Three-dimensional kinematic stress magnetic resonance image analysis shows promise for detecting altered anatomical relationships of tissues in the cervical spine associated with painful radiculopathy

For some patients with radiculopathy a source of nerve root compression cannot be identified despite positive electromyography (EMG) evidence. This discrepancy hampers the effective clinical management for these individuals. Although it has been well-established that tissues in the cervical spine move in a three-dimensional (3D) manner, the 3D motions of the neural elements and their relationship to the bones surrounding them are largely unknown even for asymptomatic normal subjects. We hypothesize that abnormal mechanical loading of cervical nerve roots during pain-provoking head positioning may be responsible for radicular pain in those cases in which there is no evidence of nerve root compression on conventional cervical magnetic resonance imaging (MRI) with the neck in the neutral position. This biomechanical imaging proof-of-concept study focused on quantitatively defining the architectural relationships between the neural and bony structures in the cervical spine using measurements derived from 3D MR images acquired in neutral and pain-provoking neck positions for subjects: (1) with radicular symptoms and evidence of root compression by conventional MRI and positive EMG, (2) with radicular symptoms and no evidence of root compression by MRI but positive EMG, and (3) asymptomatic age-matched controls. Function and pain scores were measured, along with neck range of motion, for all subjects. MR imaging was performed in both a neutral position and a pain-provoking position. Anatomical architectural data derived from analysis of the 3D MR images were compared between symptomatic and asymptomatic groups, and the symptomatic groups with and without imaging evidence of root compression. Several differences in the architectural relationships between the bone and neural tissues were identified between the asymptomatic and symptomatic groups. In addition, changes in architectural relationships were also detected between the symptomatic groups with and without imaging evidence of nerve root compression. As demonstrated in the data and a case study the 3D stress MR imaging approach provides utility to identify biomechanical relationships between hard and soft tissues that are otherwise undetected by standard clinical imaging methods. This technique offers a promising approach to detect the source of radiculopathy to inform clinical management for this pathology.

Spinal injuries after falls from hunting tree stands

BACKGROUND CONTEXT

Spinal injuries are common sequelae of falls from hunting tree stands. Significant neurological injury is not uncommon and can result in significant morbidity as well as enormous expenditure of health care dollars. Recent literature on the subject is limited.

PURPOSE

The purpose of this study was to identify precipitating causes, characterize the spectrum of spinal injury, and determine potential interventional safety and prevention recommendations.

STUDY DESIGN

A retrospective study.

METHODS

Medical record review of 22 patients admitted either directly or via referral to a level I spinal cord injury referral center over a 10-year period (1995-2005) after a fall from a hunting tree stand.

RESULTS

All patients were men with a mean age of 46 years (range, 27-80 years). Initial acute care hospitalization averaged 10 days (range, 2-28 days). The average height of fall was 18 feet (range, 10-30 feet). Four of 19 falls (21%) occurred during the morning hours, 2 of 19 falls occurred during the afternoon, and 13 of 19 falls (68%) occurred during the evening hours. Time lapse from injury to presentation to an emergency department ranged from 30 minutes to 14 hours. Alcohol use was a factor in 2 of 20 falls (10%). Hypothermia complicated 3 of 21 cases (14%). Associated injuries were present in 12 of 21 patients (57%) and included fractures to the axial and appendicular skeleton, pneumothoraces, a retroperitoneal bleed, and a brachial plexopathy. Eight of 22 patients (37%) sustained injury to the cervical spine. Five of these 8 patients (63%) had neurological deficits (3 complete and 2 incomplete spinal cord injuries). Thirteen of 22 (59%) patients sustained injury to the thoracic or lumbar spine. Ten of these 13 (77%) had neurologic deficits (3 complete and 7 incomplete). Nine of 22 (41%) patients were treated nonoperatively; the remaining 13 (59%) underwent operative intervention.

