Composite shoulder prosthesis

Abstract

The invention is a modular composite shoulder prosthesis 64, whose construct incorporates a solid autogenous bone graft 50 to be used to replace the upper humerus in certain fracture types. The prosthesis comprises a stem 22 to be inserted in the canal of the humerus, an intermediary part reduced to a medial pillar 24 and a head which is a generally spherical cap 20 that is hollow. The head of the prosthesis being hollow and coated with an osteoconductive material, the lateral aspect of the medial pillar as well as the upper part of the stem being also coated with the same material, an epiphyso-metaphyseal space is delineated in which a solid autogenous bone graft is fitted. Union can be achieved between the coated parts of the prosthesis, the bone graft 50 and the tuberosities reattached to the humerus shaft, secured to holes 62 of the medial pillar and between themselves.

Description

FEDERALLY SPONSORED RESEARCH

[0002] Not applicable

SEQUENCE LISTING OR PROGRAM

[0003] Not applicable

BACKGROUND OF THE INVENTION

[0004] Replacement of diseased or injured joints is common practice in orthopedic surgery. The replacement of a shoulder joint either for arthritic disease or for fracture by an artificial device can restore function in many cases.

[0005] Shoulder prostheses can be implanted in the presence of the so-called “four part humeral fractures”. In those fractures of the proximal part of the humerus, the humeral head, the greater tuberosity and the lesser tuberosity separate from the humeral shaft. This results in the four parts fractures described by Neer. In such cases, it is common practice to use shoulder prosthesis to reconstruct the proximal part of the humerus. However, if replacing the humeral head is relatively easy, reattaching the tuberosities often results in failure of those parts to unite to the rest of the humerus or in their union in an inappropriate position. Bad functional outcome of shoulder replacement for fracture seems to be directly correlated to this phenomenon. A number of prosthesis have been described and used to solve the problem. Among others, see for instance U.S. Pat. No. 6,171,341 and No. 5,944,758, No. 6,283,999. In those devices there are various means to keep the tuberosities in position until union. The U.S. Pat. No. 6,334,874 B1, like U.S. Pat. No. 3,228,393 for a femur prosthesis, has a metaphyseal portion with window in which a bone graft can be inserted and U.S. Pat. No. 6,171,341 has a metaphyseal portion comprising only a medial branch thereby having an area in which a bone graft can be used. In those two devices a better contact between the fractured fragments is sought. However, in the prior art, the stability of the fragments necessary to fracture healing and the provision of abundant biological material necessary to induce the union of the bony fragments are not simultaneously provided.

[0006] In another aspect of shoulder prosthesis designing relevant to the present invention, US Pat. No. 6,368,352, in order to diminish the weight of the implant, has a closed space defined between the collar and the modular head in an assembled configuration while DE patent No 4220217 has a head which is a cap with a central shaft and an inner surface with open cell or a porous structure.

[0007] In the present invention, the space of the hollow head is completely open in order to accommodate bone grafts.

[0008] The object of the invention is to restore shoulder function after three or four parts humeral fractures by providing an improved prosthesis to bring about the union of the separated tuberosities to the upper humerus while replacing the broken humeral head. To do so a modular composite shoulder prosthesis is described whose construct incorporates a solid autogenous bone graft. The prosthesis comprises a stem to be inserted in the medullary canal of the humerus, an intermediary part with a number of holes and a head that is hollow. The head of the prosthesis being a hollow spherical cap with an inner lining of an osteoconductive material, the lateral aspect of the medial pillar as well as the upper part of the stem being also coated with the same material, a large epiphyso-metaphyseal space is created in which a solid autogenous bone graft usually from the iliac crest can be impacted. Union can be achieved between the prosthesis and the autogenous iliac bone graft on one side and between the iliac bone graft, the tuberosities reattached to the humerus shaft, to the intermediary portion and between themselves by multiple sutures and/or wires. The bone graft is considered as a part of the prosthesis both from a mechanical and from a biological perspective.

[0009] This composite shoulder prosthesis results in the following:

[0010] 1. a structure formed by the cap, the ring, the medial pillar and the stem, that provides a smooth spherical surface together with mechanical support and stability;

[0011] 2. an osteoconductive coating that provides a framework amenable to the ingrowth of blood vessels and osteoprogenitor, type of bone cell consisting of undifferentiated cells from which the osteoblasts, the bone-forming cells, are derived;

[0012] 3. osteoinductive factors brought by the iliac graft for the induction or the modulation of bone formation;

[0013] 4. osteogenic cells, graft cells from the iliac bone graft that can differentiate into osteoblasts.

[0014] Accordingly, the mechanical and biological conditions to facilitate the union process between those humeral tuberosities, the composite prosthesis, and the remainder of the humerus are optimally set.

[0015] In certain cases in which the harvesting of the iliac bone graft is considered of an excessive morbidity, the prosthesis is also provided with a scaffold of an osteoconductive material, scaffold in which bone chips from the broken humeral head can be positioned for bone induction.

