32 The Microsurgical Interlaminar, Paramedian
Approach
H.M. Mayer
32.1
Terminology
The microsurgical approach through the “interlaminar window” is synonymous with the terms “microdiscec- tomy” or “microsurgical discectomy,” although from a semantic point of view these terms are misleading. The goal of the surgical procedure is not an entire “discecto- my” (which would be impossible with this approach for anatomical reasons) but a removal of slipped disc mate- rial (nucleus, endplate, anulus fibrosis) from the spinal canal in order to decompress the neural structures.
32.2
Surgical Principle
The spinal canal is reached through a limited skin inci- sion close to the midline (spinous process) on the symptomatic side. The surgical microscope can be used from “skin to skin.” The paravertebral muscles are re- tracted without cutting any insertions at the spinous processes of the laminae. The interlaminar window is exposed as well as the medial third of the facet joint.
The yellow ligament is fenestrated or lifted and the un- derlying nerve root is exposed from its origin to its en- try into the foramen at the base of the pedicle of the ver- tebra caudal to the disc space. At the levels cranial to L5/S1 subarticular decompression as well as a limited laminotomy is necessary to expose the disc space. The nerve root is mobilized by microsurgical dissection and the herniated disc material is removed with ron- geurs. The remaining loose parts of the nucleus pulpo- sus are removed from the intervertebral space carefully avoiding damage to the endplate or anterior perfora- tion of the disc space with the rongeurs. With the help of the microscope, retraction of the muscles as well as damage to the structures covering the spinal canal (fac- et joint, lamina, yellow ligament) is restricted to a mini- mum. Exposure of the nerve root can be performed with minimal manipulation. Epidural bleeding is re- stricted due to meticulous preparation and dissection of epidural veins and venous plexus. Epidural fat can be preserved to cover the nerve root at the end of the pro-
cedure in order to minimize the ongrowth of scar tis- sue. The anulus fibrosis can be closed by an inverting suture.
32.3 History
The historical aspects of microsurgical discectomy have been described in the previous chapter. However, from my personal point of view, two outstanding sur- geons have to be mentioned in this respect: Wolfhart Caspar [2 – 4] and John A. McCulloch [8, 10]. Due to their continuous and never-ending efforts, microsur- gery is now an essential part of the surgical technology applied in the treatment of spinal diseases.
32.4 Advantages
There is no doubt that it is primarily the technical ad- vantages which characterize the use of a surgical mi- croscope in lumbar disc surgery. General advantages have already been described in the previous chapter.
Table 32.1 summarizes the specific advantages of the microsurgical approach to lumbar disc herniations as compared to the standard techniques.
Table 32.1. Technical data: standard and microdiscectomy Micro Standard
Preoperative planning +++++ ++
Positioning = =
Skin incision 2 – 3.5 cm 4 – 7 cm
Exposed segments 1 2 – 3
Muscle insertions Intact Not intact
Segmental denervation Rare Always
Osteoclastic decompression Rare Always
Blood loss < 50 cc > 200 cc
Discectomy = =
Anulus suture Possible ??
Wound drainage No Yes
Time for surgery = =
They can be summarized as follows:
Small skin incision (2.5 – 3 cm) Exploration of only the target segment Preservation of muscle insertions
Preservation of segmental innervation of the para- vertebral muscles due to limited retraction Preservation of lamina and facet joint by only limited osteoclastic extension of the approach In selected cases (e.g., at L5/S1) preservation of the yellow ligament (see below)
Preservation of epidural fat and epidural venous plexus
Limited manipulation of the nerve root
Safe dissection of epidural adhesions and/or scar tissue
Safe decompression of the nerve root from its exit from the thecal sac to its entrance into the fora- men.
Safe removal of disc tissue and fragments from the spinal canal as well as from the intervertebral space
Limited blood loss of less than 50 cc on the average Suture and reconstruction of anulus fibrosis and/or yellow ligament possible
No wound drainage necessary in the majority of patients
Optimal teaching to assistants due to unobstructed view of the surgical field
OT times comparable/shorter than with standard techniques
Surgery possible as outpatient procedure due to less tissue trauma
Short rehabilitation period
32.5
Disadvantages
There are quite a few disadvantages arising from gener- al differences between wide and limited surgical ap- proaches.
32.5.1
Technical Disadvantages
The main characteristic of the microsurgical approach is the limited visualization of anatomical structures surrounding or lining the surgical target area. Simulta- neous vision of the target area and its neighborhood is not possible. Thus, the risk of indirect lesions to struc- tures outside the surgeon’s visual field has to be real- ized. It is, therefore, important to “secure” the anatomi- cal structures which have already been passed on the way to the target area (e.g., speculum to retract mus- cles). The technical disadvantage of adapting the focus
is now solved by the new generation of surgical micro- scopes which have autofocus functions. Most of these new microscopes have a very comfortable depth of fo- cus. Moreover, the individual setup for each surgeon can be programmed and easily adjusted through a touch screen (Fig. 32.1a–c). The field of vision can be enlarged by tilting the microscope thus creating a larg- er area of visualization.