CONCLUSIONS

Falls from hunting tree stands remain a significant cause of spinal injury and subsequent disability. The best intervention for these injuries is prevention. There is a continued need for hunter safety education to reduce the incidence of these injuries with emphasis on safety harness usage, proper installation and annual inspection of tree stands, hunting in groups with periodic contact, the use of communication devices, and abstinence from alcohol consumption while hunting.

A comparison of three screw types for unicortical fixation in the lateral mass of the cervical spine

STUDY DESIGN

In vitro comparison of three different screws for unicortical fixation in lateral masses of the cervical spine.

OBJECTIVES

To compare the axial load-to-failure of cervical lateral mass screws and their revision screws in a cadaveric model.

SUMMARY OF BACKGROUND DATA

Lateral mass screws are used for posterior fixation of the cervical spine. Risks to neurovascular structures have led many surgeons to advocate unicortical application of these screws, although fixation strength may vary with screw design.

METHODS

Screws from three posterior cervical fixation systems were used: Axis, Starlock/Cervifix, and Summit. Tested were 3.5-mm cancellous screws, along with revision screws for each system. The C3-C6 vertebrae from three cadaveric specimens were fixed with screws inserted into the lateral masses at a depth of 10 mm with 30 degrees cephalad and 20 degrees lateral angulation. Coaxial pullout force was recorded for each primary and revision screw.

RESULTS

Axial load-to-failure (mean +/- SD) of the screws was 459 +/- 60 N for Axis screws, 423 +/- 78 N for Starlock screws, and 319 +/- 97 N for Summit screws. The Axis and Starlock screws were significantly stronger than Summit screws (P = 0.017 and P = 0.067, respectively). The load-to-failure of revision screws was much lower than that of primary screws (Axis 54%, Starlock 56%, Summit 63% of the primary screw), without significant difference between screw types.

CONCLUSIONS

The Axis and Starlock screws resisted significantly greater axial load-to-failure than did the Summit screws. For all three systems, the revision screws could not restore the load-to-failure of the primary screw in this model. The tested unicortical screws had a consistently higher load-to-failure than those previously tested under similar conditions, suggesting that currently available screws may be superior to those previously tested.

Magnetic resonance imaging analysis of soft tissue disruption after flexion-distraction injuries of the subaxial cervical spine

STUDY DESIGN

A retrospective study was performed with the use of magnetic resonance imaging to evaluate the type and degree of soft tissue disruption associated with flexion-distraction injuries of the subaxial spine.

OBJECTIVE

To determine what soft tissue structures are injured in flexion-distraction injuries of the subaxial spine.

SUMMARY OF BACKGROUND DATA

Prior published reports of unilateral and bilateral cervical facet dislocations have described the analyzed mechanisms and biomechanics of this injury subtype. No retrospective magnetic resonance imaging analysis of associated soft tissue disruption has been documented.

METHODS

Magnetic resonance imaging evaluations of the cervical spine were obtained for all patients with a flexion-distraction injury, Stages 2 (unilateral facet dislocation) and 3 (bilateral facet dislocation), between September 1994 and May 1998. Two neuroradiologists, blinded to both clinical and radiographic findings, graded all the soft tissue structures for evidence of attenuation or disruption. The soft tissue structures were graded on a scale of 1 (intact), 2 (indeterminate), or 3 (disrupted).

RESULTS

For this study, 48 patients satisfied the inclusion criteria: 25 with unilateral facet dislocation and 23 with bilateral facet dislocation. Disruption to the posterior musculature, interspinous ligament, supraspinous ligament, facet capsule, ligamentum flavum, and posterior and anterior longitudinal ligaments was found in a statistically significant number of patients with bilateral facet dislocation. For most of these structures, disruption was found to be statistically significant in patients with a unilateral facet dislocation, except for the posterior longitudinal ligament, in which significance was not consistently demonstrated using 95% confidence intervals in the binomial testing. In a comparison between unilateral and bilateral facet dislocations using a two-sided Fisher's exact test, it was found that disruption to the anterior and posterior longitudinal ligaments and the left facet capsule were statistically significant, with all three more prominent in bilateral facet dislocation. A multivariate analysis between unilateral and bilateral facet dislocations showed that disruption to the anterior longitudinal ligament was associated significantly with a bilateral facet dislocation. Disc disruption was found to be associated significantly with both injury types, but was more common in bilateral facet dislocation, although this difference in intergroup comparisons was not statistically significant.

