Patent Publication Number: US-2021169654-A1

Title: Metal reinforced acetabular shell liner

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to orthopaedic prosthetic components and, more particularly, to acetabular prosthetic components. 
     BACKGROUND 
     Joint arthroplasty is a surgical procedure in which a patient&#39;s natural joint is replaced by a prosthetic joint. In a hip arthroplasty procedure, at least a portion of a patient&#39;s hip ball and socket joint is replaced with one or more corresponding prosthetic components. For example, the socket portion of the joint, known as the acetabulum, may be replaced with one or more acetabular prosthetic components (e.g., an acetabular shell that fits within the acetabulum and a liner that fits within the shell to act as a bearing surface). Similarly, the ball portion of the joint, known as the femoral head, may be replaced with a femoral head prosthetic component. 
     In recent years, it has been determined that decreasing the differential between the outer diameter of the acetabular prosthetic component (e.g., the acetabular shell) and the outer diameter of the femoral head prosthetic component can produce enhanced results in certain patients. 
     SUMMARY 
     In one aspect, the present disclosure includes an acetabular shell liner for use in a hip arthroplasty surgical procedure. The acetabular shell liner includes a semi-hemispherical inner bearing layer, which includes a rim and a dome attached to the rim. The semi-hemispherical inner bearing layer includes a polymeric material having a first thickness, at an apex of the dome, and a second thickness, at the rim, that is less than the first thickness. Additionally, the acetabular shell liner includes a semi-hemispherical outer reinforcement layer mated with and encasing the dome of the semi-hemispherical inner bearing layer. The semi-hemispherical outer reinforcement layer includes a metallic material to provide structural support to the semi-hemispherical inner bearing layer. 
     In some embodiments of the acetabular shell liner, the first thickness is less than four millimeters. The metallic material of the acetabular shell liner, in some embodiments, has a thickness of approximately 0.5 millimeters. In some embodiments, the semi-hemispherical outer reinforcement layer includes a concave inner wall having a porous surface engaged with the polymeric material of the semi-hemispherical inner bearing layer. The semi-hemispherical outer reinforcement layer of the acetabular shell liner may be 3D printed. Additionally or alternatively, the porous surface may be a coating on the metal material of the semi-hemispherical outer reinforcement layer. The metallic material may include at least one of titanium, cobalt chromium, stainless steel, or medium grade high strength steel. In some embodiments, the semi-hemispherical inner bearing layer may be compression molded onto the semi-hemispherical outer reinforcement layer. In other embodiments, the semi-hemispherical inner bearing layer may be injection molded onto the semi-hemispherical outer reinforcement layer. The semi-hemispherical outer reinforcement layer may be shaped to fit into an acetabular shell of a modular acetabular prosthesis system and the semi-hemispherical inner bearing layer may be shaped to receive a head of a femoral prosthesis. 
     In another aspect, the present disclosure includes a modular acetabular prosthesis. The modular acetabular prosthesis includes an acetabular shell shaped to fit in a surgically prepared acetabulum of a patient. Additionally, the acetabular prosthesis includes an acetabular shell liner. The acetabular shell liner includes a semi-hemispherical inner bearing layer that includes a rim and a dome attached to the rim. The semi-hemispherical inner bearing layer includes a polymeric material. The acetabular shell liner also includes a semi-hemispherical outer reinforcement layer mated with and encasing the dome of the semi-hemispherical inner bearing layer. The semi-hemispherical outer reinforcement layer includes a metallic material to provide structural support to the semi-hemispherical inner bearing layer. Additionally, the semi-hemispherical outer reinforcement layer is shaped to fit into the acetabular shell. 
