Posterior lumbar interbody cages do not augment segmental biomechanical stability.

The effect on stiffness of installing posterior threaded interbody cages at LA-L5 was evaluated using fresh human cadaveric spine specimens. The cages did not increase spine stiffness significantly in any tested range of motion. Supplemental posterior pedicular screw/rod instrumentation, however, significantly increased stiffness. The assertion that use of cages as isolated posterior implants improves stability may be invalid.

The effect of cigarette smoking and smoking cessation on spinal fusion.

STUDY DESIGN: The effect of cigarette smoking and smoking cessation on spinal fusion was studied in a retrospective review of 357 patients who had undergone instrumented spinal fusion. OBJECTIVE: To document the widely assumed but unreported benefit of cigarette smoking cessation on fusion rate and clinical outcome after spinal fusion surgery. BACKGROUND DATA: Cigarette smoking has been shown to inhibit lumbar spinal fusion and to adversely effect outcome in treatment of lumbar spinal disorders. Prior reports have compared smokers and nonsmokers, as opposed to comparing smokers and quitters. METHODS: This study retrospectively identified 357 patients who underwent a posterior instrumented fusion at either L4-L5 or L4-S1 between 1992 and 1996. Analysis of the medical record and follow-up telephone surveys were conducted. Clinical outcome and fusion status was analyzed in relation to preoperative and postoperative smoking parameters. RESULTS: In this study, the nonunion rate was 14.2% for nonsmokers and 26.5% for patients who continued to smoke after surgery (P < 0.05). Patients who quit smoking after surgery for longer than 6 months had a nonunion rate of 17.1%. The nonunion rate was not significantly affected by either the quantity that a patient smoked before surgery or the duration of preoperative smoking abatement. Return-to-work was achieved in 71% of nonsmokers, 53% of nonquitters, and 75% of patients who quit smoking for more than 6 months after surgery. DISCUSSION: These results validate the hypothetical assumption that postoperative smoking cessation helps to reverse the impact of cigarette smoking on outcome after spinal fusion.

The role of directly applied hypothermia in spinal cord injury.

STUDY DESIGN: The effect of intense local hypothermia was evaluated in a precision model of spinal canal narrowing and spinal cord injury in rats. The spinal cord injury was cooled with a custom cooling well used over the epidural surface. Basso, Beattie, and Bresnahan (BBB) motor scores and transcranial magnetic motor-evoked potential (tcMMEP) responses were used after injury to accurately evaluate neurologic recovery. OBJECTIVE: This study was undertaken to determine whether the prognosis for neurologic recovery in a standardized rat spinal cord injury model is altered by the direct application of precisely controlled hypothermia to the area of injury. SUMMARY OF BACKGROUND DATA: The role of hypothermia in the treatment of spinal cord injuries with neurologic deficits remains undefined. Hypothermia may decrease an area of spinal cord injury and limit secondary damage, therefore improving neurologic recovery. However, it has been difficult to consistently apply localized cooling to an area of spinal cord injury, and the use of systemic hypothermia is fraught with complications. This fact, along with the unavailability of a precise spinal cord injury model, has resulted in inconsistent results, both clinically and in the laboratory. In a rat model of spinal cord injury, 37 C and 19 C temperatures were used to study the role of hypothermia on neurologic recovery. METHODS: Male Spraque-Dawley rats (n = 52; weight, 277.7 g) were anesthetized with pentobarbital and subjected to laminectomy at T10. The rats were divided into three groups: 1) placement of a 50% spacer in the epidural space (16 rats), 2) severe (25 g/cm) spinal cord injury (16 rats), 3) 50% spacer in combination with spinal cord injury (16 rats). Eight rats in each group were tested at two temperatures: normothermic (37 C) and hypothermic (19 C). With the use of a specially designed hypothermic pool placed directly over the spinal cord for 2 hours, epidural heating to 37 C, and epidural cooling to 19 C was accomplished. Simultaneous measurements of spinal cord and body temperatures were performed. The rats underwent behavior testing using the BBB motor scores and serial tcMMEPs for 5 weeks. Statistical methods consisted of Student's t tests, one-way analysis of variance, Tukey post hoc t tests and chi2 tests. RESULTS: There was a significant improvement in motor scores in rats subjected to hypothermia compared with those that were normothermic after insertion of a 50% spacer. This improvement was observed during the 5-week duration of follow-up. In the severe spinal cord injury group and the spinal cord injury-spacer groups, no significant improvement in motor scores were obtained when the spinal cord was exposed to hypothermia. CONCLUSION: The results demonstrate that there is a statistically significant (P < 0.05) improvement in neurologic function in rats subjected to hypothermia (19 C) after insertion of a spacer that induced an ischemic spinal cord injury. This indicates that directly applied hypothermia may be beneficial in preventing injury secondary to ischemic cellular damage. The data demonstrated minimal therapeutic benefit of hypothermia (19 C) after a severe spinal cord injury.