CONCLUSIONS

Unilateral and bilateral facet dislocations of the subaxial spine are associated with damage to numerous soft tissue structures that provide stability to the lower cervical spine. Damage to the posterior longitudinal ligament did not occur consistently in unilateral facet dislocations. Bilateral facet dislocations were associated significantly with disruption to the posterior and anterior longitudinal ligaments and left facet capsule, as compared with unilateral facet dislocations. Magnetic resonance imaging allows visualization of these disruptions.

Impact of smoking on the outcome of anterior cervical arthrodesis with interbody or strut-grafting

BACKGROUND

An increased rate of pseudarthrosis has been documented following posterolateral lumbar spine grafting in patients who smoke. This same relationship has been assumed for anterior cervical interbody grafting, but to our knowledge it has never been proven. This study compared the long-term radiographic and clinical results of smokers and nonsmokers who had undergone arthrodesis with autogenous bone graft following multi-level anterior cervical decompression for the treatment of cervical radiculopathy or myelopathy, or both.

METHODS

One hundred and ninety patients were followed clinically and radiographically for at least two years (range, two to fifteen years). Fifty-nine of the patients had corpectomy with strut-grafting, and 131 patients had multiple discectomies and interbody grafting. Fifty-five of the 190 patients had a history of active cigarette-smoking; fifteen of the fifty-five had corpectomy with strut-grafting, and forty had multilevel discectomies and interbody grafting. Internal fixation was not used in any patient. The reconstruction techniques and postoperative bracing regimen were similar between smokers and nonsmokers. Osseous union was judged on dynamic lateral radiographs made at least two years following surgery, and clinical outcomes were judged on the basis of pain level, medication usage, and daily activity level.

RESULTS

Of the forty smokers who had undergone multilevel interbody grafting, twenty had a solid fusion at all levels, whereas sixty-nine of the ninety-one nonsmokers had solid fusion at all levels (p < 0.02; chi-square test). This difference was especially pronounced among patients who had had a two-level interbody grafting procedure (p < 0.002; chi-square test). With the numbers available, there was no difference in the rate of fusion between smokers (fourteen of fifteen) and nonsmokers (forty-one of forty-four) who had undergone corpectomy and strut-grafting, as 93% of both groups had a solid union. In addition, clinical outcomes were significantly worse among smokers when compared with nonsmokers (p < 0.03; rank-sum analysis).

CONCLUSIONS

Smoking had a significant negative impact on healing and clinical recovery after multilevel anterior cervical decompression and fusion with autogenous interbody graft for radiculopathy or myelopathy. Since smoking had no apparent effect upon the healing of autogenous iliac-crest or fibular strut grafts, subtotal corpectomy and autogenous strut-grafting should be considered when a multilevel anterior cervical decompression and fusion is performed in patients who are unable or unwilling to stop smoking prior to surgical treatment.

Surgical treatment of thoracic spinal stenosis: a 2- to 9-year follow-up

STUDY DESIGN

A retrospective investigation of the results of operative treatment of patients with symptomatic thoracic spinal stenosis.

OBJECTIVES

To establish the effectiveness and define the limitations of surgical treatment for stenosis of the thoracic spinal canal.

SUMMARY OF BACKGROUND DATA

In contrast to cervical and lumbar stenosis, symptomatic narrowing of the thoracic spinal canal is rarely encountered. Although the treatment of thoracic stenosis has been described in multiple case reports and in several small series with minimal follow-up evaluation, there are few studies of patients treated surgically for this condition with follow-up evaluation beyond 2 years.

