Adjacent Segment Mechanics in Cervical Arthrodesis Patients

The etiology of adjacent segment pathology following cervical fusion remains highly
controversial. Adjacent segment disease is believed to result from one or more of the
following distinct causes:

1. the natural history of the adjacent disc;

2. disruption of the adjacent segment anatomy due to the initial surgery; and

3. biomechanical stress on the adjacent level following the fusion.

The long-term goal of our research is to reduce or prevent symptomatic adjacent segment
degeneration in the spine. The overall hypothesis of this study is that adjacent segment
kinematics (i.e. translations, rotations, helical axis of motion) and arthrokinematics (i.e.
disc deformation and facet joint surface interactions) after ACDF are determined primarily by
patient-specific anatomy and iatrogenic factors, and not by increased biomechanical stress
due to the fusion.

A prospective longitudinal study is proposed to determine to what extent patient-specific
factors (Specific Aim 1), iatrogenic factors (Specific Aim 2), and altered biomechanics
(Specific Aim 3) affect dynamic cervical spine function following fusion. Participants will
be C56 (n=22) and C67 (n=22) single-level fusion patients, C456 (n=22) and C567 (n=22)
two-level fusion patients, and asymptomatic controls similar in age to the fusion patients
(n=22). Patients will be tested prior to surgery, one year post-surgery, and three years
post-surgery. At each test, participants will complete clinical questionnaires to assess pain
and function, and they will perform full range of motion flexion\extension and axial rotation
of the head and cervical spine while biplane radiographs are recorded at 30 images per
second. A highly accurate and validated volumetric model-based tracking process and custom
data analysis software will be utilized to determine intervertebral kinematics (i.e.
translations, rotations, helical axis of motion) and arthrokinematics (i.e. disc deformation
and facet joint surface interactions) at each test session.

This prospective study will identify the factors that have the greatest effect on adjacent
segment mechanics after cervical fusion. If the hypotheses are confirmed, this will provide
support for increased attention to patient-specific factors and surgical technique.
Alternatively, if the results indicate that adjacent segment mechanics are influenced
primarily by increased stress after arthrodesis, this will provide support for increased
attention to the design of motion-sparing devices.

Inclusion Criteria:

- Patients must agree to return for all follow-up visits and provide informed consent.

- Control subjects will be asymptomatic, with no injury or disease that will interfere
with spine function, such as previous spine surgery or trauma.

Exclusion Criteria:

- Participants will have no other injury or disease that will interfere with spine
function, such as previous spine surgery or trauma

- Individuals who have been previously clinically diagnosed with poor bone quality and
those who do not intend to stay in the Pittsburgh area for a period of at least 3
years post-surgery will be excluded.

- Females who are pregnant or plan to be pregnant within 3 years of surgery will be
excluded.