Anatomy of the extradural compartments of the lumbar spinal canal. Peridural membrane and circumneural sheath.

The development of newer and more accurate methods of identifying the structures within the spinal canal has given a much better understanding of the soft tissue structures that lie between the dura and the surrounding bone of the vertebral canal. One anatomic structure of special importance, but seldom spoken of, is the peridural membrane. Although it was mentioned in the writings of Fick14 as early as 1904, it was Dommissee12,13 who first described it accurately and who named it the peridural membrane. It appears to be a homologue of the periosteum. There is no periosteum at any point on the bone where this membrane is located . Spine surgeons have frequently noticed that, after removing a nuclear fragment that has extruded and crept upward or downward and has come to lie over the vertebral body, one sees only rough periosteum-free bone where the fragment had been lying. Premembranous hematomas may develop because a small fragment of nuclear material has extruded out at the rim of the vertebra, anterior to the attachment of the PLL, and in tearing loose may have caused bleeding. This fragment of nuclear material may creep upward or downward over the vertebral body. There may be a pool of blood around it. Hematomas are usually on one side or the other but can lie midline, because the bony ridge down the center of the posterior surface of the vertebral body is not always complete. In other words, there are gaps in it , and it is through these gaps or by actually lifting the deep PLL-membrane complex that the nuclear material or blood can pass, giving a midline mass seen on MR imaging. The plexus of veins in the body of the peridural membrane and penetrating it posteriorly in many places is part of Batson's plexus. They were first described by Willis38 in 1663. In recent years Dommissee13 and Crock8 have made major contributions to our understanding of these vessels. It is interesting to note that if a degenerated disk is injected with a mixture of barium, dye, and gelatin and radiographs are taken, it is seen that, in most cases, Batson's veins have filled. If the disk is not degenerated and does not take more than a few milliliters of this mixture, then Baxton's veins do not fill. It is very likely that these veins fill whenever we do diskography on anything beyond a moderately degenerated disk but we do not see them on the fluoroscope because the contrast is not dense enough and by the time we get around to taking permanent radiographs, the contrast has long since disappeared into the venous circulation. In the cadaver, the blood is not flowing so the gelatin with barium has time to set in veins. Interestingly, if contrast is injected into vertebral body by simply driving a needle through the cortex of the vertebral body, Batson's veins fill with contrast in the same way. The sheath surrounding the spinal nerves out lateral to the foramina was not well known until Kikuchi19 described it in 1982. He gave a very accurate description of it and called it the epiradicular sheath. The problem with calling it by this name is that it surrounds a true mixed peripheral nerve and not a radicule (root). Because of this, we propose the name circumneural sheath. It should be noted that there already is an epineural sheath, which is the outermost covering of peripheral nerves. There is also a perineural sheath and an endoneurium. These names have been used for nearly 100 years. The segment of spinal nerve commencing at the dura and ending just beyond the ganglion is commonly called a nerve root. It actually consists of two nerve roots, a motor and sensory, inside a sleeve of dura. At a point just beyond the ganglion the two roots blend together and become a typical mixed peripheral nerve. At this same point the dural sleeve becomes adherent to the nerve and henceforth is called the epineurium. For this 1- to 2- cm segment of spinal nerve from the dura to just beyond the ganglion we propose the name dural root sleeve. After all, it is a sleeve, it is made of dura, and it covers two nerve roots.

Comparative study of the incidence and severity of degenerative change in the transition zones after instrumented versus noninstrumented fusions of the lumbar spine.

The purpose of this study was to determine whether the addition of pedicle screws and rods to a fusion of two or more vertebrae of the lowest three motion segments of the lumbar spine increases the incidence or severity of transition zone change (TZC) above or below the fused area. A study group of 52 patients who had a fusion with fixation and a control group of 31 who had a nearly identical operation but without fixation were obtained. Radiographs and computed tomography scans of the area of study were taken preoperatively and were repeated approximately 7 years after the operation. Results showed that the addition of pedicle screw fixation does not increase the incidence or severity of TZC in the first 7 years after surgery.

