Maximizing Anterior Vertebral Maximizing Anterior Vertebral Screw - - PowerPoint PPT Presentation

▶
maximizing anterior vertebral maximizing anterior
SMART_READER_LITE
LIVE PREVIEW

Maximizing Anterior Vertebral Maximizing Anterior Vertebral Screw - - PowerPoint PPT Presentation

Jan 25, 2023 361 likes •549 views

Maximizing Anterior Vertebral Maximizing Anterior Vertebral Screw Fixation for Spinal Screw Fixation for Spinal Growth Tethering Growth Tethering 1 Eric S. Varley, DO 1 Eric S. Varley, DO 2 Christine L. Farnsworth, MS 2 Christine L.

slide-1
SLIDE 1

Maximizing Anterior Vertebral Maximizing Anterior Vertebral Screw Fixation for Spinal Screw Fixation for Spinal Growth Tethering Growth Tethering

Eric S. Varley, DO Eric S. Varley, DO1

1

Christine L. Farnsworth, MS Christine L. Farnsworth, MS2

2

Tucker Tomlinson, MS Tucker Tomlinson, MS2

2

Claire Robertson, BS Claire Robertson, BS2

2

Thomas N. Nunn, BS Thomas N. Nunn, BS2

2

Salil V. Upasani, MD Salil V. Upasani, MD1

1

Peter O. Newton, MD Peter O. Newton, MD1,2

1,2

1University of California, San Diego, CA 2Rady Children’s Hospital, San Diego, CA

slide-2
SLIDE 2

Potential Fusionless Scoliosis Potential Fusionless Scoliosis Correction Correction

  • Proposed Etiology

Proposed Etiology Theory: Anterior spinal Theory: Anterior spinal

  • vergrowth
  • vergrowth1

1

  • Propagated by: Heuter

Propagated by: Heuter-

  • Volkmann effect

Volkmann effect2

2

  • Spinal buckling

Spinal buckling

  • Fusionless treatments

Fusionless treatments

– – Tension posterior spine Tension posterior spine – – Compress anterior spine Compress anterior spine

Anterior Spinal Tethering Anterior Spinal Tethering

slide-3
SLIDE 3

Anterior Spinal Growth Tethering Anterior Spinal Growth Tethering

  • Applies a compressive

Applies a compressive force to the physes on force to the physes on convexity of the curve convexity of the curve

  • Shown to create

Shown to create deformity in animal deformity in animal models models3,4

3,4

slide-4
SLIDE 4

Pilot Study Pilot Study -

  • Anterolateral Flexible Tether

Anterolateral Flexible Tether4

4

  • 6 animals tethered over four levels

6 animals tethered over four levels

  • Scoliosis creation:

Scoliosis creation: 12.4 12.4± ±8.3 8.3° ° at 6 month (n=12) at 6 month (n=12) 26.8 26.8± ±14.4 14.4° ° at 12 month (n=6) at 12 month (n=6)

  • Vertebral wedging:

Vertebral wedging: 4.4 4.4± ±1.3mm at 6 months* 1.3mm at 6 months* 8.5 8.5± ±3.9mm at 12 months* 3.9mm at 12 months*

  • Conclusion: Tethering Alters Vertebral Growth

Conclusion: Tethering Alters Vertebral Growth

PA Lat PA Lat

Spinal Growth

slide-5
SLIDE 5

Fixation Problems Fixation Problems

Previous Bovine Growth Study: 1 Previous Bovine Growth Study: 1st

st Generation Implant

Generation Implant Screws levered & plowed through the bone Screws levered & plowed through the bone

slide-6
SLIDE 6

Effect of Intra Effect of Intra-

  • Op Deformity

Op Deformity Correction on Screw Fixation? Correction on Screw Fixation?

1.

  • 1. Immediate deformity correction

Immediate deformity correction Intra Intra-

  • Operative Tether Tensioning

Operative Tether Tensioning 2.

  • 2. Improve Screw Fixation

Improve Screw Fixation5

5

Hydroxyapatite Coating Hydroxyapatite Coating

slide-7
SLIDE 7

Purpose Purpose

To evaluate the effect of hydroxyapatite To evaluate the effect of hydroxyapatite (HA) coating of the vertebral body (HA) coating of the vertebral body screws and intra screws and intra-

  • operative tensioning of
  • perative tensioning of

the tether on screw integration as the tether on screw integration as measured by the screw extraction measured by the screw extraction torque. torque.

Clinical Application Experimental Application

slide-8
SLIDE 8

Study Design Study Design

Yucatan mini-pigs (n=8) Tensioned Tether (n=4) Un-tensioned tether (n=4)

Implant screws: (+) HA Coating (n=2) (n=8 screws) Implant screws: (-) HA Coating (n=2) (n=8 screws) Implant screws: (+) HA Coating (n=2) (n=8 screws) Implant screws: (-) HA Coating (n=2) (n=8 screws)

Instrumented 4 Levels

slide-9
SLIDE 9

Methods Methods

  • T8

T8-

  • T11

T11 – – UHMWPE Tether/Screw Construct UHMWPE Tether/Screw Construct

– – Non Non-

  • Tensioned group

Tensioned group (n=4): Slack taken out (n=4): Slack taken out – – Tensioned group Tensioned group (n=4): Intra (n=4): Intra-