The durability of small-diameter rods in lumbar spinal fusion.

The use of a small-diameter rod in lumbar fusion offers a lower hardware profile and reduced implant bulk. Concern has been raised, however, about the ability of smaller rods to withstand the cyclic loads placed on them until fusion is achieved. This study is a retrospective radiographic review designed to evaluate the durability of a 4.75-mm diameter rod in the early postoperative period before fusion healing. Examination of postoperative radiographs revealed two instances of rod failure that occurred more than 24 months after operation among 85 cases of pedicle screw instrumentation followed for an average of 32 months. Based on these preliminary data, the benefits of a small-diameter rod can be obtained without an increased incidence of rod failure during the initial healing period.

The influence of spinal canal narrowing and timing of decompression on neurologic recovery after spinal cord contusion in a rat model.

STUDY DESIGN: The effect of spinal canal narrowing and the timing of decompression after a spinal cord injury were evaluated using a rat model. OBJECTIVE: To evaluate whether progressive spinal canal narrowing after a spinal cord injury results in a less favorable neurologic recovery. Additionally, to evaluate the effect of the timing of decompression after spinal cord injury on neurologic recovery. SUMMARY OF BACKGROUND DATA: Results in previous studies are contradictory about whether the amount of canal narrowing or the timing of decompression after a spinal cord injury affects the degree of neurologic recovery. METHODS: Forty adult male Sprague-Dawley rats were equally divided into a control group, in which spacers of 20%, 35%, and 50% were placed into the spinal canal after laminectomy, and an injury group in which the spacers were placed after a standardized incomplete spinal cord injury. After spacer removal, neurologic recovery in both was monitored by Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale (Ohio State University, Columbus, OH) motor scores and transcranial magnetic motor evoked potentials for 6 weeks followed by histologic examination of the spinal cords. Subsequently, 42 rats were divided into five groups in which, after spacer placement, the time until decompression was lengthened 0, 2, 6, 24, and 72 hours. Again, serial BBB motor scores and transcranial magnetic motor evoked potentials were used to assess neurologic recovery for 6 weeks until the animals were killed for histologic evaluation. RESULTS: Spacer placement alone in the control animals resulted in no neurologic injury until canal narrowing reached 50%. All of the control groups (spacer only) exhibited significantly better (P < 0.05) motor scores compared with the injury groups (injury followed by spacer insertion). Within the injury groups the motor scores were progressively lower as spacer sizes increased from the no-spacer group to the 35% group. The results in the 35% and 50% groups were not statistically different. The results of the time until decompression demonstrated that the motor scores were consistently better the shorter the duration of spacer placement (P < 0.05) for each of the time groups (0, 2, 6, 24, and 72 hours) over the 6-week recovery period. Histologic analysis showed more severe spinal cord damage as both spinal canal narrowing and the time until decompression increased. CONCLUSION: The results in this study present strong evidence that the prognosis for neurologic recovery is adversely affected by both a higher percentage of canal narrowing and a longer duration of canal narrowing after a spinal cord injury. The tolerance for spinal canal narrowing with a contused cord appears diminished, indicating that an injured spinal cord may benefit from early decompression. Additionally, it appears that the longer the spinal cord compression exists after an incomplete spinal cord injury, the worse the prognosis for neurologic recovery.

Preoperative SF-36 responses as a predictor of reoperation following lumbar fusion.

