Rotationally asymmetric bone screw
Embodiments of the present invention provide rotationally asymmetric bone screws. Embodiments of the present invention provide mechanisms that reduce the bending stiffness of conventional shaft bone screws in order to yield a less-rigid fixation construct. Such a less-rigid construct enables a controlled amount of motion at a fracture site which in turn promotes bone healing. As a means to reduce the bending stiffness of positive-locking bone screws, embodiments of the present invention provide a bone screw having a non-circular cross-section over parts of the screw length and/or longitudinal slots along at least a portion of the bone screw.
1. An osteosynthesis construct, comprising:
a bone plate having two or more holes with locking threads for fixation of bone screws to the plate; and
two or more bone screws for positive-locking engagement with the plate, at least one of said two or more bone screws comprising
a shaft having a neck section, a mid section, and a threaded front end, at least one of said neck section and said mid section being rotationally asymmetric to impart to the bone screw a direction-dependent bending stiffness having a preferential direction of bending having a lower bending stiffness compared to a bending stiffness in a direction perpendicular to the preferential direction of bending; and
a threaded head portion adjoining the shaft, said threaded head portion having threads to provide for a positive-locking engagement of the bone screw with the bone plate, wherein said threads of said threaded head portion are rotationally timed with said threads of said plate holes to provide for a positive locking engagement of the bone screw with the bone plate resulting in a predefined final orientation of the bone screw with respect to the plate to align the bone screw to exploit the preferential direction of bending.
2. The osteosynthesis construct of claim 1 , wherein said rotationally asymmetric neck section and/or mid section comprises a non-circular cross-section.
3. The osteosynthesis construct of claim 2 , wherein said non-circular cross-section comprises an oval cross-section.
4. The osteosynthesis construct of claim 2 , wherein said non-circular cross-section comprises a rectangular cross-section.
5. The osteosynthesis construct of claim 1 , wherein said rotationally asymmetric neck section and/or mid section comprises one or more longitudinal slots.
6. The osteosynthesis construct of claim 5 , wherein at least one of said one or more longitudinal slots penetrates partially through at least a portion of said shaft and/or said threaded head portion.
7. The osteosynthesis construct of claim 5 , wherein at least one of said one or more longitudinal slots penetrates fully through at least a portion of said shaft and/or said threaded head portion.
8. The osteosynthesis construct of claim 5 , wherein at least one of said one or more longitudinal slots is curved.
9. The osteosynthesis construct of claim 1 , wherein said predefined final orientation of the bone screw with respect to the plate aligns in parallel said preferential direction of bending with a longitudinal axis of the bone plate.
10. The osteosynthesis construct of claim 1 , wherein said threaded front end is configured to secure said bone screw in a far cortex of a bone.
11. The osteosynthesis construct of claim 1 , wherein at least one of said two or more bone screws comprises a bi-cortical or uni-cortical locking screw.