32.5.2
General Considerations
The microsurgical approach implies several modifica- tions concerning surgical planning, positioning of the patient, and intraoperative control of removal of disc herniation which might appear as disadvantages to sur- geons not experienced with microsurgery. Since the surgical corridor to the target area in the spinal canal is very limited, the localization of the skin incision has to be determined very accurately (see below). Once the skin incision is placed, there is no way of altering the approach other than by enlarging the incision. The lev- el of the disc space must be localized in its exact projec- tion onto skin level so that an approach along the strict- ly vertical axis will be possible. This implies a position- ing of the patient on the surgical table which places the surface of the back horizontally. Lumbar lordosis should be completely compensated. Please note, that one of the most common mistakes with microsurgical approaches in lumbar disc surgery is exploration of the wrong level. Microsurgical dissection within the spinal canal can be extremely difficult when epidural veins are congested. Compensated lumbar lordosis as well as low or no pressure on the abdomen will diminish this prob- lem which is often faced by beginners.
32.6
Indications (see also Chapter 31)
There are no anatomical or technical limitations for the
application of microsurgery for the treatment of lumbar
disc herniations which are located between the midline
and the entrance of the foramen (medial, paramedian,
intraforaminal). In disc herniations extending to the lat-
eral third of the foramen a combined approach (parame-
dian-interlaminar and extraforaminal (see Chapter 33)
is recommended. It is indicated in all forms of disc her-
niations including associated pathology (e.g., lateral or
central spinal stenosis). Its application is limited neither
by the size or configuration of the herniated disc nor by
the clinical urgency. Since microsurgical discectomy can
be performed without prolonged operating times, it can
be applied in all the various clinical situations.
a Fig. 32.1. a OPMI Vario NC 33 (Zeiss) draped for spinal surgery. b Touch screen function to adjust the indi- vidual setting for the sur- geon. c Example of a user list on touch screen
b c
32.7
Contraindications
There are no contraindications for the application of lumbar microdiscectomy through the paramedian ap- proach except for combined intra- and extraforaminal localizations or mere extraforaminal herniations.
32.8
Patient’s Informed Consent
The patient should be informed about the following ap- proach-specific risks and hazards:
Nerve root, cauda equina, and conus medullaris lesions with postoperative neurological deficits including bladder and bowel dysfunction Dural tears with menigocele and/or CSF fistulas Injury to retroperitoneal blood vessels (requiring emergency surgery) or to other structures in the abdominal cavity (e.g., ureter, peritoneum, bowel) Meningitis
Spondylodiscitis with epidural abscess Epidural scarring with neurological deficits or permanent sciatica
Segmental instability requiring stabilizing surgical procedures
Chronic low back pain and radicular symptoms
(“failed-back-surgery” syndrome)
32.9
Surgical Technique
The surgical technique differs significantly between the approach to a “virgin back” and the approach to an
“operated back” in case of recurrent disc herniation.
The technical modifications of the technique according to the underlying pathology in a previously operated back are described below.
32.9.1
Surgical Technique in a “Virgin” Back
32.9.1.1
Preoperative Planning
Preoperative planning is paramount in microsurgical disc operations.
Plain X-rays in AP and lateral planes are necessary, as well as an MRI. The latter imaging technique has become standard in the diagnosis of lumbar disc herniations. In uncomplicated cases, a spinal CT scan can be enough for preoperative planning.
There is no need for routine lumbar myelography or discography in most of the cases.
Plain X-rays give an impression about the curva- ture of the lumbar spine, the disc height, the degree of spondylarthrosis as well as of the size and shape of the interlaminar window. The information is important because it predicts the necessity of bony enlargement of the interlaminar space. Watch the degree of lumbar lordosis!
In patients with hyperlordosis especially at L5/S1 the risk of “slipping” into the wrong, supradjacent segment is high. In combination with the MRI, the thickness and shape of the yellow ligament can be evaluated before the operation. MRI not only gives a clear picture of the underlying disc pathology (e.g., size, shape, localization of disc herniation), it also shows the size and shape of the facet joint, the yellow ligament, the size of the lateral recess and the central volume of the spinal canal. It shows the amount and localization of epidural fat, the size and shape of the spinal nerve(s) involved in the pa- thology, as well as the amount of congestion within the epidural venous system.
Lumbar disc herniation can be exactly classified so the surgeons knows whether they are dealing with a contained or non-contained disc, with subliga- mentous epidural extrusions, or with free disc fragments underneath or beyond the posterior lon- gitudinal ligament. The localization of the hernia- tion within the level of the disc space, cranial or caudal to the disc space can be determined as well as the origin and extension of the disc material.
