Pathology and pathophysiology
Lumbar spinal stenosis is different from cervical spinal stenosis and thoracic spinal stenosis. After degenerative cervical or thoracic spinal stenosis reaches a certain level, symptoms of compression of the cervical or thoracic spinal cord appear, which are usually persistent and not easily relieved, and after a long period of compression (months to years), changes in the spinal cord itself may occur due to ischemia, and a low signal is presented on MRI thoracic 1-weighted images, indicating structural changes. In contrast, lumbar spinal stenosis, after the development of cauda equina or neurological symptoms, is often intermittent, appearing when walking a lot and disappearing when sitting at rest, etc. This is due to the fact that the pathophysiology of lumbar spinal stenosis is different from that of cervical and thoracic spinal stenosis.
The size of the lumbar spinal canal can change due to changes in spinal posture. Experimental, clinical and radiographic measurements have demonstrated that when the lumbar spine is flexed forward, its physiological pronation decreases and the volume of the spinal canal increases due to tensioning of the ligamentum flavum, while when the lumbar spine is extended backward, its physiological pronation increases and the volume of the spinal canal becomes smaller due to folding of the ligamentum flavum into the spinal canal, and its anterior and posterior diameters can be reduced by 10% or more.
In the normal lumbar spinal canal, the cauda equina occupies about 21% of the transverse section of the dural sac, and the rest of the space is occupied by cerebrospinal fluid. There is an epidural space, fat and blood vessels between the dural sac and the wall of the spinal canal, so the cauda equina can have a considerable cushion when stenosis occurs in the lumbar spinal canal. When the stenosis is mild, the nerve is not compressed and thus does not produce clinical symptoms; after the stenosis reaches a certain level, it is close to the critical degree of compression of the cauda equina and nerve roots, and at this time, if the back is straightened or extended, the volume of the spinal canal is further reduced and the pressure in the spinal canal increases, causing poor venous return, increased venous pressure, and slow blood flow, which increases capillary pressure and causes a decrease in the blood oxygen level of the cauda equina nerve.
At this time, if activity and walking are carried out, the blood and oxygen demand of the nerve will increase, which will further aggravate the existing ischemia and hypoxia and produce clinical symptoms. If bending and resting, the volume of the spinal canal increases, the pressure in the spinal canal decreases, the venous return increases, the capillary pressure decreases, the blood and oxygen supply to the nerve improves, and the blood and oxygen demand of the nerve also decreases after stopping the activity, and the clinical symptoms are relieved.
The above changes are also the pathophysiological basis of neurogenic intermittent claudication. Regarding the neurophysiology of cauda equina compression, Rydevik pointed out that the spinal nerve roots in the cauda equina have regional nutrient arteries from the surrounding tissues that enter the nerve to supplement its intra-neural vascular system, which relies on the central (i.e., spinal cord portion) and peripheral (distal posterior root segments) blood supply, a relatively less vascular portion in which there is no lymphatic system and can absorb nutrients from the cerebrospinal fluid, and when a segment compresses the cauda equina, the compressed When one segment compresses the cauda equina, the compressed area is supplied with blood from both ends and can return without ischemic symptoms, while when two segments compress the cauda equina nerve fibers, ischemia occurs in 64% of the nerve fibers in the middle of the two compressed areas and venous return is blocked and stagnation occurs, resulting in neurological ischemia and compression symptoms.
Therefore, Porter also pointed out that clinical spinal stenosis is often caused by stenosis of two or more segments. If the nerve root of lateral saphenous stenosis is compressed and there is stenosis of the vertebral segment above it, the nerve root will also be ischemic and symptoms will occur. Wang Xuan, Department of Orthopedics and Traumatology, Affiliated Hospital of Shanxi College of Traditional Chinese Medicine
Schonstrom found that the cross-section of the dural nerve tissue in the lumbar 3 plane was (77±13)mm2, 44% of normal, which was the critical area. When the pressure was reduced to (63±13)mm2, 36% of normal, the intradural pressure rose to 6.67kPa (50mmHg), and when the pressure was reduced to (57±11)mm2, 32% of normal, the intradural pressure rises to 13.3 kPa (100 mmHg), while a pressure of 6.67 kPa (50 mmHg) is sufficient to produce symptoms.
The further development of stenosis can cause continuous compression on the cauda equina and nerve roots, and the symptoms can be aggravated by activity and extension, while bending and resting cannot completely release the compression and symptoms, resulting in different degrees of neurological dysfunction.
Etiology and pathogenesis
1.Congenital spinal stenosis It is caused by short lumbar arch during congenital development, resulting in a short sagittal diameter of the spinal canal. This condition is very rare in clinical practice.
