Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis

Chapter 44 Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis 44 H.M. Mayer 44.1 Terminology Microsurgical decompression of the spinal canal is defined as a mono- or multisegmental, uni- or bilateral internal enlargement of the central and/or lateral volume of the spinal canal without performing a laminectomy. Internal laminoplasty is proposed as a synonymous term. proposed by Poletti in 1995 [12]. The microsurgical interlaminar approach for the treatment of lumbar disc herniations has been adopted and modified. An extension of the ipsilateral approach to the contralateral side has been proposed in order to decompress the lateral recess bringing in the working instruments over-thetop of the thecal sac to the contralateral side. The approach was refined by McCulloch and described first in detail in 1998 [10]. 44.2 Surgical Principle The spinal canal is approached through a modified microsurgical interlaminar route (see Chapter 32) usually from the (most) symptomatic side. In cases with associated degenerative lumbar scoliosis, the approach from the convex side is preferred. The interlaminar window is opened ipsilaterally by resection of the hypertrophied yellow ligament. The insertions of the yellow ligament are resected by osteoclastic undercutting of the cranial and caudal lamina. Subarticular ipsilateral decompression is achieved by undercutting or partial resection of the medial parts of the superior facet of the infradjacent vertebra. Enlargement of the central parts of the spinal canal is achieved by dome-shaped undercutting of the laminae and resection of the ventral parts of the interspinous ligament. Contralateral decompression is performed through an over-the-top approach. 44.3 History Wide laminectomies still are considered to be the treatment of choice in degenerative spinal stenosis without instability [4 7, 13, 14, 15]. Due to the risk of destabilization of the motion segment, a limited approach was 44.4 Advantages The advantages include all advantages described in the chapters on microdiscectomy (Chapters 31, 32, 34). There are other advantages which can be divided into technical and clinical categories. The typical technical advantages are: Decreased trauma to paravertebral muscles on the ipsilateral side, no trauma to paravertebral muscles on contralateral side. Bilateral decompression of the spinal canal through aunilateralapproach. Microsurgical internal enlargement of the spinal canal preserves completely the posterior tension banding system (supraspinous, interspinous ligaments, spinous processes as well as paraspinal muscles on the contralateral side. Complete preservation of the laminae as well as of the lateral two thirds of the facet joint on the ipsilateral side. Preservation of the outer contour and more than 75% of the facet joint of the contralateral side (see also Fig. 44.14). Complete decompression of the thecal sac as well as of the spinal nerves on both sides from their dural sleeve exits to their entrance into the foramen. The clinical advantages result from the technical advantages: Decreased trauma to paravertebral muscles results in early mobilization, negligible postoperative wound pain, and an early start to rehabilitation.

398 Lumbar Spine Spinal Stenosis Decreased blood loss even in multisegmental approaches. Since the average age of the patients is >70 years (see also Section 44.12) early mobilization is an important factor to decrease postoperative complications such as deep venous thrombosis, urinary tract infection, or pneumonia due to prolonged immobilization. The risk of increasing instability is very low even in those patients who already show signs of mild (grade I) degenerative spondylolisthesis (personal observations). This is the reason why this kind of decompressive procedure can be performed without stabilization even in these patients. 44.5 Disadvantages There are several mainly technical disadvantages associated with this approach: The time for monosegmental decompression is slightly longer as compared to open central laminectomy. However, multilevel decompression occasionally results in considerably longer operating times. Decompression of the contralateral side is a technically demanding procedure. Insufficient exposure canleadtoenforcedintraoperativemanipulation of the thecal sac and cauda equina which can result in temporary and/or permanent neurological deficits. Inadequate decompression especially of the contralateral side can lead to unfavorable clinical outcomes. symptoms can rarely be verified unless there is a long history of complaints. However, there may be patients in whom mono- or oligoradicular symptoms due to lateral