Modular acetabular reinforcement system

Abstract: A modular acetabular reinforcement system includes a substantially cup-shaped reinforcement body having a peripheral flange portion. One or more fixation wings, of various sizes and shapes, are selectively and separately attachable to the flange portion of the reinforcement body. The system is mountable within the acetabulum of a patient to reinforce the acetabulum and to serve as a platform for other prosthesis components such as an acetabular shell.

Description: BACKGROUND OF THE INVENTION The invention relates to implantable prostheses, and more particularly to components of hip joint prostheses. The hip joint is a ball-and-socket type joint in which the ball-shaped femoral head is engaged with and articulates with a cup-shaped socket known as the acetabulum. Injury and/or disease may damage the hip joint to the extent that it must be replaced by or augmented with a prosthetic joint. Deterioration of the acetabulum, and particularly the cartilage within the acetabulum, requires that a prosthetic acetabular shell be mounted within a prepared area of the acetabulum. The acetabular shell receives and articulates with a prosthetic femoral head which is installed on a proximal portion of a patient's femur. In some instances, degenerative bone conditions deteriorate the acetabulum, and particularly its medial wall, to the extent that the acetabulum does not have the integrity to serve as a mounting platform for a prosthetic acetabular shell. This condition requires a reinforcement prosthesis which is implanted within the acetabulum before the acetabular cup, and at least a portion of which receives the acetabular cup. Such a reinforcement body, sometimes known as a protrusio cage, includes a main body that is at least partially cup-shaped and which includes two or more integral radially extending flanges. The protrusio cage is first stabilized within the acetabulum using bone cement or bone screws. Thereafter, the flanges are joined to the ilium, ischium and pubis to further secure the cage and to distribute forces away from the medial wall of the acetabulum. An exemplary protrusio cage is further described by Oh et al., Clin. Orthopaedics and Related Research, No. 162, pp. 175-184 (1982) and by Schatzker et al., Arch. Orthop. Traum. Surg ., Vol. 103, No. 1, pp. 5-12 (1984). U.S. Patent Nos. 4,437,193 and 4,623,352 also describe exemplary protrusio cages. While known protrusio cages can be useful, they are often difficult to install in an ideal manner due to natural anatomical differences among patients as well as anatomical differences resulting from different disease and/or injury conditions. Because of these anatomical differences, the fixed flanges of known protrusio cages must be manipulated and/or altered, during surgery, to properly install the protrusio cage. Even with such manipulation and alteration, the protrusio cages still may not be optimally implanted within some patients. Accordingly, there is need for protrusio cages, or similar acetabular reinforcement bodies, that can be more easily installed by surgeons during hip arthroplasty procedures to accommodate the varying anatomies of patients. A modular acetabular reinforcement system as set forth in the preamble of claim 1 is disclosed in EP-A-605 368. BRIEF SUMMARY OF THE INVENTION The invention provides a modular reinforcement system which can be used to augment structural weaknesses of the acetabulum caused by degenerative conditions. The reinforcement system serves as a platform upon which known hip prosthesis components, such as an acetabular shell, can be mounted. According to the invention, there is provided a modular acetabular reinforcement system as set forth in claim 1. Preferred features are set out in the dependent claims. The system includes one or more fixation wings, and the fixation wings can be provided in different sizes and shapes. The reinforcement system of the invention can be utilized by first preparing the acetabulum and then inserting the reinforcement body within the acetabulum in an appropriate position and orientation as required by the patient's anatomy. The initial fixation or stabilization of the reinforcement body within the acetabulum can be effected using bone screws or bone cement. The surgeon then selects from among a variety of differently sized and shaped fixation wings, depending on the anatomy and bone condition of a given patient, so that one or more suitable fixation wings is selected. The first end thereof is attached to the flange portion of the reinforcement body through an appropriate fixation technique. Any necessary manipulation or alteration of the fixation wing can be effected, and the second end of the fixation wing is then affixed to bone within the pelvic area of the patient. In most instances the second ends of the fixation wings are attached to the ilium and ischium and the pubis of the patient in order to properly secure the reinforcement body and to create desirable force transfer away from the medial wall of the acetabulum. It is understood that the steps noted above are intended to be exemplary and that surgeons may well deviate from the procedure noted above. For example, it may be desirable to assemble the fixation wings prior to placing the reinforcement body. