Spondylolisthesis usually refers to the forward or backward displacement of a vertebral body, commonly in the lumbar spine, and in China lumbar spondylolisthesis is one of the common diseases in orthopedics. Currently, lumbar spondylolisthesis is classified into six types: dysplasia (including high dysplasia and low dysplasia), isthmic fracture, degenerative, traumatic and pathological. Among them, isthmic fracture and degenerative are common.
I. Epidemiology and etiology of lumbar spondylolisthesis
（The incidence of lumbar spondylolisthesis varies according to race and region, ranging from 4-6% in Europe to 4.7-5% of the total population in China; isthmic fracture causes about 15% of the spondylolisthesis, and degenerative lumbar spondylolisthesis accounts for about 35%. The age of onset of lumbar spondylolisthesis in China is 20~50 years old, accounting for 85%; the incidence is more in men than in women, and the ratio of men to women is 29:1. The common sites of lumbar spondylolisthesis are L4~L5 and L5~S1, of which the incidence of lumbar 5 vertebrae is 82~90%.
(B) the etiology of lumbar spondylolisthesis the etiology of lumbar spondylolisthesis is still not very clear, a large number of studies show that congenital developmental defects and chronic strain or stress injury are two possible important causes, the latter is generally considered to be the main.
1, traumatic lumbar isthmus can be due to acute trauma, especially posterior extension trauma produces acute fracture, mostly seen in athletic sports site or strong labor porters.
2, congenital genetic factors lumbar vertebrae are born with vertebral body and arch ossification centers, each side of the arch has two ossification centers, one of which develops into the upper articular process and the vertebral arch root, and the other develops into the lower articular process, the vertebral plate and half of the spinous process. If the two do not heal, a congenital isthmus collapse (spondylolysis), also known as an isthmic discontinuity, is formed, with localized pseudoarticular-like changes. After walking, the spine above can slide forward due to standing, which is called spondylolisthesis; it can also be caused by abnormal development of the upper sacral or L5 arch, which produces spondylolysis without isthmus breakdown.
3, fatigue fracture or chronic strain injury from the biomechanical point of view, the human body is in a standing position, the lower lumbar spine weight-bearing. The force that causes forward displacement acts on the isthmus where the bone is relatively weak, and the long-term repeated action can lead to fatigue fracture and chronic strain injury.
4, degenerative factors due to prolonged and sustained lower back instability or stress increase, so that the corresponding small joints wear, degenerative changes, joint protrusion level, coupled with intervertebral disc degeneration, intervertebral instability, anterior longitudinal ligament relaxation, thus gradually slipped, but the isthmus remains intact, so also known as pseudoslip. Most often seen after 50 years of age, the incidence of women is three times that of men, mostly in L4, followed by L5 vertebrae, the degree of slippage is generally within 30%.
5, pathological fracture is a systemic or local lesion, involving the arch, isthmus, upper and lower synapses, so that the loss of stability of the posterior structure of the vertebral body, the occurrence of pathological slippage. Local bone lesions can be tumors or inflammatory diseases.
Second, the biomechanical analysis of lumbar spondylolisthesis
Most clinical lumbar spondylolisthesis occurs in L4 to L5 or L5 to S1, and this paper takes the above two segments as examples to clarify their mechanical mechanisms.
Shear forces exist in any motion segment of the spine, and are particularly pronounced in the lumbosacral region due to the tilt of the intervertebral space. Therefore, there is a tendency for the upper vertebral body to slip and rotate forward against the lower vertebral body. Under physiological loading, the lumbar vertebrae maintain normal positional relationships with each other depending on the synovial joint, the fibrous ring of the intact intervertebral disc, the surrounding ligaments, the contraction force of the dorsal extensor muscles, and normal spinal force lines. Weakening or loss of any one or several shear resistance mechanisms will lead to lumbosacral instability and, in time, to the pathological process of slippage.