canal stenosis dominate the clinical picture. Diminished walking distance ( spinal claudication ). Reduced standing time. Low back pain. Loss of segmental motion (stiffness of the low back). Loss of lumbar lordosis. Radiological investigations such as plain X-ray, MRI, (functional) myelography or myelo-ct should prove a narrowing of the central and/or lateral spinal canal in relation to the topography of the lumbar nerve roots (Fig. 44.1). Older classification systems which refer to measurement of the sagittal and/or transverse diameter of the spinal canal are not helpful for the indication for surgery since it is not the absolute width of the spinal canal 44.6 Indications The procedure is indicated in all patients showing the clinical symptoms of acquired degenerative lumbar spinal stenosis without or with insignificant and mild vertebral body translations. The following clinical signs and symptoms should be present: Uni- or bilateral symptoms in the legs. In contrast to clear radicular symptoms, for example in disc herniations, the patients complain about weakness or heaviness in the lower extremities particularly when walking. Mild sensory deficits or paresthesias can be present as well. The symptoms usually get better when the patient stops walking, as well as in inclination. On physical examination, the Fig. 44.1. MRI sagittal view. Multilevel spinal stenosis

44 Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis 399 which determines compromise of neural structures. The relation between the size and topography of neural structures and the space available is the only reliable measure which determines the clinical symptoms. Electrophysiological parameters such as electromyograms (EMG), nerve conduction studies, or somatosensory-evoked potentials (SSE) contribute mainly to rule out other diagnosis such as peripheral neuropathies. Decompression without stabilization is performed in all patients without radiological signs of vertebral body translation, in patients without low back pain despite vertebral body translation or degenerative scoliosis, in patients older than 75 years, and in patients with severe osteoporosis and multisegmental pathology. Decompression with segmental stabilization (usually posterior anterior 270 fusion or TLIF) is performed in patients exhibiting grade I or highertype spondylolisthesis on rest or functional X-rays with significant low back pain as well as in patients with unstable lumbar degenerative scoliosis. Segmental instability chronic low back pain and radicular symptoms ( Failed Back Surgery syndrome) requiring stabilizing surgical procedures 44.9 Surgical Technique The surgical technique can be divided into microsurgical decompression without and with segmental stabilization. The indications are described above. 44.9.1 Microsurgical Decompression without Instrumented Fusion 44.9.1.1 Preoperative Planning Technical preoperative planning is performed using the information given by plain X-rays of the lumbar spine, MRI, and/or CT scan/post-myelographic CT scan. 44.7 Contraindications There are no disease-specific contraindications for decompression of the spinal canal. Modern anesthetic techniques and monitoring equipment make it possible to perform general anesthesia even on old patients with alowrisk.however,theremaybeafewabsolutecontraindications for general anesthesia such as: Severe respiratory insufficiency Unstable angina pectoris Severe arterial hypertension 44.8 Patient s Informed Consent Thepatientsshouldbeinformedabouttheriskswhich are immanent of microsurgical mono- or multilevel approaches to the lumbar spinal canal: Nerve root, cauda equina, and/or conus medullaris lesions with postoperative neurological deficits including bladder and bowel dysfunction Dural tears with menigocele and/or CSF fistulas Postoperative epidural hematoma Meningitis Spondylodiscitis with epidural abscess Epidural scarring with neurological deficits or permanent sciatica 44.9.1.1.1 Plain X-rays AllpatientsrequireplainX-raysofthelumbarspine. We routinely perform AP and lateral views. If instability with vertebral body translation is suspected, functional X-rays in flexion and extension are performed as well.thex-raysgivethegrosspictureofthecurvature of the lumbar spine. They reveal degenerative scoliosis and segmental rotational or translational instability. For surgical planning, it is important to know the size and shape of the interlaminar window since this is the entrance into the spinal canal. In most of the cases, the interlaminar space is small, sometimes completely closed (Fig. 44.2). The width of the laminae cephalad andcaudadtotheinterlaminarspacerepresentsthe safety range for bony decompression without performing a hemilaminectomy. The width of the isthmic area can be judged in order to preserve it intraoperatively. 44.9.1.1.2 Magnetic Resonance Imaging, CT Scan, and Post-myelographic CT Scan These are the surgeon s most important preoperative sources of information. MRI is, in my opinion, the imaging technique of choice, as in most of the patients this investigation gives sufficient information. The size and contourofthefacetjointsareclearlyvisible.thisfacilitatesintraoperativeorientation.itisimportanttoknow how much if the medial part of the inferior facet of the cephalic vertebra can be removed without sacrificing

