Title:
In-bone implantable shaft for prosthetic joints or for direct skeletal attachment of external limb prostheses and method of its installation
Kind Code:
A1


Abstract:
An in-bone implantable shaft for prosthetic joints or for direct skeletal attachment of external limb prostheses, comprised of a central body fitted in the zone of the bone's medullary cavity conventionally prepared for implantation, and of side elements attached to the central body and fitted in the slots specially made in the bone's walls surrounding said medullary canal; said side elements have spaces between them, arranged to be filled by bone cells to provide a natural and safe osseolocking of the shaft. A method of preparing the bone for implantation of a prosthetic shaft, comprising the steps of: placing a cylindrical guide with slots made in the longitudinal direction of said guide inside said bone's canal which is conventionally prepared for implantation; cutting said bone's walls by progressing a saw along the edges of the slots of said guide; removing the guide; fitting the shaft in the bone's canal, provided that the side elements are fitted to the slots in the bone's walls.



Inventors:
Pitkin, Mark (Sharon, MA, US)
Application Number:
11/899068
Publication Date:
03/05/2009
Filing Date:
09/05/2007
Primary Class:
International Classes:
A61F2/60
View Patent Images:



Primary Examiner:
WOZNICKI, JACQUELINE
Attorney, Agent or Firm:
PRETI FLAHERTY BELIVEAU & PACHIOS LLP (BOSTON, MA, US)
Claims:
I claim:

1. An implantable shaft for prosthetic joints or for direct skeletal attachment of external limb prostheses, comprised of a central body fitted in the bone's medullary cavity conventionally prepared for implantation, and of side elements attached to the central body and fitted in the slots specially made in the bone's walls surrounding said medullary canal; said side elements have spaces between them.

2. An implantable shaft for prosthetic joints or for direct skeletal attachment of external limb prostheses described in claim 1, wherein the side elements are lined along the longitudinal direction of said bone.

3. The side elements described in claim 1, wherein the thickness of said elements approximates the width of the slots and may slightly exceed said width.

4. The side elements described in claim 1, wherein the width of each said element approximates the thickness of the bone's wall such that after installation, said elements do not extend beyond the outer circumference of said bone.

5. A method of preparing the bone for implantation of a prosthetic shaft, consisting of: placing a cylindrical guide with slots made in the longitudinal direction of said guide inside said bone's canal which is conventionally prepared for implantation; cutting said bone's walls by progressing a saw along the edges of the slots of said guide; removing the guide; fitting the shaft described in claim 1 in the bone's canal, provided that the side elements described in claim 1 are fitted to said slots in the bone's walls.

Description:

TECHNICAL FIELD

Prosthetics, surgical instruments; more particularly, methods and devices for surgically preparing a bone for the implantation of a prosthetic implant component of a prosthetic joint [1, 2] or the implantation of an abutment for direct skeletal attachment of external prostheses, as described in: http://www.sahlgrenska.se/vgrtemplates/Page33031.aspx.

BACKGROUND OF THE INVENTION

This invention relates to prosthetic implants for skeletal replacement, reconstruction and attachment in humans and animals, and, more particularly, to the design and method of installation of such devices that would reduce their loosening with time.

Implantable devices are used to partially or completely replace joints or bone segments in humans and animals, or to provide direct skeletal attachment of external prostheses to the residuum.

The known approaches to attaching the implants include fitting the implant into the medullary canal of the bone by force; securing the implant in the bone with screws or pins; bonding the implant to the bone with various adhesives; use of porous structures to stimulate ingrowth of the bone into the implant's surface.

One of the major problems involved in the use of such devices is the loosening of the attachment between the prosthetic implant and the associated bone. Loosening occurs mainly due to the cyclical application of bending moments during locomotion which eventually destroy the bond between the implant and the bone [3-5].

To decrease loosening, a more precise installation technique, anchoring elements, and surgical assemblies were introduced in U.S. Pat. Nos. 5,702,445[6], 6,159,216[7], 6,520,966[8], and 7,001,394[9]. Another approach was introduced in U.S. Pat. No. 4,828,566 where a recess is carved from the implanted region of the prosthesis in the proximal medial region, and a U-shaped wire mesh structure is fitted within the recess. The wire mesh structure allows for an ingrowth of bone tissue in the medial narrow side of the shank and for the absorption of shear micro movements between the bone and the implant [10].

