Surgical compared with nonsurgical management of fractures in male veterans with chronic spinal cord injury.

STUDY DESIGN: Retrospective review of a clinical database. OBJECTIVES: To examine treatment modalities of incident appendicular fractures in men with chronic SCI and mortality outcomes by treatment modality. SETTING: United States Veterans Health Administration Healthcare System. METHODS: This was an observational study of 1979 incident fractures that occurred over 6 years among 12 162 male veterans with traumatic SCI of at least 2 years duration from the Veterans Health Administration (VA) Spinal Cord Dysfunction Registry. Treatment modalities were classified as surgical or nonsurgical treatment. Mortality outcomes at 1 year following the incident fracture were determined by treatment modality. RESULTS: A total of 1281 male veterans with 1979 incident fractures met inclusion criteria for the study. These fractures included 345 (17.4%) upper-extremity fractures and 1634 (82.6%) lower-extremity fractures. A minority of patients (9.4%) were treated with surgery. Amputations and disarticulations accounted for 19.7% of all surgeries (1.3% of all fractures), and the majority of these were done more than 6 weeks following the incident fracture. There were no significant differences in mortality among men with fractures treated surgically compared with those treated nonsurgically. CONCLUSIONS: Currently, the majority of appendicular fractures in male patients with chronic SCI are managed nonsurgically within the VA health-care system. There is no difference in mortality by type of treatment.

Morbidity following lower extremity fractures in men with spinal cord injury.

UNLABELLED: The Veterans Affairs Spinal Cord Dysfunction Registry from 2002 to 2007 was reviewed to determine whether men with spinal cord injury (SCI) and lower extremity fractures had an increased risk of complications compared to those without fractures. We determined that fractures are associated with significant consequences, particularly during the first month postfracture. INTRODUCTION: Despite increasing longevity, patients with SCI have a substantial number of illnesses and comorbid conditions. Lower extremity fractures are frequent events in these patients. However, whether these fractures are associated with any increased risk of complications in SCI is not certain. The purpose of this report was to determine the impact of lower extremity fractures on morbidities in men with SCI. METHODS: A population-based, nested, case-control (1,027 cases and 1,027 propensity-matched controls) of men enrolled in the Veterans Affairs Spinal Cord Dysfunction Registry from fiscal years 2002 to 2007 was reviewed to determine whether lower extremity fractures were associated with an increased risk for complications. RESULTS: In propensity score models matched for demographic (age, race) and SCI-related injury factors (level/completeness of SCI), Veterans Affairs-service connection status, and comorbidities, at 1 month following the fracture, there was an increased risk for respiratory infections, pressure ulcers, urinary tract infections, thromboembolic events, depression, and delirium (p ≤ 0.03 for all). Over 12 months, the only complication more common in fracture cases was pressure ulcers (p < 0.01), with an absolute difference of less than 2 % when compared to controls. There was no significant increased risk of cardiac arrhythmias at any time examined following fracture (≥0.12). CONCLUSIONS: Lower extremity fractures are associated with significant consequences in men with SCI during the first month postfracture, but they do not persist for a long term, except for pressure ulcers. Targeted interventions to prevent complications should be considered following lower extremity fractures in SCI, particularly in the first month following fracture.

Thoracolumbar pseudarthrosis.

Pseudarthrosis is the leading cause of failed spine fusion and is of paramount concern to surgeons attempting fusion procedures. Thus, it is essential to understand this complication to direct efficient and intelligent management. A review of various modalities in the identification and diagnosis of a pseudarthrosis is presented. In addition, its histologic features and classification system are discussed. Not all pseudarthroses need treatment. When treatment is considered, however, there are both nonoperative and operative strategies. Operative alternatives include posterolateral, anterior, or anterior-posterior combined fusions.

A biomechanical study of Jefferson fractures.