400 Lumbar Spine Spinal Stenosis Fig. 44.3. MRI axial view. Hypertrophied yellow ligament contributing to central and lateral spinal stenosis Fig. 44.2. AP X-ray of a lumbar spine showing extremely narrow interlaminar spaces more than one third of its size. The thickness of the yellow ligament, its extension underneath the adjacent laminae as well as the thickness of the lamina itself can be evaluated. The extension of the yellow ligament as well as the thickness of the flavum determine the amount of undercutting which is necessary for sufficient decompression (Fig. 44.3). The size and topography of the neural structures at the level of compression as well as above and below should be evaluated carefully to avoid damage during decompression. The distribution of epidural fat tissue can lead to a modified surgical strategy which helps to protect the neural structures: for example, in an extremely narrow canal it is moreadvisabletoenterthespinalcanalthroughamore medial posterior route where more epidural fat protects the thecal sac (Fig. 44.4). Note the shape of the spinal canal (round, oval, trefoil; Fig. 44.5), and estimate whether it is mainly soft tissue (yellow ligament, joint capsule, intervertebral disc) or bone (superior facet, lamina, osteophytes) which leads to a compression of neural structures. If, as in the majority of acquired spi- Fig. 44.4. MRI axial view L5/S1. Epidural fat is preserved in the dorsal parts of the spinal canal nal stenoses, it is mainly soft tissue compression, try to preserve the bony structures as much as possible. 44.9.1.2 Anesthesiological Aspects The operation is performed under general anesthesia. Patients with spinal stenosis carry, due to their age and other concomitant diseases, higher risks and require reliable intraoperative monitoring. We recommend the introduction of a central venous line, to perform arterial blood pressure monitoring, as well as the introduc-

44 Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis 401 Fig. 44.5. Schematic drawing of the different shapes of the spinal canal tion of a urinary catheter irrespective of the expected time for the operation. Blood transfusions are not routinely necessary, and own blood donations are not required. However, if more than a two-level decompression is intended, we recommend intraoperative blood collection for retransfusion. 44.9.1.3 Positioning The patient is placed in a prone Mecca position as described in Chapter 32 (Fig. 44.6). The principles of positioning for lumbar microdiscectomy are valid. However, there are some special aspects which have to be considered in patients with acquired spinal stenosis: It is important to rule out hip joint contractures (not rare in this group of patients). Watch the hip joint and avoid luxation in patients with artificial hip joints! Watch the knees of the patient! Patients often have gonarthrosis or total joint replacement in the knee as well. Since decompression sometimes lasts more than 2 hours take care to pad the knees with a gel cushion to avoid pressure sores. Pay attention to the cervical spine! Mobility of the cervical spine is decreased in these patients. Rotation of the head is restricted. Put a soft pad under the forehead of the patient in order to avoid head rotation. Pay attention to the shoulders! Patients can have limited mobility of the shoulder joint. This requires modification of positioning of the upper extremities. Use as many gel cushions or pads as are needed to protect the neural and surface structures at risk (ulnar nerve, brachial plexus, peroneal nerve, knee, eyes, nose). 44.9.1.4 Localization The level(s) which have to be approached for microsurgical decompression are localized according to the principles described in Chapter 32. The skin incision is centered exactly over the lumbar segment of interest. If Fig. 44.6. Positioning of the patient

