CA2711010C - Monopolar constrained acetabular component - Google Patents
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- CA2711010C CA2711010C CA2711010A CA2711010A CA2711010C CA 2711010 C CA2711010 C CA 2711010C CA 2711010 A CA2711010 A CA 2711010A CA 2711010 A CA2711010 A CA 2711010A CA 2711010 C CA2711010 C CA 2711010C
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- liner
- acetabular
- constraining ring
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Abstract
The present invention provides monopolar acetabular liners (32, 54) that can enclose a femoral head (14) to form a hip replacement prosthesis (30, 50), wherein the liner (32, 54) has a rim (34) that creates an orifice, wherein the orifice has a diameter that is smaller than the diameter of the femoral head (14), and wherein the liner (32, 54) encompasses greater than 50 percent of the volume of the head (14), wherein a constraining ring (56) can be used in conjunction with the monopolar constrained acetabular liner (32, 54) to provide additional support for the femoral head (14) to stay with the acetabular liner (32, 54) and avoid dislocation. Assemblies and complete prosthetic replacements are also provided. Liners (32, 54) and constraining rings (56) having no, one or more recesses (36) also are provided.
Description
' 52701-5D
MONOPOLAR CONSTRAINED ACETABULAR COMPONENT
This application is a divisional of Canadian Patent Application 1 No. 2,416, 256 filed July 19, 2001.
4 The present invention relates to improved acetabular components, such as liners, assemblies and complete replacements, for use in the body. The 6 improved acetabular components can be used, for example, in hip arthroplasties 7 in both a primary and revision setting. The present invention provides a 8 decreased risk of dislocation while facilitating greater range of motion 9 ("ROM").
Description of the Field 12 Dislocation is a major source of morbidity at re-operation after total hip 13 arthroplasty. Dislocation rates have been quoted at 1 - 10% for primary total 14 hip arthroplasties. Many studies have shown increased rates of dislocation after revision total hip arthroplasty when compared with primary total hip 16 arthroplasty. Currently, the chance of "successful surgical management of a 17 recurrent dislocation" is 70% when a cause for the dislocation can be identified.
18 Dislocation results in significant patient anxiety. In addition, the costs 19 associated with surgical management of dislocation are significant.
A variety of approaches have been used to address dislocation, including 21 changing the angle of the femoral component, changing the angle of the 22 acetabular component, using extended lip liners, using off-set liners, advancing =
PCT/US01/22u- _ 1 the greater trochanter, and using constrained acetabular components.
Another 2 approach is to use femoral heads of larger diameter.
MONOPOLAR CONSTRAINED ACETABULAR COMPONENT
This application is a divisional of Canadian Patent Application 1 No. 2,416, 256 filed July 19, 2001.
4 The present invention relates to improved acetabular components, such as liners, assemblies and complete replacements, for use in the body. The 6 improved acetabular components can be used, for example, in hip arthroplasties 7 in both a primary and revision setting. The present invention provides a 8 decreased risk of dislocation while facilitating greater range of motion 9 ("ROM").
Description of the Field 12 Dislocation is a major source of morbidity at re-operation after total hip 13 arthroplasty. Dislocation rates have been quoted at 1 - 10% for primary total 14 hip arthroplasties. Many studies have shown increased rates of dislocation after revision total hip arthroplasty when compared with primary total hip 16 arthroplasty. Currently, the chance of "successful surgical management of a 17 recurrent dislocation" is 70% when a cause for the dislocation can be identified.
18 Dislocation results in significant patient anxiety. In addition, the costs 19 associated with surgical management of dislocation are significant.
A variety of approaches have been used to address dislocation, including 21 changing the angle of the femoral component, changing the angle of the 22 acetabular component, using extended lip liners, using off-set liners, advancing =
PCT/US01/22u- _ 1 the greater trochanter, and using constrained acetabular components.
Another 2 approach is to use femoral heads of larger diameter.
3 Some of these approaches have distinct disadvantages, however.
4 Altering the orientation of the components can increase stability in one direction (for example, posteriorly) but at the same time decrease stability in the 6 opposite direction (for example, anteriorly). Use of extended lip liners and 7 currently available constrained acetabular components which utilize additional 8 polyethylene to surround the femoral head increases joint stability but this 9 additional material also can, depending on the design, constrict the range of motion of the joint and can lead to subsequent problems related to impingement. When the hip joint is articulated (for example, flexed, extended, 12 rotated, etc.) to its limit, impingement between the femoral neck and acetabular 13 liner may occur.
14 Component impingement is undesirable for several reasons. The femoral neck impinging against the polyethylene liner can produce damage to 16 the polyethylene as well as increasing the stresses at the component bone 17 interface. Additionally, the point of impingement acts as the fulcrum through 18 which the force produced by the leg could lever the femoral head out of the 19 liner and hence lead to dislocation.
90 Many current methods of reducing the risk of dislocation, including 21 recurrent dislocation, employ the use of so called "constrained liners,"
which 22 are complex bipolar or tripolar articulations. In a study of twenty one 23 constrained acetabular components to treat preoperative or intraoperative 24 instability, six patients had recurrent dislocations. It was postulated that this increase was caused by the impingement of the femoral stem on the rim of the 26 insert due to decreased range of motion within the design. Orthopaedic 27 Knowledge Update, Chapter 38, page 474 (James H. Beatty, M.D., editor, 28 AAOS).
= = CA 02711010 2010-08-05 , NO 02/09615 PCT/US01/226,.
Constrained systems that are currently available use ultra high molecular weight polyethylene (UHMWPE) which is not crosslinked. A major limitation 3 of the material is it's high wear rate and the risk of periprosthetic osteolysis.
4 Also, their stated range of motion in flexion is between 72 and 900.
Such devices are available from Zimmer, Inc., Johnson & Jolmson/Depuy Inc., and 6 Howrnedica-Osteonics, Inc.
7 The current products have additional limitations. For example, the 8 Osteonics system utilizes only 22, 26 and 28 mm heads. The minimum 9 diameter of the acetabular shell is 50 mm. This design is "bipolar." A
bipolar system is made up of a acetabular shell with a polyethylene liner, and inside of that liner is a metal head. Inside of that metal head is another polyethylene 12 liner, which in turn captures a 22, 26, or 28 mm head that is attached to the 13 femoral stem. Thus, the Osteonics system has multiple polyethylene on metal 14 articulations. The multiple articulations generate polyethylene wear debris at a much faster rate than designs with a single metal on polyethylene articulation.
16 Additionally, the range of motion only is approximately 90 degrees.
constrained system developed by Zimmer, Inc. uses a metal shell with 18 a two-piece polyethylene liner. One piece is inserted into the acetabular metal 19 shell followed by placement of the other portion around the neck on the femoral component before the femoral head has been put on the Morse taper. The head 21 is then reduced into the acetabular component. The polyethylene portion with a 22 metal band that is around the femoral neck is then brought into contact with the 23 acetabular polyethylene component and the metal band then secured to 24 "capture" the head within the assembled polyethylene liner. Again, this design uses ultra high molecular weight polyethylene and can generate significant 26 debris as well as a limited range of motion. The limited range of motion results s WO 02/09615 PCT/US01/22t.-_, 1 in impingement in flexion, which generates a rotational torque at the bone shell 2 interface, potentially inhibiting bony in-growth into the acetabular shell.
3 In the late 1960's to early 1970's, others attempted to implant a 4 cemented conventional UHIVIWPE liner with greater than 50% head coverage.
Lagrange and Letoumel, Int Surg. 60(1):21-4 (1975); Lanzetta, Arch Ortop.
6 83(1):49-53 (1970). These designs had a 35mm inner diameter and was 7 available in only two (47 and 58mm) outer diameters. These approaches, 8 however, did not yield a replacement with acceptable performance. Long-term 9 data is not available for the LaGrange/Letournel design, likely because it did not become a widely-accepted product. Its head design (35 mm diameter) in II conjunction with conventional UHIVIWPE available at the time would have had 12 a substantial wear rate.
13 Thus, current and past designs have utilized various approaches, 14 including countersinks, in which the center of rotation of the femoral head is below the level of the flat surface of the liner. Yet even the use of a 16 countersink design using large head diameters is less than optimal because, 17 among other things, these liners did not have an orifice that was less than the 18 diameter of the femoral head, and therefore have no mechanical capture, and 19 took no other steps to avoid or minimize dislocation.
It has been shown that larger heads are effective in reducing the rate of = 21 recurrent dislocations, even when used with conventional polyethylene.
22 Amstutz et aL, 12th Annual International Symposium for Technology in 23 Arthroplasty, ISTA '99, Chicago, IL (1999). However, hip simulator studies = 24 have shown that the wear of conventional polyethylene with the larger heads is excessive. This disadvantage was demonstrated in vivo by the results of surface 26 replacement as well. Amstutz et al., Clin. Orthop. 213: 92-114 (1986).
In 27 addition, simply using a large head diameter does not produce mechanical 28 capture of the femoral head.