METHODS

Twelve patients who underwent operative decompression for symptomatic stenosis of the lower thoracic spine were followed up for an average period of 62.4 months. Surgery was performed on the thoracic spine alone in four cases and on the combined thoracolumbar spine in eight. Factors that were investigated included pain severity, lower extremity motor function, ambulatory status, and postoperative complications.

RESULTS

The level of pain after surgery was decreased in eight patients and unchanged in four patients. Of the 10 patients with a motor deficit before surgery, eight had improvement of muscle function. Of the 11 patients with a gait disturbance before surgery, ambulatory status was improved in seven, unchanged in two, and worse in two. One patient lost neural function secondary to surgical intervention. There were five cases in which the early result subsequently deteriorated because of recurrent stenosis, spinal deformity/instability, or both.

CONCLUSIONS

Thoracic stenosis can occur in isolation or, more commonly, in association with lumbar stenosis. Ideally, operative treatment should address all stenotic segments and directly decompress the primary anatomic abnormalities causing neural element compression. Although satisfactory short-term results can be expected, deterioration of the early outcome because of the potential for recurrent stenosis and deformity/instability at the thoracolumbar junction can sometimes be seen with longer follow-up evaluation periods.

Diagnosing basilar invagination in the rheumatoid patient. The reliability of radiographic criteria

BACKGROUND

Basilar invagination can be difficult to diagnose with plain radiography in patients with rheumatoid arthritis. Although numerous radiographic criteria have been described, few studies have addressed the reliability of these parameters in the rheumatoid population. The purpose of the present study was to validate and compare the most widely accepted plain radiographic criteria for basilar invagination in this patient population.

METHODS

Cervical radiographs of 131 rheumatoid patients were examined. Of these patients, sixty-seven (twenty-nine with basilar invagination and thirty-eight without it) were also evaluated with tomograms, magnetic resonance imaging, and/or sagittally reconstructed computed tomography scans to detect the presence of basilar invagination. Three observers who were blinded with regard to the diagnosis independently scored each radiograph as positive, negative, or indeterminate according to the established criteria for invagination proposed by Clark et al., McRae and Barnum, Chamberlain, McGregor, Redlund-Johnell and Pettersson, Ranawat et al., Fischgold and Metzger, and Wackenheim. Interobserver and intraobserver variability, sensitivity, specificity, total percentage of correct results, and negative and positive predictive values were determined for each criterion as well as for various combinations of the criteria.

RESULTS

No single test had a sensitivity and a negative predictive value of greater than 90% as well as a reasonable specificity and a reasonable positive predictive value. The combination of the Clark station, the Redlund-Johnell criterion, and the Ranawat criterion, scored as positive for basilar invagination if any of the three were positive, proved to be better than any single criterion; the sensitivity of the combined criteria was 94%, and the negative predictive value was 91%.

CONCLUSIONS

A screening test for basilar invagination should have a high sensitivity and a high negative predictive value, so that the disease will not be missed, and yet be specific, so that the disease will not be overdiagnosed. Our data suggest that none of the widely utilized plain radiographic criteria meet these goals. We recommend that measurements be made according to the methods described by Clark et al., Redlund-Johnell et al., and Ranawat et al. and, if any of these suggests basilar invagination, tomography or magnetic resonance imaging should be performed. Since approximately 6% of the cases of basilar invagination in rheumatoid patients would still be missed with this approach, tomography or magnetic resonance imaging should be performed on a rheumatoid patient whenever plain radiographs leave any doubt about the diagnosis of basilar invagination.

The risk of foraminal violation and nerve root impingement after anterior placement of lumbar interbody fusion cages

STUDY DESIGN

Three groups of six embalmed cadaver spines underwent placement of lumbar interbody fusion cages centered either at midline, 10% lateral of midline, or 20% lateral of midline. The spines were evaluated for evidence of neuroforamen violation or nerve root impingement.

