OUTCOME MEASURES: N/A.

METHODS: Seven fresh frozen human FSUs (L3-S1) were tested by ap-

plying pure moments of 68 Nm. Range of Motion (ROM) at L5-S1 was

obtained in flexion-extension, lateral bending and axial rotation modes.

Following intact testing, a PLIF with inclusion of interbody spacers was

performed at L5-S1. Each spine was then treated sequentially with poste-

rior fixation using 1) Bilateral pedicle screws and rods (BPS), 2) BPS þ T,

and 3) and RT. In T, the connector is added through an accessory screw/pin

construct, while in RT, the connector is integrated into the bi-lateral rod

framework through a welded joint. The sequence of treatment methods

was randomized for each spine. In a separate mechanical evaluation, com-

parison of a 6.5 mm diameter SS was made with 6.5 mm diameter DOD by

performing a pullout strength test per ASTM F1893 (n55, depth540 mm)

and a static cantilever bend test (n55), using a constant loading rate of

5 mm/min. For pullout strength, pullout force was recorded, while for can-

tilever bend tests, yield load and ultimate load were recorded. Statistical

analysis was performed using single factor one way ANOVA at p!0.05

for both ROM and strength testing.

RESULTS: In the biomechanical stability test it was observed that the tor-

sional stiffness at the L5-S1 with the RT increased significantly compared

to the intact spine. Also, this increase was significantly more than the

crosslink (T) or dual rods alone (BPS) (Fig. 1).

In flexion-extension, there was a significant reduction in ROM in all three

instrumented constructs compared to the intact, but no fixation type was

statistically separable. Similar results were observed in lateral bending.

The DOD had a significantly higher pullout load as compared to SS.

The static cantilever bend test significantly highlighted the strength of dual

outer diameter screws compared to regular screws (Fig. 2).

CONCLUSIONS: Two aspects of pedicle screw-rod fixation were exam-

ined, the influence of 1) welded (RT) versus variable (T) t-connectors and

2) layered screw thread design. RT significantly increased torsional stiff-

ness, and dual outer diameter screws (DOD) markedly improved screw-in-

terface fixation. Increased torsional stiffness and pull-out strength provide

additional options for optimizing fixation at L5-S1.

FDA DEVICE/DRUG STATUS: Revere Pedicle Screw System: Ap-

proved for this indication; H-Link Torsional Connector: Approved for this

indication.

doi: 10.1016/j.spinee.2009.08.424

P164. Adjacent Level Effects: A Novel Method for Assessing

Kinematic Changes of the Entire Thoracolumbar Spine Following

Surgical Intervention

Erin Campbell1, Kyle Elsabee1, John Wason1, John Wen1, Allen Carl, MD2,

Darryl DiRisio, MD2, Eric Ledet, PhD1; 1Rensselaer Polytechnic Institute,

Troy, NY, USA; 2Albany Medical College, Albany, NY, USA

BACKGROUND CONTEXT: Long term clinical follow up of fusion pa-

tients has led to the identification of adjacent level disease (ALD). How-

ever, the dependence of ALD on specific surgical intervention remains

controversial. Motion preserving therapies purport to eliminate deleterious

effects on adjacent levels, but these assertions will not be confirmed until

long term outcomes on large populations are evaluated. Until then, short

term outcomes and predictive models provide the best insights into adja-

cent level effects. In vitro testing affords repeatability and the opportunity

for relative comparison between treatments, but the clinical relevance of in

vitro testing based on passive motion and arbitrary loads remains

questionable.

PURPOSE: The purpose of this pilot study was to develop and test a novel

methodology based on active voluntary motion to accurately predict the

three dimensional (3D) redistribution of motion of the entire thoracolum-

bar spine following surgical intervention.

STUDY DESIGN/SETTING: The distribution of kinematic changes was

assessed in whole human thoracolumbar spines using a novel in vivo-in vi-

tro testing protocol.

PATIENT SAMPLE: Fresh cadaveric spines.

OUTCOME MEASURES:N/A.

METHODS: We have previously used Flock of Birds (FOB) 3D position

and orientation sensors to track the kinematic motion of the thoracolumbar

spine in normal healthy volunteers during voluntary range of motion of the

trunk in flexion/extension, lateral bending, and torsion. The 3D in vivo

Figure 1. Torsional Stiffness of Pedicle Screws and T-connectors.

Figure 2. Offset Yield and Ultimate Load of Bend Test for SS and DOD Screws.

