In-vivo Three-dimensional Kinematics Comparing Adjacent Segment Motion of Anterior Cervical Fusionversus Cervical Arthroplasty in 17 Patients

Azam Basheer M.D.

Victor Chang M.D., Michael Bey Ph.D.,Stephen Bartol M.D.

Department of Neurosurgery† and

Department of Orthopedics‡

Henry Ford Hospital

llDisclosures

• CNS research grant

llCervical Spondylosis

• Most common cause of cervical cord and root dysfunction in patients older than 55 years

• Common process of aging; seen in 10% of individuals by the age of 25 and 95% by the age of 652

• Can manifest as either neck pain syndromes, radiculopathy or myelopathy

llACDF and ASD

• Anterior Cervical Discectomy & Fusion (ACDF) is the most common treatment for patients with cervical spine disorders

• Increased by 114% from 1998 to 2008

• Biomechanical changes with ACDF are implicated to contribute to Adjacent Segment Disease (ASD)

• Degenerative changes seen in 25-92% of patients, and clinical symptoms presenting in 14-26% of patients.

llACDF and ASD

- The proposed mechanism of ASD is hypermobility at adjacent segments that result from fusion,

- However, it remains unclear whether the progression of ASD is a result of increased motion in the adjacent segments due to fusion, or simply a natural process related to aging

llArtificial Disc (AD)

- Alternative to ACDF to preserve motion patterns

- Preliminary reports are encouraging, the acceptance of cervical arthroplasty as

an alternative to fusion will ultimately depend on long-term clinical studies

- Adjacent segment biomechanics are less clear

- Biomechanical studies are important to better understanding neck function

post-surgery, and may provide insight into the mechanical factors that

contribute to a good or poor clinical outcome

llCurrent Motion Studies

- Studies investigating cervical spine motion are often limited to:

- 2D analysis: well suited for measuring relatively planar movements such as neck flexion and extension, but are highly susceptible to errors attributed to out-of-plane movement

- Cadaveric simulations: good for measuring three-dimensional (3D) motion patterns, they are not designed to reproduce the joint forces, muscle forces and complex motion patterns associated with in vivo conditions.

- The mechanics of cervical arthoplasty in comparsion to ACDF may be better understood using a validated 3D in vivo technique

llOur Study Goal

- Compare in vivo, 3D, dynamic cervical spine kinematics between cervical

arthroplasty and fusion patients

- We hypothesized that adjacent segment kinematics would be significantly

greater in the surgical fusion patients

llMethods

• 17 patients were enrolled into the study. 10 patients underwent C5-6 ACDF, while 7 patients underwent C5-6 AD

• Mean age for ACDF group 48±10.8 years vs 47±7.0 years

for AD group (p = 0.83).

• Mean post-op period was 24.1±7.4 mos for the ACDF group vs 22.0±3.3 mos for the AD group (P = 0.50)

• Three non-operative segments (C3-4, C4-5, and C6-7) were assessed for both inter-vertebral rotation and facet shear

llMethodology

- Subjects were seated with their neck centered in a biplane x-ray system.

- Biplane x-ray images were acquired during two motion activities: neck extension, and axial neck rotation

- Images collected at 60 Hz

- 3 trials per motion

llBi-plane X-ray System

• Originally developed to evaluate knee motion and its relationship to Osteoarthritis

llBi-plane X-ray System

Key componentsPulsed X-ray generators

Image intensifiers with high-speed video cameras

llMethodology

Image Intensifier

+

High-speed video Camera

Image Intensifier

+

High-speed video Camera

Patient

3D Imaging area where X-ray beams bisect

ll3D Model based off CT imaging

• Computed Tomography scan (1.25 mm slices)

• Manually segmented

• Reconstructed into a three-dimensional model

llModel-based Tracking

• Anatomic landmarks of the bone can be used to track 3D positioning of a bone from biplane X-ray images– Vertebral body and endplates

– Spinous Process

– Facets

llConclusions

An anatomical coordinate system was defined for the vertebral body by three landmarks: the center of the vertebral body (1), and the centers of the left (2) and right

(3) lateral masses

llModel Based Tracking

• Create a Digitally Reconstructed Radiographs (DRR) from the CT based 3D model

• Provides a 3-D estimate for the in vivo positioning for a particular bone and is accurate to within ± 0.6 mm and ± 0.6 degrees

llModel Based Tracking

• Digitally Reconstructed Radiographs (DRR) from the CT based 3D model (green)

• Optimize the similarity between DRR and the biplane X-ray images (red)

• Provides a 3-D estimate for the in vivo positioning for a particular bone

ll

Results

.