In achieving some of the advantages of the invention, in accordance with 2 one aspect of the invention, there are provided liners with one or rnore recesses.
3 The type of recesses according to the present invention, however, are different 4 than that of the unconstrained Modell St. Georg / Mark I & II and ENDO-Modell liner, which was to "prevent irritation of the psoas muscle and enable(s) 6 removal of cement,",rather than for reducing dislocation or impingement.
See 7 Englelbrechht E, Siegel A, Kluber D: The Modell St. Georg/Mark UMark II
8 Prosthesis. p. 66. In: Finerman G, Dorey F, Grigoris P, McKellop H (eds):
Total 9 Hip Arthroplasty Outcomes. Churchhill Livingstone, New York, 1998.
In view of the limitations of the commercialized designs, new ti approaches are needed that would increase the inherent stability of the head-12 liner articulation while at the same time increasing range of motion, which 13 would result in a decreased rate of dislocation for both primary and revision 14 total hip arthroplasties. Such approaches would decrease patient anxiety, eliminate the need for postoperative dislocation precautions, and reduce the 16 number of revisions performed for dislocation and recurrent dislocation 17 resulting in a net cost savings to the healthcare system. Such risks of 18 dislocation are markedly reduced while range of motion is increased, 19 particularly when a large-head design ancVor recesses are employed,_ Cut away monopolar constrained acetabular liners (U.S. Patent No. 7,169,186 21 filed May 15, 2002) for use in total hip replacement to help reduce the 22 potential of dislocation of the hip while still providing sufficient range of 23 motion for daily activities have been developed. The invention disclosed herein 24 also provides a separate constraining ring that can be used in conjunction with the monopolar constrained acetabular liner and the cut away monopolar 26 constrained acetabular liner to provide additional support for the femoral head 27 to stay with the acetabular liner and avoid dislocation.
;JZ701-5 2 Summary of the Invention 4 It is an object of the invention to provide improved prostheses for use in the hip. In accomplishing this and other objects, there is provided in 6 accordance with one aspect of the present invention a monopolar acetabular 7 liner that can enclose a femoral head to form a hip replacement prostheses, 8 wherein the liner has a rim that creates an orifice, and wherein the orifice has a 9 diameter that is smaller than the diameter of the femoral head. The rim extends beyond the center line of the head (such as the center of rotation) when the head It is enclosed by the liner, and thereby the head is constrained from dislocation.
12 The liner can, in certain embodiments, include one or more recesses or cut-13 aways to facilitate additional range of motion or be without recess or cut away 14 for use with liners that likewise lack a recess or cut away. The liner, in another einbodiment, is designed to accommodate proper fitting of a constraining ring 16 that can be used in conjunction with the monopolar constrained acetabular liner 17 and the cut away monopolar constrained acetabular liner. In accordance with 18 another embodiment, there is provided a constraining ring that can be used in 19 conjunction with the monopolar constrained acetabular liner and the cut away monopolar constrained acetabular liner. The constraining rings provide 21 additional support for the femoral head to stay with the acetabular liner and 22 avoid dislocation. Preferably, the liner comprises ultra high molecular weight 23 polyethylene, that more preferably is all or in part cross-linked.
Preferably, the 24 cross-linking is performed via irradiation. The femoral head can have a large diameter. Preferably, the femoral head has a diameter of 32 mm or larger.
26 The constraining ring can, in certain embodiments, include one or 27 more recesses or cut-aways to be compatible with the corresponding liner.
28 Alternatively, the constraining ring will be without a recess or cut away for use with liners that likewise lack a recess or cut away_ In accordance with another aspect of the present invention, there is 2 provided a monopolar acetabular assembly comprising (A) a monopolar 3 acetabular component that encloses a femoral head, wherein the liner has a rim 4 that creates an orifice, and wherein the orifice has a diameter that is smaller than the diameter of the femoral head; and (B) a metal shell. The rim extends 6 beyond the center line of the head (such as the center of rotation) when the head 7 is enclosed by the liner, and thereby the head is constrained from dislocation.
8 The liner can, in certain embodiments, include one or more recesses or cut-9 aways to facilitate additional range of motion or be without recess or cut away;
and a constraining ring which can be used in conjunction with the monopolar I constrained acetabular liner and the cut away monopolar constrained acetabular 12 liner to provide additional support for the femoral head to stay with the 13 acetabular liner and avoid dislocation. The constraining ring, which can be 14 made from a number of high strength materials (for example, cobalt chrome alloy, titanium, stainless steel, etc.), is designed to fit around the perimeter of 16 the liner. The constraining ring, in another embodiment, is designed to fit 17 properly in conjunction with the monopolar constrained acetabular liner and the 18 cut away monopolar constrained acetabular liner. Preferably, the liner 19 comprises ultra high molecular weight polyethylene, that preferably is all or in part cross-linked. Preferably, the cross-linking is performed via irradiation.
21 Preferably, the femoral head has a large diameter. Preferably, the femoral 22 head has a diameter of 32 mm or larger. The constraining ring can, in 23 certain embodiments, include one or more recesses or cut-aways to be - 24 compatible with the corresponding liner. Alternatively, the constraining ring will be without a recess or cut away for use with liners that likewise lack a 26 recess or cut away. In accordance with the invention, the constraining ring is 27 preferably made of high strength materials such as cobalt chrome alloy, titanium, or stainless steel.
In accordance with still another aspect of the present invention, there is 2 provided a hip joint replacement assembly comprising (A) a monopolar 3 acetabular liner that encloses a femoral head, wherein the liner has a rim that 4 creates an orifice, and wherein the orifice has a diameter that is smaller than the diameter of the femoral head; (B) a metal shell; and (C) a femoral head. The 6 rim extends beyond the center line of the head (such as the center of rotation) 7 when the head is enclosed by the liner, and thereby the head is constrained from 8 dislocation. The liner can, in certain embodiments, include one or more 9 recesses or cut-aways to facilitate additional range of motion or be without recess or cut away; and a constraining ring which can be used in conjunction it with the monopolar constrained acetabular liner and the cut away monopolar 12 constrained acetabular liner to provide additional support for the femoral head 13 to stay with the acetabular liner and avoid dislocation. The constraining ring, in 14 another embodiment, is designed to ftt properly in conjunction with the monopolar constrained acetabular liner and the cut away monopolar constrained 16 acetabular liner. Preferably, the liner comprises ultra high molecular weight 17 polyethylene, that preferably is all or in part cross-linked.
Preferably, the cross-Is linking is performed via irradiation. The metal shell may be made of titanium, 19 stainless steel, or a cobalt chrome alloy. Preferably, the femoral head has a large diameter. Preferably, the femoral head has a diameter of 32 mm or 21 larger. The constraining ring can, in certain embodiments, include one 22 or more recesses or cut-aways to be compatible with the corresponding liner.
23 Alternatively, the constraining ring will be without a recess or cut away for use - 24 with liners that likewise lack a recess or cutaway.
In accordance with the invention, metal shells preferably are made of 26 titanium, cobalt chrome alloys, or stainless steel. The femoral stems preferably 27 also may be made pf a cobalt chrome alloys, stainless steel, or titanium.
Preferably, the femoral heads are made of a cobalt chrome alloys, stainless steel or ceramic. Where the femoral head and stern are one piece, preferably they are 2 made of a cobalt chrome alloy or stainless steel.
3 In accordance with still a further aspect of the invention, there are 4 provided methods of replacing a hips in patients in need thereof, comprising the step of surgically implanting in a given patient a monopolar acetabular liner 6 that can enclose a femoral head to form a hip replacement prostheses, wherein 7 the liner has a rim that creates an orifice, and wherein the orifice has a diameter 8 that is smaller than the diameter of the femoral head, and thereby the head is 9 constrained from dislocation. The liner can, in certain embodiments, include to one or more recesses or cut-aways to facilitate additional range of motion or be without recess or cut away; and a constraining ring which can be used in 12 conjunction with the monopolar constrained acetabular liner and the cut away 13 monopolar constrained acetabular liner to provide additional support for the 14 femoral head to stay with the acetabular liner and avoid dislocation.
The constraining ring, in another embodiment, is designed to fit properly in 16 conjunction with the monopolar constrained acetabular liner and the cut away 17 monopolar constrained acetabular liner. Implantation of assemblies and total 18 replacements, such as shells, femoral heads and femoral stems, also are 19 provided.
=
In accordance with a further aspect of the invention, there is provided a use of a monopolar acetabular liner or monopolar component for replacing a hip in a patient in need thereof, wherein the monopolar acetabular liner or monopolar component is capable of enclosing a femoral head to form a hip replacement prostheses, and the liner has a rim that creates an orifice having a diameter that is smaller than the diameter of the femoral head, wherein the femoral head has a diameter of 32 mm or larger.