OBJECTIVES

To determine the potential for foraminal violation or nerve root impingement after correct placement and lateral misplacement of lumbar interbody fusion cages.

SUMMARY OF BACKGROUND DATA

Radicular symptoms after anterior cage placement have raised some concern about the potential for inadvertent device-related foraminal violation not adequately appreciated by intraoperative fluoroscopy.

METHODS

Preoperative computed tomography scanning and plain radiography was used to measure endplate dimensions at L4-L5 and to template the appropriately sized interbody fusion cages. The cadaveric specimens were randomly divided into three groups of six (Groups I-III) and instrumented at L4-L5 either at midline (I) or 10% (II) or 20% (III) lateral of midline. Postoperative computed tomography and plain radiography was evaluated for evidence of neuroforamen violation, followed by dissection of the specimens.

RESULTS

Foraminal violation occurred in one of six spines in group II (10% off midline) and in three of six spines in group III (20% off midline). Two of the three cadavers in group III with foraminal violation also were noted to have nerve root abutment on computed tomography scans and spinal dissection.

CONCLUSIONS

Excessive lateral placement of lumbar interbody fusion cages may result in foraminal violation and possible nerve encroachment. The "safe zone" for centering the cages extends approximately 5 mm on either side of midline.

A plate-rod device for treatment of cervicothoracic disorders: comparison of mechanical testing with established cervical spine in vitro load testing data

Posterior cervical internal fixation has long been accomplished using wires, hooks, and rods. More recently, the cervical lateral mass screw and plate or rod systems have been used effectively in unstable lower cervical spine disorders. Each form of fixation has its advantages and disadvantages. Interspinous wiring and lateral mass screw placement obviate canal penetration in the cervical region but are associated with a potential neurologic risk as a result of canal encroachment. Minor canal intrusion by laminar hooks in the thoracic spine pose a lesser neurologic risk than in the cervical region. To exploit the benefits and safety features of spinal instrumentation, a combination plate rod construct (PRC) has been developed that obviates canal penetration in the cervical region by way of lateral mass and cervical pedicle screw fixation and hooks or wires in the thoracic spine. A biomechanical analysis of the PRC device was performed and compared with the in vivo maximal load data of the cervical spine and established maximal load data of the Roy-Camille posterior cervical fixation system. The PRC has greater strength and resistance to failure than is necessary to sustain maximal in vivo cervical spine loads, and it has also compared favorably with the parameters of the Roy-Camille system. The PRC device, or variations on it, is an excellent option for spinal fixation across the cervicothoracic junction because of its superior biomechanical qualities and versatility in stabilizing a complex anatomic junction of the spine.

Degenerative lumbar stenosis: diagnosis and management

Degenerative lumbar stenosis is a common cause of disabling back and lower extremity pain among older persons. The process usually begins with degeneration of the intervertebral disks and facet joints, resulting in narrowing of the spinal canal and neural foramina. Associated factors may include a developmentally narrow spinal canal and degenerative spinal instability. Nonoperative management includes restriction of aggravating activities, physical therapy, and anti-inflammatory medications. If nonoperative treatment has failed, surgical treatment may be appropriate. Decompression should be performed so as to address all clinically relevant neural elements while maintaining spinal stability. If instability is present, autogenous intertransverse bone grafting is recommended. There may be an advantage to augmenting some of these procedures with internal fixation. Surgical success rates as high as 85% have been reported, but may be compromised by inadequate decompression, inadequate stabilization, or medical comorbidities. Short-term follow-up data indicate that operative management provides more effective relief than nonoperative treatment, but prospective studies comparing the effects of nonoperative and operative interventions on the long-term natural history of lumbar spinal stenosis are needed.

Anterior cervical corpectomy in patients previously managed with a laminectomy: short-term complications

BACKGROUND

The purpose of this study was to evaluate the complications of anterior cervical corpectomy and arthrodesis in patients who had had a previous cervical laminectomy. The results of previous studies have suggested that these patients can be managed with anterior decompression and an arthrodesis with either plate fixation or immobilization in a halo vest. However, no studies that we are aware of have specifically focused on the complications of these types of procedures.

