JBJS | The Use of Pedicle-Screw Internal Fixation for the Operative Treatment of Spinal Disorders*

The Journal of Bone & Joint Surgery, Volume 82, Issue 10

Current Concepts Review | October 01, 2000

The Use of Pedicle-Screw Internal Fixation for the Operative Treatment of Spinal Disorders*

Robert W. GainesJr., M.D.

Investigation performed at the Columbia Orthopaedic Group, Columbia Spine Center, and the Department of Orthopaedic Surgery, University of Missouri Health Sciences Center, Columbia, Missouri
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
Department of Orthopaedic Surgery, University of Missouri Health Sciences Center, One Hospital Drive, Columbia, Missouri 65212. E-mail address: rgaines@cogmds.com.

The Journal of Bone & Joint Surgery. 2000; 82:1458-1458

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Introduction

Pedicle screws have dramatically improved the outcomes of spinal reconstruction requiring spinal fusion.

Short-segment surgical treatments based on the use of pedicle screws for the treatment of neoplastic, developmental, congenital, traumatic, and degenerative conditions have been proved to be practical, safe, and effective.

The Funnel Technique provides a straightforward, direct, and inexpensive way to very safely apply pedicle screws in the cervical, thoracic, or lumbar spine.

Carefully applied pedicle-screw fixation does not produce severe or frequent complications.

Pedicle-screw fixation can be effectively and safely used wherever a vertebral pedicle can accommodate a pedicle screw - that is, in the cervical, thoracic, or lumbar spine.

Training in pedicle-screw application should be standard in orthopaedic training programs since pedicle-screw fixation represents the so-called gold standard of spinal internal fixation.

Pedicle screws have revolutionized the surgical treatment of spinal disorders, although their introduction and widespread adoption by spinal surgeons has created one of the most difficult regulatory problems ever seen in orthopaedics.

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Fig. 1:: The Roy-Camille plate^137,138 (left) and the Steffee variable-screw-placement (VSP) plate¹⁵² (right). The former plate, with its fixed screw-hole distances, was not able to accommodate the individual patient anatomy as well as the latter plate.

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Fig. 2:: Drawings clearly illustrating the benefits of screw triangulation to improve pullout strength, particularly when the screws are cross-connected to one another⁹. (Reprinted, with permission, from: Barber, J. W.; Boden, S. D.; Ganey, T.; and Hutton, W. C.: Biomechanical study of lumbar pedicle screws: does convergence affect axial pullout strength? J. Spinal Disord., 11: 216, 1998.)

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Fig. 3:: The 4R-4bar linkage collapse associated with parallel pedicle screws (left) can be resisted only by load-sharing through the fracture site (right)²³.

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Fig. 4:: The "JIKEI Index" easily relates bone-mineral density and pedicle-screw pullout strength with this simple x-ray-based scheme. Pullout strength is severely limited when there are spontaneous compression fractures as in stages 2 and 3. Pedicle-screw fixation is contraindicated when there is this much osseous deterioration¹⁵¹. (Reprinted, with permission, from: Soshi, S.; Shiba, R.; Kondo, H.; and Murota, K.: An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine, 16: 1336, 1991.)

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Fig. 5:: Model developed by the American Society for Testing and Materials for construct or subconstruct testing. Polyethylene blocks are used to mimic vertebral bodies. Here, under axial load, spinal deformity secondary to distortion at the longitudinal member-connector interface is seen^34,60. (Reprinted, with permission, from: Cunningham, B. W.; Sefter, J. C.; Shono, V.; and McAfee, P. C.: Static and cyclical biomechanical analysis of pedicle screw spinal constructs. Spine, 18: 1680, 1993.)

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Fig. 6:: Bar graphs showing the changes in pullout force (A) and bending stiffness (B) when screws with five and six-millimeter major diameters are compared. Improvements in both parameters are related directly to the major diameter of the screw^170,179. (Reprinted, with permission, from: Wittenberg, R. H.; Lee, K.-S.; Shea, M.; White, A. A., III; and Hayes, W. C.: Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength. Clin. Orthop., 296: 282, 1993.)

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Fig. 7:: Bar graphs showing differences in resistance to cyclic loading³⁴. All of these implant systems have been used extensively, although their biomechanical performance differs dramatically. The healing of the fusion is much better in patients with stiffer implants³⁴. VSP = variable screw placement (Steffee) plate, KPL = Kirschner plate, DLO = Dyna-lok plate, ISO = Isola rod, TSR = Texas Scottish Rite Hospital rod, CCD = Compact CD (Cotrel-Dubousset) rod, CDC = CD cold rolled rod, FIX = AO fixateur interne, CDS = CD standard rod, and KRO = Kirschner rod. (Reprinted, with permission, from: Cunningham, B. W.; Sefter, J. C.; Shono, V.; and McAfee, P. C.: Static and cyclical biomechanical analysis of pedicle screw spinal constructs. Spine, 18: 1681, 1993.)

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Fig. 8:: Photographs illustrating the Funnel Technique. A: The dorsal projection of the pedicle (red circle) is localized. B: A one-centimeter-diameter section of cortical bone is removed over the top of the pedicle with a burr or Lexcel rongeur. C: The cancellous bone within the pedicle is then visualized. D: The cancellous bone is removed with a curet until the cortical wall of the pedicle can be felt and visualized. This is followed by going deeper into the pedicle toward the isthmus. E: The Kerrison rongeur is used to remove the cortical bone peripherally so that the isthmus of the pedicle can be seen. F: Once the isthmus of the pedicle is directly palpated, a small two-millimeter pedicle probe is passed through the isthmus into the vertebral body. G: A larger (five-millimeter) probe then is used to enlarge the path through the isthmus of the pedicle. H and I: Small Steinmann pin segments (fifty-five millimeters in length) are placed into the probed pedicles as radiographic markers. (The anteroposterior [H] and lateral [I] c-arm images confirm the pedicle path. The lateral c-arm image [I] also confirms the length of the screw to be used; the depth of each Steinmann pin is measured after it is removed.) J: Threads then are cut into the pedicle with progressively larger taps until firm cortical purchase is achieved. The feel achieved during the tapping process determines the screw diameter that is used. K: A ball-tip probe is used to feel the pedicle in all directions: the bottom of the pedicle (in the vertebral body) and the superior, inferior, medial, and lateral inner walls of the pedicle. L: The screw then is inserted into the pedicle with the screwdriver. The purchase (insertional torque) must progressively increase until final seating. M: The anteroposterior and lateral c-arm images confirm proper positioning after all of the screws, rods, and connectors are inserted. (Grateful appreciation to Byron R. Tarbox, M.D., Wicharn Yingsakmongkol, M.D., Michael R. Viau, M.D., and Eldin E. Karaikovic, M.D., Ph.D., for assistance with the "funnel technique.")

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Fig. 9:: Graph showing improved screw-bending stiffness due to the addition of polymethylmethacrylate (PMMA) and polypropylene glycol-fumarate (PPF). (Reprinted, with permission, from: Wittenberg, R. H.; Lee, K.-S.; Shea, M.; White, A. A., III; and Hayes, W. C.: Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength. Clin. Orthop., 296: 284, 1993.)

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Fig. 10:: The load-sharing classification permits quantification of comminution of spinal fracture sites so that the load-sharing capability of the injured vertebral body itself, along with the implant system, can be determined. This approach has allowed surgeons to perform short-segment fixation for most isolated spinal fractures in cooperative patients^103,127. A: Comminution/involvement. 1 = little comminution (less than 30 percent), 2 = more comminution (30 to 60 percent), and 3 = gross comminution (more than 60 percent) on computed tomographic sagittal plane sections. B: Apposition of fragments. 1 = minimal displacement, 2 = spread of displacement (at least two millimeters of displacement of less than 50 percent of the cross section of the body), and 3 = wide displacement (at least two millimeters of displacement of more than 50 percent of the cross section of the body). C: Deformity correction. 1 = kyphotic correction of 3 degrees or less, 2 = kyphotic correction of 4 to 9 degrees, and 3 = kyphotic correction of 10 degrees or more on lateral plain radiographs. (Reprinted, with permission, from: McCormack, T.; Karaikovic, E.; and Gaines, R. W.: The load sharing classification of spine fractures. Spine, 19: 1742, 1994.)

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Fig. 11-A:: Figs. 11-A through 11-E: A patient with severe thoracic scoliosis who had excellent correction of both the primary curve and the tilt angle with use of pedicle screws for the caudal platform. The screws' ability to control the caudal segments in the fusion in a very secure manner allowed much better realignment of the tilt angle than would have been possible with only hook systems^10,67.
Fig. 11-A: Posteroanterior and forward-bending posteroanterior photographs.

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Fig. 11-B:: Posteroanterior radiographs demonstrating an 88-degree curve with the patient standing and a 53-degree right thoracic curve with the patient stretching.

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Fig. 11-C:: Posteroanterior radiograph made ten months postoperatively, demonstrating correction and restored compensation.

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Fig. 11-D:: Postoperative posteroanterior and forward-bending posteroanterior photographs, demonstrating good balance and mobility in the lumbar spine.

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Fig. 11-E:: Preoperative and postoperative standing lateral radiographs demonstrating correction of the midthoracic kyphotic deformity.

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Fig. 12:: Intermediate-grade spondylolisthesis and/or degenerative spondylolisthesis can now be well treated with reduction with the posterior approach only, with use of interbody fusion with cages and pedicle screws. The union rate is very high, and straightforward reduction of intermediate slips is safe neurologically, provided that the roots are visualized and protected carefully during the procedure.