MRI should be as actual as possible (not older than a week) in order to correlate possible intraoperati- ve findings with the preoperative picture.
Note the extension of the disc herniation and be prepared to enlarge your approach in the direction of the disc herniation (e.g., extension of the lami- notomy in fragments cranial to the disc space or extended subarticular decompression in hernia- tions within the lateral recess).
Carefully read the MRI to find out disc herniations which are located in the axilla of the nerve root.
This pathology can be extremely difficult to treat if the surgeon tries to approach the disc herniations lateral from the nerve root (see below).
In the treatment of recurrent herniations realize the amount of scar tissue and the amount of the remaining bony structures (lamina, facet joint).
The bony structures are the only reliable land- marks during microsurgical dissection in recurrent disc herniations.
Look for conjoined nerve roots! If you are not sure that a conjoined nerve root might be involved, perform an MRI myelography or a conventional myelography in order to be prepared to deal with this anatomical variation.
32.9.1.2
Positioning of the Patient
The patient is placed on a special operating table in the knee-chest position (“Mecca position”; Fig. 32.2). Posi- tioning shows the following characteristics:
Hip and knee joints are tilted 90° in order to ensure venous drainage from the lower extremities and thus diminish the risk of deep venous thrombosis.
The patient is place on their knees and thighs as well as on their chest. Anterior thighs, knees, and chest must be protected against pressure sores by gel or soft cushion pads.
Fig. 32.2. Positioning of the patient (lateral view)
The posterior part of the operating table can be tilted selectively in order to reduce or completely compensate lumbar lordosis. This not only leads to an enlargement of the spinal canal volume, it also
“opens” the interlaminar space at least in patients with motion segments of unaltered flexibility.
The arms are abducted 90° at the shoulder joint, and the forearm is flexed 90° at the elbow joint.
Both arms are placed on arm holders which are padded with gel pads to avoid pressure especially on the ulnar nerve.
Check for hyperabduction of the arms and for pressure on the axilla to prevent pressure lesions of the brachial plexus.
In young patients, the head can be rotated up to 60 – 70° and placed on the gel pad. In old patients as well as in patients with concomitant degenera- tive disc disease of the cervical spine, rotation should be avoided. In these patients, the head is placed in a prone position with a gel pad under the forehead.
Check the eyes, nose, and chin of the patient! Pres- sure on the eyes can result in postoperative blind- ness, and pressure on the nose or chin can result in pressure sores which do not heal very well and which might cause cosmetic problems for the patient.
The abdomen of the patient should be free. In fact it should hang to avoid any pressure on it. Check that the cushion place under the thorax does not compress the hypogastric area.
a b
Fig. 32.3. a Localization of the disc space with a needle. b Lateral fluoroscopy showing the needle at the level of the disc space
Tilt the table to adjust the surface of the back par- allel to the surface of the floor.
32.9.1.3 Localization
A line for the skin incision is marked after localization of the disc space to be approached. After disinfection of the skin a needle is placed parallel to the spinous pro- cess at the presumed level of the disc space. The needle is inserted on the contralateral side in order to avoid subcutaneous or intramuscular hematoma which might aggravate microsurgical dissection on the approach side. Lateral fluoroscopy verifies the correct placement of the needle at the level of the disc space (Fig. 32.3).
Note that the level of the disc space is marked with the needle, and the interlaminar space is slightly
below this mark!The skin incision is placed so that the level of the disc space is in the middle third of the incision (Fig. 32.4). This means, that the surgeon has the option to expose not only the level of the disc space but also the spinal canal cranial or caudal to the disc space.
The incision line can be adapted to the extension of the disc herniation (e.g., if there is an extension inferior to the disc space, then the skin incision may leave the disc space mark in its superior third).
If there is a cranial sequestration, the skin incision can be moved slightly in the opposite direction.
The skin incision is marked about 5 mm lateral to the midline.
If two adjacent segments have to be approached, the length of the skin incision should be adapted.
In the rare event, that two disc herniations are
symptomatic at different levels not adjacent to each
other (e.g., L5/S1 and L3/4) then two separate skin
incisions are recommended.
Fig. 32.4. Skin incision centered over the disc space
32.9.1.4
Approach to Skin–Interlaminar Space
The author recommends the use of the surgical micro- scope from the skin incision. The skin is incised and the dorsolumbar fascia is exposed close to the midline. The spinous processes as well as the space in between are palpated.
The superficial and deep layer of the fascia are cut about 5 mm from the midline and fascial splitting is completed in a semicircular manner ending on the adjacent spinous processes (Fig. 32.5). The me- dial part is gently lifted and can be temporarily se- cured by sutures.