STUDY DESIGN: Fifteen specimens of the first cervical vertebra were tested by the application of pure tensile forces to failure. Seven specimens had intact transverse ligaments, and eight had transection of the transverse ligament before testing. Specimens were tested to failure by the rapid application of laterally directed tensile force to the ring; this force then was exerted through the lateral masses to simulate the mechanism of injury for this fracture as proposed by Jefferson. OBJECTIVES: To measure the biomechanical characteristics of the C1 ring, including the fracture patterns created with tensile loading, and to describe the influence of the transverse ligament on the behavior of the ring as it failed under tension. SUMMARY OF BACKGROUND DATA: Jefferson fractures have been reproduced in the laboratory by subjecting head and neck preparations to axial load. However, no previous detailed biomechanical studies of the fracture characteristics of the isolated C1 vertebra have been reported. METHODS: Specimens were tested to failure by rapid application of laterally directed tensile forces to the ring. RESULTS: Eleven two-part and three three-part fractures occurred. The mean tensile strength of the atlas was found to be 2,280 N. The average deformation required to fracture the C1 ring was 1.57 mm. The total energy absorbed by the ring averaged 1.99 N-m. There was no statistically difference between those specimens with the transverse ligament intact and those without a transverse ligament. CONCLUSIONS: The results of this study show that fractures of the C1 ring of greater than two parts can occur with pure tensile loading. The ring will fracture with as little as 1 mm of deformation.

A biomechanical study of anterior thoracolumbar screw fixation.

STUDY DESIGN: The pullout strength of unicortical and bicortical screws in thoracic and lumbar vertebral bodies was measured as a function of bone mineral density. OBJECTIVES: To determine the influence of bone mineral density and screw insertion technique on the stability of anterior thoracolumbar spine screw fixation. SUMMARY OF BACKGROUND DATA: No previous study has addressed the specific technique of screw insertion or stability of screw fixation in the anterior spine. METHODS: Fifty-one human thoracic vertebral bodies were tested in pullout with 6.55-mm cancellous screws inserted using unicortical and bicortical techniques. RESULTS: Pullout force increased exponentially with increasing bone mineral density for unicortical and bicortical screws. Bicortical screws were significantly stronger in resisting pullout than unicortical screws. CONCLUSION: Advancing an anterior vertebral body screw to engage the second cortex increases resistance to pullout by 25-44%, depending on vertebral bone mineral density. The difference in resistance between unicortical and bicortical techniques was smaller in specimens with low mineral densities.

Use of computed tomography image processing for mapping of human cervical facet surface geometry.

Vertebral facets transmit a significant percent of spinal loading, provide translational, rotational, and axial stability for the spine, and are responsible for the coupling between lateral bending and rotational motions. The shape and the orientation of vertebral facets vary with level and are influenced by degenerative processes. These variations may play an important role in many cases of neck pain, back pain, and instability. To determine whether the shape and orientation of cervical facets can be accurately measured from computed tomography (CT) data, the surfaces of 39 human cervical facets were non-invasively digitized from reconstructed three-dimensional CT data and then invasively digitized using a hand-held three-dimensional probe before and after bleaching away the cartilage. Digitized data describing the facet surfaces were fit to both plane and spherical surfaces. For the adult cervical vertebrae that we measured, the presence of cartilage had no significant effect on the measured shape or orientation of the facets. The orientation of the facet surfaces measured from CT data was within 11 deg of that measured using the hand-held probe. Quantitative measurements of facet shape (flat or spherical) and surface irregularity were similar between CT and hand digitized surfaces. These results suggest that individual facet geometries can be accurately quantified using non-invasive CT examinations. Non-invasively determined variations in facet geometries may assist in the diagnosis of back pain, neck pain and instability.

Quantitative anatomy of the occiput and the biomechanics of occipital screw fixation.