     In some embodiments of the modular acetabular prosthesis, the polymeric material of the semi-hemispherical inner bearing layer has a thickness, at an apex of the dome, that is less than four millimeters. Additionally, the metallic material of the semi-hemispherical outer reinforcement layer may have a thickness of approximately 0.5 millimeters. The semi-hemispherical outer reinforcement layer may include a concave inner wall having a porous surface engaged with the polymeric material of the semi-hemispherical inner bearing layer. In some embodiments, the semi-hemispherical outer reinforcement layer is 3D printed. Additionally or alternatively, the porous surface may be a coating on the metal material of the semi-hemispherical outer reinforcement layer. The metallic material of the semi-hemispherical outer reinforcement layer may include at least one of titanium, cobalt chromium, stainless steel, or medium grade high strength steel. 
     In yet another aspect, the present disclosure includes a method for using a modular acetabular prosthesis in a hip arthroplasty surgical procedure. The method includes inserting an acetabular shell into a surgically prepared acetabulum of a patient. The method also includes securing, into the acetabular shell, a liner that includes a polymeric semi-hemispherical inner layer that is at least partially encased in a metal semi-hemispherical outer reinforcement layer. The method may also include fitting a head of a femoral prosthesis into a cavity defined by the polymeric semi-hemispherical inner layer of the liner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The concepts described herein are illustrated by way of example and not by way of limitation in the accompanying figures. For simplicity and clarity of illustration, elements illustrated in the figures are not necessarily drawn to scale. Where considered appropriate, reference labels have been repeated among the figures to indicate corresponding or analogous elements. The detailed description particularly refers to the accompanying figures in which: 
         FIG. 1  is an exploded perspective view of an embodiment of a modular acetabular prosthesis having a metal reinforced acetabular shell liner; 
         FIG. 2  is a perspective view of the metal reinforced acetabular shell liner of  FIG. 1 ; 
         FIG. 3  is a plan view of the metal reinforced acetabular shell liner of  FIG. 1 ; 
         FIG. 4  is an elevation view of the metal reinforced acetabular shell liner of  FIG. 1 ; 
         FIG. 5  is a cross-sectional elevation view of one embodiment of the metal reinforced acetabular shell liner of  FIG. 1  taken generally along line  5 - 5  of  FIG. 3 ; 
         FIG. 6  is a cross-sectional elevation view of another embodiment of the metal reinforced acetabular shell liner of  FIG. 1  taken generally along line  5 - 5  of  FIG. 3 ; 
         FIG. 7  is a perspective view of a patient&#39;s acetabulum with an acetabular shell being advanced towards the acetabulum; 
         FIG. 8  is a perspective view of the patient&#39;s acetabulum with the acetabular shell inserted into the acetabulum and the metal reinforced acetabular shell liner being advanced towards the acetabular shell; 
         FIG. 9  is a perspective view of the patient&#39;s acetabulum with the acetabular shell and liner inserted and a femoral prosthesis component being advanced towards a cavity in the liner; and 
         FIG. 10  is a perspective view of the femoral prosthesis fitted into the liner. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described herein in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives consistent with the present disclosure and the appended claims. 
     Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout the specification in reference to the orthopaedic implants or prostheses and surgical instruments described herein as well as in reference to the patient&#39;s natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the written description and claims is intended to be consistent with their well-understood meanings unless noted otherwise. 
     Referring now to  FIG. 1 , an illustrative modular acetabular prosthesis  20  includes a metal reinforced acetabular shell liner  10  and an acetabular shell  70 . In use, as discussed in more detail below, the metal reinforced acetabular shell liner  10  is configured to be received in the acetabular shell  70  and forms a bearing surface for a corresponding femoral component. As shown, the metal reinforced acetabular shell liner  10  includes a semi-hemispherical (i.e., generally hemispherical in shape but not necessarily defining a perfect hemisphere) inner bearing layer  30  and a semi-hemispherical outer reinforcement layer  50  or sleeve. In the illustrative embodiment, the semi-hemispherical inner bearing layer  30  includes a rim  32  and a dome  44  attached to the rim  32 . The dome  44  is defined by, or otherwise includes, a concave inner wall  34  and a convex outer wall  36  opposite the concave inner wall  34 . The concave inner wall  34  extends inwardly from the rim  32  to define a cavity  42 , sized and shaped to receive a head of a femoral prosthesis component, and the convex outer wall  36  extends from the rim  32  and defines an outer surface of the dome  44 . As shown in  FIG. 1 , the rim  32  includes a substantially cylindrical portion  38 , which is attached to or integral with the dome  44 , and a rim edge  40 . 