With the help of a blunt Langenbeck hook and bi- polar coagulation, the superficial layer of the para- vertebral muscle group is retracted from the inter- spinous ligament and the adjacent laminae
Fig. 32.5. Ope- ning of the fascia (with permission of Aesculap, Tuttlingen)
Fig. 32.6. Retraction of the paravertebral muscles (with permis- sion of Aesculap)
(Fig. 32.6). Good illumination and magnification by the microscope helps to identify traversing veins which are coagulated and dissected.
With peanut swabs, the interlaminar space is cleared from soft tissue and identified (Fig. 32.7).
The insertions of the small rotators of the multifi- dus muscle group are sharply dissected from the lateral superior lamina and from the facet joint capsule (Fig. 32.8).
A speculum which retracts the muscles from the interlaminar space is inserted, turned 90° toward the assistant and opened. Care has to be taken not to overstretch the skin!
The lateral retractor is inserted to complete lateral retraction of the muscles (Fig. 32.9). Take care that the interlaminar window with the yellow ligament and the inferior part of the superior lamina are in the center of your vision field.
Fig. 32.7. Identification of the interlaminar window. y.l. Yellow ligament
Fig. 32.8. Detachment of the rotators and insertion of the spec- ulum (with permission of Aesculap)
Fig. 32.9. Insertion of the lateral retractor (with permission of Aesculap)
32.9.1.5
Approach to the Spinal Canal
32.9.1.5.1“Open-door” Flavectomy
The topography of the interlaminar space shows a great variability. At L5/S1 the yellow ligament sometimes re- veals a nearly horizontal orientation thus facilitating the entrance into the spinal canal. It is at this level that an “open-door” technique is possible to enter the spinal canal. With a microsurgical scalpel, the yellow ligament can be detached from the laminae as well as from its at- tachments to the facet joint capsule whereas the medial part is left in place. Thus, the ligament can be elevated toward the midline without resection. At the end of the operation, the ligament is simply relocated and covers the spinal canal again.
32.9.1.5.2
“Conventional” Microsurgical Flavectomy and Decompression
In the majority of the cases the inferior lateral corner of the surgical field is first identified, and this is where the inferior border of the inferior facet is marked by the facet fat pad which leads the surgeon in between the layers of the yellow ligament. With a Kerrison rongeur, the fat pad can be entered and the inferior lateral part of the outer layer of the yellow ligament can be re- moved. This is the safest way to start entry into the spi- nal canal. The outer layer of the yellow ligament is re- sected and the inner layer is left in place. Resection is easy in most instances since the surgeon is still on the safe side (i.e., outside the spinal canal).
Once the thin internal layer of the yellow ligament is exposed, the spinal canal can be opened safely. Using a medium-size microdissector, the yellow ligament can be bluntly perforated moving the dissector in a cranio- caudal direction applying only slight pressure (Fig.
32.10). As soon as the dissector enters the spinal canal, the surgeon feels a sudden loss of resistance at the tip of the instrument. This kind of preparation minimizes the risk of perforating the dura. The perforation of the yel- low ligament is enlarged by a bigger blunt dissector which splits the yellow ligament fibers. With Kerrison rongeurs of different sizes, the lateral third of the yellow ligament is resected. Resection must be completed in the caudal direction down to the superior border of the inferior lamina. If there is hypertrophy of the yellow ligament, the lamina should at least be undercut or re- sected (“laminotomy”) until the posterolateral circum- ference of the thecal sac is decompressed. The same is true for the cranial aspect of the interlaminar window.
However in the majority of cases (even sometimes at L5/S 1), a few millimeters of the inferior border of the supradjacent lamina have to be resected as well. What has been described up to here is the easier part of the clockwise opening of the spinal canal (from 9 to 3 o’clock; Fig. 32.10). However, once this is achieved, the surgeon is on the safe side, since the dura can now be identified clearly under the epidural fat tissue. Avoid coagulation of the fat tissue since it can be used at the end of the operation for covering the neural structures.
32.9.1.6
Exposure of the Nerve Root
I recommend to start exposure of the nerve root at
6 o’clock. If the facet joint does not show any hypertro-
phy, resection can be continued from medial to lateral
with the Kerrison rongeur carefully avoiding pressure
on the theca. Thus, the medial part of the joint capsule
is opened, and the medial parts of the inferior articular
process of the supradjacent vertebra are resected. This
Fig. 32.10. Opening of the yellow ligament (9 – 3 o’clock) (with permission of Aesculap)
Fig. 32.11. Removal of medial part of the superior facet with high-speed burr
part of the procedure can be accelerated with the use of high-speed drills (Fig. 32.11).