STUDY DESIGN: The surgically relevant osseous anatomy of the human anatomy was carefully studied and described. The stability of cortical and cancellous screws placed in anatomic sites commonly used for internal fixation of the occiput was tested. OBJECTIVES: To define the bony anatomy of the occiput in quantitative terms and to measure the ability of cortical and cancellous screws inserted at sites commonly used for internal fixation. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, no previous studies described the gross anatomy of the occiput in specific relation to the internal venous structures in the cranium and to the biomechanical strength of screw fixation in different areas of the occiput. METHODS: Thirty-seven human occiputs were carefully measured using calipers. Thin sections from six such specimens were analyzed with specific attention to cortical thicknesses. Stability of screws placed in various locations in the occiput were tested in axial pullout. RESULTS: The thickness of the occiput varied from extremely thin to a 0.1-mm thickness in the region of the cerebellar fossa and increased to a maximum of 8.3 mm at the level of the superior nuchal line and at the transverse sulcus. Results of pullout testing showed that the cancellous screws were as strong as the cortical screws in this area. In areas of the occiput thicker than 7 mm, unicortical fixation was as strong as bicortical fixation. CONCLUSION: There is a wide variation in thickness of the bone of the occiput. The strength of screw fixation was proportional to the bone's thickness.

The internal bony architecture of the sacrum.

STUDY DESIGN: Radiographic and direct quantitative measurements were made of the cortical and the trabecular anatomy of the sacrum. OBJECTIVES: To define the trabecular patterns and the cortical thickness of the sacrum. SUMMARY OF BACKGROUND DATA: The sacrum is a frequent site of internal fixation. In previous anatomic studies, investigators have focused on specific dimensional measurements of the sacrum, whereas others have described the anatomic course of the anterior sacral neurovascular or visceral structures. Computed tomographic imaging also has been used to quantify the sacral trabecular bone density. The internal architecture of the sacrum has yet to be described in detail. METHODS: Seventeen cadaveric sacra were studied by computed tomographic imaging and then were sectioned at 3-mm intervals in the axial or sagittal plane. The cortical thickness of each section was measured under microscopic visualization. The sections were radiographed with high-resolution imaging to delineate their trabecular patterns. RESULTS: The trabecular bone was densest adjacent to the endplates. The sacral body trabeculae were arranged in a cruciate pattern, and bony atrophy occurred in a systematic fashion. An alar void was a consistent finding in all specimens with definable boundaries. The cortical thickness was uniform throughout the surface of each specimen. The computed tomographic images correlated with the anatomy observed in the cadaveric sections. CONCLUSION: The internal bony architecture of the sacrum has several consistent features. The relatively uniform cortical thickness seen in each sacral specimen may have clinical significance in the internal fixation of this region.

A motion analysis of the cervical facet joint.

STUDY DESIGN: The stability of motion segments of human cervical spines was sequentially tested as portions of the vertebral anatomy were removed or cut. Isolated, individual facet joints were then similarly studied. OBJECTIVES: To define the laxity of isolated cervical facet joints and the relative contribution of the different components of the vertebral anatomy to the overall stability of the cervical spine. SUMMARY OF BACKGROUND DATA: Facet joints are known to be important in determining cervical stiffness and mobility. This is the first known study in which the biomechanical behavior of isolated cervical facet joints has been documented. METHODS: From five fresh frozen human cervical spines, three C3-C4 and five C5-C6 motion segments were dissected and potted. Rotations and translations in response to 10 bending or twisting moments were recorded by tracking the motion of a testing plate fixed to the superior vertebrae using an articulated arm digitizer. Each motion segment was tested five times, with sequential dissections performed as follows: intact; after removal of the anterior longitudinal ligament intervertebral disc, and posterior longitudinal ligament; after cutting the interspinous ligament; after isolation of the left facet joint; and after isolation of the right facet joint. Each testing sequence involved applying low and high forces 10 cm from the center of the testing plate in each of 10 testing directions. After completion of rotational testing, landmarks on the superior vertebral body and facet joints were digitized to calculate vertebral translations. RESULTS: Isolated facet joints allowed up to 19 degrees of flexion, 14 degrees of extension, 28 degrees of lateral bending, and 17 degrees of rotation. Coupled motions were less in isolated facet joints compared with those in intact vertebral bodies. Isolated facet joints allowed up to 9 mm of translation between superior and inferior surfaces. CONCLUSIONS: Isolated cervical facet joints are highly mobile in comparison with their motions within the constraints of intact motion segments; gliding motions of the isolated facet to near dislocation is possible before the facet capsule constrains motion. Cervical coupled motions are a result of an intact vertebral ring and a combination of the two facet joints. The vertebral ring with facet joints and capsules all intact is necessary for lateral bending stability and rotational stability in the cervical spine.

