Surgical Decompression for Spinal Stenosis

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CHAPTER 87 Surgical Decompression for Spinal Stenosis

Franco Postacchini, G. Cinotti, R. Postacchini

DEFINITION

Lumbar spinal stenosis is an abnormal narrowing of the osteoligamentous vertebral canal and/or the intervertebral foramina, which is responsible for compression of the thecal sac and/or the caudal nerve roots; narrowing of the vertebral canal may involve one or more levels and, at a single level, may affect the entire canal or a part of it.¹ Thus, abnormal narrowing of the spinal canal may be considered as stenosis if two criteria are fulfilled: the narrowing involves the osteoligamentous spinal canal, and it causes compression of the neural structures.

If the concept of stenosis is not limited to the osteoligamentous canal, even disc herniation is, in the strictest sense, a stenotic condition because it causes a pathological narrowing of the spinal canal. However, the two conditions – disc herniation and stenosis – are so different in the pathogenesis and anatomoclinical characteristics, that they cannot be considered as a single pathological entity.

The second criterion emphasizes the concept of compression of the thecal sac and nerve roots. The term stenosis indicates a disproportion between the caliber of the container and the volume of the content. If the content is solid or semifluid, as in the vertebral canal, the dimensional disproportion results in compression of the content by the walls of the container. However, the disproportion is not strictly related to the anteroposterior dimensions of the vertebral canal, as believed by Verbiest.² Severe compression of the neural structures may occur even if the sagittal dimensions of the canal are within normal limits. On the other hand, a midsagittal diameter of 10 mm or less does not necessarily lead to compression of the cauda equina.³ This is probably due to the fact that the neural structures develop in harmony with the dimensions of the canal. When this does not occur, the reserve space available for the thecal sac and/or the caudal nerve roots is variably reduced and, therefore, acquired constrictive conditions of even minor degree are sufficient to cause stenosis. If the narrowing is not severe enough to cause compression of the neural structures, the spinal canal is to be considered narrow but not stenotic. Therefore, a diagnosis of stenosis cannot be made solely on the basis of measurements of the size of the vertebral canal or the area of the thecal sac in the axial sections. The radiologic diagnosis of stenosis should be predicated upon the demonstration of compression of the neural structures, whether clinically symptomatic or asymptomatic, by an abnormally narrow osteoligamentous spinal canal (Fig. 87.1).

Fig. 87.1 Central lumbar stenosis at L3–4 and L4–5 (L5 vertebra is sacralized). The thecal sac shows the posterior indentations typical of the osteoligamentous compression by the posterior vertebral arch.

CLASSIFICATION

Site of constriction

Lumbar spinal stenosis can be distinguished, based on the site of constriction, as stenosis of the spinal canal or central stenosis, isolated stenosis of the nerve root canal or lateral stenosis, and stenosis of the intervertebral foramen (Table 87.1).

Table 87.1 Classification of Lumbar Spinal Stenosis

CENTRAL STENOSIS
	Primary
	Congenital
	Developmental
	Achondroplastic
	Constitutional
	Secondary
	Degenerative
	Simple
	With degenerative spondylolisthesis or scoliosis
	Late sequelae of fractures or infections
	Paget’s disease
	Combined
	Association of primary and secondary forms at the same vertebral level
ISOLATED LATERAL STENOSIS
	Primary
	Secondary
	Combined
STENOSIS OF THE INTERVERTEBRAL FORAMEN
	Primary
	Secondary
	Combined

In stenosis of the spinal canal, the entire area of the canal, as viewed on the axial plane, is usually constricted (Fig. 87.2). In other words, both the central portion of the canal and the lateral parts, occupied by the emerging nerve roots, are constricted. Therefore, the expression stenosis of the spinal canal is more correct than that of central stenosis, which would indicate constriction only of the central area. However, the authors will use the latter term because it has become the one commonly adopted.

Fig. 87.2 MRI scan at L4–5 level showing central spinal stenosis. The spinal canal is constricted in the central portion, containing the thecal sac, as well as in the lateral portions occupied by the emerging nerve roots.

Central stenosis, except for the rare forms due to vertebral malformations, or sequelae of fractures or infections, is located at the level of the intervertebral space, where there are the anatomical structures, such as the intervertebral disc, the apophyseal joints, and the ligamenta flava, which can change with aging or disease.

The nerve root canal or radicular canal corresponds to the lateral portion of the spinal canal (Fig. 87.3). This canal, which is more of an anatomical concept than a true canal, is the semitubular structure in which the nerve root, exiting from the thecal sac, travels before entering the intervertebral foramen. As for the central form, in the last decade, the term lateral stenosis has become the most widely used for this type of stenosis.

Fig. 87.3 Lateral stenosis at L4–5. CT scan showing constriction of the nerve root canals due to degenerative changes of the facet joints.

The term lateral stenosis is often used to indicate both nerve root canal stenosis and stenosis of the intervertebral foramen. The authors believe that the intervertebral foramen, which begins and ends at the level of the medial and the lateral border of the pedicle, respectively, should be considered as a distinct anatomical entity. Therefore, stenosis of the foramen should be differentiated from the other two forms of stenosis, although it can be associated, albeit rarely, with one of the two.

