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, 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,
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 coating of hydroxyapatite,
wherein said threaded shaft has threads of two different pitches, and
wherein a reduced minor diameter and a chamfer bridge said two different pitches, and said two different pitches, said reduced minor diameter, and said chamfer are disposed distally to the unthreaded shaft.
2. The half pin according to claim 1 , wherein said unthreaded shaft is cylindrical and said threaded shaft has a uniform outer diameter.
3. The half pin according to claim 1 wherein said hydroxyapatite coating has between 1-5% porosity.
4. The half pin according to claim 3 wherein the pore size diameter within said hydroxyapatite coating is 10 micrometers or less.
5. The half pin according to claim 4 wherein each of said head end, said leading tip, said unthreaded shaft, and said threaded shaft comprise a surgical stainless steel.
6. The half pin according to claim 5 wherein said threaded shaft has an inner diameter which tapers from said chamfer toward said leading tip.