Legacy: "Atlast of Neurosurgery" / L.Karaguiosov, A. Ramadan, K.Karaguiosov / Kiwait/ 1998
NEXT< 12 SURGICAL TREATMENT OF SPINAL INJURY
PART TWO
SPINE AND SPINAL CORD SURGERY
11. PRINCIPLES OF SPINAL CORD SURGERY
APPROACHING THE SPINAL CANAL
ANATOMICAL BASIS OF SURGICAL OPENING OF THE SPINAL CANAL
All operations on the spinal cord, its meninges and nerve roots are performed after operative opening of the spinal canal. The spinal canal is approached through different routes, which depend on the location of the lesion in the canal, its relation to the structure of the spine and spinal cord and the biomechanical consequences, which will result from the approach alone.
All surgical methods have two technical stages: penetration through the soft tissues on the way to the spine and the opening of the canal itself. The posterior wall of the spinal canal is situated relatively superficially in the posterior midline of the neck and the back; this makes it the most accessible to exposure. The lateral and anterior walls of the spinal canal are surrounded by more complex and vitally important structures at different levels of the spine corresponding to the neck, thorax and abdomen. Many lesions that require surgical treatment simultaneously affect both the spine and the spinal canal, and the approach is adjusted accordingly.
The same refers to the conditions of compromised spinal stability, either by the lesion or the proposed approach. In these last cases the surgery is concluded by an appropriate stabilizing technique.
The posterior approach to the spine remains the "classical", standard for reaching the neural structures. It will be presented in the introductory chapter of the spinal section. Several other important techniques, especially the microscopic ones such as the anterior approach to the cervical spine will be dealt with completely when dealing with the corresponding problems. Some methods related more to orthopedic spinal techniques, will be mentioned only in principles.
Paravertebral soft tissues. From the surgical anatomical point of view the paravertebral soft tissues can be divided in four regions: nuchal, thoracic, lumbar and sacrococcygeal (Fig.11-1).
Nuchal region. The topographical limits of the nuchal region are considered as follows: superiorly - the external occipital protuberance and the superior nuchal line, inferiorly - the horizontal line, passing through the apex of the spinous process of the VIIth cervical vertebra, which is easily palpated. The lateral border of the trapezius muscle serves as a lateral limit. The skin is compact and thick especially in the superior half and sometimes presents some difficulties in suturing.
The subcutaneous fatty tissue, as that of the scalp, is compact and contains fibrous bands that connect the skin and the underlying aponeurosis. Due to this, it is difficult during the operation to separate the external surface of the aponeurosis, which covers the trapezius muscle. Superiorly the aponeurosis is adherent to the external occipital protuberance and the superior nuchal line. Covering the trapezius muscle laterally, it continues into the superficial neck fascia. Along the midline the fascia is connected with the external edge of the nuchal septum, which is extended from the spinous process of the VIIth cervical vertebra to the external occipital protuberance. The nuchal septum is triangular in shape and is situated along the midline on the sagittal plane, connecting the external occipital crest with the spinous processes of the cervical vertebrae.
The muscles of the nuchal region are rather voluminous and can be divided into four layers in a transverse section. The trapezius muscle forms the first layer. Under it, as a second layer is revealed the splenius muscle. The third layer consists of muscles situated vertically: longitudinal major and minor muscles, longissimus capitis and cervicis, and multifidus muscles. The fourth layer, the deepest one, contains the following muscles: the two straight muscles, the two oblique muscles, transversospinal and inter-spinal muscles. These last muscles are short and serve for extension and rotation of the head.
These four layers of muscles are separated from one another in the occipital region by fine fascias.
The soft tissues in the nuchal region draw their blood supply from the occipital and deep cervical arteries. The occipital artery is a branch of the external carotid artery and enters the occipital region medially to the mastoid process. At its very beginning, it is situated deeper than the place of attachment of the sternocleidomastoid muscle. After that, its course changes upward and inward and 2,5 - 4 cm laterally from the external occipital protuberance, it penetrates into the scalp. The deep cervical artery is a branch of the subclavian artery, which goes to the neck upward between the iliocostal and transversospinal muscles, where it branches.