Type of stenosis

Three forms of stenosis can be identified: primary, secondary and combined (see Table 87.1).

Primary forms

Secondary forms

Central stenosis

If the sagittal dimensions of the spinal canal are normal, or at the lower limits, and compression of the caudal nerve roots is the result of one or more acquired conditions, such as spondylotic changes of the facet joints, abnormal thickening of the ligamenta flava, and bulging of the intervertebral discs, then this form is defined as simple degenerative stenosis (Fig. 87.6).

Fig. 87.6 Simple degenerative stenosis. T2-weighted sagittal MRI showing stenosis at L3–4 and L4–5. The sagittal dimension of the thecal sac is normal in size at intervertebral levels.

Very often, however, degenerative spondylolisthesis of the cranial vertebra of the motion segment is also present at one or, occasionally, two or more levels (Fig. 87.7). Degenerative spondylolisthesis is consistently responsible for narrowing of the spinal canal, but may not cause lateral or central stenosis. This is because the presence, type, and severity of stenosis is related to several factors, such as the constitutional dimensions of the spinal canal, the orientation (more or less sagittal), and the severity of degenerative changes of the facet joints, and the amount of vertebral slipping, which may in some cases play a minor role. For example, a grade I spondylolisthesis in a patient with a constitutionally large spinal canal produces no significant narrowing of the canal, would be categorized as no stenosis. In contrast, the same or even lesser grade of spondylolisthesis in a patient with a primarily narrow canal can be associated with clinically significant stenosis. The type of stenosis, that is whether stenosis is central or lateral, depends on the orientation of the articular processes and the length of the pedicles. Usually, stenosis initially presents as lateral and then central in later stages. Instability, that is hypermobility on flexion–extension radiographs, is one of the main characteristics of degenerative spondylolisthesis. However, in many cases there is no appreciable hypermobility of the slipped vertebra. The authors consider the latter condition as a potential instability, which can become unstable as a result of surgery. Such a scenario may arise following removal of a large part of one or both facet joints, unilateral or bilateral discectomy, or when destabilizing factors unable to stabilize a normal vertebra intervene, such as disc degeneration or severe degenerative changes of the facet joints. In degenerative spondylolisthesis, the intervertebral disc often bulges into the intervertebral foramen to cause stenosis. However, true stenosis of the foramen is rarely present as the foramen becomes larger in the sagittal dimensions in the presence of slipping of the cranial vertebra.

Fig. 87.7 Plain radiographs of a patient with severe degenerative spondylolisthesis of L5 and mild slipping of L4.

A particular form of acquired stenosis is the type that is associated with degenerative scoliosis. In this instance a role may be played by the scoliotic curve in tandem with the pure degenerative changes of the facet joints and the intervertebral discs.

Other forms of secondary stenosis include late sequelae of fractures or infectious diseases of the spine, which, however, are rare conditions. Rarely, stenosis can occur secondary to systemic bone diseases such as Paget’s disease. Paget’s disease can lead to an increase in volume and/or deformation of one or more vertebral components.

Lateral stenosis

Most often, this form of stenosis is degenerative in nature. Usually, degenerative stenosis involves only the lateral portions of the spinal canal in the initial stages and become central in more advanced stages when spondylotic changes becomes more severe. This is particularly true for degenerative spondylolisthesis.

Lateral stenosis can occur due to a cyst of the facet joint when it compress the emerging root in the nerve root canal (Fig. 87.8).

Fig. 87.8 Lateral stenosis due to a synovial cyst of the left facet joint at L4–5 level.

Stenosis of the neuroforamen

Stenosis of the intervertebral foramen is rarely encountered, especially as an isolated condition. In most cases, foramenal stenosis is associated with a central or lateral stenosis. At times, root compression occurs when there is a lateral disc herniation or disc bulge in the presence of advanced degenerative changes of the articular processes.

Combined forms

These forms occur when primary narrowing of the spinal canal, the nerve root canal, or the intervertebral foramen is also associated, at the same vertebral level, with secondary narrowing, which is generally spondylotic in nature. Combined stenosis can be differentiated from primary stenosis by the presence of milder developmental narrowing, but more severe degenerative changes.

INDICATIONS FOR SURGERY

Surgery is contraindicated for a narrow spinal canal and is generally not indicated in patients who complain only of back pain, in the absence of deformities, such as degenerative spondylolisthesis or scoliosis. In patients with an unstable motion segment who have only back pain, it is usually sufficient to perform a fusion alone if stenosis is mild, because it is unlikely that neural compression will significantly increase and become symptomatic over time after fusion of the motion segment. In patients with no hypermobility it may be useful to apply a rigid corset for 2 weeks. If the back pain improves significantly, there may be an indication for surgery.

In patients with leg symptoms, surgery is indicated when comprehensive conservative management as described in other chapters of this book have been carried out for 4–6 months without resulting in significant improvement (Fig. 87.9). The exception to this recommendation is for patients with a severe motor and/or sensory deficit consistent with cauda equina syndrome, who require emergent neural decompression.

Fig. 87.9 Algorithm for treatment of simple stenosis.

