Eduardo Hevia

Anthropometry and body composition profile of girls with nonsurgically treated adolescent idiopathic scoliosis.

Study Design. Cross-sectional study with level III of evidence. Objective. To describe different anthropometric and body composition parameters of adolescent girls with adolescent idiopathic scoliosis (AIS), comparing them with the standards of a healthy age-matched population. Summary of Background Data. Body growth and development of adolescent girls with AIS seems to differ from the healthy subjects, especially at perpubertal stages. Young scoliotic adults have been found to be taller, lighter, and thinner than age-matched healthy population. Body composition profile taken from measurements of skin-fold thickness, bony diameters at different levels, and arm and legs perimeters has not been previously reported in AIS patients. Methods. A nonconsecutive series of 52 AIS girls (mean age: 13.9 years) with an average scoliotic curve of 27° Cobb (range: 20–58) underwent an anthropometric study. None of the AIS girls had been treated previously with spinal surgery. The control group consisted of 92 girls without spine deformity, matched in age (mean: 13.8 years). Weight, height, and skin-fold thickness in millimeters at six levels were measured. Body mass index (BMI), Ponderal index, percentage of body fat, percentage of muscular tissue, fat mass, lean body mass, muscular weight, bony weight, and residual weight were calculated using standard rules to estimate body composition. The somatotype components (endomorphy, mesomorphy, and ectomorphy) were calculated according to the Carter equations. Results. Compared with the control population, scoliotic girls had a significantly lower mean weight (51.4 ± 10.2 kg vs. 54.7 ± 8.1 kg; P < 0,05), a lower BMI (20.1 ± 3.4 vs. 21.4 ± 2.4; P < 0.001), and a higher Ponderal index (43.2 ± 2.4 vs. 42.2 ± 1.6; P < 0.01). Girls with AIS showed a progressive decrease of the BMI as the age increased. The percentage of body fat was also lower in scoliotic girls, without significant statistical differences (14.1 ± 3.8 vs. 15 ± 3.6). Out of the 52 AIS girls, 11 (21.2%) showed a BMI below 17.5, which has been considered the limit for anorexia. In the control group, only 3 of 92 girls (3.3%) had BMI below that level. The somatotype differed also between scoliotics and controls: higher in the ectomorphic component (3.29 ± 1.68 vs. 2.40 ± 1.11; P < 0.001), and lower in the mesomorphic component (2.86 ± 0.82 vs. 3.70 ± 1.11; P < 0.01) in AIS patients. Conclusion. The differences in some anthropometric parameters (weight, IMC, IP) and in the somatotype suggest that the idiopathic scoliosis not only disturbs normal spine growth but also seems to have implications on the whole corporal development. Whether these changes could be related to abnormal spinal growth or subsequent to nutritional changes in AIS still remains uncertain. Presumably, some endocrine factors affecting body composition and growth might be involved in the etiology of idiopathic scoliosis.

Using triggered electromyographic threshold in the intercostal muscles to evaluate the accuracy of upper thoracic pedicle screw placement (T3-T6).

Study Design. A prospective clinical study of high thoracic pedicle screws monitored with triggered electromyographic (EMG) testing. Objective. To evaluate the sensitivity of recording intercostal muscle potentials to assess upper thoracic screw placement. Summary of Background Data. Triggered EMG testing from rectus muscle recordings, which are innervated from T6 to T12, has identified medially placed thoracic pedicle screws. No clinical study has correlated an identical technique with the intercostal muscle for upper pedicle screws placed in the upper thoracic spine (T3–T6). Methods. A total of 311 high thoracic screws were placed in 50 consecutive patients. Screws were placed from T3 to T6 and were evaluated using an ascending method of stimulation until a compound muscle action potential was obtained from the intercostal muscles. Screw position was then evaluated using computed tomography and results were compared with evoked EMG threshold values. Results. Fifteen screws (5%) showed penetration on postoperative computed tomography scans. Eleven screws showed medial cortical breakthrough (3.6%), 6 had stimulation thresholds ≤6 mA, and 5 had stimulation thresholds between 6 and 10 mA. Stimulation values for all breached screws decreases 60% to 65% from their mean. Four screws (1.3%) showed lateral cortical breakthrough with stimulation thresholds >20 mA. Of the 296 screws with thresholds between 6 and 20 mA, 285 (91%) were within the vertebra. No postoperative neurologic complications were noted in any of the 50 patients. Conclusion. In this series, cortical violation is highly unlikely in patients whose stimulation threshold lies between 6 and 20 mA with values 60% to 65% decreased from the mean (98% negative predictive value). Although verification of screw placement should not depend solely on stimulation thresholds, pedicle screw stimulation provides rapid and useful intraoperative information on screw placement during procedures involving the use of thoracic pedicle screws.