Once the medial edge of the superior articular pro- cess is identified, it is undercut until the lateral border of the traversing nerve root can be identified (Fig. 32.12). Now, topographic orientation is easy. With a blunt-tipped probe, the medial border of the inferior pedicle can be palpated. Once it is identified, exposure of the nerve root is completed until its entrance into the foramen caudal and lateral to the pedicle can be visual- ized. We feel that this is the safest way to start decom- pression, since the rongeurs are used parallel to the course of the nerve root. This minimizes the risk of du- ral tears. After this stage of the operation the “axilla” of the nerve root can be identified as well (Fig. 32.13). The other advantage is that the nerve can now be mobilized
Fig. 32.12. Identification of lateral border of nerve root (with permission of Aesculap)
Fig. 32.13. Identification of the “axilla” of the nerve root (with permission of Aesculap)
more easily during exposure of its cranial part (“shoul- der”).
Exposure is then continued along the lateral border
of the nerve root until the superior border of the disc
space can be identified. It is recommended to first ex-
pose just the shoulder of the nerve root. It then can be
moved slightly toward the midline thus exposing the
disc herniation. In most of the cases, the herniation is
covered by a more or less vascularized epidural mem-
brane. At L5/S1 it is a common finding that a layer of epi-
dural fat covers the nerve root as well as the lateral as-
pect of the disc herniation. Care should be taken to avoid
crude coagulation of these structures. However, con-
gested epidural veins covering the disc herniation
should be coagulated and dissected sharply to avoid
tears and major bleeding during removal of the herniat-
ed disc tissue. (Cave: Before starting coagulation identi-
fy the veins! Coagulation of venous lacunae may result in
severe bleeding. In these cases handle the veins carefully
using small neuroswabs for covering and preparation.)
32.9.1.7
Exposure of the Herniated Disc
Once the nerve is gently mobilized it can be retracted slightly with a dissector toward the midline. Now the size and extent of the herniation can be identified (Fig. 32.14). If it is a “free” peridural fragment, it is gently mobilized and removed. Removal of disc materi- al leads to a “release” of the spinal nerve and facilitates further decompression. We try to avoid using hooks which exert permanent pressure on the nerve. It is less traumatizing using the blunt tip of the surgical sucker to intermittently pushing the nerve away from the tar- get area. Now, decompression can be completed in the craniolateral part with less risk of damage to the tra- versing nerve root (Fig. 32.15). The extent of cranial de- compression depends on the topographic localization of the superior border of the disc space as well as on the cranial extension of the disc herniation. Intraforaminal herniations usually extend cranial and lateral to the disc space (see also Chapter 34). This affords a wider resection of caudal and lateral parts of the superior lamina. However, care should be taken not to resect the isthmus between the superior and inferior articular facet which might result in segmental instability. There is an increasing risk for destruction of the isthmic re- gion if the decompression is extended more then 10 mm into the superior lamina (Fig. 32.16).
32.9.1.8
Removal of the Herniated Disc
Removal of the disc material is achieved in different ways depending on the size, configuration, and extent of the disc herniation.
a b
Fig. 32.14. a Exposure of the disc herniation (with permission of Aesculap). b Exposure of the disc herniation intraoperative view Fig. 32.15. Completion of subarticular decompression
Fig. 32.16. Extent of decompression (watch the isthmus!)
32.9.1.8.1
Disc Protrusions (“Contained” Disc Herniations)
This type of herniation is the domain of percutaneous discectomy procedures (see Chapters 35, 37). Accord- ing to the indication criteria generally accepted, it is rarely seen in “open” surgical exposures. However, since the disc herniation is not perforated, it should be a surgical principle to limit opening of the disc space to a minimum. In these cases, the posterior longitudinal ligament as well as the anulus fibrosus are opened with one incision parallel to the disc space. Thus a slit is cre- ated which is enough to perform intradiscal decom- pression. Removal of nucleus pulposus is started with the smallest rongeur (1.5 mm) and continued with the medium-sized (2.5 mm) straight and angulated forms.
At the end of removal of the herniated and loose parts of the nucleus pulposus, the slit can be closed with one resorbable inverting suture.
32.9.1.8.2
“Perforated” Herniations (Extrusions)
In theses types of herniations, the outer limits of the anulus fibrosus and/or the posterior longitudinal liga- ment are ruptured (“non-contained” disc herniations).
After removal of the perforated part of the herniation, the disc space is opened extending the incision from the perforation to the posterolateral circumference.
Here again, the anulus can be sutured if technically possible.
32.9.1.8.3
“Epidural Fragments”
Usually, the fragments are removed first. In most of the cases, there is still continuity between the fragment and the perforation in the posterior anulus. We prefer re- moval of the nucleus pulposus in these cases to de- creases the risk of recurrent herniation. Sometimes, es- pecially in older herniations, the fragment is dislocated from the perforation which might be closed or covered with scar tissue in the meantime. We believe that, in these patients, removal of the fragment might be suffi- cient.