When the presentation is that of weakness with associated pain, then surgery is indicated when two criteria are met. The stenosis should be advanced and the symptoms should be of less than a few months duration. If the paresis or paralysis has been present for more that 6–8 months, then it is the authors’ opinion that there can be no indication for decompression. Such an extended duration of neural compression leads to irrevocable changes and ultimately surgery offers small or no chance of improvement of muscle function.

The ideal surgical candidates are less than 70 years old, without comorbidities, who have radiologic evidence of severe or very severe stenosis, long-standing leg symptoms and severe intermittent claudication, moderate or no motor deficits, and mild or no back pain. This is in contrast to patients who have mild stenosis, mild or inconsistent leg symptoms without a precise radicular distribution, a history of claudication after many hundreds of meters, no motor deficit and back pain of similar severity to, or more severe than, the leg symptoms. A less predictable outcome is associated with surgery in this latter group.

Usually, there is no need for spinal fusion. Arthrodesis may be indicated when there is a concern that wide surgical decompression could result in postoperative instability. Additionally, fusion may be required for the patient that is experiencing simultaneous radicular pain from spinal stenosis and axial back pain due to internal disc disruption syndrome (see Fig. 87.9).

Advanced age

Surgical decompression may offer significant relief of symptoms also to patients older than 70 years.⁵^–⁸ In the authors’ experience, there is no significant difference in the results of surgery between the patients in early senile age and those aged 80–90 years old, provided the stenosis is severe and the patient’s general health is satisfactory.

Comorbidity

In one study,⁷ a high rate of comorbid illnesses was found to be inversely related to the rate of satisfactory results after surgery. Another study⁹ compared the long-term results of surgery in 24 diabetic and 22 nondiabetic patients. In the diabetic group there was a 41% rate of satisfactory results, compared with 90% in the nondiabetic group. Different results, however, were observed in a similar study,¹⁰ in which the outcome was satisfactory in 72% of the diabetic and 80% of the nondiabetic patients. Neither the duration of the diabetes before surgery nor its type correlated with the outcome. A mistaken preoperative diagnosis was the main cause of failure in diabetic patients. In many of the failures, diabetic neuropathy or angiopathy had elicited symptoms that had been confused with pseudoclaudication.

Previous surgery

Surgery for spinal stenosis tends to give less satisfactory results in patients who had previously undergone decompressive procedures in the lumbar spine.^7,¹¹^–¹⁴ This is particularly true when stenosis is at the same level or levels at which the previous surgery for disc herniation or stenosis had been performed.¹⁵

Type of stenosis

There is no significant difference in outcomes between the various types of central stenosis. However, patients with degenerative or combined stenosis at a single level are the best candidates for surgery because they tend to have a better outcome than those with stenosis at multiple levels. In patients with constitutional stenosis, the intervertebral disc may play a significant role in the compression of the neural structures. When the disc bulges considerably in the spinal canal, but it is not truly herniated, it may be difficult to eliminate the anterior compression of the neural structures. Consequently, less satisfactory outcomes may be obtained when compared with the cases in which the neural compression is caused exclusively by the articular processes. Patients with lateral stenosis, particularly at a single level, tend to have better results than those with central stenosis.

SURGICAL MANAGEMENT

Definition of terms

Decompression of the lumbar spinal canal can be carried out by total laminectomy, also defined as bilateral or complete laminectomy (Fig. 87.10). More focal decompression can be accomplished with a laminotomy, also called keyhole laminotomy, hemilaminectomy, or partial hemilaminectomy. Laminotomy consists in the removal of the caudal portion of the proximal lamina, the cranial portion of the distal lamina and a varying portion of the articular processes, together with a part of, or the entire, ligamentum flavum on the side of surgery. Laminotomy can be performed at a single level on one side or both sides (Fig. 87.11). Less frequently it is performed at multiple levels (Fig. 87.12).

Fig. 87.10 Total laminectomy at two contiguous levels.

Fig. 87.11 Unilateral laminotomy (arrow) (A) and bilateral laminotomy (arrows) (B) at two contiguous levels.

Fig. 87.12 AP radiograph showing bilateral laminotomy at L2–3 to L4–5 in a patient with constitutional stenosis at those levels.

The term foraminotomy indicates removal of a part of the posterior wall of the intervertebral foramen, while the term foraminectomy refers to complete excision of the wall of the foramen.

Surgical planning

General concepts

Surgical treatment is aimed at decompressing the neural structures by means of a total laminectomy or laminotomy at one or more vertebral levels.

It is crucial to accurately plan the extent of decompression before surgery because during the operation it may be difficult to determine whether, at a certain level, the central or lateral canal is stenotic, particularly if stenosis is mild. Lack of sufficient care in planning the operation may give rise to inadequate decompression, which would leave areas of stenosis, or too wide a decompression, which might cause iatrogenic instability. This process entails a careful review of the history, examination, electrodiagnostic testing, and all radiologic studies. The authors invariably require flexion–extension plain radiographs to assess for instability. In addition, a high-quality MRI or multiplanar reformatted CT scan is a necessary component. Rarely does myelography need to be performed. A review of these multiple elements of the diagnostic work-up allow for thorough and accurate presurgical planning.