402 Lumbar Spine Spinal Stenosis twoormorelevelshavetobeexposedfordecompression, the skin incision is enlarged. If two non-adjacent levels have to be approached (e.g., L2/3 and L4/5), two separate approaches with separate skin incisions are recommended. Avoid movements of the patient (table) in the sagittalortransverseplaneafterlocalizationisperformed and the skin incision is marked as this may lead to the wrong level. As soon as the right level is approached, the table can be tilted. 44.9.1.5 Skin to Interlaminar Space The operation is started with the microscope from the skin level. The interlaminar space is approached using the same technique as described in Chapters 31 and 32. The fascia is opened in a semicircular manner leaving the medial parts attached to the supraspinous ligament andthelamina.theparavertebralmusclesareretracted after subperiosteal elevation. Retraction does not extend beyond the lateral border of the facet joint in order to avoid disruption of segmental innervation. The laminae of the adjacent vertebrae are exposed and the interlaminar window is cleaned of soft tissue (Fig. 44.7). Usually the window is very small and the yellow ligament is bulging. The speculum-retractor is then inserted. Make sure that the inferior (ventral) part of the interspinous ligament is exposed as well and that the visual axis toward the midline is not obstructed by a hypertrophied or dysplastic spinous process. 44.9.1.6 Microsurgical Ipsilateral Decompression Decompression is started with the removal of the inferior parts of the cephalic lamina. This is performed step by step using a high-speed burr. I recommend to start this microsurgical laminotomy at the transition zone between the lateral aspects of the lamina and the spinous process. The reason is that even in severe spinal stenosis you always find remnants of epidural fat underneath the posterior yellow ligament. Resection of the inferior parts of the lamina is extended until the insertion of the yellow ligament fades out and the dura or epidural fat can be identified. Laminotomy is extended laterally and caudally. Depending on the size of the inferior facet, its medial aspect is removed until the medial parts of the superior facet can be identified. Note that the spinal canal is not yet opened except for its cranial and medial part. Exposure of the yellow ligament is completed by resection of the superior part of the caudad lamina. It is now that the yellow ligament can be easily removed with rongeurs including the ventral parts of the interspinous ligament. Thus the back of the thecal sac is exposed. Adhesions of the dura to the yellow ligament can now be gently dissected from medial to lateral. After removal of the yellow ligament and its insertion underneath the lamina in most of the cases the central portion of the spinal canal is already decompressed. However, if there is still narrowing by a hypertrophied lamina, undercutting has to be continued in cranial and caudal directions. The surgeon now looks onto the back of the thecal sac and the roof of the lateral recess which is formed by the medial aspects of the superior facet and the remains of the yellow ligament and joint capsule (Fig. 44.8). Subarticular decompression can be the most difficult part of the operation. Usually there is no space between the lateral parts of the thecal sac, the nerve root, and the superior facet. With a blunt microdissector, the neural structures are gently mobilized from the yellow ligament. With a 1.5- or 2-mm Kerrison rongeur, the lateral recess is opened stepwise. I recommend to start in the middle portion and to proceed first in a caudal Fig. 44.7. Interlaminar window exposed. y.l. Yellow ligament Fig. 44.8. Part of the dura (d) is exposed. Narrow lateral recess ipsilateral

44 Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis 403 Fig. 44.9. Direction of Kerrison rongeur for decompression of the ipsilateral recess. d Dura, r rongeur, l lamina of supradjacent vertebra Fig. 44.11. Resection of the medial half of the pedicle direction. This means that the shoe of the rongeur is always introduced parallel to the route of the nerve. It thus can slide over the nerve and the risk of dural laceration or nerve injury is minimized (Fig. 44.9). Thus first the posterior aspect and then the lateral border of the nerve are exposed. At this stage, the caudal part of the lateral recess is already decompressed. However, there is still compression at the shoulder of the spinal nerveaswellasattheentranceintotheforamen. First, decompression is extended along the nerve until the medial border of the pedicle can be visualized (Fig. 44.10). In rare cases, the medial border of the pedicle leads to a kinking or compression of the nerve root. Itisdifficulttodrillandsmooththemedialpartsofthe pedicle since the high-speed burr has to be introduced into the narrow space between the nerve and the pedicle border. In these cases, the pedicle can be