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of an acetabulum reinforcement system constructed according to the present invention. Figure 2 is an exploded view of the modular acetabular reinforcement system of Figure 1. Figure 3 is a perspective view of an alternative embodiment of a modular acetabular reinforcement system according to the present invention. Figures 4A - 4D illustrate various designs of fixation wings useful with the system of the present invention. Figure 5 is a sectional view of an acetabulum having mounted therein a reinforcement system according to the present invention. Figure 6 is a front view of a modular acetabular system of the invention mounted within the acetabulum. Figure 7 illustrates an exemplary rivet connection that is utilized to join a fixation wing to the reinforcement body. DETAILED DESCRIPTION OF THE INVENTION Referring to Figures 1-3, the acetabular reinforcement system 10 of the invention includes a reinforcement body 12, which is substantially cup-shaped. The body 12 has dome 14 and rim 16 ends, and a peripheral flange portion 18 is formed as a part of the rim end. One or more fixation wings 20 are selectively and separately attachable to flange portion 18. In one embodiment, fixation elements 22, such as screws or rivets and the like, can be used to secure the fixation wings 20 to the flange portion 18. The reinforcement body, as illustrated in Figures 1-3. may have an open dome end 14, represented by apical hole 24. Alternatively, as illustrated in Figure 5, the dome end 14 may be closed to form a roof-like structure 13 for the reinforcement body. The rim end 16 must be open and should be of suitable dimensions to receive an acetabular shell (not shown) of known structure. The structure sidewall 26 of reinforcement body 12 preferably is at least partially dome-shaped such that the nominal diameter (D 1 ) of the opening at rim end 16 is greater than the nominal diameter (D 2 ) of the opening at the dome end 14. Structural sidewalls 26 preferably include countersinks 28 which can accommodate bone screws or, alternatively, encourage bone-growth. Flange 18 can be formed in a continuous manner (not illustrated) about the perimeter of the rim end of the reinforcement body 12. As illustrated in Figures 1-3, flange 18 preferably is discontinuous. Figures 1 and 2 illustrate a reinforcement body in which flange 18 includes superior-lateral flange 30 and a smaller, inferior-medial flange 32. Figure 3 illustrates a reinforcement body in which flange 18 includes superior-lateral flange 30 and an inferior-medial flange tab 34. The flange 18 includes holes 36 that can assist in affixing the fixation wings to the reinforcement body. The fixation wings 20 include a first end 38 and an opposed second end 40. Fixation holes 42 are formed on the first end 38 of the fixation wings 20. Holes 42 should be of a size and shape such that they are suitable to cooperate with holes 36 disposed in flange portion 18. Fixation elements 22, such as screws, rivets, and the like, can be inserted through holes 36 and 42 to selectively join fixation wings 20 to the reinforcement body 12. The body portion 44 of the fixation wing preferably includes one or more countersinks 29 that can be used to seat bone screws 46 to secure the fixation wings 20 to portions of bones within the pelvis of a patient. A variety of fixation techniques can be used to selectively join fixation wings 20 to reinforcement body 12. For example, the fixation elements 22 can be such that they include a combination of nuts and bolts that firmly and selectively secure the fixation wings to the reinforcement body. Alternatively, a crimping tool (not shown) can be used to deform the interfacing portions of the fixation wings 20 and the flange portion 18 in order to create an interlocking mechanical engagement of these elements. Figure 2 illustrates an embodiment in which the fixation elements 22 are rivets 23. Rivet 23a is an unassembled, unactuated rivet including mandrel portion 25. Adjacent rivet 23a is rivet 23b which is assembled within the fixation wing, but which is not actuated. Figure 2 also illustrates rivet 23c which is assembled and actuated within a hole 42 of fixation wing 20. Rivet 23d is an example of an actuated rivet exploded from hole 42. Figure 7 illustrates a rivet connection in which rivet components 48 and 50 cooperate to secure the flange 18 and the fixation wing 20 to each other. Although Figures 1 and 2 illustrate the use of two fixation elements to secure each fixation wing 20 to flange 18, it is understood that it may be desirable to use only one fixation