Self drilling, self-tapping bone screw and method of installing for bicortical purchase

A bone screw configured to self-drill and to self-thread into bone structure as the screw is installed in said bone structure, said bone structure having a proximal cortical bone layer initially to be penetrated by said screw, an inner region of cancellous bone, and a distal cortical bone layer, said screw comprising a shank having a drill tip at the distal end of the shank, a plurality of helical bone screw threads along a portion of said shank, said shank having a longitudinal axis extending generally lengthwise of said screw, each of said threads having a root, a crest, and a pitch, where the diameter of the roots of said threads constitutes a minor diameter of said threads, said drill tip having a drill tip diameter of about said minor diameter of said threads, said drill tip being free of threads along its length and having a pair of substantially diametrically opposed lands at the distal end of said drill tip with each of said lands sloping inwardly toward a longitudinal axis of the screw, said drill tip further having a pair of diametrically opposed helical flutes with one edge of each said flute constituting a cutting edge and with the other edge of said flute and the other flute constituting a trailing edge, each of said flutes having a pitch substantially greater than the pitch of said threads and having a length such that each said flute extends proximally from said drill tip and intersects at least one of said threads, each said flute having a depth that diminishes along its length such that the depth of the flute distal from said drill tip is only somewhat less than the crest of the thread with which it intersects, said cutting edge of said flute being configured to cut bone from said bone structure so as to form bone debris as said screw is rotatably driven into said bone structure with said bone debris being conveyed along said flutes as said screw is advanced into said bone structure with said bone debris being compressed due to the diminished depth of said flutes, and wherein the length of said drill tip is configured to be about the thickness of said cortical bone layer such that a most distal thread does not threadably engage said proximal cortical bone layer until said drill tip has substantially penetrated through said proximal cortical bone layer thereby to substantially avoid stripping the threads formed in said proximal cortical bone layer.

A bone screw configured to self-drill and to self-thread into bone structure as the screw is installed in said bone structure, said bone structure having a proximal cortical bone layer at the outer margin of said bone structure to be initially drilled through by said screw, an inner region of cancellous bone, and a distal cortical bone layer, said screw comprising a shank having a head at the proximal end of the shank and a self-drilling, self-tapping tip at the distal end of the shank with a plurality of substantially uniformly spaced helical bone screw threads along a portion of said shank, said shank having a longitudinal axis extending generally lengthwise of said screw, each of said threads having a root, a crest, and a pitch where the diameter of the roots of said threads constitutes a minor diameter of said threads, with the exception of a lead thread proximate said drill tip each of said threads having a sloped leading flank and a trailing flank more perpendicular to the axis of said screw than the leading flank, said lead thread being configured to tap internal threads in said bone structure as said screw is installed in said bone structure, said drill tip having a drill tip diameter of about said minor diameter of said threads, said drill tip being free of threads along its length and having a pair of substantially diametrically opposed lands at the distal end of said drill tip with each of said lands sloping inwardly toward the axis of the screw, said drill tip further having a pair of diametrically opposed helical flutes with one edge of each flute between one of said lands and said flute constituting a cutting edge and with the other edge of said flute and the other flute constituting a trailing edge, each of said flutes having a pitch substantially greater than the pitch of said threads and having a length such that each said flute intersects at least one of the threads closest to the drill tip, each said flute having a depth that diminishes along its length such that the depth of the flute distal from said drill tip is only somewhat less than the crest of the thread with which it intersects with said cutting edge of said flute being configured to cut bone from said bone structure so as to form bone debris as said screw is inserted into said bone structure with said bone debris moving along said flutes as said screw is advanced into said bone structure with said bone debris being compressed due to the diminished depth of said flutes, and wherein the length of said drill tip is configured to be about the thickness of said cortical bone layer such that said lead thread does not threadably engage said proximal cortical bone layer until said drill tip has substantially penetrated through said proximal cortical bone layer thereby to substantially avoid stripping the threads formed in said proximal cortical bone layer.