This study examined preoperative SF-36 (Medical Outcomes Study Short Form 36-item questionnaire) data in patients who required a subsequent surgical procedure following lumbar spine fusion to identify potential predictors of this adverse surgical outcome. Of the 235 patients treated by lumbar fusion, 27 patients required an additional procedure. Analysis of preoperative SF-36 responses revealed higher scores in social function (P=.013), and pain (P=.021) for the 208 patients who underwent only the initial fusion versus the 27 patients requiring a subsequent intervention. This study suggests that components of the SF-36 carry prognostic value for lumbar spinal surgery.

Effect of prior lumbar discectomy on outcome of lumbar fusion: a prospective analysis using the SF-36 measure.

This study prospectively measured patient-reported quality-of-life outcome in patients undergoing fusion for recurrent symptoms after prior discectomy. Analysis of SF-36 data revealed statistically significant improvement in physical function, social function, and bodily pain 1 year postoperatively. Analysis of variance revealed significant interactions based on worker's compensation, litigation status, educational level, and age. The results support the conclusion that the SF-36 is a useful and applicable tool for measuring patient perception and quality-of-life parameters after spinal surgery. SF-36 outcomes demonstrated a reasonable level of success for lumbar fusion in revision spine surgery, with the most significant improvements noted in the categories of pain, physical function, and social function.

Clinical outcome after fusion of the thoracic or lumbar spine in the adult patient.

This article highlights those disease processes for which fusion is used most frequently in the adult. Although the focus is on clinical outcome after fusion, the indications and natural history of the process itself are also briefly discussed to provide a comparative basis on which outcomes may be judged.

A human cadaver model for determination of pathologic fracture threshold resulting from tumorous destruction of the vertebral body.

STUDY DESIGN: Thoracic vertebrae were subjected to compressive loads after drilling of the centrum to simulate destruction from metastatic tumorous involvement. OBJECTIVE: To determine whether a threshold exists that is predictive of fractures to establish a correlation between significant variables and vertebral strength. SUMMARY OF BACKGROUND DATA: The mechanical effects of metastatic destruction of thoracic vertebral bodies and their correlation to pathologic fractures has been analyzed in few studies. In additional studies on intact vertebral strength, investigators have determined that bone mineral density and geometric factors are important. METHOD: Fifty-four cadaveric thoracic vertebrae were studied. All were examined by quantitative computed tomography. T4 and T10 served as mechanical controls to predict the intact strength of T7. The test vertebrae were drilled from the anterior cortex through to the posterior cortex before they were loaded. RESULTS: Linear correlation between the strength of T4 and T10 in each spine supported the predicted strengths of T7. Because of variation from other factors, no threshold defect size was noted beyond which failure consistently occurred. Results of linear correlation analyses showed that the best combination of parameters for predicting vertebral strength was the product of bone mineral density and the remaining intact vertebral body cross-sectional area. This vertebral strength index correlated linearly with the strength of intact and compromised T7 vertebrae (r2 = 0.52). CONCLUSIONS: The vertebral strength index can be used to predict the strength of any thoracic vertebra. When compared with an idealized vertebral strength index based on the intact vertebral cross-sectional area and normal bone mineral density, a patient's actual vertebral strength index can be used as one of the criteria for prophylactic stabilization.

The effect of postoperative nonsteroidal anti-inflammatory drug administration on spinal fusion.

STUDY DESIGN: The influence of ketorolac on spinal fusion was studied in a retrospective review of 288 patients who underwent an instrumented spinal fusion. OBJECTIVE: To assess the effect of postoperative ketorolac administration on subsequent fusion rates. SUMMARY OF BACKGROUND DATA: Nonsteroidal anti-inflammatory drugs are widely used compounds, which are known to inhibit osteogenic activity and have been shown to decrease spinal fusion in an animal model. No previous studies have examined the influence of nonsteroidal anti-inflammatory drugs on spinal fusion in clinical practice. METHODS: The medical records of 288 patients who underwent instrumented spinal fusion from L4 to the sacrum between 1991 and 1993 were reviewed retrospectively. The 121 patients who received no nonsteroidal anti-inflammatory drugs were compared with the 167 patients who received ketorolac after surgery. The groups were demographically equivalent. RESULTS: Ketorolac had a significant adverse effect on fusion, with five nonunions in the nondrug group and 29 nonunions in the ketorolac group (P > 0.001). Ketorolac administration also significantly decreased the fusion rate for subgroups including men, women, smokers, and nonsmokers. The odds ratio demonstrated that nonunion was approximately five times more likely after ketorolac administration. Cigarette smoking also decreased the fusion rate (P > 0.01); smokers were 2.8 times more likely to develop nonunion. CONCLUSION: These data suggest that nonsteroidal anti-inflammatory drugs significantly inhibit spinal fusion at doses typically used for postoperative pain control. The authors recommend that these drugs be avoided in the early postoperative period.

