Arthroplasty implants, systems, and methods

A bone implant comprising:

• a shaft comprising:
• a proximal end;
• a distal end;
• a longitudinal axis;
• a minor diameter;
• and
• a threaded shaft portion;
• an articulating member disposed at the proximal end of the shaft;
• and
• a helical thread disposed about the shaft defining a length of the threaded shaft portion, the helical thread comprising a concave undercut surface on a first side of the helical thread, and a convex undercut surface on a second side of the helical thread,
• wherein:
• the concave undercut surface extends from the minor diameter of the shaft to a crest of the helical thread on the first side of the helical thread;
• the convex undercut surface extends from the minor diameter of the shaft to the crest of the helical thread on the second side of the helical thread;
• the concave undercut surface is angled towards one of the proximal end and the distal end of the shaft;
• and
• a ratio of the length of the threaded shaft portion to the minor diameter of the shaft is less than 1.50.

A shoulder joint implant comprising:

• a shaft comprising:
• a proximal end;
• a distal end;
• and
• a longitudinal axis;
• a helical thread disposed about the shaft along the longitudinal axis between the proximal and distal ends of the shaft, the helical thread comprising:
• a first undercut surface;
• a second undercut surface;
• a third undercut surface;
• and
• a fourth open surface, wherein:
• the helical thread does not have mirror symmetry with itself across any plane perpendicular to the longitudinal axis of the shaft;
• at least one of the first undercut surface, the second undercut surface, the third undercut surface, and the fourth open surface comprises a flat surface;
• the first undercut surface and the third undercut surface are angled towards one of the proximal end and the distal end of the shaft;
• and
• the second undercut surface and the fourth open surface are angled towards the other one of the proximal end and the distal end of the shaft;
• and
• a shoulder joint implement comprising an articular surface at the proximal end of the shaft.

A bone implant comprising:

• a shaft comprising:
• a proximal end;
• a distal end;
• a longitudinal axis;
• a proximal shaft portion comprising:
• a first minor diameter;
• and
• a first helical thread disposed about the proximal shaft portion defining a first major diameter of the proximal shaft portion, the first helical thread comprising a first concave undercut surface;
• and
• a distal shaft portion comprising:
• a second minor diameter;
• and
• a second helical thread disposed about the distal shaft portion defining a second major diameter of the distal shaft portion, the second helical thread comprising a second concave undercut surface,
• wherein:
• the first helical thread does not have mirror symmetry with itself across any plane perpendicular to the longitudinal axis of the shaft;
• the second helical thread does not have mirror symmetry with itself across any plane perpendicular to the longitudinal axis of the shaft;
• the first concave undercut surface and the second concave undercut surface are angled towards one of the proximal end and the distal end of the shaft;
• the second minor diameter of the distal shaft portion is smaller than the first minor diameter of the proximal shaft portion forming a shoulder intermediate the proximal shaft portion and the distal shaft portion;
• and
• the second major diameter of the distal shaft portion is smaller than the first major diameter of the proximal shaft portion.

A bone implant comprising:

• a shaft comprising:
• a proximal end;
• a distal end;
• a longitudinal axis;
• a minor diameter;
• and
• a threaded shaft portion;
• an articulating member disposed at the proximal end of the shaft;
• and
• a helical thread disposed about the shaft defining a length of the threaded shaft portion, the helical thread comprising a concave undercut surface,
• wherein:
• the concave undercut surface is angled towards one of the proximal end and the distal end of the shaft;
• and
• the concave undercut surface is formed by a first undercut surface, a second undercut surface, and an inflection point intermediate the first undercut surface and the second undercut surface, wherein the first undercut surface extends from the minor diameter of the shaft to the inflection point, and the second undercut surface extends from the inflection point to a crest of the helical thread.

A shoulder joint implant comprising:

• a shaft comprising:
• a proximal end;
• a distal end;
• and
• a longitudinal axis;
• a helical thread disposed about the shaft along the longitudinal axis between the proximal and distal ends of the shaft, the helical thread comprising:
• a first undercut surface;
• a second undercut surface adjacent the first undercut surface forming a first inflection point intermediate the first undercut surface and the second undercut surface;
• a third undercut surface;
• and
• a fourth open surface adjacent the third undercut surface forming a second inflection point intermediate the third undercut surface and the fourth open surface,
• wherein:
• the first undercut surface extends from a minor diameter of the shaft to the first inflection point, and the second undercut surface extends from the first inflection point to a crest of the helical thread;
• the third undercut surface extends from the minor diameter of the shaft to the second inflection point, and the fourth open surface extends from the second inflection point to the crest of the helical thread;
• the first undercut surface and the third undercut surface are angled towards one of the proximal end and the distal end of the shaft;
• and
• the second undercut surface and the fourth open surface are angled towards the other one of the proximal end and the distal end of the shaft;
• and
• a shoulder joint implement comprising an articular surface at the proximal end of the shaft.