Mechanisms for strut length measurement
A strut for use with an external fixation system may include first and second joints proximate the first and second ends of the strut, the first and second joints configured to couple to first and second rings of the external fixation system. The strut may include a threaded rod coupled to the first joint, a tube that receives the threaded rod, a fluctuation counter coupled to the tube, and a needle coupled to the fluctuation counter. The needle may extend through a bore in the outer tube, and the needle may have a free end in contact with the threaded rod. The strut may be an adjustable-length strut whereby the threaded rod is moveable axially into or out of the tube, and while the threaded rod moves into or out of the tube, the free end of the needle may be configured to maintain contact with the threaded rod.
1 . A strut for use with an external fixation system, the strut comprising:
a first joint proximate a first end of the strut, the first joint configured to couple to a first ring of the external fixation system;
a second joint proximate a second end of the strut, the second joint configured to couple to a second ring of the external fixation system;
a threaded rod having a first end coupled to the first joint;
a tube that receives the threaded rod;
a fluctuation counter coupled to the tube; and
a needle coupled to the fluctuation counter, the needle extending through a bore in the tube, the needle having a free end in contact with the threaded rod,
wherein the strut is an adjustable-length strut whereby the threaded rod is moveable axially into or out of the tube, and while the threaded rod moves into or out of the tube, the free end of the needle is configured to maintain contact with the threaded rod.
2 . The strut of claim 1 , wherein while the threaded rod moves into or out of the tube, the free end of the needle is configured to maintain contact with the threaded rod by riding along peaks and valleys of threads of the threaded rod.
3 . The strut of claim 2 , wherein as the free end of the needle rides along peaks and valley of threads of the threaded rod, a position of the fluctuation counter is configured to fluctuate relative to the tube.
4 . The strut of claim 3 , wherein the fluctuation counter is configured to count a total number of fluctuations as the free end of the needle rides along peaks and valleys of threads of the threaded rod, with one fluctuation corresponding to one complete revolution of the threaded rod.
5 . A method of determining a change in length of a strut of an external fixation system, the method comprising:
axially translating a threaded rod of the strut into or out of a tube of the strut to increase or decrease an effective length of the strut such that, during the axial translating, a free end of a needle that is coupled to a fluctuation counter that is coupled to the tube moves radially inward toward thread valleys of the threaded rod or radially outward toward threads peaks of the threaded rod;
counting, via the fluctuation counter, a total number of fluctuation cycles of the needle, each fluctuation cycle corresponding to one revolution of the threaded rod relative to the tube; and
determining a total length change of the strut by multiplying the total number of fluctuation cycles by a pitch of the threaded rod.
6 . The method of claim 5 , wherein each time the free end of the needle moves from one peak of the threaded rod to an axially adjacent peak of the threaded rod, the fluctuation counter increases the total number of counted fluctuation cycles by one.
7 . The method of claim 6 , wherein prior to determining the length change of the strut, the pitch of the threaded rod is entered into software of a computer system.
8 . The method of claim 7 , wherein after counting the total number of fluctuation cycles of the needle, the total number of counted fluctuation cycles is entered into the software of the computer system, and the step of determining the total length change of the strut is performed using the software of the computer system.
9 . The method of claim 5 , wherein each time the free end of the needle moves from one valley of the threaded rod to an axially adjacent valley of the threaded rod, the fluctuation counter increases the total number of counted fluctuation cycles by one.
10 . The method of claim 5 , wherein prior to counting the total number of fluctuation cycles of the needle, the total number of counted fluctuation cycles is set to zero.