Allen L. Carl

Pedicle Screw Instrumentation for Thoracolumbar Burst Fractures and Fracture-dislocations

Thirty-eight patients with unstable thoracolumbar and lumbar (T12–L5) spine fractures were treated with Cotrel-Dubousset pedicle screw instrumentation. They were followed for an average of 22.73 months (range 12–39). Measurements of canal compromise. wedge index, and kyphosis correction at follow-up examination were made. Thirty-three (86%) patients responded to a questionnaire concerning overall satisfaction, use of pain medication and return to work. There was an overall correction of kyphosis at follow-up of only one degree after a loss of six degrees from operative correction. There were nine cases of bent or broken screws that occurred at the thoracolumbar junction. Only one patient with instrumentation required continued pain medication and most had returned to work. Thirty-two of thirty-three patients were satisfied with the overall surgical result and twenty-eight of thirty-three patients had returned to work.

New percutaneous access method for minimally invasive anterior lumbosacral surgery.

Preliminary cadaver, animal, and human studies were performed to determine the feasibility of axial anterior lumbosacral spine access using a percutaneous, presacral approach. Custom instruments were directed under fluoroscopic guidance along the midline of the anterior sacrum to the surface of the sacral promontory where an axial bore was created into the lower lumbar vertebral bodies and discs. Imaging and gross dissection were performed in cadavers and animals. The procedure was used for lumbosacral biopsy in human subjects guided by intraoperative imaging and clinical monitoring. All procedures were technically successful. This study demonstrates the feasibility of the axial access technique to the anterior lower lumbar spine.

In vitro simulation : Early results of stereotaxy for pedicle screw placement

Study Design. Frameless stereotaxy with doppler ultrasound and three dimensional computer model registration is assessed in vitro for pedicle screw placement. Objective. To identify feasibility of pedicle screw navigation and placement using this technology. Summary of Background Data. Inaccurate pedicle screw placement can lead to neurovascular injury or suboptimal fixation. Present techniques in pedicle screw placement involve only confirmation of hole orientation. Method. Forty‐four pedicle screws were placed in lumbosacral models and cadaver specimens. Accuracy was assessed with a computed tomography scan and vertebral cross sectioning. Results. All screws were intrapedicular. Accuracy of anterior cortical fixation was 1.5 mm, with a range of 2.5 mm. Conclusion. In vitro frameless stereotaxy is accurate for pedicle screw placement. This technology adds a component of navigation to pedicle screw placement.

The effect of pinealectomy on scoliosis development in young nonhuman primates.

Study Design. Prospective study on pinealectomy in primates. Objective. To evaluate whether pinealectomy in a bipedal nonhuman primate model will result in the development of scoliosis. Summary of Background Data. Pinealectomy in newborn chickens consistently resulted in scoliosis development. Published data suggest that the surgical removal of the pineal, loss of melatonin secretion, and a bipedal posture are important elements in the development of scoliosis in lower animal models. Method. There were 18 rhesus monkeys between 8 and 11 months old that underwent pineal excision. All monkeys were kept in a regulated 12-hour light-dark cycle. Monthly radiographs assessed scoliosis development. Completeness of pineal excision was assessed by measurement of a major metabolite of melatonin in the urine, 6-sulfatoxymelatonin, using an enzyme-linked immunosorbent assay assessed. Results. Mean follow-up was 28 months (range 10− 41). Seven monkeys died prematurely, and 11 survived to date; the data from those that died could still be used, although follow-up was shortened. At the latest follow-up or death, scoliosis did not develop in any of the monkeys. Urinary 6-sulfatoxymelatonin measurements revealed 3 patterns. Group 1 consisted of 10 monkeys, which showed definite evidence of complete pineal excision. Group 2 consisted of an uncertain group of 2 monkeys in which the nighttime melatonin level is slightly high. Group 3 consisted of 6 monkeys that had incomplete pineal excision or ectopic melatonin production. Conclusions. To our knowledge, this is the first report of pinealectomy in nonhuman primates. Of the 18 monkeys, 10 had a loss of melatonin secretion, for a mean of 29 months after surgery. Because none of the monkeys had scoliosis develop, this study strongly suggests that the possible etiologic factors producing idiopathic scoliosis in lower animals are different from primates, and findings in lower animals cannot necessarily be extrapolated to human beings.

