Heated bolt for modular hip stem

Patent metadata

Field	Value
Publication number	US-2016106543-A1
Application number	US-201414787853-A
Country	US
Kind code	A1
Filing date	May 15, 2014
Priority date	May 23, 2013
Publication date	Apr 21, 2016
Grant date	—

Abstract

During hip replacement surgery, a practitioner can attach a distal stem to a femur of the patient and can then fixedly attach a proximal body to the distal stem using a bolt. Prior to tightening, the bolt can be heated to an elevated temperature greater than average human core body temperature. The practitioner can tighten the bolt to a specified torque while the bolt is at the elevated temperature. After tightening, the bolt cools to average human core body temperature and experiences a tensile stress due to the effects of thermal expansion. The tensile stress in the bolt produces a compressive force between the distal stem and the proximal body. The compressive force can increase the attachment strength of the bolt to the distal stem and the proximal body, beyond what can be achieved by solely torquing the bolt to the specified level during surgery without first heating the bolt.

First claim

1 . A modular hip stem, comprising:
a distal stem configured to be implanted within a femur of a patient; a proximal body configured to attach to a proximal end of the distal stem; a bolt configured to secure the proximal body to the distal stem; and an electrical resistive heater, disposed within or around the bolt, configured to heat the bolt to a temperature greater than average human core body temperature.

2 . The modular hip stem of claim 1 , wherein the bolt includes at least one electrode, configured to supply current to the electrical resistive heater, extending therefrom.

3 . The modular hip stem of claim 2 , wherein the at least one electrode is detachable from the bolt at a perforation.

4 . The modular hip stem of claim 2 ,
wherein the bolt includes two electrodes extending therefrom; and wherein the electrical resistive heater has an electrical path extending from one of the two electrodes to the other of the two electrodes.

5 . The modular hip stem of claim 2 ,
wherein the bolt extends longitudinally between a proximal end and a distal end; wherein the bolt includes a head at its proximal end; and wherein the at least one electrode extends proximally from the head of the bolt.

6 . The modular hip stem of claim 1 ,
wherein the electrical resistive heater is surrounded by an electric insulator; and wherein the electrical resistive heater and the electric insulator are disposed in an interior of the bolt.

7 . The modular hip stem of claim 6 , wherein the electrical resistive heater and the electric insulator are disposed in a volume surrounding a longitudinal axis of the bolt.

8 . The modular hip stem of claim 1 , wherein the bolt includes a material having a positive thermal expansion coefficient.

9 . The modular hip stem of claim 1 , wherein, in a temperature region that includes average human core body temperature, the bolt includes a material causing its longitudinal length to increase linearly with an increase in temperature.

10 . The modular hip stem of claim 1 ,
wherein the bolt extends longitudinally between a proximal end and a distal end; wherein the bolt includes a helical thread, engageable with the proximal end of the distal stem, at its distal end; and wherein the bolt include a head, engageable with the proximal body, at its proximal end.

11 . The modular hip stem of claim 1 , wherein the bolt is formed from a material including at least one of cobalt, chromium, titanium, titanium alloys, stainless steel, and stainless steel alloys.

12 . A method for assembling a modular hip stem, comprising:
attaching a proximal end of a distal stem, implantable within a femur of a patient, and a proximal body; heating a bolt to an elevated temperature greater than average human core body temperature; inserting the bolt through a lumen of the proximal body and into a lumen of the proximal end of the distal stem; tightening the bolt to a specified torque while the bolt is at a temperature greater than average human core body temperature; and allowing the bolt to cool to average human core body temperature.

13 . The method of claim 12 , wherein heating the bolt to the elevated temperature greater than average human core body temperature comprises:
immersing the bolt in a warm liquid bath having an elevated temperature greater than average human core body temperature; raising the temperature of the bolt; and removing the bolt from the warm liquid bath.

14 . The method of claim 12 , wherein heating the bolt to the elevated temperature greater than average human core body temperature comprises:
inserting an external heater into an elongated hollow cavity within the bolt; raising the temperature of the bolt to an elevated temperature greater than average human core body temperature; and removing the external heater from the bolt.

15 . The method of claim 12 , wherein heating the bolt to the elevated temperature greater than average human core body temperature comprises:
providing an electric current to an electrical resistive heater disposed within or around the bolt; raising the temperature of the bolt to an elevated temperature greater than average human core body temperature; and removing the electric current.

16 . The method of claim 15 , wherein providing the electric current to the electrical resistive heater disposed within the bolt comprises:
providing an electric current to a pair of detachable electrodes electrically connected to the electrical resistive heater.

17 . The method of claim 16 , wherein removing the electric current comprises:
detaching the electrodes from the bolt.

18 . The method of claim 12 , wherein tightening the bolt to the specified torque while the bolt is at the temperature greater than average human core body temperature comprises:
moving the proximal end of the distal stem further within a lumen of the proximal body.

19 . The method of claim 12 , wherein heating the bolt to the elevated temperature greater than average human core body temperature comprises:
temporarily increasing a longitudinal length of the bolt.

20 . The method of claim 12 , wherein allowing the bolt to cool to average human core body temperature comprises:
imparting a tensile stress to the bolt, the tensile stress producing a compressive force between the distal stem and the proximal body.

Assignees

• Zimmer Inc

Inventors

• Borries Paul

Classifications

• A61F2/3094

  Designing or manufacturing processes · CPC title

• A61F2002/30604

  modular · CPC title

• A61F2/3609 Primary

  Femoral heads or necks; Connections of endoprosthetic heads or necks to endoprosthetic femoral shafts (A61F2/3601 takes precedence) · CPC title

• A61F2002/3652

  Connections of necks to shafts · CPC title

• A61F2002/30077

  shrinkable · CPC title