129SProceedings of the NASS 23rd Annual Meeting / The Spine Journal 8 (2008) 1S–191S

the translation decreases as the core mobility increases (p!0.0001). Sagit-

tal ROM averaged 11.9 �65.1 and 8.8 �64.1 for respectively implanted

L4L5 and L5S1, versus 11.2 �64.1 and 6.7 �64.1 for respectively un-

treated L4L5 and L5S1. Differences were not significant. At each level,

both implanted and untreated groups started the flexion-extension motion

at virtually identical angles. No correlation was found between core trans-

lation and sagittal rotation suggesting a non-linear phenomenon. The cor-

relation between vertebral translation and core translation with the sagittal

rotation revealed that the direction of the core translation is not constant

during sagittal rotation and that the L5S1 core translation was higher

and occurred later during vertebral translation compared to L4L5 core

translation. Additionally, the Mobidisc prosthesis maintained or normal-

ized the MCR location.

CONCLUSIONS: The different characteristics of segmental rotational-

translation motion including the intervertebral translation were statistically

similar between both implanted and untreated adjacent levels. Furthermore

some physiologic mechanical behaviors were respected: intervertebral

translation was lower at L5S1 implanted than at L4L5 implanted and core

translation appeared as a non linear phenomenon. Thus, we can speculate

that the presence of a mobile core helps to restore segmental kinematics

closed to ‘‘physiology’’ of a forty-year-old population and may avoid

the increasing of strain on facet joints at the implanted level.

FDA DEVICE/DRUG STATUS: Mobidisc: Investigational/Not approved.

doi:10.1016/j.spinee.2008.06.300

P57. The Impact of Postoperative Disc Height Following

Arthroplasty on Long-term Clinical and Radiographic Outcomes: A

5-Year Follow-up Study

Richard D. Guyer, MD1, Fred Geisler, MD, PhD2, Richard T. Holt, MD3,

Mohammed Majd, MD3, John Regan, MD4, Douglas Wong, MD5,

Louis Jenis, MD6, Robert Banco, MD6, Scott Blumenthal, MD1,

George DeMuth, MSc7, Brian Hetzell, MSc7; 1Texas Back Institute, Plano,

TX, USA; 2Illinois Neuro-Spine Center, Aurora, IL, USA; 3Spine Surgery

PSC, Louisville, KY, USA; 4G&P Orthopedic Associates, Beverly Hills,

CA, USA; 5Panorama Orthopedics, Golden, CO, USA; 6Boston Spine

Group, Boston, MA, USA; 7Stat-Tech Services, LLC, Chapel Hill, NC, USA

BACKGROUND CONTEXT: Preoperatively, patients with degenerative

disc disease (DDD) may present with decreased disc heights at the dis-

eased levels. Restoring disc height is achieved with arthrodesis or arthro-

plasty. However, no evidence exists on the impact of post-operative disc

height restoration on clinical and radiographic outcomes.

PURPOSE: Evaluate pain and disability improvements and well as range

of motion in the CHARITE IDE patient population as a function of post-

operative disc height.

STUDY DESIGN/ SETTING: Multicenter controlled trial, 5-year follow-

up.

PATIENT SAMPLE: 112 CHARITE patients

OUTCOME MEASURES: Visual analog scales; Oswestry Disability

Index; Range of Motion (ROM), Disc height, Translation.

METHODS: All CHARITE patients from the 5-yr CHARITE IDE study

(including CHARITE training cases) with complete preoperative and 5-

year postoperative radiographic data were included herein. To determine

whether the index-level disc height was optimally restored, the post-oper-

ative disc height at the index level was compared to that of the adjacent

superior level (i.e.; for L4-L5 index-level, the L4-L5 disc height was

compared to the height of the L3-L4 disc space. For L5-S1 index-level,

the L5-S1 disc height was compared to the height of the L4-L5 disc space).

Two groups were generated: 1) the Large Disc Group (LDG) ($ 5mm dif-

ference between index- and superior-level disc space and superior-level

disc space greater than 6mm) and 2) anatomically-sized group (ASG).