Anterolateral dynamized instrumentation and fusion for unstable thoracolumbar and lumbar burst fractures.

Study Design. A retrospective chart review of 36 patients treated with dynamized anterolateral instrumentation and fusion after decompression for thoracolumbar and lumbar burst fractures is presented. Objectives. To evaluate a device that allows continual bone graft vertebral endplate compression and determine its potential for healing in patients with thoracolumbar and lumbar burst fractures. Summary of Background Data. Anterior spinal surgery has led to implant adaptations. Such implants have undergone an evolution in hopes of improving the rate of healing and avoiding neurovascular catastrophes. Methods. Thirty‐six patients underwent anterior decompression dynamized instrumentation and fusion for thoracolumbar and lumbar burst fractures. This involved a dual‐rod, quadrilateral, cross‐linked frame that allows for continual compression but deters rotation and shear stresses. Results. All patients healed solidly without instrumentation failure. An average recovery of 1.3 Frankel grades was recorded. Subsidence of bone graft vertebral endplate was less than in those placed in a trough. Conclusions. Dynamized load‐sharing anterolateral Cotrel‐Dubousset instrumentation led to solid bone graft healing without implant failure by allowing continual compression while deterring shear and rotational stresses.

Intradiscal therapy: a review of current treatment modalities.

Study Design. A systematic review of the medical literature regarding current intradiscal therapeutic methods. Objectives. To establish an understanding of the current intradiscal treatment options for the management of low back pain. Summary of Background Data. Current treatment of intradiscal disease is rapidly evolving and as such should be a multidisciplinary effort that follows a logical, orderly algorithm. Minimally invasive techniques, namely, intradiscal electrothermal therapy (IDET), radiofrequency ablation (RFA), percutaneous endoscopic laser discectomy (PELD), and cryoablation have challenged the conventional surgical management of back pain. Methods. Thirty-eight research reports, published between 1986 and 2005, were systematically reviewed for disease classification, surgical intervention, and treatment outcomes (neurologic status, pain scores, and ambulation). Results. The surgical literature on the management of intradiscal disease continues to be limited to large series with short clinical follow-ups. Arthrodesis continues to be the primary treatment modality in the majority of patients. Newer treatment options including IDET, RFA, PELD, and cryoablation have shown promising results with regards to symptomatic relief and early return to function. Conclusion. Low back pain is an extremely common and potentially debilitating problem. Adding biophysical methods to well-tested biomechanical and newly investigated biomolecular solutions allows for multiple avenues of therapeutic interventions. With future clinical and basic science studies regarding intradiscal therapies forthcoming, we may soon alter our current treatment algorithms for the management of discogenic back pain.

