# US 5,347,894 A · Torque limiting device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,347,894 A - Document ID: US5347894A - Status: Granted - Kind: A - Application number: 08/069,160 - Filed: 1993-05-28 - Granted: 1994-09-20 - Earliest claimed: 1993-05-28 - Assignees: PMT Corporation - Inventors: Paul D. Fischer - Web page: https://patentgrep.com/patent/US5347894A ## CPC - B25B 23/1415: {Break members; Arrangements specially adapted for break-bolts (break-bolts per se F16B31/00)} - A61B 17/6433: {specially adapted for use on body parts other than limbs, e.g. trunk or head} - A61B 17/8875: {Screwdrivers, spanners or wrenches} - A61B 90/14: Fixators for body parts, e.g. skull clamps; Constructional details of fixators, e.g. pins - A61B 2017/606: {with resilient spring element} - A61B 2090/031: {torque limiting} - A61B 2090/037: {with a frangible part, e.g. by reduced diameter} - B25B: TOOLS OR BENCH DEVICES NOT OTHERWISE PROVIDED FOR, FOR FASTENING, CONNECTING, DISENGAGING, OR HOLDING - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract The present invention relates to a torque limiting device for use in the affixation of a halo-type traction tool to the skull of a person. The torque limiting device has a shaft or shank embedded in a handle member which rotatably engages a skull pin during the fixation of a halo-type traction device to an individual. The torque limiting device has a first shear point at a reduced shank intermediate portion which prevents rotational torque forces in excess of a predetermined level from being applied to a skull pin during the attachment procedure of a medical cervical traction brace or tool. The present invention also includes a second shear point at the shank-handle interface which acts as a second safety mechanism to ensure that excessive pressure is not applied, and undesirable skull penetration does not occur, during the attachment procedure of a skull pin and halo to an individual's skull. The torque limiting device further includes a skull pin engaging end. The handle encapsulates a substantial portion of the shank, including the first and second shear points, and a handle-shank interface retaining collar and groove arrangement from which the pin engaging end extends also from the handle. Upon release of the first shear point or the second shear point, the handle and skull pin engaging end may rotate free of each other without separation of the handle from the skull pin engaging end, thereby keeping the device in one piece for easy handling, loss prevention and protecting an individual from risk of injury. ## Claims ### Claim 1 A torque limiting device for applying rotational force to a medical related tool, comprising: (a) a shank having a handle end portion, an intermediate shearing portion, and a tool engaging end portion, the intermediate shearing portion is adapted to shear the shank into two pieces at a determined rotational force; (b) a handle grippable by a human hand encapsulating the handle end portion and the intermediate shearing portion to apply rotational force to the tool through the device; and (c) a retaining interface means between the handle and the shank encapsulated by the handle adjacent the tool engaging end portion as to keep the device in one piece upon shearing of the intermediate portion of the shank. ### Claim 2 (depends on 1) The torque limiting device of claim 1, wherein the handle end portion and tool engaging end portion have a cross-sectional configuration other than cylindrical while the cross-sectional configurations of the intermediate shearing portion and the retaining interface means are cylindrical. ### Claim 3 (depends on 2) The torque limiting device of claim 2, wherein the handle end portion of the shank and the encapsulating handle interface therewith form a second strippable shearing portion. ### Claim 4 (depends on 1) The torque limiting device of claim 1, wherein the handle is made of plastic. ### Claim 5 (depends on 1) The torque limiting device of claim 1, wherein the shank is made of brass. ### Claim 6 (depends on 1) The torque limiting device of claim 1, wherein the shank is integrally one piece. ### Claim 7 (depends on 1) The torque limiting device of claim 1, wherein the retaining interface means comprises a rotatably interlockable protruding ring and annular channel arrangement between the handle and the shank. ### Claim 8 (depends on 7) The torque limiting device of claim 7, wherein the ring is on the handle and the channel is on the shank. ### Claim 9 (depends on 7) The torque limiting device of claim 7, wherein the ring is on the shank and the channel is on the handle. ### Claim 10 (depends on 7) The torque limiting device of claim 7, wherein the annular channel is surrounded by a collar. ### Claim 11 (depends on 1) The torque limiting device of claim 1, wherein the grippable handle is T-shaped with outwardly extending pegs. ### Claim 12 (depends on 1) The torque limiting device of claim 1, wherein the tool engaging end portion is engageable for rotation with a head of a screw for mounting the medical related tool to an individual. ### Claim 13 (depends on 12) The torque limiting device of claim 12, wherein the tool engaging end has a cross-sectional configuration other than cylindrical. ### Claim 14 (depends on 13) The torque limiting device of claim 13, wherein