llDisc Height

C5:C6 disc height in the arthroplasty group was significantly greater than in the fusion group

llTotal Extension

No difference in total neck extension comparing ACDF and AD

llExtension at Each Level

Greater at C5-6 for AD, but greater at C3-4 and C6-7 for ACDF

llTotal Axial Rotation

Total rotation was the same for both groups. Vertebral rotation was greater in the arthroplasty group at C5:C6. There were no significant differences in motion between groups at C3:C4, C4:C5 and C6:C7.

llAxial Rotation at Each Level

Greater motion seen at C5-6 for AD. While more motion at the adjacent (C4:C5 and C6:C7) and remote (C3:C4) segments in ACDF group; these were not significant

llFacet Shear

Facet translation was greater in the arthroplasty group at C5:C6

and greater in the fusion group at C3:C4 and C4:C5 M-L facet shear .

llResults

• There was no difference in total neck motion comparing ACDF and AD for neck extension (p=0.866) and rotation (p=0.576)

• For extension, when measured as a percentage of total neck motion there was a greater amount of extension at the non-operated segments in the ACDF versus AD (p=0.003)

llResults

• There was greater rotation at the nonoperative segments in the ACDF versus AD (p=0.024)

• Increased M-L facet shear was seen on neck extension with ACDF versus AD (p=0.008).

• Comparing each segment, C3-4 (p = 0.039) C4-5 (p = 0.022) showed increased shear while C6-7 (p =0.767) did not in ACDF

What does all this mean?What does all this mean?

• This study illustrates increased motion at non-operative segments in ACDF patients compared to AD.

• Whether these changes contribute to adjacent segment disease will require further study

• Facet shear can also be measured and may also be a topic of interest in the future

In-vivo Three-dimensional Motion Analysis Correlated with Clinical Outcomes in 11 Cervical Fusion

Patients: A CNS Fellowship Funded Study

Azam Basheer M.D.

Victor Chang M.D., Michael Bey Ph.D.,Stephen Bartol M.D.

Department of Neurosurgery† and Department of Orthopedics‡

Henry Ford Hospital

llMethods

- 11 patients 2 years post C5-6 ACDF enrolled for the study

- Motion analysis performed using bi-planar fluoroscopy

and a model based tracking technique for C3-4 and C4-5

- Clinical measures were assessed using: Neck Disability Index (NDI), Visual Analog Score (VAS) for arm and neck pain, and the Short Form (36) Health Survey physical component score (SF36).

- Spearman’s method was used to measure correlation between motion analysis parameters and clinical scales.

llVAS

llNDI

llSF-36

SF-36® Health Survey Scoring Demonstration

This survey asks for your views about your health. This information will help you keep track of how you feel and how well you are able to do your usual activities.

Answer every question by selecting the answer as indicated. If you are unsure about how to answer a question, please give the best answer you can.

1. In general, would you say your health is:

- Excellent- Very good- Good- Fair- Poor

2. Compared to one year ago, how would you rate your health in general now?

- Much better now than one year ago- Somewhat better now than oneyear ago- About the same as oneyear ago- Somewhat worse now than oneyear ago- Much worse now than one year ago

llMethodology

- Each subject was seated with their neck centered in the imaging field of view

- X-ray images were acquired during two motion tasks: axial neck rotation and neck extension.

llResults

Mean NDI was 6±6.08, mean neck VAS was 0.75±1.1, mean arm VAS 0.52±0.68, and mean SF36 was 44.55±10.11

llC3-4

During neck rotation, there was a positive correlation with increased C3-4 axial rotation with NDI (0.731, p=0.025), neck VAS (0.790, p=0.011), and a negative correlation with SF36 (-0.778, p=0.023)

During neck extension, there was also a positive correlation with increased C3-4 extension and neck VAS (0.685, p=0.042), and

llC4-5

There was a positive correlation between increased C4-5 extension with SF36 (0.743, p=0.035)

There was a a negative correlation with C4-5 axial rotation with NDI (-0.714, p=0.031) and neck VAS (-0.896, p=0.001)

llConclusions

- Increasing rotation at the C3-4 level correlates with worse clinical outcome after C5-6 ACDF

- Increased rotation at the C4-5 level correlates with better clinical outcome

- This suggests that a mobile C4-5 segment is a healthier state, and that increased mobility at C3-4 indicates an unhealthy state, perhapscompensatory for C4-5 immobility from degeneration - These findings may help illustrate the pathogenesis of ASD

- Longitudinal follow-up may also illustrate the natural history as well

Thank You

llReferences

1. Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999;81:519-28

2. Hilibrand AS, et al. The effect of anterior cervical fusion on neck motion. Spine. 2006; 31:1688-1692

3. Kolstad F, Nygaard OP, Leivseth G. Segmental motion adjacent to anterior cervical arthrodesis: a prospective study. Spine. 2007; 32:512-517

4. Bey MJ, Zauel R, Brock SK, et al. Validation of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics. J Biomech Eng 2006;128:604-9.