opened with the high-speed burr and the medial half is eggshelled and then broken off with a rongeur (Fig. 44.11). Decompression of the shoulder of the nerve root is now completed by removal of the yellow ligament in the superior Fig. 44.10. Decompression in caudal direction down to the entrance of the foramen. r Rongeur, d dura, inf. l. lamina of infradjacent vertebra Fig. 44.12. Complete ipsilateral decompression (intraoperative view). n Nerve root lateral corner of the surgical field. Decompression in this area must be performed until the inferior border of the exiting nerve root can be identified or palpated with the blunt nerve hook (Fig. 44.12). In cases with pronounced narrowing of the intervertebral space there is often impingement of the exiting nerve root by the tip of the superior facet. This tip can now be removed with a rongeur thus achieving a complete decompression of the exiting nerve root in the foramen. 44.9.1.7 Microsurgical Contralateral Decompression The table is now tilted away from the surgeon and the microscope is adjusted to give an oblique view into the spinal canal (Fig. 44.13a, b). The next step is the resection of the ventral parts of the interspinous ligament and its transition zone into the fibers of the contralateral yellow ligament. The rongeur can now be introduced underneath the yellow ligament of the contralateral side. The ligament is resected to create more space posterior as well as posterolateral on the contralateral side. It is occasionally necessary to resect ventral parts of the base of the spinous process. It is always necessary to continue undercutting of the supra- and infradjacent lamina to increase the spinal canal volume as well as to have a free visual axis toward the contralateral recess and foramen entrance. Decompression is facilitated if the surgeon first follows the inner surface of the infradjacent lamina to identify the medial border of the con-

404 Lumbar Spine Spinal Stenosis a b Fig. 44.13. a Oblique view into the contralateral spinal canal (schematic drawing). b Oblique view into contralateral compartment of the spinal canal (intraoperative view). d Dura mater, di. blunt dissector, i.l. interspinous ligament a b Fig. 44.14. a Decompression contralateral (schematic drawing). b Decompression of the contralateral compartment (intraoperative view). n Contralateral spinal nerve, t thecal sac, d blunt dissector in contralateral recess tralateral inferior pedicle. This can be achieved with minimum retraction of the thecal sac. Then decompression by subarticular undercutting as well as by undercutting of the supradjacent lamina can be accomplished (Fig. 44.14a, b). Although it will be occasionally necessary to use a blunt dissector or a nerve hook to temporarily retract the dura, it is possible to achieve this in most of the cases simply by using the metal sucker probe. 44.9.1.8 Closure At the end of the procedure there should be dural pulsations and four free nerves (two traversing and two exiting nerves). The bone surface is sealed with small amounts of bone wax if significant oozing of blood is visible. Hemostatic agents such as FloSeal (Baxter Healthcare, Fremont, CA, USA) or Arista (Medafor, Bad Wiessee, Germany) can be used. If possible, the insertion of a drain is avoided. We recommend not to place any foreign material (e.g., Gelfoam, Surgicel, etc.) into the spinal canal. If there is a significantamountofepiduralfattissueleft,thespinal nerves can be covered after gentle mobilization of the fat. The surgical field is irrigated with saline solution, andthefasciaandtheskinareclosedwithresorbable sutures. 44.9.2 Microsurgical Decompression with Instrumented Fusion 44.9.2.1 Posterior Approach The surgical technique of posterior anterior instrumented fusion in patients with spinal stenosis and vertebral body translation is described in detail elsewhere [9]. The anterior part of the operation is described in Chapters 45 and 46. We prefer, for biomechanical reasons, the combination of posterior instrumented fusion with a pedicle screw system in combination with anterior interbody fusion or a TLIF using a microsurgical approach. Since the posterior approach is not a minimally invasive approach, it will not be described in detail in this chapter. 44.9.2.2 Preoperative Planning Preoperative planning includes the acquisition of CT scan data for intraoperative navigation. The pedicle screws are inserted with the help of a spinal navigation system (Stealth system; Sofamor Danek) [2, 3, 8, 11] (Fig. 44.15). If no navigation system is used, measurementofthepediclediameter,aswellasofthesagittal length of the vertebral body is performed manually and the size and length of the pedicle screws is determined.