The normal body center of gravity is located in front of the lumbosacral joint, once slippage occurs, the gravity arm of the anterior load increases, which will significantly increase the shear force between L5 and S1, which can accelerate disc degeneration and lead to small joint degeneration or ligament tear of the joint capsule, etc. In severe slippage of L5, the posterior and inferior part of L5 vertebrae is located above the anterior part of S1 vertebrae, and the longitudinal load is concentrated in a small area, which will cause local deformation. Typical manifestations are a decrease in the lumbar spine index (lumbar posterior edge height/ lumbar anterior edge height), wedge-shaped changes in the L5 vertebral body, and changes in the S1 dome-shape, resulting in accelerated lumbar tilt rotation and increased lumbosacral kyphosis deformity. In addition, due to the pressure of L5 on the proximal end of the sacrum, the sacrum gradually becomes vertical and the angle of sacral tilt becomes smaller. When the patient stands, due to the excessive anterior convexity of the lumbar spine, it is easy to cause L4 to slip back and pelvic flexion compensate, and the cord and iliopsoas muscles are tense, which intensifies the pelvic verticality, thus making the L5-S1 kyphosis deformity.
L4-L5 is a common site of degenerative lumbar spine slippage. With age, the nucleus pulposus of the intervertebral disc absorbs water, the annulus fibrosus relaxes, the gap narrows, the intervertebral instability, the small joint synapse degenerates, the cushioning effect of the intervertebral disc disappears, the rotation axis of the lower lumbar spine moves from the nucleus pulposus to the small intervertebral joints, and the forward slip force of the lumbar spine increases in the standing position, the intervertebral activity increases, the small joint synapse overactivity and the load on it increases, the joint surface reshapes, the joint gap moves forward, and the small joint cartilage in between In the interval, the small articular cartilage is stripped and the subchondral bone is exposed, so that the alignment of the bone trabeculae is abnormal in compliance with the force, and the L4 slips forward due to wear and resorption behind the superior articular eminence of L5, and the small articular eminence and articular surface under the action of abnormal rotational force, the articular eminence is hypertrophied, the joint capsule is relaxed, and the vertebral body moves forward. In neutral position, the normal alignment can be maintained, but in excessive flexion and extension, a certain degree of anterior displacement and backward slippage can gradually occur, and in serious cases, the intervertebral foramen can be narrowed, compressing the nerve roots and producing sciatica.
Third, the pathology of lumbar spine slippage
The pathological features of the altered vertebral slippage are mainly the destruction of the lumbar spine anatomical structure stimulating or squeezing the nerve, causing different clinical symptoms. Depending on the location of the lesion, symptoms such as low back pain, lower limb pain, lower limb numbness, and even urinary and fecal dysfunction are produced. Since discontinuity of the vertebral arch and degenerative lumbar spondylolisthesis are the most common types of lumbar spondylolisthesis in clinical practice, this article focuses on the pathological changes of these two types.
Arch isthmus discontinuity lumbar spondylolisthesis: Arch disintegration is considered a precursor lesion to vertebral slippage and occurs mainly in the isthmus between the upper and lower synapses, involving L5 in 90% of cases, but arch disintegration is not always accompanied by slippage, with adolescent onset with slippage predominating. In the event of a disarticulated slippage, the nerve roots may be compressed laterally by local scarring, crusting and fibrous hyperplasia of the spinal canal, or the sagittal diameter of the spinal canal may be narrowed by folding of the spinal canal, compressing the dura mater and cauda equina. The compression is more obvious at the step-like protrusion of the posterior edge of the inferior vertebra. In severe cases of slippage, the nerve roots are strained, but the symptoms are not proportional to the degree of slippage.
Degenerative lumbar spondylolisthesis: The course of degenerative lumbar spondylolisthesis can be divided into the following stages: lumbar instability (especially evident in L4 and L5) overactivity protective overmuscle spasm increased synovial load osteophyte joint laxity (with joint wear) anterior displacement. Forward slippage occurs mostly in the L4 plane because L4 is subjected to greater anterior slippage stress. The superior lumbar spine is located in the lower lumbar lordosis and has a tendency to move backward, so in the case of disc and small joint degeneration and intervertebral instability, it can slip backward, and in severe cases, it can cause intervertebral foramen narrowing, compressing the nerve roots and producing sciatica. Sagittal volume of the vertebral canal can be reduced due to slippage, hypertrophy of the ligamentum flavum, thickening of the periarticular process and formation of bone redundancy, which can aggravate the narrowing of the vertebral canal and compress the dura mater and nerve roots.
