155SProceedings of the NASS 23rd Annual Meeting / The Spine Journal 8 (2008) 1S–191S

METHODS: Bilateral SEPs were elicited by posterior tibial nerve stimu-

lation while tcMEPs were elicited by standard scalp stimulation. ‘‘Signif-

icant’’ EP changes prompted evaluation for possible technical causes and

neurolgical injury. In reliably-monitored patients who had no technical

monitoring problems, significant EP changes were deemed true positives

and prompted rapid intervention (e.g. wake up tests, corticosteroids and/

or hardware modification).

RESULTS: 151 of 162 (93%) patients had EP signals considered adequate

for reliable monitoring. In patients with unreliable monitoring, 4 of 11 had

neuromuscular scoliosis. Of the 151 reliably monitored patients, 12 (7.9%)

had changes in either SEPs or tcMEPs. In four patients, changes were

noted in tcMEP but not SEP monitoring. The determined causes of EP

changes included curve correction (n58), hypotension (n52), direct cord

trauma (n51), and pedicle screw malposition (n51). Appropriate and im-

mediate intervention resulted in the return of normal EP signals in 10 pa-

tients. One patient had a persistent but improved abnormal neurologic

examination at last follow up. Patients with cardiopulmonary disease had

a significantly higher rate of EP events compared to patients with no such

comorbidities (p50.011).

CONCLUSIONS: Combined SEP/tcMEP monitoring is an effective

method for preventing neurologic injury in patients undergoing all types

of pediatric spinal deformity surgery. Despite the potential for false posi-

tive results, we recommend setting a low threshold to define significant in-

traoperative EP changes. Rapid intervention can reverse changes in EPs

and avoid potentially significant neurological complications. Patients with

cardiopulmonary comorbidities may be at higher risk of significant EP

events, and should be approached with caution and careful electrophysio-

logic monitoring.

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

doi:10.1016/j.spinee.2008.06.357

P112. PEMF Increases ACDF Fusion Rates in Patients 50 or Older

Kevin Foley, MD; University of Tennessee, Memphis, TN, USA

BACKGROUND CONTEXT: Although multiple factors have been re-

ported to influence fusion rates following ACDF surgery, patient age

greater than 50 has been found to have the only statistically significant cor-

relation with delayed union.

PURPOSE: To determine the influence of pulsed electromagnetic field

stimulation (PEMF) on ACDF after age 50.

STUDY DESIGN/ SETTING: Randomized, prospective, controlled, mul-

ticenter clinical trial.

PATIENT SAMPLE: The data for this study were obtained from a clinical

trial examining the effects of PEMF on cervical fusion (1). Patients with

symptomatic radiculopathy and correlating radiographic evidence of cervi-

cal nerve root compression were candidates for entry into the study. All

patients were either smokers (at least 1 pack/day) or required multi-level

surgery and underwent anterior cervical discectomy and Smith-Robinson

fusion using allograft bone and anterior cervical plating (single plating

system).

OUTCOME MEASURES: Radiographs were read blindly by two inde-

pendent orthopedic spine surgeons, as well as an independent radiologist,

and rated as ‘‘fused’’ or ‘‘not fused’’ based upon radiolucency, bony bridg-

ing, and motion on flexion-extension views. The motion assessment was

performed using a customized software package (QMA�, Medical Met-

rics, Inc.) that produced a digitized overlay of the flexion and extension

views.

METHODS: Patients were randomized to receive post-operative pulsed

electromagnetic field stimulation (PEMF) or not (non-PEMF). All patients

wore a soft cervical collar for one week post-operatively. Those random-

ized to the PEMF stimulation group started within 7 days post-operatively

and wore the Cervical-Stim device (Orthofix, Inc.) for 4 hours per day for 3

months. Follow-up visits occurred at 1, 2, 3, 6, and 12-month intervals.

Compliance was assessed at each post-operative visit via a print-out of

PEMF ‘‘on’’ time, which was automatically monitored by the Cervical-

Stim device. Radiographic examinations, including anteroposterior, lateral,

and flexion/extension lateral images were performed at 3, 6 and 12 months

post-operatively.

RESULTS: Fusion results in the control (non-PEMF) group were stratified

by various risk factors. Age was the only factor significantly related to fu-

sion rate. By six months post-op, patients younger than 50 had an overall

fusion rate of 74.4%, whereas only 55.6% of patients 50 or older were clas-

sified as fused by this time point. At one year, 91.6% of patients younger

than 50 were rated as fused, whereas only 75.7% of patients 50 years of

age or older had osseous unions (p50.0180). The control group was then

compared with the PEMF group to determine the influence of PEMF on the

fusion rates in the patient population stratified by age. The use of postop-

erative PEMF resulted in a fusion rate of 85.3% in patients younger than

50 at 6 months and 92.1% at one year post-op (not significant compared

to the control patients of the same age, p50.0891 and p50.9014, respec-

tively). In contrast, for patients 50 years of age or older, the use of post-

operative PEMF resulted in a fusion rate of 80.9% at 6 months

(p50.0128, compared to control patients in the same age group) and

93.9% at one year (p50.0159, compared to controls).