Types of stenosis

Stenosis without concurrent spondylolisthesis or scoliosis

Central stenosis

Number of levels to decompress

The stenotic levels should be distinguished accurately to levels at which the need for decompression is absolute and levels where the need is relative.

In the former case, compression of the neural structures is marked or, regardless of the severity, is responsible for clinical symptoms and signs. In the latter case, compression of the neural structures is mild and asymptomatic. In most instances, one or two levels, contiguous to the area of absolute stenosis, are involved. At these levels, imaging studies (MRI, CT, myelography) usually reveal: a posterior indentation on the thecal sac; decreased sagittal and transverse diameters of the thecal sac on the axial views; lateral indentation or a mild hourglass deformation of the thecal sac; or medial deviation and/or partial filling of the nerve root emerging from the thecal sac on the coronal view.

The consideration of performing a prophylactic decompression at the levels of relative stenosis stems from the evaluation of several factors, such as the patient age, the site of stenosis, the presence of disc abnormalities, and vertebral stability.

In patients aged over 75 years the need for a prophylactic decompression is less than in middle-aged or early-old-age patients. Posterior compression of the thecal sac is less likely to become symptomatic than is compression of the nerve roots in the radicular canal. Marked bulging of the anulus fibrosus, which with passing time may become symptomatic, represents an indication for prophylactic decompression. In the presence of instability of the motion segment, it is usually advisable to limit the decompression in the transverse plane as much as possible. Conversely, the presence of intersomatic osteophytes producing spontaneous vertebral arthrodesis represents a guarantee against postsurgical instability.

Unilateral or bilateral decompression

For the intervertebral levels at which the need for decompression is absolute and stenosis is bilateral, the decompression should be performed bilaterally. This is true for patients with bilateral leg symptoms and/or signs, and for those with unilateral symptoms. When, at a given level, stenosis is severe and symptomatic on one side and mild and asymptomatic on the other, unilateral decompression may be considered, if discectomy has to be performed for associated disc disease. However, even in these cases, bilateral decompression is generally recommended.

For levels at which the need for decompression is relative, the choice between unilateral and bilateral decompression should be made taking into consideration the severity of stenosis on the two sides, and the factors taken into account in determining the number of levels to decompress. In general, if total laminectomy is planned at the level of absolute stenosis, it is advisable to extend it also to the level of relative stenosis. On the other hand, when laminotomy is planned for the area of absolute stenosis, it is often sufficient to limit the decompression for the area of relative stenosis to the side of the more marked compression of the neural structures.

Extent of decompression

The long-term results of surgery may deteriorate with time because of regrowth of the resected portion of the posterior vertebral arch.¹⁶ This is more likely to occur when a narrow decompression is performed. The authors believe that decompression should be as wide as possible in the lateral portion of the spinal canal, while at the same time preserving vertebral stability. The optimal facetectomy is that in which the medial two-thirds of the superior and inferior articular processes are removed. An important concept is that in lumbar stenosis radicular symptoms originate from compression of the nerve root after it has emerged from the thecal sac, that is in the radicular canal, rather than within the thecal sac.

Compression of the thecal sac and spinal nerve roots usually occurs at the intervertebral level. To achieve adequate decompression the entire area facing the intervertebral disc needs to be addressed. That is, decompression should extend as far as half of the height of the vertebrae above and below the stenotic area.

Methods of decompression

Surgery for lumbar stenosis is aimed at adequately decompressing the neural structures, particularly the nerve roots in their extrathecal course, without significant compromise of vertebral stability. Preservation of vertebral stability is paramount because the disappearance of leg symptoms may not make the patient satisfied if back pain appears or worsens after surgery. This is especially true for middle-aged or early-senile-aged patients.

In the past few years, the technique of multiple laminotomy, or its variants, has become widely used in the treatment of central spinal stenosis because it preserves vertebral stability better than central laminectomy does.^17,¹⁸ However, a major role is still played by total laminectomy, which often allows for a more effective decompression of the neural structures. Multiple laminotomy is the treatment of choice for constitutional stenosis because the patients are usually middle-aged, the stenosis is rarely severe, and disc excision is often necessary in addition to decompression.¹⁸ Similarly, a multilevel laminotomy is preferred for degenerative or combined stenosis when narrowing of the spinal canal is mild or moderate, particularly if a disc excision has been planned. Total laminectomy is typically more effective for severe stenosis, providing that the involved segments are stable preoperatively. When this is not the case, the choice is between multiple laminotomy and total laminectomy combined with fusion of the decompressed segments.

Spinal fusion

In addition to degenerative spondylolisthesis and scoliosis, spinal fusion should be planned if the area to decompress is unstable or when total laminectomy and bilateral discectomy are to be performed. Spinal fusion should also be planned when there are high chances that, at surgery, the articular processes will be completely removed on both sides or when the articular processes will be excised on one side and discectomy performed bilaterally. Also, fusion will be needed for the patient complaining of chronic back pain, determined to originate from the motion segment needing decompression.