BRIEF SUMMARY OF THE INVENTION

[0016] This invention relates to a shoulder prosthesis for upper humeral fractures that comprises a stem part to be fixed in the medullary canal of the upper humerus. The stem is extended upwards by a medial pillar on which is attached at an angle a ring. This ring has on its upper, lower and inner aspects a lining of an osteoconductive material. On the ring is fixed a modular hollow head whose cavity also has an inner lining made of an osteoconductive material.

[0017] This construct delineate an open epiphyso-metaphyseal space in which an iliac bone graft is impacted while bone chips from the broken humeral head are used to complete the filling of the head of the prosthesis. The result achieved is a composite shoulder prosthesis whose lateral part is made of autologous graft on which the tuberosities can be fixed in a bone to bone full contact fashion.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0018] Notes:

[0019] 1. Positional references such as anterior/posterior, medial/lateral, proximal/distal and upper/lower used herein are made with reference to the prosthesis as it would be positioned in a left shoulder.

[0020] 2. Details of design, manufacture and procedure may be modified without departing from the spirit, intent and scope of the invention described herein.

[0021] Embodiments of the invention are described in more detail in the next section using the drawings. There are shown in:

[0022] FIG. 1: a front elevational view of the shoulder prosthesis

[0023] FIG. 2: a right elevational view of the prosthesis showing the inside of the head and of the ring as well as the coating of the medial pillar.

[0024] FIG. 3: a left elevational view of the prosthesis showing the medial aspect of the head and of the medial pillar.

[0025] FIG. 4-A: a front elevational view of the shoulder prosthesis showing the various parts of the prosthesis.

[0026] FIG. 4-B: a cross sectional view of the medial pillar.

[0027] FIG. 5: a perspective view of the prosthesis showing the upper aspect and the inside of the ring.

[0028] FIG. 6: a sectional view of the head and ring of the prosthesis, showing the inside of the head and of the ring.

[0029] FIG. 7: a front elevational view of the prosthesis fitted with a bone graft.

[0030] FIG. 8-A: a sectional view of the empty proximal part of the prosthesis.

[0031] FIG. 8-B: a sectional view of the proximal part of the prosthesis after positioning the graft and the bone chips.

[0032] FIG. 9: a sectional view of the proximal part of the prosthesis showing the filling of the head, the bone graft, and the tuberosities in position.

[0033] FIG. 10: a front elevational view of the prosthesis fitted with a scaffold of osteoconductive material.

DETAILED DESCRIPTION OF THE INVENTION

[0034] FIG. 1 shows the shoulder prosthesis 64 according to the invention. It is made of a head, which is a generally spherical cap 20 and a stem 22 with a medial pillar 24 with on its lateral aspect a coating of a material 26 that allows for bone ingrowth and holes 62 to attach an iliac bone graft and the tuberosities.

[0035] The stem 22, on its most upper part 28, is coated with a material that allows for bone ingrowth and its lower part 30 is made of metal to allow cementation. It has longitudinal grooves 32 to facilitate cementation.

[0036] FIG. 2 is a right elevational view of the prosthesis 64 showing the inner lining 34 of the spherical cap 20, the inner lining 36 of the ring 38, of the medial pillar 26, the coating of the upper part 28 of the stem 22 and its slightly hollow coated superior aspect 46.

[0037] FIG. 3 is a left elevational view of the prosthesis 64 showing the medial aspect of the spherical cap 20 and of the medial pillar 24.

[0038] FIG. 4-A shows parts of the prosthesis 64:

[0039] the spherical cap 20 which is the head of the prosthesis 64 and its inner lining 34,

[0040] the ring 38 on which the head 20 is to be attached,

[0041] the lining on the upper 42 and lower 44 surface of the ring.

[0042] FIG. 4-B is a cross-section of the medial pillar 24 along a 48-48 line of FIG. 4-A showing that its is an arc of a circle with on its lateral aspect a coating of a material 26 that allows for bone ingrowth;

[0043] FIG. 5 is a perspective view of the prosthesis 64 according to the invention. The coating of the ring 38 is visible on its upper 42 and inner 36 aspects. The superior aspect 46 of the stem 22 is slightly hollow with a coating of a material that allows for bone ingrowth.

[0044] FIG. 6 shows a sagittal sectional view of the spherical cap 20 and of the ring 38 along the 40-40 line of FIG. 3 showing the inner lining 34 of the cap and the inner lining 36 of the ring.

[0045] FIG. 7 shows the prosthesis 64 ready for implantation with a solid bone graft 50 fitted in the epiphyso-metaphyseal space delineated by the hollow cap 20, the lateral aspect of the medial pillar 24 and the superior aspect of the stem 46.

[0046] FIG. 8-A shows a sagittal sectional view along the 40-40 line of FIG. 3 of the upper part of the prosthesis 64 showing the epiphyso-metaphyseal space 18 extending from the spherical cap 20 to the upper part of the stem 46.