CONCLUSIONS: There was a statistically significant improvement in the

fusion rates at 6 months and one year postoperatively for patients 50 years

of age or older who were treated with postoperative PEMF following

ACDF with allograft and a cervical plate.

FDA DEVICE/DRUG STATUS: Cervical-Stim: Approved for this

indication.

doi:10.1016/j.spinee.2008.06.358

P113. Clinical and Radiological Outcomes of Stand-alone Anterior

Lumbar Interbody Fusion: Two Year Results

Christopher Cain, MBBS, FRACS, MD1, David Ardern, MBBS, FRACS1,

Martin Wilby1, Simon Tizzard2, Bernard LaRue2, Russell Morcom3,

David Hall, MD2; 1Adelaide, South Australia, Australia; 2Royal Adelaide

Hospital, Adelaide, South Australia, Australia; 3Dr Jones & Partners,

Radiologists, Adelaide, South Australia, Australia

BACKGROUND CONTEXT: Anterior lumbar interbody fusion (ALIF)

is an accepted surgical treatment for disabling discogenic pain. Additional

posterior fixation has been advocated; however this is associated with sig-

nificant surgical morbidity. This is a prospective clinical study evaluating

a stand-alone anterior fusion cage with an integrated titanium plate and

four divergent locking screws.

PURPOSE: To evaluate the clinical and radiographic outcome of a new

stand alone anterior lumbar fusion device in the management of discogenic

low back pain.

STUDY DESIGN/ SETTING: Prospective clinical and radiographic eval-

uation of patients undergoing surgical treatment of discogenic low back

pain utilizing a standalone anterior fusion cage was undertaken since

Nov 1st 2005.

PATIENT SAMPLE: Patients with one or two level symptomatic lumbar

disc degeneration identified by lumbar discography and who had failed ap-

propriate non-operative management for at least six months were consid-

ered for surgical treatment and recruited into the study.

OUTCOME MEASURES: Visual Analogue Pain Scores (VAS), Oswes-

try Disability Index (ODI) and SF-36 data was collected pre-operatively, at

3, 6, 12 and 24 months post surgery. Plain radiographs were undertaken at

similar intervals and fine-cut helical CT with reconstructions was

performed at one and two years post-operatively.

METHODS: Surgery was performed through an anterior retro-peritoneal

approach. The fusion cage was packed with autogenous bone graft. Fusion

was defined as continuous bony trabeculae joining the vertebral bodies.

Compensation, smoking and other demographic factors were also evalu-

ated in relation to the clinical outcome.

156S Proceedings of the NASS 23rd Annual Meeting / The Spine Journal 8 (2008) 1S–191S

RESULTS: Fifty-five levels were operated on in 43 patients with a mean

age of 40 years (22-57). Thirty-nine patients have completed one-year fol-

low-up and 19 have completed two-year follow-up. The mean operative

time was less than 120 minutes, and mean blood loss less than 200 ml.

Radiographic fusion at one year was 78% and 100% at two years. Two

year mean VAS scores for back pain improved from 7 to 3.5 (p!0.01)

and for leg pain from 6.3 to 2.8 (p!0.01). The mean ODI scores decreased

from 48 to 33 (p!0.01), and SF-36 physical function scores increased from

30 to 37 (p!0.01). Compensation was identified as a significant negative

factor in relation to clinical outcome. There were no major complications

and no patients have required supplementary posterior fixation.

CONCLUSIONS: This technique has been shown to be safe and is as ef-

fective as 360o fusion in achieving fusion in the management of discogenic

back pain over one and two levels. It also has the additional advantage of

avoiding the morbidity associated with additional posterior fixation.

FDA DEVICE/DRUG STATUS: SynFix-Synthes: Approved for this

indication.

doi:10.1016/j.spinee.2008.06.359

P114. Biomechanics of Multilevel Cervical Arthroplasty and

Combined Arthrodesis and Arthroplasty

Neil Crawford, PhD, Sam Safavi-Abbasi, MD, PhD, Seungwon Baek, MS,

Phillip Reyes, BS, Mehmet Senoglu, MD, Volker Sonntag, MD; Barrow

Neurological Institute, Phoenix, AZ, USA

BACKGROUND CONTEXT: Little research exists on the biomechanics

of combined cervical arthroplasty/arthrodesis and multilevel arthroplasty

instrumentation. Simply studying the range of motion of these conditions

in vitro provides little useful information.

PURPOSE: To investigate how arthrodesis/arthroplasty affect posture and

distribution of segmental angles under physiologic loads.

