gear shift technique for pedicle screw insertion

1. DR.J.V.MODI
PROFFESOR,BJMC,
DEPT OF ORTHOPAEDICS

2. INTRODUCTION
Accepted techniques for pedicle screw insertion
•Free hand technique
•Funnel technioque
•In Out In technique
•Minimally Invasive Technique
•Gear Shift Technique-lesser chances of medial wall perforation.

3. Lumbar vertebra Anatomy
Body
Pedicles
Transeverse processs(l3 has
longest)
Lamina
Articular process
Spinous process
Maxillary process

5. Define entry point
Opening of the cortex
Probe insertion
Tapping
Screw insertion

6. Entry point
The entry point of the pedicle screw is
defined as the confluence of any of the four
lines:
Pars interarticularis
Mamillary process
Lateral border of the superior articular
facet
Mid transverse process.

7. Opening of Cortex
Open the superficial cortex of the
entry point with a burr or a
rongeur or a nibbler.

8. Creating the Pedicle Tract
A entry owl is used to navigate down the isthmus of the pedicle into the
vertebral body. The appropriate trajectory of the pedicle probe is
required in both cranial caudal direction and mediolateral direction.

9. Cranio Caudal Angulation
The appropriate trajectory of the pedicle probe
in the cranial caudal direction occurs by aiming
for the contralateral transverse process
thereby aiming to be parallel to the
superior endplate.

10. Medio Lateral Inclination
L1 has 5 degree medial convergence in most
cases
There is 5 degrees of additional convergence
below L1
Thus L2 has 10 degrees, L3 has 15 degrees and
so on

11. we advance it 20 mm with the tip
pointing laterally as a safety
measure to prevent medial pedicle
wall breach.
At this point the tip would have
traversed the pedicle
It is then removed, rotated 180
degrees so that the tip points
medially and advanced into the
body

12. Probing
A ball tip probe is used to palpate 5 surfaces (medial, lateral, superior,
inferior and floor) to check their integrity.

13. We then either undertap by 1mm
or don’t tap at all to optimise
screw purchase
Pedicle path is again palpated with
the ball tip probe and length of
the tract is marked with a clamp
Tapping

14. Screw
Insertion
Pedicle screw is inserted which crosses the
pedicle and 80% of the vertebral body

15. How to increase pullout strength
of pedicle screw
Length – 2/3 of the body
Larger diameter screw
Larger pitch of screw
Use of interconnecting/ cross fixation rods

16. Patient Profile
25 yr male
H/o fall in well
Presented with traumatic l1 wedging with
paraplegia with bladder bowel involvement with
out bedsores

17. Pre operative

18. Post Operative X rays

19. Thank you