Lumbar spine duplication presenting as adolescent scoliosis. A case report.

STUDY DESIGN: A report of a case of lumbar spine duplication with the clinical appearance of adolescent scoliosis. OBJECTIVE: To increase knowledge about the pathogenesis and treatment of lumbar spinal duplication. SUMMARY OF BACKGROUND DATA: Although there have been other reports of lumbar spine duplication of this magnitude, these malformations typically are associated with severe neurologic abnormalities (dicephalus, myelomeningocele) or gastrointestinal abnormalities (omphalocele, neurenteric fistulas). Several investigators have recommended early surgical intervention for this abnormality because of the perceived risk of progressive neurologic abnormality from tethering of the cord. METHODS: In a 13-year-old girl who had truncal asymmetry, lumbar spine duplication was noted on plain radiographs. A magnetic resonance study was obtained, and the patient was observed with conservative treatment for 3 years. RESULTS: Although extensive abnormalities were noted on the magnetic resonance images, which were related to duplication of spinal cord and vertebral bodies, the patient was neurologically intact and remained so until skeletal maturity. CONCLUSIONS: This rare malformation typically has severe neurologic sequelae. Conservative management in the reported patient did not result in a progressive neurologic lesion at the time of skeletal maturity.

Morphologic study of lumbar vertebral osteophytes.

BACKGROUND: Vertebral osteophytes are one of the principal radiographic diagnostic criteria for degenerative change in the lumbar spine. These osteophytes have been previously classified by morphologic features into two groups, the "traction spur" and the "claw spur." It has been stated that the traction spur is a sign of spinal instability. METHODS: Lumbar spines from 20 cadavers provided 120 vertebrae from T-11 to L-5 and 240 vertebral rims for study. The presence of osteophytes was determined by measurement with digital calipers. The type of osteophyte was then determined visually, using the Macnab classification. RESULTS: Sixty vertebral rims were found to have significant osteophytes. Twenty-four vertebral rims had osteophytes of the claw type only, and 11 had osteophytes of the traction type only. Of the eight vertebrae with traction osteophytes alone and with the adjacent vertebra available for study, none had such a corresponding osteophyte. CONCLUSION: Traction spurs and claw spurs frequently coexist on the same vertebral rim. This suggests that they may result from the same degenerative process and do not necessarily reflect the results of two distinct pathologic processes.

Innervation of the human vertebral body: a histologic study.

The histology of 69 human vertebral bodies from 23 individuals was studied by hematoxylin and eosin staining using a technique that allowed the creation of complete, large histologic sections of individual vertebral bodies. Particular attention was directed toward the documentation of intraosseous nerves. The vertebral bodies were dissected free of soft tissue, and then sectioned using a diamond wafering saw into 3-mm sagittal segments. Sections were then decalcified and whole-mounted in paraffin blocks before tissue sectioning using a very-large-format microtome. One hundred thirty-eight tissue sections were prepared for evaluation. Neurovascular bundles and intraosseous nerves were routinely identified within human vertebral bone. Nerves were noted to enter the vertebral body via the centrally located posterior vascular foramen and were found to accompany the basivertebral vessels. Branches from these nerves coursed to both central and peripheral areas of the vertebral body. Nerves were also documented that entered the vertebral body by penetrating the anterior cortex to course into the marrow. Although previous studies have documented nerves within long bones, and others have described the histology of the intervertebral disc and associated soft tissues, previous literature that documents the innervation of the human vertebral body has been very sparse. The documentation of nerve tissue within normal human vertebrae further supports the proposed role of neuronal factors in the regulation of bone physiology. Furthermore, it is possible that such intraosseous nerves may play a role in the clinical problem of back pain.