In contrast to current bipolar and tripolar constrained components the monopolar constrained design has:
(i) increased range of motion, (ii) decreased wear of the articulation, (iii) simpler intraoperative assembly, (iv) decreased risk of impingement of the femoral neck upon the liner rim, (v) decreased stress transfer to the acetabular component-cement interface, (vi) decreased stress transfer to the cement-bone interface, (vii) decreased stress transfer to the metal shell-bone interface, (viii) eliminates the thin polyethylene articulating surfaces associated with multi-polar designs, (ix) eliminates multipolar locking rings, which have had reported malfunctions and failure, (x) allows for the use of 9a , - WO 02/09615 PCT/US01/226,0 1 large head diameters, (xi) has smaller possible acetabular shell outer diameters, 2 (xii) utilizes thicker polyethylene bearing surfaces, (xiii) and further facilitate 3 range of motion in preferred directions.
4 In contrast to the Legrange /Letoumel design, the monopolar constrained design according to the invention has: (i) a different and superior bearing 6 surface, (ii) larger head diameters, (iii) decreased wear, (iv) increased ROM, (v) 7 the capacity to be use in cemented or bony in-growth acetabular replacements, 8 (vi) thicker polyethylene bearing surfaces, (vii) modularity for use with 9 uncemented acetabular shells, (viii) can be easily exchanged at the time of primary or revision surgery, and (ix) and can be designed to facilitate movement in preferred directions.
12 Although large head diameters with standard LTHMWPE bearing 13 surfaces have been used for the treatment of dislocation and recurrent 14 dislocation by Amstutz et al. In contrast to the designs employed by Amstutz, the monopolar constrained has: (i) has a mechanical capture of the femoral 16 head, (ii) reduced wear, (iii) decreased periprosthetic osteolysis, (iv) modularity 17 for easy conversion between different amounts of constraint, and (v) can be 18 designed to facilitate movement in preferred directions.
19 In embodiments employing the recesses, the liner can have one or more recess. A recess, often referred to herein as a cut away, can be positioned to 21 further facilitate movement in a desired direction.
22 Embodiments employing a constraining ring can be used in conjunction 23 with the monopolar constrained acetabular liner and the cut away monopolar 24 constrained acetabular liner to provide addition restraint against dislocation of the hip joint while at same time not impeding the range of motion of the hip 26 joint. The constraining ring, in another embodiment, is designed to fit properly 27 in conjunction with the monopolar constrained acetabular liner and the cut 28 away monopolar constrained acetabular liner.
= CA 02711010 2010-08-05 , NO 02/09615 .
The constraining ring can be secured to the acetabular liner by means of 2 a number of locking mechanisms that are similar to those that are currently used 3 to secure acetabular liners into their mating metal acetabular shell.
4 Embodiments of this invention have used a locking mechanism which relies on the spatial interference between the polyethylene acetabular liner and the metal 6 acetabular shell. This invention is not limited by the use of the locking 7 mechanism used in such embodiments and the use of other locking mechanisms 8 are possible.
9 In another embodiment of this invention have used a locking mechanism which relies on the spatial interference between the polyethylene acetabular liner and the metal constraining ring. As the constraining ring is being seated 12 onto the acetabular liner the polyethylene must deform as it moves past a ridge 13 on the constraining ring. Once the ring is fully seated then the deformed 14 polyethylene relaxes behind the ridge hence securing the constraining ring to the liner. This invention is not limited by the use of the locking mechanism 16 used in such embodiments and the use of other locking mechanisms are 17 possible. Yet in another the constraining ring can also be fastened to the 18 acetabular liner by direct screw fixation where screws are passed directly 19 through the constraining ring into the polyethylene liner.
In another embodiment of this invention the constraining ring can be 21 secured to the liner by means of a retaining ring which is designed in an 22 unstressed state to sit in grooves in both the constraining ring and acetabular 23 liner. Upon setting the constraining ring onto the liner the retaining will deform 24 until the constraining ring is fully seated onto the liner at which point the retaining ring relaxes into the designed grove in the liner.
26 The constraining ring can, in certain embodiments, include one or more 27 recesses or cut aways to be compatible with the corresponding liner.
.11 ' 52701-5D
Alternatively, the constraining ring will be without a recess or cut away for use with liners that likewise lack a recess or cut away.
According to another aspect of the invention, there is provided a constraining ring that is used in conjunction with a monopolar constrained acetabular liner or a cut away monopolar constrained acetabular liner, wherein the constraining ring contains at least one positioned recess that is compatible with the corresponding acetabular liner, wherein the ring fits around the perimeter of the monopolar constrained acetabular liner, and wherein the ring is set onto the acetabular liner during the operative procedure after the femoral head is reduced into the acetabular liner.
These and other aspects of the present invention will become apparent to the skilled person in view of the description set forth below.
Brief Description of the Figures Figure 1 is a schematic view of a monopolar liner in functional relation with a femoral head and neck.
Figure 2 is a perspective view of a monopolar liner containing 2 recesses to facilitate greater range of motion.
Figure 3 depicts the components of the cut away monopolar constrained acetabular system with a constraining ring: metal acetabular shell (52) which is secured to the acetabulum, polyethylene cut away monopolar constrained acetabular liner (54), and constraining ring (56). Note the metal acetabular shell is not essential for this invention as the acetabular liner can be directly secured into the acetabulum with bone cement.
Figure 4 depicts constraining rings (56) in different perspectives.
Detailed Description of Aspects of the Invention The present invention decreases the risk of dislocation of total hip arthroplasty in both the primary and revision setting. See U.S. Patent No. 7,169,186, filed May 15, 2002.
In conjunction with large diameter femoral heads, such as disclosed in WO
01/05337, the present invention can achieve a range of motion that is greater than is t currently available so called "constrained" systems using 22, 26, 28 and 32 mm 2 heads. A decrease in the rate of dislocation will have a positive effect on 3 patient satisfaction as well as hospital re-admission for treatment of dislocation.
4 The increased range of motion in this invention will afford patients a more normal life style than the currently available constrained systems. The present 6 invention can be surgically implanted in a patient in the same or similar manner 7 as currently employed implants. Thus, the present invention results in an s improved quality of life as well as improved patient satisfaction.
9 The present invention advantageously employs UHMWPE liners, to preferably using UHMWPE that is cross-linked, including highly cross-linked tt UHMWPE. UHMWPE can be cross-linked by a variety of approaches, 12 including those employing cross-linking chemicals and/or irradiation.
Preferred 13 approaches for cross-linking employ irradiation, and are taught in 14 WO 97/29793.
According to the invention, there is preferably a two part acetabular 16 assembly, namely a metal shell for bony in-growth with UHMWPE liner, 17 preferably where the bearing surface of the liner that comes into contact with ts the femoral head is comprised of erosslinked UHMWPE.
19 The liner of the present invention preferably is "monopolar" system.
The monopolar constrained ac,etabular preferably has a one piece design and 21 has a single metal to polyethylene articular surface, and thus preferably is not 22 bipolar or tripolar in design. The monopolar design allows for the use of 23 thicker polyethylene in the acetabular liner. Compared to the bipolar and 24 tripolar constrainedkaptured designs, the monopolar design decreases the surface area of contact between metal and polyethylene because there is only 26 one metal-polyethylene articulation, rather than two or more found in other 27 designs. Moreover, the use of crosslinked UHMWPE will decrease the amount 28 of debris particles generated to articulation. Moreover, in the modular form of 13 =
14 Component impingement is undesirable for several reasons. The femoral neck impinging against the polyethylene liner can produce damage to 16 the polyethylene as well as increasing the stresses at the component bone 17 interface. Additionally, the point of impingement acts as the fulcrum through 18 which the force produced by the leg could lever the femoral head out of the 19 liner and hence lead to dislocation.
90 Many current methods of reducing the risk of dislocation, including 21 recurrent dislocation, employ the use of so called "constrained liners,"
which 22 are complex bipolar or tripolar articulations. In a study of twenty one 23 constrained acetabular components to treat preoperative or intraoperative 24 instability, six patients had recurrent dislocations. It was postulated that this increase was caused by the impingement of the femoral stem on the rim of the 26 insert due to decreased range of motion within the design. Orthopaedic 27 Knowledge Update, Chapter 38, page 474 (James H. Beatty, M.D., editor, 28 AAOS).
= = CA 02711010 2010-08-05 , NO 02/09615 PCT/US01/226,.
Constrained systems that are currently available use ultra high molecular weight polyethylene (UHMWPE) which is not crosslinked. A major limitation 3 of the material is it's high wear rate and the risk of periprosthetic osteolysis.
4 Also, their stated range of motion in flexion is between 72 and 900.
Such devices are available from Zimmer, Inc., Johnson & Jolmson/Depuy Inc., and 6 Howrnedica-Osteonics, Inc.
7 The current products have additional limitations. For example, the 8 Osteonics system utilizes only 22, 26 and 28 mm heads. The minimum 9 diameter of the acetabular shell is 50 mm. This design is "bipolar." A
bipolar system is made up of a acetabular shell with a polyethylene liner, and inside of that liner is a metal head. Inside of that metal head is another polyethylene 12 liner, which in turn captures a 22, 26, or 28 mm head that is attached to the 13 femoral stem. Thus, the Osteonics system has multiple polyethylene on metal 14 articulations. The multiple articulations generate polyethylene wear debris at a much faster rate than designs with a single metal on polyethylene articulation.
