DR.J.V.MODI PROFFESOR,BJMC,

DEPT OF ORTHOPAEDICS

GEAR SHIFT TECHNIQUE FOR PEDICLE SCREW FIXATION

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.

Lumbar vertebra Anatomy

Body

Pedicles

Transeverse processs(l3 has longest)

Lamina

Articular process

Spinous process

Maxillary process

Exposure of Surgical Site Landmarks

To minimise error in finding the pedicle and to have good purchase

Includes exposure of:

1. Facet joint

2. Transverse process

3. Lateral portion of pars interarticularis

Insertion Technique StepsDefine entry pointOpening of the cortexProbe insertionTappingScrew insertion

Entry pointThe entry point of the pedicle screw is defined as the confluence of any of the four lines:

Pars interarticularisMamillary processLateral border of the superior articular facetMid transverse process.

Opening of Cortex

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

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.

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.

Medio Lateral Inclination

L1 has 5 degree medial convergence in most casesThere is 5 degrees of additional convergence below L1Thus L2 has 10 degrees, L3 has 15 degrees and so on

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

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

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

Tapping

ScrewInsertion

Pedicle screw is inserted which crosses the pedicle and 80% of the vertebral body

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

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

Pre operative

Post Operative X rays

Thank you