32.9.2
Surgical Technique in Recurrent Disc Herniation
32.9.2.1
Preoperative Planning
The principles of preoperative planning are basically the same for first and second or third operations in the same motion segment. However, additional consider- ations have to be made before starting the operation:
Preoperative X-ray films should be “read” carefully to find out the amount and configuration of bone removal (e.g., hemilaminectomy, partial facetecto- my) in order to be prepared for the bony land- marks during the approach to the motion segment.
A preoperative MRI should include examination with and without gadolinium in order to be able to evaluate the size of the “true” recurrent herniation within the epidural scar tissue. There is always epidural scar tissue accompanying or covering the recurrent disc herniation. MRI can show edema of the spinal nerve distal to the compression/adhe- sion. Take care to exclude a “new” disc herniation at another (adjacent) level. Carefully evaluate the lateral recess region and determine the necessity and amount of bony decompression.
Look for scar tissue along the approach track to the spinal canal. In patients not operated on using a microsurgical technique, there is usually signifi- cant scar tissue in the paravertebral muscles cover- ing the interlaminar space.
Look for pseudomeningocele! Sometimes, there is no information available from the first operation.
You can never be sure that the dura has remained intact.
Look for Modic I changes in the adjacent vertebral bodies! If a recurrent disc herniation is associated with Modic I findings, and if the patient has low back pain contributing significantly to his com- plaints (> 50 %), we would prefer to combine micro- surgical rediscectomy with segmental stabilization (instrumented fusion).
Spinal CT scan is not routinely used in recurrent herniations because it does not give information additional to MRI. However, the configuration of the facet joints as well as the osseous borders of the central spinal canal and the lateral recess can be evaluated.
We do not see hard indication for lumbar myelo- graphy or discography in recurrent herniations.
32.9.2.2
Positioning of the Patient See Section 32.9.1.2.
32.9.2.3 Localization
Do not rely on the scar in the back. Even if the first op- eration was a microsurgical procedure, the localization of the scar may be superior or inferior to the disc space.
The reason for this is that you do not know how the pa-
tient was positioned during the first operation. For ex-
ample, if, for the first operation, the lumbar spine was
in less kyphosis than during the recurrent operation,
the scar will localize inferior to the approach track. So we strongly recommend localization as described above.
32.9.2.4
Approach to Skin–Interlaminar Space
The approach from skin to fascia is the easiest part of the operation. Sometimes you will find non-resorbable sutures of the fascia. Beware: Non-resorbable sutures are sometimes used to prevent late CSF fistulas in case of dural tears. So be prepared during dissection of the scar tissue close to the interlaminar window.
The fascia is cut as describe above.
In case of scar tissue within the paravertebral mus- cles, this scar tissue is retracted by subperiosteal dissection with a sharp Cobb-type elevator. I rec- ommend to start retraction on the hemilamina above or below the interlaminar space depending on the amount of laminotomy which has been performed at the first operation.
Thus, first the hemilaminae bordering the inter- laminar space are exposed. These are the most reliable landmarks.
Dissection is continued laterally using different types of elevators, dissectors, and rongeurs to identify and expose the facet joint (or the remains of it).
Then the speculum is inserted as described above.
32.9.2.5
Approach to the Spinal Canal and Exposure of the Nerve Root
The approach to the spinal canal is the most difficult and hazardous part of this operation. First, the scar tis- sue covering the interlaminar space is “thinned-out”
layer by layer down to the level of the laminae. Do not go deeper than the laminar level to avoid dural lacera- tion (Fig. 32.17)! The scar which covers the posterior and medial parts of the spinal canal is not responsible for the clinical symptoms!
Entry into the spinal canal is performed from the superior border of the interlaminar space. Using a high-speed burr, the caudal border of the supradja- cent lamina is identified. A diamond drill is used to thin out the inferior part of the lamina. Thus, the interface between bone and scar tissue (or rem- nants of yellow ligament) can be exposed. With a blunt-tipped dissector, the scar tissue is dissected from the inner surface of the lamina, and an en- trance for a small (2 mm) Kerrison rongeur is cre- ated. Stepwise resection of the inferior parts of the lamina will then expose “healthy” dura superior to the target area (Fig. 32.18).
Fig. 32.17. Dissection of scar tissue down to the level of the lam- ina. Do not go deeper than the lamina
Fig. 32.18. Resection of inferior parts of lamina to expose
“healthy” dura. s.t. Scar tissue, d dura, l lamina
If bony resection is completed from 3 to 6 o’clock within the surgical field, the superior part of the lateral recess can be entered staying lateral to the shoulder of the nerve root (Fig. 32.19). The key for safe dissection is always the orientation to bony structures and the dissection of the fibrotic tissue from the inner surface of the osseous structures bordering the spinal canal.
