Bone plate
A bone plate includes one or more locking devices which rotate to inhibit or prevent bone screws from backing out of the plate when installed on a patient. The locking devices can be in the shape of a bow tie or a capital letter I.
1. A bone plate comprising:
a plate having a top surface and a bottom surface;
at least two screw holes extending through the plate, the at least two screw holes having centers positioned apart at a distance A;
a hole extending through the plate, the hole positioned generally between the at least two screw holes at a distance X from a line connecting the centers of the at least two screw holes;
a rotatable locking device positioned in the hole, the rotatable locking device including first portions which extend above the plate top surface, second portions extending through the hole toward the bottom surface, and a center of rotation coincident with the center of said hole;
wherein the first portions define
a longest portion of length L, extending laterally from one side of said center of rotation to another side of said center of rotation,
a curved top surface having a radius of curvature R 1 ,
a thickness T at said center of rotation,
a widest portion of width W 1 at an end of the longest portion, and
a narrowest portion of width W 2 , adjacent said center of rotation; and
wherein
L= 1·(sqrt( R 1 2 −( R 1 −T ) 2 )), with 1.5≦1≦2.5,
W 1 =R 1 /w 1 , with 2.0 ≦w 1 ≦2.7, and
W 2 =R 1 /w 2 , with 3.0 ≦w 2 ≦3.7.
2. A bone plate according to claim 1 , wherein 1.8≦1≦2.2.
3. A bone plate according to claim 1 , wherein 1=2.
4. A bone plate according to claim 1 , wherein 2.2≦w 1 ≦2.5.
5. A bone plate according to claim 1 , wherein w 1 =2.331.
6. bone plate according to claim 1 , wherein 3.2≦w 2 ≦3.5.
7. bone plate according to claim 1 , wherein w 2 =3.339.
8. A bone plate according to claim 1 , wherein the first portions define a curved outer edge at said longest portion having a diameter of curvature D 1 , D 1 =(d 1 )·(W 1 ), and 1.0≦d 1 ≦2.0.
9. A bone plate according to claim 8 , wherein 1.4≦d 1 ≦1.8.
10. A bone plate according to claim 8 , wherein d 1 =1.633.
11. A bone plate according to claim 1 , wherein T=A/t, with 8≦t≦12.
12. A bone plate according to claim 11 , wherein 9≦t≦11.
13. A bone plate according to claim 11 , wherein t=10.
14. A bone plate according to claim 1 , wherein R 1 =(r)·(A), with 0.8≦r≦1.2.
15. A bone plate according to claim 14 , wherein 0.9≦r≦1.1.
16. A bone plate according to claim 14 , wherein r=1.06.
17. A bone plate according to claim 1 , wherein the first portions are generally in the shape of a bow tie.
18. A bone plate according to claim 1 , wherein the first portions are generally in the shape of a capital letter I.
19. A bone plate according to claim 1 , wherein said hole includes a countersunk portion extending from said bone plate bottom surface, and said locking device second portions include a malleable portion extending laterally into said countersunk portion.
20. A bone plate according to claim 1 , wherein W 1 , the radii of the screw holes, the distance A, and the distance X, are mutually selected so that there is a rotated position of the first portions at which the first portions do not overlap the screw holes.