Regional variation in vertebral bone density and trabecular architecture are influenced by osteoarthritic change and osteoporosis.

STUDY DESIGN: The effects of age-related osteoarthritic disease and bone loss on cortical and trabecular bone density in the human spine were analyzed. Changes were quantified by a new method of computed quantitative radiography. Using this method, the relative losses of bone mineral from specific areas and the specific redistribution of bone within vertebrae as a function of age-related bone loss and osteoarthritic change were determined. OBJECTIVES: To quantify the effects of age-related bone loss and osteoarthritic disease on cortical and trabecular density in the human spine by the use of a new method of computed quantitative radiography. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, osteoarthritic and age-related changes resulting in the relative loss of bone mineral from specific areas within vertebrae have never been quantitatively studied. METHODS: Seventy-four vertebrae were obtained from 23 normal, human subjects at autopsy. Vertebral bodies were measured by dual-energy x-ray absorption, and then sectioned for analysis by computerized quantitative radiography. Attention was focused on overall bone density, regional cancellous bone density, and cortical bone density (anterior cortex, superior, and inferior endplates) for both mid-sagittal and para-sagittal sections. One hundred forty sections were so analyzed. RESULTS: Quantitative radiography demonstrated previously undescribed, well defined patterns of cortical and trabecular architecture and bone density within vertebral bodies that were uniform among vertebrae, but strongly influenced by osteoarthritic change and bone loss. These changes were neither detected nor documented by dual-energy x-ray absorption. CONCLUSIONS: Understanding the patterns of bone lose, and knowing how osteoarthritic change affects normal bone loss yields insight into the pathophysiology of the aging process and osteoarthritic disorders. Knowledge of the variations in density and microanatomy within vertebrae may improve techniques of internal fixation and designs of spinal implants, and may help to clarify the pathogenesis of clinical problems such as fractures.

Severe angioedema causing airway obstruction after anterior cervical surgery.

STUDY DESIGN: A case of severe postoperative angioedema after excision of cervical osteophyte is presented. Emergent tracheostomy was required. OBJECTIVES: To discuss the etiologies, diagnosis, and management of this unusual cause of acute respiratory distress after an anterior cervical spinous procedure. SUMMARY OF BACKGROUND DATA: To our knowledge, angioedema as a complication of cervical spine surgery has not been reported previously. The patient had no history of angioedema, was not receiving an acetyl choline esterase inhibitor, and had a normal C1-esterase-inhibitor level. METHODS: The patient was a 61-year-old man with ankylosing spondylitis who, because of progressive dysphagia and choking episodes, underwent excision of a large C3-C4 osteophyte and anterior cervical discectomy and fusion. While in the postanesthesia care unit, the patient experienced massive edema of the tongue and neck, with associated difficulty breathing. Reexploration of the wound revealed a small (30 cc) hematoma, which was removed with no obvious benefit to the patient, who ultimately required a tracheotomy. RESULTS: The patient was managed with intravenous corticosteroids. The tracheotomy tube was removed without incident after 7 days. The patient noted decreased neck pain and dramatic improvement in his ability to swallow postoperatively. He has had no further incidents of angioedema, to date. CONCLUSION: Angioedema should be considered in the differential diagnosis in patients with upper extremity respiratory obstruction after anterior surgery of the cervical spine.

The trabecular anatomy of thoracolumbar vertebrae: implications for burst fractures.