Dissection is continued along the shoulder of the nerve thus decompressing the lateral recess. This can be achieved with only slight manipulation as long as removal of scar from the nerve root sleeve is not attempted.
The inferior borderline for safe dissection is the
pedicle. The spinal nerve can be gently dissected
from the medial border of the pedicle and decom-
pressed. Usually the epidural scar tissue ends cau-
dal to the pedicle at the entrance into the foramen.
Fig. 32.19. Decompression along the superior lateral border of the lateral recess
The spinal nerve is now exposed and decompres- sed from its root sleeve exit to its entrance into the foramen. However, it might still be covered with scar tissue. We do not recommend performing ex- ternal neurolysis in the posterior and lateral cir- cumference of the nerve.
32.9.2.6
Removal of the Herniated Disc
The next step is mobilization of the nerve from the posterior aspect of the disc space. In most cases, there is significant scar tissue which strongly ad- heres the spinal nerve and the thecal sac to the
“floor” of the spinal canal. Dissection is continued carefully with angulated, blunt microdissectors to separate the neural structures from the underlying scar and/or disc herniation. In true recurrent herni- ations, it is safer to leave a thin layer consisting of scar tissue and the remains of the posterior longitu- dinal ligament and anulus fibrosis between the theca and the herniation. This means that the scar tissue is opened lateral to the shoulder of the nerve and the recurrent herniation is entered directly with a blunt microdissector. The herniation thus can be mobi- lized and removed from underneath the fibrous layer adherent to the dura. In the majority of cases, the re- current herniation contains endplate material [1].
32.9.3 Hemostasis
At the end of nucleus pulposus removal, meticulous he- mostasis must be achieved. Please avoid leaving Gelfoam
or other types of hemostatic agents in the spinal canal. If there is epidural bleeding or oozing of blood, try to tam- ponade the veins temporarily with Gelfoam or Surgicel, irrigate with cold saline solution, and wait. Be patient, since most epidural bleedings will stop after a couple of minutes. Then carefully remove the hemostatic agents.
Very often, the fragile epidural veins adhere to the Gelfo- am or Surgicel. The result is recurrent bleeding while re- moving the hemostatic agents. This can be avoided by re- moval of the Gelfoam or Surgicel pieces under continu- ous irrigation which mollifies the adherences. In case of severe bleeding from the central venous plexus (Batson) gel- or powder-type hemostatic agents can be used (e.g., FloSeal; Baxter Healthcare, Fremont, CA, USA, or Arista;
Medafor, Bad Wiessee, Germany) can be used.
32.9.4
Closure of the Anulus
In subanular disc herniations, the anulus should be opened in a way which allows resuturing of the anular flaps. If there has already been a perforated disc hernia- tion, the rest of the anulus can be adapted and closed with one or two microsurgical inverting sutures. Usual- ly a 5 – 0 non-resorbable suture with a TF-4 small radius needle can be used (Fig. 32.20). This can be achieved in about 20 – 50 % of all patients. Although there is now proof that suturing the anulus prevents early recur- rences, the author believes that readapting the ends of the anulus fibrosus can promote and support the low healing potential of this structure.
If there is enough epidural fat tissue, it is mobilized with microsurgical dissection and used to cover the spinal nerve in order to diminish the risk for adherent epidural fibrosis. Two neuroswabs are placed into the spinal canal during closure of the fascia with resorbable sutures. This avoids blood from the paravertebral mus- cles dripping into the spinal canal during closure.
Before the last suture is closed, the swabs are removed.
Fig. 32.20. Inverting suture of the anulus fibrosus after discec- tomy (L4-5 right side). Note the traversing L5 nerve root
One of the subcutaneous resorbable sutures is fixed to the superior fascial layer to avoid subcutaneous sero- ma formation. The skin is closed with a monofilament resorbable intracutaneous suture.
32.10
Postoperative Care
The patient is allowed to mobilize 6 hours after the op- eration. From the first postoperative day isometric ex- ercises are performed. However, we recommend to re- strict postoperative physiotherapy to a minimum in the first 2 – 3 weeks following the operation. Patients are in- structed to mobilize themselves ad libitum, i.e., they are allowed to carry out all activities which do not cause or worsen low back pain and/or sciatica. Thus, the postoperative course is determined by the patients themselves. Postoperative hospitalization ranges be- tween 1 and 8 days depending on the individual case.
From the medicolegal point of view, the procedure can be performed on an outpatient basis. However, in our own experience we can not recommend it since control of early postoperative complications as well as postop- erative pain management within the first 24 hours can best be performed within the hospital.
