DynaTranTM

Biomechanical Review

Dynamic Anterior Cervical Plating System

2

Introduction

Table of Contents

The DynaTran™ Anterior Cervical Plating system offers stability to the cervical spine during fusion.

The DynaTran™ plate is a dynamic translational plate, designed to allow axial settling so as to maintain load sharing on the graft. The DynaTran™ system consists of internally-dynamized plates, which means the screws can remain fixed in the vertebral bodies while the plate can translate. This is in contrast to the “slotted” dynamic plates which allow the screws to move within the plate, potentially causing the plate to impinge on the adjacent disc.

The system is used with the Reflex® Hybrid bone screws that include both fixed angle bone screws for a rigid construct and variable angle bone screws for a semi-constrained construct.

The DynaTran™ ACP System was shown to be mechanically sound in a series of biomechanical tests designed to challenge the structural integrity of the system. The DynaTran™ ACP system was compared to the Synthes CSLP system; all systems were tested in accordance with the applicable ASTM standards.

In addition to the standard anterior cervical plating ASTM tests of compressive bending, torsion, and screw back-out, tests specific to dynamic plating included a) torsional testing in both the open and closed positions and b) hyperextension studies to assess the performance of the modular plate in a whiplash situation.

The following tests are included in this report:

Implant Fatigue Compressive Bending Strength 3

Implant Static Compressive Bending Strength 4

Implant Static Open and Closed Torsion Strength 5

Locking Ring Performance 6

Implant Subassembly Strength 7

Bone Screw Pullout Strength 8

Implant Hyperextension Testing 9

3

Implant Fatigue Compressive Bending Strength

1. Methods:

The implant fatigue compressive bending strength was determined using a corpectomy model in accordance with the ASTM F1717-01 standard (set-up shown in Figure 1). The fatigue strength is measured as the maximum load that can be cyclically applied to an implant assembly for 5 million cycles without failure (5 million cycles represents approximately 2 years of human activity as denoted by ASTM F1717-01).

2. Results* (Figure 2):

• All values were normalized to the worst-case construct (CSLP, Synthes), denoted by 100%.

• The DynaTran™ ACP is 14% stronger in fatigue compressive bending than the CSLP.

3. Conclusion:

The fatigue run-out loads for the DynaTran™ ACP system were greater than the run-out loads for the comparable CSLP system.

Figure 1. DynaTran™ system fatigue testing set-up

Figure 2.Fatigue compressive bending run-out loads in a corpectomy model

100%

114%

50%

100%

150%

CSLP DynaTranTM

Ru

n-O

ut L

oad

*Data on file at Stryker Spine.

4

Implant Static Compressive Bending Strength

1. Methods:

The implant static compressive bending strength was determined using a corpectomy model in accordance with the ASTM F1717-01 standard (set-up shown in Figure 1). The static strength is measured as the maximum load that can be applied to an implant assembly before failure.

2. Results* (Figure 3):

• All values were normalized to the worst-case construct (CSLP, Synthes), denoted by 100%.

• The DynaTran™ ACP is 196% stronger in static compressive bending than the CSLP.

3. Conclusion:

The static yield load for the DynaTran™ ACP system was greater than the yield load for the comparable CSLP system.

Figure 3.Static compressive bending run-out loads in a corpectomy model

100%

296%

0%

50%

100%

150%

200%

250%

300%

350%

Yie

ld L

oad

CSLP DynaTranTM

*Data on file at Stryker Spine.

5

Implant Static Open and ClosedTorsion Strength

1. Methods:

The implant static torsion strength was determined using a corpectomy model in accordance with the ASTM F1717-01 standard (set-up shown in Figure 1). The torsion strength of an implant construct is measured as the maximum amount of torsional load an implant assembly can withstand before failure or yielding occurs. Testing was performed with the plate both in the closed position and the fully open position.

2. Results* (Figure 4):

• Values are normalized to the worst case construct (CSLP, Synthes), denoted by 100%.

• The DynaTran™ ACP is 55% stronger in closed torsion and 74% stronger in open torsion than CSLP.

3. Conclusion:

The static torsion peak loads for the DynaTran™ system constructs were greater than the CSLP system construct.

Figure 4.Static torsion loads in a corpectomy model

174%

100%

155%

0%

50%

100%

150%

200%

CSLP DynaTranTM Closed DynaTranTM Open

Pea

k To

rqu

e (N

m)

*Data on file at Stryker Spine.

6

Locking Ring Performance

1. Methods:

Static push-through testing was used to assess the assembly strength of the locking mechanism. The push-through strength is measured as the load needed to force the screw to disengage from the plate (set-up shown in Figure 5.) Bone screws were assembled and locked into each plate. The plate was then assembled into a testing fixture and a compressive load was applied along the longitudinal axis of each bone screw.

2. Results* (Figure 6):

• The DynaTran™ System utilizes the Reflex® Hybrid bone screws. These screws are locked into place by means of a locking ring. The CSLP screws are locked by means of expansion screws. Both systems use peripheral locking of the bone screw head to prevent screw back-out.

• Values are normalized to the worst case construct, denoted by 100%.

• The DynaTran™ system is 613% stronger in push-through strength than the CSLP.

3. Conclusion:

The DynaTran™ System provided higher resistance to screw back-out than the CSLP system.

Figure 5.DynaTran™ push-through testing set-up

Figure 6.Static push-through strength

100%

713%

0%

100%

200%

300%

400%

500%

600%

700%

800%

CSLP (fixed screws) DynaTranTM (fixed screws)

Loa

d (

N)

*Data on file at Stryker Spine.