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Fig. 13:: Reconstruction of spinal fractures is much more secure with pedicle screws. In this patient, realignment of adjacent-level injuries at the third and fourth thoracic vertebrae was accomplished with short-segment pedicle-screw instrumentation in the second and fifth thoracic vertebrae. (Case contributed by Dr. Marc Asher.)

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Fig. 14-A:: Figs. 14-A through 14-D: Spinal osteotomy has become a much more predictable surgical technique since the adoption of pedicle screws, which provide more secure fixation than any previous technique.
Fig. 14-A: The site of the corrective osteotomy should be at the apex of the deformity, with removal of the laminar arch, the pedicles, and the part of the vertebral body and disc that represent the apex of the deformity.

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Fig. 14-B:: This patient had a post-fracture flatback deformity after Harrington instrumentation, with fixed deformity in the lumbar spine. The osteotomy was performed through the third lumbar level.

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Fig. 14-C:: Close-up preoperative and postoperative lateral radiographs.

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Fig. 14-D:: Preoperative and postoperative lateral photographs showing dramatic realignment.

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Fig. 15:: In tumor reconstructions, pedicle screws permit segmental resection, realignment, and reconstruction over shorter segments than was possible before their introduction. In this patient, a chordoma of the sacrum was resected, and reconstruction was performed with use of short-segment anterior and posterior approaches along with pedicle screws and sacral and iliac screws¹⁵⁵. (Case contributed by Dr. Stefano Boriani.)

History of Spinal Internal Fixation with Pedicle Screws

Hadra⁶⁵ first used silver-wire internal fixation for the treatment of a cervical fracture-dislocation and tuberculous spondylitis in 1891. Later, King⁸⁴ introduced facet screws for the treatment of degenerative lumbar conditions. Although Boucher¹⁷ has been widely credited with the first use of pedicle screws in North America, his report suggests that his innovation was a longer facet screw that occasionally obtained oblique purchase across the pedicle. His screws were not aimed down the long axis of the pedicle. Thus, it seems that Harrington and Tullos⁶⁸ deserve credit for the first deliberate attempt to put pedicle screws through the isthmus of the pedicle. Their report, published in 1969, described the attempted reduction of two cases of high-grade spondylolisthesis.

Pioneering the use of pedicle-screw internal fixation proceeded in France and Switzerland during the 1970s. Clinical success with the screws was reported during the 1980s by investigators including Cotrel and Dubousset³¹, Dick⁴⁰, Roy-Camille et al.^137,138, and Louis⁹⁹.

A strong stimulus to North American use of the pedicle-screw technique was the presentation by Roy-Camille at the 1979 American Academy of Orthopaedic Surgeons meeting in San Francisco. Subsequently, a number of American surgeons began to use pedicle screws in the United States. Arthur Steffee used them most creatively.

Steffee et al.¹⁵² developed the variable-screw-placement (VSP) plate, which permitted pedicle screws to be placed according to individual patient anatomy. This device provided much more clinical latitude than the Roy-Camille plate^137,138, which had fixed screw-hole distances for application of the screws (Fig. 1).

Recognizing the clinical utility of pedicle-screw fixation, the North American Spine Society and the Scoliosis Research Society collaborated on a series of introductory meetings to educate spinal surgeons about this new technique. The first of these meetings was held in 1984. These two societies subsequently mutually sponsored the International Meeting on Advanced Spine Techniques, and this annual meeting continues to be held to the present day.

Since the introduction of pedicle screws, engineers, surgeons, radiologists, neurophysiologists, anatomists, epidemiologists, and statisticians have made fundamental efforts to improve what was recognized universally as a clinical liability in surgical spine care: the lack of truly high-quality spinal internal fixation similar to what was available for internal fixation of long bones.

The basic and clinical science of pedicle screws developed from their introduction and infancy in the early 1970s to widespread acceptance, as indicated in "State-of-the-Art Treatment" statements by the North American Spine Society in 1993 and 1996, which endorsed the use of pedicle screws by experienced surgeons. Review articles described the evolution of treatment methods as surgical experience accumulated^{33,48,62,114,158}.

Anatomy of the Human Pedicle

The anatomy of the human pedicle has been studied exhaustively in different races^{6,25,26,73,83}, in children^50,108,140, and in adults^123,146. Patterns of pedicle anatomy unique to the cervical spine^44,81,82, the thoracic and the lumbar spine^{45,46,109,126,132,146,148,159,160}, and the sacrum^{47,94,120,172,173} have been clearly identified. Measurements of the outer and inner diameters of the pedicle have been performed extensively^71,121. The inner diameter of the pedicle - the critical surgical dimension - has been shown to be more directly related to the height of the patient than to the gender⁸¹. However, wide individual variations within common patterns of anatomy are the rule. This forces the surgeon to understand the individual anatomy of the patient, in order to achieve clinical success, and to appreciate the patterns of pedicle anatomy that are common to the human race in general. There do not seem to be more than modest differences in pedicle anatomy from race to race^{6,25,26,73,83}.

Biomechanical Studies of Pedicle Screws and Pedicle-Screw-Based Constructs

In 1986, we^52,53 clearly demonstrated the improved quality of spinal internal fixation provided by a pedicle-screw implant with a fixed link to a plate, in the first nonfailure stability testing done for spinal fractures. We also showed the fundamental importance of load transfer across the spinal column itself along with the implant - a concept known as load-sharing⁵³, which was subsequently widely adopted by the spinal surgery community.

Biomechanical tests of pedicle-screw constructs have demonstrated the fundamental importance of the bone-implant interface, bone density, and screw pullout strength^{11,28,63,66,87,179}. The essential need for fit and fill of the screw in the isthmus of the pedicle has been proved^19,88,106. The direct relationship between pullout strength and insertional torque has been well demonstrated¹⁷⁸, and the fundamental improvement in pullout strength obtained by cross-linking^{39,64,100,130} (that is, attachment of the two screws in an individual vertebra with use of a metal cross-link) has been documented. The stabilizing influence of using converging screws (a high pedicle angle [Fig. 2]), if possible, also was emphasized^9,23,139.

The internal forces and moments of bilevel constructs have been measured exhaustively with strain gauges on all components of rod and plate-based constructs, and the fundamental importance of load-sharing through the vertebral column has been reemphasized. Without load-sharing, an unstable four-bar mechanism was clearly demonstrated when all four pedicle screws were parallel (Fig. 3)²³. In addition to in vitro testing, finite-element modeling has been used extensively^59,96 to analyze stress transfer through implants as well as through implant-based constructs.

The bone-mineral density of vertebrae has been evaluated exhaustively with densitometry. Japanese investigators demonstrated conclusively that patients with multiple spontaneous compression fractures were very poor candidates for pedicle-screw-based internal fixation because their bone-mineral density was poor (one-fifth of normal bone density) preoperatively (Fig. 4)¹⁵¹. Other authors have strongly suggested the routine use of bone-mineral-density testing before pedicle-screw-based surgery, although mild osteoporosis (bone-mineral density of less than 100 milligrams per milliliter) did not seem to affect screw purchase or clinical outcome adversely⁸⁷.

The success of hook-based constructs compared with that of screw-based constructs was shown to be based on bone-mineral density^28,112. In very osteoporotic specimens, hook-based claw constructs performed as well as screw-based constructs²⁸. A few authors have suggested use of both a screw and a hook at the same level^111,174.

The enthusiasm for pedicle-screw fixation among spinal surgeons created a group of engineering collaborators who quickly became extremely knowledgeable regarding the engineering issues related to structural and clinical success. A model for fatigue testing that is now widely used was adopted by the American Society for Testing and Materials (Fig. 5)^34,60. A corpectomy model is created with two polyethylene blocks to mimic vertebrae, which are attached to a standard Instron tester (Instron, Canton, Massachusetts). This model can be used for subcomponent or construct testing.

The major diameter of a pedicle screw has been shown to control pullout strength (Fig. 6)^170,179. Bicortical purchase both in individual vertebrae and in the sacrum increased pullout strength fundamentally¹⁵², although bicortical purchase, except at the sacrum, has not been widely adopted by surgeons because of the risk of injury to the aorta or vena cava. Bicortical sacral purchase, however, has been proved to be extremely safe and has gained widespread acceptance. The first sacral segment has been analyzed exhaustively, and several safe and secure fixation sites have been demonstrated within it^{47,94,120,172,173}. The anatomical liabilities of the second sacral segment also have been clearly shown.

The presence of one or more pedicle fractures has been shown to reduce, although not to completely eliminate, the integrity of pedicle-screw-based constructs⁸⁵.

Many different styles of mechanisms have been developed by manufacturers to attach a pedicle screw to a longitudinal member (a plate or a rod); some are quite rigid and some, less rigid. All of these designs have shown some clinical utility, although there were dramatic differences in their biomechanical performance in vitro (Fig. 7)³⁴. The patient's body weight has been shown to be the main determinant affecting structural survival of rods used for scoliosis correction⁷⁵.

Nitrite has been added to the surface of the screw to improve surface hardness⁹⁷, and both titanium and steel implants have been widely investigated, manufactured, and used. Titanium implants are used for patients who are allergic to nickel, chromium, or cadmium or for those who may require frequent postoperative magnetic resonance imaging or computed tomographic scans^43,128,163.

Techniques of Safe Pedicle-Screw Application

Roy-Camille et al.^137,138 suggested that a pedicle screw should be introduced by drilling the path and then applying the screw. Most American surgeons realized the danger of this approach; they adopted a blunt technique to identify the pedicle and routinely used biplane image intensification during the placement of pedicle screws¹⁵². The use of taps of gradually increasing diameter to assess the quality of cortical purchase through the isthmus of the pedicle, and the use of image intensification to assess the length of the screw necessary to obtain purchase in the vertebral body but not through the anterior vertebral cortex, have become standard procedures for safe screw application, resulting in strong fixation. This technique, called the Funnel Technique, is now used widely (Fig. 8).