The posterior branches of the cervical nerves supply the nuchal region. The posterior branch of the second cervical nerve, which is the thickest one (the great occipital nerve) penetrates into the occipital region between the Ist and the 2nd cervical vertebrae. It envelopes the inferior edge of the oblique muscle, perforates the splenium and trapezius muscles and leaves the muscles 2 cm under and 2 - 4 cm lateral to the external occipital protuberance. Its branches innervate the soft tissues of the occipital region of the head. The nerve is situated medially and close to the occipital artery. The nuchal region
is rich in venous vessels, situated in the inter-muscular spaces. The veins flow into the vertebral veins, the posterior jugular vein and often have anastomoses with the sinuses of the dura.
Thoracic region. The thoracic region has a quadrangular form. The lines passing along the angles of the ribs serve as the lateral limits. The superior limit is the horizontal line, passing at the level of the spinous process of the VIIth cervical vertebra. The inferior limit follows the course of the XIIth ribs.
The skin in the thoracic region is thick and movable regarding the fascia, the spinous processes and the ribs.
The fascia covering the muscles is thin. The muscle can be divided as in the occipital region into four layers. The trapezius and latissimus dorsi muscles, which are flat, are the most superficial. The rhomboid muscles are situated under them as a second layer. The serrate muscles are situated as a third layer. Under them, in the deepest layer, are the iliocostal and longissimus muscles and the small muscles - transversospinal, interspinal and intertransversal muscles. The thoracolumbar fascias separate the third from the fourth layers.
Lumbar region. The paravertebral soft tissues in the lumbar region occupy a quadrangular area. Its limits are: superiorly - the line passing along the course of the XIIth rib on both sides, inferiorly - the arcuate line, which begins from the sacral bone and continues along the iliac crests to end laterally at the vertical line along the lateral border of sacrospinal muscles.
The skin and the subcutaneous fatty tissues have the same characteristics as they do in the thoracic region. The aponeurosis is more compact and is more easily separated than in the thoracic region. The muscles are of a larger volume and are also in four layers. The latissimus dorsi muscle is situated superficially with its aponeurosis. Under it in a second layer is located the inferior serratus muscle. The sacrospinal muscles are situated deeper as a third layer and in the last fourth layer, are the interspinal and intertransversal muscles.
Sacro-coccigeal region. This region is triangular in shape and corresponds to the posterior surface of the sacrum and coccyx. The muscular layer is thinner than in the thoracic, as the fibrous beginnings of paravertebral muscles are attached on the posterior surface of these bones.
Spinal canal. The spinal canal occupies the internal part of the entire length of the spine. Its upper end communicates with the cranial cavity through the foramen magnum and its caudal end is in the sacral hiatus.
The dimensions and the form of the spinal canal are specific to the different segments of the spine. In the cervical region the cross-section of the canal is triangular, in the thoracic region it is oval, and in the lumbosacral region the shape becomes triangular again. The dimensions of the spinal canal vary for the different segments. It is broad in the cervical and the lumbar regions, while in the thoracic region, where the vertebrae are less mobile, it is narrower. The narrowest part is in the sacral region. These dimensions accommodate the corresponding changes of diameter in the spinal cord. The anterior wall of the spinal canal is formed by the posterior surface of the vertebral bodies and the intervertebral disks, and is covered by the posterior longitudinal ligament. The posterior wall is composed by the vertebral laminae and the ligamenta flava between them. The pedicles of the laminae and the intervertebral joints form the lateral walls. Between every adjacent pair of pedicles, are formed foramina through which the spinal canal communicates with the paravertebral area. Through these openings pathological processes penetrate from the paravertebral tissue toward the spinal canal or vice versa (tumours, abscesses, etc.). Through these foramina emerge the spinal nerves and spinal veins and the arterial vessels enter to supply the spinal cord and meninges. Interlaminar spaces are accessible without additional flexion in the upper cervical and lower lumbar areas.
GENERAL TECHNIQUE OF LAMINECTOMY
Laminectomy is a technique of removal of vertebral laminae to expose the content of the spinal canal. It is performed in a prone, sitting or lateral position (Fig. 11-2). When the prone position is used, the patient's body is laterally supported by elongated cushions or a special bridge, leaving a free space under the thoracic and abdominal cavities, not obstructing the respiratory movements and relieving congestion of the veins, which would increase the pressure in the veins of the spinal canal. In an operation on the cervical region the head is supported in a special headrest or the three-pin head holder.
