Patent ID: 7153281

Claim:
Apparatus for measuring instability of a motion segment unit of a spine comprising: a) motor means comprising a housing and a motor contained within the housing for applying a controllable force to a distractor arm assembly; b) a distractor arm assembly operatively engaged to the motor means comprising: 1. a collar assembly fixedly secured to the housing of the motor means, said collar assembly having an opening to allow a screw means to pass therethrough, 2. screw means having a first end operatively engaged to the motor means and a second end operatively engaged to a pivot collar assembly, said screw means having an unthreaded portion passing through said collar assembly and being rotatable when the motor means is operational, 3. a pair of segmented arms each having at least two arm segments pivotal with respect to each other, a first arm segment being attached to the collar assembly and a second arm segment being pivotally attached to a pivot collar assembly and having a remote end for engaging a portion of the motion segment unit of the spine wherein the second arm segments transverse each other at said pivot collar assembly, and 4. a pivot collar assembly for engaging the second arm segments enabling the second arm segments to transverse each other and be pivotally movable with respect to each other to enable the remote ends to engage and disengage the motion segment unit, wherein rotation of the screw means causes the pivot collar assembly to move along the screw means causing the first and second arm segments to move in said transverse relationship relative to each other whereby the remote ends of the arms move away from each other to provide a controllable force on adjacent portions of a motion segment unit and toward each other to release the controllable force against said adjacent portions.