Irrigation with saline solution down the pedicle⁵, and visualization of the pedicle by an endoscope⁵¹, have both been used to assess proper screw placement. Routine monitoring of somatosensory¹³⁵ and dermatomal somatosensory²⁹ evoked potentials, as well as electromyography^{21,27,36,37,56,72,135,136,166}, also have been used for this purpose. Unpublished data have suggested the need for routine laminectomy in patients with pedicle-screw fixation, although this approach has not been adopted widely. Hertlein et al.⁷⁰ described the application of pedicle screws from the anterior approach. The use of robotics¹ and of computer-based guidance technology also has been investigated^{14,22,58,79,115,116,124,125}.

Supplemental Techniques of Pedicle-Screw Fixation

Methylmethacrylate has been used in vitro and in vivo to improve the fixation of pedicle screws in vertebrae^129,170,179 (Fig. 9). The improvement in pullout strength is obvious. However, the occasional spread of the cement into the spinal canal limits the successful application of this technique. The use of calcium phosphate¹²² has been reported, but there has been very limited acceptance of this option. The use of carbonated apatite also has been reported⁹⁸.

Early clinical reports of pedicle-screw fixation demonstrated that most pedicle screws did not obtain cortical purchase (only cancellous purchase was obtained), whereas recent reports have emphasized the essential nature of cortical purchase and the direct relationship between pullout strength, insertional torque, and bone-mineral density^121,178. In our practice, the use of the direct Funnel Technique to identify the pedicle isthmus permits tapping the isthmus to obtain cortical purchase for each inserted screw. Bicortical purchase is routinely used at the first sacral level but never at any other level.

Supplemental Screw Sites

The improvements in fixation at individual vertebral levels stimulated the need for improvements in spinopelvic fixation to manage spinopelvic disorders with greater security. Iliosacral screws, iliac-wing screws, intrasacral fixation, and lumbosacral end-plate fixation all have been recommended, researched, and adopted in limited applications for specific indications^102,119.

Use of Bone-Grafting Materials

With improved spinal internal fixation, surgeons have attempted to limit their use of extra autogenous bone graft to avoid morbidity at the donor site. Bone stimulators¹³⁴, allograft materials¹⁸, synthetic hydroxyapatite, calcium phosphate, and coral all have been used with pedicle-screw-based constructs, with greater or lesser success depending on the pathology and the host-related variables⁴. Smoking has been demonstrated to be a risk factor for pseudarthrosis in some series but not others^8,55.

Alterations in Spinal Fusion Techniques Due to Improved Skeletal Fixation Provided by Pedicle-Screw-Based Implants

Many surgeons have abandoned formerly routine techniques of spinal fusion such as decortication of the posterior elements or facet fusion when pedicle-screw-based implants are used. The time to healing of a scoliosis fusion was reduced from six to twelve months in the 1960s to two to four months in the 1990s because of the secure internal fixation provided by pedicle-screw-based implants⁶⁷. There has been a decrease in the need for postoperative bracing of patients with constructs based on internal fixation with pedicle screws. This has been particularly notable in patients with scoliosis^{10,67,95,110,154,155}.

Spinal Column Biology Around Pedicle-Screw-Based Implants

Stress-shielding of bypassed vertebrae under implants that were deliberately disproportionately large has been well documented in dogs³². However, loosening of these huge implants from the host spine occurred when the bypassed spinal segment was osteoporotic. After screw-loosening, the stress-shielding effect of the disproportionately large implants was alleviated and the bone density of the bypassed segment of the spinal column returned to normal.

Imaging of Pedicle-Screw-Based Constructs to Assess Screw Placement and to Document Union of a Spinal Fusion

The limitations of plain radiographs and computed tomography in demonstrating proper screw position have been well documented^54,117,165. Surgical exploration is the reference standard for determining union. Only the radiographic demonstration of trabeculation across the intertransverse (lateral) or interbody area comes close to surgical exploration with regard to accuracy in determining the presence or absence of solid union of a spinal fusion¹⁵.

Changes in Adjacent Segments

Static kinematic testing has been used to examine and identify the increased motion that occurs at motion segments adjacent to spinal constructs immobilized by pedicle-screw-based implants¹⁷⁵. Finite-element models also have demonstrated this increased motion⁹⁶.

Case reports^30,93 of spinal fractures occurring adjacent to spinal instrumentation constructs have documented clinically the vulnerability of the spine after a violent injury. Disc pressures are substantially changed adjacent to a spinal instrumentation construct as well^35,164. Other case reports have demonstrated the necessity of protecting the supraspinous and interspinous ligaments, the ligamentum flavum, and the capsular ligaments at segments adjacent to a spinal instrumentation construct, and they have shown the importance of restoring balance in the sagittal plane to avoid degeneration of adjacent segments⁴⁹.

Indication for Pedicle-Screw-Based Fixation

Although the initial clinical use of pedicle-screw-based implants was based on their theoretical benefits, their effectiveness in facilitating fusion now has been demonstrated conclusively^{55,144,145,149,177}. Collaborative and individual studies^{8,55,167,176,177} have demonstrated statistically higher fusion rates associated with use of these implants. The functional benefits for patients also have been demonstrated conclusively with use of preoperative and postoperative testing¹⁶⁷.

Addition of Interbody Fusion to Supplement Pedicle-Screw-Based Posterolateral Fusion

Mainly on the basis of the results of treatment of scoliosis and the desire to ensure load-sharing in the anterior column, many low-back surgeons in the United States routinely began to use circumferential fusion for all cases of degenerative spinal disease after anterior and middle-column load-sharing was demonstrated to be beneficial biomechanically^55,152,156. Anterior grafting was performed either with an anterior open procedure, a laparoscopically based anterior procedure, or posterior lumbar interbody fusion at the same time as the pedicle-screw-based surgery. Some authors have suggested that the routine use of circumferential fusion improves the healing rate in smokers⁵⁵ and that the union rate is better than that obtained with pedicle-screw-based intertransverse fusion alone⁸.

The development of prosthetic devices that contain autograft or allograft has added another variable to this clinical interface that is still under investigation. An unpublished review of the results in our patients demonstrated a 92 percent union rate with pedicle-screw-based posterolateral fusion alone, without cages, using only the autograft obtained from laminectomy for the majority of patients. None of the patients had anterior surgery. The union rate in smokers and nonsmokers was the same.

Complications Associated with the Use of Pedicle Screws

Complications have accompanied the use of pedicle screws. The rate of screw misplacement has ranged from 0 percent¹⁰ to 2 percent²⁰ to 25 percent⁹⁵ in patients with scoliosis and to nearly 4.2 percent^{8,16,49,101,160,168} in those with degenerative diseases. A learning curve has been demonstrated for surgeons in general⁵⁴.

A variable prevalence of nerve-root and/or cauda equina injury has been reported to be associated with pain and sensory deficit in some patients^{20,55,113,167,168}. The prevalence has been reported to be as high as 11 percent¹¹⁴ and as low as 1 percent¹⁵⁰ to 2 percent^20,113. However, most misplaced screws do not create nerve-root injury^{20,54,145,154}. Safe removal of screws that were drilled into the spinal canal has been reported⁴¹.

A high prevalence of screw misplacement associated with drilling¹⁶⁰ rather than with the blunt technique of screw application has been clearly demonstrated²⁰. Computer-based navigation techniques have been developed and have been suggested for clinical application^{14,22,58,79,115,116,124,125}. Some authors have suggested that the routine use of computer navigation improves screw placement. Our own experience, however, has been that the increased operating time does not improve the quality of screw placement but increases tremendously the expense and potential danger.

A dural injury was reported in seven of 124 patients¹⁶⁸ and in two of eighty-nine patients¹⁴⁵ in two series of pedicle-screw fixation for the treatment of degenerative spine disease. Deep-infection rates have ranged from 1.1 percent (five of 470 patients)⁸ to 1.2 percent⁵⁵ to 2.3 percent (two of eighty-five patients)⁵⁷ to 4.2 percent (four of ninety-six patients)¹⁴⁹. Prompt wound débridement and administration of antibiotics, with preservation of the implant and subsequent delayed primary closure, have been adopted routinely, with acceptable intermediate-term clinical outcomes⁵⁷. The use of pedicle-screw-supplemented fusion has been reported to enhance the results of primary operative treatment of hematogenous discitis and osteomyelitis¹³¹.

The frequency of screw breakage has ranged from 2.6 percent⁸ to 4.9 percent⁵⁵ to 9 percent⁶ to36 percent¹¹⁴ to as high as 60 percent¹⁰⁵. However, survivorship analysis of a series of patients who had degenerative disease indicated that the clinical survival of pedicle-screw-based constructs was similar to that of total hip and total knee reconstructions¹⁰¹. The two alarmingly high screw-breakage rates^105,114 were reported when highly comminuted spinal fractures were internally fixed with posterior short-segment pedicle-screw-based instruments. The load-sharing classification^103,127 provides a simple way to differentiate fractures according to comminution. It suggests that anterior vertebrectomy, strut-grafting, and instrumentation be performed in patients with severely comminuted injury to avoid the high screw-breakage rates that occur when short-segment posterior pedicle-screw-based instrumentation is used for highly comminuted injuries (Fig. 10).

Screw pullout and screw-connector disengagement have been reported both in in vitro testing and in patients^8,16,55. Rod breakage has been reported only rarely. Most authors have described problems with the screw or the bone-screw interface but not with the longitudinal component^8,16,55.