The head and the upper part of the body are slightly elevated to decrease the venous pressure in the cervical region. For operations in the thoracic and lumbar region, with the patient in prone position, the head is turned to one side and the arms are extended and placed on both sides of the head. Care is taken for this not to be excessive and that the vessels and nerves in the axillar region are not compressed.
With the patient in the lateral position during laminectomy, many of the problems of the prone position are avoided. There is less compression on the abdominal veins resulting in minimal congestion inside the spinal canal, better control of the respiration, and blood and CSF naturally drain out of the operative field. The sitting position may also be used in operations on the cervical spine, and the conveniences of avoided venous bleeding and drained blood and CSF are obvious. This position presents some danger of brain ischaemia, air embolism, and quick drainage of CSF, which may lead to the accumulation of a subdural haematoma.
Anaesthesia. The opening of the spinal canal is almost always performed under general anaesthesia combined with infiltration of the soft tissues around the spine with local anaesthetic or saline mixed with adrenaline (1 mg to 400 ml).
The infiltration with local anaesthetic begins with an intradermal injection along the path of the incision. After that the subcutaneous fatty tissue and the paravertebral muscles are successively infiltrated over a larger area. This is accomplished by introducing the needle vertically until its tip reaches the resistance of the vertebral laminae. The injections are made at a distance of 2,5 - 3 cm on both sides of the spinous processes. The direction of the needle should be strictly vertical or with a slight downward inclination in order not to penetrate into the spinal canal. The use of a local anaesthetic considerably decreases the bleeding during the incision and helps the separation of soft tissues from the vertebrae.
Operative technique. In order to determine the level at which the operation is to be performed correctly, the following main reference points must be considered:
1. Spinous process of the VIIth cervical vertebra, which must be prominent and easy to palpate.
2. The horizontal line, which passes at the level of the inferior angle of the two scapulae, indicating the VIIth thoracic vertebra.
3. The line that passes through the iliac crests is situated at the level of the IVth lumbar vertebra.
4. X-ray film with a metallic marker in the presumed level of the pathology as a reference before incision.
5. X-ray film or fluoroscopic control during the surgery.
The skin incision is made along the midline over the spinous processes or in the shape of an arch, whose ends are on the midline; the convex part is separated 2 - 3 cm away from it (Fig. 11-3). The incision must be prolonged to expose one vertebra above and one below the place where the lesion is. With obese patients and those with well-developed muscles, the skin incision must be even longer. Together with the skin, the subcutaneous fatty tissue is also incised until the spinous processes are reached. The surface of the muscle fascia is dissected at a distance not more than 2 - 3 cm from the midline on both sides along the entire incision. The fascia and the tendinous attachments of the muscles are divided from the spinous processes as close as possible to the bone along the whole length of the skin incision. From this layer down diathermy can be used as a dividing tool and that reduces bleeding.
The next stage of the operation is separation of the paravertebral muscles from the spinous processes, the vertebral laminae and the ligaments situated between them. This separation is made with a periosteal elevator or plane chisel, in order to lift the muscle subperiostally (Fig. 11-4). Sometimes tendinous attachments of muscles, especially those in the lower part of the spinal column, are divided with a scalpel. The separation continues until the articular processes are reached. The separated muscles and the stripped surface of the laminae are packed for 4 - 5 minutes to obtain good haemostasis. After this the packs are removed and self-retaining retractors inserted (Fig. 11-5). The proper stripping of the surface of the laminae and the spinous processes from soft tissues is of great importance and facilitates very much the next stage of the operation. In the cervical region the incision of the subcutaneous fatty tissue exposes the muscles, and in order to reach the spinous processes, the surgeon must penetrate more deeply exactly along the midline and strictly follow the course of the nuchal septum. In the sacral region a few muscles and more ligaments cover the external surface of the sacrum. After a good separation of the muscles, precise haemostasis is required.
Supraspinal and intraspinal ligaments are cut between neighbouring spinous processes, which are prepared for removal. These processes must be removed as low as possible together with their bases, exposing the laminae and the flavum ligaments. Ligamentum flavum in the space between two laminae is opened until epidural fatty tissue appears. This opening is done at one of the ends of the exposed spine - above or below the lesion.
