In vivo ranges of motion of cervical segments in patients with cervical spondylosis during dynamic neck motions

0
0
0

In vivo ranges of motion of cervical segments in patients with cervical spondylosis during dynamic neck motions

Nearly 85% of people over 60 live with cervical spondylosis—age-related wear and tear on the neck’s spinal discs and bones—but how this condition changes real-world neck movement has long been a mystery. Now, a study from Harvard Medical School and Newton-Wellesley Hospital reveals that spondylosis at the C5–6 level (a common trouble spot for nerve or spinal cord compression) alters motion in surprising, movement-specific ways—findings that could reshape how doctors treat neck pain and engineers design implants.

What Is Cervical Spondylosis?

Cervical spondylosis describes degenerative changes in the lower cervical spine (C3–7), such as disc thinning, bone spurs, or ligament thickening. These changes can press on nerves or the spinal cord, causing axial neck pain, numbness, weakness, or even myelopathy (spinal cord damage). The most common surgery, anterior cervical discectomy and fusion (ACDF), removes a damaged disc and fuses two vertebrae to relieve pressure. But over 90% of patients develop adjacent segment degeneration (ASD), where nearby discs wear out faster, and up to 25% need reoperation.

Total disc replacement (TDR)—which swaps a damaged disc for an artificial one to preserve motion—was meant to fix this. Yet clinical trials show TDR doesn’t reduce ASD rates or improve outcomes more than ACDF. Scientists suspect the issue: Surgeries don’t match the body’s natural neck motion. Until now, no one had measured in vivo (living body) motion in people with symptomatic spondylosis—those with pain or neurological symptoms.

How the Study Worked

The research team, led by Tao Guo (Guizhou Provincial People’s Hospital) and Yan Yu (Tongji Hospital) with colleagues from Harvard Medical School-affiliated institutions, studied 8 patients with spondylosis at C5–6 (causing myelopathy or radiculopathy) and 10 asymptomatic controls (matched for age and sex). Here’s how they measured motion:

  1. 3D Spinal Models: MRI scans (3 Tesla, Siemens) created detailed 3D models of each participant’s cervical spine (C3–7).
  2. Dynamic Imaging: A dual fluoroscopic imaging system (DFIS)—two X-ray machines positioned at right angles—captured orthogonal images of the neck at 30 frames per second during two daily movements:
    • Flexion-extension: Bending the neck forward (flexion) and backward (extension).
    • Left-right twisting: Turning the head side to side (e.g., looking over your shoulder).
  3. Consistency & Safety: Participants followed a metronome to ensure smooth, repeatable motions. Each cycle lasted <3 seconds (three cycles per movement) to minimize radiation exposure—total dose was ~1 mSv, or 2% of annual background radiation.
  4. Motion Analysis: A validated 3D-2D registration technique matched the 3D vertebral models to the fluoroscopic images. The team calculated range of motion (ROM) for each segment (C3–4, C4–5, C5–6, C6–7) as the difference between maximum and minimum angles during a cycle.

Key Findings: Spondylosis Alters Motion by Level and Movement

The results, published in Chinese Medical Journal, showed spondylosis at C5–6 changes motion in level- and action-specific ways:

1. Flexion-Extension (Bending)

  • Diseased Level (C5–6): The spondylosis group had a significantly higher ROM (18.4° ± 5.9°) compared to controls (15.1° ± 3.6°, P < 0.05). This means the C5–6 segment was looser (more lax) when bending—opposite to the “stiff neck” stereotype.
  • Other Segments: No meaningful differences at C3–4, C4–5, or C6–7.

2. Left-Right Twisting (Turning)

  • Diseased Level (C5–6): The spondylosis group had a significantly lower ROM (6.3° ± 2.4°) vs. controls (11.6° ± 3.8°, P < 0.05).
  • Adjacent Level (C4–5): The spondylosis group also had a significantly lower ROM (7.5° ± 2.4°) vs. controls (10.9° ± 2.9°, P < 0.05).

Both the diseased and adjacent segments were stiffer during twisting—a common daily action (e.g., checking blind spots, talking to someone beside you).

Why This Matters for Patients and Doctors

These findings challenge assumptions about spondylosis and surgery:

  • Motion-Specific Issues: Current TDRs are designed to restore flexion-extension but offer little resistance to axial rotation (twisting). This study suggests TDR might work better for bending than twisting—explaining why it hasn’t reduced ASD rates (if the implant doesn’t handle twisting, adjacent segments still take extra stress).
  • Pre-Surgery Motion Matters: Spondylosis changes how the neck moves before surgery. For example, decompression surgery (which relieves pressure without fusing vertebrae) might be better for some patients, as it causes minimal damage to natural motion.
  • Implant Design Needs Upgrade: Engineers should design implants that work with all neck motions—not just one. Hybrid surgeries (combining fusion for stability and TDR for motion) could balance constraint and flexibility, but more research is needed.

Limitations to Consider

The study had a small sample size, so the flexion-extension findings need validation (a post-hoc power analysis showed only 25% power for that measure). The team also didn’t evaluate soft tissue changes (e.g., disc hydration via MRI T2 values), which could affect motion. Future research should include larger groups, different cervical levels, and long-term follow-up to track how surgery changes motion over time.

The Takeaway

This study is the first to measure real-world neck motion in people with symptomatic spondylosis—and it shows the condition doesn’t just “stiffen” the neck. Spondylosis at C5–6 makes the segment looser during bending and stiffer during twisting, with ripple effects on adjacent levels. For patients, this means more personalized treatment: Doctors can use pre-surgery motion data to choose between fusion, TDR, or decompression. For engineers, it’s a roadmap to implants that work with the neck’s natural mechanics.

The research was conducted by Tao Guo, Yan Yu, Chao-Chao Zhou, Kamran Khan, Hai-Ming Wang, Guo-An Li (Orthopaedic Bioengineering Research Center, Newton-Wellesley Hospital and Harvard Medical School), and Thomas Cha (Department of Orthopaedic Surgery, Massachusetts General Hospital and Harvard Medical School). Funding came from the National Institutes of Health (1R03AG056897) and a scholarship from Guizhou Provincial People’s Hospital.

The study was published in Chinese Medical Journal (2021) by Tao Guo, Yan Yu, Chao-Chao Zhou, Kamran Khan, Hai-Ming Wang, Guo-An Li, and Thomas Cha. doi.org/10.1097/CM9.0000000000001209

Was this helpful?

0 / 0