  • op tensioning (250N)
  • p tensioning (250N)
  • Animals grow for 12 months

Animals grow for 12 months

– – Monthly Biplanar X Monthly Biplanar X-

  • rays

rays – – Post Harvest 12 month 3T MRI Post Harvest 12 month 3T MRI

  • Following Harvest: Uncoated screws placed

Following Harvest: Uncoated screws placed

T7 & T8 T7 & T8 T12 &T13 T12 &T13 Time Zero (T0) Time Zero (T0)

Controls Controls

slide-10
SLIDE 10

Screw Extraction Analysis Screw Extraction Analysis

  • Focus on the bone

Focus on the bone-

  • screw interface

screw interface6

6

  • Screws rotated with

Screws rotated with custom jig custom jig

  • No Axial load

No Axial load

  • Data processed for

Data processed for 1. 1.Yield Torque Yield Torque 2. 2.Yield Angle Yield Angle

slide-11
SLIDE 11

Biomechanical Data Collection Biomechanical Data Collection

S t i f f n e s s Yield Torque Yield Angle

Degrees of Rotation (°) Force x moment (N-mm)

slide-12
SLIDE 12

Statistical Analysis Statistical Analysis

4 experimental groups 4 experimental groups:

1. 1. Tensioned & HA Coating Tensioned & HA Coating 2. 2. Tensioned & No Coating Tensioned & No Coating 3. 3. Un Un-

  • tensioned & HA Coating

tensioned & HA Coating 4. 4. Un Un-

  • tensioned & No Coating

tensioned & No Coating

TWO TWO-

  • WAY ANOVA

WAY ANOVA Effects of HA & Tensioning Effects of HA & Tensioning (1) Coating the screws (1) Coating the screws (2) tensioning the tether (2) tensioning the tether (3) Interaction (3) Interaction ONE ONE-

  • WAY ANOVA

WAY ANOVA Changes with time Changes with time

  • Each Group vs. Controls

Each Group vs. Controls

slide-13
SLIDE 13

Deformity Creation Deformity Creation

  • Tensioned Group: Greater initial deformity

Tensioned Group: Greater initial deformity

  • Equal total growth modulation to non

Equal total growth modulation to non-

  • tensioned group

tensioned group

  • 5

5 10 15 20 25 30 35 Pre-

  • p

Post-

  • p

1 2 3 4 5 6 7 8 9 10 11 12

Months Post-op Created Coronal Deformity (degrees)

Tensioned Non-Tensioned

* * * * * * *

Disc

Vertebral body + Disc

slide-14
SLIDE 14

Post-harvest MR Analysis (3T)

Non-Tensioned

  • Nucleus Pulposus migrated

toward tether in both surgical groups

tensioned >> non-tensioned (p=0.02)

12 months post-op, all discs “healthy” except one tensioned and one non-tensioned motion segment with no T2 bright signal: 2/36 = 6% of all discs

12-mo post-op T2 12-mo post-op T2

Tensioned

slide-15
SLIDE 15

Yield Angle Comparison Yield Angle Comparison

1-WAY ANOVA (p<0.05)

  • Tensioned, Coated Group

2-WAY ANOVA (p<0.05)

  • Tensioning the screw
  • Coating the screw
slide-16
SLIDE 16

Yield Torque Comparison Yield Torque Comparison

  • No screws had Torque < 500 Nmm

No screws had Torque < 500 Nmm

1-WAY ANOVA (p<0.05)

  • Tensioned, Coated Group
  • Tensioned, Uncoated Group

2-WAY ANOVA (p<0.001)

  • Tensioning the screw
slide-17
SLIDE 17

Conclusions Conclusions

Deformity Creation Deformity Creation

1. 1. Greater initial deformity, Same ultimate deformity Greater initial deformity, Same ultimate deformity 2. 2. NP Migration: Tension>>Non NP Migration: Tension>>Non-

  • tensioned

tensioned 3. 3. Disc Health: No difference Disc Health: No difference

Screw out testing: bone Screw out testing: bone-

  • implant interface integrity

implant interface integrity

1. 1. Contrary to initial concerns Contrary to initial concerns Tensioning appears to Tensioning appears to INCREASE INCREASE fixation fixation

– – More vigorous response to the greater biomechanical forces trans More vigorous response to the greater biomechanical forces transmitted mitted to the bone to the bone-

  • screw interface

screw interface

2. 2. HA coating may moderately enhance osseous integration HA coating may moderately enhance osseous integration

– – Osteoconductive properties Osteoconductive properties

slide-18
SLIDE 18

References References

1. Somerville EW. Rotational lordosis: the development of the single curve. J Bone Joint Surg (Br) 1952 2. Stokes IA et al., Biomechanical spinal growth modulation and progressive adolescent scoliosis-a test of the ‘vicious cycle’ pathogenetic hypothesis: summary of an electronic focus group debate of the IBSE, Scoliosis 2006 3. Newton PO et al., Spinal growth modulation with use of a tether in an immature porcine model, JBJS 2008 4. Newton PO et al., Multilevel Spinal Growth Modulation with an Anterolateral Flexible Tether in an Immature Bovine Model, Spine 2005 5. Upasani VV et al., Pedicle screw surface coatings improve fixation in nonfusion spinal constructs, Spine 2009 6. Sandén B et al., Improved extraction torque of hydroxyapatite- coated pedicle screws, Eur Spine J 2000