Herophilus of Alexandria (325-255 B. C.). The father of anatomy.

Herophilus (325-255 B. C.) is one of the group that has been called the great Greek physicians. All members of this group lived during the last 400 years of Greek intellectual leadership and the first 200 years of Roman domination. Herophilus was born in the Greek town of Chalcedon. He received his medical training under Praxagoras, a famous physician and anatomist who taught at the Hippocratean medical school on the island of Cos (Kos). He moved to Alexandria, Egypt, as a young man and lived there for the rest of his life. With his younger contemporary, Erasistratus, he did the first ever scientific human cadaveric dissections for a short period of no more than 30-40 years. Human dissection then was forbidden and was not allowed again for 1800 years. It seems that only these two physicians ever performed human dissection until the Renaissance, around 1530 A. D. The anatomic and physiologic discoveries of Herophilus were phenomenal. As Hippocrates is called the Father of Medicine, Herophilus is called the Father of Anatomy. Most would argue that he was the greatest anatomist of antiquity and perhaps of all time. The only person who might challenge him in this assessment is Vesalius, who worked during the 16th century A. D.

The transition zone above a lumbosacral fusion.

STUDY DESIGN: The clinical and radiographic effect of a lumbar or lumbosacral fusion was studied in 42 patients who had undergone a posterolateral fusion with an average follow-up of 22.6 years. OBJECTIVE: To examine the long-term effects of posterolateral lumbar or lumbosacral fusion on the cephalad two motion segments (transition zone). SUMMARY OF BACKGROUND DATA: It is commonly held that accelerated degeneration occurs in the motion segments adjacent to a fusion. Most studies are of short-term, anecdotal, uncontrolled reports that pay particular attention only to the first motion segment immediately cephalad to the fusion. METHODS: Forty-two patients who had previously undergone a posterolateral lumbar or lumbosacral fusion underwent radiographic and clinical evaluation. Rate of fusion, range of motion, osteophytes, degenerative spondylolisthesis, retrolisthesis, facet arthrosis, disc ossification, dynamic instability, and disc space height were all studied and statistically compared with an age- and gender-matched control group. The patient's self-reported clinical outcome was also recorded. RESULTS: Degenerative changes occurred at the second level above the fused levels with a frequency equal to those occurring in the first level. There was no statistical difference between the study group and the cohort group in the presence of radiographic changes within the transition zone. In those patients undergoing fusion for degenerative processes, 75% reported a good to excellent outcome, whereas 84% of those undergoing fusion for spondylolysis or spondylolisthesis reported a good to excellent outcome. CONCLUSION: Radiographic changes occur within the transition zone cephalad to a lumbar or lumbosacral fusion. However, these changes are also seen in control subjects who have had no surgery.

A system for reporting the size and location of lesions in the spine.

STUDY DESIGN: A description of a method for standardizing the nomenclature used in reporting the size and location of lesions in the lumbar or thoracic spine is presented. OBJECTIVES: To make the reporting of findings on computed tomography or magnetic resonance imaging scans simpler and more accurate. SUMMARY OF BACKGROUND DATA: Over the past 10 years, three other systems have been proposed, and parts of each have been incorporated in this system. METHODS: This is a multicenter report. A group of 12 prominent physicians, including radiologists, neurosurgeons, orthopedic surgeons, and physiatrists, at 11 centers collaborated in the formulation of this system. RESULTS: In this system, areas in the axial plane, i.e., medial to lateral, are called "zones," and in the caudocranial direction, they are called "levels." The zones are the central canal zone, the subarticular zone, the foraminal zone, and the extraforaminal zone. In the caudocranial direction, the levels from above downward are the suprapedicle level, the pedicle level, the infrapedicle level, and the disc level. The size of a lesion can be rated by the descriptive words normal, mild, moderate, moderately severe, and severe, or by the numbers 1 to 5, with the number 1 indicating normal and the number 5 indicating severe. CONCLUSIONS: The authors of the present study believe that all health care professionals who care for the spine will find this nomenclature valuable in communicating with each other, in writing medical reports, in presenting reports at meetings, or in writing scientific articles.

