SURGICAL IMPLANT FOR SUPPORTING A PROSTHETIC DEVICE

Abstract

A surgical implant for supporting a prosthetic device at a distal end of an amputated limb, including:

a cup having a base and surrounding side wall for defining therein a volume for accommodating a terminal end of a bone of the amputated limb;

a central intramedullary stem extending from the cup base for insertion into a medullary cavity of the bone;

a plurality of extramedullary struts extending from the side wall generally parallel to the central intramedullary stem and locatable in contact with or in a closely adjacent relation with an outer surface of the bone; and

an attachment member extending from an outer face of the cup base.

Claims

1. A surgical implant for supporting a prosthetic device at a distal end of an amputated limb, including: a cup having a base and surrounding side wall for defining therein a volume for accommodating a terminal end of a bone of the amputated limb; a central intramedullary stem extending from the cup base for insertion into a medullary cavity of the bone; a plurality of extramedullary struts extending from the side wall generally parallel to the central intramedullary stem and locatable in contact with or in a closely adjacent relation with an outer surface of the bone; and an attachment member extending from an outer face of the cup base.

2. A surgical implant according to claim 1, wherein the dimension and shape of the intramedullary stem is selected to minimise stress shielding of the bone.

3. A surgical implant according to claim 1, wherein the intramedullary stem is tapered.

4. A surgical implant according to claim 1, wherein the intramedullary stem is joined to the cup base through a generally frustoconical section.

5. A surgical implant according to claim 1, wherein the dimension and shape of each extramedullary strut is selected to stabilise the implant when fitted and to minimise stress shielding of the bone.

6. A surgical implant according to any claim 1, wherein each extramedullary strut has a curved profile closely corresponding to the bone outer surface.

7. A surgical implant according to claim 6, wherein each extramedullary strut has a peripheral edge that tapers from the cup wall.

8. A surgical implant according to claim 7, wherein each extramedullary strut tapers to a rounded lip thereof.

9. A surgical implant according to claim 1, wherein the attachment member is a prosthesis stem.

10. A surgical implant according to claim 1, further including a coating agent to facilitate osseointegration between the implant and the bone.

11. A surgical implant according to claim 10, wherein the coating agent is hydroxyapatite.

12. A surgical implant according to claim 1, further including olive wires passing through and extending between opposing extramedullary struts when the implant is fitted.

13. A surgical implant according to claim 1, including a surface coating on an outer surface of the implant to encourage skin growth of the amputated limb into the outer surface surrounding the attachment member.

14. A method of surgically fitting a surgical implant to an amputated limb according to claim 1, including: press fitting the implant to the terminal end of the bone of the amputated limb by inserting the intramedullary stem into the medullary cavity of the bone such that the terminal end of the bone is accommodated within the cup, and the extramedullary struts extend in contact with or in a closely adjacent relation with the outer surface of the bone.

15. A method according to claim 14, including passing olive wires through and between opposing extramedullary struts and through the bone to reinforce the extramedullary struts.

16. A method according to claim 14 when appended to claim 13, further including thinning a soft tissue flap of the amputated limb surrounding the attachment member of the implant when fitted, and pressing said soft tissue flap against the outer surface of the implant surrounding the attachment member to encourage skin growth into said outer surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] It will be convenient to further describe the invention with respect to the accompanying drawings which illustrate a preferred embodiment of the surgical implant of the present invention. Other embodiments of the invention are possible, and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

[0028] In the drawings:

[0029] FIG. 1 is a perspective view of a surgical implant for supporting a prosthetic device at a distal end of an amputated limb according to the present invention;

[0030] FIG. 2 is a cross-sectional view of the surgical implant of FIG. 1; and

[0031] FIG. 3 is a photographic image of a bone model upon which has been fitted with the surgical implant of FIG. 1.

DETAILED DESCRIPTION

[0032] The surgical implant according to the present invention needs to be custom made to suit the amputee. This therefore requires the partially amputated limb to be imaged using imaging equipment such as a CT scan or an MRI scan. Once a 3D scan of the amputated limb has been generated, the surgical implant can be modified to conform to the specific geometry of the amputated limb.

[0033] The surgical implant 1 includes a cup 3 having a base 4 and a surrounding side wall 7. The cup 3 defines a volume 5 adapted to accommodate a terminal end of a bone 2 of the amputated limb.