Biomechanical Evaluation of a Novel Lumbosacral Axial Fixation Device

BACKGROUND Interbody arthrodesis is employed in the lumbar spine to eliminate painful motion and achieve stability through bony fusion. Bone grafts, metal cages, composite spacers, and growth factors are available and can be placed through traditional open techniques or minimally invasively. Whether placed anteriorly, posteriorly, or laterally, insertion of these implants necessitates compromise of the anulus--an inherently destabilizing procedure. A new axial percutaneous approach to the lumbosacral spine has been described. Using this technique, vertical access to the lumbosacral spine is achieved percutaneously via the presacral space. An implant that can be placed across a motion segment without compromise to the anulus avoids surgical destabilization and may be advantageous for interbody arthrodesis. The purpose of this study was to evaluate the in vitro biomechanical performance of the axial fixation rod, an anulus sparing, centrally placed interbody fusion implant for motion segment stabilization. METHOD OF APPROACH Twenty-four bovine lumbar motion segments were mechanically tested using an unconstrainedflexibility protocol in sagittal and lateral bending, and torsion. Motion segments were also tested in axial compression. Each specimen was tested in an intact state, then drilled (simulating a transaxial approach to the lumbosacral spine), then with one of two axial fixation rods placed in the spine for stabilization. The range of motion, bending stiffness, and axial compressive stiffness were determined for each test condition. Results were compared to those previously reported for femoral ring allografts, bone dowels, BAK and BAK Proximity cages, Ray TFC, Brantigan ALIF and TLIF implants, the InFix Device, Danek TIBFD, single and double Harms cages, and Kaneda, Isola, and University plating systems. RESULTS While axial drilling of specimens had little effect on stiffness and range of motion, specimens implanted with the axial fixation rod exhibited significant increases in stiffness and decreases in range of motion relative to intact state. When compared to existing anterior, posterior, and interbody instrumentation, lateral and sagittal bending stiffness of the axial fixation rod exceeded that of all other interbody devices, while stiffness in extension and axial compression were comparable to plate and rod constructs. Torsional stiffness was comparable to other interbody constructs and slightly lower than plate and rod constructs. CONCLUSIONS For stabilization of the L5-S1 motion segment, axial placement of implants offers potential benefits relative to traditional exposures. The preliminary biomechanical data from this study indicate that the axial fixation rod compares favorably to other devices and may be suitable to reduce pathologic motion at L5-S1, thus promoting bony fusion.

Spinal Deformities: The Comprehensive Text

I. Gross Anatomy: Surgical Anatomy of the Sacrum and Pelvis Surgical Anatomy of the Lumbar Spine Surgical Anatomy of the Thoracic Spine Surgical Anatomy of the Cervical Spine Muscles and Ligaments. II. Microanatomy: Development and Maturation of the Spine and Spinal Cord Microscopic Anatomy of Bone Macro and Microscopic Anatomy of the Disc and Endplate Nervous System and Muscle. III. Physiology: Physiology of Bone Nerve and Muscle Physiology Pulmonary and Chest Cage Physiology Electrophysiology Cerebral Spinal Fluid (CSF) Physiology. IV. Biomechanics: Biomechanics Biomechanics of the Intervertebral Disc Spine Testing Modalities. V. Pharmacology: Antibiotic Therapy in Spine Surgery Osteoporosis: Evaluation and Pharmacologic Treatment Pharmacologic Agents that Minimize Perioperative Blood Loss... Common Medications in Spinal Afflictions. VI. Pathology: Pathophysiology of Lumbar Degenerative Disc Disease Spinal Inflammatory Arthritides Spinal Neuroarthropathy (Charcots Spine) Pyogenic Vertebral Infection Coagulation Disorders in Spine Surgery Blood Conservation Strategies in Spine Surgery Management of Metastatic Disease to the Spine. VII. Clinical Evaluation: Evaluation of the Patient with Congenital Spine Deformity Clinical Evaluation of the Patient with a Spine Deformity Clinical Evaluation for Neuromuscular Scoliosis and Kyphosis Evaluation of Back Pain in the Spinal Deformity Patient. VIII. Neurology: Spinal Cord Injury, Reflexes, and Syndromes Anterior Horn Cell Disease: Poliomyelitis, Spinal Muscular Congenital and Developmental Spinal Cord Abnormalities The Spine in Friedrichs Ataxia, Charcot-Marie-Tooth Disease Cerebral Palsy, Myelodysplasia, Hydrosyringomyelia, Rett... IX. Anesthesia: Anesthetic Considerations for Spinal Surgery. X. Radiology: Radiology. XI. Rehabilitation: Rehabilitation. XII. Treatment of the Adult Spine: Degenerative Lumbar Stenosis Degenerative Disc Disease and Degenerative Spondylolisthesis of... Adult Spine Trauma Inflammatory Arthritis of the Spine Vertebral Osteomyelitis Neoplasms of the Spine. XIII. Surgical Techniques: Tables and Positioning Halo and Cranial Traction Approaches to the Cervical Spine Open Thoracic and Lumbar Spine Surgical Approaches Cervical Decompression Decompression for Lumbar Spinal Stenosis Spine Fusion Spine Osteotomy and Resection Staging Plus Complications of Approaches Thoracoplasty Endoscopic and Mini-Open Approaches to the Spine. XIV. Instrumentation and Complications: Basic Principles of Deformity Correction A Biomechanical Approach to Posterior Spinal Instrumentation Sacropelvic Fixation in Spinal Deformity Neurological Injury Complicating Surgery Postoperative Complications Revision Surgery. XV. Pediatric Spine: Etiology of Scoliosis Idiopathic Scoliosis: Prevalence and Natural History Congenital Scoliosis and Kyphosis Inflammatory and Infectious Disorders of the Childs Spine The Spine in Skeletal Syndromes and Dysplasias Neuromuscular Scoliosis Pediatric Spine Trauma Spine Tumors in Childhood and Adolescence. XVI. Deformities: Idiopathic Scoliosis: General Considerations, Natural History and... Bracing in Scoliosis Spinal Deformities Associated with Metabolic Diseases Perioperative Blood and Blood Product Management for Spinal... Scheurmann Kyphosis Spondylolysis and Spondylolisthesis Intraoperative and Immediate Postoperative Complications.