Screw-thread fracture has never been reported, to my knowledge. There are established methods for removing broken screws^42,104.

Union Rate Associated with Pedicle-Screw-Based Constructs

The union rate associated with pedicle-screw-based constructs generally has been reported to be nearly 90 percent^{8,20,55,167,176,177}. The benefits provided by very stiff implants were demonstrated statistically in a prospective, randomized trial comparing the rate of union associated with these implants with the rates obtained without use of an implant and with use of a semirigid implant¹⁷⁷.

Late Results Associated with the Presence of Implants

Implant-related pain has led to the need to remove the implant from some patients. The clinical benefits of implant removal have not been uniformly demonstrated⁷⁴.

Clinical Advances Secondary to the Use of Pedicle Screws and Pedicle-Screw-Based Constructs

The use of pedicle screws has resulted in dramatic clinical improvements in the surgical care of spinal diseases; these improvements can be catalogued according to the disease process involved.

Scoliosis

Detailed assessment of patients who have been surgically treated for scoliosis has demonstrated that the routine use of pedicle screws produces better results, in terms of correction in the coronal and sagittal planes and maintenance of the correction, than does the use of hook-based constructs^10,67. There is also better tilt-angle correction and rotational correction (Fig. 11-A, Fig. 11-B, Fig. 11-C, Fig. 11-D, and Fig. 11-E)^10,67. The routine use of pedicle-screw-based constructs has induced many surgeons to abandon the use of braces or casts postoperatively, with low rates of screw and rod breakage^10,20,67, and it also has greatly facilitated the care of adult patients with degenerative scoliosis^38,110. However, when fusion of the spine to the pelvis is necessary, it should include iliac fixation for routine success³⁸.

Spondylolisthesis

Routine use of pedicle screws for the treatment of spondylolisthesis has increased the union rate to 94 percent and improved the ability to reduce and maintain reduction of higher-grade slips^{7,80,141,149,152}. The ability to spare levels from fusion also has been demonstrated clearly in these patients^152,156 (Fig. 12). Monosegmental fusion with use of posterior lumbar interbody fusion and pedicle-screw-based reduction has proved very successful in children.

Vertebrectomy at the fifth lumbar level with reduction of the fourth lumbar vertebra onto the first sacral vertebra and with use of only single-level instrumentation and fusion has been widely accepted as a routine treatment for spondyloptosis⁹¹.

Spinal Fracture

The use of pedicle screws for the treatment of spinal fracture has allowed most surgeons to accomplish short-segment instrumentation (instrumentation extending from only one vertebra cephalad to the damaged vertebra and to one vertebra caudad to it)^{13,86,103,105,142}. Although initial screw-breakage rates were high¹⁰⁵, they can be reduced to zero when the influence of comminution of the injured vertebral body is appreciated and the choice between anterior and posterior short-segment instrumentation is based predominantly on the load-sharing classification¹²⁷ (Fig. 13). The limits of in situ bending have been clearly defined⁶³.

Pedicle screws have dramatically facilitated the management of burst fractures of the fifth lumbar vertebra^118,147 as well as the treatment of posttraumatic kyphosis in second and third-world countries^24,90,171.

Simple Lumbar Degenerative Disc Disease

The use of pedicle-screw-based implants has resulted in union rates of approximately 95 percent after simple lumbar fusions for two and three-level lesions^{8,55,107,167,176,177}. This union rate was possible previously only with a single-level fusion.

Spinal Osteotomy

The fixation provided by pedicle screws has markedly altered the clinical course in patients with fixed multiplanar spinal deformities due to ankylosing spondylitis^69,89,161 and in those with severe flatback deformity⁹². Patients now can walk with use of a removable brace after the osteotomy. They spend no time in bed, whereas periods of one to two months in bed were routine for patients who wore a plaster cast before the advent of the secure fixation provided by pedicle screws. Although it is difficult to prove, the postoperative neurological problems encountered secondary to major osteotomy are also thought to be greatly reduced by the secure short-segment fixation provided by pedicle screws. The loss of correction also must be somewhat reduced (Fig. 14-A, Fig. 14-B, Fig. 14-C, and Fig. 14-D).

Spina Bifida

The unique benefits of pedicle screws in the correction, stabilization, and maintenance of correction of spina bifida and postlaminectomy deformities have been well documented¹³³. The reduction in the period of immobilization and the quality of the final outcome are difficult to demonstrate statistically because these deformities are unusual and the treatment is rarely standardized. However, the acceptance of pedicle screws for the treatment of these particularly difficult problems has been notable.

Pars Interarticularis Defects

Repair of pars interarticularis defects has been facilitated considerably by the use of a pedicle screw at the cephalad end of the defect; a hook, wire, or cable then is used to provide internal fixation to the lamina^78,141,150. The infrequent need for surgical repair of these defects makes statistical documentation of the effectiveness of screws difficult to prove. However, their use has made a number of new and different techniques available to surgeons and patients.

Neoplasms

Pedicle screws have facilitated the short-segment treatment, including total vertebrectomy, of primary and metastatic neoplasms^61,77. Short-segment instrumentation is more appropriate in some of these patients than it is in others. The use of short-segment treatment facilitated by pedicle screws has provided the opportunity to perform safe radical resection of primary spinal tumors for the first time^153,157 (Fig. 15). Sacral and lumbosacral resection of chordomas is now practical, and the outcomes are predictable⁶¹.

Lesions of the Cervical Spine and the Cervicothoracic Junction

The use of pedicle screws has been very helpful in the treatment of traumatic and developmental lesions at the cervicothoracic junction. Pedicle screws were used frequently from the second to the seventh cervical vertebra by Abumi and Kaneda² and at the cervicothoracic junction by Albert et al.³. Pedicle-screw constructs have been compared favorably with lateral-mass plate constructs⁷⁶.

Spinopelvic Trauma

Severe, traumatic spinopelvic disruption and vertical fractures of the sacrum have been repaired successfully with surgical use of a combination of either iliac or iliosacral screws and caudad lumbar pedicle screws^12,143.

Overview

Although the routine use of pedicle screws has not been free of complications, it has dramatically improved the prevalence of union after spinal fusion. It also has facilitated shorter-segment instrumentation for fractures and spondylolisthesis and has made total vertebrectomy for neoplasms practical, with predictable outcomes. In addition, the chance of achieving proper realignment and relief of pain has been improved greatly, with fewer complications after the surgical procedure.

The proper use of pedicle screws requires a detailed knowledge of the patient's pedicle anatomy, the routine use of image intensification during application of the screws, the use of blunt identification of the isthmus of the pedicle with employment of the Funnel Technique, meticulous attention to wound care, the use of primarily autograft material to achieve fusion, and the availability of a full inventory of implants. Slow, supervised rehabilitation, with acknowledgment of the fundamental importance of load-sharing by the spinal column itself along with the implant, is also essential until healing of the fusion occurs.

References

Abdel-Malek, K.; McGowan, D. P.; Goel, V. K.; Kowalski, D.; and Smith, S. B.: Bone registration method for robot assisted surgery: pedicle screw insertion. Proc. Inst. Mech. Eng., Part H - J. Eng. Med., 211: 221-233, 1997.

Abumi, K., and Kaneda, K.: Pedicle screw fixation for nontraumatic lesions of the cervical spine. Spine, 22: 1853-1863, 1997; erratum, Nurse Pract., 22: 143, 1997.

Albert, T. J.; Klein, G. R.; Joffe, D.; and Vaccaro, A. R.: Use of cervicothoracic junction pedicle screws for reconstruction of complex cervical spine pathology. Spine, 23: 1596-1599, 1998.

An, H. S.; Lynch, K.; and Toth, S.: Prospective comparison of autograft vs. allograft for adult posterolateral lumbar spine fusion: differences among freeze-dried, frozen, and mixed grafts. J. Spinal Disord., 8: 131-135, 1995.

An, H. S., and Benoit, P. R.: Saline injection technique to confirm pedicle screw path: a cadaveric study. Am. J. Orthop., 27: 362-365, 1998.

Anand, N., and Tanna, D. U.: Unconventional pedicle spinal instrumentation. The Bombay experience. Spine, 19: 2150-2158, 1994.

Aota, Y.; Kumano, K.; Hirabayashi, S.; and Ogawa, Y.: Reduction of lumbar spondylolisthesis using a CDI pedicle screw system. Arch. Orthop. and Trauma Surg., 114: 188-193, 1995.

Bailey, S. I.; Bartolozzi, P.; Bertagnoli, R.; Boriani, S.; van Beurden, A. F.; Cross, A. T.; Friedl, H. P.; Gurr, K. R.; Halm, H.; Kruls, H. J.; Metz-Stavenhagen, P.; and Schulze, K. J.: The BWM spinal fixator system. A preliminary report of a 2-year prospective, international multicenter study in a range of indications requiring surgical intervention for bone grafting and pedicle screw fixation. Spine, 21: 2006-2015, 1996.

Barber, J. W.; Boden, S. D.; Ganey, T.; and Hutton, W. C.: Biomechanical study of lumbar pedicle screws: does convergence affect axial pullout strength? J. Spinal Disord., 11: 215-220, 1998.

Barr, S. J.; Schuette, A. M.; and Emans, J. B.: Lumbar pedicle screws versus hooks. Results in double major curves in adolescent idiopathic scoliosis. Spine, 22: 1369-1379, 1997.

Bennett, G. J.; Serhan, H. A.; Sorini, P. M.; and Willis, B. H.: An experimental study of lumbar destabilization. Restabilization and bone density. Spine, 22: 1448-1453, 1997.

Bents, R. T.; France, J. C.; Glover, J. M.; and Kaylor, K. L.: Traumatic spondylopelvic dissociation. A case report and literature review. Spine, 21: 1814-1819, 1996.