44 Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis 405 44.9.2.5 Localization Localization of the level(s) to be approached follows the criteria described above. If the pedicle screws are inserted without the help of an intraoperative navigation system, the level of the pedicle entrances are marked as they project onto the skin surface in AP fluoroscopic control. Lateral fluoroscopy is added to gain an impression of the inclination in the sagittal plane of the vertebrae to be instrumented. Fig. 44.15. Stealth system MRI as well as CT scans give an impression about the angles of the pedicles as well as the localization of the retroperitoneal vessels in relation to the bony structures. 44.9.2.3 Anesthesiological Aspects The operation is performed under general anesthesia. Patients with spinal stenosis carry, due to their age and other concomitant diseases, higher risks and require reliable intraoperative monitoring. We recommend the introduction of a central venous line, to perform arterialbloodpressuremonitoring,aswellastheintroduction of a urinary catheter irrespective of the expected time for the operation. Blood transfusion are not usually necessary. 44.9.2.4 Positioning The patient is placed in a prone, comfortable position on a soft foam frame on a radiolucent table. The general principles of protection of neural structures and the skin are respected. The hips and knees are slightly (20 30 ) flexed, and the anterior iliac crest is padded in order to avoid pressure on the lateral femoral cutaneous nerve. 44.9.2.6 Skin to Interlaminar Space The operation is started without the microscope. The interlaminar space, the facet joints of the segment to be decompressed and fused, as well as the facet joint above are exposed bilaterally using a conventional technique [1]. Even in cases which afford segmental instrumented fusion, we try to avoid retraction of the muscles beyond the lateral border of the facet joint. Since we do not perform intertransverse fusion, the transverse process does not need to be exposed. However, it must be palpated as well as the transition zone between the transverse process and the superior facet. The operation is continued with the following steps: 1. Insertion of pedicle screws (Click X, Synthes). 2. Opening of the facet joint capsule and mobilization of the facet joint. 3. Insertion of the mono- (Click X, Synthes) or multisegmental (USS II, Synthes) internal fixation system (Fig. 44.16). 4. Reduction and reconstruction of normal curvature. 5. Microsurgical decompression (see above). Removal of cartilage from the rest of the facet joints. Interfacet bone grafting using the removed parts of the laminae. 44.9.2.7 Closure In these patients, two wound drains are inserted underneath the fascia without applying suction. The wound is then closed as described above. 44.9.3 Anterior Interbody Fusion The anterior microsurgical approach for interbody fusionisdescribedindetailinchapters44and45.usually the operation is performed in the same session, however, it can be also be performed in a second session after an interval of 7 14 days.

406 Lumbar Spine Spinal Stenosis a b Fig. 44.16. Pedicle screw systems. a Click x Pedicle screw system. b USSIIPedicle Screw System, Synthes Oberdorf Switzerland 44.10 Postoperative Care The patients are allowed to mobilize within 6 hours in cases without instrumented fusion. Otherwise, the patients get out of bed the day after the operation. In patients with more than two-level decompression, as well as in patients with instrumented fusion, a short Boston brace is recommended for 4 6 weeks postoperatively. 44.11 Complications Dural tears leading to a pseudomeningocele or even CSF fistulas are the most common complications during decompressive procedures in spinal stenosis.theyaredescribedtobeashighas13% [18]. In the group of patients described above, we had 2/57 (3.5%) dural tears which had to be sutured. There are several reasons for the high rates of dural injuries. The dura usually is very thin in this old patient population. If the patient is placed correctly (see Section 44.9), the spinal CSF pressure is low so that the dura does not behave like a taut, well-rounded structure. Introduction of the rongeurs can lead to infolding of parts of the dura. This increases the risk of dural laceration. The cauda equina is at risk especially in patients with spinal stenosis. The nerve roots are compromised usually for years, and the arterial supply may be diminished by other concomitant diseases (e.g., diabetic microangiopathy, microangiopathy due to arterial hypertension). This makes the fibers of the cauda equina more vulnerable as compared to the young patient. Moreover, the surgical technique includes the risk of temporary direct compression of the cauda equina roots during decompression of the contralateral side (see Section 44.9). We had one patient with a postoperative transient hemicauda syndrome (1/57 = 1.75%). Epidural hematoma. Special attention has to be made to complications secondary to positioning. The risk for such complicationsishigherascomparedtomicrosurgical discectomy, since microsurgical decompression requires longer operating times and thus the patient has to remain in the intraoperative position for a longer time which increases the risk of pressure injury to the structures mentioned above. Care must be taken to avoid pressure on the eyes since this might lead to postoperative blindness or corneal lesions. Delayed complications: Segmental instability Destabilization of the adjacent segment Arachnoiditis Epidural scar formation 44.12 Results Comparativeanalysisoftheresultsofmicrosurgical segmental decompression with conventional laminectomy techniques is difficult because we could not find any prospective, comparative studies in the literature. McCulloch has reported recently about a good and excellent outcome in 90.9% of 22 patients with acquired degenerative spinal stenosis. In these cases, microsurgical decompression was combined with a minimally invasive modification of intertransverse fusion [10]. Pseudoarthrosis rate was 13.6%, and complications ranged from 4.5% (urinary tract infection) to 9.1% (deep venous thrombosis, upper respiratory tract infection, superficial wound infection).