The gross osseous anatomy of the spine has been the subject of much study but the internal architecture and trabecular anatomy of thoracolumbar vertebrate has not previously been well described. This study is based on high resolution x-ray images of 56 isolated thoracolumbar vertebrae and thick sections obtained from them. A previously undescribed array of trabeculae was documented which originated from the medial corner of the base of the pedicles and extended in a radial array throughout the vertebral body. This trabecular array persisted even in severely osteoporotic specimens. The cortex of the vertebral canal thinned abruptly near the base of the pedicle creating what may be a stress concentration at this site. This corresponded to the site of origin of the trabecular array. The presence of this possible stress concentration, in proximity to the trabecular array, may provide an explanation for the trapezoidal shape of the bony fragments that are frequently retropulsed into the spinal canal in axial load type burst fractures, common in this area of the spine.

Discography of lumbar discs after surgical treatment for disc herniation.

STUDY DESIGN: Eighty-three patients were identified who had discography performed at a disc level that had been subject to previous laminectomy and partial discectomy, and who had also undergone discography at one or more additional levels. The results of these studies were retrospectively reviewed. OBJECTIVE: To define the results of discography performed on previously operated discs. SUMMARY OF BACKGROUND DATA: It is not uncommon for the physician to encounter patients with complaints of persistent chronic back pain after surgical treatment of a lumbar disc herniation. Although such patients are frequently studied by discography, there is very little scientific literature to document the expected results. METHODS: A retrospective study of the results of discography on previously operated disc was performed. RESULTS: A positive pain response was significantly more likely in the previously operated discs than in the unoperated discs (P < 0.0001). Posterior extravasation of dye was noted in 34% (35 of 102) of the postoperative discs and 21% (29 of 136) of the unoperated discs. Positive concordant pain provocation was noted in 48 (75%) of the 64 discs showing posterior dye extravasation; 28 were postoperative discs and 20 were unoperated discs. CONCLUSIONS: Patients presenting with disabling back pain who had previously undergone surgical treatment for a herniated nucleus pulposus show a high (72%) incidence of concordant pain with discography of the previously operated level. Only 34% of the previously operated discs demonstrated posterior extravasation of discography dye. Persistence of a posterior anular defect was associated with a higher incidence of positive concordant pain response.

Pitfalls in the measurement of bone mineral density by dual energy x-ray absorptiometry.

STUDY DESIGN: Fifty-three human thoracic and lumbar vertebrae were analyzed by dual energy x-ray absorptiomety to obtain projectional (g/cm2) and volumetric (g/cm3) bone mineral density. OBJECTIVES: To determine the effect of volume on the measurement of bone mineral density by DEXA. SUMMARY OF BACKGROUND DATA: Despite the widespread use of dual energy x-ray absorptiomety to measure bone mineral density expressed as grams per projectional unit area (g/cm2), the effect of volume has been ignored in many published biomechanical studies. METHODS: Projectional bone mineral density (g/cm2) of fifty-three human vertebrae was obtained by dual energy x-ray absorptiometry measurement. This was compared to bone mineral density expressed as grams per unit volume. RESULTS: Many specimens with near equal projectional bone mineral density were demonstrated to have significantly different true densities when measured by dual energy x-ray absorptiomety in grams per unit volume. The difference in true bone mineral density for these specimens ranged from 24.1% to 139%. CONCLUSION: The effect of volume on bone mineral density data based on projectional areas can cause very significant perturbations of the data in biomechanical studies.

Quantitative anatomy of the second cervical vertebra.