Comparing the clinical and radiological outcomes of pedicular transvertebral screw fixation of the lumbosacral spine in spondylolisthesis versus unilateral transforaminal lumbar interbody fusion (TLIF) with posterior fixation using anterior cages.

Study Design. This study retrospectively compares the clinical and radiologic outcomes of unilateral transforaminal lumbar interbody fusion (TLIF) with those of transvertebral screw fixation of the lumbosacral spine in high-grade spondylolisthesis. Objective. To examine the outcome and perioperative complications of unilateral TLIF and compare those results with Transvertebral Screw Fixation in the treatment of high-grade spondylolisthesis. Summary of Background Data. High-grade spondylolisthesis has been associated with a high complication and failure rate regardless of the method of treatment. We compare 2 techniques to improve success rates. Methods. Forty patients were divided into 2 groups: group A, unilateral TLIF, and group B, transacral screws. The mean age was 33 years (range, 19–48 years), and the mean follow-up was 35 months (range, 24–48 months). The mean grade of spondylolisthesis measured by Meyerding grading was 3.6 (range, 3–5). A Scoliosis Research Society outcome score was obtained on all patients. Fusion was determined by both radiograph and computed tomography scan. Results. Group A: 100% fusion. The slip angle improved from 38.6° (range, 24−78°) before surgery to 23.8° (range, 12–38°) after surgery. Group B: 95% of patients evidenced solid fusion by the 6-month follow-up. The slip angle, improved from 38.2° (range, 22–78°) before surgery to 23° (range, 9–36°) after surgery. There was no significant improvement in the percentage slip or the sacral inclination in any of the groups. Complications: A: 7 unintended durotomies and 3 wound infections. B: 1 unintended durotomy, 1 pseudarthrosis, 2 wound infections, and 1 implant failure. There were no neurologic complications in any of the groups. The Scoliosis Research Society outcome instrument demonstrated good postoperative pain control, function, self-image, and satisfaction in both groups. Conclusion. No significant differences in radiologic and clinical outcome were found, in either group. Both procedures appear to be safe and effective surgically and radiographically.

Cervical and thoracic sagittal misalignment after surgery for adolescent idiopathic scoliosis: a comparative study of all pedicle screws versus hybrid instrumentation.