One of the reasons for loosening, after all these approaches or their several combinations are used, is that the approaches are all in conflict with the structure and function of the medullary cavity canal, into which the implants are inserted. With the conventional method of installation of the shank, a drill first bores the tube bone to prepare an area into which the shaft of the implant fits exactly. Then, the implant is installed into the bone as described in: http://biomedtrix.com/sur.html.

The procedure destroys, completely or in part, the layer of endosteal bone trabeculae, or endosteum, which fills the medullary cavity of the bone [11], as illustrated in FIGS. 1 and 2.

After the medullary canal is drilled (see FIG. 2) in preparation for device implantation, osteocytes begin to remodel the internal canal walls and fill the gaps between the implant and the walls, including the specially designed cavities or pores in the implant. The remodeling proceeds in the direction out from the outer walls toward the interior walls of the medullary canal [12].

Such ossification fixes the implant inside the bone canal by developing multiple micro locks, and is therefore useful for anchoring and preventing further loosening.

However, the preexisting position of the endosteum limits the potential volume of the remodeled ossified bone tissue in the outward-inward direction. This is the natural mechanism which protects the area designated for bone marrow from filling with cortical bone, in the process of bone remodeling as a consequence of bone fracture [12].

Therefore for additional anchoring, to augment the effects of slight ossification, the implant is often secured with screws (1) (see FIG. 3) inserted from the outside of the bone into the implanted shaft of the prosthesis, as described in: http://www.enar.ncsu.edu/news/newsletters/pdfs/frontline1105.pdf.

This locking and anchoring approach requires additional operation time and techniques for exact positioning of the screws relative to the holes of the shaft implanted into the medullary canal.

All described approaches depend on ossification inside the medullary canal, which has aforementioned natural limitations to the volume of the remodeled bone tissues.

In contrast to ossification in the outer-to-inner direction, the ossification in the direction of the longitudinal axis of a bone can be achieved in significantly higher volumes of remodeled bone tissues. This well-known phenomenon is utilized in bone lengthening techniques, when an external apparatus is applied for the fixation of the bone fragments that are created after the bone is dissected perpendicularly to its longitudinal axis. Then, with the aid of the given external apparatus, bone fragments are moved apart 1-2 mm per day. Continued ossification, when properly controlled, allows the bone to lengthen up to 33% of its original length [13, 14]. Similar volume of ossification occurs in the lateral direction when the bone is widened [15]. However, this approach has never been applied to lock the implanted shaft.

Accordingly, it is an object of the present invention to prevent the occurrence of the implant loosening. It is another object of the invention to utilize the natural anchoring (osseolocking) of an implant in a bone by introducing a corresponding device and method of its installation.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to the creation of favorable conditions for the ingrowth of bone cells and tissues between and throughout the sides of the implanted shaft (“osseolocking”). To increase the positive effect of osseolocking, the bone walls are specially prepared in conjunction with the standard drilling of the medullary canal. That specific preparation includes fashioning one or more slots in the bone walls in the longitudinal direction. The protruding sides of the installed implant are positioned in the slots, and the ossification begins. That ossification process between and throughout the side elements progresses in the direction of the widening bone, and is able to naturally lock the implant's shaft with an anchoring effect similar to the inter-locking nailing, but without its complications [16].

Another object of the present invention is the method of preparing a bone for the implantation of a prosthetic shaft, which consists of the following steps: placing a cylindrical guide with slots in the longitudinal direction into the bone's canal already conventionally prepared for implantation; cutting the bone's walls by progressing a saw along the sides of the slots in the guide; removing the guide; fitting the shaft into the bone's canal, provided that the protruding side elements are fitted into the slots in the bone's walls.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail in the following description of one of the preferred embodiments of the invention with references to the accompanying figures:

FIG. 4 presents a 3D view of the shaft with central part 1 and protruding side elements 2. The elements 2 are separated from each other by open spaces, and can each be of different shape, with or without one or more holes 3, and either solid, porous, composite or meshed in composition. The partially sectioned side view of the bone 6 with the implanted shaft 1 shows newly ossified zones 3 and 5 of the bone's walls 8, and serves to demonstrate how the device is integrated with the bone at the end of the healing process. The top view shows the shaft 1 after healing, following the shaft's installation into the pre-drilled cylindrical cavity in the medullary canal 7, and into the pre-cut slots 4 in the walls 8.

