|SYMPOSIUM - CERVICAL SPONDYLOMYELOPATHY
|Year : 2019 | Volume
| Issue : 1 | Page : 42-51
Posterior surgical options for spondylotic cervical myelopathy
Shankar Acharya, Nikhil Jain
Department of Orthospine, Sir Ganga Ram Hospital, New Delhi, India
|Date of Web Publication||11-Jan-2019|
Dr. Shankar Acharya
Department of Spine Surgery, Room No: 1218 A, Sir Ganga Ram Hospital, New Delhi
Source of Support: None, Conflict of Interest: None
Cervical spondylotic myelopathy (CSM) is a common presentation in the middle-aged to elderly population. The cause of myelopathy is multifactorial, and cervical spondylosis is the most common cause. This review looks into the treatment options, timing of the surgery, and the advantages and disadvantages of the various posterior approaches for multilevel spondylotic myelopathy. CSM is a disabling disorder that should be addressed in its early phases. There are limited surgical options available, and each procedure has its advantages and disadvantages. Since the neurological and functional outcomes are the same for all well-performed decompressions, the choice of surgical approach depends on various other factors. Posterior approaches are good for multilevel disease as they make the surgery simpler, shorter and with reduced complications in comparison to multilevel anterior surgeries.
Keywords: Cervical, management, myelopathy, posterior, surgery
|How to cite this article:|
Acharya S, Jain N. Posterior surgical options for spondylotic cervical myelopathy. Indian Spine J 2019;2:42-51
| Introduction|| |
Cervical spondylotic myelopathy (CSM) is a fairly common presentation in the middle-aged to the elderly population. With the life expectancy in the Indian population increasing in the past two decades, more and more people are presenting with symptoms of myelopathy. Furthermore, Indians are at a higher risk of diabetes due to lifestyle and genetic predisposition. In such a scenario, it becomes important to be able to understand the nuances of the disease with its presentation because it is not uncommon to have diabetes and concomitant myelopathy. These patients present with numbness and tingling in the limbs, clumsiness of hands, difficulty walking, and instability of gait along with frequents falls. At this age hearing difficulty, visual impairment, osteoarthritis of hip and knee joints may add to the cause of instabilities and gait disturbances, sometimes masking or mimicking the symptoms of myelopathy. Hence, in our country, recognizing the problem and selecting the correct patient for surgery is of utmost importance.
The cause of myelopathy is multifactorial and cervical spondylosis is the most common cause. Aging discs with concomitant facet osteoarthropathy, ligamentum flavum hypertrophy and buckling, lead to focal stenosis and cord compression. Chronic cervical cord compression and subsequent cord ischemia lead to neural tract degeneration and causes myelopathy. Ossification of the posterior longitudinal ligament (OPLL) in genetically predisposed patients and fluorosis in endemic areas also leads to compressive myelopathy.
Noncompressive myelopathy due to nutritional deficiency (Vitamin B12), inflammatory, toxic, vascular, hereditary, postradiation, paraneoplastic syndromes, and motor neuron diseases must be ruled out because such patients will not benefit from surgery. On the contrary surgery in these patients could make the condition worse.
| History and Physical Examination|| |
A detailed history of a patient of cervical myelopathy should be taken, and problems such as bad knees, poor vision, hearing loss, cerebrovascular accident, diabetes, or brain disorders should be ruled out. A combination of multiple comorbidities can be a diagnostic challenge. Patients with lumbar spinal stenosis present with heaviness, numbness, and paresthesia in the lower limbs and difficulty in walking after a certain distance. Such patients should be cautiously examined for any symptoms of upper limb or neck pain, as cervical stenosis coexists in 30% of the cases.,,
A detailed physical examination should include examination of all the large and small joints to rule out osteoarthritis and inflammatory arthritis. Peripheral neuropathies and peripheral vascular diseases should be ruled out. Clinical findings in myelopathy patients include a variety of signs, and they should be properly assessed.,,,
All the clinical findings should be radiologically and electrophysiologically confirmed. Investigations include X-ray, magnetic resonance imaging (MRI), computed tomography (CT) scan and peripheral Doppler studies. These tests are crucial in patients with multiple comorbidities such as diabetes, neuropathy, arthritis, and stroke.,,,
Electrophysiological testing is helpful in very early cases where the signs and symptoms are minimal and confusing, and the MRI findings are also not clear. These tests include motor and somatosensory evoked potentials, electromyography, and nerve conduction studies. They help differentiating between cervical cord, nerve root, brachial plexus, and more peripheral lesions.
| Patient Selection|| |
The patient selection for surgery from this diverse group of patients is of the utmost importance, necessitating a systemic approach. Once sure that the history, clinical examination, electrophysiological tests, and radiological findings correlate with the clinical picture, it is important to know when to intervene. Not all patients require surgery and not all surgically treated patients benefit from it. Nurick grading and modified Japanese Orthopedic Association Score (mJOA) are the two clinical scales that classify these patients as per the symptoms and are followed worldwide.,
In the Nurick system, high grade means increased disability, and in mJOA a low score means increased disability. The mJOA is divided into three types: mild, moderate, and severe and they are as follows: mild: 17–12; moderate: 12–9; and severe: <9.