Study Design. A comparative study of 2 cohort series of surgically treated patients with adolescent idiopathic scoliosis (AIS) who were retrospectively analyzed, with level III evidence. Objective. To compare the effect on the cervical sagittal balance of 2 AIS correction constructs, namely, all pedicle screws and hybrid instrumentation using hooks and pedicle screws. Summary of Background Data. An inverse relationship between cervical and thoracic kyphosis in AIS has been found in pediatric patients after concave derotation using hybrid constructs with pedicle screws and hooks. Methods. Two series of 25 nonconsecutive patients with Lenke type-I AIS who underwent spinal fusion were retrospectively reviewed. In 1 series, the patients were treated with all thoracic pedicle screw constructs. In the other series, the correction was achieved by using hybrid constructs. Preoperative and 2-year follow-up radiographical examinations were evaluated, measuring the following parameters: C2–C7 sagittal angle, displacement of C2–C7 plumb line, T1 sagittal tilt, T1–T5 and T5–T12 sagittal profile, and C7–S1 global sagittal balance. Results. In both groups, there was a lordotic effect on the T5–T12 kyphosis after surgery, with an average loss of 6.1° for hybrid and 7.7° for pedicle screws. When the postoperative data were compared, the intergroup differences were found only in the sagittal C2–C7 Cobb angle, showing a mean kyphotic trend (−5.2°) in the pedicle screws group compared with a mean lordotic trend (1.8°) in the hybrid group (P < 0.05). In both techniques, the patients with upper-instrumented vertebra at T4 or below showed a lordotic effect that was more evident in the hybrid constructs (+9.4° ± 11.3 vs. +0.3° ± 11.4). In those with the upper-instrumented vertebra at T3 or higher levels, both techniques had a kyphotic effect that was more severe in the patients of the pedicle screws group (−7.0° ± 12.6 vs. −2.8° ± 10.5). Conclusion. Independent of the surgical technique used, the cervical spine had a tendency to decompensate and acquire a kyphotic sagittal profile. Constructs based on all pedicle screws have a stronger hypokyphotic effect on the thoracic spine, with a predisposition to greater decompensation of the cervical spine. Kyphotic changes in the C2–C7 sagittal alignment induced by scoliosis correction are correlated with the level of the upper-instrumented vertebra. Level of Evidence: 4

Safe pedicle screw placement in thoracic scoliotic curves using t-EMG: stimulation threshold variability at concavity and convexity in apex segments.

Study Design. A cross-sectional study of nonconsecutive cases (level III evidence). Objective. In a series of young patients with thoracic scoliosis who were treated with pedicle screw constructs, data obtained from triggered electromyography (t-EMG) screw stimulation and postoperative computed tomographic scans were matched to find different threshold limits for the safe placement of pedicle screws at the concavity (CC) and convexity (CV) of the scoliotic curves. The influence of the distance from the medial pedicle cortex to the spinal cord on t-EMG threshold intensity was also investigated at the apex segment. Summary of Background Data. Whether the t-EMG stimulation threshold depends on pedicle bony integrity or on the distance to neural tissue remains elusive. Studying pedicle screws at the CC and CV at the apex segments of scoliotic curves is a good model to address this issue because the spinal cord is displaced to the CC in these patients. Methods. A total of 23 patients who underwent posterior fusions using 358 pedicle thoracic screws were reviewed. All patients presented main thoracic scoliosis, with a mean Cobb angle of 58.3 degrees (range, 46–87 degrees). Accuracy of the screw placement was tested at surgery by the t-EMG technique. During surgery, 8 screws placed at the CC showed t-EMG threshold values below 7 mA and were carefully removed. Another 25 screws disclosed stimulation thresholds within the range of 7 to 12 mA. After checking the screw positions by intraoperative fluoroscopy, 15 screws were removed because of clear signs of malpositioning. Every patient underwent a preoperative magnetic resonance imaging examination, in which the distances from the spinal cord to the pedicles of the concave and convex sides at 3 apex vertebrae were measured. Postoperative computed tomographic scans were used in all patients to detect screw malpositioning of the final 335 screws. Results. According to postoperative computed tomographic scans, 44 screws (13.1%) showed different malpositions: 40 screws (11.9%) perforated the medial pedicle wall, but only 11 screws (3.2%) were completely inside the spinal canal. If we considered the 23 screws removed during surgery, the true rate of misplaced screws increased to 18.7%. In those screws that preserved the pedicle cortex (well-positioned screws), EMG thresholds from the CC showed statistically significantly lower values than those registered at the CV of the deformity (21.1 ± 8.2 vs 23.9 ± 7.7 mA, P < 0.01). In the concave side, t-EMG threshold values under 8 mA should be unacceptable because they correspond to screw malpositioning. Threshold values above 14 mA indicate an accurate intrapedicular position with certainty. At the convex side, threshold values below 11 mA always indicate screw malpositioning, and values above 19 mA imply accurate screw placement. At the 3 apex vertebrae, the average pedicle–spinal cord distance was 2.2 ± 0.7 mm at the concave side and 9.8 ± 4.3 mm at the convex side (P < 0.001). In well-positioned screws, a correlation between pedicle–dural sac distance and t-EMG threshold values was found at the concave side only (Pearson r = 0.467, P < 0.05). None of the patients with misplaced screws showed postoperative neurological impairment. Conclusion. Independent of the screw position, average t-EMG thresholds were always higher at the CV in the apex and above the apex regions, presuming that the distance from the pedicle to the spinal cord plays an important role in electrical transmission. The t-EMG technique has low sensitivity to predict screw malpositioning and cannot discriminate between medial cortex breakages and complete invasion of the spinal canal.