44 Microsurgical Decompression of Acquired (Degenerative) Central and Lateral Spinal Canal Stenosis 407 Between March 1998 and April 2002 we have treated a total of 702 patients with the techniques described above. The consecutive series of the first 275 patients (men 52%, women 48%) is presented here. The average age was 69 years (range 34 89 years). The average history of complaints was >2 years. All patients had had severalunsuccessfultrialsofconservativetherapy.two hundred patients (73%) complained of sciatica with increasing pain during walking and standing as well as heaviness and/or sensory disturbances in the leg after different walking distances/standing times. In all cases, the leg symptoms were predominant. Only 75 patients (27.3%) complained about sciatica alone. Neurogenic claudication was evident in 252 patients (91.6%). A relatively high percentage of patients presented with neurological deficits (125/275 = 45.5%). The average preoperative walking distance was 250 m. Pain-free standing time was 10 min on average. In 99% of cases, surgery was elective, however, due to neurological deficits in 52% of the patients, it was performed usually within 1 2 weeks of first presentation in our hospital. In 1% of the patients there was a chronic cauda equina syndrome with bladder and bowel dysfunction. A total of 568 segments (in 275 patients) were decompressed (2.1 segments/patient). The mean operating time was 37 min/segment, blood loss averaged 57 cc/segment, and all patients were mobilized within 24 hours. After a mean follow-up of 24 months, the average pain-free standing time was 82 min (as compared to 10 min preoperative). Pain-free walking distance was increased from 250 m preoperative to 5,017 m postoperative. In 45% of the patients there was also a significant decrease of low back pain. Overall complication rate was 15.6%, with 5% intraoperative dural leaks. In 3.8% of patients postoperative epidural hematomas needed early revision. Together with persistent symptoms (2%) they presented the most frequent postoperative complications. Microsurgical decompression with instrumented posterior anterior fusion was performed in 18 patients. The age range in this group was between 43 and 76 years, averaging 62 years. Indication for fusion was the association of spinal stenosis with degenerative spondylolisthesis grade I or more in all cases. In 86% of the patients, surgery was elective. Only 14% presented with progressive or severe neurological deficits. There were no emergency cases. The mean operating time for decompression as 70 min/level for microsurgical bilateral decompression and 140 min/level for decompression and posterior instrumentation with pedicle screws. The average blood loss for decompression was 240 ml and for decompression and instrumentation 760 ml. We observed a total of 4/57 (7%) complications. There were two patients with dural tears (3.5%), one patient with a hemi-cauda equina syndrome (1.7%), and one patient with a superficial wound infection (1.7%). The cauda equina symptoms resolved within 2 weeks, and the wound infection healed without intervention. Hospitalization was between 5 and 10 days in patients with just microsurgical decompression and between12and14daysinpatientswithadditionalinstrumentedfusion.preliminaryresultswithafollowup time of between 3 and 12 months showed a significant improvement in leg symptoms in 90% of patients, and a significant improvement in low back pain in 80% of the fused patients. The walking distance was significantly improved in 70% of the patients. In one third of our patients, there was partial or complete regression of neurological deficits. 44.13 Critical Evaluation The goal of surgery in degenerative spinal stenosis is the improvement of leg and low back symptoms, to increase the pain-free walking distance, and to improve the quality of life in a group of old-aged patients. No patient will be completely free of complaints and no patientwillhaveanewlumbarspineaftertheoperation. Extensive surgery is associated with increased risks in old patients with various associated diseases. Therefore,inthispopulationinparticular,theprincipleof maximum effect with minimum trauma should be applied. Our experience with microsurgical decompression, although limited, strongly supports our efforts to further miniaturize the surgical approaches to the spinal canal. Postoperative mobilization as well as rehabilitation is facilitated since peri- and postoperative morbidity is decreased. The patients virtually have nooronlyslightwoundpain.theyexperienceavery quick improvement of their leading symptoms, such as increase of walking distance. Low back pain is not a significant problem even in those cases in which instrumented fusion is performed. Microsurgical anterior approaches even allow for circumferential fusion which is associated with low pseudarthrosis rates [9]. We believe, that in acquired degenerative spinal stenosis there is no need to perform wide laminectomies. This may not be true for congenital central spinal stenosis. This disease requires a more extensive decompression which often ends with a conventional multisegmental laminectomy. The reason for this is that narrowing of the spinal canal not only affects the interlaminar interval but also the sublaminar space in multiple segments. Efficient decompression thus requires laminectomy, a technique which is not microsurgical and therefore not dealt with in this book.

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