STUDY DESIGN: While the gross anatomy of the second cervical vertebra has been well described qualitatively, our evolving understanding of spinal pathology makes it necessary for the modern surgeon to have more quantitative information. OBJECTIVES: The authors' goal was to directly measure clinically relevant dimensions of the second cervical vertebra, using a collection of anatomic specimens. SUMMARY OF BACKGROUND DATA: Many existing studies have been based on analysis of radiographic images, which are subject to errors of magnification, rotation, and projection. Several recent studies of dens morphology have been based on direct measurements. These studies in general did not extend to the lateral masses or posterior ring, however. METHODS: Direct measurements using digital calipers and goniometer were taken from 51 dried human second cervical vertebrae. The maximum and minimum anteroposterior and lateral diameters of the dens, and the anteroposterior and lateral diameters of the end-plate and foramen and were measured. The heights of the dens and superior facet surfaces were measured relative to a plane defined by the anterior-most point of the inferior endplate and the inferior-most points of the inferior facet surfaces. RESULTS: The greatest variation was found in the dens angle, with specimen dens angles ranging from -2 degrees to 42 degrees. The most significant correlations were between the total height of the vertebra and the height to the base of the dens (r2 = 0.81), between the total height of the vertebra and the maximum lateral diameter of the dens (r2 = 0.77), and between the minimum lateral diameter of the dens and the maximum lateral diameter of the dens (r2 = 0.63). CONCLUSIONS: The dimensions measured in this study confirm a significant degree of anatomic variation in the second cervical vertebra, and show no important correlations among the various measured dimensions. In particular, no significant correlation was found between dens height and canal diameter. Dens angle in the sagittal plane was the most variable measurement.

The quantitative anatomy of the atlas.

STUDY DESIGN: This study is based on direct quantitative caliper measurements of 88 isolated anatomic specimens of the C1 vertebra. OBJECTIVES: The study was undertaken to establish the range and variability of the external dimensions of the atlas and to describe the cortical thicknesses and trabecular distribution of this unique vertebra. SUMMARY OF BACKGROUND DATA: Before this study, Francis in 1952 reported the total anterior and posterior diameter of 285 atlas vertebrae. Liu et al reported detailed external dimensions and facet joint surface morphologies on a total of three C1 vertebrae. METHODS: Measurements were made of overall dimensions, canal diameters, and the dimensions of the anterior and posterior arches of 88 dried human C1 vertebrae. Eight specimens were sectioned in the frontal plane, eight in the sagittal plane, and four in the coronal plane. The anatomy of these sections was documented by radiographic imaging. Cortical thicknesses on the sections were then obtained by direct measurement. RESULTS: The canal diameter ranged from 32 mm (SD 2 mm) in the sagittal plane, and 29 mm (SD 2 mm) in the lateral dimension. The mean thickness of the anterior ring was 6 mm (SD 1 mm) and posteriorly was 8 mm (SD 2 mm). Cortical bone was thinnest posteriorly. CONCLUSIONS: These measurements indicated remarkably constant dimensions for the ring itself, suggesting there may be significant functional restraints on the canal size of this unique vertebra. In contrast, a significant variability was noted in objective measurements of lateral mass height and sagittal plane widths of the entire bone.

A histologic study of soft-tissue reactions to spinal implants.

OBJECTIVES: The biologic reactions to orthopedic spinal implants were determined. METHODS: Biopsies of soft tissue immediately adjacent to spinal implants were done in 36 consecutive patients undergoing elective lumbar spinal hardware removal and was studied histologically. RESULTS: A fibrous tissue matrix was noted in all specimens. In 11 of 36 specimens, a discrete layer of cells with epithelial characteristics was noted on the surface immediately opposed to the metal implant. Results of immunohistochemical staining were negative using antibodies to markers, which suggests that these unique cell layers are probably of histiocytic origin. Black amorphous metallic debris was seen in nine of the specimens. In seven of these specimens, this material was associated with an inflammatory foreign-body reaction. Refractile non-biorefringent crystalline bodies were noted in five specimens. These crystalline deposits provoked a local foreign-body reaction in all cases. CONCLUSION: The role of soft-tissue inflammatory reactions in the production of clinical symptoms of pain is discussed.