Implant connector

• US 5,605,457 A
• Filed: 02/13/1995
• Issued: 02/25/1997
• Est. Priority Date: 02/13/1995
• Status: Expired due to Fees

• Current Assignee: Crystal Medical Technology
• Original Assignee: Crystal Medical Technology
• Inventors: Folsom, Aubrey C. Jr., Bailey, A. Gregory
• Primary Examiner(s): O'Connor, Cary E.
• Application Number:
  US08/387,320
• Time in Patent Office: 743 Days
• Field of Search: 433/169, 433/172, 433/173, 433/174, 433/175, 606/65, 606/73, 411/309, 411/307, 411/310, 411/311, 411/411, 411/414, 411/415, 411/423, 411/426, 285/333, 285/334
• US Class Current: 433/174
• CPC Class Codes: A61B 17/742 having one or more longitudinal elements oriented along or parallel to the axis of the neck
• CPC Class Codes: A61C 8/005 Connecting devices for joining an upper structure with an implant member, e.g. spacers
• CPC Class Codes: A61C 8/0059 with additional friction enhancing means
• CPC Class Codes: A61C 8/0069 tapered or conical connection
• CPC Class Codes: A61F 2/30749 Fixation appliances for connecting prostheses to the body
• CPC Class Codes: A61F 2/3601 for replacing only the epiphyseal or metaphyseal parts of the femur, e.g. endoprosthetic femoral heads or necks directly fixed to the natural femur by internal fixation devices non-prosthetic internal fixation devices for the femoral head or neck A61B17/74
• CPC Class Codes: A61F 2002/30143 hexagonal
• CPC Class Codes: A61F 2002/30329 Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
• CPC Class Codes: A61F 2002/30408 Conical threadings
• CPC Class Codes: A61F 2002/30425 Square threads
• CPC Class Codes: A61F 2002/30433 using additional screws, bolts, dowels, rivets or washers e.g. connecting screws
• CPC Class Codes: A61F 2002/30574 with an integral complete or partial collar or flange
• CPC Class Codes: A61F 2002/3079 Stepped or enlarged apertures, e.g. having discrete diameter changes
• CPC Class Codes: A61F 2002/30797 internally-threaded
• CPC Class Codes: A61F 2002/30919 Sleeves
• CPC Class Codes: A61F 2002/3611 Heads or epiphyseal parts of femur
• CPC Class Codes: A61F 2002/3621 pierced with a longitudinal bore
• CPC Class Codes: A61F 2002/365 Connections of heads to necks
• CPC Class Codes: A61F 2220/0008 Fixation appliances for connecting prostheses to the body
• CPC Class Codes: A61F 2220/0025 Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
• CPC Class Codes: A61F 2220/0041 : using additional screws, bolts, dowels or rivets, e.g. connecting screws
• CPC Class Codes: A61F 2230/0017 : Angular shapes

Abstract

A threaded connection for use in medical implant surgery which utilizes a read profile which includes a load flank, a stab flank, a root intermediate the stab flank and load flank, and a crest intermediate the load flank and stab flank. The distance, measured paraxially, which the screw moves one complete revolution of the connection, is the lead of the thread. In the invention, the lead varies for either the male or female member of the connector such that the load flank, effectively, is moved away from axial interference with the cooperative member as the thread is "made up" or engaged. Accordingly, the load flank interface along the length of the connection is stressed, rather than having the load flank interface stressed predominately at the end turns of the thread, as often occurs under loading of the thread. In this manner, the stress loading of the thread is spread over the multiple turns of the thread, and pre-load is not lost by the yielding of the end turn.

Claims

1. An implant assembly for use in a medical implant, including an implant provided with an abutment for attachment to a prosthesis by a threaded fastener, said abutment and said implant having a cooperative male and female thread and a thrust connection between connected parts, wherein the improvement comprises a thread profile for reducing stress on selected highly stressed threads of said abutment and implant by varying the incremental lead between the male and female thread.

2. An assembly as defined in claim 1, wherein said female thread has a variable lead and said male thread has a constant lead.

3. An assembly as defined in claim 2, wherein said female thread has a profile including a load flank, a stab flank, and interstitial root and crest landings between said load flank and stab flank, and wherein said variable lead moves the load flank of selected turns of the thread away from high axial interference.

4. An assembly as defined in claim 2, wherein the lead of said female thread increases along the length of the fastener.

5. An assembly as defined in claim 1, wherein said male thread has a variable lead and said female thread has a constant lead.

6. An assembly as defined in claim 5, wherein said male thread has a profile including a load flank, a stab flank, and interstitial root and crest landings between said load flank and stab flank, and wherein said variable lead moves the load flank of said male thread away from axial interference with said female thread in selected turns of the thread.

7. An assembly as defined in claim 5, wherein the lead of said male thread varies along the length of the fastener.

8. An assembly as defined in claim 1, wherein said thread profile of each threaded member includes a stab flank positioned such that the stab flanks of each member are held in confronting spaced relation when said threaded members are engaged.

9. An assembly as defined in claim 1, wherein said prosthesis is connected to said abutment by a threaded connector having a male thread for engagement with the female thread of said abutment, said male thread of said prosthesis and said female thread of said abutment having cooperative thread profiles such that pre-load tension stress is distributed along the length of said connector engaged with said abutment.

10. An assembly as defined in claim 9, wherein said female thread has a variable lead and said male thread has a constant lead.

11. An assembly as defined in claim 1, wherein the lead of a selected turn of said thread is varied in accordance with the formula:

space="preserve" listing-type="equation">L=k+n(x)

Where, L equals the incremental lead, k equals the lead at a nominal turn, n equals the incremental deviation from the lead of the nominal turn, and x equals the number of increments over which the deviation is applied.

12. An implant assembly for use in a medical implant, including an implant provided with an abutment for attachment to a prosthesis by a threaded fastener, wherein said abutment, said implant, and said fastener each have a cooperative male and female thread and a thrust connection therebetween, wherein the improvement comprises a thread profile for reducing stress on selected threads of said male and female thread by varying the lead of one of the mating threads.

13. An assembly as defined in claim 12, wherein said male and female thread has a profile including a load flank, a stab flank, and interstitial root and crest landings between said load flank and stab flank, and wherein said variable lead, in the selected thread, effectively moves the load flank thereof away from axial interference with the load flank of the other mating thread in selected axial of the connection.

14. An implant assembly in a medical implant, including an implant provided with an abutment for attachment to a prosthesis by a threaded fastener, wherein said abutment, said implant, and said fastener each have a cooperative male and female thread and a thrust connection therebetween, wherein the improvement comprises a thread profile varying the lead of one of the cooperative threads, said male thread of said fastener and said female thread of said abutment having cooperative thread profiles such that the pre-load tension stress is distributed along the length of said fastener engaged with said abutment.

15. An assembly as defined in claim 14, wherein said female thread has a variable lead and said male thread has a constant lead.

16. An assembly as defined in claim 14, wherein said male thread has a variable lead and said female thread has a constant lead.