16 Additionally, the range of motion only is approximately 90 degrees.
constrained system developed by Zimmer, Inc. uses a metal shell with 18 a two-piece polyethylene liner. One piece is inserted into the acetabular metal 19 shell followed by placement of the other portion around the neck on the femoral component before the femoral head has been put on the Morse taper. The head 21 is then reduced into the acetabular component. The polyethylene portion with a 22 metal band that is around the femoral neck is then brought into contact with the 23 acetabular polyethylene component and the metal band then secured to 24 "capture" the head within the assembled polyethylene liner. Again, this design uses ultra high molecular weight polyethylene and can generate significant 26 debris as well as a limited range of motion. The limited range of motion results s WO 02/09615 PCT/US01/22t.-_, 1 in impingement in flexion, which generates a rotational torque at the bone shell 2 interface, potentially inhibiting bony in-growth into the acetabular shell.
3 In the late 1960's to early 1970's, others attempted to implant a 4 cemented conventional UHIVIWPE liner with greater than 50% head coverage.
Lagrange and Letoumel, Int Surg. 60(1):21-4 (1975); Lanzetta, Arch Ortop.
6 83(1):49-53 (1970). These designs had a 35mm inner diameter and was 7 available in only two (47 and 58mm) outer diameters. These approaches, 8 however, did not yield a replacement with acceptable performance. Long-term 9 data is not available for the LaGrange/Letournel design, likely because it did not become a widely-accepted product. Its head design (35 mm diameter) in II conjunction with conventional UHIVIWPE available at the time would have had 12 a substantial wear rate.
13 Thus, current and past designs have utilized various approaches, 14 including countersinks, in which the center of rotation of the femoral head is below the level of the flat surface of the liner. Yet even the use of a 16 countersink design using large head diameters is less than optimal because, 17 among other things, these liners did not have an orifice that was less than the 18 diameter of the femoral head, and therefore have no mechanical capture, and 19 took no other steps to avoid or minimize dislocation.
It has been shown that larger heads are effective in reducing the rate of = 21 recurrent dislocations, even when used with conventional polyethylene.
22 Amstutz et aL, 12th Annual International Symposium for Technology in 23 Arthroplasty, ISTA '99, Chicago, IL (1999). However, hip simulator studies = 24 have shown that the wear of conventional polyethylene with the larger heads is excessive. This disadvantage was demonstrated in vivo by the results of surface 26 replacement as well. Amstutz et al., Clin. Orthop. 213: 92-114 (1986).
In 27 addition, simply using a large head diameter does not produce mechanical 28 capture of the femoral head.
In achieving some of the advantages of the invention, in accordance with 2 one aspect of the invention, there are provided liners with one or rnore recesses.
3 The type of recesses according to the present invention, however, are different 4 than that of the unconstrained Modell St. Georg / Mark I & II and ENDO-Modell liner, which was to "prevent irritation of the psoas muscle and enable(s) 6 removal of cement,",rather than for reducing dislocation or impingement.
See 7 Englelbrechht E, Siegel A, Kluber D: The Modell St. Georg/Mark UMark II
8 Prosthesis. p. 66. In: Finerman G, Dorey F, Grigoris P, McKellop H (eds):
Total 9 Hip Arthroplasty Outcomes. Churchhill Livingstone, New York, 1998.
In view of the limitations of the commercialized designs, new ti approaches are needed that would increase the inherent stability of the head-12 liner articulation while at the same time increasing range of motion, which 13 would result in a decreased rate of dislocation for both primary and revision 14 total hip arthroplasties. Such approaches would decrease patient anxiety, eliminate the need for postoperative dislocation precautions, and reduce the 16 number of revisions performed for dislocation and recurrent dislocation 17 resulting in a net cost savings to the healthcare system. Such risks of 18 dislocation are markedly reduced while range of motion is increased, 19 particularly when a large-head design ancVor recesses are employed,_ Cut away monopolar constrained acetabular liners (U.S. Patent No. 7,169,186 21 filed May 15, 2002) for use in total hip replacement to help reduce the 22 potential of dislocation of the hip while still providing sufficient range of 23 motion for daily activities have been developed. The invention disclosed herein 24 also provides a separate constraining ring that can be used in conjunction with the monopolar constrained acetabular liner and the cut away monopolar 26 constrained acetabular liner to provide additional support for the femoral head 27 to stay with the acetabular liner and avoid dislocation.
;JZ701-5 2 Summary of the Invention 4 It is an object of the invention to provide improved prostheses for use in the hip. In accomplishing this and other objects, there is provided in 6 accordance with one aspect of the present invention a monopolar acetabular 7 liner that can enclose a femoral head to form a hip replacement prostheses, 8 wherein the liner has a rim that creates an orifice, and wherein the orifice has a 9 diameter that is smaller than the diameter of the femoral head. The rim extends beyond the center line of the head (such as the center of rotation) when the head It is enclosed by the liner, and thereby the head is constrained from dislocation.
12 The liner can, in certain embodiments, include one or more recesses or cut-13 aways to facilitate additional range of motion or be without recess or cut away 14 for use with liners that likewise lack a recess or cut away. The liner, in another einbodiment, is designed to accommodate proper fitting of a constraining ring 16 that can be used in conjunction with the monopolar constrained acetabular liner 17 and the cut away monopolar constrained acetabular liner. In accordance with 18 another embodiment, there is provided a constraining ring that can be used in 19 conjunction with the monopolar constrained acetabular liner and the cut away monopolar constrained acetabular liner. The constraining rings provide 21 additional support for the femoral head to stay with the acetabular liner and 22 avoid dislocation. Preferably, the liner comprises ultra high molecular weight 23 polyethylene, that more preferably is all or in part cross-linked.
Preferably, the 24 cross-linking is performed via irradiation. The femoral head can have a large diameter. Preferably, the femoral head has a diameter of 32 mm or larger.
26 The constraining ring can, in certain embodiments, include one or 27 more recesses or cut-aways to be compatible with the corresponding liner.
28 Alternatively, the constraining ring will be without a recess or cut away for use with liners that likewise lack a recess or cut away_ In accordance with another aspect of the present invention, there is 2 provided a monopolar acetabular assembly comprising (A) a monopolar 3 acetabular component that encloses a femoral head, wherein the liner has a rim 4 that creates an orifice, and wherein the orifice has a diameter that is smaller than the diameter of the femoral head; and (B) a metal shell. The rim extends 6 beyond the center line of the head (such as the center of rotation) when the head 7 is enclosed by the liner, and thereby the head is constrained from dislocation.
8 The liner can, in certain embodiments, include one or more recesses or cut-9 aways to facilitate additional range of motion or be without recess or cut away;
and a constraining ring which can be used in conjunction with the monopolar I constrained acetabular liner and the cut away monopolar constrained acetabular 12 liner to provide additional support for the femoral head to stay with the 13 acetabular liner and avoid dislocation. The constraining ring, which can be 14 made from a number of high strength materials (for example, cobalt chrome alloy, titanium, stainless steel, etc.), is designed to fit around the perimeter of 16 the liner. The constraining ring, in another embodiment, is designed to fit 17 properly in conjunction with the monopolar constrained acetabular liner and the 18 cut away monopolar constrained acetabular liner. Preferably, the liner 19 comprises ultra high molecular weight polyethylene, that preferably is all or in part cross-linked. Preferably, the cross-linking is performed via irradiation.
21 Preferably, the femoral head has a large diameter. Preferably, the femoral 22 head has a diameter of 32 mm or larger. The constraining ring can, in 23 certain embodiments, include one or more recesses or cut-aways to be - 24 compatible with the corresponding liner. Alternatively, the constraining ring will be without a recess or cut away for use with liners that likewise lack a 26 recess or cut away. In accordance with the invention, the constraining ring is 27 preferably made of high strength materials such as cobalt chrome alloy, titanium, or stainless steel.
In accordance with still another aspect of the present invention, there is 2 provided a hip joint replacement assembly comprising (A) a monopolar 3 acetabular liner that encloses a femoral head, wherein the liner has a rim that 4 creates an orifice, and wherein the orifice has a diameter that is smaller than the diameter of the femoral head; (B) a metal shell; and (C) a femoral head. The 6 rim extends beyond the center line of the head (such as the center of rotation) 7 when the head is enclosed by the liner, and thereby the head is constrained from 8 dislocation. The liner can, in certain embodiments, include one or more 9 recesses or cut-aways to facilitate additional range of motion or be without recess or cut away; and a constraining ring which can be used in conjunction it with the monopolar constrained acetabular liner and the cut away monopolar 12 constrained acetabular liner to provide additional support for the femoral head 13 to stay with the acetabular liner and avoid dislocation. The constraining ring, in 14 another embodiment, is designed to ftt properly in conjunction with the monopolar constrained acetabular liner and the cut away monopolar constrained 16 acetabular liner. Preferably, the liner comprises ultra high molecular weight 17 polyethylene, that preferably is all or in part cross-linked.