FIG. 5 presents a 3D view of a guide 9 with slots 4, which frame the interior of the section of bone to be excised from the bone walls 8, once the guide is inserted into the pre-drilled cylindrical cavity in the medullary canal 7 (see FIG. 4).

DETAILED DESCRIPTION OF THE INVENTION

The device in the present invention, namely, the implantable shaft of the prosthetic joint or the abutment for the attachment of an external limb prosthesis, has a central portion 1 situated in the cavity of the medullary canal 7 of the bone 6. The side elements 2 of this device are situated in the slots 4 pre-cut out of the walls 8 of the bone.

The method of installation of the device is also a component of the present invention, and is implemented once the marrow cavity of the bone in which implantation is planned is prepared in the conventional manner (by drilling a cavity in the medullary canal 7). Specifically, a guide 9 with slots 4 (see FIG. 5) is inserted into a pre-drilled cavity in the medullary canal 7. The diameter of the drill that prepares the cylindrical cavity has to correspond to the diameter of the cavity and the depth of drilling should correspond to the height of the shaft 1 to allow the guide to be easily inserted and removed manually without additional tools. The slots 4 of the guide 9 should be oriented in the sagittal plane or otherwise depending on the patient's conditions. Then, the surgical saw is positioned against the slots of the guide and the cut is performed through the bone's walls 8 down to the limit provided by the depth of the slots 4 of the guide. Next, the guide is removed from the cavity, and the shaft 1 is implanted from the open end of the bone by positioning the side elements 2 against the slots just made in the walls 8. Insertion of the shaft should be performed carefully in order not to split the bone.

The described method of installation of the shaft activate the ossification of the bone inside the free spaces of the slots 4, which form the newly formed zones 3 and 5 with the locking effect with respect to the shaft 1 and the implant, for which the shaft 1 is a supporting element.

REFERENCES

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  • 2. Shuler, M. S., Rooks, M. D., Roberson, J. R., Porous tantalum implant in early osteonecrosis of the hip: preliminary report on operative, survival, and outcomes results. J Arthroplasty, 2007. 22(1): p. 26-31.
  • 3. Nakamura, S., Kusuzaki, K., Murata, H., Takeshita, H., Hirata, M., Hashigushi, S., Hirasawa, Y., Bone reaction induced by femoral stem of titanium alloy endoprosthesis for malignant bone tumors at the distal femur. Oncol Rep, 2001. 8(4): p. 877-81.
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  • 9. Gundlapalli, R., Goldstein, W., Marcoccio, D., Mccue, D., Method and apparatus for surgically preparing a tibia for implantation of a prosthetic implant component which has an offset stem, in U.S. Pat. No. 7,001,394 2006: U.S. Pat. No. 7,001,394.
  • 10. Griss, P., Hip joint implant. 1989: U.S. Pat. No. 4,828,566
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  • 12. Salter, R. B., Textbook of disorders and injuries of the musculoskeletal system: an introduction to orthopaedics, fractures, and joint injuries, rheumatology, metabolic bone disease, and rehabilitation. 3rd ed. 1999, Baltimore: Williams & Wilkins. xxxiv, 687 p.
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  • 15. Ilizarov, G. A., The tension-stress effect on the genesis and growth of tissues. Part I. The influence of stability of fixation and soft-tissue preservation. Clin Orthop, 1989(238): p. 249-81.
  • 16. Malik, Z. U., Hanif, M. S., Safdar, A., Masood, T., Planned external fixation to locked intramedullary nailing conversion for open fractures of shaft of femur and tibia. J Coll Physicians Surg Pak, 2005. 15(3): p. 133-6.