consistent with the physiological curvature of the cervical spine? The anterior controllable antedisplacement fusion (ACAF) proposed by Professor Shi Jiangang can simultaneously achieve the purpose of expanding the spinal canal and restoring the physiological curvature of the cervical spine and cervical spinal cord, and realize the "in situ decompression" of the spinal cord and nerves (Figures 4 and 5). This technique is especially suitable for patients with degenerative kyphosis with spinal stenosis and ossification of the posterior longitudinal ligament of the cervical spine, and has achieved good clinical efficacy11-15.
Technical advantages:
1) The anterior road is grooved close to the inner wall of the pedicle root, which realizes the complete decompression of bilateral nerve roots;
2) The vertebral body (ossification) is moved forward as a whole, realizing the comprehensive expansion of the spinal canal and completely reducing the pressure on the spinal cord;
3) Restore the physiological anteriorosis of the cervical spine, and at the same time restore the physiological anterior convexity of the cervical spinal cord, and realize the "in situ decompression" of the spinal cord;
4) Avoid the backward drift of the spinal cord in posterior surgery, and at the same time avoid the risk of excessive precocity of the spinal cord or even spinal cord herniation after multi-segment subtotal total resection of the spine due to dural or even arachnoid defects;
5) Both sides of the slot avoid the harassment of the spinal cord, basically avoid spinal cord injury;
6) Greatly reduce the incidence of cerebrospinal fluid leakage.
Of course, this technique was initially used to treat the ossification of the posterior longitudinal ligament of the cervical spine, due to the excessive width of the ossification base of some patients, the initial experience of the surgeon was insufficient, and clinical cases of nerve root damage caused by slotted decompression were also encountered, but they were well recovered through postoperative conservative treatment. In the later stage, with the accumulation of experience, the rate of slotting is slowed down when the ossified substrate is too wide, and the surgical instruments are refined, which basically avoids this complication.
At present, the number of clinical cases of this technology is gradually increasing, the key points of technical operation and clinical precautions are being improved, and the results of longer-term follow-up will be reported to domestic and foreign counterparts one after another.
Figure 4 ACAF technology is applied to degenerative kyphosis with spinal stenosis:
A, B, Cervical spine X-ray and CT suggest degenerative kyphosis and spinal stenosis;
C, Cervical MRI suggests C3/4 to C5/6 spinal cord compression;
D, CT cross section presented vertebral tube stenosis;
E, F, ACAF (C4, C5) postoperative X-ray and CT suggest satisfactory spinal canal enlargement, physiological curvature is better than before surgery;
G, MRI suggests complete decompression of the spinal cord and the return of the cervical spinal cord to normal physiological bulge;
H, CT cross-section shows the groove range on both sides, achieving spinal cord decompression at the same time, and completely reducing the nerve roots on both sides;
I-L, follow-up results at 6 months postoperatively.
Figure 5 ACAF is used to treat ossification of the posterior longitudinal ligament of the cervical spine:
A and B, X-rays and CT of the cervical spine indicate that the physiological curvature of the cervical spine is straightened, and the longitudinal ligament is ossified after C2 to C7.
C, MRI of the cervical spine suggests anterior compression of the cervical spinal cord;
D, E, ACAF (C3-C6 vertebral body) postoperative X-ray and CT suggest spinal canal enlargement, cervical spine physiological curvature recovery is good;
F, CERVICAL MRI suggests complete decompression and the restoration of physiological anterior convexity of the cervical spinal cord;
G-I, follow-up results at 6 months postoperatively.
summary
The ultimate goal of cervical spine surgery is for the spinal cord and nerve roots. While restoring the physiological curvature of the cervical spine is important, it is even more important to restore the physiological curvature of the cervical spinal cord. In clinical work, all forms of cervical spine surgery, on the basis of ensuring the complete decompression of the spinal cord and nerve roots, should restore the physiological anterior bulge of the cervical spinal cord as much as possible, avoid forward and backward drift, realize in situ decompression of the spinal cord, and escort the improvement of clinical efficacy of patients.