Benzel, E. C., and Baldwin, N. G.: Crossed-screw fixation of the unstable thoracic and lumbar spine. J. Neurosurg., 82: 11-16, 1995.

Berlemann, U.; Monin, D.; Arm, E.; Nolte, L. P.; and Ozdoba, C.: Planning and insertion of pedicle screws with computer assistance. J. Spinal Disord., 10: 117-124, 1997.

Blumenthal, S. L., and Gill, K.: Can lumbar spine radiographs accurately determine fusion in postoperative patients? Correlation of routine radiographs with a second surgical look at lumbar fusions. Spine, 18: 1186-1189, 1993.

Blumenthal, S., and Gill, K.: Complications of the Wiltse pedicle screw fixation system. Spine, 18: 1867-1871, 1993.

Boucher, H. H.: A method of spinal fusion. J. Bone and Joint Surg., 41-B(2): 248-259, 1959.

Brantigan, J. W.: Pseudarthrosis rate after allograft posterior lumbar interbody fusion with pedicle screw and plate fixation. Spine, 19: 1271-1279, 1994.

Brantley, A. G.; Mayfield, J. K.; Koeneman, J. B.; and Clark, K. R.: The effects of pedicle screw fit. An in vitro study. Spine, 19: 1752-1758, 1994.

Brown, C. A.; Lenke, L. G.; Bridwell, K. H.; Geideman, W. M.; Hasan, S. A.; and Blanke, K.: Complications of pediatric thoracolumbar and lumbar pedicle screws. Spine, 23: 1566-1571, 1998.

Calancie, B.; Madsen, P.; and Lebwohl, N.: Stimulus-evoked EMG monitoring during transpedicular lumbosacral spine instrumentation. Initial clinical results. Spine, 19: 2780-2786, 1994.

Carl, A. L.; Khanuja, H. S.; Sachs, B. L.; Gatto, C. A.; vomLehn, J.; Vosburgh, K.; Schenck, J.; Lorensen, W.; Rohling, K.; and Disler, D.: In vitro simulation. Early results of stereotaxy for pedicle screw placement. Spine, 22: 1160-1164, 1997.

Carson, W. L.; Duffield, R. C.; Arendt, M.; Ridgely, B. J.; and Gaines, R. W., Jr.: Internal forces and moments in transpedicular spine instrumentation. The effect of pedicle screw angle and transfixation - the 4R-4bar linkage concept. Spine, 15: 893-901, 1990.

Chang, K. W.: Oligosegmental correction of post-traumatic thoracolumbar angular kyphosis. Spine, 18: 1909-1915, 1993.

Chen, I. H.; Hou, C. H.; Huang, C. I.; and Lee, L. S.: Measurement of Chinese lumbar pedicles: with special reference to transpedicular screw fixation. Chung Hua I Hsueh Tsa Chih, 53: 351-356, 1994.

Cheung, K. M.; Ruan, D.; Chan, F. L.; and Fang, D.: Computed tomographic osteometry of Asian lumbar pedicles. Spine, 19: 1495-1498, 1994.

Clements, D. H.; Morledge, D. E.; Martin, W. H.; and Betz, R. R.: Evoked and spontaneous electromyography to evaluate lumbosacral pedicle screw placement. Spine, 21: 600-604, 1996.

Coe, J. D.; Warden, K. E.; Herzig, M. A.; and McAfee, P. C.: Influence of bone mineral density on the fixation of thoracolumbar implants. A comparative study of transpedicular screws, laminar hooks, and spinous process wires. Spine, 15: 902-907, 1990.

Coscia, M. F.; Trammell, T. R.; Popp, B.; Gawande, S. R.; Fitzgerald, J.; and Scott, J. R.: Effect of anesthetic variables on dermatomal somatosensory-evoked potential monitoring in elective lumbar spinal surgery. J. Spinal Disord., 8: 451-456, 1995.

Coscia, M. F.: Pediatric Chance fracture associated with pedicle screw use: a case report. Spine, 22: 2698-2701, 1997.

Cotrel, Y.; Dubousset, J.; and Guillaumat, M.: New universal instrumentation in spinal surgery. Clin. Orthop., 227: 10-23, 1988.

Craven, T. G.; Carson, W. L.; Asher, M. A.; and Robinson, R. G.: The effects of implant stiffness on the bypassed bone mineral density and facet fusion stiffness of the canine spine. Spine, 19: 1664-1673, 1994.

Crawford, M. J., and Esses, S. I.: Indications for pedicle fixation. Results of NASS/SRS faculty questionnaire. North American Spine Society and Scoliosis Research Society. Spine, 19: 2584-2589, 1994.

Cunningham, B. W.; Sefter, J. C.; Shono, V.; and McAfee, P. C.: Static and cyclical biomechanical analysis of pedicle screw spinal constructs. Spine, 18: 1677-1688, 1993.

Cunningham, B. W.; Kotani, Y.; McNulty, P. S.; Cappuccino, A.; and McAfee, P. C.: The effect of spinal destabilization and instrumentation on lumbar intradiscal pressure: an in vitro biomechanical analysis. Spine, 22: 2655-2663, 1997.

Darden, B. V., II; Wood, K. E.; Hatley, M. K.; Owen, J. H.; and Kostuik, J.: Evaluation of pedicle screw insertion monitored by intraoperative evoked electromyography. J. Spinal Disord., 9: 8-16, 1996.

Darden, B. V., II; Owen, J. H.; Hatley, M. K.; Kostuik, J.; and Tooke, S. M.: A comparison of impedance and electromyogram measurements in detecting the presence of pedicle wall breakthrough. Spine, 23: 256-262, 1998.

Devlin, V. J.; Boachie-Adjei, O.; Bradford, D. S.; Ogilvie, J. W.; and Transfeldt, E. F.: Treatment of adult spinal deformity with fusion to the sacrum using CD instrumentation. J. Spinal Disord., 4: 1-14, 1991.

Dick, J. C.; Zdeblick, T. A.; Bartel, B. D.; and Kunz, D. N.: Mechanical evaluation of cross-link designs in rigid pedicle screw systems. Spine, 22: 370-375, 1997.

Dick, W.: The "fixateur interne" as a versatile implant for spine surgery. Spine, 12: 882-900, 1987.

Donovan, D. J.; Polly, D. W., Jr.; and Ondra, S. L.: The removal of a transdural pedicle screw placed for thoracolumbar spine fracture. Spine, 21: 2495-2498, 1996.

Duncan, J. D., and MacDonald, J. D.: Extraction of broken pedicle screws: technical note. Neurosurgery, 42: 1399-1400, 1998.

Ebraheim, N. A.; Rupp, R. E.; Savolaine, E. R.; and Reinke, D.: Use of titanium implants in pedicular screw fixation. J. Spinal Disord., 7: 478-486, 1994.

Ebraheim, N. A.; Xu, R.; Knight, T.; and Yeasting, R. A.: Morphometric evaluation of lower cervical pedicle and its projection. Spine, 22: 1-6, 1997.

Ebraheim, N. A.; Xu, R.; Ahmad, M.; and Yeasting, R. A.: Projection of the thoracic pedicle and its morphometric analysis. Spine, 22: 233-238, 1997.

Ebraheim, N. A.; Jabaly, G.; Xu, R.; and Yeasting, R. A.: Anatomic relations of the thoracic pedicle to the adjacent neural structures. Spine, 22: 1553-1557, 1997.

Ebraheim, N. A.; Xu, R.; Challgren, E.; and Heck, B.: Location of the sacral pedicle, foramina, and ala on the lateral aspect of the sacrum: a radiographic study. Orthopedics, 21: 703-706, 1998.

Esses, S. I., and Bednar, D. A.: The spinal pedicle screw: techniques and systems. Orthop. Rev., 18: 676-682, 1989.

Faraj, A. A., and Webb, J. K.: Early complications of spinal pedicle screw. European Spine J., 6: 324-326, 1997.

Ferree, B. A.: Morphometric characteristics of pedicles of the immature spine. Spine, 17: 887-891, 1992.

Frank, E. H.: The use of small malleable endoscopes to assess pedicle screw placement: technical note. Minim. Invasive Neurosurg., 41: 10-12, 1998.

Gaines, R. W.; Carson, W. L.; Satterlee, C. C.; and Groh, G. I.: Improving quality of spinal internal fixation - evolution toward "ideal immobilization" - a biomechanical study. Orthop. Trans., 11: 86-87, 1987.

Gaines, R. W., Jr.; Carson, W. L.; Satterlee, C. C.; and Groh, G. J.: Experimental evaluation of seven different spinal fracture internal fixation devices using nonfailure stability testing. The load-sharing and unstable-mechanism concepts. Spine, 16: 902-909, 1991.

Gertzbein, S. D., and Robbins, S. E.: Accuracy of pedicular screw placement in vivo. Spine, 15: 11-14, 1990.

Gertzbein, S. D.; Betz, R.; Clements, D.; Errico, T.; Hammerberg, K.; Robbins, S.; Shepherd, E.; Weber, A.; Kerina, M.; Albin, J.; Wolk, D.; and Ensor, K.: Semirigid instrumentation in the management of lumbar spinal conditions combined with circumferential fusion. A multicenter study. Spine, 21: 1918-1925, 1996.

Glassman, S. D.; Dimar, J. R.; Puno, R. M.; Johnson, J. R.; Shields, C. B.; and Linden, R. D.: A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation. Spine, 20: 1375-1379, 1995.

Glassman, S. D.; Dimar, J. R.; Puno, R. M.; and Johnson, J. R.: Salvage of instrumental lumbar fusions complicated by surgical wound infection. Spine, 21: 2163-2169, 1996.