198S Proceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S

kinematic data were post-processed and reduced to command sets used to

drive a six degree-of-freedom industrial robot. When whole thoracolumbar

cadaveric spines are mounted to the robot, it is capable of moving the spine

through 3D motions which replicate with high fidelity the active motions

of the volunteers. For this pilot study, we harvested one fresh cadaveric bo-

ny-ligamentous thoracolumbar spine (C7-S1) which was stored frozen un-

til the time of use. After thawing, the caudal free-end (S1) of the specimen

was potted and fixed to a stationary platform. The cranial free-end (C7)

was attached to the end-effector of the robot. The cadaveric spine was di-

mensionally matched to one of the 3D kinematic data sets in the database.

To track the individual 3D motion of each vertebra, FOB sensors were at-

tached to six levels (T12-L5) of the spine, as shown in Figure 1. The spine

was then driven through the prescribed motions by the robot while 3D data

were collected from the sensors. The resultant 3D motions were analyzed

at each level to determine the distribution of motion among the levels.

RESULTS: The motion of the cadaveric spine replicated with high fidelity

in vivo motion in all directions. The maximum error between actual and

prescribed motion was 2.2%. The distribution of motion was recorded in

3D at a rate of over 61 samples per second. The intersegmental lateral

bending range of motion (Figure 2) increased with decreasing level cranial

to caudal: T12-L1 4.6�, L1-L2 6.0�, L2-L3 8.3�, L3-L4 8.1�, and L4-L5

8.9�.

CONCLUSIONS: The novel method introduced in this study provides

a tool for quantitatively assessing the 3D redistribution of motion of the

entire thoracolumbar spine following surgical interventions. This model

provides unique insight into adjacent level disease by determining redistri-

bution of motion using in vivo kinematics. Future work will include 8 ad-

ditional FOB sensors and comparison of motion before and after surgical

intervention.

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

any applicable devices or drugs.

doi: 10.1016/j.spinee.2009.08.425

P165. Three Level Cervical ADR: Long-Term Clinical and

Radiographic Outcomes

Rick B Delamarter, MD, Alexandre Rasouli, MD, Brandon Strenge, MD,

Nomaan Ashraf, MD, L.E.A. Kanim, MA, Hyun Bae, MD, Michael Kropf,

MD; The Spine Institute at Santa Monica, Santa Monica, CA, USA

BACKGROUND CONTEXT: A recent FDA-sponsored randomized con-

trolled study of the Prodisc-C (Synthes Spine, Westchester, PA) cervical

artificial disc replacement (ADR) established superior clinical outcomes

as compared to anterior cervical discectomy and fusion (ACDF) for sin-

gle-level spondylotic disease. However, no previous study has reported

on the clinical and radiographic outcomes of adjacent three-level cervical

ADR.

PURPOSE: To evaluate the clinical outcomes and sagittal range of motion

of adjacent three-level ProDisc-C disc replacements.

STUDY DESIGN/SETTING: Prospective Cohort.

PATIENT SAMPLE: Twenty-four patients receiving consecutive three-

level cervical ADR between C3 and C7.

OUTCOME MEASURES: Angular motion (extension and flexion mea-

surements) on preoperative and postoperative sagittal-projection cervical

films at each operative motion segment as well as at the segments adjacent

to the prosthetic construct. Neck Disability Index (NDI), Visual Analog

Score Pain (VAS-P), and Visual Analog Score Satisfaction (VAS-S) data

were also collected.

METHODS: Patients were evaluated pre-operatively, at six weeks, three

months, six months, and annually for 2-5 years postoperatively with lateral

flexion-extension dynamic films and with completion of NDI and VAS

surveys.

RESULTS: At motion segments adjacent to the ADR construct, the mean

preoperative range of motion was 10.53� (SD 2.59�), compared to 12.32�

postoperatively (SD 1.92�, pO0.05). The mean preoperative range of mo-

tion at all levels undergoing ADR was 9.20� (SD 2.11�) versus 10.02�

postoperatively (SD 1.47, pO0.05), indicating no significant difference.

At 2-5 years postoperatively, all patients had significant reductions in both

NDI and VAS scores relative to preoperative levels (p!0.05). At up to five

years follow-up, no patient underwent revision surgery or surgeries at ad-

jacent levels.

CONCLUSIONS: The use of the three-level cervical ADR construct does

not inhibit preservation of range of motion at the individual ADR levels.

Most significantly, the nonoperative levels adjacent to the construct main-

tain their preoperative range of motion at 2-5 years postoperatively. At up

to five years of follow-up, there has been no need for revision or adjacent-

segment surgery. Patients also demonstrate significant improvement in

pain, disability, and satisfaction.

FDA DEVICE/DRUG STATUS: ProDisc-C: Investigational/Not

approved.

doi: 10.1016/j.spinee.2009.08.426

Figure 1.

Figure 2.

199SProceedings of the NASS 24th Annual Meeting / The Spine Journal 9 (2009) 1S-205S