Preferably, the cross-Is linking is performed via irradiation. The metal shell may be made of titanium, 19 stainless steel, or a cobalt chrome alloy. Preferably, the femoral head has a large diameter. Preferably, the femoral head has a diameter of 32 mm or 21 larger. The constraining ring can, in certain embodiments, include one 22 or more recesses or cut-aways to be compatible with the corresponding liner.
23 Alternatively, the constraining ring will be without a recess or cut away for use - 24 with liners that likewise lack a recess or cutaway.
In accordance with the invention, metal shells preferably are made of 26 titanium, cobalt chrome alloys, or stainless steel. The femoral stems preferably 27 also may be made pf a cobalt chrome alloys, stainless steel, or titanium.
Preferably, the femoral heads are made of a cobalt chrome alloys, stainless steel or ceramic. Where the femoral head and stern are one piece, preferably they are 2 made of a cobalt chrome alloy or stainless steel.
3 In accordance with still a further aspect of the invention, there are 4 provided methods of replacing a hips in patients in need thereof, comprising the step of surgically implanting in a given patient a monopolar acetabular liner 6 that can enclose a femoral head to form a hip replacement prostheses, wherein 7 the liner has a rim that creates an orifice, and wherein the orifice has a diameter 8 that is smaller than the diameter of the femoral head, and thereby the head is 9 constrained from dislocation. The liner can, in certain embodiments, include to one or more recesses or cut-aways to facilitate additional range of motion or be without recess or cut away; and a constraining ring which can be used in 12 conjunction with the monopolar constrained acetabular liner and the cut away 13 monopolar constrained acetabular liner to provide additional support for the 14 femoral head to stay with the acetabular liner and avoid dislocation.
The constraining ring, in another embodiment, is designed to fit properly in 16 conjunction with the monopolar constrained acetabular liner and the cut away 17 monopolar constrained acetabular liner. Implantation of assemblies and total 18 replacements, such as shells, femoral heads and femoral stems, also are 19 provided.
=
In accordance with a further aspect of the invention, there is provided a use of a monopolar acetabular liner or monopolar component for replacing a hip in a patient in need thereof, wherein the monopolar acetabular liner or monopolar component is capable of enclosing a femoral head to form a hip replacement prostheses, and the liner has a rim that creates an orifice having a diameter that is smaller than the diameter of the femoral head, wherein the femoral head has a diameter of 32 mm or larger.
In contrast to current bipolar and tripolar constrained components the monopolar constrained design has:
(i) increased range of motion, (ii) decreased wear of the articulation, (iii) simpler intraoperative assembly, (iv) decreased risk of impingement of the femoral neck upon the liner rim, (v) decreased stress transfer to the acetabular component-cement interface, (vi) decreased stress transfer to the cement-bone interface, (vii) decreased stress transfer to the metal shell-bone interface, (viii) eliminates the thin polyethylene articulating surfaces associated with multi-polar designs, (ix) eliminates multipolar locking rings, which have had reported malfunctions and failure, (x) allows for the use of 9a , - WO 02/09615 PCT/US01/226,0 1 large head diameters, (xi) has smaller possible acetabular shell outer diameters, 2 (xii) utilizes thicker polyethylene bearing surfaces, (xiii) and further facilitate 3 range of motion in preferred directions.
4 In contrast to the Legrange /Letoumel design, the monopolar constrained design according to the invention has: (i) a different and superior bearing 6 surface, (ii) larger head diameters, (iii) decreased wear, (iv) increased ROM, (v) 7 the capacity to be use in cemented or bony in-growth acetabular replacements, 8 (vi) thicker polyethylene bearing surfaces, (vii) modularity for use with 9 uncemented acetabular shells, (viii) can be easily exchanged at the time of primary or revision surgery, and (ix) and can be designed to facilitate movement in preferred directions.
12 Although large head diameters with standard LTHMWPE bearing 13 surfaces have been used for the treatment of dislocation and recurrent 14 dislocation by Amstutz et al. In contrast to the designs employed by Amstutz, the monopolar constrained has: (i) has a mechanical capture of the femoral 16 head, (ii) reduced wear, (iii) decreased periprosthetic osteolysis, (iv) modularity 17 for easy conversion between different amounts of constraint, and (v) can be 18 designed to facilitate movement in preferred directions.
19 In embodiments employing the recesses, the liner can have one or more recess. A recess, often referred to herein as a cut away, can be positioned to 21 further facilitate movement in a desired direction.
22 Embodiments employing a constraining ring can be used in conjunction 23 with the monopolar constrained acetabular liner and the cut away monopolar 24 constrained acetabular liner to provide addition restraint against dislocation of the hip joint while at same time not impeding the range of motion of the hip 26 joint. The constraining ring, in another embodiment, is designed to fit properly 27 in conjunction with the monopolar constrained acetabular liner and the cut 28 away monopolar constrained acetabular liner.
= CA 02711010 2010-08-05 , NO 02/09615 .
The constraining ring can be secured to the acetabular liner by means of 2 a number of locking mechanisms that are similar to those that are currently used 3 to secure acetabular liners into their mating metal acetabular shell.
4 Embodiments of this invention have used a locking mechanism which relies on the spatial interference between the polyethylene acetabular liner and the metal 6 acetabular shell. This invention is not limited by the use of the locking 7 mechanism used in such embodiments and the use of other locking mechanisms 8 are possible.
9 In another embodiment of this invention have used a locking mechanism which relies on the spatial interference between the polyethylene acetabular liner and the metal constraining ring. As the constraining ring is being seated 12 onto the acetabular liner the polyethylene must deform as it moves past a ridge 13 on the constraining ring. Once the ring is fully seated then the deformed 14 polyethylene relaxes behind the ridge hence securing the constraining ring to the liner. This invention is not limited by the use of the locking mechanism 16 used in such embodiments and the use of other locking mechanisms are 17 possible. Yet in another the constraining ring can also be fastened to the 18 acetabular liner by direct screw fixation where screws are passed directly 19 through the constraining ring into the polyethylene liner.
In another embodiment of this invention the constraining ring can be 21 secured to the liner by means of a retaining ring which is designed in an 22 unstressed state to sit in grooves in both the constraining ring and acetabular 23 liner. Upon setting the constraining ring onto the liner the retaining will deform 24 until the constraining ring is fully seated onto the liner at which point the retaining ring relaxes into the designed grove in the liner.
26 The constraining ring can, in certain embodiments, include one or more 27 recesses or cut aways to be compatible with the corresponding liner.
.11 ' 52701-5D
Alternatively, the constraining ring will be without a recess or cut away for use with liners that likewise lack a recess or cut away.
According to another aspect of the invention, there is provided a constraining ring that is used in conjunction with a monopolar constrained acetabular liner or a cut away monopolar constrained acetabular liner, wherein the constraining ring contains at least one positioned recess that is compatible with the corresponding acetabular liner, wherein the ring fits around the perimeter of the monopolar constrained acetabular liner, and wherein the ring is set onto the acetabular liner during the operative procedure after the femoral head is reduced into the acetabular liner.
These and other aspects of the present invention will become apparent to the skilled person in view of the description set forth below.
Brief Description of the Figures Figure 1 is a schematic view of a monopolar liner in functional relation with a femoral head and neck.
Figure 2 is a perspective view of a monopolar liner containing 2 recesses to facilitate greater range of motion.
Figure 3 depicts the components of the cut away monopolar constrained acetabular system with a constraining ring: metal acetabular shell (52) which is secured to the acetabulum, polyethylene cut away monopolar constrained acetabular liner (54), and constraining ring (56). Note the metal acetabular shell is not essential for this invention as the acetabular liner can be directly secured into the acetabulum with bone cement.
Figure 4 depicts constraining rings (56) in different perspectives.
Detailed Description of Aspects of the Invention The present invention decreases the risk of dislocation of total hip arthroplasty in both the primary and revision setting. See U.S. Patent No. 7,169,186, filed May 15, 2002.
In conjunction with large diameter femoral heads, such as disclosed in WO
01/05337, the present invention can achieve a range of motion that is greater than is t currently available so called "constrained" systems using 22, 26, 28 and 32 mm 2 heads. A decrease in the rate of dislocation will have a positive effect on 3 patient satisfaction as well as hospital re-admission for treatment of dislocation.
4 The increased range of motion in this invention will afford patients a more normal life style than the currently available constrained systems. The present 6 invention can be surgically implanted in a patient in the same or similar manner 7 as currently employed implants. Thus, the present invention results in an s improved quality of life as well as improved patient satisfaction.
9 The present invention advantageously employs UHMWPE liners, to preferably using UHMWPE that is cross-linked, including highly cross-linked tt UHMWPE. UHMWPE can be cross-linked by a variety of approaches, 12 including those employing cross-linking chemicals and/or irradiation.
Preferred 13 approaches for cross-linking employ irradiation, and are taught in 14 WO 97/29793.