the head of the screw has a cup the interior of which is cross-sectionally configured to rotatably interlock with the tool engaging end upon insertion of the tool engaging end into the cup. ### Claim 15 (depends on 1) The torque limiting device of claim 1, wherein the medically related tool comprises a halo traction device affixable to a human head with skull screws. ### Claim 16 A torque limiting device for applying rotational force to a medical related tool, comprising: (a) a metallic, integral shank having a handle end portion, an intermediate shearing portion, and a tool engaging end portion, the intermediate shearing portion is adapted to shear the shank into two pieces at a determined rotational force; (b) a plastic handle grippable by a human hand encapsulating the handle end portion and the intermediate shearing portion to apply rotational force to the tool through the device; and (c) a retaining interface means between the handle and the shank encapsulated by the handle adjacent the tool engaging end portion comprising a rotatably interlockable protruding ring and annular channel arrangement between the handle and the shank as to keep the device in one piece upon shearing of the intermediate portion of the shank. ### Claim 17 (depends on 16) The torque limiting device of claim 16, wherein the handle end portion and tool engaging end portion have a cross-sectional configuration other than cylindrical while the cross-sectional configurations of the intermediate shearing portion and the retaining interface means are cylindrical. ### Claim 18 (depends on 16) The torque limiting device of claim 16, wherein the handle end portion of the shank and the encapsulating handle interface therewith form a second strippable shearing portion. ### Claim 19 (depends on 16) The torque limiting device of claim 16, wherein the ring is on the handle and the channel is on the shank. ### Claim 20 (depends on 16) The torque limiting device of claim 16, wherein the ring is on the shank and the channel is on the handle. ### Claim 21 (depends on 16) The torque limiting device of claim 16, wherein the annular channel is surrounded by a collar. ### Claim 22 (depends on 16) The torque limiting device of claim 16, wherein the grippable handle is T-shaped with outwardly extending pegs. ### Claim 23 (depends on 16) The torque limiting device of claim 16, wherein the tool engaging end portion is engageable for rotation with a head of a screw for mounting the medical related tool to an individual. ### Claim 24 (depends on 23) The torque limiting device of claim 23, wherein the tool engaging end has a cross-sectional configuration other than cylindrical. ### Claim 25 (depends on 24) The torque limiting device of claim 24, wherein the head of the screw has a cup the interior of which is cross-sectionally configured to rotatably interlock with the tool engaging end upon insertion of the tool engaging end into the cup. ### Claim 26 (depends on 16) The torque limiting device of claim 16, wherein the medically related tool comprises a halo traction device affixable to a human head with skull screws. ### Claim 27 A torque limiting device for applying rotational force to a medical related tool, comprising: (a) a metallic shank having a handle end portion, an intermediate shearing portion, and a tool engaging end portion, the intermediate shearing portion is adapted to shear the shank into two pieces at a determined rotational force; (b) a plastic handle grippable by a human hand encapsulating the handle end portion and the intermediate shearing portion to apply rotational force to the tool through the device; (c) a second strippable shearing portion formed between the interface of the handle end portion of the shank and the encapsulating handle; and (d) a retaining interface means between the handle and the shank encapsulated by the handle adjacent the tool engaging end portion as to keep the device in one piece upon shearing of the intermediate portion of the shank. ### Claim 28 (depends on 27) The torque limiting device of claim 27, wherein the handle end portion and tool engaging end portion have a cross-sectional configuration other than cylindrical while the cross-sectional configurations of the intermediate shearing portion and the retaining interface means are cylindrical. ### Claim 29 (depends on 27) The torque limiting device of claim 27, wherein the retaining interface means comprises a rotatably interlockable protruding ring and annular channel arrangement between the handle and the shank. ### Claim 30 (depends on 27) The torque limiting device of claim 27, wherein the tool engaging end portion is engageable for rotation with a head of a screw for mounting the medical related tool to an individual. ### Claim 31 (depends on 30) The torque limiting device of claim 30, wherein the tool engaging end has a cross-sectional configuration other than cylindrical. ### Claim 32 (depends on 31) The torque limiting device of claim 31, wherein the head of the screw has a cup the interior of which is cross-sectionally configured to rotatably interlock with the tool engaging end upon insertion of the tool engaging end into the cup. ### Claim 33 (depends on 27) The torque limiting device of claim 27, wherein the medically related tool comprises a halo traction device affixable to a human head with skull screws.