element to enable pivotal movement of the fixation wing with respect to the reinforcement body to accommodate anatomical differences among patients. Alternatively, more than two fixation elements can be used to secure a single fixation wing to flange 18. Figures 4A-4D illustrate various shapes in which fixation wing 20 can be created. Figure 4A illustrates a substantially rectangular fixation wing 52, and 4B illustrates a substantially wedge shaped fixation wing 54. Figure 4C illustrates an L-shaped fixation wing 56 in which the first end 38 is part of the body 53 of the fixation wing and the second end 40 is formed on the leg 55 of the L-shaped device. Figure 4D illustrates a T-shaped fixation wing 58 in wnich the first end 38 is part of the leg 57 of the T-shaped device and the second end 40 is part of the head 59 of the T-shaped device. It is understood that various alternative designs can be utilized for fixation wings. Figures 1 and 2 illustrate a reverse wedge design for a fixation wing in which first end 38 is slightly wider than second end 40. Figure 3 illustrates another embodiment of the reinforcement system 10 of the invention. As shown, reinforcement body 12 includes a peripheral flange 30 and a hook flange 34. Peripheral flange 30 and hook flange 34 each include holes 36. In addition, the structural sidewalls 26 of the reinforcement body 12 include countersinks 28. Figure 3 also illustrates the joinder of fixation wings 54 and 58 to peripheral flange 30. Although not illustrated, it is understood that if desired, an additional fixation wing, of a desired size and shape, may be affixed to hook flange tab 34. As illustrated in Figure 5, a reinforcement body 12, having a closed dome end 13 is mounted within the acetabulum 15. A bone screw 46 initially secures the reinforcement body within the acetabulum. Fixation wings 20 are joined to the flange portion 18 of the reinforcement body and are affixed to the ilium 60 and pubis 62 through bone screws 46. Figure 6 further illustrates a reinforcement body 12 mounted within the acetabulum. As shown, fixation wing 54 is affixed to peripheral flange 30, and bone screws 46 secure the peripheral flange to the ilium 60. As illustrated fixation wing 56 is secured to hook flange 34 and fixation wing 56 is secured to the pubis 62 by bone screw 46. The reinforcement system of the invention preferably is made of a biocompatible metallic material. The reinforcement body 12, fixation wings 20 and fixation elements 22 preferably are made of a soft, malleable metal that enables a surgeon to manipulate these components during surgery, if necessary, to properly conform them to a patient's anatomy. One exemplary material includes commercially pure titanium metal. Alternatively, fixation elements 22, like bone screws 46 and rivets 23, can be made of known biologically compatible metals or metal alloys including titanium alloys, cobalt-chromium alloys and stainless steel. The use of the reinforcement system of the invention will be readily apparent to one having ordinary skill in the art. Briefly, however, the patient's acetabulum is prepared in a known manner, and the reinforcement body 12 is positioned therein in a desired orientation. The reinforcement body can be initially secured or stabilized within the acetabulum through the use of one or more bone screws or bone cement. If necessary, the flange portion, as well as other portions of reinforcement body 12 can be manipulated (i.e., deformed) to achieve a desired fit or position with respect to the patient's anatomy. The surgeon can then select the appropriate size and shape of fixation wing to be used, as well as the dimensions of the fixation wing. The fixation wings can then be secured to the reinforcement body in desired locations of flange portion 18 through the appropriate fastening technique. Any manipulation of the fixation wings to achieve appropriate fit can be accomplished by deforming or altering (i.e., cutting) the fixation wings, and the fixation wings are then secured to desired areas of the pelvis through one or more bone screws. The fixation wings can vary in size as required by a patient's anatomy. Generally, the fixation wings have a length of about 20 to 70 mm and a width of about 10 to 70 mm. One of ordinary skill in the art can readily determine the appropriate dimensions to be assumed by the fixation wings. It will be apparent to those of ordinary skill in the art that an important advantage of the invention is that the reinforcement system provides added flexibility to a surgeon. The surgeon can select from among a variety of fixation wings, having different sizes and shapes, and mount these fixation wings at an appropriate location on the reinforcement body. Variations in the surgical technique used to implant the reinforcement body of the invention are anticipated as well. It is understood that various modifications may be made to the invention without departing from the scope thereof.