Relationship of the dura, Hofmann's ligaments, Batson's plexus, and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament. An anatomical, radiologic, and clinical study.

With the advent of computed tomography (CT) and magnetic resonance imaging (MRI), visualization of soft tissue structures in the spinal canal, which were previously undetectable, is possible. This study was undertaken to more accurately identify these soft tissue layers and to determine factors such as when is a disc contained and when is it not; in discography, when the disc leaks, into what layer is the contrast going; or when a nuclear fragment creeps upward or downward, just where is it. The works of Fick, Dommisse, Kikuchi, Schellinger, Hofmann, Batson, and Parke were studied. The professors of anatomy of four major medical schools were consulted along with several neuroradiologists and embryologists. Forty lumbar spines were dissected (20 fresh, 20 preserved). Magnetic resonance imaging scans were taken. Photographs and photomicrographs were made. A fibrous membrane, first mentioned by Fick, can be identified lying anterior to the posterior longitudinal ligament and attaching to the deep layer of the posterior longitudinal ligament. It has been given relatively little attention in the past. This membrane has about one fourth the toughness of the dura and is made up largely of fibrous tissue. The veins of Batson lie on its dorsal surface and pierce it to go ventral to this membrane and enter the vertebral body. Batson's plexus crosses the disc space. The peridural membrane extends from one side to the other, spanning the width of the vertebral body and encircling the bony canal around the outside of the dura. There is a potential space between it and the dura. It does not cross the disc space. A probe can easily be passed posterior or anterior to it, between it and the posterior longitudinal ligament or between it and the vertebral body. We also identified Hofmann's ligament anterior to the dura, attaching the dura to the posterior longitudinal ligament. Laterally, tiny attachments between this fibrovascular membrane and the circumneural sheaths of the spinal nerves can be observed as the nerves enter the foramina. The posterior longitudinal ligament (PLL) is very tough and strong and seldom ruptures. The annulus frequently ruptures. Fragments of nucleus pulposus can creep out at the vertebral rim and get under the PLL and the peridural membrane. Hematoma can form by the same route and have the exact appearance as a sequestrated disc. There is no periosteum inside the vertebral canal. With MRI, hematomas can be differentiated from an extruded fragment. They may cause symptoms similar to an extruded disc but will probably heal with time.(ABSTRACT TRUNCATED AT 400 WORDS)

Unilateral lumbar fusion.

Unilateral fusion of the lumbar spine is rarely necessary or indicated. However, in patients with a "far-out syndrome" requiring decompression or in cases where unilateral posterior element resection is necessary for any reason, it may be both necessary and indicated. This unilateral destabilization effectively removes one leg of the tripod, rendering that intervertebral joint potentially unstable. The charts and radiographs of 13 patients (seven men, six women) with an average age of 60 years (range, 25 to 76) who underwent unilateral fusion were retrospectively reviewed. Follow-up time ranged from 12 1/2 to 2 years with a median follow-up of 8 years. Eleven of the fusions were at one level, and two were at two levels. Seven patients had a far-out syndrome secondary to degenerative scoliosis; four were secondary to spondylolisthesis. Two patients had an osteoid osteoma involving a pedicle. A paraspinal approach was used in the majority of patients. Autologous bone graft was used in all patients. Unilateral pedicle screw fixation was used in the last patient in the series. The fusion rate was 85% (11/13). Three patients were smokers, two of whom developed pseudarthrosis. Disc space height did not appear to affect fusion rate. There was no progression of slip noted in any of the patients. One complication was noted in this group: a moderate postoperative infection, which cleared spontaneously.

The long-range prognosis of arachnoiditis.