METHODS

The records and radiographs of eighteen patients who had been managed with a one to four-level corpectomy with strut-grafting were retrospectively reviewed. The reviews were independently performed by the three of us who were not involved in the original operation. The interval between the laminectomy and the corpectomy ranged from one month to twenty-two years (mean, eight years).

RESULTS

Eleven of the eighteen patients sustained a total of sixteen complications during the follow-up period, which averaged 2.7 years (range, seven months to six years and four months), and nine of the eleven had graft-related complications. Five grafts extruded or collapsed, or both. There were four reoperations. Immobilization in a halo vest did not prevent extrusions, as three of the four extrusions occurred while the patient wore a halo vest. Four patients had a pseudarthrosis. In three patients, the kyphosis increased by 10 degrees or more from the immediate preoperative period to the most recent follow-up evaluation. Two patients had respiratory distress that necessitated reintubation, one patient had a small dural tear, and one had transient dysphagia.

CONCLUSIONS

Our data suggest that anterior cervical corpectomy without instrumentation in a patient who has had a previous laminectomy is associated with a great risk of graft-related complications despite the use of a halo vest. This previously unreported finding is relevant in that it contradicts the recommendation previously made by Zdeblick and the senior one of us, who advocated postoperative immobilization in a halo vest for these patients. Anterior cervical corpectomy should be performed with caution and knowledge of the potential complications in a patient who has had a previous laminectomy.

Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis

BACKGROUND

We studied the incidence, prevalence, and radiographic progression of symptomatic adjacent-segment disease, which we defined as the development of new radiculopathy or myelopathy referable to a motion segment adjacent to the site of a previous anterior arthrodesis of the cervical spine.

METHODS

A consecutive series of 374 patients who had a total of 409 anterior cervical arthrodeses for the treatment of cervical spondylosis with radiculopathy or myelopathy, or both, were followed for a maximum of twenty-one years after the operation. The annual incidence of symptomatic adjacent-segment disease was defined as the percentage of patients who had been disease-free at the start of a given year of follow-up in whom new disease developed during that year. The prevalence was defined as the percentage of all patients in whom symptomatic adjacent-segment disease developed within a given period of follow-up. The natural history of the disease was predicted with use of a Kaplan-Meier survivorship analysis. The hypothesis that new disease at an adjacent level is more likely to develop following a multilevel arthrodesis than it is following a single-level arthrodesis was tested with logistic regression.

RESULTS

Symptomatic adjacent-segment disease occurred at a relatively constant incidence of 2.9 percent per year (range, 0.0 to 4.8 percent per year) during the ten years after the operation. Survivorship analysis predicted that 25.6 percent of the patients (95 percent confidence interval, 20 to 32 percent) who had an anterior cervical arthrodesis would have new disease at an adjacent level within ten years after the operation. There were highly significant differences among the motion segments with regard to the likelihood of symptomatic adjacent-segment disease (p<0.0001); the greatest risk was at the interspaces between the fifth and sixth and between the sixth and seventh cervical vertebrae. Contrary to our hypothesis, we found that the risk of new disease at an adjacent level was significantly lower following a multilevel arthrodesis than it was following a single-level arthrodesis (p<0.001). More than two-thirds of all patients in whom the new disease developed had failure of nonoperative management and needed additional operative procedures.

CONCLUSIONS

Symptomatic adjacent-segment disease may affect more than one-fourth of all patients within ten years after an anterior cervical arthrodesis. A single-level arthrodesis involving the fifth or sixth cervical vertebra and preexisting radiographic evidence of degeneration at adjacent levels appear to be the greatest risk factors for new disease. Therefore, we believe that all degenerated segments causing radiculopathy or myelopathy should be included in an anterior cervical arthrodesis. Although our findings suggest that symptomatic adjacent-segment disease is the result of progressive spondylosis, patients should be informed of the substantial possibility that new disease will develop at an adjacent level over the long term.