2.Degenerative spinal stenosis is the most common clinical condition and is the result of degeneration of the lumbar spine, with age, degenerative degeneration includes
(1) Degeneration of the lumbar intervertebral disc first;
(2) ensuing labral hyperplasia of the vertebral body;
(3) the posterior small joints also proliferate, hypertrophy, coalesce, and protrude into the spinal canal, and in the case of hypertrophy and hyperplasia of the superior articular processes, narrowing occurs in the lateral saphenous fossa consisting of the back of the superior articular processes and the posterior edge of the vertebral body in the lower lumbar spine (lumbar 4, lumbar 5 or lumbar 3, lumbar 4, lumbar 5), which is passed by the nerve roots and can thus be compressed;
(4) thickening of the vertebral plate;
(5) thickening or even ossification of the ligamentum flavum, all of which occupy a certain space in the spinal canal and together become degenerative lumbar spinal stenosis (Figure 1).
The sagittal diameter of the lumbar spinal canal varies greatly among individuals, as do the cervical and thoracic spinal canals. In those with a wider sagittal diameter of the spinal canal, although there are various degenerative changes, they do not produce spinal stenosis symptoms because of the large space in the spinal canal, whereas in those with a smaller sagittal diameter of the spinal canal, degenerative changes can cause spinal stenosis symptoms, and a relatively narrow spinal canal does not mean congenital spinal stenosis. It is an inter-individual variation.
Diagnostic points
Overview of diagnostic points
Based on the aforementioned clinical symptoms and signs, we can determine whether central lumbar spinal stenosis or lateral saphenous stenosis or a mixture of the two is present.
1. MRI and CT manifestations Spinal dural compression is an important diagnostic basis, but it is diagnostic only when it is clinically compatible. If MRI lumbar dural sac compression is obvious, or CT synovial hypertrophy and hyperplasia is obvious, but clinical symptoms are absent, then lumbar spinal stenosis cannot be diagnosed. On the contrary, if MRI spinal dural compression is not very heavy, but clinical symptoms and signs are obvious, lumbar spinal stenosis should also be diagnosed. In other words, the severity of the changes in the lumbar spinal canal on MRI and CT is not entirely consistent with the clinical picture, so the clinician should make a diagnosis based on the clinical picture combined with the positive imaging.
2. Length of lumbar spinal stenosis As described in the previous pathophysiology, lumbar spinal stenosis is not just one segment, but often multiple segments. Lumbar 4 is the most involved, followed by lumbar 3, lumbar 5, and again lumbar 2. The length depends on.
(1) clinical symptoms with or without anterior or anterolateral thigh pain and whether the knee tendon reflex is reduced.
(2) Whether the MRI spinal stenosis segment reaches lumbar 3 or even lumbar 2.
(3) Whether the SEP femoral nerve has pathology, with these 3 items indicates that the stenotic segment reaches lumbar 3 and lumbar 2.
3. Coexisting diseases Lumbar spinal stenosis often coexists with.
(1) Lumbar degenerative slippage of lumbar 4 is the most frequent, followed by lumbar 3, for which the stability of the slipped vertebral space should be checked.
(2) coexisting lumbar disc herniation, which should be explored and dealt with during surgery, and lumbar disc bulge is more common and does not need to be dealt with, these coexisting diseases are all part of lumbar degeneration and should be dealt with at the same time.
Clinical manifestations
The typical symptom of lumbar spinal stenosis is intermittent claudication, that is, after walking a certain distance, numbness, pain, soreness and weakness in one or both lower limbs, mostly in the posterior femur to the posterior or anterior calf, and after stopping walking or bending slightly forward, the lower limb symptoms disappear, and then after walking forward to a certain distance, the above symptoms appear again and disappear again after rest. At the beginning, it can walk thousands of meters, gradually decreasing, and can only walk hundreds of meters or dozens of meters, and even need to sit down or squat down to rest to relieve. When resting, there is no symptom, sitting for a long time and riding a bicycle, but when the symptom is serious, the symptom appears when lying down because the waist is held forward, and the symptom is relieved when lying on the side and flexing the waist and legs. Some patients start with lower back pain, walking symptoms, low back pain and single or double lower extremity pain, no symptoms at rest, this is central lumbar stenosis.
When the nerve roots of the lateral saphenous fossa are compressed, sciatica is more typical, very similar to lumbar disc herniation. When the nerve roots of the lumbar 5 are compressed, the numbness and pain is from the posterior hip and posterior femur to the dorsum of the foot outside the front of the calf. The difference between central lumbar spinal stenosis and central lumbar spinal stenosis is that the symptoms are more constant and relatively fixed, without obvious aggravation by walking and relief by rest.
Central lumbar spinal stenosis alone is more common, while lateral saphenous stenosis alone is less common than the former, while mixed stenosis, in which both central and lateral saphenous stenosis are present, is not uncommon.