Because the degenerative slipped vertebral plate and vertebral body displacement are between two adjacent vertebrae, the isthmus collapse slipped more than one segment of the buffer, so although the degree of degenerative slippage is small, but the narrowing of the spinal canal is much more serious than the lower collapse slippage.
Fourth, the clinical manifestations and diagnosis of lumbar spondylolisthesis
(A) Clinical manifestations of lumbar spondylolisthesis
Not all slippages have clinical symptoms, which are related to the compensatory ability of the structures around the spine, but also depend on the degree of secondary damage, such as articular synostosis, spinal stenosis, cauda equina and nerve root compression, etc. The main symptoms of lumbar spondylolisthesis include the following.
1, lumbosacral pain: the pain involves the lumbosacral region, mostly dull pain, and very few patients may experience severe coccyx pain. The pain may appear gradually after exertion or persist after a single sprain. It is aggravated when standing or bending, and is relieved or disappears after bed rest.
2. Sciatic nerve involvement: fibrous connective tissue or hyperplastic bone scabs at the isthmus fracture may compress the nerve roots, and the lumbar 5 or sacral 1 nerve roots are stretched when slipping, resulting in radiating pain and numbness of the lower limbs; straight leg raising test is mostly positive, and Kemp’s sign is positive. Pain and numbness symptoms can appear on both sides, but the twisted scoliosis after the lumbar disorder can cause different degrees of damage on both sides, and the symptoms can be mild or severe, or even appear only unilaterally.
3, intermittent claudication: if the nerve is compressed or combined with lumbar spinal stenosis, intermittent claudication symptoms often appear.
4, the cauda equina nerve is strained or compressed symptoms: when the slippage is serious, the cauda equina nerve involvement can appear lower limb weakness, saddle area numbness and urinary and fecal dysfunction and other symptoms.
2, physical signs lumbar examination can be seen as increased lumbar anterior convexity, hip lordosis, and also straightening of the lumbar spine due to nerve root compression. The lumbar spine activity is restricted and the pain is often aggravated during forward flexion. Pressure pain at the spinous processes of the affected vertebrae can be palpated with the anterior displacement of the last spinous process, resulting in the local formation of a step sensation. Signs of sciatic nerve damage are often uncertain, and careful neurological examination may reveal signs of nerve root involvement to varying degrees in most patients, such as weakness of dorsal extension of the bunion, decreased dorsal foot pain, and weakened Achilles tendon reflex. If the slippage is severe, bladder or rectal sphincter disorders may occur due to cauda equina involvement.
(B) Imaging changes of lumbar spondylolisthesis
Radiographic manifestations are very important for the diagnosis of lumbar spondylolisthesis and the formulation of treatment plans. Anyone suspected of this disease should routinely take anterior-posterior, left-right oblique, lateral and power radiographs in the standing position.
1. Anterior-posterior film: it is not easy to show the isthmus lesion. In patients with significant slippage, the slipped vertebral body shows reduced height due to overlap with the inferior vertebral body, and the vertebral body is tilted, the lower edge is blurred, and the density is high, overlapping with the shadow of the transverse process and sacral vertebrae on both sides, called Brailsford’s arch. The spinous processes of the slipped lumbar vertebrae may be raised upward, or they may touch the spinous processes of the inferior vertebral bodies and deviate from the midline.
2, lateral film: can clearly show the arch collapse pattern. The fissure is below the posterior arch of the vertebral root, between the superior and inferior synapses, from the posterior to the anterior oblique, and the edge often has sclerotic signs. The lateral radiograph shows incomplete or unclear fissure on one side of the lesion, while the lateral radiograph shows more clearly on both sides.
Lateral radiographs can show the signs of lumbar spondylolisthesis and measure the gradation and classification of spondylolisthesis.
a. Grading determination: Meyerding grading is commonly used in China, that is, the upper edge of the inferior vertebral body is divided into 4 equal parts, and the vertebral body is divided into I-IV degrees according to the degree of forward slippage of the vertebral body relative to the inferior vertebral body.
I: the vertebral body sliding forward does not exceed 1/4 of the sagittal diameter of the middle of the vertebral body.