The use of diagnostic imaging to assess spinal arthrodesis

Despite advances in surgical techniques and internal fixation devices, pseudarthrosis remains a significant factor in the clinical failure of attempted fusions in the cervical, thoracic, and lumbar spine. This article reviews the use of diagnostic imaging in the assessment of spinal fusion, with a focus on the accuracy of different imaging modalities based on surgical exploration. A cost-effective strategy for the radiographic follow-up of patients after spinal fusion surgery also is presented.

The success of anterior cervical arthrodesis adjacent to a previous fusion

STUDY DESIGN

A retrospective review of all patients surgically treated for adjacent segment disease of the cervical spine over a 20-year period.

OBJECTIVES

To determine the clinical and radiographic success of discectomy with interbody grafting and corpectomy with strut grafting in the treatment of adjacent segment disease of the cervical spine.

SUMMARY OF BACKGROUND DATA

Up to 25% of all patients undergoing anterior cervical fusion have new disease due to degeneration of an adjacent segment within 10 years. The success of surgical treatment in these patients with adjacent segment disease has not been reported.

METHODS

Thirty-eight patients were surgically treated for adjacent segment disease by discectomy with interbody grafting or corpectomy with strut grafting. Arthrodesis was evaluated by flexion-extension lateral radiographs and clinical outcomes were assessed using Robinson's criteria at least 2 years after surgery. Fusion rates were compared by Fisher's exact test, and outcomes were compared by rank-sum analysis.

RESULTS

The rate of arthrodesis was significantly lower in the 24 patients treated by discectomy with interbody grafting at one or more levels (63%) than in the 14 patients treated by corpectomy with strut grafting (100%; P = 0.01). Clinical outcomes were similar for the corpectomy and discectomy groups (P = 0.55). There was a trend toward better outcomes in patients who achieved a solid arthrodesis (P = 0.13).

CONCLUSIONS

Achieving fusion is more difficult when anterior cervical arthrodesis is performed adjacent to a prior fusion. Strut grafting resulted in a significantly higher rate of arthrodesis than interbody grafting.

The role of melatonin in the pathogenesis of adolescent idiopathic scoliosis

STUDY DESIGN

A matched, case-control study comparing melatonin production in female patients with and without adolescent idiopathic scoliosis.

OBJECTIVES

To determine whether melatonin production is decreased in adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

A central etiology for idiopathic scoliosis has never been established. Previous authors have produced experimental scoliosis in chickens after pinealectomy, preventable by administration of melatonin. They suggested that a defect in melatonin synthesis might be involved in the pathogenesis of human idiopathic scoliosis.

METHODS

Nine female adolescents with no medical problems, normal neurologic examinations, radiographic idiopathic scoliosis of 15-40 degrees, and Risser Stage I-III were in the patient group. Eighteen healthy adolescent girls with no medical problems, a negative school screening, and no family history of scoliosis were control subjects. Patients and control subjects were matched for age, weight, Tanner stage, sleep duration, and light exposure by multiple linear regression. Nighttime and daytime urine samples were analyzed for melatonin by high-performance liquid chromatography.

RESULTS

Although nighttime melatonin levels were significantly higher than daytime levels in all volunteers (P < 0.00002), there were no significant differences in nighttime (P > 0.63) or daytime (P > 0.78) melatonin levels between patients and control subjects, even after matching by multiple linear regression analysis. A statistical analysis demonstrated that if a melatonin deficiency of 25% or more did exist in patients with scoliosis compared with control subjects, the likelihood that it would have been detected in this study was more than 98%.

CONCLUSION

Although melatonin deficiency may cause scoliosis in the chicken, this study suggests that it is not a mechanism in the pathogenesis of adolescent idiopathic scoliosis in humans.

The role of pediculolaminar fixation in compromised pedicle bone

STUDY DESIGN

This in vitro study analyzed the effects of a supralaminar hook on pedicle screw fixation in compromised pedicle bone.

