Vertebral burst fractures: an experimental, morphologic, and radiographic study

Spinal burst fractures are produced by rapid compressive loading, and may result in spinal cord injury from bone fragments forced from the vertebral body into the spinal canal. This fracture is one of the most difficult injuries of the spine to successfully treat, in part because the biomechanics of reduction and the exact mechanism by which the distraction forces are transmitted to the intracanal fragments of the burst fracture have not been adequately investigated. The authors developed a reproducible technique for creating these fractures in vitro. The fractures produced were identical to those observed in clinical practice, and were used for investigating the mechanics of this fracture and its reduction. This work describes the pathologic anatomy of the burst fracture both on the gross structure and also on microtome sections of the vertebrae, and examines the biomechanics of fracture reduction. The margins of the vertebral bone fragment, which was forced posteriorly into the spinal canal during fracture, were noted to extend far laterally beyond the pedicles. The authors also found extensive damage not only to the disc above the injured level, but also to that below, explaining the clinical observation that disc degeneration frequently occurs at both levels. Examination of anatomic data provided by microtome section supported the hypothesis that the fibers that actually reduce the intracanal fragment originate in the anulus of the superior vertebra in the midportion of the endplate and insert into the lateral margins of the intracanal fragment. Investigations using magnetic resonance imaging confirmed that these obliquely directed fibers account for the indirect reduction of the fragment. The authors' studies demonstrate that the posterior longitudinal ligament provides only a minor contribution in the reduction of the fracture in comparison to the attachments of the posterior portion of the anulus fibrosus. The forces required to reduce this fragment were studied. Distraction was found to be the predominant force required for indirect posterior reduction. This was confirmed by a series of tests using devices that provided segmental fixation. The application of uniform distraction forces was most effective in the posterior reduction of the intracanal fragment.

Vertebral body fractures in child abuse. Radiologic-histopathologic correlates

RATIONALE AND OBJECTIVES

Vertebral injuries are rarely reported sequelae of child abuse, and little is known concerning the mechanisms of injury and healing. A preliminary investigation of these issues included correlating radiologic and histologic findings in children with vertebral injuries who died of complications relating to physical abuse.

METHODS

Ten vertebral body fractures from four abused infants and young children were studied radiologically and histopathologically.

RESULTS

Infants ranged in age from 7 to 36 months (mean, 21 months). Three patients died of associated head injuries. One child died after abandonment. There were three pure vertebral body compression fractures, two superior end-plate fractures without compression deformity, and five anterosuperior end-plate fractures with associated compression deformity. Vertebral compression was generally mild (less than 25%). Typically, end-plate injuries were manifest histologically by extension of the fracture through the medullary trabeculae into the proliferative zone of the superior end plate. The resultant pattern was analogous to that described in a previous study, and could potentially result in a growth disturbance at the vertebral end plate.

CONCLUSIONS

Observed radiologic patterns and histologic correlates may help explain previously described findings, such as vertebral notching, in abused infants.

CT image analysis of the vertebral trabecular network in vivo

A method of computed tomography (CT) image analysis of lumbar vertebrae has been developed, providing a visualization of the trabecular network as it is represented in a 1.5 mm-thick CT image. We measured the length of the network and the number of discontinuities found in the image. The ratio of these measurements was called the "trabecular fragmentation index" (TFI). CT images from 71 women between the ages of 50 and 59, and 94 women between the ages of 60 and 69 were divided into three groups according to quantitative computed tomography (QCT) vertebral density and to the presence or absence of crushing and fractures. The measure of the network length versus the vertebral area was significantly higher in normal subjects than in osteoporotics. A TFI threshold at 0.195 could separate the normal subjects, regardless of the decade, from osteoporotic ones. In females between 50 and 69 years of age, TFI was 0.166 (SD = 0.031) for the normal group and 0.248 (SD = 0.082) for osteoporotics. The osteopenic group without fractures but low bone mineral density (BMD) showed an intermediate TFI of 0.195 (SD = 0.05), placing this population on both sides of the threshold. Correlation between TFI and BMD was only -0.60. TFI could provide new information in vivo about the state of trabecular structure, particularly in the osteopenic group.