Signs, in the early stage of central lumbar stenosis, patients report obvious symptoms, and when they go to the hospital for examination, the symptoms disappear because they are waiting for rest, and when the physician examines them, there are often no positive signs, which is a characteristic of central lumbar stenosis, but after a long time, there are still some signs, such as numbness in a certain area of the lower leg, but the straight leg raising test is not limited, and the knee tendon and Achilles tendon reflexes exist, and after the symptoms become severe, the Achilles tendon reflexes often The Achilles tendon reflex often disappears after severe symptoms. The meaningful sign is the lumbar back extension test, the patient’s back to the doctor standing, hip and knee straight, do lumbar back extension, the examination needs to hold the patient’s back, to help him maintain the back extension, in standing no symptoms, back extension 10 ~ 20s, appear one or both lower limbs sore and numb, is positive, this is because when the back extension, lumbar yellow ligament to squeeze inward, lumbar spinal canal further become smaller, affect the blood supply and symptoms, lumbar intervertebral and paravertebral often no pressure pain. The lumbar intervertebral and paravertebral pains are often absent, and the muscle strength of the foot is not significantly reduced, but in severe cases, the muscle strength of the foot is weakened and even paralyzed.
The signs of lateral saphenous fossa stenosis are similar to those of lumbar disc herniation, with numbness in the innervated area of the lower leg, possibly reduced dorsiflexion of the c-toe (lumbar 5), reduced or absent Achilles tendon reflex (sacral 1), or reduced or absent posterior tibial tendon (lumbar 5), and a positive straight leg lift test, while the movement of the lumbar spine is not as obvious as that of lumbar disc herniation in relation to the nerve roots, and the paravertebral pressure pain is not as obvious as that of lumbar disc herniation.
Treatment overview
When lumbar spinal stenosis develops to a certain extent, surgery is required. The requirements for symptom relief are not uniform, as some patients can walk only tens of meters with severe lower extremity pain and need surgical relief, while others can walk hundreds of meters, but their requirements are higher and they want to return to normal activities, which also need surgical relief. The indications for surgery are that once the diagnosis of lumbar stenosis is established and the patient has a request for symptom relief, that is the indication for surgery.
(1) Expanded hemilaminectomy and decompression: indicated for central canal stenosis and lateral saphenous fossa stenosis.
(1) Anesthesia: epidural anesthesia or other anesthesia.
(ii) Position: prone or lateral position; according to the custom, in prone position, the abdomen must be empty to prevent compression.
③Side selection.
a. Side with lateral saphenous stenosis;
b. The side with lower extremity symptoms, if both lower extremities have symptoms, the side with the heavier symptoms is selected;
c. Without lower extremity symptoms, the side with more adequate decompression according to MRI.
④Surgical steps: according to the preoperative determination of the length of stenosis, determine the length of the posterior median incision, the proposed resection of half of the vertebral segments plus the length of the next one vertebrae, cut the supraspinous ligament from the middle, only peel off to reveal half of the lateral vertebral plate, starting from the most inferior vertebrae, usually the lumbar 5 vertebrae, up to the predetermined number of vertebral segments, outward to the inner edge of the articular eminence, to the midline to the subspinous process, oblique to the opposite side, sometimes the upper edge of sacral 1 also needs to be bitten off, according to Depending on the dural bulge and the insertion of a catheter to test whether the upper vertebral canal is still narrowed, the procedure is terminated when it is considered satisfactory. In case of lateral saphenous fossa stenosis, the superior articular process of the nerve is explored, and in case of nerve compression, the nerve root side of the superior articular process is removed with small biting forceps or small bone chisels, until the nerve is completely released, and in case of herniated nucleus pulposus, the herniated nucleus pulposus is removed.
(5) The treatment of coexisting degenerative spinal slippage, preoperative flexion and extension of the lateral X-ray, the slipped vertebral space is stable, no more treatment, postoperative still maintain the degree of slippage, such as the preoperative intervertebral space in an unstable state, the intervertebral fusion should be performed, the method of fusion can be selected intervertebral bone graft fusion, fusion of the contralateral vertebral plate + synovial bone graft or posterior lateral fusion, according to the placement of the internal fixator can help the successful fusion to get up early The fusion can be performed by interbody fusion, contralateral laminar + synovial fusion or lateral fusion.
(6) The mechanism of action of hemi-laminectomy decompression is not identical to that of cervical and thoracic spinal stenosis laminectomy decompression. In cervical spinal stenosis, if the spinal cord is compressed, the expanded hemi-laminar decompression has to reach a certain length (more than the stenotic segment) and width in order to make the dura of the cervical spinal cord swell and open, so that the pressure can be relieved and the herniated disc in front can be displaced to the posterior. In lumbar spinal stenosis, except for lateral saphenous stenosis which is direct decompression, decompression of the central canal opens up the space, breaks the obstruction of venous return, improves blood flow, and relaxes the cauda equina within the dura and does not require posterior displacement.