Glossop, N. D.; Hu, R. W.; and Randle, J. A.: Computer-aided pedicle screw placement using frameless stereotaxis. Spine, 21: 2026-2034, 1996.

Goel, V. K.; Kim, Y. E.; Lim, T. H.; and Weinstein, J. N.: An analytical investigation of the mechanics of spinal instrumentation. Spine, 13: 1003-1011, 1988.

Goel, V. K.; Winterbottom, J. M.; and Weinstein, J. N.: A method for the fatigue testing of pedicle screw fixation devices. J. Biomech., 27: 1383-1388, 1994.

Gokaslan, Z. L.; Romsdahl, M. M.; Kroll, S. S.; Walsh, G. L.; Gillis, T. A.; Wildrick, D. M.; and Leavens, M. E.: Total sacrectomy and Galveston L-rod reconstruction for malignant neoplasms. Technical note. J. Neurosurg., 87: 781-787, 1997.

Gurr, K. R., and McAfee, P. C.: Cotrel-Dubousset instrumentation in adults. A preliminary report. Spine, 13: 510-520, 1988.

Gurr, K. R.; McAfee, P. C.; and Shih, C. M.: Biomechanical analysis of posterior instrumentation system after decompressive laminectomy. J. Bone and Joint Surg., 70-A: 680-691, June 1988.

Hadjipavlou, A. G.; Nicodemus, C. L.; al-Hamdan, F. A.; Simmons, J. W.; and Pope, M. H.: Correlation of bone equivalent mineral density to pull-out resistance of triangulated pedicle screw construct. J. Spinal Disord., 10: 12-19, 1997.

Hadra, B. E.: Wiring the spinous processes in Pott's disease. Trans. Am. Orthop. Assn., 4: 206, 1891.

Halvorson, T. L.; Kelley, L. A.; Thomas, K. A.; Whitecloud, T. S., III; and Cook, S. D.: Effects of bone mineral density on pedicle screw fixation. Spine, 19: 2415-2420, 1994.

Hamill, C. L.; Lenke, L. G.; Bridwell, K. H.; Chapman, M. P.; Blanke, K.; and Baldus, C.: The use of pedicle screw fixation to improve correction in the lumbar spine of patients with idiopathic scoliosis. Is it warranted? Spine, 21: 1241-1249, 1996.

Harrington, P. R., and Tullos, H. S.: Reduction of severe spondylolisthesis in children. Southern Med. J., 62: 1-7, 1969.

Hehne, H.-J.; Zielke, K.; and Böhm, H.: Polysegmental lumbar osteotomies and transpedicled fixation for correction of long-curved kyphotic deformities in ankylosing spondylitis. Report on 177 cases. Clin. Orthop., 258: 49-55, 1990.

Hertlein, H.; Mittlmeier, T.; Schurmann, M.; and Lob, G.: Anterior transpedicular instrumentation of the lumbar spine: an anatomical study. J. Spinal Disord., 5: 330-334, 1992.

Hirano, T.; Hasegawa, K.; Takahashi, H. E.; Uchiyama, S.; Hara, T.; Washio, T.; Sugiura, T.; Yokaichiya, M.; and Ikeda, M.: Structural characteristics of the pedicle and its role in screw stability. Spine, 22: 2504-2509, 1997.

Holland, N. R.; Lukaczyk, T. A.; Riley, L. H., III; and Kostuik, J. P.: Higher electrical stimulus intensities are required to activate chronically compressed nerve roots. Implications for intraoperative electromyographic pedicle screw testing. Spine, 23: 224-227, 1998.

Hou, S.; Hu, R.; and Shi, Y.: Pedicle morphology of the lower thoracic and lumbar spine in a Chinese population. Spine, 18: 1850-1855, 1993.

Hume, M.; Capen, D. A.; Nelson, R. W.; Nagelberg, S.; and Thomas, J. C., Jr.: Outcome after Wiltse pedicle screw removal. J. Spinal Disord., 9: 121-124, 1996.

Johnston, C. E., II; Ashman, R. B.; Sherman, M. C.; Eberle, C. F.; Herndon, W. A.; Sullivan, J. A.; King, A. G.; and Burke, S. W.: Mechanical consequences of rod contouring and residual scoliosis in sublaminar segmental instrumentation. J. Orthop. Res., 5: 206-216, 1987.

Jones, E. L.; Heller, J. G.; Silcox, D. H.; and Hutton, W. C.: Cervical pedicle screws versus lateral mass screws. Anatomic feasibility and biomechanical comparison. Spine, 22: 977-982, 1997.

Jonsson, B.; Sjostrom, L.; Olerud, C.; Andreasson, I.; Bring, J.; and Rauschning, W.: Outcome after limited posterior surgery for thoracic and lumbar spine metastases. European Spine J., 5: 36-44, 1996.

Kakiuchi, M.: Repair of the defect in spondylolysis. Durable fixation with pedicle screws and laminar hooks. J. Bone and Joint Surg., 79-A: 818-825, June 1997.

Kalfas, I. H.; Kormos, D. W.; Murphy, M. A.; McKenzie, R. L.; Barnett, G. H.; Bell, G. R.; Steiner, C. P.; Trimble, M. B.; and Weisenberger, J. P.: Application of frameless stereotaxy to pedicle screw fixation of the spine. J. Neurosurg., 83: 641-647, 1995.

Kamioka, Y., and Yamamoto, H.: Lumbar trapezoid plate for lumbar spondylolisthesis. A clinical study on preoperative and postoperative instability. Spine, 15: 1198-1203, 1990.

Karaikovic, E. E.; Daubs, M. D.; Madsen, R. W.; and Gaines, R. W., Jr.: Morphologic characteristics of human cervical pedicles. Spine, 22: 493-500, 1997.

Karaikovic, E. E.; Kunakornsawat, S.; Daubs, M. D.; and Gaines, R. W., Jr.: Surgical anatomy of the cervical pedicles: landmarks for posterior cervical pedicle entrance localization. J. Spinal Disord., 13: 63-72, 2000.

Kim, N. H.; Lee, H. M.; Chung, I. H.; Kim, H. J.; and Kim, S. J.: Morphometric study of the pedicles of thoracic and lumbar vertebrae in Koreans. Spine, 19: 1390-1394, 1994.

King, D.: Internal fixation for lumbosacral fusion. J. Bone and Joint Surg., 30-A: 560-565, July 1948.

Kothe, R.; Panjabi, M. M.; and Liu, W.: Multidirectional instability of the thoracic spine due to iatrogenic pedicle injuries during transpedicular fixation. A biomechanical investigation. Spine, 22: 1836-1842, 1997.

Kramer, D. L.; Rodgers, W. B.; and Mansfield, F. L.: Transpedicular instrumentation and short-segment fusion of thoracolumbar fractures: a prospective study using a single instrumentation system. J. Orthop. Trauma, 9: 499-506, 1995.

Kumano, K.; Hirabayashi, S.; Ogawa, Y.; and Aota, V.: Pedicle screws and bone mineral density. Spine, 19: 1157-1161, 1994.

Law, M.; Tencer, A. F.; and Anderson, P. A.: Caudo-cephalad loading of pedicle screws: mechanisms of loosening and methods of augmentation. Spine, 18: 2438-2443, 1993.

Lazennec, J. Y.; Saillant, G.; Saidi, K.; Arafati, N.; Barabas, D.; Benazet, J. P.; Laville, C.; Roy-Camille, R.; and Ramare, S.: Surgery of the deformities in ankylosing spondylitis: our experience of lumbar osteotomies in 31 patients. European Spine J., 6: 222-232, 1997.

Lee, T. C.: Complications of transpedicular reduction and stabilization of the thoracolumbar spine. J. Formosan Med. Assn., 94: 738-741, 1995.

Lehmer, S. M.; Steffee, A. D.; and Gaines, R. W., Jr.: Treatment of L5-S1 spondyloptosis by staged L5 resection with reduction and fusion of L4 onto SI (Gaines procedure). Spine, 19: 1916-1925, 1994.

Lehmer, S. M.; Keppler, L.; Biscup, R. S.; Enker, P.; Miller, S. D.; and Steffee, A. D.: Posterior transvertebral osteotomy for adult thoracolumbar kyphosis. Spine, 19: 2060-2067, 1994.

Levine, D. S.; Dugas, J. R.; Tarantino, S. J.; and Boachie-Adjei, O.: Chance fracture after pedicle screw fixation. A case report. Spine, 23: 382-386, 1998.

Licht, N. J.; Rowe, D. E.; and Ross, L. M.: Pitfalls of pedicle screw fixation in the sacrum. A cadaver model. Spine, 17: 892-896, 1992.

Liljenqvist, U. R.; Halm, H. F.; and Link, T. M.: Pedicle screw instrumentation of the thoracic spine in idiopathic scoliosis. Spine, 22: 2239-2245, 1997.

Lim, T. H.; Goel, V. K.; Weinstein, J. N.; and Kong, W.: Stress analysis of a canine spinal motion segment using the finite element technique. J. Biomech., 27: 1259-1269, 1994.

Liu, Y. K.; Njus, G. O.; Bahr, P. A.; and Geng, P.: Fatigue life improvement of nitrogen-ion-implanted pedicle screws. Spine, 15: 311-317, 1990.

Lotz, J. C.; Hu, S. S.; Chiu, D. F.; Yu, M.; Colliou, O.; and Poser, R. D.: Carbonated apatite cement augmentation of pedicle screw fixation in the lumbar spine. Spine, 22: 2716-2723, 1997.

