Patent Application
20080243134
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to ratcheting surgical instruments, such as those for fastening screws or bolts, and more particularly, to such instruments which can be set to ratchet in either of two rotational directions or locked into a non-ratcheting state.
2. Description of the Related Art
Ratcheting drivers are commonly employed to apply fasteners, such as screws, bolts and the like. One type of ratcheting driver has a handle shaped like that of a conventional fixed blade screwdriver. However, the working end of the handle contains an actuator that maneuvers a gear and pawl assembly to selectively enable the handle to rotate the gear in either direction while allowing ratcheting in the opposite direction. A tool bit, such as a screwdriver blade or fastener socket, is attached to the gear and is driven by the handle motion.
In using a ratcheting driver, torque is applied by the user's hand to the handle and then via the pawl to the gear. The torque is transferred further to the tool bit which engages a workpiece, such as a screw, nut, or bolt. It is important to have the assembly arranged for optimum transmission of the applied hand torque in a reliable and consistent manner. That achievement is dependent on the construction, mounting, and location of the pawls.
Ratcheting drivers of this type are used as surgical instrument for orthopedic operations and other procedures. For example, a surgeon uses a ratcheting instrument to insert screws into bones to fasten plates to the skeleton of the patient. Surgical instruments have special requirements that common tools do not have to meet. Such instruments must be capable of withstanding high sterilizing temperatures of an autoclave. Any lubricants must be approved by the Food and Drug Administration of the United States Government if the surgical instrument is to be used in that country. Ratcheting driver also must be very durable as its failure during surgery may have serious consequences.
A ratcheting surgical instrument has a handle to which a ratchet housing is fixedly attached. A gear is rotatably located within the housing and a tool bit is operably connected to the gear. A first pawl is pivotally disposed in the housing and selectively engages the gear to enable the handle to drive the gear and the tool bit only in a first direction. A second pawl also is pivotally disposed within the housing and selectively engages the gear to enable the handle to drive the gear and the tool bit only in a second direction. In a preferred embodiment of the surgical instrument, each pawl has a plurality of teeth that mesh with teeth of the gear to reliably transfer of torque between those components. Preferably, separate compression springs bias the first and second pawls with respect to the housing and toward engagement with the gear.
An actuator selectively retracts the first pawl away from engagement with the gear and retracts the second pawl away from engagement with the gear. In a preferred embodiment, the actuator is attached to a cap that can be rotated into different positions with respect to the housing. In a first position of the cap, actuator retracts the first pawl out of engagement with the teeth of the gear, in a second position the actuator retracts the second pawl out of engagement with the teeth of the gear, and in a third position neither the first pawl nor the second pawl is retracted by the actuator.
In the preferred construction of the surgical instrument, the housing is secured to a metal core and the handle is formed by a plastic, preferably an elastomer and in particular silicone rubber, that is molded around the core and the housing. In addition, the tool bit has a shaft that extends through a bore in the gear and the shaft has an end section onto which a nut is threaded. At least a portion of the bore in the gear has a non-circular cross section and the tool bit has a segment that mates with that non-circular cross section to rotationally lock the tool bit to the gear.
With initial reference to
As shown in
The opposite end 26 of the grip 22 that is remote from the working end 14 has an aperture 28 there through that opens into the central bore 30 extending along an axis 31 through the core 20. This aperture 28 enables a guide wire and the like to pass through the surgical instrument 10 to the work site in the patient.
The remaining components are then assembled onto the molded handle 12. With reference to
With reference to
The gear and pawl assembly 16 further includes a pair of oppositely arranged pawls 54 and 55 that are received within grooves 56 and 57, respectively, within the housing 24. Each pawl 54 and 55 has a dog-leg shape with a rounded first end 58 that is pivotally received within the curved groove 56 or 57 in the housing. An arm 60 projects from the curved end 58 and out of the groove 56 into a cavity 62 within the housing 24. Each pawl has a plurality of teeth 64 that selectively engage the teeth 34 of the gear 32. The plurality of teeth 64 on each pawl 54 and 55 provide a secure engagement over a relatively large surface area between the respective pawl and the gear 32. Each pawl has an aperture 59 in its outward facing surface within which one end of a pawl spring 66 is received. The other end of the pawl spring 66 is received within a cap-like, hemispherical plunger 68 that engages a wall of the housing cavity 62. The pawl spring 66 biases the respective pawl 54 or 55 toward engagement with the teeth 34 of gear 32. As seen in
In a first rotational position of the cap 38 shown in
The user of the surgical instrument 10 selects the desired direction of ratchet motion by rotating the cap 38 about the handle 12 into one of the three detent positions. The first position at one extreme of the cap rotation shown in
The hemispherical plunger 68 enables an end of the pawl spring 66 to pivot with respect to the wall of the housing cavity 62 as the associated pawl 54 or 55 ratchets over the gear teeth 34. This avoids the pawl spring from binding or bending during the ratcheting which could impede the operation of the surgical instrument 10. The spring pivoting enabled by the plunger 68 also facilitates the retraction and engagement of each pawl 54 and 55 with respect to the gear 32 in response to rotation of the cap 38.
To tighten a fastener, the cap 38 placed into the second position, which is at the opposite end of the cap rotation with respect to the first position shown in
When the cap 38 is rotated by the user into the center, or third position, the pawl actuator 70 is located between the two pawls 54 and 55 without engaging either pawl. Thus both the first and second pawls 54 and 55 are biased by their respective springs 66 into engagement with the teeth of the gear 32. In this dual pawl engaging position, the first pawl 54 prevents the handle 12 from ratcheting when rotated in the counterclockwise direction and the second pawl 55 prevents the handle from ratcheting when rotated in the clockwise direction. Thus, the handle is now locked to the gear in both rotational directions.
The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.
