Bone Plate with Variable Torsional Stiffness at Fixed Angle Holes

Abstract

A bone plate includes at least one torsional modification feature (TMF). Each TMF is structured to decrease the torsional rigidity of the plate relative to longitudinally opposite portions, but may be modified to increase the torsional rigidity thereat. Each TMF is defined by beams contiguous with the lateral sides of the plate, and an opening extending laterally therebetween. In a preferred embodiment, opposed projections extend into the opening to define threaded discontinuous wall portions for receiving an insert, such as a set screw. In one embodiment, bioabsorbable and/or bioactive inserts may be used to temporarily increase the torsional rigidity of the plate during initial fixation and thereafter have reduced torsional rigidity to mimic normal callus. The plate is preferably used with fixed angle fasteners that may be subject to high torsional loads post-operatively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a first embodiment of a bone plate according to the invention.

FIG. 2 is an enlarged top view of an end of the bone plate of FIG. 1.

FIG. 3 is a section view along the longitudinal axis of the bone plate of FIG. 1.

FIG. 4 is an exploded assembly view of bone plate with a set screw insert for increasing the torsional rigidity of the bone plate, according to the invention.

FIG. 5A is a top perspective view of a modular combination of a bone plate according to the invention in combination with a metaphyseal plate.

FIG. 5B is an exploded top perspective view of the assembly of the modular combination of FIG. 5A.

FIG. 6A is a bottom perspective view of the modular combination of FIG. 5A.

FIG. 6B is an exploded bottom perspective view of the assembly of the modular combination of FIG. 5A.

Claims

1. A bone plate for use with a least one cortical bone screw, comprising: an elongate bone plate having a longitudinal center, opposite first and second ends, and opposing lateral sides, said plate including a screw hole located between said center and said first end, anda torsional modification feature (TMF) located between said center and said screw hole, said TMF decreasing the torsional rigidity of the plate relative to two portions of the plate adjacent said TMF on longitudinally opposite sides of the TMF, said TMF comprising beams contiguous with said two portions and lateral sides of said plate and an opening therebetween; andmeans for coupling a cortical bone screw to said plate in a fixed axial orientation.

2. A bone plate according to claim 1, wherein: said TMF includes longitudinal slots extending along said beams.

3. A bone plate according to claim 1, wherein: said TMF includes a first projection including a first thread portion and an opposing second projection including a second thread portion extending into the opening, said first and second thread portions forming discontinuous wall portions of a full thread.

4. A bone plate according to claim 3, wherein: said first and second projections are opposing cantilevered beams.

5. A bone plate according to claim 3, wherein: said first and second projections are provided with an upper recess.

6. A bone plate according to claim 3, wherein: said first and second thread portions are approximately centered on the longitudinal axis of said plate.

7. A bone plate according to claim 1, further comprising: an insert positionable in said TMF to bridge said two portions of said plate on longitudinally opposite sides of said TMF to increase a torsional rigidity of said plate at said TMF.

8. A bone plate according to claim 7, wherein: said insert is a set screw.

9. A bone plate according to claim 7, wherein: said insert is bioabsorbable.

10. A bone plate according to claim 9, wherein: said insert includes a bioactive substance.

11. A bone plate according to claim 1, wherein: said bone plate does not include a substantial widthwise change in lateral dimension relative to said two portions.

12. A bone plate system for use with at least one cortical bone screw, comprising: an elongate bone plate having a longitudinal center and first and second ends, said plate including at least one cortical screw hole located between said center and a first end for receiving the at least one cortical bone screw for extension of the screw into bone, anda torsional modification feature (TMF) located between said center and said screw hole, said TMF decreasing the torsional rigidity of said plate relative to two portions of the plate adjacent to said TMF on longitudinally opposite sides of said TMF and providing said plate with a torsional rigidity at said TMF that is less than said at least one cortical screw hole; andan insert positionable in said TMF to bridge said two portions of said plate on longitudinally opposite sides of said TMF to increase a torsional rigidity of said plate at said TMF.

13. A bone plate system according to claim 12, wherein: said TMF comprises beams contiguous with said two portions and an opening therebetween.

14. A bone plate system according to claim 12, wherein: said TMF includes a first projection including a first thread portion and an opposing second projection including a second thread portion extending into the opening, said first and second thread portions forming discontinuous wall portions of a full thread, said insert being threadably engageable within said thread.

15. A bone plate system according to claim 14, wherein: said first and second projections are opposing cantilevered beams.

16. A bone plate system according to claim 14, wherein: said insert is a set screw including a head portion, and said first and second projections include an upper recess that receives said head portion.

17. A bone plate system according to claim 14, wherein: said first and second thread portions are approximately centered on the longitudinal axis of said plate.

18. A bone plate system according to claim 12, wherein: said insert is bioabsorbable.

19. A bone plate system according to claim 18, wherein: said insert includes a bioactive substance.

20. A bone plate system according to claim 12, wherein: said bone plate does not include a substantial widthwise change in lateral dimension relative to said two portions.

21. A method of treating a fracture of a bone, comprising: a) positioning a bone plate for fixation of the fracture, the bone plate including a bone screw hole, and a torsional modification feature (TMF) located between a center of the bone plate and said screw hole, the TMF decreasing the torsional rigidity of the plate relative to two portions of the plate adjacent to the TMF on longitudinally opposite sides of the TMF;b) inserting at least one fixed angle screw through the plate and into bone to couple the plate to the bone; andc) positioning an insert into the TMF to increase torsional rigidity of the plate at the TMF by bridging the two portions of the plate on longitudinally opposite sides of the TMF.

22. A method according to claim 21, wherein: said positioning an insert occurs after the plate is coupled to the bone.