Except for these situations, there is no need to carry out spinal fusion in stenotic patients undergoing decompression of the neural structures. These guidelines, previously indicated on the basis of clinical experience,¹⁵ were confirmed by a prospective, randomized study.¹⁹

Isolated lateral stenosis

In this condition, only one vertebral level is usually involved.

In the presence, at a single level, of a symptomatic nerve root compression on both sides, bilateral decompression should be carried out. This should be done even if on one side the leg symptoms are mild and no neurological abnormalities are detectable.

When imaging studies show bilateral nerve root compression in the presence of radicular symptoms and signs on one side only, bilateral decompression should generally be planned, especially in the middle-aged patient or when electrophysiological investigations show evidence of acute denervation of the clinically asymptomatic nerve root. However, in the elderly patient in which a rapid surgical procedure is desired, there can be an indication for unilateral decompression. This is particularly true when the symptomatic side is considerably more stenotic than the asymptomatic side.

Discectomy should generally be planned for patients in whom preoperative investigations show evidence of a bulging intervertebral disc at the stenotic level. Preoperatively, however, it is often difficult to determine the precise role played by the intervertebral disc in the etiology of nerve root compression. In these cases, the decision about whether to carry out disc excision must be made on the basis of the operative findings after exploring the canal.

Spinal fusion is rarely needed in cases of isolated lateral stenosis. It is indicated when bilateral decompression is carried out at a preoperatively unstable level, particularly if a unilateral or bilateral disc excision is planned. Fusion may also be indicated in patients complaining of chronic low back pain due to disc degeneration at the stenotic level or levels.

Stenosis of the neuroforamen

This type of stenosis is often better appreciated on CT or MRI. However, in the vast majority of cases, narrowing of the intervertebral foramen causes no compression of the nerve root. Osteoligamentous decompression for foraminal narrowing is rarely indicated, unless protrusion or marked bulging of the intervertebral disc coexists.

Degenerative spondylolisthesis

In the authors’ experience, bilateral laminotomy, or even total laminectomy, may be carried out with no concomitant fusion in patients with mild olisthesis, no vertebral hypermobility on flexion–extension radiographs, mild central stenosis or any degree of isolated lateral stenosis, and mild or no back pain (Fig. 87.13). Similarly, in elderly patients with moderate olisthesis and marked resorption of the disc below, no vertebral hypermobility, and stenosis requiring total laminectomy, there may be no indication for fusion. This tenet is particularly applicable in the absence of significant chronic low back pain or in the presence of comorbid diseases which require a rapid operation. The indications for monolateral laminotomy with no fusion are: moderate central stenosis in elderly patients with unilateral symptoms; lateral stenosis only on one side; and unilateral additional pathology, such as a ipsilateral synovial cyst provided there is no contralateral leg pain and no chronic back pain.

Fig. 87.13 Algorithm for treatment of degenerative spondylolisthesis.

In the presence of moderate or severe olisthesis, vertebral hypermobility even of mild degree, and/or severe central stenosis and chronic back pain patients should undergo decompression and fusion (see Fig. 87.13). In these instances, the association of an arthrodesis allows the surgeon to decompress the neural structures as widely as necessary.

Arthrodesis should usually be limited to the involved motion segment, but this is not an absolute rule. When there is spondylolisthesis of L4, the presence of a degenerated L5–S1 disc may necessitate extension of the fusion to the sacrum. Such a procedure is performed to avoid persistent postoperative back pain, if the disc above the slipped vertebra is normal on MRI. If the disc above (L3–4) is degenerated, then fusion should be limited to the level of spondylolisthesis, particularly when surgery is mainly aimed at resolving leg symptoms. Others use discography to determine whether a concurrent fusion is necessary, feasible, and at which levels.

Posterolateral (intertransverse process) fusion with no pedicle screw instrumentation is the gold standard because the fusion is less rigid and a small residual mobility of the fused vertebrae remains, which decreases the mechanical stresses on the adjacent motion segments. However, the drawbacks are the necessity of a prolonged, rigid immobilization following surgery. Posterolateral instrumented fusion, using pedicle screw fixation, has become the most common procedure (Fig. 87.14). The procedure can be done at multiple levels when olisthesis is present at more than one level (Fig. 87.15). In both cases it requires no, or a short period of, postoperative immobilization.

Fig. 87.14 Postoperative radiographs taken 4 years after total laminectomy and bilateral pedicle screw instrumentation and intertransverse fusion at L4–5 in patient with degenerative spondylolisthesis and stenosis.

Fig. 87.15 Degenerative spondylolisthesis at multiple levels associated with mild lumbar scoliosis. Pedicle screw instrumentation and intertransverse fusion at L2–5 with partial correction of scoliosis. The patient had complete relief of symptoms.

Internal fixation may be bilateral or unilateral. The latter, which decreases the potential morbidity of the bilateral fixation (increased stress on the adjacent unfused segments) was found to give similar results in terms of fusion rate as the bilateral instrumentation.²⁰ The authors have performed bilateral bone grafting and unilateral instrumentation or unilateral bone grafting and instrumentation in 36 cases with a 97% rate of solid fusion. The advantages of the unilateral instrumentation are a shorter operative time, decreased risk of neurological complications, and reduced costs. The main indications are: back pain with mild segmental instability in the elderly, or concern of producing gross instability after a total laminectomy.

