Adjacent Segment Mechanics in Cervical Arthrodesis Patients

Study Overview
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Brief Summary
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This study aims to determine to what extent patient-specific factors, iatrogenic factors, and biomechanical factors influence cervical spine mechanics after single-level and two-level arthrodesis.

Detailed Description
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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: the natural history of the adjacent disc; disruption of the adjacent segment anatomy due to the initial surgery; and 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.

Official Title
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Adjacent Segment Mechanics in Cervical Arthrodesis Patients

Conditions
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Intervertebral Disc Degeneration

Intervention / Treatment
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* Procedure: C5-C6 arthrodesis


Participation Criteria
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Eligibility Criteria
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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.

Ages Eligible for Study
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Minimum Age: 21 Years
Maximum Age: 60 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Asymptomatic Controls<br>Individuals who have no history of neck pain, trauma or surgery, similar in age and sex to the surgical patients | |
| C5-C6 arthrodesis<br>Patients scheduled to undergo C5-C6 anterior cervical arthrodesis | Procedure: C5-C6 arthrodesis<br>* A standard Smith Robinson anterior medial approach to the cervical spine. Vertebral endplates will be prepared by removing the cartilage endplate. Tricortical anterior iliac crest autografts will be harvested with a low-speed oscillating saw. Allografts will be fresh-frozen, vacuum-sealed, nonradiated tricortical grafts. All grafts will be fashioned in a typical Smith-Robinson formation. The motion segment will be distracted approximately 2-mm beyond the graft height before the insertion of each graft. Fusion plate will be contoured to cervical lordosis. Cervical plates will be positioned using surgical midline markers. All rigid anterior plate fixations will be performed using titanium anterior fixed-angle screw systems.<br>|
| C6-C7 arthrodesis<br>Patients scheduled to undergo C6-C7 anterior cervical arthrodesis | Procedure: C5-C6 arthrodesis<br>* A standard Smith Robinson anterior medial approach to the cervical spine. Vertebral endplates will be prepared by removing the cartilage endplate. Tricortical anterior iliac crest autografts will be harvested with a low-speed oscillating saw. Allografts will be fresh-frozen, vacuum-sealed, nonradiated tricortical grafts. All grafts will be fashioned in a typical Smith-Robinson formation. The motion segment will be distracted approximately 2-mm beyond the graft height before the insertion of each graft. Fusion plate will be contoured to cervical lordosis. Cervical plates will be positioned using surgical midline markers. All rigid anterior plate fixations will be performed using titanium anterior fixed-angle screw systems.<br>|
| C4-C5-C6 arthrodesis<br>Patients scheduled to undergo C4-C5-C6 anterior cervical arthrodesis | Procedure: C5-C6 arthrodesis<br>* A standard Smith Robinson anterior medial approach to the cervical spine. Vertebral endplates will be prepared by removing the cartilage endplate. Tricortical anterior iliac crest autografts will be harvested with a low-speed oscillating saw. Allografts will be fresh-frozen, vacuum-sealed, nonradiated tricortical grafts. All grafts will be fashioned in a typical Smith-Robinson formation. The motion segment will be distracted approximately 2-mm beyond the graft height before the insertion of each graft. Fusion plate will be contoured to cervical lordosis. Cervical plates will be positioned using surgical midline markers. All rigid anterior plate fixations will be performed using titanium anterior fixed-angle screw systems.<br>|
| C5-C6-C7 arthrodesis<br>Patients scheduled to undergo C5-C6-C7 anterior cervical arthrodesis | Procedure: C5-C6 arthrodesis<br>* A standard Smith Robinson anterior medial approach to the cervical spine. Vertebral endplates will be prepared by removing the cartilage endplate. Tricortical anterior iliac crest autografts will be harvested with a low-speed oscillating saw. Allografts will be fresh-frozen, vacuum-sealed, nonradiated tricortical grafts. All grafts will be fashioned in a typical Smith-Robinson formation. The motion segment will be distracted approximately 2-mm beyond the graft height before the insertion of each graft. Fusion plate will be contoured to cervical lordosis. Cervical plates will be positioned using surgical midline markers. All rigid anterior plate fixations will be performed using titanium anterior fixed-angle screw systems.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Kinematics | range of motion (ROM) in degrees | pre-surgery to 3 years post-surgery | 
| Iatrogenic factors | adjacent segment disc height and sagittal alignment; graft height, plate placement | pre-surgery to 3 years post-surgery | 
| Kinematics | The helical axis of motion (HAM) | pre-surgery to 3 years post-surgery | 
| Kinematics | The continuous 3D intervertebral kinematics (translations and rotations). | pre-surgery to 3 years post-surgery | 
| Arthrokinematics | Disc deformation | pre-surgery to 3 years post-surgery | 
| Arthrokinematics | Facet joint capsule deformation | pre-surgery to 3 years post-surgery |