According to the invention, there is preferably a two part acetabular 16 assembly, namely a metal shell for bony in-growth with UHMWPE liner, 17 preferably where the bearing surface of the liner that comes into contact with ts the femoral head is comprised of erosslinked UHMWPE.
19 The liner of the present invention preferably is "monopolar" system.
The monopolar constrained ac,etabular preferably has a one piece design and 21 has a single metal to polyethylene articular surface, and thus preferably is not 22 bipolar or tripolar in design. The monopolar design allows for the use of 23 thicker polyethylene in the acetabular liner. Compared to the bipolar and 24 tripolar constrainedkaptured designs, the monopolar design decreases the surface area of contact between metal and polyethylene because there is only 26 one metal-polyethylene articulation, rather than two or more found in other 27 designs. Moreover, the use of crosslinked UHMWPE will decrease the amount 28 of debris particles generated to articulation. Moreover, in the modular form of 13 =
PCT/US01/226..,_ =
this acetabular design, since the polyethylene component is not cemented into 2 place, some revision surgeries are more feasible. Moreover, with the modular 3 design different types of heads and liners can be used with the shell, and can be 4 selected by the surgeon during surgery.
According to one aspect of the invention, more than 50% of the volume 6 of the femoral head is enclosed within the polyethylene liner. The diameter of 7 the opening/orifice of the polyethylene liner is less than the diameter of the 8 femoral head that is inserted, as shown in Figure 1.
this acetabular design, since the polyethylene component is not cemented into 2 place, some revision surgeries are more feasible. Moreover, with the modular 3 design different types of heads and liners can be used with the shell, and can be 4 selected by the surgeon during surgery.
According to one aspect of the invention, more than 50% of the volume 6 of the femoral head is enclosed within the polyethylene liner. The diameter of 7 the opening/orifice of the polyethylene liner is less than the diameter of the 8 femoral head that is inserted, as shown in Figure 1.
9 Figure 1 depicts at (10) a liner (12) in functional relation with a femoral head (14) and neck (20). The rim surface (16) of the liner (12) extends beyond ti the center line (18), representing the center of rotation of both the femoral head 12 and the acetabular liner. Preferably the liner rim surface is flat in this 13 embodiment. The inner portions of the rim circumscribe the orifice. If desired, 14 a metal shell, not pictured, would be positioned between the liner and the bone at the mount site, and preferably is configured so as to promote in-growth of the 16 bone.
17 Figure 2 depicts at (30) a type of recessed or cut away liner (32). In the 18 pictured embodiment, the rim surface (34) is interrupted by two cut aways (36) 19 which permit greater range of motion while preserving a constraint to hold a head in place by a snap fit. Region (38) shows that the rim surface (34) of the 21 liner (32) extends beyond the center line (not specifically depicted) in such a 22 manner that the opening/orifice of the liner (32) is less than the diameter of the 23 femoral head that is inserted therein. Thus, the inner portions of the rim 24 circumscribe the orifice in such a manner that the head is held within the liner.
If desired, a metal shell, not pictured, would be positioned between the liner 26 and the bone at the mount site, and preferably is configured so as to promote in-27 growth of the bone.
= CA 02711010 2010-08-05 PCT/US01/226..
The embodiments that employ one or more recesses can have the 2 recesses positioned to further facilitate movement in a desired direction. For 3 example, a liner might have a single recess to provide increased range of 4 motion in flexion. Another arrangement can be a liner with two recesses with the second recess to provide increased range of motion in extension and/or 6 extension plus external rotation. Moreover, the increased range of motion 7 provided by the cut-away design also allows for greater tolerance for the s variations in the orientation of the acetabular component that can occur during 9 insertion.
As stated above, recesses can be positioned to further facilitate it movement in a desired direction, such as in the common directions of 12 impingement. Recesses can be placed in several different positions, but 13 preferentially would be placed in the position to produce the range of maximum 14 motion in a desired direction. For example, in a left hip, when looking at the acetabular component in position and considering it to be the face of a clock, 16 the recess would be preferentially placed at about 1-2 o'clock. Under similar 17 circumstances one would place a recess for a right hip at about 10-11 o'clock.
18 Recesses in these positions assist with flexion alone and flexion plus internal 19 rotation. For embodiments with two or more recesses, at least one recess also would be placed in the position to maximize extension alone and extension plus 21 external rotation, and thus these recesses would be placed at about 4-5 o'clock 22 in the left hip and about 7-8 o'clock in the right hip.
23 The recesses preferably are of sufficient size to accommodate the 24 femoral head and stern (including the neck), while still constraining the head within the liner. The size of the recess in terms of width and depth depend 26 upon the size of the stem neck and the range of motion of motion sought, which 27 are readily determinable by the skilled person based upon a patient's size, age 28 and needs. If the liner is comprised of a cross-linked polymer, like irradiated PCT/US01/22(...., ultra high molecular weight polyethylene, then the recesses preferably are 2 machined into the liner. The liner, in another embodiment, is modified to 3 acconunodate a constraining ring that can be used in conjunction with the 4 monopolar constrained acetabular liner and the cut away monopolar constrained acetabular liner to provide additional support for the femoral head to stay with 6 the acetabular liner and avoid dislocation.
7 Figure 3 depicts at (50) a type of constraining ring (56). In the pictured 8 embodiment, showing components of the cut away monopolar constrained 9 acetabular system with a constraining ring: optional metal acetabular shell which is secured to the acetabulum (52), polyethylene cut away monopolar 11 constrained acetabular liner (54), and the constraining ring (56). It is notable 12 that the metal acetabular shell is not essential for this invention as the 13 acetabular liner can be directed secured into the acetabulum with bone cement.
14 If desired, the metal shell (52), would be positioned between the liner and the bone at the mount site, and preferably is configured so as to promote in-growth 16 of the bone.
17 Figure 4 depicts at (70) a constraining ring (56) shown in different 18 perspectives.
19 The opening in the monopolar constrained acetabular liner and the cut away monopolar constrained acetabular liner through which the femoral head 21 passes upon reducing the femoral head into the liner is smaller than the femoral 22 head, which allows a snap-fit. Therefore, the constrained liner, which is 23 typically made of polyethylene, must deforni slightly to allow the femoral head 24 to be embraced by the liner. The constraining ring, which can be made from a number of high strength materials (for example, cobalt chrome alloy, titanium, 26 stainless steel, etc.), is designed to fit around the perimeter of the monopolar 27 constraining acetabular liner and is intended to serve as a structural support of = CA 02711010 2010-08-05 the liner to further ensure that the femoral head will stay within the acetabular 2 liner.
3 The constraining ring is circular in shape and has "cutouts" similar to 4 that of the cut away monopolar constrained acetabular liner (Figure 3 & 4).
This prevents the constraining ring from interfering with the range of motion of 6 the hip.
7 The constraining ring is preferably designed to be a single piece which 8 can be set onto the acetabular liner during the operative procedure after the 9 femoral head has been snap-fitted into the acetabular liner. This allows for the femoral head to stay snapped within the constrained liner.
The constraining ring can, in certain embodiments, include one or more 12 recesses or cut-aways to be compatible with the corresponding liner.
13 Alternatively, the constraining ring will be without a recess or cut away for use 14 with liners that likewise lack a recess or cut away.
Gross sliding or micro motion between separate metallic surfaces of the 16 total hip components can generate wear debris which upon release into the joint 17 space can elicit a biological response that can lead to the development of 18 osteolysis and hence increasing the of potential of component loosening.
The 19 design of the constraining ring and the acetabular liner are such that to prevent contact between metallic surfaces. The constraining ring is designed to fit 21 properly in conjunction with the monopolar constrained acetabular liner and the 22 cut away monopolar constrained acetabular liner.
23 The components are designed such that the femoral neck will impinge 24 against the polyethylene liner and not thè metallic constraining ring in all directions of motion. Also, the constraining ring fastens directly to the 26 polyethylene acetabular liner and has no direct contact with the metal shell into 27 which the liner is set. Another advantage to this feature is that the use of the 28 constraining ring is not dependent on the use of a metal shell, hence allowing . WO 02/09615 1 this system to be used with an acetabular liner which is cemented directly into 2 the acetabulum.
3 The constraining ring (see Figures 3 & 4) can be secured to the 4 acetabular liner by means of a number of locking mechanisms which are currently used to secure acetabular liners into their mating metal acetabular 6 shell. Embodiments of this invention have used a locking mechanism which 7 relies on the spatial interference between the polyethylene acetabular liner and 8 the metal acetabular shell. This invention is not limited by the use of the 9 locking mechanism used in such embodiments and the use of other locking mechanisms are possible.
It In another embodiment of this invention have used a locking mechanism 12 which relies on the spatial interference between the polyethylene acetabular 13 liner and the metal constraining ring. As the constraining ring is being seated 14 onto the acetabular liner the polyethylene must deform as it moves past a ridge on the constraining ring. Once the ring is fully seated then the deformed 16 polyethylene relaxes behind the ridge hence securing the constraining ring to 17 the liner. This invention is not limited by the use of the locking mechanism 18 used in such embodiments and the use of other locking mechanisms are 19 possible and contemplated by the invention.
