3D™ Technology Provides Unparalleled Strength of Fixation

 

PANTERA^® STRUCTURAL STUDY

Description of PANTERA^®

The PANTERA^® Proximal Humerus Fracture Fixation Plate System assembly consists of shoulder plates, posts with cross elements, cross elements, locking and non-locking cortical screws, post cap screws, suture clips, and surgical instrumentation. 

 

The shoulder plates are made of titanium and are contoured to provide a close fit with the anatomy of the proximal humerus.  The titanium cortical locking and non-locking screws are used to affix the plate to the humerus.  The titanium posts are used to affix the proximal end of the plate to the proximal end of the humerus.  The posts allow for cross elements to be inserted perpendicular to the longitudinal post axis such that additional support to the humeral head may be provided.  The head of the post accepts an expansion cap screw to lock the post to the plate. 

 

 

 

Strength Study of Cross-Element Design Feature

The PANTERA^® cross-element design effectively creates an internal scaffold within the proximal head.  This minimizes loss of reduction and increases the overall strength properties of the fracture fixation system.  To emphasize the effects of the cross-element design, a series of push/pull strength tests were performed on the posts using a variety of cross-element configurations. 

The cross-element Push-Out and Pull-Out tests were performed using the MTS 858 Mini BIONIX II biomedical testing system and Grade 5 solid polyurethane foam purchased from SAWBONES.  The foam test blocks simulated osteoporotic bone commonly found in the humerus.  Three types of configurations were tested:  1) Post only  2) Post with Qty 1 cross-element installed and  3) Post with Qty 2 cross-elements installed.  Three specimens of each configuration were tested and sample data is presented below.  The average maximum push-out or pull-out force is labeled on the trend line for each configuration.

With only one cross-element installed, a 30% minimum strength increase was apparent for both load directions.  Two cross-elements resulted in a push/pull strength improvement of nearly 100% compared to the post alone.  The force curves above also demonstrate that the use of cross-elements promotes a more passive failure mode after the maximum pull-out or push-out force is achieved. 

Structural Fatigue Study of PANTERA^® Plate vs. A Leading Competitor Plate

Dynamic testing was performed to compare the strength and fatigue life of the PANTERA^® plate vs. a competitor plate.  The test setup for each plate was similar to the photographs shown below, except that the moment arm was slightly different due to the different lengths of the plates used.  A 7-mm thickness was removed from the 4th Generation SAWBONE humerus slightly below the articular surface and a 3-mm gap was cut into the humerus above the third fixation screw.  Incremental fatigue loads were applied at a 90° angle to the diaphysis, starting at 178N (40lb) for 100,000 cycles and increasing in 89N (20lb) increments every 100,000 cycles until failure.

Test Setup Photo 1  Test Setup Photo 2

The results in the chart above demonstrate that the PANTERA^® plate outperformed a leading competitor plate both in strength and overall fatigue life during this dynamic load study.  The PANTERA^® plate reached a maximum load 67% higher than the competitor plate while enduring more than double the fatigue life cycles before "failure."  Whereas the leading competitor plate cracked on both sides near the screw closest to the gap, the PANTERA^® fatigue specimen was stopped because the screw pulled from the humerus (i.e. no plate breakage).

Static Stiffness Testing

Fundamental static compression tests were also performed to compare the stiffness of the PANTERA^® plate to a leading competitor plate.  The test specimens and test setups were very similar to the fatigue tests described above, except that the loading axis was varied between 0°, 45° and 90° relative to the diaphysis.

The methodology was limited to non-destructive testing.  Therefore, only a minimal force was applied to the bones such that the measured displacements were less than 1-mm and the plates would not yield.  The results displayed in the chart on the right side of the page show that the competitor plate had a much higher stiffness in the 0° load orientation and the PANTERA^® plate stiffness measured slightly higher in the 45° and 90° load directions. 

 

Conclusions

Optimal plate design for bone fractures must consider the stiffness of the bone in an effort to best approximate the native bone, and at the same time provide the necessary rigidity to allow the fracture to heal.  Excessively rigid fracture plates may impair proper bone healing through stress shielding or simply by pull-out or push-through failures.  The PANTERA^® design better matches the stiffness of the native bone with its uniformity in all directions.  In addition, the superior PANTERA^® system is ideally suited to resist cyclical loads and pull-out/push-through failure modes as documented through independent testing.