Bone fastener

• US 4,716,893 A
• Filed: 12/23/1985
• Issued: 01/05/1988
• Est. Priority Date: 03/11/1985
• Status: Expired due to Fees

• Current Assignee: Arthur Fischer
• Original Assignee: Artur Fischer
• Inventors: Kramer, Wolfgang, Fischer, Artur
• Primary Examiner(s): Rosenbaum, C. Fred
• Assistant Examiner(s): SHEDD, CHARLES W
• Application Number:
  US06/813,221
• Time in Patent Office: 743 Days
• Field of Search: 128/92 YF, 128/92 R, 128/92 YP, 411/57, 411/60, 411/71, 411/72, 411/128, 411/395
• US Class Current: 606/66
• CPC Class Codes: A61B 17/686 Plugs, i.e. elements forming interface between bone hole and implant or fastener, e.g. screw
• CPC Class Codes: A61B 17/80 Cortical plates , i.e. bone plates; Instruments for holding or positioning cortical plates, or for compressing bones attached to cortical plates
• CPC Class Codes: F16B 13/124 fastened by inserting a threaded element, e.g. screw or bolt F16B13/122, F16B13/128 take precedence
• CPC Class Codes: Y10S 606/912 Radiolucent material

Abstract

A fastener for anchoring in a bore in a bone has a screw extending along an axis and having a substantially cylindrical outer surface formed with a helical screwthread. The screw has at the screwthread a thread diameter and between the turns of the thread at the surface a root diameter smaller than the thread diameter. An anchor sleeve normally fitted in the bore and of an outside diameter corresponding generally to the diameter of the bore has an outer end formed with a laterally projecting rim normally lying against the bone around the bore, an outer end portion of an inside diameter greater than the root diameter but smaller than the thread diameter, and an inner end portion of an inside diameter smaller than the root diameter. Thus when the screw is threaded into the sleeve its thread cuts into the outer portion without substantially deforming and spreading same and into the inner portion with substantial outward deformation and spreading of same.

Claims

1. A fastener for anchoring in a bore in a spongy interior of a bone, the fastener comprising:

a screw extending along an axis and having a substantially cylindrical outer surface formed with a helical screwthread, the screw having at the screwthread a thread diameter and between the turns of the thread at the surface a root diameter smaller than the thread diameter;

an anchor sleeve normally fitted in the bore and having an outside diameter corresponding generally to the diameter of the bore, the sleeve having

an outer end formed with a laterally projecting rim normally lying against the bone around the bore,

an outer portion with an inside diameter greater than the root diameter but smaller than the thread diameter, and

an inner portion with an inside diameter smaller than the root diameter, said sleeve thereby being formed so that when the screw is threaded into the sleeve its thread cuts into the outer portion without substantially deforming and spreading same and into the inner portion with substantial outward deformation and spreading of same, said inner portion being formed resilient to deflect inward when said screw is unthreaded out of said inner portion thereby enabling said sleeve to be entirely withdrawn out of the bore when pulling out the screw;

a rib projecting and extending generally longitudinally on said inner end portion so that said rib is forced into radial contact with a spongy interior of the bone when said inner end portion deforms outward and spreads by said screw threading into said inner end portion; and

means for preventing said sleeve from splitting when said screw passes through said sleeve and including an inner end of said sleeve being formed with an inside diameter generally corresponding to said inside diameter of said outer end portion, said inner end being arranged so that said inner portion lies between said inner end and said outer portion.

2. The fastener defined in claim 1 wherein the ribs extend at least generally helically on the inner end portion.

3. The fastener defined in claim 1 wherein the outer end portion has an outer surface clad with metal.

4. The fastener defined in claim 1 wherein the sleeve is internally formed as a surface of revolution, the portions being internally cylindrical.

5. The fastener defined in claim 1 wherein the screwthread has a sharp cutting edge.

6. The fastener defined in claim 1 wherein the sleeve is of a deformable synthetic resin.

7. A method of mounting a screw-type fastener in and removing it from a bore in a spongy interior of a bone, the method comprising the steps of:

threading a screw into and through an anchor sleeve in the bore, the screw extending along an axis and having a substantially cylindrical outer surface formed with a helical screwthread, the screw having at the screwthread a thread diameter and between the turns of the thread at the surface a root diameter smaller than the thread diameter, the anchor sleeve normally fitted in the bore and having an outside diameter corresponding generally to the diameter of the bore, the sleeve having

an outer end formed with a laterally projecting rim normally lying against the bone around the bore,

an outer portion with an inside diameter greater than the root diameter but smaller than the thread diameter,

an inner portion with an inside diameter smaller than the root diameter, and

an inner end having an inside diameter generally corresponding to said inside diameter of said outer portion, said inner end being arranged so that said inner portion lies between said inner end and said outer portion, the threading of the screw into and through the sleeve causing the thread to cut into the outer portion without substantially deforming and spreading same and into the inner portion with substantial outward deformation and spreading of same, the substantial outward deformation of the inner portion forcing a rib to radially engage with the spongy interior of the bone so as to solidly secure the sleeve in the bone while the engagement of the threads in the sleeve solidly secures the screw in the sleeve, the rib projecting and extending generally longitudinally on said inner portion;

thereafter unthreading the screw out of the inner portion so that the screw partially engages only the outer portion of the sleeve and so that the inner portion deflects inward to allow pulling of the sleeve with the screw; and

pulling the thus partially engaged screw away from the bone to thereby pull the sleeve out of the bore with the screw.