Ⅱ: those who exceed 1/4, but not more than 2/4
Ⅲ: more than 2/4, but not more than 3/4.
Ⅳ: more than 3/4 of the sagittal diameter of the vertebral body.
b. Newman’s grading method: the upper edge of the first sacral vertebra is divided into ten equal parts, and then the same division is made in front of the sacrum according to the same size. Its evaluation and grading is based on the location of the anterior edge of the upper lumbar vertebrae; for example, Ⅰ=3+0, Ⅱ=8+6, Ⅲ=10+10.
3, oblique film: can clearly show the isthmus lesion. In the arch collapse, the isthmus can appear a band-like fissure, called the Scottish (Scotty) dog neck rupture sign or long-necked dog (Greyhound) sign. It is often located anteriorly and inferiorly a few millimeters above the apex of the supra-sacral articular process, and occasionally slightly anterior to the apex.
④Powered radiographs: they can determine the mobility of the slip and are of high value in determining the presence or absence of lumbar instability. The X-ray diagnostic criteria for lumbar instability are >3 mm forward or backward displacement or endplate angle change >15o on hyperextension and hyperflexion position films, >3 mm lateral displacement on orthostatic films; disc wedge change >5o. In hyperflexion, the isthmus can be separated, which helps in the diagnosis.
CT scan, MRI and myelography CT have a high diagnostic rate for isthmus lesions. In addition, CT can not only observe the abnormalities of the vertebral body and disc, but also clearly show the small joint structures and soft tissue abnormalities in the posterior part of the vertebral body. The CT manifestations of lumbar spondylolisthesis mainly include: ① bilateral sign ② double tube sign ③ disc deformation i.e. deformation of the fibrous annulus at the level of slippage, which is manifested by the appearance of symmetrical soft tissue shadow at the posterior inferior edge of the preceding vertebral body, while there is no disc tissue at the posterior inferior edge of the next vertebral body. The isthmus fissure appears in the plane of the inferior edge of the vertebral arch, with variable direction of travel and serrated edges.
Three-dimensional CT or sagittal multi-frame reconstruction can clarify intervertebral foraminal changes and the extent of slippage.
Magnetic resonance imaging (MRI) can observe the compression of lumbar nerve roots and the degree of degeneration of each intervertebral disc, which can help determine the extent of decompression and fusion.
Vertebrogram is an invasive test that is of greater value in detecting herniations in the spinal canal. Because there are very few cases (0%-6%) of slippage with disc herniation, it is only used when neurological signs are obvious, when tumors are not excluded, or when intraoperative repositioning is planned.
(C) Diagnosis of lumbar spondylolisthesis
The criteria for diagnosing lumbar spondylolisthesis mainly include the following.
1, clinical symptoms and signs are described in section I
2.X-ray film should include frontal, lateral, left and right oblique position, and if necessary, add power position film
3, CT, MRI combined with severe neurological symptoms, check the degeneration of the intervertebral disc
4. except for the diagnosis of the disease can be diagnosed by the clear X-ray film, but should pay attention to the concomitant disease.
V. Treatment of lumbar spondylolisthesis
(A) treatment principles of lumbar spondylolisthesis
The principles of lumbar spondylolisthesis treatment include the following: ① Not all lumbar spondylolisthesis need treatment. In fact, a considerable proportion of patients with lumbar spondylolisthesis have no symptoms of lumbar pain throughout their lives and are untreated; the latest research results confirm that the degree and type of chronic lumbar pain in patients with acquired lumbar spondylolisthesis are not substantially different from normal people. ②Lumbar spondylolisthesis with low back pain does not always require surgery. For patients with lumbar spondylolisthesis who have symptoms of low back pain, first of all, the location and nature of their pain should be clarified to determine whether their pain is related to the spondylolisthesis, because degeneration of the intervertebral disc adjacent to the spondylolisthesis, small joint lesions or soft tissue injuries can lead to low back pain; symptomatic treatment or experimental treatment, such as braking and physiotherapy, should be carried out to address the causes; if conservative treatment is ineffective or if the pain is determined to be related to the spondylolisthesis, then surgery should be considered. Treatment. ③Select the appropriate surgical procedure according to the severity of the slippage. It is important to make a comprehensive evaluation of the patient’s age, the type of slippage, the degree of slippage, and the state of the intervertebral disc and spinal canal before surgery, so as to select the appropriate surgical method with a view to achieving the expected results. ④ Fusion of the slipped vertebra is the ultimate goal of surgical treatment. For patients with lumbar spondylolisthesis, an ideal surgery should include decompression of the compressed neural tissue, repositioning and internal fixation of the slipped vertebral body, and fusion of the slipped vertebral body with the adjacent vertebral body.