Yet in another the constraining ring can also be fastened to the 21 acetabular liner by direct screw fixation where screws are passed directly 22 through the constraining ring into the polyethylene liner.
23 In another embodiment of this invention the constraining ring can be 24 secured to the liner by means of a retaining ring which is designed in an unstressed state to sit in grooves in both the constraining ring and acetabular 26 liner. Upon setting the constraining ring onto the liner the retaining will deform 27 until the constraining ring is fully seated onto the liner at which point the 28 retaining ring relaxes into the designed grove in the liner.
, NO 02/09615 PCT/US01/226...,.
The constraining ring can, in certain embodiments, include one or more 2 recesses or cut-aways to be compatible with the corresponding liner.
3 Alternatively, the constraining ring will be without a recess or cut away for use 4 with liners that likewise lack a recess or cut away.
Description of the Assembly of Cut Away Monopolar Constrained 6 Acetabular Liner with Constraining Ring (see Figure 3): Components of the cut 7 away monopolar constrained acetabular system consisting of: i) metal 8 acetabular shell which is secured to the acetabulum, ii) polyethylene cut away 9 monopolar constrained acetabular liner, and iii) constraining ring. The metal 113 acetabular shell is not essential for this invention as the acetabular liner can be it directed secured into the acetabulum with bone cement. The cut away 12 monopolar constrained acetabular liner is set into the metal acetabular.
The 13 constraining ring is placed over the femoral component and the femoral head is 14 snap-fitted into the acetabular liner. The constraining ring is then set onto the cut away monopolar constraining acetabular liner with the cutouts of the 16 constraining ring aligned with the cutouts of the acetabular liner.
17 Demonstration of the Position of the Acetabular Component within the 18 Hip and Range of Motion: The actual position of the acetabular component 19 within the hip will be set during the operative procedure and will depend on the patient's anatomy and gait. The cut away portion of the acetabular component 21 allows for sufficient range of motion in flexion. The cut away portion of the 22 acetabular component allows for sufficient internal rotation at 900 of flexion.
23 The cut away portion of the acetabular component allows for sufficient external 24 rotation at neutral flexion.
In any of the embodiments of the invention, the liners of the invention 26 can be used with hemispherical and non-hemispherical acetabular shells.
27 Also, the invention can be used with any head diameter, including large 28 head diameters (for example, 35 mm or greater, such as 38 mm, 40 mm, 42 =
1 mm, 44 mm, and any diameter in between or larger) in order to increase the 2 range of motion in comparison with currently available constrained systems.
3 The invention is further demonstrated by the following example, which 4 do not limit the invention in any manner.
6 Example 1 8 The load required for insertion and dislocation of femoral heads in a 9 constrained liner according to the invention was quantified by inserting 32 and 38 mm heads into simulated liners of electron beam crosslinked UHMWPE.
Two and three dimensional modeling was performed to assess ROM and 12 stability itz vitro. The liner had no chamfer.
13 The ROM, and the loads required for insertion and dislocation using 14 different opening diameters for 32 mm and 38 mm heads in simulated monopolar liners were measured. A 32 mm head with a 31 mm liner opening 16 required 60 lbs. for insertion and 55 lbs. for dislocation. When the opening was 17 increased to 31.5 mm the forces for insertion and dislocation decreased to 29 18 lbs., and 24 lbs., respectively. Testing of 35.5 mm, 36.5 mm, and 37.5 mm 19 openings with a 38 min head was performed. The insertional loads were 157, 130, and 28 lbs. The force necessary to produce dislocation of the femoral head 21 were 135, 126, and 28 lbs., respectively.
22 The ROM for the 38 mm head and a 35.5nun orifice liner is 110 .
This 23 increases to 118 and 131 as the orifice diameter is increased to 36.5 and 37.5 24 = mm. The 32 mm head and 31 mm orifice liner has 116 ROM. The ROM
increases to 124 when a 31.5 mm orifice is used with the 32 mm head.
26 These data demonstrate that the constrained design according to the 27 invention can minimize the occurrence of dislocation, even with heads and 28 liners that are constructed to permit enhanced range of movement.
=
PCT/US01/226¨
.
1 It is to be understood that the description, specific examples and data, 2 while indicating exemplary embodiments, are given by way of illustration and 3 are not intended to limit the present invention. Various changes and 4 modifications within the present invention will become apparent to the skilled artisan from the discussion, disclosure and data contained herein, and thus are 6 considered part of the invention.
17 Figure 2 depicts at (30) a type of recessed or cut away liner (32). In the 18 pictured embodiment, the rim surface (34) is interrupted by two cut aways (36) 19 which permit greater range of motion while preserving a constraint to hold a head in place by a snap fit. Region (38) shows that the rim surface (34) of the 21 liner (32) extends beyond the center line (not specifically depicted) in such a 22 manner that the opening/orifice of the liner (32) is less than the diameter of the 23 femoral head that is inserted therein. Thus, the inner portions of the rim 24 circumscribe the orifice in such a manner that the head is held within the liner.
If desired, a metal shell, not pictured, would be positioned between the liner 26 and the bone at the mount site, and preferably is configured so as to promote in-27 growth of the bone.
= CA 02711010 2010-08-05 PCT/US01/226..
The embodiments that employ one or more recesses can have the 2 recesses positioned to further facilitate movement in a desired direction. For 3 example, a liner might have a single recess to provide increased range of 4 motion in flexion. Another arrangement can be a liner with two recesses with the second recess to provide increased range of motion in extension and/or 6 extension plus external rotation. Moreover, the increased range of motion 7 provided by the cut-away design also allows for greater tolerance for the s variations in the orientation of the acetabular component that can occur during 9 insertion.
As stated above, recesses can be positioned to further facilitate it movement in a desired direction, such as in the common directions of 12 impingement. Recesses can be placed in several different positions, but 13 preferentially would be placed in the position to produce the range of maximum 14 motion in a desired direction. For example, in a left hip, when looking at the acetabular component in position and considering it to be the face of a clock, 16 the recess would be preferentially placed at about 1-2 o'clock. Under similar 17 circumstances one would place a recess for a right hip at about 10-11 o'clock.
18 Recesses in these positions assist with flexion alone and flexion plus internal 19 rotation. For embodiments with two or more recesses, at least one recess also would be placed in the position to maximize extension alone and extension plus 21 external rotation, and thus these recesses would be placed at about 4-5 o'clock 22 in the left hip and about 7-8 o'clock in the right hip.
23 The recesses preferably are of sufficient size to accommodate the 24 femoral head and stern (including the neck), while still constraining the head within the liner. The size of the recess in terms of width and depth depend 26 upon the size of the stem neck and the range of motion of motion sought, which 27 are readily determinable by the skilled person based upon a patient's size, age 28 and needs. If the liner is comprised of a cross-linked polymer, like irradiated PCT/US01/22(...., ultra high molecular weight polyethylene, then the recesses preferably are 2 machined into the liner. The liner, in another embodiment, is modified to 3 acconunodate a constraining ring that can be used in conjunction with the 4 monopolar constrained acetabular liner and the cut away monopolar constrained acetabular liner to provide additional support for the femoral head to stay with 6 the acetabular liner and avoid dislocation.
7 Figure 3 depicts at (50) a type of constraining ring (56). In the pictured 8 embodiment, showing components of the cut away monopolar constrained 9 acetabular system with a constraining ring: optional metal acetabular shell which is secured to the acetabulum (52), polyethylene cut away monopolar 11 constrained acetabular liner (54), and the constraining ring (56). It is notable 12 that the metal acetabular shell is not essential for this invention as the 13 acetabular liner can be directed secured into the acetabulum with bone cement.
14 If desired, the metal shell (52), would be positioned between the liner and the bone at the mount site, and preferably is configured so as to promote in-growth 16 of the bone.
17 Figure 4 depicts at (70) a constraining ring (56) shown in different 18 perspectives.
19 The opening in the monopolar constrained acetabular liner and the cut away monopolar constrained acetabular liner through which the femoral head 21 passes upon reducing the femoral head into the liner is smaller than the femoral 22 head, which allows a snap-fit. Therefore, the constrained liner, which is 23 typically made of polyethylene, must deforni slightly to allow the femoral head 24 to be embraced by the liner. The constraining ring, which can be made from a number of high strength materials (for example, cobalt chrome alloy, titanium, 26 stainless steel, etc.), is designed to fit around the perimeter of the monopolar 27 constraining acetabular liner and is intended to serve as a structural support of = CA 02711010 2010-08-05 the liner to further ensure that the femoral head will stay within the acetabular 2 liner.
3 The constraining ring is circular in shape and has "cutouts" similar to 4 that of the cut away monopolar constrained acetabular liner (Figure 3 & 4).
This prevents the constraining ring from interfering with the range of motion of 6 the hip.
7 The constraining ring is preferably designed to be a single piece which 8 can be set onto the acetabular liner during the operative procedure after the 9 femoral head has been snap-fitted into the acetabular liner. This allows for the femoral head to stay snapped within the constrained liner.
