Bone fastener

Claim 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to deflect inward when said screw is unthreaded out of said inner portion thereby enabling said sleeve to be entirely withdrawn out of the bore when pulling out the screw; a rib projecting and extending generally longitudinally on said inner end portion so that said rib is forced into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.

Claim 8

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.

Claim 9

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.