Clinical scales only judge the patient as per their present condition. Since myelopathy is a chronic disorder, how the patients have behaved in the recent past is also important. About 70% of the patients have a slow, steady deterioration with intervening periods of stability/minimal progression, 20% of the patients deteriorate steadily with no stable intervals, and 5% deteriorate rapidly in a very short time. So along with the present clinical score, the progression of the disease is also very important for selecting the right treatment option for the patient.,
| Ideal Patients For Surgery|| |
Undergoing surgery is a major step and has its inherent risk and morbidity. Ideal patients for the surgery would be the ones who are likely to get significant benefit from it. The patients who have Nurick grades <2 or mJOA scores >12 are minimally disabled and do not have significant MRI changes. For such patients, the risk and morbidity of the surgery might be more than the disorder morbidity itself. Such patients may be put under observation and conservative management. The patients with Nurick grade >3 and a mJOA score <9 are in the advanced stage of the disease, the cord is severely atrophied, MRI shows cystic changes, neural tissue has ischemic changes, and the chances of recovery are slim. Such patients should be cautiously managed as they might deteriorate from surgical insult. The ideal patients for surgery are the ones with moderate and progressive symptoms, with minimal changes of the cord in the MRI. A mJOA score of ≤12 and Nurick Grade 2 and 3 are good indicators for surgery. The success of surgery depends on the duration of onset of symptoms, and generally better results are obtained when operated within 6 months of onset of symptoms [Table 1].,,,,,
Patients with mild or moderate mJOA scores but nonprogressive disability can be managed with observation and supportive treatment. However, these patients have a very high risk of spinal cord injury leading to hospitalization and disability if there is a sudden forceful movement of the neck like in a whiplash injury. Hence, conservatively managed patients should be explained all the precautions in detail.,,,
Hirabayashi et al., as per their experience and observation of 53 patients operated for OPLL over 16 years, gave a formula to help us assess the expected rate of recovery for the patients using mJOA scores.,
Postoperative score − preoperative score
17 maximum score − p
This formula can be used to calculate the expected recovery rate of these patients as per their mJOA scores. Low mJOA scores have poor recovery rates, and high mJOA scores indicate better recovery rates. 17 is the score of a normal individual and is the maximum score on mJOA.
The statistically significant factors that affect the outcome of a surgery are a follows:,,
- Preoperative transverse area of the spinal cord at the level of maximum compression (<30 mm2 had unsatisfactory surgical results. The cord is not able to survive below 30 mm2 transverse area)
- Chronicity of the myelopathy symptoms (longer the duration, poorer the surgical outcome)
- High signal changes on T2-weighted imaging sequences of the spinal cord before surgery (multisegmental areas of high intensity have a poor prognosis, indicating more severe pathologic changes in the spinal cord)
- Low-signal intensity changes in the spinal cord in T1 weighted imaging sequences indicate poor prognosis
- The multiplicity of the involvement (single level involvement has the best postoperative outcome)
- Age at the time of surgery (with increasing age, surgical results worsen).
| Choice of Approach and Type of Surgery|| |
Once the decision to operate on a patient with CSM is taken, then the question remains as to which approach and what method should be used. The optimal surgical approach is not yet clear, and the debate still goes on. The main factors are:
- Cervical curvature – lordotic, neutral or kyphotic spine
- C2–C7 Sagittal Vertical Axis (SVA)
- Number of levels involved 1, 2, 3, or more
- Location of compression: anterior or posterior
- The pattern of compression soft to hard disc, OPLL (continuous vs. intermittent)
- Surgeon preference and other facilities
- Patients risk factor such as diabetes mellitus, smoking, and any other illness.
