Orthopedic compression screw
View Patent ↗A cannulated compression screw is used as an orthopedic implant and has a threaded distal end with an insertion tip that includes at least one and preferably two, three or four flutes to allow the screw to be self-tapping. Optionally, the screw also includes one or more reverse cutting flutes proximal to the insertion tip. The distal threads are cancellous threads having a generally constant minor diameter and a generally constant major diameter and a generally constant thread pitch. An intermediate portion of the screw is non-threaded and the proximal end includes a compression wedge or taper that has at least one, and preferably two to five flutes that terminate before the top of the screw. The proximal end further includes a radiused bevel to the terminal surface that includes a hexagonal torque driving recess. The diameter of the non-threaded shaft section is constant distal from the compression wedge to the distal tip where it defines the minor diameter of the threaded portion. The screw optionally includes a tapered insertion tip.
1. An orthopedic screw for implantation into bone comprising:
a proximal end and a distal end and a longitudinal axis extending therebetween;
a cannula extending through the screw along the longitudinal axis;
a distal portion having an insertion tip which includes from 3 to 5 grooves equally radially spaced and extending in the direction of the longitudinal axis which each form a distal cutting flute that cuts as the screw is being screwed into the bone;
a threaded portion adjoining the distal portion having a substantially constant minor diameter and a substantially constant major diameter and a substantially constant thread pitch, said thread being a cancellous thread, said threaded portion including at least one reverse flute which cuts as the screw is being screwed out of the bone;
an intermediate cylindrical portion adjoining the threaded portion which is substantially free from the cancellous thread of the threaded portion and having a diameter which is substantially the same diameter as the minor diameter of the threaded portion, and which is from about one half to about twice the longitudinal length of the threaded portion; and
a proximal non-threaded wedge portion adjoining the intermediate cylindrical portion and which has a diameter that constantly increases from the diameter of the intermediate portion to a maximum diameter which is larger than the major diameter of the threaded portion so as to form a cone that defines a side wall which defines a plane that has an angle with the longitudinal axis of from about 11° to 13° and the side wall including from 3 to 5 radially equally spaced proximal cutting flutes that have a first surface which defines a plane that transects the longitudinal axis and a second surface that forms an angle of from about 60° to about 120° to the first surface and a radial angle of about 20° to about 40° to the plane of the first surface, the proximal cutting flutes cutting when the screw is being screwed into the bone and being radially offset from the distal cutting flutes, the side wall proximally terminating in a rounded shoulder portion that joins a proximal end terminal surface, and the proximal cutting flutes each terminating in the longitudinal direction distal to the rounded shoulder portion to form a lip that is open toward a distal end of the screw, the proximal gad terminal surface including a torque driving recess that extends distally along the longitudinal axis of the screw and which terminates at a first distance from the proximal end of the screw whereby the lip is located at or distal to a widest portion of the proximal non-threaded wedge portion and comprises a circumferential fillet which acts as a stop portion in use, and the second surface of the proximal cutting flutes each defining a compound curve so that the material of the screw is augmented in the proximal portion of the screw at the first distance from the proximal end of the screw.
2. An orthopedic screw as set forth in claim 1 in which the torque driving recess is a hexagon or a hexalobe shape.
3. An orthopedic screw as set forth in claim 1 wherein the insertion tip includes a taper.