STUDY DESIGN/ SETTING: 3D motion of individual motion segments

was monitored during in vitro loading after different combinations of mul-

tilevel arthroplasty and arthrodesis.

PATIENT SAMPLE: 7 human cadaveric C3-T1 specimens (32-67 years).

OUTCOME MEASURES: Segmental compensation to restore the origi-

nal neutral postural balance, tendency for buckling while maintaining

global neutral postural balance, and shift in sagittal plane axis of rotation.

METHODS: After completing normal tests, C4-5, C5-6 and C6-7

received arthroplasty using ProDisc-C (Synthes Spine, Paoli, PA). Then,

using a rigid screw-rod system with 3 points of fixation per vertebra,

various combinations of fusion (‘‘f’’) adjacent to arthroplasty (‘‘A’’) were

simulated at C4-C5, C5-6 and C6-7 respectively: fAA, AfA, AAf, ffA, fAf,

Aff, fff. C3-4 and C7-T1 were left intact during all tests. A compressive

belt apparatus was used to simulate normal muscle co-contraction and

gravitational preload. This apparatus controlled the angle of C3 relative

to T1 but did not interface with intermediate levels. All motion segments

(C3-4, C4-5, C5-6, C6-7 and C7-T1) were individually monitored using

3D optical tracking.

RESULTS: During all 7 conditions in which one or more levels were

mobile, the arthroplasty levels preferentially moved toward upright

posture more easily than the normal intact levels. This difference was

significant in the AAA, fAA, fAf, ffA configurations (p!0.05, paired

Student’s t-tests). To keep a global, upright posture of 0 �, the buckling

(sum of unsigned segmental angles) was greatest for 3-level arthroplasty,

less for 2-level arthroplasty, and least for 1-level arthroplasty (Figure).

Among the three 1-level arthroplasty groups (ffA, fAf, Aff), arthroplasty

at the caudalmost level resulted in significantly greater buckling than

when arthroplasty was in the rostralmost or middle segment (p!0.04,

ANOVA/Holm-Sidak). The IAR location was related to buckling such

that anterior IAR shift resulted in extension and posterior IAR shift re-

sulted in flexion. Although worse buckling tended to occur with greater

shifts in the axis of rotation, this correlation did not reach significance

(p50.112).

CONCLUSIONS: Arthroplasty levels provide the ‘‘path of least resis-

tance,’’ through which initial motion is more likely than normal levels,

possibly related to focal kyphosis seen clinically with cervical arthroplasty.

The tendency for buckling under compression became greater with more

arthroplasty levels. Buckling appeared more severe with arthroplasty more

caudal. Buckling only moderately correlated to IARshifts, implying that

slight device malpositioning should not predispose the patient to buckling.

Figure. Buckling under 70N compression, measured as the sum of un-

signed segmental angles after restoring zero degrees global posture

(sum of signed segmental angles). From C3-C4 to C6-C7, A=arthro-

plasty level, f=fusion level. Error bars show std. dev.

FDA DEVICE/DRUG STATUS: ProDisc-C: Approved for this indica-

tion; CSLP: Approved for this indication.

doi:10.1016/j.spinee.2008.06.360

P115. Low Profile Pelvic Fixation Anatomic Parameters for Sacral

Alariliac Fixation vs. Traditional Iliac Fixation

Tai-Li Chang, Paul Sponseller, MD, Khaled Kebaish, MD, Elliot Fishman,

MD; Johns Hopkins University, Baltimore, MD, USA

BACKGROUND CONTEXT: Compared to traditional iliac fixation of

insertion through the posterior superior iliac spine (PSIS), insertion of iliac

anchors through the S2 ala may provide nearly equal length with a starting

point that is more in-line and 1.9cm deeper. Three-dimensional radio-

graphic analysis describes an ideal pathway of approximately 40 � of cau-

dal and lateral angulation for this technique.

PURPOSE: Long anchors projecting into the ilium provide optimal pelvic

fixation. A traditional starting point in the PSIS requires muscle dissection

and complex rod bends. Such obstacles may be reduced with a better-cov-

ered, more midline approach via a sacral starting point. We demonstrate

pathway parameters for insertion of iliac anchors through a sacral starting

point and compare it with insertion through the PSIS.

STUDY DESIGN/ SETTING: CT feasibility analysis of a new technique

for sacral pelvic fixation.

PATIENT SAMPLE: Twenty pelvic CTs of mature adolescents were an-

alyzed using INSPACE, a 3-D CT imaging program, by two surgeons.

METHODS: The CT imaging plane was manipulated until it provided

a trajectory with maximal length and width through the sacral ala and iliac

wing. The trajectory distance, starting point coordinates, angulation, depth,

and width were measured (Figure). The same parameters were evaluated

and compared for insertion from the PSIS.

RESULTS: Based on the ideal trajectory, the mean starting point was in

S2 25mm caudal to the superior endplate of S1 and 22mm lateral to the