32.11
Complications
Overall complications of microsurgical discectomy range between 1.5 % and 15.8 % in the literature with an average of 7.8 % [6, 7, 12 – 14]. There are significantly less severe intraoperative complications as compared to non-microsurgical discectomies [15]. The same is true for the rate of postoperative spondylodiscitis which averages 0.8 % (versus 2.8 % for macrosurgery) in a study published in 1986 [5].
The most important as well as the most frequent complications are listed below [9, 15]:
Urinary retention (5 %) Perineural fibrosis (3 %)
Superficial wound infection (2 %) Dural tears (1 %)
Deep venous thrombosis (1 %)
Postoperative segmental instability (1 %) Disc space infection (< 1 %)
Missed pathology (< 1 %) Root injury (< 1 %)
Lesions due to positioning (< 1 %) Cauda equina syndrome (< 0.1 %)
Retroperitoneal blood vessel injury (< 0.1 %) Epidural hemorrhage (< 1 %)
32.12
Critical Evaluation
The most frequently used arguments against microsur- gery are aimed at the technical aspects. It is often stated that microdiscectomy requires longer OT times as com- pared to conventional surgery. This is true, but only for surgeons not trained in microsurgery and at the begin- ning of their learning curve [11]. Wrong level explora- tion as well as the rate of early recurrences (which can be an indicator for “missed” fragments in the spinal ca- nal) do not show a significantly different rate as com- pared to non-microsurgical techniques. There are no technical or clinical limitations for the use of the micro- scope in lumbar disc herniation. This is also true for the treatment of disc herniations which are associated with other types of pathology such as lateral recess of central spinal canal stenosis [9]. There is no evidence from the literature that the frequency of complications is higher in microsurgical discectomy. However, it has been proved that the number of severe intraoperative com- plications was significantly higher when no microscope was used [15] (see above).
There is of course no direct relationship between the clinical long-term result and the surgical technique.
This fact erroneously leads to the statement that the mi- crosurgical technique is simply “not necessary.” How- ever, this is in contradiction to the basic philosophy of all surgical specialties which commits us to achieve a good clinical and technical result with the least iatro- genic trauma.
References
1. Brock M, Patt S, Mayer HM (1992) The form and structure of the extruded disc. Spine 17:1457 – 1461
2. Caspar W (1977) A new surgical procedure for lumbar disc herniation causing less tissue damage through a microsur- gical approach. In: Wüllenweber R, Brock M, Hamer J, et al (eds) Advances in Neurosurgery, vol 4. Springer, Berlin Hei- delberg New York, pp 74 – 77
3. Caspar W (1986) Die mikrochirurgische OP-Technik des lumbalen Bandscheibenvorfalls. Empfehlungen zum Ope- rationsablauf. Aesculap, Tuttlingen
4. Caspar W, Campbell B, Barbier DD, Kretschmer R, Gotfried Y (1991) The Caspar microsurgical discectomy and com- parison with a conventional standard lumbar disc proce- dure. Neurosurgery 28:78 – 87
5. Dauch WA (1986) Infection of the intervertebral space fol- lowing conventional and microsurgical operations on the herniated lumbar intervertebral disc. A controlled clinical trial. Acta Neurochir (Wien) 82:43 – 49
6. De Deviti R, Spazinate R, Stella L, et al (1984) Surgery of the lumbar intervertebral disc: results of a personal minimal technique. Neurochirurgia 27:16 – 19
7. Ebeling U, Reulen HJ (1983) Ergebnisse der mikrochirurgi- schen lumbalen Bandscheibenoperation – Vorläufige Mit- teilung. Neurochirurgia 26:12 – 17
8. McCulloch JA (1989) Principles of microsurgery for lumbar disc disease. Raven, New York
9. McCulloch JA (1998) Complications (adverse effects) in lumbar microsurgery. In: McCulloch JA, Young PH (eds) Essentials of spinal microsurgery. Lippincott-Raven, Phil- adelphia, pp 503 – 529
10. McCulloch JA, Young PH (eds) (1998) Essentials of spinal microsurgery. Lippincott-Raven, Philadelphia
11. Nyström B (1987) Experience of microsurgical compared with conventional technique in lumbar disc operations.
Acta Neurol Scand 76:129 – 141
12. Oppel F, Schramm J, Schirmer M (1977) Results and com- plicated courses after surgery for lumbar disc herniations.
In: Wüllenweber R, Brock M, Hamer J, et al (eds) Advances
in Neurosurgery, vol 4. Springer, Berlin Heidelberg New York, pp 36 – 51
13. Stolke D, Sollmann WP, Seifert V (1989) Intra- and postop- erative complications in lumbar disc surgery. Spine 14:56 – 59
14. Weber H (1983) Lumbar disc herniation. A controlled, prospective study with ten years of observation. Spine 8:131 – 140
15. Wildförster U (1991) Intraoperative Komplikationen wäh- rend lumbaler Bandscheibenoperationen. Neurochirurgia 34:53 – 56