OBJECTIVES

To determine the ability of pediculolaminar fixation to restore pedicle screw pull-out strength after stripping of senile pedicle bone.

SUMMARY OF BACKGROUND DATA

Despite improvements in pedicle screw design, the bone-screw interface remains the "weakest link" in pedicle screw fixation. This interface is especially vulnerable in osteoporotic bone previously instrumented pedicles, and at the ends of long instrumentation constructs.

METHODS

Side-to-side testing between a pedicle screw and a pedicle screw supplemented with a supralaminar hook (pediculolaminar fixation) was performed in human cadaveric lumbar vertebrae. Comparisons were made for intact and compromised pedicle bone.

RESULTS

Pediculolaminar fixation restored 89% of intact pedicle screw pull-out strength whereas the pedicle screw alone restored only 19% of intact pull-out strength. The role of pediculolaminar fixation was greatest in weaker bone. Significant differences were noted in energy to failure and post-failure energy. In intact bone, the pediculolaminar construct did not increase pull-out strength or energy to failure, although it did have a greater post-failure energy.

CONCLUSIONS

Pediculolaminar fixation can augment pedicle screw fixation in pedicle bone compromised by previous stripping or significant osteoporosis or both.

The sagittal alignment of the cervical spine in adolescent idiopathic scoliosis

To assess the sagittal orientation of the cervical and thoracolumbar spine, 38 adolescents with idiopathic scoliosis were studied. The C7 plumb line and Cobb angles from C2-6, T1-12, and L1-S1 were measured on preoperative films. Lateral radiographs with > 1-year follow-up after surgical correction were available for the same measurements in 28 patients. The preoperative curve from C2-6 was 6 +/- 11 degrees of kyphosis. There was a significant correlation between the loss of thoracic kyphosis and the development of cervical kyphosis for the entire group preoperatively (p = 0.009). Postoperatively, cervical kyphosis increased to 11 +/- 9 degrees at 1-year follow-up (p = 0.05). There was no progression of cervical kyphosis in patients with "thoracic hypokyphosis" (kyphosis < 20 degrees). Cervical kyphosis increased in patients with "normal" thoracic kyphosis (20-40 degrees) and in patients with hyperkyphosis (kyphosis > 40 degrees) after surgery, despite preservation of thoracolumbar sagittal contour. There were no significant differences between the sagittal contour of patients treated with Cotrel-Dubousset or Harrington instrumentation.

Acute spondylolytic spondylolisthesis. Risk of progression and neurological complications

Acute spondylolytic spondylolisthesis was diagnosed after major trauma in five patients. The level of injury was between the third and fourth lumbar vertebrae in one patient and between the fifth lumbar and first sacral vertebrae in four. The initial spondylolisthesis was grade I in four patients and grade III in one. Four of the patients were initially managed non-operatively. The deformity did not progress in a five-year-old boy with grade-I spondylolisthesis who had been managed with immobilization in a body cast. The deformity progressed in two of the adolescents who had been managed non-operatively; the progression was from grade I to grade III in one of these patients and from grade III to grade V (spondyloptosis) in the other, in whom a cauda equina syndrome also developed. The latter patient was subsequently managed with posterior reduction and arthrodesis followed by an anterior arthrodesis, and the neurological deficits resolved. The deformity also progressed, from grade I to grade II over three years, in a fifty-seven-year-old woman who had been managed non-operatively. One patient who had a grade-I deformity was managed with immediate operative stabilization followed by immobilization in a thoracolumbosacral orthosis; the deformity did not progress. Although minor or repetitive trauma is often associated with spondylolysis, high-energy trauma may produce a more severe form of spondylolysis with spondylolisthesis. These deformities are more unstable, with instability similar to that of a fracture-dislocation, and they have a greater propensity to progress than the usual form of spondylolytic spondylolisthesis.(ABSTRACT TRUNCATED AT 250 WORDS)