Fifty patients with arachnoiditis were studied, and long-term follow-up ranging from 10 to 21 years was obtained on 36 (72%). Prior to developing arachnoiditis, 90% originally had intervertebral disc disease, Pantopaque (Alcon Surgical, Ft. Worth, Texas) myelography, and subsequent lumbar spine surgery. Pain and functional disability tended to remain the same as at the time of diagnosis, although severity of symptoms fluctuated. Increased neurologic deficits were more frequently due to surgical intervention than to the natural course of the disease. Urinary symptoms characterized by urgency, frequency, and occasional incontinence, with no other apparent cause, developed late in 23%. Although the majority were able to walk and drive a car without limitation, ability to return to previous full-time occupations was markedly limited. The majority depended on daily narcotic analgesics; a few admitted to alcohol abuse. There were two deaths by suicide. Although other deaths were not directly related to arachnoiditis, the average lifespan was shortened by 12 years. Treatment results were disappointing. Arachnoiditis may be disabling; however, longterm follow-up indicates that progression of symptoms and functional impairment are not the natural course of the disease.

Anatomic analysis of pedicle cortical and cancellous diameter as related to screw size.

The effective thoracic and lumbar pedicle diameter as related to screw size for that pedicle was studied in six fresh-frozen human cadaver spines. Measurements of the pedicle were obtained before screw insertion using axial and coronal reformatted computed tomographic (CT) images, as well as graduated sounding of the pedicle. After sequentially loading each pedicle with increasingly larger screws, measurements were taken of the outer cortical diameters. Plastic deformation of the pedicle preceded pedicle fracture or cutout when the screw thread diameter became larger than the endosteal diameter or within 80% of the outer cortical diameter as measured from the CT scan. Pedicle screws did not obtain cortical purchase within the pedicle.

The Wiltse pedicle screw fixation system. Early clinical results.

Ninety-nine patients were studied prospectively after spine fusion augmented with the Wiltse pedicle screw fixation system. Follow-up ranged from 12 to 34 months, averaging 20 months. There were 33 men and 66 women. Their ages ranged from 20 to 86, with the average age of 52. This was the first spine surgery in 23 patients. Seventy-six patients had had prior spine surgery. Spine fusion was attempted at one to four levels of the lumbosacral spine. Major perioperative complications were seen in seven patients (7%). Hardware failure was seen in seven cases (7%). Union was assessed by radiographs at 1 year or more after surgery in 82 patients (85%). In those 82 patients, union was seen in 56 (68%) and nonunion in 26 (32%). Change in lordosis was measured in 54 patients. The average change was a loss of 1.7 degrees lordosis per level fused. A questionnaire was answered by 79 patients (81%). Overall, 55 (70%) stated that they had some benefit from surgery, ten (13%) had no change, and 13 (17%) were worse.

In situ arthrodesis without decompression for Grade-III or IV isthmic spondylolisthesis in adults who have severe sciatica.

Eight adults who had back pain and sciatica that was caused by Grade-III or IV isthmic spondylolisthesis of the fifth lumbar vertebra on the sacrum were treated consecutively by in situ arthrodesis without decompression. The anterior displacement of the fifth lumbar vertebra averaged 82 per cent (range, 66 to 118 per cent). The length of follow-up averaged 5.5 years (range, two to fourteen years). All of the arthrodeses resulted in a solid fusion and excellent relief of both the back pain and the sciatica. All of the preoperative neurological deficits resolved, with the exception of a decreased or absent Achilles-tendon reflex in two patients. There were no complications, and all of the patients returned to their preoperative occupations.

The Wiltse pedicle screw fixation system.

This article illustrates the application of the Wiltse pedicle screw fixation system and the general principles of pedicle screw insertion. The system is designed for stabilization of the lumbosacral spine. Indications complications, and personal results are reviewed.

New uses and refinements of the paraspinal approach to the lumbar spine.