After that the opening is enlarged until it is possible to insert an angulated bone rongeur, and in small fragments remove the necessary number of laminae (Fig. 11-6). The resection of the laminae advances laterally until the joint processes are reached but without opening the joints. Always before removing the laminae the content of the canal (fat, dura, etc.) should be dissected away. When manipulating with the bone rongeur, the dural sac must always be protected from compression. In case of subdural tumours, when the dura is under pressure, the resection of the laminae is made on both sides of the lesion if possible. Last is removed the laminar part located over the compressed area of the spinal cord.
Bleeding from the resected bone is easily stopped with haemostatic wax. When the sacral canal is opened, the surgeon must begin from the lumbo-sacral interlaminar space or hiatus sacralis.
The epidural space is revealed under the laminae and ligamenta flava. It is occupied by friable fatty tissue with multiple venous vessels. This tissue is rather easily separated with any dissecting instrument and, if venous bleeding occurs, it is easily stopped by bipolar coagulation. In this way the dural surface is exposed along the entire length of the laminectomy. Before undertaking any further step, a thorough revision is made of the entire operative wound with a final haemostasis. The whole operative field, with the exception of the dura is covered with wet cottonoids, to prevent blood collection from structures external to the dura and to isolate it from the other tissues. The unchanged dura of the spinal canal is a brilliant grayish-blue layer with pulsations simultaneous with ventilator movements and the heart rate.
Before opening the dura the patient's head must be placed slightly lower than the level of the laminectomy in order to prevent the loss of large quantities of CSF. The revision of the epidural space can be completed by gentle palpation of the dural sac or with the ultrasonic probe.
The dura is opened with a longitudinal incision on the midline, after elevating it with a fine sharp hook (Fig. 11-7). It is desirable that during dural opening, the arachnid, which has the tendency to protrude as a transparent bubble, be preserved. After a sufficiently large incision has been made a thin wet cottonoid is inserted under the dura in the direction of the continuing incision, serving as a protection from the scissors. The edges of the dura are lifted with traction sutures.
After that the spinal cord is inspected. The arachnoid is opened with a fine hook or with the tip of a scalpel and in normal conditions, CSF begins to leak immediately. The posterior surface of the spinal cord is inspected first, followed by the lateral, using a dissector for slight retraction. If this inspection uncovers a pathological process, situated anteriorly to the spinal cord, the exploration continues in greater detail. Two or three dentate ligaments are divided after lifting them with a hook. Slight elevation of the spinal cord by the free ends of the divided ligaments induces rotation of the spinal cord (Fig. 11-8). When there is a complete block of the subarachnoid space the amount of CSF that leaks is much less.
After everything necessary has been done in the spinal canal, and depending on the lesion. the operative wound is closed in layers. The dura is sutured by interrupted or continuous sutures. Its closing must be watertight to avoid leakage of CSF and also to prevent blood from entering the subarachnoid space (Fig. 11-9). An indication of good quality of the suture is when compression of the jugular veins does not evoke CSF leak between the dural edges. The muscles are closed by single sutures in two or three layers at a distance 2 - 3 cm one from another. The fascia is sutured by single sutures at a shorter distance (Fig. 11-10). The subcutaneous tissue and the skin are sutured last. As a cavity always remains between the dura and the deepest layer of sutured paravertebral muscles, haemostasis can be fragile, and vacuum drainage should be left there for 24 hours.
The spinal canal can be opened in an osteoplastic way (laminotomy), with cutting the laminae laterally with the the saw or a small drill, and at the end of the operation closing them by wiring (Figs. 11-11; 11-12; 11-13)
The postoperative care of patients, who have undergone a laminectomy varies according to the characteristics of the lesion, the localization and the extent of the operation. After the effect of the anaesthesia is over, the neurological condition of the patient is reassessed. Frequent evaluations in the following hours aims at detecting any deterioration and detecting the first manifestation of compression from an extradural haematoma. If the dura is not opened and the resection of the bone is comparatively small, the biomechanical effect of the laminectomy is minimal and the patient can get up and walk with support even on the day after surgery. After extended laminectomies, patients must remain in bed for several days to allow the paravertebral muscles to initiate the healing process before being loaded with normal activity.
Postoperative complications are rare. The CSF fistulae must be treated in the same way as after cranial operations.
In case of a second operation on the same site, the incision passes along the scar of the previous one. The fibrosis in the epidural space is exposed and tight adhesions to the external dural surface are dissected. This dissection can be difficult and, for reasons of safety, it is started at the edges of the laminectomy over unaffected dura, even with removal of small part of the intact adjacent lamina at the borders of the laminectomy.