Paraspinal pyomyositis, a rare cause of severe back pain: case report and review of the literature.

Pyomyositis, a pyogenic infection of skeletal muscle, is rarely reported in temperate climates. A case of pyomyositis within the paraspinal muscles of a 63-year-old man is reported, with details of diagnostic evaluation and medical and surgical treatment of the condition. Failure to recognize this clinical entity can lead to diagnostic delay and inappropriate management.

Management of iatrogenic spinal stenosis complicating placement of a fusion cage. A case report.

STUDY DESIGN: A case of iatrogenic spinal stenosis secondary to fusion cage retropulsion is presented. OBJECTIVES: To highlight fusion cage retropulsion, a potential complication that may become more prevalent as the use of fusion cage instrumentation expands. The difficulty in management of this complication is emphasized. SUMMARY OF BACKGROUND DATA: Early reports regarding fusion cage instrumentation have been encouraging. At this point, however, the potential benefits are better defined than the potential complications. METHODS: A significant complication of fusion cage instrumentation and the limited literature on this subject are reviewed. RESULTS: The patient underwent successful revision surgery after retropulsion of a fusion cage, however, an extensive surgical procedure including partial vertebral body resection was required. CONCLUSIONS: The frequency and severity of complications related to fusion cage instrumentation remain poorly defined. Caution should be used in patient selection until additional experience more clearly defines the risk-to-benefit ratio for a given application of this new technology.

Salvage of instrumental lumbar fusions complicated by surgical wound infection.

STUDY DESIGN: This study retrospectively reviewed instrumented lumbar fusions complicated by surgical wound infection and managed by a protocol including antibiotic impregnated beads. OBJECTIVE: To evaluate the potential for an acceptable clinical outcome in cases of instrumented lumbar fusion complicated by wound infection. SUMMARY OF BACKGROUND DATA: Initial studies of pedicle screw instrumentation suggested an increased infection rate versus noninstrumented fusion. The presence of a metallic implant also complicates wound management. METHODS: Eight hundred fifty-eight instrumented fusions were reviewed with 22 (2.6%) deep wound infections identified. Analysis included preoperative risk factors, surgical procedure, postoperative course, and clinical outcome. RESULTS: Nineteen patients (mean age, 55 years) were reviewed at a minimum of 1 year after surgery. Sixteen (83%) reported significant preoperative health problems. Forty-seven percent of the patients had three- and four-level fusions. Mean operative time was 342 minutes. Mean estimated blood loss was 1620 mL. Infection was diagnosed at an average of 16 days after surgery with wound drainage as the most common presenting feature. Patients underwent between two and 10 (mean, 4.7) irrigation procedures. Seven patients had other significant noninfectious complications. At follow-up evaluation, no patient had recurrence of infection. By comparison to preoperative symptoms, 15 patients were improved, three were unchanged, and one deteriorated. Fusion was apparently solid in 14 patients, probable in four patients, and nonunion occurred in one patient. CONCLUSION: Although wound infection is a significant complication, this study suggests that aggressive surgical management can result in preservation of an adequate fusion rate and maintenance of an acceptable postoperative outcome.

The effects of nonsteroidal anti-inflammatory drugs on posterior spinal fusions in the rat.

