Stripping resistances of conical and cylindrical pedicle screws

Entry

Transpedicular instrumentation

widely preferred for vertebral fusion

It is a surgical technique.

of pedicle screws in instrumentation

mechanical performance of the bone-screw surface

biomechanical properties and physical properties of the screw

associated with its structure. screw the bone

quality of clutch bone mineral

density, surgical technique and screw

screw depending on fit

length, diameter, thread height and screw

It also depends on the design of the shaft.

1,2

Common in pedicle screw applications

detection of complications

loss, improper placement, metal

fatigue, dural tears, CSF leaks,

nerve root injuries and

are infections.

3-8 Most common implant

insufficiency is the bending of the pedicle screw.

and breaks.

9 Bending and breaking of the screw

minor diameter, length, stroke depth,

orientation and transverse connection

associated with its use.

5,10,11 Pedicle

Twisting and breaking of the screw is often the screw–

slightly distal to the shaft junction,

in the pedicle (interpedicular)

takes place in the part.

9,12,13

Two basic designs in pedicle screws

shape is available. Conical screws, screw head

reduced in diameter up to the tip; cylindrical screws

the diameter of the screw is constant from the head to the end.

defined as the remaining screws. Conical

screws, bending and breaking resistance

better to increase and pedicle the screw

to ensure adherence

they were produced.

6,14,15 Biomechanics

pedicle screw fixation force in studies.

Stripping resistance of the test that evaluates best

test and bone mineral density,

cortical fixation, pedicle morphology, screw

such as its orientation and screw removal region.

stripping resistance of many variables

has been reported to be affected.

16 Stripping

biomechanics in which resistance is analyzed

cylindrical screws in most of the studies

used.

1,5,17,18 Analysis of conical screws

In fewer studies in which conical

stripping resistance of screws, input torque and

are superior in resistance values

expressed.

In transpedicular instrumentation

a concern against the use of tapered screws

has. The first to be used in clinical applications

the small screw is in the screw-rod connection

difficulties experienced, mono-multiaxial screw

need to be changed, the first screw

ensure that adequate entry screw tightness is

same entry for reasons such as not being able to obtain

More than one screw sending from the hole

may have to do. Conical

After the first insertion of the screws

detection when partially retracted

that they may lose their strength

is considered.

6.15 With what intensity

decrease will occur and that

It is clear whether it means

has not been revealed.

In this study, it is commonly

used titanium conical and cylindrical

pedicle screws in calf vertebra model

subjected to a series of axial stripping tests

evaluated from a biomechanical point of view. stripping

resistance, stiffness and input torque values.

between conical and cylindrical screws

comparison from the same point

repeated screw throw and screw retraction

fixing forces of screws

assessment of the effects on

was intended.

Method

To be applied to transpedicular screws

skeleton for biomechanical tests

completed its maturation, 400-600 kg

weighing 24-32 weeks in a slaughterhouse

fresh lumbar cut from 8 veal

vertebrae were used. vertebrae

by cutting through their intervertebral joints and

stripped of all soft tissues

turned into vertebrae and pedicle screw

frozen at (-) 16 ºC before

was stored. 30 calves in total for testing

vertebra was prepared. prepared

screw placement under the vertebrae

due to cortical injury during

was excluded from work. Total of 24 vertebrae

Both of the L1, L2, L3 and L4 vertebrae

screw into his pedicle (48 pedicles in total)

biomechanical tests by placing

Done. No vertebra after test

was not excluded.

Pedicle screw selection

Two test screws used in the study

different company (Tasarimmed Medical Mamuller

Singing. Trade Ltd. Sti. Istanbul Turkey; Medicon

Ltd. St. Ankara, Turkey) produced by

conical and cylindrical pedicle screws. Conical

screw due to the diameter variability of the screws

The dimensions were measured with a digital calimeter.

Diameters of tapered screws from screw head to end

from 7.0 mm to 4.5 mm with 35.7% thinning

It was going down to mm. Groove heights each

2.8 mm for screw, thread depth 1 mm, thread

The contours were proprietary and the same for each screw.

Clinically comparable test results

In order to obtain screw size determination;

isthmus of pedicles of calf vertebrae

average major transverse

the diameter is 8.1 mm (range; 7.8-8.6 mm)

detected. isthmus level lamina

1.2-1.6 cm from the entry point of the screw

was located distal to it. This is detected

7 mm diameter, 45 mm due to values

test length screws (7/45 mm)

selected as screws.

Pedicle screw placement procedure

Only one surgeon per vertebra

by one pedicle conical, the other pedicle

cylindrical screw was placed (Figure 1A).

Adjacent before preparation of the pilot-hall

a small portion of the facet, the screw head to the facet

ronger to prevent it from resting

was excised using Screw entry point

Weinstein et al.

defined by 4

determined by the parameters. cortex;

transverse process, superior facetin inferior

margin and at the junction of the pars interarticularis

Drilled using awl. Pediculated intervention

cranio-caudal and medio-lateral angulations

with direct observation

was carried out. Each pedicle is 4.5 mm

width and 40mm depth

was drilled. Awl and drill diameters of screws

was smaller than the minor diameter. Test

Since the screws are self-taping

no topping was done.