Bone histomorphometry of the iliac crest, and spinal fracture prevalence in atrophic and hypertrophic osteoarthritis of the hip

While some authors report high bone density in osteoarthritis (OA), surgical experience with total hip arthroplasty (THA) for primary OA suggests the existence of osteoporotic subsets of patients. To identify these we analysed 107 iliac crest bone biopsies, taken at THA, by routine histomorphometry for trabecular structural and bone turnover features, and examined radiographs of the spine for vertebral fractures. Patients were grouped by hip osteophyte size (none, atrophic; small, hypotrophic; moderate, supertrophic; large, hypertrophic OA), and by major architectural disorganization of the hip (hip joint destruction, protrusio). We found hip joint destruction to be 3 times more common in atrophic than in supertrophic and hypertrophic OA (p less than 0.05). Overall, the OA patients had lower bone volume (p less than 0.05) and thinner trabeculae (p less than 0.05) than controls. Worst affected were patients with hip joint destruction and with protrusio: they also had fewer and more widely spaced trabeculae than controls (p less than 0.05). The spinal fracture prevalence was highest in patients with hip joint destruction (higher than in the general population), intermediate in those with protrusio or atrophic OA, and lowest in patients with supertrophic or hypertrophic OA. We conclude that OA hip patients with joint destruction or protrusio have a high prevalence of generalized osteoporosis, and that the larger the hip osteophytes, the lower is the prevalence of generalized osteoporosis. Our findings suggest that the generalized bone status may influence the outcome of OA of the hip.

[Hyperextension somersault trauma]

Neurological failure can occur as one feature of hyperextension trauma of the cervical spine. Apart from predisposing factors, such as dorsal osteophytes and congenital spinal stenosis, an acute narrowing of the spinal canal caused by a hyperextension somersault trauma can cause such a trauma. We observed three cases of paraplegic syndrome resulting from hyperextension somersault trauma of the cervical spine. Fast recovery from the symptoms within 12 h indicates vascular damage. The mechanism of the accident is shown with reference to clinical and experimental investigations. Hyperextension somersault trauma is characterized by a plunge from a low height, with the danger of somersaulting of the body and impact at the forehead while the head is retroflected. For this reason, extension treatment ought to be contraindicated if an accident of this kind has happened. Emphasis should be placed on adequate positioning of the patient.

Trabecular spacing in post-menopausal Australian women with and without vertebral fractures

Histomorphometric measurements were made from iliac crest biopsies of 32 women with vertebral fractures and 37 women without fracture. All were post-menopausal Australian women who had presented with back pain to a hospital out-patient endocrinology clinic. Bone from the fracture cases was characterised by loss of individual trabecular elements, with the remaining trabeculae being spaced further apart than those in the non-fracture women (p less than 0.0001). This resulted in a significant decrease in trabecular bone volume (p less than 0.01). In addition osteoid surface was reduced (p less than 0.01). Dynamic parameters of bone turnover were not significantly different between the two groups. These data should be useful for the assessment of iliac bone histomorphometry in Australian post-menopausal women suspected of having osteoporosis.

Unstable thoracolumbar injuries

The treatment of thoracolumbar fractures was traditionally conservative. With increasing demands for early mobilization, operative reduction and stabilization has become more popular, even in less severe injuries. The Harrington instrumentation is still useful and efficient. However, in fractures with posterior element ruptures, the internal fixator is superior in stabilizing the fracture. Early mobilization in a body cast is an equivalent treatment to surgery in less severe burst fractures if the neurology is intact. A treatment program for different fractures is presented.

[Experimental study of laminectomy of the cervical spine]

The influence of laminectomy on the statics of the cervical spine was experimentally investigated. Pressure tests were carried out with isolated supravital cervical vertebrae with and without intact vertebral arches. Changes occurring during the pressure test were registered by stretching measurement strips. We tried to determine the relation between the height of laminectomy and the dorsal forces being necessary for the maintenance of lordosis in another series of experiments. The experiments were taken with a model developed by ourselves. Following results were reached: The vertebral arch is involved in the interception of axial forces. It shores up the back bird of the vertebral body. This is only visible with reaching the breaking load. A dorsal flexion wedge tilting over in the spinal canal breaks off at vertebrae without intact vertebral arch. After a laminectomy the lordosis of the cervical spine can only be kept up by the increase of dorsal forces. The necessary increase of forces is biggest with the laminectomy of the second and fifth vertebra. A motion-study shows that there occurs a buckling in the area of laminectomy during flexion.