The paraspinal approach was described by our group in 1968. It differs from the approach described by Melvin Watkins in 1953 in that it is a longitudinal separation of the sacrospinalis group between the multifidus and longissimus, and not between the lateral border of the entire sacrospinalis group and quadratus lumborum. Also, Watkins removed a flake of the iliac crest with muscles attached, which he swung cranially and medially. This article also describes several refinements not mentioned in the original article and gives several new uses for the approach. Specifically, its use for removing a far lateral disc, decompressing a far out syndrome, inserting pedicle screws, and for decompressing the opposite side from inside the vertebral canal is described.

Analysis of the morphometric characteristics of the thoracic and lumbar pedicles.

A total of 2,905 pedicle measurements were made from T1-L5. Measurements were made from spinal computerized tomography (CT) scan examinations and individual vertebral specimen roentgenograms. Parameters considered were the pedicle isthmus width in the transverse and sagittal planes, pedicle angles in the transverse and sagittal planes, and the depth to the anterior cortex in a line parallel to the midline of the vertebral body and along the pedicle axis. There was no significant difference between data obtained from CT scans and specimen roentgenograms. Pedicles were widest at L5 and narrowest at T5 in the transverse plane. The widest pedicles in the sagittal plane were seen at T11, the narrowest at T1. Due to the oval shape of the pedicle, the sagittal plane width was generally larger than the transverse plane width. The largest pedicle angle in the transverse plane was at L5. The posterolateral to anterolateral pedicle axis orientation in the transverse plane, seen at other levels throughout the thoracolumbar spine, reversed at T12. In the sagittal plane, the pedicles angled caudally at L5 and cephaladly from L3-T1. The depth to the anterior cortex was significantly longer along the pedicle axis than along a line parallel to the midline of the vertebral body at all levels with the exception of T12 and T11.

The management of patients with back pain and idiopathic vertebral sclerosis.

Twenty-two patients with severe back pain associated with radiologic evidence of vertebral sclerosis are reported. There were 19 women and 3 men; the average age was 42 years. Duration of pain averaged 4.3 years. The characteristic radiologic findings were diffuse sclerosis of the anterior inferior portion of the vertebral body and narrowing of the adjacent disc space. There was no extension of the sclerosis beyond the vertebral body, no paravertebral mass, and no loss of vertebral height. These radiologic characteristics, in conjunction with other clinical findings, should permit a diagnosis without the need for biopsy.

Chemonucleolysis. A ten-year retrospective study.

An 11.8-year median follow-up evaluation of 42 "ideal" patients who had chemonucleolysis was obtained by examination, questionnaire, and roentgenograms. The excellent and good rating of this group was 81%, as compared to the total of 135 patients previously evaluated at 42 months and showing 85.2%. No complications were noted. Disc space rewidening, after initial narrowing, was observed in eight patients and 26% of all discs injected. While all who showed rewidening had excellent results, widening was not necessary to achieve an excellent rating. Marked narrowing and sclerosis of intervertebral margins were seen in many excellent and good clinical results. Chemonucleolysis represents a viable option as definitive treatment for a herniated nucleus pulposus in carefully selected patients.

A biomechanical study of intrapeduncular screw fixation in the lumbosacral spine.

This laboratory experiment was undertaken to identify factors contributing to intrapeduncular screw fixation in the vertebra. Testing was performed in axial pull-out and cyclic loading modes using multiple screw designs inserted to various depths into fresh human lumbosacral vertebra. The degree of osteoporosis played a major role in pull-out strength. Larger diameter, full-threaded screws inserted deep enough to engage the anterior vertebral cortex resulted in the most secure fixation. In the sacrum, the second sacral pedicle was the weakest location of insertion. Screws aimed laterally into the ala at 45 degrees or medially into the first sacral pedicle resisted larger axial pull-out loads than those inserted straight anteriorly into the ala. Methyl methacrylate was found to restore secure fixation in previously-loosened screws and pressurization of cement doubled the pull-out force. In cyclic load tests, deeper-inserted screws were found to withstand a greater number of cycles before loosening. Measurements of pedicle outer cortical diameters were found in many specimens to be smaller than both the 4.5-mm and 6.5-mm diameter screws.