[0034] Extending from the cup base 4 and through the accommodating volume 5 is a central intramedullary stem 8. The intramedullary stem 8 includes a frustoconical base portion 9 extending from the base 4 and a tapered upper portion 10. The accommodating volume 5 is shaped to closely accommodate the terminal end of the bone 2. The tapered shape of the stem 8 helps to minimise shielding of the loading applied to the bone that can lead to bone atrophy. Also, the frustoconical base portion 9 can act to compact the cancellous bone (i.e. marrow), helping to get better initial stability of the implant 1 when first fitted. This also helps to achieve osseointegration of the implant 1 to the bone 2.

[0035] Extending from the cup side wall 7 are a plurality of extramedullary struts 11. While four struts 11 are shown in the drawings, it is to be appreciated that the invention is not limited to this number. The extramedullary struts 11 extend generally parallel to the intramedullary stem 8. When the implant 1 is fully press-fitted onto the bone 2, the extramedullary struts 11 will be in contact with or in a closely adjacent relationship with an outer surface of the bone 2. Each extramedullary strut 11 therefore has a curved inner profile 17 to facilitate the in contact or closely adjacent relation with the bone 2. Each extramedullary strut 11 may have a peripheral edge 18 that tapers from the side wall 7 to a rounded tip 19.

[0036] It is envisaged that the extramedullary struts 11 be reinforced using olive wires (not shown). An olive wire has small beads called olives therealong. Olive wires may pass through and between the extramedullary struts 11 and through the bone 2 encompassed by the struts 11. Tension on the olive wire will pull the olive and the struts 11 against the bone 2. The olive wires, once inserted and tensioned in opposite directions can produce compression on the bone 2.

[0037] On the opposing side of the cup 3 is provided an engagement member in the form of a prosthesis stem 15. A prosthetic device can then be attached to the prosthesis stem 15 using known methods.

[0038] The dimensions and shape of the central intramedullary stem 8 and the extramedullary struts 11 may vary depending on the configuration of the bone 2 at its terminal end. This will vary due to the type of limb that has been amputated, and the location of the amputation along the bone. The geometry of the intramedullary stem 8 and the extramedullary struts 11 may therefore be determined to suit the location of the bone terminal end, and to reduce the stress shielding of the bone 2. This may be achieved by ensuring that the intramedullary stem 8 is located away from the walls of the medullary cavity so that the bone 2 is not shielded from loading leading to stress shielding. Otherwise, bone atrophy can occur due to the load carried by the bone being reduced or eliminated.

[0039] The dimension and shape of each extramedullary strut 11 are also selected to ensure stability of the implant 1, once fitted. This will depend on factors including the length of the bone and its geometry at the terminal end thereof. As well as providing sufficient strength for the implant 1, the struts 11 are also shaped to minimise stress shielding of the bone 2.

[0040] The implant 1 can be produced using a variety of different materials and may use manufacturing processes such as 3D printing or CNC machining depending on the material being used. The implant 1 may be coated with an agent to facilitate osseointegration between the implant 1 and the bone 2. The implant 1 can for example be coated with hydroxyapatite. The use of other coating agents is however also envisaged.

[0041] The present invention also proposes a means to prevent ongoing skin irritation and low grade infection through a foreign body reaction on the skin implant interface. Current implants use a concept where the implant has a polished surface which sticks through the soft issues and skin. This creates an ongoing open wound which increases temperature and a skin irritation and possible infection which needs day to day wound care and cleaning to avoid infection. This contributes to a lot of those devices failing and getting loose.

[0042] The present invention proposes to thin out the soft tissue flap where the implant leaves the skin and to use a surface coating on an outer surface of the implant 1, in particular surround the prosthesis stem 15, to allow the skin to grow into the implant surface and allow wound healing without creating an open wound. It creates an interface similar to that around an antler or horns in a cow.

[0043] It is to be appreciated that the implant 1, once press fitted, can be used immediately. This is because the extramedullary struts 11 act to stabilise the implant 1 once installed. It is not necessary to wait for osseointegration of the implant 1 with the bone 2 before use.

[0044] The extramedullary struts 11 according to the present invention therefore facilitates a simple press fit installation of the implant 1, while at the same time limiting the amount of stress shielding exhibited by the bone 2. The extramedullary struts 11, in combination with the central intramedullary stem 8, results in a smaller device which allows for instant loading and limits the amount of stress shielding that occurs.

[0045] Modifications and variations that would be deemed obvious to the person skilled in the art are included within the ambit of the present invention as claimed in the appended claims.