(7) Advantages of hemilaminectomy decompression.
a. Hemi-lateral exposure, preserving the spinous process, spinous ligament synapses and contralateral structures in situ, maintaining the stability of the lumbar spine;
b. The decompression is effective and complete, and no recurrent cases have been encountered;
c. Unilateral exposure of soft tissues results in rapid recovery, with a 2-week postoperative wake up. Due to the same results, total laminectomy is no longer necessary.
There are many reports of lumbar spinal stenosis, and the results of the cases are not listed here.
(2) Lumbar intervertebral opening for subtle expansion decompression, prone located after revealing each lamina gap, remove the ligamentum flavum, and then perform a subtle expansion of the lamina medialis resection with a lamina bite forceps or lateral bite forceps, focusing on removing the bone crest of the upper half of the lamina, requiring bilateral decompression.
This procedure also serves to decompress the lumbar spine with the same mechanism as the previous procedure, but requires bilateral operation and preserves the stability of the lumbar spine as well.
In order to prevent scar formation after laminectomy and decompression in lumbar spinal stenosis and to restore the stability of the lumbar spine after decompression, some authors have designed different vertebroplasty procedures using the spine of the cut vertebral plate and replanting it back, and the postoperative recovery period of these methods is longer than that of simple hemivertebral plate resection.
Complex lumbar spinal stenosis Complex lumbar spinal stenosis means that in addition to the symptoms of lumbar spinal stenosis, there are other problems that may need to be addressed, mainly the following.
(1) Spinal stenosis with degenerative lumbar scoliosis, degenerative lumbar scoliosis is mainly seen in the elderly and will be described in Section 10. In such patients, stable or simple lumbar scoliosis, i.e., not accompanied by rotational subluxation or instability, can still be treated as simple lumbar spinal stenosis by performing hemi-plate decompression, while those with rotational subluxation and instability will undergo fusion of the segment along with hemi-plate decompression, and moderate correction of scoliosis. The lateral curvature is also moderately corrected.
Age is also one of the factors to be considered. In elderly people aged 65-70 years or older, the causes of lumbar back pain are more complex.
(2) Lumbar spinal stenosis with intervertebral instability, there is a trend of increasing strictness regarding the criteria of lumbar intervertebral instability. Frymoyer et al. concluded that the distance of adjacent intervertebral movement varies from site to site, with >3mm and angle >15° being considered unstable in lumbar 4-5 and above, and >5mm in lumbar 5~sacral 1.
White et al. considered static lateral radiographs with vertebral body horizontal displacement >4.5 mm or more than 15% of the sagittal diameter of the adjacent vertebral body or adjacent vertebral body sagittal angle >22° as lumbar instability, and dynamic lateral radiographs with adjacent vertebral body angle >20° in lumbar 1~2~lumbar 4~5 and >25° in lumbar 5~sacral 1 as lumbar instability. With extensive laminectomy, the incidence of postoperative lumbar instability can be up to 10%, and if part of the articular process is also removed, the incidence of instability can be up to 20%.
For the treatment of lumbar spinal stenosis with lumbar instability, most advocate performing bone graft fusion of the unstable segment at the same time as laminectomy and decompression, with or without internal fixation, there is no agreement.
For lumbar degenerative instability, Zhang Liguo et al. reported that 103 cases in one group were divided into 49 cases in the surgical fusion group and 54 cases in the non-surgical treatment group, and the follow-up results were 1 year and 10 years after treatment, concluding that for young and middle-aged patients, lumbar fusion can reduce symptoms, shorten the course of the disease, and resume work early, while the effect of non-surgical treatment for elderly patients is not lower than that of surgical treatment.
(3) In degenerative lumbar spinal stenosis combined with degenerative slippage, most scholars believe that if there are no signs of instability, decompression alone is feasible, and if there are signs of instability, fusion is required along with decompression. There was no significant difference in the improvement of symptoms and signs between the two groups 1 to 3 years after surgery, but the occurrence of lower back pain was significantly reduced in the internal fixation group. Hadlow et al. observed that those with implant fixation were not better than those with simple fusion, and the proportion of the former reoperated after 2 years was significantly increased.
(4) intervertebral foraminal stenosis: seen in those who still have radicular pain after lumbar spinal canal decompression, there is no compression at the lateral saphenous fossa on imaging, it can be compressed by fibrous tissue or bony hyperplasia at the outlet of the intervertebral foramen, if treated with intervertebral foramen opening and decompression, although it can relieve the symptoms, but 1 side of the articular process is removed, which will lead to intervertebral instability, now with the help of spinal canaloscopy or discoscopy, inserted at the lumbar side to the intervertebral foramen, and removed the compression at the microscope The fibrous strips or bone lips that compress the nerve roots are removed microscopically.