Both groups were compared for pain (VAS), disability (ODI) as well as

ROM and translation, at the 5-year time point. In addition, a receiver op-

erating characteristic (ROC) curve was constructed to evaluate if post-

operative disc height was predictive of successful outcome. The AUC (area

under the curve) and associated statistical test were calculated for the ROC

curve.

RESULTS: There were 81 subjects in the ASG group vs. 31 in the

LDG group. Using the parameters defined above, the average disc height

was 12.461.79mm in the ASG group vs. 14.261.37mm in the LDG. De-

mographics between groups were similar for gender, race, age, weight and

body mass index. In the ASG, 23 subjects were implanted at L4-L5 and 58

at L5-S1. In the LDG, 6 were implanted at the L4-L5 and 25 at L5-S1. To-

tal surgery time was comparable for both (ASG: 116.6644.38min; LDG:

111.8654.17min, p50.6339), however there was a statistically significant

difference in blood loss between groups (ASG 179.96157.0cc; LDG

371.06410.5cc, p50.0005). Duration of hospitalization also showed

a trend towards shorter times for the ASG vs. LDG (ASG53.860.94 days;

LDG53.560.68 days, p50.0717). ODI scores were very similar between

groups (Change in ODI scores: ASG5 �25.2622.5 points vs LDG5

�25.4625.2 points). VAS pain scores and translation were also similar

(Change in VAS scores: ASG5-40.6630.2 vs. LDG5-43.5634.4; Trans-

lation: ASG50.660.85mm; LDG: 0.560.42mm). Mean ROM showed

trends towards reduced motion in the LDG vs. ASG (L4-L5: Mean

ROM for ASG: 5.9 �65.58 �; Mean ROM for LDG: 5.1 �64.35 �; L5-S1:

Mean ROM for ASG: 6.5 �65.24 �; Mean ROM for LDG: 4.8 �64.16).

These differences were not statistically significant. The ROC analyses fur-

ther showed that postoperative disc height was not a strong predictor for

clinical success (AUC50.5023, p50.9605).

CONCLUSIONS: Large disc implantation resulted in increased blood

loss and hospital stay but did not affect the long-term pain and disability

outcomes.

FDA DEVICE/DRUG STATUS: Charite Artificial Disc: Approved for

this indication.

doi:10.1016/j.spinee.2008.06.301

P58. Long-term Follow-up of Complications of ICBG Harvesting

Carolyn Schwartz, ScD1, Julia Martha, BS1, Paulette Kowalski, BA1,

David Wang, BS1, Rita Bode, PhD2, Ling Li, MPH1, David Kim, MD1;1New England Baptist Hospital, Boston, MA, USA; 2Northwestern

University, Chicago, IL, USA

BACKGROUND CONTEXT: Autogenous Iliac Crest Bone Graft (ICBG)

has been the ‘‘gold standard’’ for spinal fusion. However, bone graft harvest

may lead to complications, such as chronic pain, numbness and poor cosmesis.

The long-term impact of these complications on patient function and well-be-

ing has not been established but is critical in determining the value of expensive

bone graft substitutes such as recombinant bone morphogenic protein.

PURPOSE: To investigate the prevalence of chronic graft site pain and the

impact of this pain on long-term quality of life and disability in a cohort of

patients undergoing autologous ICBG harvest for various spinal procedures.

STUDY DESIGN/ SETTING: Prospective study at an orthopedic subspe-

cialty hospital.

PATIENT SAMPLE: The study population included 158 Spinal fusion

patients with ICBG with a mean age of 51.5 years (SD512.3) and bal-

anced gender (49% male). Lumbar fusion patients predominated (cervical

n522; lumbar5142).

OUTCOME MEASURES: The SF-36v2, the Oswestry Disability Index,

and a 14-item follow-up questionnaire addressing persistent pain, functional

limitation, and cosmesis were administered with a 73% response rate.

METHODS: Multiple regression analyses examined the independent ef-

fect of ICBG complications on physical and mental health and disability.