The constraining ring can, in certain embodiments, include one or more 12 recesses or cut-aways to be compatible with the corresponding liner.
13 Alternatively, the constraining ring will be without a recess or cut away for use 14 with liners that likewise lack a recess or cut away.
Gross sliding or micro motion between separate metallic surfaces of the 16 total hip components can generate wear debris which upon release into the joint 17 space can elicit a biological response that can lead to the development of 18 osteolysis and hence increasing the of potential of component loosening.
The 19 design of the constraining ring and the acetabular liner are such that to prevent contact between metallic surfaces. The constraining ring is designed to fit 21 properly in conjunction with the monopolar constrained acetabular liner and the 22 cut away monopolar constrained acetabular liner.
23 The components are designed such that the femoral neck will impinge 24 against the polyethylene liner and not thè metallic constraining ring in all directions of motion. Also, the constraining ring fastens directly to the 26 polyethylene acetabular liner and has no direct contact with the metal shell into 27 which the liner is set. Another advantage to this feature is that the use of the 28 constraining ring is not dependent on the use of a metal shell, hence allowing . WO 02/09615 1 this system to be used with an acetabular liner which is cemented directly into 2 the acetabulum.
3 The constraining ring (see Figures 3 & 4) can be secured to the 4 acetabular liner by means of a number of locking mechanisms which are currently used to secure acetabular liners into their mating metal acetabular 6 shell. Embodiments of this invention have used a locking mechanism which 7 relies on the spatial interference between the polyethylene acetabular liner and 8 the metal acetabular shell. This invention is not limited by the use of the 9 locking mechanism used in such embodiments and the use of other locking mechanisms are possible.
It In another embodiment of this invention have used a locking mechanism 12 which relies on the spatial interference between the polyethylene acetabular 13 liner and the metal constraining ring. As the constraining ring is being seated 14 onto the acetabular liner the polyethylene must deform as it moves past a ridge on the constraining ring. Once the ring is fully seated then the deformed 16 polyethylene relaxes behind the ridge hence securing the constraining ring to 17 the liner. This invention is not limited by the use of the locking mechanism 18 used in such embodiments and the use of other locking mechanisms are 19 possible and contemplated by the invention.
Yet in another the constraining ring can also be fastened to the 21 acetabular liner by direct screw fixation where screws are passed directly 22 through the constraining ring into the polyethylene liner.
23 In another embodiment of this invention the constraining ring can be 24 secured to the liner by means of a retaining ring which is designed in an unstressed state to sit in grooves in both the constraining ring and acetabular 26 liner. Upon setting the constraining ring onto the liner the retaining will deform 27 until the constraining ring is fully seated onto the liner at which point the 28 retaining ring relaxes into the designed grove in the liner.
, NO 02/09615 PCT/US01/226...,.
The constraining ring can, in certain embodiments, include one or more 2 recesses or cut-aways to be compatible with the corresponding liner.
3 Alternatively, the constraining ring will be without a recess or cut away for use 4 with liners that likewise lack a recess or cut away.
Description of the Assembly of Cut Away Monopolar Constrained 6 Acetabular Liner with Constraining Ring (see Figure 3): Components of the cut 7 away monopolar constrained acetabular system consisting of: i) metal 8 acetabular shell which is secured to the acetabulum, ii) polyethylene cut away 9 monopolar constrained acetabular liner, and iii) constraining ring. The metal 113 acetabular shell is not essential for this invention as the acetabular liner can be it directed secured into the acetabulum with bone cement. The cut away 12 monopolar constrained acetabular liner is set into the metal acetabular.
The 13 constraining ring is placed over the femoral component and the femoral head is 14 snap-fitted into the acetabular liner. The constraining ring is then set onto the cut away monopolar constraining acetabular liner with the cutouts of the 16 constraining ring aligned with the cutouts of the acetabular liner.
17 Demonstration of the Position of the Acetabular Component within the 18 Hip and Range of Motion: The actual position of the acetabular component 19 within the hip will be set during the operative procedure and will depend on the patient's anatomy and gait. The cut away portion of the acetabular component 21 allows for sufficient range of motion in flexion. The cut away portion of the 22 acetabular component allows for sufficient internal rotation at 900 of flexion.
23 The cut away portion of the acetabular component allows for sufficient external 24 rotation at neutral flexion.
In any of the embodiments of the invention, the liners of the invention 26 can be used with hemispherical and non-hemispherical acetabular shells.
27 Also, the invention can be used with any head diameter, including large 28 head diameters (for example, 35 mm or greater, such as 38 mm, 40 mm, 42 =
1 mm, 44 mm, and any diameter in between or larger) in order to increase the 2 range of motion in comparison with currently available constrained systems.
3 The invention is further demonstrated by the following example, which 4 do not limit the invention in any manner.
6 Example 1 8 The load required for insertion and dislocation of femoral heads in a 9 constrained liner according to the invention was quantified by inserting 32 and 38 mm heads into simulated liners of electron beam crosslinked UHMWPE.
Two and three dimensional modeling was performed to assess ROM and 12 stability itz vitro. The liner had no chamfer.
13 The ROM, and the loads required for insertion and dislocation using 14 different opening diameters for 32 mm and 38 mm heads in simulated monopolar liners were measured. A 32 mm head with a 31 mm liner opening 16 required 60 lbs. for insertion and 55 lbs. for dislocation. When the opening was 17 increased to 31.5 mm the forces for insertion and dislocation decreased to 29 18 lbs., and 24 lbs., respectively. Testing of 35.5 mm, 36.5 mm, and 37.5 mm 19 openings with a 38 min head was performed. The insertional loads were 157, 130, and 28 lbs. The force necessary to produce dislocation of the femoral head 21 were 135, 126, and 28 lbs., respectively.
22 The ROM for the 38 mm head and a 35.5nun orifice liner is 110 .
This 23 increases to 118 and 131 as the orifice diameter is increased to 36.5 and 37.5 24 = mm. The 32 mm head and 31 mm orifice liner has 116 ROM. The ROM
increases to 124 when a 31.5 mm orifice is used with the 32 mm head.
26 These data demonstrate that the constrained design according to the 27 invention can minimize the occurrence of dislocation, even with heads and 28 liners that are constructed to permit enhanced range of movement.
=
PCT/US01/226¨
.
1 It is to be understood that the description, specific examples and data, 2 while indicating exemplary embodiments, are given by way of illustration and 3 are not intended to limit the present invention. Various changes and 4 modifications within the present invention will become apparent to the skilled artisan from the discussion, disclosure and data contained herein, and thus are 6 considered part of the invention.
Claims (9)
1. A constraining ring that is used in conjunction with a monopolar constrained acetabular liner or a cut away monopolar constrained acetabular liner, wherein the constraining ring contains at least one positioned recess that is compatible with the corresponding acetabular liner, wherein the ring fits around the perimeter of the monopolar constrained acetabular liner, and wherein the ring is set onto the acetabular liner during the operative procedure after the femoral head is reduced into the acetabular liner.
2. The constraining ring according to claim 1, wherein the shape of the ring is circular.
3. The constraining ring according to claim 1 or 2, wherein the ring is made of metallic material.
4. The constraining ring according to claim 3, wherein the metallic material is cobalt chrome alloy, titanium, or stainless steel.
5. The constraining ring according to any one of claims 1 to 4, wherein the ring is a single piece.
6. The constraining ring according to any one of claims 1 to 5, wherein the ring has at least two recesses.
7. The constraining ring according to any one of claims 1 to 5, wherein the liner has no recess.
8. The constraining ring according to any one of claims 1 to 5, wherein the liner has at least one recess.
9. The constraining ring according to any one of claims 1 to 5, wherein the liner has at least two recesses.
Applications Claiming Priority (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US22204900P | 2000-07-31 | 2000-07-31 | |
| US60/222,049 | 2000-07-31 | ||
| US23434500P | 2000-09-22 | 2000-09-22 | |
| US60/234,345 | 2000-09-22 | ||
| US28952801P | 2001-05-09 | 2001-05-09 | |
| US60/289,528 | 2001-05-09 | ||
| CA2416256A CA2416256C (en) | 2000-07-31 | 2001-07-19 | Monopolar constrained acetabular component |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2416256A Division CA2416256C (en) | 2000-07-31 | 2001-07-19 | Monopolar constrained acetabular component |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2711010A1 CA2711010A1 (en) | 2002-02-07 |
| CA2711010C true CA2711010C (en) | 2013-10-15 |
Family
ID=42979782
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2711010A Expired - Lifetime CA2711010C (en) | 2000-07-31 | 2001-07-19 | Monopolar constrained acetabular component |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2711010C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107638233A (en) * | 2017-10-27 | 2018-01-30 | 北京大学国际医院 | The anti-dislocation hip prosthesis and its manufacture method of a kind of 3D printing femoral head |
-
2001
- 2001-07-19 CA CA2711010A patent/CA2711010C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2711010A1 (en) | 2002-02-07 |
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