Some surgeons prefer to perform a posterior lumbar interbody fusion (PLIF) in lieu of a posterolateral fusion. This procedure, when used in tandem with pedicle screw instrumentation, provides excellent results and a high rate of solid fusion. The devices inserted in the disc space are normally represented by cages filled with bone chips. An alternative is to use blocks of porous tantalum (hedrocel), the stiffness of which is very similar to that of subchondral bone. Animal model studies have shown bone ingrowth within the pores of the implant and maturation of the osteoid in some 3 months. The authors have used blocks of hedrocel for 3 years with excellent results of this interbody fusion (Fig. 87.16). In 16 cases followed for at least 2 years, there has been no observed migration of the implant or loosening of the pedicle screws. The authors have invariably observed a tight union between the implant and the adjacent vertebral endplates as assessed by MRI and/or plain X-rays.

Fig. 87.16 Central stenosis in a patient with degenerative spondylolisthesis at L4–5. (A–C) Preoperative radiograph and MRI scans showing degenerative olisthesis and stenosis. (D,E) Functional radiographs demonstrate hypermobility of the olisthetic vertebra. (F,G) Radiographs taken after total laminectomy, bilateral pedicle screw instrumentation, and PLIF at L4–5 level.

Degenerative scoliosis

Lumbar scoliosis, particularly of the degenerative type, is not uncommonly associated with spinal stenosis. In patients with both conditions, total laminectomy may not relieve compression of the nerve roots when their compromise is related to pedicle and facet migration and rotation. Furthermore, in scoliotic patients, decompression may lead to an aggravation of the curve and/or lateral vertebral slipping. Laminectomy alone may yield a poor outcome because of increased deformity or instability. These risks should lead one to limit the indications for decompression or, if surgery is undertaken, to concomitantly carry out a spinal fusion after correction of the curve using segmental pedicle screw instrumentation.

SURGICAL TECHNIQUE

Total laminectomy

Skin incision and superficial hemostasis

The skin incision extends from the cranial edge of the spinous process above to the caudal edge of the spinous process below that of the vertebra, or the group of vertebrae, needing decompression. Dermal and subdermal vessels may be cauterized or preferably clamped together with a small portion of superficial subcutaneous tissue; clamps (usually placed at a distance of approximately 1 cm from each other) are then turned outwards of the surgical wound and held together with an elastic band anchored to the surgical drape. This method makes hemostasis of the superficial vessels very rapid. The deep portion the subcutaneous tissue may be detached from the supraspinous ligament and adjacent portions of the thoracolumbar fascia with a dry sponge.

Disinsertion of paraspinal muscles

The thoracolumbar fascia is incised, starting on the side of the surgeon, immediately adjacent and parallel to the tip of the spinous processes and interspinous ligaments, using an electric cautery knife. Frequently, the tip of the spinous processes can be palpated, but is not visible. In these cases, the fascia can be erroneously incised along the midline or one may inadvertently pass over to the opposite side. To avoid this, the assistant surgeon should press down the paraspinal muscles on his side using a periosteal elevator applied against the outer surface of the spinous processes. The surgeon may carry out the same maneuver on his side, while incising the fascia.

Elevation of the paraspinal muscles from their insertion starts at the most cranial of the exposed vertebrae. A broad periosteal elevator is introduced deep to the muscle mass and allowed to slip along the outer surface of the spinous process and lamina to detach the paraspinal muscles from the bone surface until the lateral border of the facet joints is reached. Dry sponges are then packed, using the periosteal elevator, beneath the muscle mass. This maneuver is aimed at both disengaging the paraspinal muscles from the lateral portion of the laminae and apophyseal joints, and arresting bleeding from the posterior branches of the lumbar arteries and veins. Sponges packed at the level of two contiguous vertebrae are subsequently removed and, while retracting the muscle mass, the residual musculotendinous attachments to the base of the spinous processes and interspinous ligaments are sectioned. When decompression is needed at more than one motion segment, dry sponges are again packed into the depth of the wound and the vertebrae and intervertebral spaces below are exposed.

The maneuvers described above are then performed on the opposite side by the surgeon himself or the assistant surgeon.

One or two self-retaining retractors, depending upon the number of exposed vertebrae, are applied. Hemostasis is completed and remnants of muscle and fat tissue still adherent to the laminae, facet joints, and yellow and interspinous ligaments are removed using gouge forceps or a large curette.

Opening of the spinal canal

After exposure of the yellow and interspinous ligaments, the vertebrae included in the operative field are identified by locating the lumbosacral interspace, when exposed, or counting the spinous processes starting from the fifth lumbar. Fluoroscopic imaging should be used to confirm levels by inserting a spinal needle into one, or two contiguous, interspinous spaces. Identification, at this stage, of the individual vertebrae is extremely important, because, once the spinous processes have been removed and laminectomy started, it becomes exceedingly difficult to identify the vertebral levels.

When a single intervertebral level is to be decompressed, the cranial half of the spinous process of the distal vertebra and the caudal half or two-thirds of the spinous processes of the proximal vertebra as well as the interspinous ligament are resected. Resection of the spinous process, using a sharp-angled bone biter, should be carried out as far as its base.