(ii) Non-surgical treatment of lumbar spondylolisthesis
It is suitable for patients with short history, mild symptoms and no obvious slippage, patients with simple isthmic cleft and patients who are too old and poor in constitution to tolerate surgery. Non-surgical treatment mainly includes: rest physiotherapy, lumbar back muscle exercise, lumbar girth or brace, symptomatic treatment, etc. After standardized conservative treatment, most patients can have their symptoms relieved.
(C) Surgical treatment of lumbar spondylolisthesis
Indications for surgery: (1) no or symptomatic; slippage greater than 50%; adolescents in the growth period (2) progressive slippage (3) non-surgical treatment can not correct the spinal deformity and gait abnormalities (4) non-surgical treatment can not relieve pain (5) lower limbs with neurological symptoms or cauda equina compression syndrome.
The surgical principles of slippage are: decompression, repositioning, fusion and stabilization of the spine. The purpose of surgery is to relieve the patient’s symptoms, so we should accurately determine the cause, location and extent of the symptoms before surgery, and focus on several steps such as decompression, fixation and fusion, and then combine them with relevant imaging examinations to develop a reasonable surgical plan.
1.Decompression
Decompression is the main means to relieve symptoms. It is controversial whether nerve root decompression is needed for mild lumbar spondylolisthesis. Most authors advocate nerve decompression for severe slippage to relieve symptoms. The decompression should include the ligamentum flavum, intervertebral discs, hyperplastic synapses, lateral fossa, and in cases of spinal stenosis, vertebroplasty. In addition to relieving the compression of the dura and nerve roots, decompression is also beneficial for slippage repositioning. Since decompression destroys the posterior lumbar column structure and weakens the stability of the spine, fusion should be performed at the same time. The intervertebral disc is an important structure to maintain intervertebral stability, so it is necessary to clarify whether the symptoms are related to the intervertebral disc before surgery, and try to preserve the useful intervertebral disc, which can reduce surgical trauma and operation time.
2.Reset
So far, there is a big controversy on whether the slipped disc needs to be reset or not. At present, most domestic scholars believe that in principle, we should try to reset; if we can’t reset completely, partial reset can also be done. The advantages of resetting slippage include: (1) restoring the physiological curvature and weight-bearing curve of the lumbosacral spine, and the normal weight-bearing curve has the effect of promoting bone fusion. (2) There is a relatively wide bone graft bed after resetting, which is conducive to bone graft fusion. (3) It can relieve the nerve root strain and reduce the complications of nerve damage. (4) It restores the normal biomechanical relationship of the spine, reduces the slip shear of the slipped vertebrae on the inferior vertebrae, stabilizes the spine; and relieves the secondary lower back pain due to the improvement of the lesions of the joint capsule, ligaments and muscles. Resetting should be performed during surgery on the basis of adequate decompression, with no nerve compression and relaxation of the intervertebral structures after decompression, making resetting simpler and easier. With the development of spinal instrumentation, it is no longer a problem to reset for severe slippage.
3.Internal fixation
Strong internal fixation not only helps to prevent the progression of deformity and improve the early and mid-term clinical outcome; it also increases the rate of spinal canal fusion. But the anterior surgery can not use internal fixation. The pedicle nail can achieve three-column fixation, which can be braced and lifted to reset, and its anti-rotation and shear properties are very strong, so it is the main internal fixation used in posterior surgery. Since Roy-Camille’s invention of the pedicle screw 30 years ago, there have been significant improvements in the material, shape, rod attachment, fixation, and repositioning of the pedicle nail instrumentation. Modern pedicle nails are accurate, simple to operate, firm in structure, easy to reset, and have high resistance to dial-out strength and fatigue strength.