STUDY DESIGN: This was a prospective study to determine the potential effects of indomethacin on spinal fusions in the rat. OBJECTIVES: To determine if indomethacin exerts a deleterious effect on spinal fusions in the rat model. SUMMARY OF BACKGROUND DATA: Nonsteroidal anti-inflammatory drugs are a class of compound that affect bone osteogenesis during fracture healing and heterotopic ossification. Spinal fusion is a process that occurs via osteogenesis and, therefore, may be similarly affected. METHODS: Thirty-nine adult, Sprague-Dawley rats underwent a three-level posterior spinal fusion. Fusion was performed using morselized autogenous vertebral bone graft obtained via caudectomy and stabilized using a cerclage wiring technique. The 39 rats were divided into two groups consisting of 17 study animals and 22 control animals. The control group was injected with 1.5 cc of 0.9 normal saline subcutaneously for 12 weeks, whereas the test animals were injected on an identical schedule using 3 mg/kg of indomethacin sodium salt. Two control animals died, and three animals in the treatment group died of drug-related complications. Twelve weeks after surgery, all animals were killed, and the involved spinal segments were evaluated by direct manual examination. A fusion was probable if the spinal segments exhibited decreased scaled micromotion. RESULTS: Sixty segmental levels in 20 control animals were assessed. Overall, 27 of 60 levels (45%) achieved fusion. In the indomethacin-treated group, 42 levels in 14 animals were evaluated. Overall, four of 42 levels (10%) achieved a fusion. Chi-square analysis demonstrated a significant difference (P < 0.001) between the control and indomethacin-treated groups. CONCLUSIONS: This study raises serious questions about the inhibitory effects of nonsteroidal anti-inflammatory drugs on spinal fusion. Clinically, the widespread use of nonsteroidal anti-inflammatory drugs in the postoperative period after spinal fusion may need to be avoided.

Perioperative complications of anterior procedures on the spine.

We reviewed the operative and hospital records of 447 patients in order to determine the rates of perioperative complications associated with an anterior procedure on the thoracic, thoracolumbar, or lumbar spine. The anterior procedures were performed to treat spinal deformity or for débridement or decompression of the spinal canal. The diagnostic groups that we studied included idiopathic scoliosis in adolescents or young adults (100 patients), scoliosis in mature adults (sixty-three patients), kyphosis (sixty-one patients), neuromuscular scoliosis (sixty patients), fracture (forty-seven patients), a revision procedure (thirty-nine patients), congenital scoliosis (thirty-six patients), tumor (nineteen patients), vertebral osteomyelitis or discitis (eight patients), and miscellaneous (fourteen patients). Complications occurred in 140 (31 per cent) of the 447 patients and were classified as major or minor. Forty-seven patients (11 per cent) had at least one major complication and 109 (24 per cent) had at least one minor complication. Two patients died, both from pulmonary complications after the operation. The most common type of major complication was pulmonary; the most common type of minor complication was genito-urinary. The adolescent or young adult patients who had idiopathic scoliosis had the lowest rate of complications, and the patients who had neuromuscular scoliosis had the highest. An age of more than sixty years at the time of the operation was associated with a higher risk of complications. The duration of the procedures involving a thoracic approach was shorter than that of those involving a thoracolumbar or lumbar approach; however, the rate of complications was not significantly different among the three approaches. Vertebrectomies took longer to perform and were associated with a greater estimated blood loss than discectomies; however, there was no significant difference in the rate of complications between the two types of procedures. The patients who had a fracture or a tumor lost more blood than those from the other diagnostic groups. Blood loss increased as the duration of the operation increased for all procedures. Combined anterior and posterior procedures performed during the same anesthesia session were associated with a higher rate of major complications than were procedures that were staged. A logistical regression analysis showed that the variables that increased the risk of a major complication were an estimated blood loss of more than 520 milliliters and an anterior and posterior procedure performed sequentially under the same anesthesia session. This analysis also demonstrated that the diagnosis of idiopathic scoliosis in adolescents or young adults was associated with a reduced risk of major complications. Compared with other major operations, an anterior procedure on the thoracic, thoracolumbar, or lumbar spine performed for the indications mentioned in this study is relatively safe.

Thoracolumbar burst fractures treated with combined anterior and posterior surgery.