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Implant Subassembly Strength

1. Methods:

The implant subassembly strength was measured by performing cantilever-bending tests (set-up shown in Figure 7). The strength is measured as the load an implant subassembly can endure before slippage or failure occurs. Implants were tested according to ASTM F1798-97.

2. Results* (Figure 8):

• All values are normalized to the worst-case construct denoted by 100%.

• Mode of failure for both systems was loss of connection at the screw/plate interface.

• The DynaTran™ system is 38% stronger in cantilever bending than the CSLP.

3. Conclusion:

The DynaTran™ System provided higher resistance to cantilever bending than the CSLP system.

Figure 7.DynaTran™ subassembly testing set-up

Figure 8. Cantilever bending strength

138%

100%

0%

50%

100%

150%

200%

CSLP DynaTranTM

New

ton

s (N

)

*Data on file at Stryker Spine.

8

Bone Screw Pullout Strength

1. Methods:

Pullout Strength was measured by inserting the screws into ø2.5mm holes drilled into ASTM 1839-01 polyurethane grade 10 foam blocks (set-up shown in Figure 8). The strength is measured as the amount of axial load the screw can endure until failure or removal occurs.

2. Results* (Figure 10):

• All values are normalized to the worst-case construct.

• The Reflex® Hybrid Screw is 89% stronger than the CSLP Screw.

3. Conclusion:

The screw pullout loads for the Reflex® Hybrid screws utilized in the DynaTran™ System were higher than the CSLP System.

Figure 9.DynaTran™ screw pullout test set-up

Figure 10.Screw pullout strength

189%

100%

0%

50%

100%

150%

200%

250%

CSLP Reflex Hybrid

*Data on file at Stryker Spine.

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Implant Hyperextension Testing

1. Methods:

Testing the plate performance through hyperextension simulates the performance of the plate under a whiplash scenario. Hyperextension of the plate can be simulated through subjection of the plate test block construct to a compressive load similar to the loading used in ASTM compression testing (see pages 3 and 4). Loading in this manner pivots the plate along an arc centered at the back of the test blocks (where the load is applied) and creates tension on the plate, causing the plate to enter hyperextension.

2. Results* (Figure 11):

The DynaTran™ ACP remained intact during hyperextension testing through a 30° intervertebral angle without plate disassembly.

3. Conclusion:

Through this testing, the DynaTran™ system has shown to be sufficiently robust to prevent disassembly of the plate in vivo through high trauma angulation.

Figure 11:Trauma zones for the varying intervertebral angles overlayed on the

hyperextension results graph.

The curve demonstrates the plate behavior as angulation increases. DynaTran™ withstood the angulation well into the trauma zone. When the load reaches DynaTran™’s compressive yield, the plate began to deform but remained intact through test completion.

Safe Zone: Angulation fits within the physiologic range for the majority of cervical spinal levels.

Possible Trauma Zone: Intervertebral Angulation has entered the trauma range for all vertebral levels exceptfor C0-C1 and C1-C2.

Trauma Zone: Intervertebral Angulation has entered the trauma range and has passed the physiologic range for all vertebral levels except for C0-C1. This may result in injury ranging from soft tissue and ligamentous injury to vertebral body fracture depending on level and angulation.

Whiplash Injuries: Current Concepts in Prevention, Diagnosis, and Treatment of the Cervical Whiplash Syndrome. Edited by R. Gunzburg and M. Szpalski. Lippincott-Raven Publishers, Philadelphia, 1998. p. 83.

0 10

Com

pre

ssiv

e L

oad

(N

)

Angulation (degrees)15 20 25 30

SAFEZONE

POS.TRAUMA TRAUMA ZONE

Dynamic Anterior Cervical PlateHyperextension - 30°

DynaTran™ ACP Static Compressive Yield Load

Compressive load is applied to the test construct to begin plate construct deflection. This increasing load creates angulation within the construct.

Test completed at 30° angulation. Plate bent with anatomy, but remains intact.

Plate begins to deform with anatomy – but remains intact.

*Data on file at Stryker Spine.

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References

EA Reflex Translational ACP System-280508

Stryker Spine Internal Testing Report #RLAB-070907

Stryker Spine Internal Testing Report #RLAB-090104

Stryker Spine Internal Testing Report #RLAB-031007 Rev B

Stryker Spine Internal Testing Report #RLAB-080604

Stryker Spine Internal Testing Report #RLAB-031201

Stryker Spine Internal Testing Report #RLAB-001009

Stryker Spine Internal Testing Report #RLAB-080602-U

Stryker Spine Internal Testing Report #RLAB-030917

Final SummaryThe test results show that the mechanical strength of the DynaTran™ ACP System was equal to or superior to the Synthes CSLP system when tested under the same conditions for: · Implant Fatigue Compressive Bending Strength· Implant Static Compressive Bending Strength· Implant Static Open and Closed Torsion Strength· Locking Ring Performance· Implant Subassembly Strength· Bone Screw Pullout

Further, DynaTran™ has been shown to be sufficiently robust to prevent disassembly of the plate in vivo through high trauma angulation.

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A surgeon must always rely on his or her own professional clinical judgment when deciding whether to use a particular product when treating a particular patient. Stryker does not dispense medical advice and recommends that surgeons be trained in the use of any particular product before using it in surgery.

The information presented is intended to demonstrate the breadth of Stryker product offerings. A surgeon must always refer to the package insert, product label and/or instructions for use before using any Stryker product. Products may not be available in all markets because product availability is subject to the regulatory and/or medical practices in individual markets. Please contact your Stryker representative if you have questions about the availability of Stryker products in your area.

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