Louis, R.: Fusion of the lumbar and sacral spine by internal fixation with screw plates. Clin. Orthop., 203: 18-33, 1986.

100

Lynn, G.; Mukherjee, D. P.; Kruse, R. N.; Sadasivan, K. K.; and Albright, J. A.: Mechanical stability of thoracolumbar pedicle screw fixation. The effect of crosslinks. Spine, 22: 1568-1573, 1997.

101

McAfee, P. C.; Weiland, D. J.; and Carlow, J. J.: Survivorship analysis of pedicle spinal instrumentation. Spine, 16 (Supplement 8): S422-S427, 1991.

102

McCord, D. H.; Cunningham, B. W.; Shono, Y.; Myers, J. J.; and McAfee, P. C.: Biomechanical analysis of lumbosacral fixation. Spine, 17 (Supplement 8): S235-S243, 1992.

103

McCormack, T.; Karaikovic, E.; and Gaines, R. W.: The load sharing classification of spine fractures. Spine, 19: 1741-1744, 1994.

104

McGuire, R. A., Jr.: A method for removal of broken vertebral screws. Orthop. Rev., 21: 775-776, 1992.

105

McLain, R. F.; Sparling, E.; and Benson, D. R.: Early failure of short-segment pedicle instrumentation for thoracolumbar fractures. A preliminary report. J. Bone and Joint Surg., 75-A: 162-167, Feb. 1993.

106

McLain, R. F.; Fry, M. F.; Moseley, T. A.; and Sharkey, N. A.: Lumbar pedicle screw salvage: pullout testing of three different pedicle screw designs. J. Spinal Disord., 8: 62-68, 1995.

107

Mac Millan, M. M.; Cooper, R.; and Haid, R.: Lumbar and lumbosacral fusions using Cotrel-Dubousset pedicle screws and rods. Spine, 19: 430-434, 1994.

108

Maat, G. J.; Matricali, B.; and van Persijn van Meerten, E. L.: Postnatal development and structure of the neurocentral junction. Its relevance for spinal surgery. Spine, 21: 661-666, 1996.

109

Marchesi, D.; Schneider, E.; Glauser, P.; and Aebi, M.: Morphometric analysis of the thoracolumbar and lumbar pedicles, anatomo-radiologic study. Surg. and Radiol. Anat., 10: 317-322, 1988.

110

Marchesi, D. G., and Aebi, M.: Pedicle fixation devices in the treatment of adult lumbar scoliosis. Spine, 17 (Supplement 8): S304-S309, 1992.

111

Margulies, J. Y.; Casar, R. S.; Caruso, S. A.; Neuwirth, M. G.; and Haher, T. R.: The mechanical role of laminar hook protection of pedicle screws at the caudal end vertebra. European Spine J., 6: 245-248, 1997.

112

Margulies, J. Y.; Caruso, S. A.; Chattar-Cora, D.; Gorup, J. M.; Puri, R.; Thampi, S. P.; and Haher, T. R.: Substitution of transpedicular screws by hook claws in a vertebrectomy model. J. Spinal Disord., 11: 36-40, 1998.

113

Masferrer, R.; Gomez, C. H.; Karahalios, D. G.; and Sonntag, V. K.: Efficacy of pedicle screw fixation in the treatment of spinal instability and failed back surgery: a 5-year review. J. Neurosurg., 89: 371-377, 1998.

114

Matsuzaki, H.; Tokuhashi, Y.; Matsumoto, F.; Hoshino, M.; Kiuchi, T.; and Toriyama, S.: Problems and solutions of pedicle screw plate fixation of lumbar spine. Spine, 15: 1159-1165, 1990.

115

Merloz, P.; Tonetti, J.; Eid, A.; Faure, C.; Lavallee, S.; Troccaz, J.; Sautot, P.; Hamadeh, A.; and Cinquin, P.: Computer assisted spine surgery. Clin. Orthop., 337: 86-96, 1997.

116

Merloz, P.; Tonetti, J.; Pittet, L.; Coulomb, M.; Lavallee, S.; and Sautot, P.: Pedicle screw placement using image guided techniques. Clin. Orthop., 354: 39-48, 1998.

117

Meter, J. J.; Polly, D. W., Jr.; Miller, D. W.; Popovic, N. A.; and Ondra, S. L.: A method for radiographic evaluation of pedicle screw violation of the vertebral endplate. Technique. Spine, 21: 1587-1592, 1996.

118

Mick, C. A.; Carl, A.; Sachs, B.; Hresko, M. T.; and Pfeifer, B. A.: Burst fractures of the fifth lumbar vertebra. Spine, 18: 1878-1884, 1993.

119

Miller, M. D.; Cain, J. E.; Lauerman, W. C.; Littlefield, W. G.; Platenberg, R. C.; and Wilson, M. R.: Posterior sacroiliac fixation using a sacral pedicle targeting device: an anatomical study. J. Orthop. Trauma, 7: 514-520, 1993.

120

Mirkovic, S.; Abitbol, J. J.; Steinman, J.; Edwards, C. C.; Schaffler, M.; Massie, J.; and Garfin, S. R.: Anatomic consideration for sacral screw placement. Spine, 16 (Supplement 6): S289-S294, 1991.

121

Misenhimer, G. R.; Peek, R. D.; Wiltse, L. L.; Rothman, S. L.; and Widell, E. H., Jr.: Anatomic analysis of pedicle cortical and cancellous diameter as related to screw size. Spine, 14: 367-372, 1989.

122

Moore, D. C.; Maitra, R. S.; Farjo, L. A.; Graziano, G. P.; and Goldstein, S. A.: Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement. Spine, 22: 1696-1705, 1997.

123

Moran, J. M.; Berg, W. S.; Berry, J. L.; Geiger, J. M.; and Steffee, A. D.: Transpedicular screw fixation. J. Orthop. Res., 7: 107-114, 1989.

124

Nolte, L. P.; Zamorano, L. J.; Jiang, Z.; Wang, Q.; Langlotz, F.; and Berlemann, U.: Image-guided insertion of transpedicular screws. A laboratory set-up. Spine, 20: 497-500, 1995.

125

Nolte, L.; Zamorano, L.; Arm, E.; Visarius, H.; Jiang, Z.; Berlemann, U.; and Schwarzenbach, O.: Image-guided computer-assisted spine surgery: a pilot study on pedicle screw fixation. Stereotact. and Funct. Neurosurg., 66: 108-117, 1996.

126

Panjabi, M. M.; O'Holleran, J. D.; Crisco, J. J., III; and Kothe, R.: Complexity of the thoracic spine pedicle anatomy. European Spine J., 6: 19-24, 1997.

127

Parker, J. W.; Lane, J. R.; Karaikovic, E. E.; and Gaines, R. W.: Successful short segment instrumentation and fusion for thoracolumbar spine fractures: a consecutive 4 year series. Spine, 25: 1157-1170, 2000.

128

Petersilge, C. A.; Lewin, J. S.; Duerk, J. L.; Yoo, J. U.; and Ghaneyem, A. J.: Optimizing imaging parameters for MR evaluation of the spine with titanium pedicle screws. AJR: Am. J. Roentgenol., 166: 1213-1218, 1996.

129

Pfeifer, B. A.; Krag, M. H.; and Johnson, C.: Repair of failed transpedicle screw fixation. A biomechanical study comparing polymethylmethacrylate, milled bone, and matchstick bone reconstruction. Spine, 19: 350-353, 1994.

130

Pintar, F. A.; Maiman, D. J.; Yoganandan, N.; Droese, K. W.; Hollowell, J. P.; and Woodard, E.: Rotational stability of a spinal pedicle screw/rod system. J. Spinal Disord., 8: 49-55, 1995.

131

Rath, S. A.; Neff, U.; Schneider, O.; and Richter, H. P.: Neurosurgical management of thoracic and lumbar vertebral osteomyelitis and discitis in adults: a review of 43 consecutive surgically treated patients. Neurosurgery, 38: 926-933, 1996.

132

Robertson, P. A.; Novotny, J. E.; Grobler, L. J.; and Agbai, J. U.: Reliability of axial landmarks for pedicle screw placement in the lower lumbar spine. Spine, 23: 60-66, 1998.

133

Rodgers, W. B.; Williams, M. S.; Schwend, R. M.; and Emans, J. B.: Spinal deformity in myelodysplasia. Correction with posterior pedicle screw instrumentation. Spine, 22: 2435-2443, 1997.

134

Rogozinski, A., and Rogozinski, C.: Efficacy of implanted bone growth stimulation in instrumented lumbosacral spinal fusion. Spine, 21: 2479-2483, 1996.

135

Rose, R. D.; Welch, W. C.; Balzer, J. R.; and Jacobs, G. B.: Persistently electrified pedicle stimulation instruments in spinal instrumentation. Technique and protocol development. Spine, 22: 334-343, 1997.

136

Rose, R. D.; Welch, W. C.; and Donaldson, W. F., III: Correlation of late intraforaminal screw removal with somatosensory evoked potentials and neurologic improvement. Arch. Phys. Med. and Rehab., 79: 226-229, 1998.

137

Roy-Camille, R.; Saillant, G.; and Mazel, C.: Internal fixation of the lumbar spine with pedicle screw plating. Clin. Orthop., 203: 7-17, 1986.

138

Roy-Camille, R.; Saillant, G.; and Mazel, C.: Plating of thoracic, thoracolumbar, and lumbar injuries with pedicle screw plates. Orthop. Clin. North America, 17: 147-159, 1986.

139

Ruland, C. M.; McAfee, P. C.; Warden, K. E.; and Cunningham, B. W.: Triangulation of pedicular instrumentation. A biomechanical analysis. Spine, 16 (Supplement 6): S270-S276, 1991.