Acute burst fractures. A comparative analysis of a modern fracture classification and pathologic findings

Ten acute thoracolumbar burst fractures (T11-L3) in eight spinal specimens were investigated regarding injuries to the bony, ligamentous, and neural structures. The fractures were subdivided into three groups, which were compared to the different burst fractures proposed by Denis in 1983. In the specimens, it was impossible to separate Denis Type A and B fractures. The Type D fractures showed pronounced instability. These latter fractures were subdivided into two groups: one with rupture of the bony vertebral arch (D) and one with rupture of the posterior ligaments (D2). The Denis A or B fractures were not associated with macroscopic or microscopic damage to the spinal cord or cauda equina, or both. However, in the six Denis D fractures, the neural tissue was transected in one case and severely compressed in four cases.

[The morphological analysis of the vertebral spongiosa in quantitative CT]

The diagnostic ranking of trabecular morphology for the evaluation of osteoporosis in quantitative CT (QCT) is presented. 5 patterns of cancellous bone correlating with trabecular density may be discerned. However, these patterns may indicate osteoporotic changes in particular cases only, by confluent rarefactions if the density is still within the normal range. There is neither a predictive value for the degree of spontaneous or therapy-induced bone loss, nor for therapy response. The trabecular appearances remain unchanged in short term even under strong quantitative changes and are therefore of no value for follow-up.

Sagittally oriented fractures of the lateral masses of the cervical vertebrae

Lateral flexion of the cervical spine may cause a sagittally oriented fracture of the lateral mass with shearing of all or part of the lateral mass away from the vertebral body. We report 22 patients with 24 sagittal fractures of the cervical lateral masses. Cross-table lateral roentgenograms suggested the presence of a sagittal lateral mass fracture in two thirds of the cases based upon malalignment or widening of the facet joints, displaced fracture fragments, subluxation of the spine, or rotation of the spine above the level of abnormality. However, the cross-table lateral roentgenogram was normal in one third of cases. Oblique roentgenograms were available in eight cases; these were positive in five, equivocal in one, and negative in two. Visible fracture lines, often associated with lateral displacement of part or all of the lateral mass, allowed all 24 fractures to be detected on the supine anteroposterior view films. Sagittal lateral mass fractures were unstable in 59% (13/22) of the cases; neurologic deficits, including quadriplegia, hemiplegia, and radiculopathy, were present in 45% (10/22). Computed tomography and complex-motion tomography were useful in confirming the sagittal lateral mass fracture and in detecting other associated fractures.

Magnetic resonance imaging evaluation of the spinal canal following arthrodesis and removal of sublaminar wires

Seven patients who underwent posterior spinal fusion with Harrington instrumentation and sublaminar wires, and subsequently had these implants removed, were evaluated for evidence of spinal canal compromise with magnetic resonance imaging (MRI) at the sites of the sublaminar wires. All fusions were solid. The sites of 33 wires (27 levels) were evaluated with MRI. The average time the wires were in the spinal canal was 24.6 months. The average time following wire removal at the time of MRI was 61.7 months. Twenty-eight of 33 (85%) wire sites had no evidence of spinal canal compromise. Five sites had minimal (less than 15%) spinal canal compromise. The permanent structural changes in the spinal canal attributable to sublaminar wires appears to be quite modest.

[Anatomical restoration of thoracolumbar spine with burst fracture]

A burst fracture was created in the L1 vertebra of six fresh human cadaver spines and reduction was performed using AO fixator intern, reduction fixation (RF) device, and Steffee plate instrumentation systems to determine the reduction force (distraction vs distraction plus lordosis) contributing to the anatomical restoration of thoracolumbar spine. These three pedicular screw devices were applied to the specimens following the use of standard clinical technique for each device. The AO fixator intern and the RF device provided independent control of distraction and lordosis correction. The Steffee device maintained a set distraction and lordosis. The RF device provided pre-set fixed incremental lordosis, while the AO provided variable angular correction. Plain X-rays and CT scans were taken of the specimens before and after creation of the fracture and following application of each device. Results demonstrated that the symmetric lordotic distraction of the disc space and vertebral body provided by the RF device achieved the best possible reduction of the intracanal fragment and sagittal alignment.

A new approach to defining normal vertebral dimensions

We developed a method for estimating the mean and standard deviation of ratios of normal vertebral heights from a sample that includes people with and without vertebral fractures. This method assumes that the measurements in normal vertebrae have a Gaussian distribution and that, for any vertebral level, the prevalence of abnormal measurements is less than 10%. Under these assumptions, normal values for nonfractured vertebrae can be estimated from several statistical properties of Gaussian distributions. We applied these methods to the lateral spinal radiographs of 2992 women aged 65-70 years who were recruited from population-based listings. The estimated means and standard deviations for ratios of dimensions in nonfractured vertebrae were very similar to those based on studies of premenopausal women. Our method may be useful for defining normal values from large populations that include normal and abnormal women, does not require x-rays of normal premenopausal women, avoids the potential biases of defining normality based on qualitative judgment, and can be applied to other types of physical and biochemical measurements.