If well performed, the neurologic recovery and functional outcomes have been found similar in both anterior and posterior approaches. The posterior approaches rely on the ability of the cord to “drift away” from the anterior pathology. Here, the role of cervical curvature becomes very important. Significant kyphosis prevents the cord from drifting back and away from the pathology. Earlier C2–C7 Cobbs' angle was used to measure cervical lordosis. Now, we use the C2–C7 sagittal vertical axis to assess the cervical sagittal alignment. It is calculated as anterior deviation of C2 plumb line from posterior superior endplate of C7 [Figure 1].
|Figure 1: C2–C7 Sagittal Vertical Axis calculated as anterior deviation of C2 plumb line from posterior superior corner of C7|
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Posterior approaches remove the posterior tension band of the cervical spine. Kyphosis will progress if a noninstrumented nonfusion posterior surgery is performed in an already kyphotic cervical spine. The cord is not able to drift away in such a scenario, and decompression fails. More than 40 mm SVA deviation is associated with poor outcome with posterior nonfusion approaches.
The K-line helps assess the extent of the encroachment of the cervical canal by the anterior pathology. It is measured on lateral neutral radiographs of the cervical spine where a line is drawn from the center of the canal at C2 to center of the canal at C7 vertebra. K-Line can also be reproduced on the mid-sagittal sections of the MRI cervical spine films. The anterior pathologies extending beyond the K line are termed K (−) and the pathologies falling short of the K line are termed K (+). The K (−) pathologies are unsuitable for posterior-only approach [Figure 2]a and [Figure 2]b.,
|Figure 2: (a and b) Diagram showing cervical cord alignment (black solid line) over a kyphotic versus a lordotic cervical vertebrae|
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Anterior surgical approach
This approach directly removes the pathology compressing the cervical cord from the anterior and is useful in lordotic, straight, and kyphotic cervical spine. The details with the advantages and disadvantages of the anterior approach have been discussed in another article.
Posterior surgical approach
The earliest surgeries of the cervical spine employed the posterior approach because posterior elements are superficial and easy to palpate. Laminectomy is the oldest of all procedures in this approach. Around the time of World War II, the posterior surgeries fell into disfavor, but now, they have become the procedures of choice in multilevel spondylotic myelopathy. The posterior approach does not remove the pathology present anteriorly, but it allows the spinal cord to be able to float/drift away from the anterior discogenic or retrovertebral compression. This is possible only in neutral or lordotic cervical curvatures, as a kyphotic spine will stay draped with the cord due to its weight and alignment, even if the posterior elements have been removed completely., Posterior approaches involve removal of posterior muscles and midline bony structures, making the spine unstable. Such procedures are useful only where anterior procedures are not feasible. In cases where the pathology extends to 3 or more levels, it is prudent to decompress posteriorly because the risk of complications from an anterior approach might outweigh the benefits. Because the posterior approach makes cervical spine unstable, postoperative neck pain and postoperative kyphosis are common complications. One noteworthy point is that the C5 nerve root is short, thin and hence prone to traction injury. When the cord is decompressed, and it drifts away, the C5 nerve root gets pulled, leading to deltoid and biceps weakness along with numbness along the outer aspect of the arm.
Laminectomy, laminectomy with instrumented fusion and laminoplasty
Laminectomy was the original procedure described for posterior surgeries. The first successful laminectomy was performed by Alban G Smith in 1828 who performed a 3 level laminectomy in a paraplegic patient and the patient improved. The first laminectomy to remove a herniated disc was performed by Scaglietti in 1949. French window laminectomy was introduced by Kirita et al. in 1975. In this, the lamina was thinned using an air drill and then the lamina and flavum was cut from the midline. The two flaps created to look like a French window would then be excised. The present surgical technique involves using a high-speed burr drill. The supraspinous and interspinous ligaments above and below the level of laminectomy are cut. Then using the burr at the lamina-lateral mass junction on both sides, the outer cortex and the cancellous bone is drilled away, and the inner cortical bone is thinned. The thinned out lamina and the underlying ligamentum flavum is cut using a Kerrisons rongeur and using a Kocher's forceps the whole of the posterior element is lifted off the dorsal surface of the cord. During the surgery it is important to be gentle and not to put any instrument blindly under the lamina else it may compress the cord and cause a neural deficit. Decompression up to the lateral border of the dural sac is considered as sufficient. Undercutting of the C2 and C7 can be done to prevent kinking of the cord. Laminectomy of the C2 and C7 laminas is not advisable as it makes the head unstable and the neck rapidly progresses to kyphosis. It is imperative not to remove more than 25% of the facet joints. 50% or more of facets, if resected lead to instability and posterior instrumentation will be necessary. Although laminectomy provides good posterior decompression, many complications have been noted. Laminectomy increases the flexibility and makes the cervical spine unstable at the lower ends, leading to kyphosis. A kyphotic, hypermobile, and unstable spine causes neck pain and spinal cord trauma. After laminectomy cases have been reported where a membrane gets formed over the dura, called as the “postlaminectomy membrane” which can lead to restenosis and late neurological symptoms.,, It is also important to preserve the muscle attachment to C2 and C7 to preserve the cervical lordosis. Laminectomy alone is contraindicated for kyphotic cervical spines, especially if the kyphosis is >13° [Figure 3]a,[Figure 3]b,[Figure 3]c.
