“Lumbar Segmental Instability” The Role of Interbody Fusion

1. “Lumbar Segmental Instability”The Role of Interbody Fusion • Role of Interbody Spacers are to provide a means to stabilize the anterior column • Anterior column stability decreases the motion at unstable segments and unloads the posterior instrumentation • “Carson et al” showed a seven fold decrease in bending moment with anterior column support

2. “Lumbar Segmental Instability”The Role of Interbody Fusion • Interbody fusion can be accomplished thru anterior or posterior approaches • Not a Stand-Alone (requires hardware) • Each has their own advantages and disadvantage • Posterior Interbody Fusions advantages include: total disc excision, restoration of disc height, enhanced foraminal decompression, and high arthrodesis rates

3. “Lumbar Segmental Instability”The Role of Interbody Fusion • Posterior Interbody fusion disadvantages include: graft displacement, neurologic injury, and nonunion • Anterior Interbody Fusion advantages include: reduced operative time, reduced blood loss, maintain posterior structures, complete discectomy, and avoidance of scarring in the canal

4. “Lumbar Segmental Instability”The Role of Interbody Fusion • Anterior Interbody fusion disadvantages include: second surgical approach and access surgeon, potential vascular injury, graft displacement, and GI and GU injury or complication

5. “Lumbar Segmental Instability”The Role of Interbody Fusion “Patient Selection for Interbody Fusion” • Indications include the following: spondylolisthesis to stabilize the anterior column, pseudoarthrosis repair, recurrent disc herniation’s and re-operations, fractures for anterior and middle column reconstruction, correction of deformity either scoliosis or degenerative disc disease

6. “Lumbar Segmental Instability”The Role of Interbody Fusion • Types of Interbody Allograft Spacers available include: femoral rings, cortical dowels, cortical ramps, and composite cortical and cancellous bone spacers • Each have specific benefits and disadvantages though

7. “Lumbar Segmental Instability”The Role of Interbody Fusion “Femoral Ring Allografts”

8. “Lumbar Segmental Instability”The Role of Interbody Fusion • Femoral Ring Allograft Spacer’s have the advantages of ready availability, fashion many grafts from a single femoral shaft, size for each level as well as shape the graft, and reconstitute the disc height • Disadvantages include migration, anterior placement only, less surface area for grafting around it, small area for autograft, and loss of full contact

9. “Lumbar Segmental Instability”The Role of Interbody Fusion “Cortical Dowels”

10. “Lumbar Segmental Instability”The Role of Interbody Fusion • Cortical Dowels have the advantage of greater fixation through threads, approach anterior or posterior, restore disc height, and better contact with surface of endplates and bone • Disadvantages include less surface area for grafting around although better than femoral rings, limited autograft placement, less lordotic correction, and potential for loss of contact (L5S1)

11. “Lumbar Segmental Instability”The Role of Interbody Fusion “Cortical Ramps”

12. “Lumbar Segmental Instability”The Role of Interbody Fusion • Cortical Ramps advantages include lordotic producing, large surface area for bone grafting, better fixation through serrations, less migration than femoral ring, and both anterior or posterior appraoch • Disadvantages include migration, loss of surface contact, rotation of graft, and less surface area for incorporation compared to dowels or rings

13. “Lumbar Segmental Instability”The Role of Interbody Fusion “Metallic Devices”

14. “Lumbar Segmental Instability”The Role of Interbody Fusion • Advantages include being metallic and not dependent on bone availability • Available in a vast array of sizes and shapes for the specific needs • Greater structural support • Instantaneous stability while bone graft consolidates • Better fixation to inner space

15. “Lumbar Segmental Instability”The Role of Interbody Fusion • Disadvantages include less bone ingrowth potental • Less surface area for bone ingrowth • Not an end plate sparing: dependent on device and insertion technique • Potential for subsidence • Potential for loss fit and migration • Re-establishment segmental lordosis

16. “Lumbar Segmental Instability”The Role of Interbody Fusion “Biomaterial Devices”

17. “Lumbar Segmental Instability”The Role of Interbody Fusion • Advantages: readily available • Can be fabricated in any size and shape • Good structural stability dependent on composite: ie. PEEK • End plate sparring: dependent on device and technique • Re-establish segmental lordosis • Good fixation to inner space

18. “Lumbar Segmental Instability”The Role of Interbody Fusion • Disadvantages: less surface area for bone ingrowth • Potential for ingrowth less than cortical ramps • Potential for migration • Potential for subsidence • Potential for reactive changes due to device: ie PEEK or bioabsorbables

19. “Lumbar Segmental Instability”The Role of Interbody Fusion • Maintain and/or re-establish segmental lordosis of individual disc spaces • Re-establish disc height • Promote foraminal decompression • Eliminate rotation of the graft (fins) • Serration’s for fixation and limitation of graft migration • Provide larger surface area for incorporation (serration’s and fins)