A small curette is used to detach the ligamentum flavum from the deep surface of the proximal laminae. The curette should be introduced between the ligament and bone and maintained in close contact with the latter. Laminectomy is initiated in the central portion of the laminar arch, that is, at the level of the posterior angle of the spinal canal, not occupied by the thecal sac. The lamina can be removed using a small gouge forceps, or a punch rongeur when the spinal canal is severely stenotic. Laminectomy is then continued, alternately on one side and the other, after the ligamenta flava have been further detached with a curette from the residual ventral aspect of the laminae. The ligamenta flava are subsequently detached from the proximal border of the laminae of the distal vertebra starting from the most medial portion. The cut edge of the ligament is lifted with forceps, sectioned longitudinally using scissors or the tip of a small scalpel, and removed as extensively as possible. The lateral portion of the laminae and the inferior articular processes are removed using a rongeur.

An alternative technique, which the authors prefer, is to perform laminectomy using chisels. After removal of the spinous processes and detachment of the ligamentum flavum from the lamina of the proximal vertebra, a chisel is used to remove, first, the caudal half of the lamina of the proximal vertebra and then the medial half of the inferior articular process of the same vertebra. The proximal portion of the lamina of the distal vertebra can be removed partly by the chisel (posterior portion) and partly using a rongeur (deep portion, closer to the thecal sac and nerve root). After removal of the ligamentum flavum as extensively as possible and exposure of the thecal sac, the residual lateral portions of the articular processes are removed using both chisels, 1 or 2 cm in width, and punch rongeurs. When using chisels, these should be orientated at 45° in a mediolateral and posteroanterior direction to undermine the articular processes, that is to remove only the ventral portion of the bone in order to preserve vertebral stability.¹²

Since stenosis occurs at the intervertebral level, when performing decompression at multiple levels, care should be taken to extend laminectomy, proximally and distally, beyond the intervertebral discs located at the extremities of the stenotic area, until it is certain that the neural structures are no longer compressed.

Exploration of intervertebral discs and spinal nerve roots

The spinal canal is opened laterally until the nerve root emerging from the thecal sac is visualized. The emerging root and the thecal sac are then retracted medially and the disc is exposed at each of the intervertebral levels included in the area of laminectomy. Consistency of the anulus fibrosus is tested with a blunt probe. If the anulus is hard in consistency, the disc should not be entered, even when it protrudes posteriorly. Discectomy is carried out only when the disc is herniated or, in the absence of a true herniation, it is soft in consistency and easily depressed by the probe.

A right-angled blunt probe is then used to evaluate the width of the nerve root canal and the intervertebral foramen. If difficulty is encountered in introducing the probe into the nerve root canal and the foramen, removal of the articular processes should be continued and the foramen opened until complete decompression of the root is obtained. It is important to free the spinal nerve root adequately, even if this implies complete excision of the articular processes. This is rarely necessary and one should not hesitate to perform unilateral foraminectomy because it does not jeopardize vertebral stability if the disc has been preserved and the motion segment is preoperatively stable. Bilateral foraminectomy is needed very rarely and may require spinal fusion, especially when the disc has been excised.

Wound closure

Where the spinous processes have been removed, the paraspinal muscles of the two sides are sutured by interrupted sutures. In these areas the thoracolumbar fascia is closed with interrupted sutures or a continuous suture, which is more rapid and better closes the fascia. Where the spinous processes have been preserved, the fascia is anchored to the supraspinous ligament.

The formation of a hematoma between the subcutaneous tissue and thoracolumbar fascia can be avoided by passing a few sutures in both the deep and middle subcutaneous layer and the fascia.

Laminotomy

Single level

Skin incision extends from the cranial border of the spinous process of the proximal vertebra to the caudal border of the spinous process of the distal vertebra.

For unilateral laminotomy, the thoracolumbar fascia is incised only on the symptomatic side, in close proximity to the spinous processes. Gradually, as the paraspinal muscles are disinserted from the bone surface, dry sponges are packed into the osteomuscular space to control bleeding and to strip the muscles as far as the lateral portion of the articular processes.

A Taylor retractor is installed against the external aspect of the articular processes and held by a metal weight of some 2 kg. The ligamentum flavum is detached using a curette from the deep surface of the proximal lamina, and the distal one-third to half of it is excised using a gouge forceps or a punch rongeur. The ligamentum flavum is disinserted from the proximal border of the distal lamina. This allows a rongeur to be introduced under the lamina, about one-third of which is initially removed. Rongeurs of varying sizes are used to excise the medial half to two-thirds of the facet joint as well as the ligamentum flavum inserted on the facets. An alternative method is to use a chisel, or a high-speed microdrill, to remove a portion of the proximal lamina and the medial portion of the inferior articular process of the proximal vertebra. The remaining ligamentum flavum is excised by cutting it with a scalpel or a rongeur.

Facetectomy should be extended laterally to expose the emerging nerve root: retracting the sac and the nerve root medially, the intervertebral disc is exposed and the degree of its prominence and consistency is evaluated. Disc excision is not usually necessary when the disc is hard and fibrous in consistency and does not appear to compress the nerve root. If any uncertainty exists, it is better to proceed with discectomy rather than risk leaving a disc protrusion responsible for root compression.