Between 1985 and 1992, 84 burst fractures were surgically managed with anterior decompression, autologous iliac crest strut graft, and posterior instrumentation and fusion. Fifteen were lost to follow-up, leaving 69 patients for detailed review. Of the 22 patients with complete or partial neurologic injury, 12 patients either totally or partially recovered function following surgery. Of these 12 patients, 6 improved 1 Frankel grade; 5 improved 2 Frankel grades, and 1 improved 3 Frankel grades. Follow-up was 12 to 91 months (average 41 months). For all of the fractures in this series, the mean operative correction in sagittal kyphosis was 14 degrees, but this decreased to 7 degrees at final review. No patient had significant scoliosis, and 66 patients achieved solid arthrodesis with 3 pseudoarthroses (4%). Mean operative time for 2-in-1 procedures was 5 hours 42 minutes, with an estimated blood loss of 1,455 mL. Of 62 patients available for follow-up telephone interview, 42 (68%) had minimal or no pain; 11, mild pain; 8, moderate pain; and 1, severe pain. Function in daily activities was assessed as normal or minimally impaired in 43 of 51 patients (84%) with normal neurologic function by physical examination. We conclude that anterior decompression, strut autografting, and posterior instrumented autogenous fusion, either as a combined or staged procedure, is a safe surgical option for thoracolumbar burst fractures.

Idiopathic juvenile osteoporosis. An unusual cause of back pain in an adolescent.

Idiopathic juvenile osteoporosis represents a rare bone disorder that affects prepubescent children of both sexes. The diagnosis is generally one of exclusion, ruling out other potential metabolic bone diseases. Here, the authors present a representative case of this rare disorder in an otherwise healthy male, along with the clinical history, physical presentation, and review of the available literature. Finally, it is important to note that patients with this disorder often have profound involvement of the spinal column with multiple compression fractures.

A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation.

STUDY DESIGN: In a prospective study of 90 patients undergoing lumbar pedicle screw instrumentation, 512 screws were tested intraoperatively using electrical stimulation. The accuracy of this technique was verified after surgery by computed tomography. OBJECTIVES: Computed tomographic scans taken after surgery were used to evaluate the efficacy of intraoperative screw stimulation and electromyographic monitoring of pedicle screw placement. SUMMARY OF BACKGROUND DATA: Previous cadaveric and clinical studies showed the risk of pedicle screw malposition and the inadequate reliability of intraoperative radiographs to identify misplaced screws. METHODS: Screws (total, 512) in 90 patients were stimulated intraoperatively, and stimulation threshold was recorded. Computed tomographic scans were taken after surgery to document pedicle screw position. Electromyographic thresholds and computed tomographic data were evaluated independently and compared to assess the accuracy of the electromyographic screw stimulation technique. RESULTS: Intraoperative screw stimulation was extremely accurate in confirming the adequacy of screw position. A stimulation threshold greater than 15 mA provided a 98% confidence that the screw was within the pedicle. In eight of 90 patients (9%), electromyographic monitoring detected a screw malposition that was not identified on lateral radiograph. CONCLUSIONS: Screw stimulation monitoring is a valuable and efficacious adjunct to lumbar pedicle screw instrumentation. A stimulation threshold greater than 15 mA reliably indicates adequate screw position. A stimulation threshold between 10 and 15 mA was generally associated with adequate screw position, although exploration of the pedicle is recommended. A stimulation threshold less than 10 mA was associated with a significant cortical perforation in most instances.

The use of somatosensory evoked potentials to prevent ischemic neural damage during preoperative embolization of a vascular renal metastasis.

Tumors at the spinal cord level present challenging surgical problems. Hypernephromas and other tumors may have copious bleeding at the time of resection. This bleeding can be reduced by preoperative embolization resulting in a dramatic decrease in surgical morbidity. However, embolization does carry a risk of spinal cord infarction and resultant neurologic injury. To monitor this, somatosensory evoked potentials (SSEPs) were evaluated during embolization, with a resultant termination of the procedure after significant SSEP changes and clinical symptoms indicated cord ischemia. The SSEP readings normalized 24 hours later, by the time of surgical resection. We present a relevant case history and review of the literature on this subject. Clearly, SSEPs, and in the future, motor evoked potentials (MEPs), serve as a valuable adjunct to monitoring spinal cord function during embolization and may prevent preoperative ischemic injury.