| abstract |
A torque driver for measuring the amount of torque being applied during implanting of an interference screw, includes a handle, drive shaft and drive head, a sleeve disposed around the proximal portion of the shaft, and a torque measurement assembly connected between the handle and the sleeve. The torque measurement assembly includes a proximal cup and a distal cup, and a coil spring encased between the cups, with one end of the spring fixed in the proximal cup and the other end of the spring fixed in the distal cup. The proximal cup is fixed to the distal end of the sleeve, and the proximal portion of the sleeve is fixed in the handle. The distal cup is fixed to the drive shaft, which rotates freely within the sleeve. Thus, the drive shaft and distal cup move together as one unit while the handle, sleeve, and proximal cup move together as one unit, so that the two units are physically connected to each other only by the torque spring. When the torque driver is used to insert an interference screw, the driver head is inserted into the socket of the screw and the driver is turned, the rotational force exerted to drive the screw causes the torque spring to tighten. A torque scale is marked on one of the proximal and distal cups in accordance with the spring constant of the torque spring, while a reference marking is provided on the other. As the spring tightens, the reference mark moves relative to the scale to indicate the torque measurement exerted on the spring. Using this torque driver, a surgeon can be confident that a desired minimum torque load is being applied which translates to a correspondingly desirable level of fixation strength for the graft. If the desired minimum torque load is not reached, the surgeon can then either exchange the interference screw with another having a larger diameter or install a supplemental fixation device. Also, the surgeon is made aware if too much torque is being exerted, to avoid damaging the bone, whereupon the surgeon can then either exchange the interference screw with another having a smaller diameter or widen the bone tunnel. |