140

Sairyo, K.; Scifert, J.; Goel, V. K.; Grosland, N.; and Grobler, L. J.: Neurocentral synchondrosis fracture in immature spines associated with pedicle screw type fixation devices. J. Spinal Disord., 11: 142-145, 1998.

141

Salib, R. M., and Pettine, K. A.: Modified repair of a defect in spondylolysis or minimal spondylolisthesis by pedicle screw, segmental wire fixation, and bone grafting. Spine, 18: 440-443, 1993.

142

Sasso, R. C., and Cotler, H. B.: Posterior instrumentation and fusion for unstable fractures and fracture-dislocations of the thoracic and lumbar spine. A comparative study of three fixation devices in 70 patients. Spine, 18: 450-460, 1993.

143

Schildhauer, T. A.; Josten, C.; and Muhr, G.: Triangular osteosynthesis of vertically unstable sacrum fractures: a new concept allowing early weight-bearing. J. Orthop. Trauma, 12: 307-314, 1998.

144

Schnee, C. L.; Freese, A.; and Ansell, L. V.: Outcome analysis for adults with spondylolisthesis treated with posterolateral fusion and transpedicular screw fixation. J. Neurosurg., 86: 56-63, 1997.

145

Schwab, F. J.; Nazarian, D. G.; Mahmud, F.; and Michelsen, C. B.: Effects of spinal instrumentation on fusion of the lumbosacral spine. Spine, 20: 2023-2028, 1995.

146

Scoles, P. V.; Linton, A. E.; Latimer, B.; Levy, M. E.; and Digiovanni, B. F.: Vertebral body and posterior element morphology: the normal spine in middle life. Spine, 13: 1082-1086, 1988.

147

Shirado, O., and Kaneda, K.: Lumbosacral fracture-subluxation associated with bilateral fractures of the first sacral pedicles: a case report and review of the literature. J. Orthop. Trauma, 9: 354-358, 1995.

148

Sim, E.: Location of transpedicular screws for fixation of the lower thoracic and lumbar spine. Computed tomography of 45 fracture cases. Acta Orthop. Scandinavica, 64: 28-32, 1993.

149

Soini, J.; Laine, T.; Pohjolainen, T.; Hurri, H.; and Alaranta, H.: Spondylodesis augmented by transpedicular fixation in the treatment of olisthetic and degenerative conditions of the lumbar spine. Clin. Orthop., 297: 111-116, 1993.

150

Songer, M. N., and Rovin, R.: Repair of the pars interarticularis defect with a cable-screw construct. A preliminary report. Spine, 23: 263-269, 1998.

151

Soshi, S.; Shiba, R.; Kondo, H.; and Murota, K.: An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine, 16: 1335-1341, 1991.

152

Steffee, A. D.; Biscup, R. S.; and Sitkowski, D. J.: Segmental spine plates with pedicle screw fixation. A new internal fixation device for disorders of the lumbar and thoracolumbar spine. Clin. Orthop., 203: 45-53, 1986.

153

Steffee, A. D.; Sitkowski, D. J.; and Topham, L. S.: Total vertebral body and pedicle arthroplasty. Clin. Orthop., 203: 203-208, 1986.

154

Suk, S. I.; Lee, C. K.; Min, H. J.; Cho, K. H.; and Oh, J. H.: Comparison of Cotrel-Dubousset pedicle screws and hooks in the treatment of idiopathic scoliosis. Internat. Orthop., 18: 341-346, 1994.

155

Suk, S. I.; Lee, C. K.; Kim, W. J.; Chung, Y. J.; and Park, Y. B.: Segmental pedicle screw fixation in the treatment of thoracic idiopathic scoliosis. Spine, 20: 1399-1405, 1995.

156

Suk, S. I.; Lee, C. K.; Kim, W. J.; Lee, J. H.; Cho, K. J.; and Kim, H. G.: Adding posterior lumbar interbody fusion to pedicle screw fixation and posterolateral fusion after decompression in spondylolytic spondylolisthesis. Spine, 22: 210-220, 1997.

157

Tomita, K.; Kawahara, N.; Baba, H.; Tsuchiya, H.; Fujita, T.; and Toribatake, Y.: Total en bloc spondylectomy. A new surgical technique for primary malignant vertebral tumors. Spine, 22: 324-333, 1997.

158

Vaccaro, A. R., and Garfin, S. R.: Internal fixation (pedicle screw fixation) for fusions of the lumbar spine. Spine, 20 (Supplement 24): S157-S165, 1995.

159

Vaccaro, A. R.; Rizzolo, S. J.; Allardyce, T. J.; Ramsey, M.; Salvo, J.; Balderston, R. A.; and Cotler, J. M.: Placement of pedicle screws in the thoracic spine. Part I: Morphometric analysis of the thoracic vertebrae. J. Bone and Joint Surg., 77-A: 1193-1199, Aug. 1995.

160

Vaccaro, A. R.; Rizzolo, S. J.; Balderston, R. A.; Allardyce, T. J.; Garfin, S. R.; Dolinskas, C.; and An, H. S.: Placement of pedicle screws in the thoracic spine. Part II: An anatomical and radiographic assessment. J. Bone and Joint Surg., 77-A: 1200-1206, Aug. 1995.

161

Van Royen, B. J.; de Kleuver, M.; and Slot, G. H.: Polysegmental lumbar posterior wedge osteotomies for correction of kyphosis in ankylosing spondylitis. European Spine J., 7: 104-110, 1998.

162

Voor, M. J.; Roberts, C. S.; Rose, S. M.; and Glassman, S. D.: Biomechanics of in situ rod contouring of short-segment pedicle screw instrumentation in the thoracolumbar spine. J. Spinal Disord., 10: 106-116, 1997.

163

Wang, J. C.; Sandhu, H. S.; Yu, W. D.; Minchew, J. T.; and Delamarter, R. B.: MR parameters for imaging titanium spinal instrumentation. J. Spinal Disord., 10: 27-32, 1997.

164

Weinhoffer, S. L.; Guyer, R. D.; Herbert, M.; and Griffith, S. L.: Intradiscal pressure measurements above an instrumented fusion. A cadaveric study. Spine, 20: 526-531, 1995.

165

Weinstein, J. N.; Spratt, K. F.; Spengler, D.; Brick, C.; and Reid, S.: Spinal pedicle fixation: reliability and validity of roentgenogram-based assessment and surgical factors on successful screw placement. Spine, 13: 1012-1018, 1988.

166

Welch, W. C.; Rose, R. D.; Balzer, J. R.; and Jacobs, G. B.: Evaluation with evoked and spontaneous electromyography during lumbar instrumentation: a prospective study. J. Neurosurg., 87: 397-402, 1997.

167

West, J. L., III; Bradford, D. S.; and Ogilvie, J. W.: Results of spinal arthrodesis with pedicle screw-plate fixation. J. Bone and Joint Surg., 73-A: 1179-1184, Sept. 1991.

168

West, J. L., III; Ogilvie, J. W.; and Bradford, D. S.: Complications of the variable screw plate pedicle screw fixation. Spine, 16: 576-579, 1991.

169

Willett, K.; Hearn, T. C.; and Cuncins, A. V.: Biomechanical testing of a new design for Schanz pedicle screws. J. Orthop. Trauma, 7: 375-380, 1993.

170

Wittenberg, R. H.; Lee, K.-S.; Shea, M.; White, A. A., III; and Hayes, W. C.: Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength. Clin. Orthop., 296: 278-287, 1993.

171

Wu, S. S.; Hwa, S. Y.; Lin, L. C.; Pai, W. M.; Chen, P. Q.; and Au, M. K.: Management of rigid post-traumatic kyphosis. Spine, 21: 2260-2267, 1996.

172

Xu, R.; Ebraheim, N. A.; Mohamed, A.; el-Gamal, H.; and Yeasting, R. A.: Anatomic considerations for dorsal sacral plate-screw fixation. J. Spinal Disord., 8: 352-356, 1995.

173

Xu, R.; Ebraheim, N. A.; Yeasting, R. A.; Wong, F. Y.; and Jackson, W. T.: Morphometric evaluation of the first sacral vertebra and the projection of its pedicle on the posterior aspect of the sacrum. Spine, 20: 936-940, 1995.

174

Yerby, S. A.; Ehteshami, J. R.; and McLain, R. F.: Offset laminar hooks decrease bending moments of pedicle screws during in situ contouring. Spine, 22: 376-381, 1997.

175

Yoganandan, N.; Pintar, F.; Maiman, D. J.; Reinartz, J.; Sances, A., Jr.; Larson, S. J.; and Cusick, J. F.: Kinematics of the lumbar spine following pedicle screw plate fixation. Spine, 18: 504-512, 1993.

176

Yuan, H. A.; Garfin, S. R.; Dickman, C. A.; and Mardjetko, S. M.: A historical cohort study of pedicle screw fixation in thoracic, lumbar, and sacral spinal fusions. Spine, 19 (Supplement 20): S2279-S2296, 1994.

177

Zdeblick, T. A.: A prospective, randomized study of lumbar fusion. Preliminary results. Spine, 18: 983-991, 1993.

178

Zdeblick, T. A.; Kunz, D. N.; Cooke, M. E.; and McCabe, R.: Pedicle screw pullout strength. Correlation with insertional torque. Spine, 18: 1673-1676, 1993.

179

Zindrick, M. R.; Wiltse, L. L.: Widell, E. H.; Thomas, J. C.; Holland, W. R.; Field, B. T.; and Spencer, C. W.: A biomechanical study of intrapeduncular screw fixation in the lumbosacral spine. Clin. Orthop., 203: 99-112, 1986.

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