4.Fusion
Lumbar spondylolisthesis fusion is divided into anterior, posterior fusion and combined anterior and posterior surgery according to the surgical approach; it is divided into isthmus repair, lamellar bone graft fusion, interbody fusion and lateral and posterior bone graft fusion according to the bone graft site.
Simple isthmus repair and bone graft fusion can preserve the motion function of the diseased segment, with little interference to the normal physiological range of motion of the lumbar spine, little surgical trauma and simple operation technique. However, the indications for surgery must be strictly controlled, and special attention should be paid to the following two points: ① Only for patients with simple isthmic cleft. It is not indicated for patients with combined vertebral slippage, even if it is mild, or for patients with combined disc herniation or spinal stenosis requiring extensive decompression. ② For adolescent patients. For those older than 30 years, direct repair is difficult to achieve success.
Posterior laminar fusion includes matchstick implants and large H-shaped implants, which were pioneered by Albee and Hibb in 1911 and are now less commonly used because of the high incidence of pseudoarthrosis.
Interbody fusion has the advantages of large implant volume, rapid implant fusion, high fusion rate, support of the anterior vertebral column and maintenance of spinal stability. From a biomechanical analysis, interbody implant fusion is theoretically the ideal method for repairing the anterior mid-column. The main procedures of interbody fusion are trans-anterior (ALIF), posterior (PLIF), and transvertebral foraminal approach (TLIF).
The advantage of ALIF is the ability to perform repositioning and fusion with bone grafting under direct vision. The shortcomings of this procedure are the high operator requirements, the high degree of injury, the tendency to cause sexual dysfunction and postoperative adhesions, and the inability to relieve neurological symptoms caused by posterior compression of the spinal canal.
The advantages of posterior interbody fusion (PLIF) are: (1) it can preserve or strengthen the stabilizing factors of the spine (2) the operation of bone grafting is simple and easy to implant (3) the fusion can determine the stabilization of the spine (4) the decompression is complete (5) the postoperative complications are less. However, the procedure has an increased potential for injury to the dura mater and nerve roots.
Transvertebral foramen approach interbody fusion (TLIF) is a new technique that has emerged in recent years and has the tendency to gradually replace PLIF. The main features of this technique are (1) unilateral posterior-lateral access to the intervertebral space and feasible bilateral intervertebral implant support in the anterior column, which is less traumatic than PLIF’s bilateral access intervertebral implants, reduces operative time and bleeds less. (2) The TLIF procedure preserves the supraspinous and interspinous ligaments and posterior longitudinal ligaments, which have the effect of tension band on the vertebral implants and promote fusion by compressing the implants; at the same time, it can prevent the implants from falling backward into the spinal canal. (3) The TLIF procedure only removes the small joint on one side, preserving the vertebral plate and the small joint on the other side, which has relatively less damage to the integrity of vertebrae and increases the bone graft area during surgery, thus improving the fusion rate of bone graft. (4) No traction on the dura and nerve roots is required, which will not cause damage to the nerve roots and cauda equina and round vertebrae.
The advantages of lateral posterior fusion (PLF) are: (1) decompression surgery can be performed at the same time (2) the bone grafting site is closer to the flexion and extension axis of the lumbar spine, and the surrounding blood circulation is rich, which facilitates bone healing (3) the postoperative bed rest time is relatively short (4) it can be used simultaneously with intervertebral bone grafting and lamellar bone grafting to make 360° fusion. However, the fusion pseudo-joint formation rate of lateral posterior implant is high; the postoperative posterior lateral implant area is under strong tension, and under the effect of long-term repeated shear stress, elongation of the fusion area or fatigue fracture may occur, causing further development of lumbar spondylolisthesis.
There are many materials that can be used for intervertebral bone grafting, besides the traditional autologous and allogeneic bone blocks, there are also various Cage and Spacer. intervertebral fusion device (Cage) has developed rapidly since its application 10 years ago. The shape has changed from a threaded cylinder to a square and box shape, and the material has changed from titanium to carbon fiber and PEEK, which is more biocompatible; now there are special fusion devices for various accesses, and there is even a HA-coated Spacer, which can induce bone growth without bone grafting.