Recording Diffusion Responses From Contralateral Intercostal Muscles After Stimulus-triggered Electromyography: Refining a Tool for the Assessment of Thoracic Pedicle Screw Placement in an Experimental Porcine Model

Study Design. A new stimulus-triggered electromyography (EMG) test for detecting stimulus diffusion to contralateral intercostal muscles during thoracic pedicle screw placement was assessed in a porcine model. Objective. To determine if electromyographic thresholds in the intercostal muscles of both sides of the thorax could discriminate thoracic pedicle screw malpositions with and without neural contact at different aspects of the spinal cord and nerve roots. Summary of Background Data. There is controversy about the value of triggered EMG stimulation for aiding precise insertion of thoracic pedicle screws. A universally validated threshold that confirms screw malposition has not been established. Diffusion of EMG responses to the contralateral intercostal muscles has not previously been investigated. Methods. Nine domestic pigs weighing 60 to 75 kg had 108 pedicle screws placed bilaterally in the thoracic spine from T8–T13. Before spine instrumentation, neural structures were stimulated in 4 animals under direct vision at different anatomic locations from T9–T12. Recording electrodes were placed over the right and left intercostal muscles. Increasing stimulus intensity was applied until muscle response was detected at the contralateral side (EMG diffusion phenomenon). After this first experiment, the thoracic spine was instrumented in all 9 animals. Screws were placed in the pedicle in different positions, the anatomic intrapedicular location and within the spinal canal, with and without contact with the neural elements. Results. Response thresholds to direct nerve root stimulation were significantly lower than those obtained by stimulation of the dorsal aspect of the spinal cord (0.44 ± 0.22 mA vs. 1.38 ± 0.71 mA, P < 0.01). However, a 14-fold stimulation intensity (6.50 ± 0.29 mA) was necessary to obtain diffusion of the EMG response to the opposite (left) side if the right nerve root was stimulated. A 2-fold increment (3.17 ± 0.93 mA) elicited diffusion of the EMG responses to the contralateral side when stimulation was applied to the dorsal aspect of the spinal cord. EMG recordings of the 108 stimulated screws showed a significant decrease in the EMG response when the screw was in contact with the spinal cord (2.72 ± 1.48 mA; P < 0.01) compared with that found when the pedicle track was intact (mean: 5.01 ± 1.89 mA). Screws violating the medial wall of the pedicle, but not touching neural tissues, responded to slightly lower intensities than well-positioned screws, but this was not statistically significant (3.91 ± 1.39 mA vs. 4.89 ± 1.30 mA, P > 0.05). Conclusion. Stimulus-triggered EMG can identify screws that violate the medial pedicle wall if they are in contact with neural tissues. EMG thresholds could not discriminate screws that violated the medial pedicle wall without neural contact from screws with accurate intraosseous placement. However, recording EMG potentials at the contralateral intercostal muscles (stimulus diffusion phenomenon) proved to be a reliable method for identifying the neural structures at risk.