|Figure 3: (a-c) Preoperative X-ray cervical spine lateral view, magnetic resonance imaging cervical spine sagittal section and computed tomography cervical spine sagittal section showing maintained cervical lordosis, degenerative cervical spondylosis, multilevel cervical stenosis and cord oedema. C3–C6 laminectomy was performed|
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Postlaminectomy instability and preoperative deficient posterior elements in the cervical spine were the reason why posterior instrumentation and fusion with laminectomy were introduced. In 1989 Roy Camille introduced the lateral mass plates and screws which were further refined by Magerl et al. Abumi et al. in 1994 introduced subaxial cervical spine pedicle screws instrumentation following the idea of 3 column fixation by pedicle screws in thoracic and lumbar spine. Modern equipment includes cervical lateral mass, pedicle, and translaminar screws along with local or iliac crest bone graft for fusion after central laminectomy. With instrumented fusion, the incidence of postoperative neck pain and kyphosis was minimized. However, there was the problem of decreased postoperative range of motion in the neck, graft site pain, nonunion at fusion site, implant failure, increased costs of surgery, adjacent segment disease and infection. The risk of C5 nerve root palsy remained the same. It is important that while operating on a postlaminectomy kyphotic cervical spine, correction of more than 9° at each segment can lead to excessive translation of cord posteriorly, and this can lead to neurological deterioration sooner or later. Vertebral artery injuries can happen during the cervical spine surgery at any time, and it is very important to know how to handle it. It is a life-threatening situation for the patient and a frightening emergency for the surgeon. The surgeon needs to control the hemorrhage, prevent central neural ischemia, and prevent air embolism. The best option is to have a competent vascular surgeon available and let him handle the situation. If the injury is due to the screw perforating the vertebral artery, do not remove the screw as it provides the tamponade effect and prevents frank hemorrhage. If the injury has happened at another site, the site of bleeding should be digitally pressed on and packed with Gelfoam and cottonoids. Then expose the vertebral artery in the foramen transversarium one level above and one level below the injury site and clip both the ends with aneurysm clips. Injury site can then be repaired. In case the vessel is irreparable, and the contralateral vertebral artery is patent, the decision to ligate the injured vertebral artery or bypass the artery can be taken which should be done by a competent vascular surgeon. It is important to keep the neck neutral during the whole procedure to prevent kinking of the contralateral vertebral artery and prevent any embolism [Figure 4]a, [Figure 4]b and [Figure 5].
|Figure 4: (a and b) Preoperative X-ray and magnetic resonance imaging sagittal sections, of degenerative cervical spondylotic myelopathy with multilevel cervical stenosis|
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|Figure 5: Postoperative X-ray cervical spine, lateral view, following C3–C6 central laminectomy and posterior instrumented fusion with C3–C6 lateral mass screws|
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While the world was focusing on instrumentation, the Japanese were working on motion preserving posterior surgery called “Laminoplasty.” In 1981, Hukuda et al. introduced French window laminoplasty by suturing the two flaps created by Kirita, to the paraspinal muscles. Oyama and Hattori from Japan modified this technique by cutting the thinned lamina into a Z shape and then lifting them and fixing them with sutures; “Z laminoplasty” [Figure 6].
Tsuji would cut the lamina bilaterally at the lamina and lateral mass junction and let them float freely over the cord [Figure 7].
Hirabayashi et al. used the Tsuji technique and developed the expansive “open door” laminoplasty, and this is a popular technique. The author also uses this technique. At present, we have three types of commonly used laminoplasty; open door technique, French door/double door technique, and the T-saw technique. “Open door” technique involves cutting the lamina-lateral mass junction on one side and opening the posterior elements, like a single door hinged over the contralateral lamina-lateral mass junction. “French door/double door” technique involves splitting the spinous process from the midline and holding both the laminas wide apart. “T-saw” technique is the same as the French door technique but uses a T-saw instead of a high-speed burr. Fixation is done using metal plates and bone grafts [Figure 8]a and [Figure 8]b.
