Assessment of different nucleotomy techniques using ultra-high resolution MRI — The International Society for the Study of the Lumbar Spine
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  2. SESSION #13 - TECHNIQUE AND MRI
  3. Assessment of different nucleotomy techniques using ultra-high resolution MRI

Assessment of different nucleotomy techniques using ultra-high resolution MRI (#72)

Tamanna Rahman 1 , Nicoleta Baxan 1 , Robert T Murray 1 , Saman Tavana 1 , Thomas P Schaer 2 , Nigel Smith 3 , Jonathan Bull 4 , Nicolas Newell 1
  1. Imperial College London, London, United Kingdom
  2. University of Pennsylvania School of Veterinary Medicine, Philadelphia
  3. University College London, London, United Kingdom
  4. BARTS Health NHS Trust, London, United Kingdom

Introduction

Nucleus pulposus replacement has the potential to be an early treatment for younger patients1, who require a spinal surgery2. The surgery involves removal (nucleotomy) and replacement of the native degenerated nucleus with a material designed to restore the segment’s biomechanical properties. Multiple techniques have been considered for nucleotomy, but a detailed quantitative comparison of them is lacking. This study aims to compare three nucleotomy techniques: forceps, automated-shaver and laser.

Methods

Fifteen human (40±13years) vertebra-disc-vertebra lumbar specimens (Pfirrmann:3±13) were split into three groups of five, with each group assigned to a nucleotomy-technique. A posterolateral approach was used to insert 3mm-diameter forceps, an automated-shaver (Nucleotome®), and an 18G needle for laser-nucleotomy. The laser-nucleotomy followed methods reported in literature (1200J, 1s pulses at 10W). To compare changes in disc stiffness each specimen was axially compressed to 1kN (5 cycles at 1Hz) both when intact and after nucleotomy. T2-weighted MRIs were acquired at 9.4T pre- and post-nucleotomy and used to quantify disc height change and volume of disc material removed.

Results

The automated-shaver group reported the largest reduction in disc height, with 13.15±1.63% (9.13±1.13mm), compared to 6.57±1.23% and 0.69±0.13% from the forceps and laser groups, respectively. The automated-shaver and forceps removed similar volumes of disc material (2.51±1.10% and 2.76±1.39%, respectively), whilst the laser removed a considerably smaller volume (0.12± 0.07%). The automated shaver group had the smallest reduction in stiffness post-nucleotomy (8.74±0.86%) while the forceps and laser groups had drops of 22.31±5.53% and 15.93±4.49%, respectively. The automated-shaver removed the largest dry-nucleus mass, 0.25±0.07g compared to the 0.23±0.01g removed by the forceps, meanwhile, the laser removed 0.23±0.04g of wet-nucleus mass (dry-mass could not be calculated for this technique).

Discussion

The automated-shaver created more homogeneous cavities compared to forceps. Conversely, laser ablation formed localized cavities (Fig.1). The small volume of material removed, suggests that the laser-parameters used in this study are not suitable to ablate the large volumes that are required for nucleus-replacements without causing severe thermal damage. Optimising parameters such as power and frequency may however render the technique suitable. The damage to the annulus could not be fully quantified using the MRIs therefore, the change in disc stiffness was used as a marker to assess this effect4,5. The automated-shaver removed similar masses of nucleus as the forceps, with the advantage of a smaller annulus incision and change in stiffness, suggesting that it may be the most appropriate technique to achieve nucleotomy for nucleus replacement surgery.

 

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  1. 1.Coric et al., Neurosurgery Spine-8, 115–120 (2008).
  2. 2.Dang et al., Musculoskeletal Disorder-8, 1–4 (2007).
  3. 3.Pfirrmann et al.,Spine-26, 1873–1878 (2001).
  4. 4.Iatridis et al.,Biomechanics-38, 557–565 (2005).
  5. 5.Bezci et al., Biomechanical Engineering-137, 1–8 (2015).
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