Electromyographic thresholds after thoracic screw stimulation depend on the distance of the screw from the spinal cord and not on pedicle cortex integrity

BACKGROUND CONTEXT Present studies concerning the safety and reliability of neurophysiological monitoring during thoracic pedicle screw placement remain inconclusive, and therefore, universally validated threshold levels that confirm osseous breakage of the instrumented pedicles have not been properly established. PURPOSE The objective of this work was to analyze whether electromyographic (EMG) thresholds, after stimulation of the thoracic pedicle screw, depend on the distance between the neural structures and the screws. The modifier effect of different interposed tissues between a breached pedicle and neural structures was also investigated. STUDY DESIGN This experimental study uses a domestic pig model. METHODS Electromyographic thresholds were recorded after the stimulation of 18 thoracic pedicle screws that had been inserted into five experimental animals using varying distances between each screw and the spinal cord (8 and 2 mm). Electromyographic thresholds were also registered after the medial pedicle cortex was broken and after different biological tissues were interposed (blood, muscle, fat, and bone) between the screw and the spinal cord. RESULTS Mean EMG thresholds increased to 14.1±5.5 mA for screws with pedicle cortex integrity that were placed 8 mm away from the dural sac. After the medial pedicle cortex was broken and without varying the distance of the screw to the dural sac, the mean EMG thresholds were not appreciably changed (13.6±6.3 mA). After repositioning the screw at a distance of 2 mm from the spinal cord and after medial cortical breach of the pedicle, the mean threshold significantly slowed to 7.4±3.4 mA (p<.001). When the screw was placed in contact with the spinal dural sac, even lower EMG thresholds were registered (4.9±1.9, p<.001). Medial pedicle cortex rupture and the interposition of different biological tissues in experimental animals did not alter the stimulation thresholds of the thoracic pedicle screws. CONCLUSIONS In the experimental animals, the observed electrical impedance depended on the distance of screws from the neural structures and not on the integrity of the pedicle cortex. The screw-triggered EMG technique did not reliably discriminate the presence or absence of bone integrity after pedicle screw placement. The response intensity was not related to the type of interposed tissue.

Intraoperative Neurophysiological Changes Induced by Thoracic Pedicle Screws Intentionally Placed Within the Spinal Canal: An Experimental Study in Pigs

STUDY DESIGN Experimental study, OBJECTIVES: To document and analyze the neurophysiological changes during spinal cord monitoring when thoracic pedicle screws are intentionally placed within the spinal canal. SUMMARY OF BACKGROUND DATA Although the rate of misplaced screws is relatively high, few patients have neurological impairment. This suggests that a significant degree of medullary displacement and/or compression is necessary to produce neurophysiological changes. METHODS The spinal cord of 3 experimental pigs was surgically exposed at 3 different levels (T11, T9, and T6). Two pedicle screws were placed within the spinal canal at each vertebral level under direct vision. One was placed on the lateral edge of the dural sac, causing only a slight cord displacement; a second screw was placed in the middle of the spinal canal, producing marked displacement of the neural structures. During the procedure, neurophysiological monitoring of the spinal cord was performed. RESULTS No neurophysiological changes were observed in any screws placed at the lateral edge of the dural sac for 20 minutes after screw placement. When the screws were placed in the center of the spinal canal, neurophysiological changes occurred with a mean latency of 10.1 ± 2.1 minutes, and at 11.6 ± 1.9 minutes there was complete loss of the spinal cord evoked potentials in all cases. After these centered screws were removed, evoked potentials began to recover, with a latency of 9.7 ± 3.0 minutes in 7 of 9 cases. CONCLUSIONS Neurophysiological monitoring of the spinal cord does not detect moderate compression even 20 minutes after neural compression. Only thoracic pedicle screws provoking marked displacement of the spinal cord were able to cause delayed neurophysiological changes leading to loss of spinal cord evoked potentials, which in 22% of cases did not recover after the pedicle screw was removed.