RESULTS: At 3.5 years mean follow-up, patients reported being bothered

by harvest site scar appearance (6%), numbness (23%), and 14% reported

that the numbness was bothersome. Harvest site pain resulted in difficulty

with household chores (19%), recreational activity (19%), walking (16%),

sexual activity (16%), their job (9%), and irritation from clothing (9%).

Univariate regression analysis revealed that ICBG complications

130S Proceedings of the NASS 23rd Annual Meeting / The Spine Journal 8 (2008) 1S–191S

significantly impaired physical and mental health as well as disability.

Multivariate regression analyses revealed that persistent ICBG complica-

tions were associated with significantly worse disability 3.5 years post sur-

gery, after adjusting for workers’ compensation status, surgical site pain,

and extremity pain (B5 1.7, p!0.02, R250.59). There was a trend asso-

ciation with physical health, after adjusting for age, workers’ compensa-

tion status, surgical site pain, and extremity pain (B5 �1.55, p!0.08,

R250.39). There was no association with mental health in the multivariate

model (B5 �1.61, p50.15, R250.30).

CONCLUSIONS: Chronic ICBG harvest site pain is reported by a signif-

icant percentage of patients undergoing this procedure over three years fol-

lowing surgery. In affected patients, persistent pain is associated with

a wide range of functional limitation and negatively impacts patient-

reported disability.

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

any applicable devices or drugs.

doi:10.1016/j.spinee.2008.06.302

P59. Spinal Hemiepiphysiodesis Affects Compressive Stresses in

Intervertebral Joint

Eric Wall, MD, David Glos, BA, Donita Bylski-Austrow, PhD,

Frank Sauser, Vivek Sharma, MD, Alvin Crawford, MD; Cincinnati

Children’s Hospital Medical Center, Cincinnati, OH, USA

BACKGROUND CONTEXT: Staple hemiepiphysiodesis methods have

been shown to alter spine growth in animal models by inducing physeal

structural gradients. The presumed mechanism is asymmetrically increased

compression of the joint, including interposed disc, bone, and physes.

PURPOSE: To determine normal physiologic dynamic disc compressive

stresses and whether staple implantation increased the mean baseline com-

pressive stress.

STUDY DESIGN/ SETTING: An in vivo animal model (approved by IA-

CUC) combined with in vitro biomechanical tests.

PATIENT SAMPLE: A series of 6 skeletally immature domestic pigs un-

derwent survival surgery and a post-operative evaluation time of 8 weeks.

For in vitro tests, 5 porcine motion segments were harvested from normal,

unoperated spines.

OUTCOME MEASURES: Compressive stresses measured bilaterally in

the disc annulus.

METHODS: For invivo tests, 4 custom sensors and a staple were implanted.

Custom stress sensors were placed in pairs at T7-8 and T5-6, and the staple

was placed across the right side of one disc space. Stresses were measured

during staple implantation, and then postoperatively under defined activities

and loading conditions. For in vitro tests, bilateral stresses were measured

during cyclic compression tests, before and after staple implantation, as well

as during staple insertion. Load-displacement curves were used to define

baseline and peak compressive stresses and tangent modulus.

RESULTS: Staple insertion resulted in an increase in baseline stress of 0.1

to 0.2 MPa in vivo (Fig. 1) and 0.10 MPa (6 0.03) in vitro. During normal

activities of the animal, compressive stresses were dynamic at both stapled

and control levels, including on the stapled side. After stapling, mean peak

dynamic compressive stresses were 77% of control values, while mean tan-

gent modulus was 81% of control.

CONCLUSIONS: Spinal hemiepiphysiodesis using a staple-like implant im-

mediately increased baseline static compressive stresses in the intervertebral

disc in a porcine model, both invivo and invitro. Treatment also decreased peak

dynamic compressive stresses, but not dramatically. Therefore, staples that

have been shown to slow growth and decrease physeal zone and cell size asym-

metrically increased the static baseline stress at time of implantation. The disc,

however, was not isolated from physiological compressive loads.