Laminotomy of the distal vertebra is then enlarged and the medial portion of the base of the superior articular process is removed with a rongeur or a small chisel to expose the nerve root as far as the medial surface of the pedicle. A blunt probe is used to evaluate the width of the distal portion of the lateral recess and the neuroforamen, continuing the laminofacetectomy until complete decompression of the nerve root is achieved.

For bilateral laminotomy at a single level, the procedure is carried out firstly on one side and then on the opposite side.

Multiple levels

Bilateral laminotomy can be performed at two or more adjacent intervertebral levels. The surgical technique is similar to that described for single level laminotomy. However, when performing laminotomy at two adjacent levels on the same side, much care should be taken to leave intact, for at least 5 mm, the lamina between the two motion segments.

This type of decompression is particularly indicated for patients with constitutional stenosis, in whom constriction of the spinal canal is usually moderately severe and disc excision is often required at one or more levels, and for patients with degenerative spondylolisthesis when spinal fusion is not planned.

Microsurgery

Most technical difficulties encountered in performing laminotomy, particularly at a single level, are related to poor lighting of the operative field. These difficulties may be overcome with the use of the operating microscope.

The microscope, by providing a vertical light beam not obstructed by the surgeon’s head or hands, ensures excellent lighting, regardless of the extent of surgical exposure, which is 2–3 or 4–6 cm long for one or two levels, respectively. Furthermore, by slanting the objective, any part of the operative field can be illuminated. Thus, surgical maneuvers may be performed with greater precision, the causes of compression of the neural structures may be more easily identified, and fewer risks are run of causing undue trauma to the emerging nerve root or thecal sac. Moreover, only occasionally is an excessively large portion of the articular processes resected or a complete facetectomy inadvertently performed when using the microscope.

The microsurgical technique is very similar to the naked-eye technique in as much as the same instruments are needed, with the exception of the paraspinal muscle retractor, which should be as narrow as possible. The authors use a Taylor retractor about one-third the width of the standard instrument. Excision of the laminae and articular processes can be carried out using the same instruments used for naked-eye technique, including the chisel. However, many surgeons use a high-speed microdrill for laminoarthrectomy.

The microscope is particularly useful for single-level laminotomy. However, surgeons accustomed to the microscope often use this tool also for surgery at multiple levels.

RESULTS OF SURGERY

Overall results

Central stenosis

Of the 92 patients followed by Verbiest,² for 1–20 years, 18% had no significant symptoms. In the remaining cases, back pain was the most frequent symptom. The highest rate of excellent results was obtained in the patients with the most severe stenoses. Lassale et al.²¹ evaluated 128 patients 2–14 years after surgery using a grading scale of 0 to 20. Satisfactory results were observed in 83% of patients. On the grading scale, four profiles were identified: a stable result (60%), regular improvement (14%), improvement with episodic aggravation of symptoms (19%), and subsequent worsening (8%). In a prospective study²² of 140 patients, an average leg pain improvement of 82% and back pain improvement of 71% was found a mean of 3 years after surgery. Similar results were reported in other series of the 1970s and 1980s.^12,²³^–²⁵ In a series of 77 patients,²⁶ average age of 65 years of age, who were followed for 2–5 years, 83% had a satisfactory result. Younger patients had a greater reduction in severity scores. However, satisfaction was similar in both older and younger patients.

Postacchini et al.²⁷ reviewed 64 patients at a mean of 8 years (range, 4–21 years) after surgery. The long-term results were excellent or good in 67% of patients and fair or poor in 33%. However, of the patients with unsatisfactory results, 15% already showed an unsatisfactory outcome in the first year after surgery. Thus, only 13% of patients had a deterioration of the result with time. The majority of the patients who underwent radiographs during the follow-up period and/or at the most recent follow-up showed regrowth of the resected portion of the posterior vertebral arch.¹⁶ Regrowth was marked in 13% of cases (Fig. 87.17). In two cases, the regrowth produced recurrence of stenosis, which required repeat surgery.

Fig. 87.17 Regrowth of the posterior vertebral arch after central laminectomy. (A) Early postoperative radiograph. (B) Radiograph taken 7 years after surgery showing marked regrowth of the posterior vertebral arch.

In a study in which 37 patients were followed for a minimum of 10 years, no impairment in activity of daily living was found in 62% of the cases.²⁸ The rate of improvement was evaluated as excellent or good in 57%, fair in 22% and poor in 22%.

Lateral stenosis

Proportions of satisfactory results ranging 79–93% were obtained by several authors using laminotomy or total laminectomy.^17,²⁹^–³¹ Venner and Crock³² reviewed 45 patients with stenosis of the S1 radicular canal and isolated resorption of the fifth lumbar disc. An excellent result was obtained by 62% and a good result by 25% of patients. Results were satisfactory in 83% of 43 cases followed for 3 years on average by Postacchini;¹⁵ good to excellent outcomes were observed in 90% of patients with preoperative motor deficit or reflex changes and in 71% of those without neurological deficits.