Cardiorespiratory Function Does Not Improve 2 Years After Posterior Surgical Correction of Adolescent Idiopathic Scoliosis

Study Design. A prospective evaluation of cardiorespiratory function following spinal fusion in adolescent idiopathic scoliosis (AIS). Objective. To evaluate the cardiopulmonary function during exercise in patients with severe AIS, before and 2 years after undergoing a posterior spinal fusion. Summary of Background Data. After surgical correction of scoliosis, a greater cardiorespiratory adaptation to exercise would be expected from correction of the rib cage associated with the spine deformity. However, there is no clear evidence regarding whether tolerance to maximum exercise improves in the medium term after surgery in patients with severe curves. Methods. We include patients with AIS proposed for posterior surgical correction aging between 12 and 17 years. Every patient had a Cobb angle >45° and a Lenke type 1A scoliosis. Cardiac and respiratory functional measures, such as heart rate and blood pressure, maximum oxygen consumption (VO2max), eliminated volume of carbon dioxide (VCO2), quotient between ventilation and volume of exhaled carbon dioxide (VE/CO2), respiratory exchange rate, ventilatory capacity at maximal exercise (VEmax), were recorded before and 2 years after surgery. Results. Twenty patients were included in our study, 15 girls and 5 boys, with an average age of 13 years. The main scoliotic curve was corrected in the coronal plane in an average of 71.9%. The maximal aerobic power expressed by body weight normalized VO2max was found preoperatively to have an average of 30.9 ± 6.2 mL/kg/minute, indicating a poor aerobic capacity, which did not improve at final follow-up, decreasing to a mean value of 29.3 ± 5.7 but without statistical significance. However, the percentages of curve correction showed a statistically significant correlation with VO2max (r = 0.534; P < 0.05). Conclusion. Patients with severe adolescent idiopathic scoliosis Lenke type 1A showed limited cardiorespiratory tolerance to maximum exercise that did not improve 2 years after surgery. Level of Evidence: 3

Influence of hypotension and nerve root section on the ability to mobilize the spinal cord during spine surgery. An experimental study in a pig model

BACKGROUND CONTEXT The correction of severe spinal deformities by an isolated posterior approach often involves cord manipulation together with hypotensive anesthesia. To date, the efficiency of methods to increase the tolerance of the cord to displacement and the influence of hypotension on this tolerance is yet to be assessed. PURPOSE The objective of this study was to determine the limits of cord displacement before the disappearance of neurophysiologic signals. The influence of the type of force applied, the section of the roots, and the induced hypotension on the cords tolerance to displacement was also assessed. STUDY DESIGN Experimental study using a domestic pig model. OUTCOME MEASURES Successive records of cord-to-cord motor evoked potentials were obtained during displacement maneuvers. Displacing forces were released immediately after the absence of neurophysiologic signals. METHODS Surgical procedures were performed under conventional general anesthesia. The spinal cord and nerve roots from T6 to T10 levels were exposed by excision of the posterior elements, allowing for free cord movement. Three groups were established according to the method of spinal cord displacement: the separation (Group 1, n=5), the root stump pull (Group 2, n=5), and the torsion groups (Group 3, n=5). An electromechanical external device was used to apply the displacing forces. The three displacement tests were repeated after sectioning the adjacent nerve roots. The experiments were first carried out under normotension and afterward under induced hypotension. RESULTS In Group 1, evoked potential disappeared with a displacement of 10.1±1.6 mm with unharmed roots and 15.3±4.7 mm after the sectioning of four adjacent roots (p<.01). After induced hypotension, potentials were lost at 4.0±1.2 mm (p<.01). In Group 2, the absence of potentials occurred at 20.0±4.3 mm and increased to 23.5±2.1 mm (p<.05) after cutting the two contralateral roots. Under hypotensive conditions, the loss of neurophysiologic signals was detected at 5.3±1.2 mm (p<.01). In Group 3, the cord allowed torsion of 95.3±.2° that increased to 112.4±7.1° if the contralateral roots were cut. Under hypotension, the loss of potentials was found at 20±6.2° (p<.01). CONCLUSIONS In this experimental model, it was possible to displace the thoracic spinal cord by a distance superior to the spinal cord width without suffering neurophysiologic changes. The limits of cord displacement increase when the adjacent nerve roots are sacrificed. Induced hypotension had a dramatic effect on the tolerance of the spinal cord for displacement. This work has an important clinical significance because induced hypotension during specific spine surgery procedures requiring spinal cord manipulation in humans may increase the risk of neurologic spinal cord injury.