Vertebral dimension differences between Caucasian populations, and between Caucasians and Japanese

Various criteria have been proposed for using vertebral measurements to identify vertebral fractures. It is known that the normal distributions of vertebral heights and ratios vary with location within the spine. However, very little is known regarding the degree to which differences in these parameters may exist between populations. We report the vertebra-specific distributions of vertebral dimensions and ratios for Japanese-Americans, and compare these values to published data for Caucasians. The mean Japanese vertebral heights were 1 to 2 mm shorter than Caucasians, which may be due in part to the shorter stature of Japanese. However, differences in mean values were also observed between Caucasian populations. Furthermore, anterior/posterior vertebral height ratios differed between Caucasian studies, and between races. Additional studies are needed to determine to what degree these differences are due to technical and biological factors before criteria derived from one population can be used for identifying vertebral fractures in other populations of the same, or different, race.

A comparison of morphometric definitions of vertebral fracture

To compare the accuracy of several approaches for defining prevalent vertebral fractures from measurements of vertebral dimensions (morphometry), we measured the lateral dimensions of vertebral bodies of 115 normal premenopausal and 100 postmenopausal women. Of the postmenopausal women two observers agreed that 49 had definite vertebral fractures and 38 were definitely normal. Using these classifications as an independent reference, women were then classified as fractured or normal by several definitions based on vertebral morphometry. No morphometric definition of vertebral fracture agreed perfectly with the consensus classifications. In general, definitions that involved combinations of measurements of anterior (Ha), middle (Hm), and posterior (Hp) vertebral height classified women more accurately than did definitions based on a single measurement or ratio. The Ha/Hp ratio produced many false positives unless it was adjusted for normal variations in the shapes of different vertebral bodies. Definitions of fracture based on a greater than 15% reduction in heights or ratios had higher sensitivity but more false positives than definitions that used a more stringent (greater than 20%) criterion. All morphometric definitions of vertebral fracture separated the post-menopausal women into two groups (fractured and normal) that had significantly (P less than 0.001) different mean spine bone density by quantitative computed tomography. Definitions that had the lowest rates of false positives also produced the largest differences in bone density between those defined as fractured and those defined as normal.

Cervical spine injury patterns in three modes of high-speed trauma: a biomechanical porcine model

Cervical spine fractures and dislocations account for a large number of deaths and disabilities in the United States each year. More knowledge of the anatomic injuries produced by known trauma may yield practical information regarding injury mechanisms and treatment alternatives. In this experiment, 16 porcine cervical spine three-vertebrae segments were subjected to flexion-compression, extension-compression, and compression-alone trauma modes. The resultant injuries were scored by anatomic dissection. The results were analyzed for variance with trauma mode using nonparametric analysis. The three modes of trauma were found to have statistically significant differences in the degree of injury to the spine and its structural components. Extension-compression trauma produced the greatest injury scores to the whole spine and to the anterior structures. Flexion-compression trauma produced the highest posterior element injury scores. Compression trauma alone produced the lowest injury scores and no definitive pattern of anatomic injuries. The severity of anatomic injuries in this model relates most to the addition of bending moments to high-speed axial compression of the spine segment.

Bone mineral density of the lumbar spine by dual photon absorptiometry: age-related regression in normal Japanese subjects and fracture threshold in osteoporotics

The bone mineral density (BMD) of the lumbar spine was determined by DPA in 280 normal Japanese volunteers and 11 osteoporotic women with compression fractures. In women, bone loss started from the mid thirties and accelerated after the age of 50 years at the rate of 0.75% (0.0074 g/cm2) per year. In men, bone loss started from the mid twenties and occurred linearly at the rate of 0.30% (0.0032 g/cm2). The overall diminutions in vertebral BMD throughout life in men and women were 13.0% and 24.3%, respectively. The mean vertebral BMD of the osteoporotic women with recent compression fractures was 37.5% lower than that of age-matched controls. The 90th percentile for vertebral BMD in this group was 0.584 g/cm2. By the age of 80 years, approximately one-fifth of normal Japanese women have BMD values less than this.