FDA DEVICE/DRUG STATUS: HemiBridge Staple, Vertebral Locking

Screw: Investigational/Not approved.

doi:10.1016/j.spinee.2008.06.303

P60. Response Shift in Patients Following Lumbar Spine Surgery

Impact on Intepretation of Oswestry Disability Index

Carolyn Schwartz, ScD1, Rita Bode, PhD2, Helen Razmjou, MScPT,

PhD(C), MDT3, David Kim, MD1, Joel Finkelstein, MD3; 1New England

Baptist Hospital, Boston, MA, USA; 2Northwestern University, Chicago,

IL, USA; 3Sunnybrook Health Science Centre, Toronto, Ontario, Canada

BACKGROUND CONTEXT: Traditional outcome measures utilize pre-

and post-treatment self administered questionnaires measuring change

from baseline to follow-up. Response shift is a psychological phenomenon

that occurs with a change in health status and leads to (1) a change in in-

ternal standards of measurement (i.e. scale recalibration) (2) a change in

values (i.e. reprioritization) or (3) reconceptualization of QOL. In a pro-

spective longitudinal study, this may be a source contributing to occasional

discordance between patient and surgeon perceptions of outcome.

PURPOSE: To investigate whether there is evidence of response shift in

patients treated surgically for degenerative spinal conditions.

STUDY DESIGN/ SETTING: Prospective outcome study.

PATIENT SAMPLE: 215 patients with spinal conditions requiring sur-

gery (134 stenosis; 83 herniated disc; 24 degenerative disk disease; 10

spondylosis; 28 other); 43% female; mean age5 52.51 (15.30).

OUTCOME MEASURES: Oswestry Disability Index (ODI) scores.

METHODS: Differential Item Function (DIF) analysis is a statistical method

which controls for the overall disability score and analyzes how the same item

in a questionnaire is used or may have a different meaning to subgroups of peo-

ple over the trajectory of their recovery. DIF can be used to identify response

shift if an individual changes how s/he measures an item in a questionnaire.

DIF was examined by gender. Reconceptualization DIF examined whether

the groups conceptualize these items the same at each time point. Recalibration

DIF examined differences over time. Follow-up period for this study was 6

weeks which is an early point in the trajectory of recovery.

RESULTS: The pre-op ODI score was 33.04 (SD57.74;range 10–53) and

the post-op was 22.67(10.38, range 7–53). The DIF analysis suggested, how-

ever, that two of the ODI items demonstrated response shift. Both males and

females reported similar and significant improvement in their overall ODI

scores after surgery (p!.001). However, perceived improvement on individ-

ual items varied, with the greatest improvement in pain intensity and the least

improvement in pain when lifting. The lifting pain reported by females post-

surgery was similar to that reported by males pre-surgery, and pre-to-post

surgery improvement in lifting pain was non-significant for females. Relative

to their overall ODI scores, both males and females perceived their pain in-

tensity to be worse pre-surgery and their lifting pain to be worse post-surgery.

These findings reflect recalibration DIF such that surgical patients change

their internal standards on these items after experiencing surgery. Reconcep-

tualization DIF by gender revealed no differences pre-surgery but lifting pain

post-surgery was perceived to be worse by females compared to males at

a similar level of disability.

CONCLUSIONS: Recalibration response shifts were found for two ODI

items: pain intensity and lifting for all surgical patients. Reconceptualization

response shifts were found for female patients regarding the lifting item. Re-

sponse shift has the potential to obfuscate true impact of change in specific out-

comes. Our results indicate that response shift does occur in patients following

spine surgery. Future research is indicated to determine if our traditional out-

come measures as a whole are underestimating the true improvement in pa-

tients following surgery. Adjustment for response shift may give a more

accurate assessment of outcomes in patients undergoing spinal surgery.

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

any applicable devices or drugs.

doi:10.1016/j.spinee.2008.06.304

P61. Two and Five Year Lumbar Index Level Motion Following

Arthroplasty Impact of Heterotopic Ossification

Mohammad Majd, MD1, Richard Holt, MD1, Richard D. Guyer, MD2,

Robert Banco, MD3, Fred Geisler, MD, PhD4, Louis Jenis, MD5,