Half pins for external fixators
The invention is a half pin for use in conjunction with external fixators, in which the half pin has a thin hydroxyapatite coating over a substantial portion thereof, a not-sharp hole-finding tip, and a variable pitch pattern in the threaded portion of the half pin. The hydroxyapatite coating must be thin—40-70 microns, deposited by plasma spray—and with limited porosity and pore size, and must extend not only over all the threads of the half pin but also a substantial portion of the unthreaded shaft proximal to the threaded end. The invention also includes a pin cube for use in association with the coated half pins. Wires may also be coated with the hydroxyapatite coating.
1. A half pin for use in an external fixator, the half pin comprising:
a head end;
a leading tip at a distal end; and
both an unthreaded shaft and a threaded shaft in between said head end and said leading tip,
wherein said unthreaded shaft is at least as long as said threaded shaft, and
wherein said threaded shaft has threads of a first pitch and has threads of a second pitch, said threads of said first pitch and said threads of said second pitch being disposed distally to said unthreaded shaft, said threads of said second pitch being more distally disposed to said unthreaded shaft than said threads of said first pitch, said second pitch being larger than said first pitch, said threads of said first pitch having a uniform first major diameter and a uniform first minor diameter, said threads of said second pitch having a uniform second major diameter, said threads of said second pitch having a first end proximal to said leading tip, wherein said leading tip is unthreaded and said threads of said second pitch comprise the threads closest to said unthreaded leading tip, said threads of said second pitch having a second end proximal to said threads of said first pitch, said threads of said second pitch having a second minor diameter gradually increasing from said first end to said second end.
2. The half pin according to claim 1 , wherein said threaded shaft includes an axially-extending portion separating said threads of said first pitch from said threads of said second pitch, and said axially-extending portion has an outer diameter being smaller than said first minor diameter and smaller than said second minor diameter at said second end.
3. The half pin according to claim 2 , wherein said second pitch is about 1.7 mm and said first pitch is about 1.2 mm.
4. The half pin according to claim 1 , wherein at least a portion of said threaded shaft and at least a substantial portion of said unthreaded shaft are coated with a 40-70 micron plasma-spray-deposited hydroxyapatite coating.
5. The half pin according to claim 4 , wherein said hydroxyapatite coating has between 1-5% porosity.
6. The half pin according to claim 5 , wherein said hydroxyapatite coating has a pore size diameter of 10 micrometers or less.
7. The half pin according to claim 6 , wherein each of said head end, said leading tip, said unthreaded shaft, and said threaded shaft comprise a surgical stainless steel.
8. The half pin according to claim 4 , wherein said threaded shaft includes an axially-extending portion separating said threads of said first pitch from said threads of said second pitch, and said axially-extending portion has an outer diameter being smaller than said first minor diameter and smaller than said second minor diameter at said second end.