Small intestinal submucosa for anular defect closure: long-term response in an in vivo sheep model.

Study Design. After undergoing anulotomy, lumbar intervertebral discs from sheep were treated with small intestinal submucosa (SIS) and assessed functionally at 24 weeks after surgery. Objective. To determine the efficacy of an SIS-based patch and plug scaffold to facilitate anular defect closure and anular functional recovery after anulotomy and partial discectomy. Summary of Background Data. The incidence of reherniation following discectomy remains high and mechanical means of anular closure have met with limited success. SIS is a naturally occurring collagen-based material, which acts as a resorbable scaffold in vivo that promotes soft tissue regeneration. Methods. Twelve sheep underwent retroperitoneal exposure of the lumbar spine. Three levels were assigned to either: no additional procedure, box anulotomy alone, or box anulotomy followed by placement of an SIS “patch and plug” anchored by titanium bone screws. At 26 weeks after surgery, 18 motion segments underwent pressure-volume testing to assess the competency of the anulus. High resolution MRI images were taken of the remaining 18 segments. Undecalcified histology was conducted on all specimens. Results. Radiographs, MRI images, and histology indicate that there was an exuberant tissue response at SIS-treated levels. New tissue formation in SIS-treated specimens was integrated well with the native anulus, but did not resemble the organization of native anulus. The extent of anular closure was substantial enough to allow the disc a functional recovery to a mean 66% of its capacity to develop internal pressure. MRI images indicate that SIS-treated levels did not maintain signal intensity comparable to exposure-only (intact) levels, but SIS-treated discs were statistically significantly higher than anulotomy-only levels. Conclusion. SIS-treated discs were better able to maintain hydration and resulted in a functional recovery relative to anulotomy alone levels. The SIS patch and plug reduced the cascade of functional degeneration that an intervertebral disc undergoes following anulotomy.

In vivo pedicle screw placement: Image-guided virtual vision

Near-real-time frameless stereotaxy registering intraoperative anatomy to a preoperative three-dimensional computer model has been developed for use with in vivo pedicle screw placement. Eight patients underwent thoracolumbar and lumbar spine stabilization surgery using this new technology, and 32 pedicle screws were placed. Three additional patients had 12 pedicle screws removed during revision surgery, and they allowed the authors to estimate the accuracy of this navigational system. Accuracy was determined by comparing pedicle screw position on postoperative computed tomographs for the first eight patients and on preoperative computed tomographs for the latter three patients, with the intraoperative computer trajectory data gathered during operation. In the group of eight patients, all screws were intrapedicular. In evaluating all 11 patients, the overall accuracy was +/- 2 mm, but the greatest error of 5.4 mm was noted in the sagittal plane measurement. During the development phase of this technology, time constraints prolong surgery, but this may be addressed once the tools accuracy has been confirmed and intraoperative radiographic confirmation becomes unnecessary. In vivo real-time frameless stereotaxy for pedicle screw placement offers promise for the future. Refinements are needed to improve accuracy and address time constraints.