A bone screw configured to self-drill into bone structure as the screw is installed in said bone structure, said bone structure having a proximal cortical bone layer at the outer margins thereof to be initially drilled through by said screw, an inner region of cancellous bone, and a distal cortical bone layer, said screw comprising a shank having a head at the proximal end of the shank and a self-drilling drill tip at the distal end of the shank with a plurality of substantially uniformly spaced helical bone screw threads along a portion of said shank, said shank having a longitudinal axis extending generally lengthwise of said screw, each of said threads having a root, a crest, and a pitch, where the diameter of the roots of said threads constitutes a minor diameter of said threads, with the exception of a first thread proximate said drill tip each of said other threads having a sloped leading flank and a trailing flank more perpendicular to the axis of said screw than the leading flank, said drill tip having a drill tip diameter of about said minor diameter of said threads, said drill tip being free of threads along its length and having a pair of substantially diametrically opposed lands at the distal end of said drill tip with each of said lands sloping inwardly toward the axis of the screw, said drill tip further having a pair of diametrically opposed helical flutes with one edge of each flute constituting a cutting edge, each of said flutes having a pitch substantially greater than the pitch of said threads and having a length such that each said flute intersects at least one of the threads closest to the drill tip, each said flute having a depth that diminishes along its length such that the depth of the flute distal from said drill tip is only somewhat less than the height of the thread with which it intersects, said cutting edge of said flute being configured to cut bone from said bone structure so as to form bone debris as said screw is rotatably driven into said bone structure with said bone debris moving along said flutes as said screw is advanced into said bone structure with said bone debris being compressed as the bone debris move along said flutes, and wherein the length of said drill tip is configured to be about the thickness of said proximal cortical bone layer such that none of said threads contacts said proximal cortical bone layer until said drill tip has substantially penetrated through said proximal cortical bone.

A bone screw configured to self-drill and to self-thread into bone structure as the screw is installed in said bone structure, said bone structure having a proximal cortical bone layer to be initially drilled through by said screw, said screw comprising a shank and a self-drilling drill tip at the distal end of the shank, said shank having a plurality external helical bone screw threads therealong, said screw having a longitudinal axis, each of said threads having a root and a crest where the spacing of said threads along said shank has a substantially uniform pitch and where diameter of the roots of said threads constitutes a minor diameter for said threads, said drill tip being substantially free of threads along its length and having a diameter substantially the same as said minor diameter of said threads, said drill tip further having a pair of substantially diametrically opposed lands with each of said lands sloping inwardly toward the axis of the screw, each of said lands having a cutting edge configured to cut bone from said bone structure as said screw as installed in said bone structure, said one thread closest to the drill tip constituting a lead thread which is an incomplete thread initially of about the diameter of said drill tip and where the height of said lead thread gradually increases from said minor diameter until the lead thread becomes a fully formed thread, said lead thread being adapted to form internal threads in said bone structure as said screw is rotatably driven into said bone structure, and wherein the length of said drill tip is configured to be at least about the thickness of said proximal cortical bone layer such that said lead thread does not threadably engage said proximal cortical bone layer until said drill tip has substantially penetrated through said proximal cortical bone layer.

A method of installing a self-drilling, self-tapping bone screw into a bone structure, said bone screw having a cannula extending lengthwise of the screw and having a self-drilling and self-tapping drill tip at its distal end and bone threads along at least a portion of its length, said bone structure having a proximal and a distal cortical bone layer with a cancellous bone region therebetween, said drill tip having a length approximately equal to or greater than said proximal cortical bone layer, said thread adjacent said drill tip constituting a lead thread configured to tap internal threads in said bone structure as said screw is installed in said bone structure, said method comprising instructing a surgeon to perform the following steps in order to install said screw into bone structure:

• Install a guide wire into a proximal area of said bone structure;
• Pass said cannulated screw along said guide wire until the tip of the screw is in close proximity to said bone structure at a desired location for the insertion of the screw;
• Remove the guide wire;
• and
• Drive said screw into said bone structure by rotating said screw with said drill tip penetrating substantially through said proximal cortical bone layer before said lead thread begins to form threads in said proximal cortical bone layer.

A method of installing a self-drilling, self-tapping bone screw into a human sacrum having a proximal and a distal cortical bone layer with a cancellous bone region therebetween, said bone screw having a cannula extending lengthwise of the screw and having a self-drilling and self-tapping drill tip at its distal end and bone threads along at least a portion of its length, said drill tip having a length approximately equal to or greater than said proximal cortical bone layer, said thread adjacent said drill tip constituting a lead thread configured to tap internal threads in said bone structure as said screw is installed in said sacrum, said method comprising instructing a surgeon to perform the following steps in order to install said screw into bone structure:

• Install a guide wire in a proximal area of said sacrum with the guide wire establishing an insertion point on the sacrum for the insertion of said screw and establishing an approximate line of insertion for said screw;
• Pass said cannulated screw along said guide wire until the tip of the screw engages the sacrum at said insertion point;
• and
• Drive said screw into the sacrum by rotating said screw with said drill tip penetrating through said proximal cortical bone layer and with said lead thread forming internal threads in said proximal cortical bone layer after said drill tip has substantially penetrated through said proximal cortical bone layer.