Segmental Instability in the Lumbar Spine

Flexion has long been associated with clinical issues, including

  • instability associated with degenerative spondylolisthesis
  • post-operative instability after surgical decompression
  • adjacent segment disease

The LimiFlex™ Paraspinous Tension Band is a new surgically implanted device that provides lumbar sagittal plane stability. Typical patients have degenerative spinal disease requiring decompression, such as lumbar spinal stenosis with or without degenerative spondylolisthesis.

Flexion Instability

Lumbar spinal flexion, or forward bending of the spinal column, is the most important motion of the lumbar spine. It has the largest range of motion.1 Flexion control is particularly important, as flexion is used most often during daily activity.2,3

Lumbar Flexion / Extension

Normal functional range of motion of the lumbar spine during 15 activities of daily living.1

Flexion instability is coupled with translational instability (movement of vertebrae on the sagittal plane).4,5 Facets limit sagittal translation. Less of the facets’ articular surfaces are engaged when a lumbar spinal segment is in flexion. This results in decreased resistance of the segment to shear forces.6,7

HP5 Facets

The facet joints are less engaged in flexion, and those parts of the facets that are engaged provide less resistance to shear.

Patients with degenerative spondylolisthesis may have sagittal plane instability due to facet degeneration.

Facets in patients with degenerative spondylolisthesis

Healthy level: facets more coronally oriented and less ramped
Level with degenerative spondylolisthesis: ramped sagittal facet profile makes the segment less stable in flexion

Instability after Surgical Decompression

Decompression surgery is commonly performed to relieve pressure on nerve roots in the lumbar spine. Surgical decompression is very effective at resolving the back, leg and hip pain caused by spinal stenosis. However, all decompression surgeries involve resection of dorsal spinal structures, often resulting in varying degrees of flexion instability.8 With a hypermobile segment, or pathology such as degenerative spondylolisthesis, additional stabilization may be required to ensure that symptoms do not recur.

Typical decompression techniques and resected dorsal spinal structures:
HP2 Bilateral Decompression

Bilateral

HP3 Unilateral Decompression

Unilateral

HP4 Midline Decompression

Midline

Instability after Decompression: Video by Todd F. Alamin, MD.9

References

1. Benzel E American Association of Neurological Surgeons (distributed by Thieme), New York 2001
2. Bible JE et al. J Spinal Disord Tech 2010;23:106-12
3. Wilke HJ et al. Spine 1999;24:755-62
4. Hipp JA et al. Advanced techniques and controversies (Saunders Elsevier) Philadelvia 2008
5. Fielding LC et al. Eur Spine J 2013;22:2710-2718
6. Toyone T et al. Spine 2009;34:2259-62
7. Grobler LJ et al. Spine 1993;18:80-91
8. Fry RW et al. Spine 2014;39:E74-81
9. Todd F. Alamin, MD, orthopedic spine surgeon at Stanford University School of Medicine and co-founder of Simpirica Spine