Laminoplasty preserves the lamina, and the risk of postlaminectomy membrane formation over dura is minimal. Although the posterior elements are preserved in laminoplasty, the patients still have been found to develop axial neck pain and deformity after the surgery. To prevent this, muscles from C2 and C7 spinous process should not be detached. If injured, they should be repaired properly.,
Furthermore, “muscle sparing laminoplasty” techniques can be used. First technique involves subperiosteal dissection of the muscles of the spinous process on one side, then cutting the spinous process at the base, separating it from the lamina and then retracting the spinous process away, with the contralateral muscles still attached to it. The Shiraishi technique involves severing the interspinalis attachments and preserving the semispinalis. Kim performs myoarchitectonic spinolaminoplasty where he splits the spinous process in the midline, cuts the spinous processes from the base and retracts them with their muscles attached to their respective sides, away from the midline, to expose the lamina [Figure 9].
Laminoplasty is indicated for patients with a stable spine, maintained cervical lordosis, minimal neck pain, local kyphosis <13° and in patients with OPLL not crossing the K line (K +) [Figure 10]a, [Figure 10]b and [Figure 11]a,[Figure 11]b,[Figure 11]c,[Figure 11]d, [Table 2] and [Table 3].
|Figure 10: (a and b) Preoperative magnetic resonance imaging sagittal and axial images of stenotic cervical canal with cord compression and cord oedema|
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|Figure 11: (a-d) Postoperative X-ray cervical spine lateral view, sagittal magnetic resonance imaging, sagittal computed tomography scan and axial computed tomography scan cervical spine postlaminoplasty, with miniplates in situ, showing widened cervical canal area and cervical cord floating away from the anterior pathology|
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|Table 2: Comparison of laminectomy, laminectomy with lateral mass fusion and laminoplasty|
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| Clinical Outcomes Following Posterior Surgery in Cervical Spondylotic Myelopathy|| |
Laminoplasty versus laminectomy with instrumented fusion
The patients with well-performed cervical laminectomy, cervical laminoplasty, and laminectomy with instrumented fusion have a similar functional and neurological recovery. Comparing the other complications of each procedure, the operative time and blood loss is more in the patients who undergo laminectomy and instrumented fusion. The incidence of dysphagia and wound infection is also higher in the instrumented fusion group. The possible reasons are increased duration of surgery, more extensive dissection and muscle trauma and more hardware implanted compared to the laminoplasty group. Although the incidence of these complications is higher in the instrumentation group, it is not statistically significantly different from the laminoplasty group. The risk of C5 palsy also stays the same in both techniques.,, The muscle preserving techniques in laminoplasty have demonstrated a significant decrease in postoperative neck pain, shoulder pain, adjacent segment degeneration and instability compared to older laminoplasty techniques, and laminectomy with instrumented fusion. These techniques claim to preserve the muscle attachments, cervical extensor musculature, and cervical curvature compared to the older laminoplasty techniques. The old laminoplasty techniques focused more on lamina but missed out on musculature reconstruction. Laminectomy with instrumented fusion involves stripping off all the posterior cervical musculature and wide dissection that makes cervical spine prone to postoperative neck pain and instability. But still more studies are required to establish these results.
Anterior versus posterior approach
The neurological and functional outcomes are similar for a well-performed surgery through an anterior or posterior approach. If we compare the complication rates, the posterior approaches have a higher incidence of infection and blood loss, even though the operative time remains similar in both the approaches. The factors can be more extensive muscle dissection, more hardware implanted, rich blood supply of the face and anterior neck, and a very important fact that posterior approaches are being employed mainly for multilevel (3 or more) disease. The incidence of dysphagia and C5 nerve palsy remains the same in both the approaches [Table 4].
| Conclusion|| |
CSM is a disabling disorder that should be addressed in its early phases. Any suspicious finding should be thoroughly evaluated. The treatment depends on the stage of the disease, progression of the disease and the MRI changes in the cervical cord. The choice of surgical approach depends on various other factors, as the neurological and functional outcomes are the same for both anterior and posterior approaches. At our center, we perform both laminoplasty and laminectomy with fusion in cases of multiple level spondylotic myelopathy in the indicated patients. We have found the functional and neurological results to be satisfactory with minimal complications and none of the cases needing revision surgery. Posterior approaches are good for multilevel disease as they make the surgery simpler and shorter compared to multilevel anterior surgeries. This also decreases the risk of complication rates postoperatively and aids in a faster rehabilitation of the patient. The patients should also be given total rehabilitative care, and they should be followed up closely to watch for late complications.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
[Table 1], [Table 2], [Table 3], [Table 4]