[0047] FIG. 8-B shows a sagittal sectional view along the 40-40 line of FIG. 3 of the upper part of the prosthesis 64, with a solid bone graft 50 being fitted in and the spherical cap 20 filled with bone chips 52 and the continuity of bone from the head 20 to the upper part of the stem 46.

[0048] FIG. 9: a transaxial section of the spherical cap 20, along the 54-54 line of FIG. 7, showing the positioning of the greater tuberosity 56 and of the lesser tuberosity 58 with respect to the bone graft 50 and the bone chips 52 filling the head.

[0049] FIG. 10 shows the prosthesis 64 ready for implantation with a scaffold of osteoconductive material 60.

Drawing Reference Numerals Worksheet

[0050] Part Name Number

[0051] PROSTHESIS 64

[0052] EPIPHYSO-METAPHYSEAL SPACE 18

[0053] MODULAR CAP 20

[0054] STEM 22

[0055] MEDIAL PILLAR 24

[0056] COATING OF PILLAR 26

[0057] UPPER STEM 28

[0058] LOWER STEM 30

[0059] LONGITUDINAL GROOVE 32

[0060] COATING OF CAP 34

[0061] LINING INNER RING 36

[0062] RING 38

[0063] SECTIONAL LINE FIG. 340-40

[0064] COATING UPPER RING 42

[0065] COATING LOWER RING 44

[0066] SUPERIOR ASPECT STEM 46

[0067] SECTIONAL LINE FIG. 448-48

[0068] ILIAC GRAFT 50

[0069] BONE CHIPS 52

[0070] SECTIONAL LINE FIG. 754-54

[0071] GREATER TUBEROSITY 56

[0072] LESSER TUBEROSITY 58

[0073] SCAFFOLD 60

[0074] HOLES 62

Claims

1) A prosthesis for the upper humeral fractures comprising a. a stem to be inserted in the medullary canal of the upper humerus; b. an intermediary section which is the upward extension of the stem; said intermediary section being limited to a medial pillar when viewed from the front c. a ring fixed at an angle to said medial pillar d. a modular generally spherical cap, which is the head of the prosthesis, attachable to said ring; e. an epiphyso-metaphyseal space with on its medial, superior and inferior boundaries a coating of an osteoconductive material.

2) Said stem of the shoulder prosthesis of claim 1 comprising two slightly tapered longitudinal grooves means to facilitate efficient cementation and having on its most upper part a coating of osteoconductive material, that is, a material conductive to bone ingrowth;

3) Said most upper part of the stem of claim 2 being free of cement;

4) In an alternative embodiment, said stem being provided for cement-less fit within the medullary canal of the humerus.

5) Said medial pillar of said shoulder prosthesis of claim 1 being curved, its concavity, which is its medial aspect, being smooth and polished; having a lining of an osteoconductive material on its convexity, which is its lateral aspect and a C-shaped cross-section that ensures more resistance to bending stresses, and a plurality of holes means of fixation.

6) Said ring attached to the medial pillar of the shoulder prosthesis of claim 1 having its upper, lower and inner surfaces coated with an osteoconductive material and an outer surface without coating.

7) Said modular spherical cap of the shoulder prosthesis of claim 1 being hollow with a polished outer surface, being attachable to the ring and having an inner coating of an osteoconductive material.

8) A construct such that after the modular spherical cap of claim 7 is attached on the ring of claim 6, there is a continuity of the osteoconductive inner lining of said ring and said modular head.

9) Whereby delineating between the upper aspect of the stem, the lateral aspect of the medial pillar and the inside of the spherical cap, said epiphyso-metaphyseal space coated with an osteoconductive material that can accommodate a solid autogenous bone graft.

10) A method of treating a fracture of the upper humerus with a separation of the humeral head and of the tuberosities comprising a plurality of steps: a. harvesting an autogenous iliac bone graft; b. removing a broken humeral head; c. filling with said iliac bone graft and chips from said broken humeral head the space coated with an osteoconductive material of the shoulder prosthesis of claim 1;d. inserting and cementing said shoulder prosthesis e. attaching separated segments of the broken upper part of the humerus called tuberosities, to the remainder of the humerus, to said shoulder prosthesis and between themselves, additional means being used through a plurality of holes of the medial pillar to provide optimum stability to the construct.

11. Whereby achieving a composite shoulder prosthesis with a smooth surfaced spherical cap on the medial side and an area of autogenous bone on the lateral, anterior and posterior sides to which the tuberosities can unite.

12. According to the method of claim 10, considering the potential morbidity of iliac bone graft harvesting, the composite shoulder prosthesis of claim 11 may alternatively be provided with a metaphyseal scaffold of material conductive to bone ingrowth as a substitute for the autologous iliac bone graft. In said scaffold, bone chips from the broken humeral head can be positioned for osteoinduction.