Research Shows that Rod Placement and Size Matter When It Comes to Stability After Cervical Spine Surgery

Research Shows That Rod Placement and Size Matter When It Comes to Stability After Cervical Spine Surgery.

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A man massages his painful neck.

New research published in Neurosurgery examines the quantity and types of material used in spinal implants, which provide stabilization following reconstructive surgery of the cervicothoracic junction. 


A first-of-its-kind study from MedStar Health Research Institute published in the journal Neurosurgery examines the benefits of different methods to stabilize the cervicothoracic junction (CTJ), where the neck meets the upper back, after reconstructive surgery to manage conditions such as spinal deformity, degeneration, trauma, and tumors

Reconstructive surgery at the CTJ involves implanting rods and screws in the spine to provide support as it heals from surgery, much like a cast on the outside of a broken arm. With the normal daily forces produced during spinal motion, screws can loosen from the spine over time and rods can break. One recent study put the failure rate at 25%.

Our research shows that rod size and number of rods implanted matter when it comes to stabilizing the CTJ. We found that 4.0mm cobalt chrome rods provide greater stability than 3.5mm titanium rods and cobalt chrome rods are strained less than titanium rods during motion testing. Implanting four rods instead of the traditional two-rod reconstruction significantly improves stability as patients heal. 

Knowing which materials to use and how many rods to implant can help reduce the likelihood that patients will return to the operating room with spinal instrumentation complications such as rod breakage or screw dislodgement. 

Testing motion, stability, and strain.

Researchers prepared 10 cervicothoracic spines from cadavers of individuals who generously donated their bodies to be used for medical research.  A custom-designed spinal simulator was used to biomechanically evaluate how the implanted rods responded to the normal cervical spine motion, including flexion-extension (forward and backward), lateral bending (sideways), and angular displacement (rotation).

After implanting the rods and screws, the spinal motion simulator replicated physiologic motions and the resulting data was analyzed and demonstrated the following:


  • Using a total of four rods significantly improves stability with cobalt and titanium rods.
  • Adding two additional rods did not considerably reduce the amount of rod strain, but cobalt chrome performed better than titanium materials.
  • 4.0 mm cobalt chrome rods are more stable than 3.5 mm titanium rods.
  • Cobalt chrome rods provide the greatest stability when opting for two rods instead of four.

While four rods provided the best stabilization, doubling the number of rods and screws means doubling the cost of the treatment, increasing operative time and the chance of interference with imaging such as CT scan or MRI.


              Illustration of the spine with variations of rods.

Next steps: Understanding real-world outcomes.

To advance this research in a clinical retrospective study, researchers could evaluate patients who received two versus four rods and compare instrumentation failure and surgery-related complications. 

Our study of the CTJ is the first and most thorough of its kind to examine the stabilization questions related to the number and materials of rods, answering some of the most critical questions in posterior cervical spine surgery. 

There’s no greater feeling than helping patients return to work and normal life activities from debilitating spinal pathology. The results of this research study serve to assist spinal surgeons in implant selection based on spinal pathology, and thereby, improve patient outcomes.

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