Claims: A modular acetabular reinforcement system (10) comprising: a reinforcement body (12) having dome (13; 14) and rim (16) ends, and at least one peripheral flange portion (18) extending along at least a portion of a perimeter of the rim end, each of the at least one flange portions including a plurality of holes (36); at least one separately attachable fixation wing (20; 52; 54; 56; 58), each of the at least one fixation wings having a first end (38) attachable to the reinforcement body and an opposed, second end (40), the first end including one or more holes (42) suitable for cooperation with the flange holes (36); at least one bone fixation hole (29) disposed in the fixation wing; and means for affixing the first end of the fixation wing to the flange portion, characterised in that the means for affixing comprises an element (22) for insertion in a selected flange hole (36) and a corresponding wing hole (42) such that the fixation wing (20; 52; 54; 56; 58) is selectively attachable to the flange portion (18) in a desired location and in a desired orientation at said location. The system of claim 1 wherein the at least one fixation element (22) comprises a rivet (23). The system of claim 1, wherein the at least one fixation element (22) comprises a threaded element. The system of claim 1, 2 or 3 wherein the reinforcement body (12) includes an outer, bone-engaging surface and an opposed inner surface, the outer bone-engaging surface being adapted to mount within the natural acetabulum (15) of a patient. The system of any preceding claim wherein the rim (16) and dome (14) ends are each open. The system of any preceding claim wherein the rim end (16) has a diameter (D 1 ) that is greater than the dome end (13; 14, D 2 ). The system of any preceding claim wherein at least one bone fixation hole (28) is disposed in the reinforcement body (12). The system of claim 7 wherein the bone fixation holes (28) are screw holes. The system of claim 8 further comprising one or more fixation elements (46) effective to affix the reinforcement body within the acetabulum (15). The system of any preceding claim wherein a plurality of bone fixation holes (29) are disposed along the length of the or each fixation wing (20; 52; 54; 56; 58), the bone fixation holes being effective to assist in securing the fixation wing to pelvic bone (60, 62). The system of claim 10 further comprising a plurality of bone screws (46) which, in cooperation with the bone fixation holes (29), secure the fixation wing (20; 52; 54; 56; 58) to pelvic bone (60, 62). The system of any preceding claim wherein the or each fixation wing (54) is of a wedge-like structure in which the first end (38) is narrower than the second end (40). The system of any one of claims 1-11 wherein the or each fixation wing (56) is substantially L-shaped such that the second end (40) includes a segment (55) that extends substantially orthogonally to the first end (38). The system of any one of claims 1-11 wherein the or each fixation wing (58) is substantially T-shaped, wherein a leg portion (57) represents the first end (38) and a head portion (59) represents the second end (40). The system of any one of claims 1-11 wherein the or each fixation wing (52) is rectangular. The system of any preceding claim wherein the length of the or each fixation wing (20; 52; 54; 56; 58) is in the range of about 20 to 70 mm. The system of any preceding claim wherein the flange portion (18) is discontinuous. The system of any preceding claim wherein the reinforcement body (12) is substantially cup-like, the dome (13; 14) end being mountable within a patient's acetabulum (15) and the opposed rim (16) end being mountable adjacent a lip of the acetabulum.

Inventors: CORNELL ALAN, GROSS ALLAN E, REVIE IAN, SANDERS ANTHONY P, CORNELL, ALAN, GROSS, ALLAN E., REVIE, IAN, SANDERS, ANTHONY P.
Applicants: DEPUY PRODUCTS INC, DEPUY PRODUCTS, INC.
Application year: 1997
Main classification: A61F2
IPC codes: A61F2, A61B17