     As described in more detail herein, the inner bearing layer  30 , in the illustrative embodiment, is made of a polymeric material such as polyethylene (e.g., ultra-high-molecular-weight polyethylene (UHMWPE)), though in other embodiments, the inner bearing layer  30  may be made from a different material (e.g., ceramic). The material (e.g., polymeric material) of the inner bearing layer  30  may be thinner near the rim  32  (e.g., the rim edge  40 ) and thicker at an apex  46  of the dome  44 , as shown in more detail with respect to  FIGS. 5 and 6 . 
     The inner bearing layer  30  is mated with, or otherwise attached to, the semi-hemispherical outer reinforcement layer  50 , which is made of metal (e.g., titanium, cobalt chromium, stainless steel, and/or medium grade high strength steel) and is comparatively much thinner than the inner bearing layer  30 . The metal construction enables the outer reinforcement layer  50  to provide structural reinforcement to the polymer inner bearing layer  30  thereby allowing thinner polymer inner bearing layers to be utilized relative to the case of an unreinforced polymer inner bearing layer. As such, due to the reduction in the amount of material (e.g., the overall thickness of the liner  10 ) between the femoral head and the acetabular shell  70 , a larger femoral head can be used with an acetabular shell  70  of a given size (the outer diameter of which is limited by the size of the patient&#39;s acetabulum) relative to the size of the head that could be used with the same shell in conjunction with a thicker liner. In some patients, such a pairing of implant components may provide enhanced results. 
     Still referring to  FIG. 1 , the outer reinforcement layer  50  is similar in shape to the inner bearing layer  30 , in that the outer reinforcement layer  50  is semi-hemispherical, includes a rim  52 , a concave inner wall  54  extending inwardly from the rim  52  to define a cavity  62 , and a convex outer wall  56  opposite the inner wall  54 . Further, the outer reinforcement layer  50  includes a dome  64  that is defined by, or otherwise includes, the concave inner wall  54  and the convex outer wall  56 . The rim  52  includes a substantially cylindrical portion  58 , which is attached to or integral with the dome  64  and a rim edge  60 . In the illustrative embodiment, the substantially cylindrical portion  58  may be tapered by a predefined amount (e.g., ten degrees), such that the diameter near the rim  52  (e.g., the rim edge  60 ) is greater than the diameter near the dome  64 . The taper may help the acetabular liner  10  lock into the acetabular shell  70  when the liner  10  is pressed into the acetabular shell  70  during a hip arthroplasty procedure. 
     During manufacture, in the illustrative embodiment, the inner bearing layer  30  is molded onto the outer reinforcement layer  50  (e.g., via injection molding or compression molding), such that the outer reinforcement layer  50  encases and provides structural support to the comparatively softer inner bearing layer  30 . Further, in the illustrative embodiment, the inner wall  54  of the outer reinforcement layer  50  is porous, to help the polymeric material of the inner bearing layer  30  securely mate with (e.g., interdigitate with, affix to, etc.) the inner wall  54 . For example, in some embodiments, during the molding process, the polymeric material of the inner bearing layer  30  is forced into or otherwise interdigitated with the porous surface of the inner wall  54 , thereby enhancing a mechanical connection therebetween. 
     In some embodiments, the porosity of the inner wall  54  is provided by a porous coating. One type of porous coating is Porocoat® Porous Coating which is commercially available from DePuy Synthes Products, Inc. of Warsaw, Ind. In other embodiments, the porosity may be an inherent feature of the inner wall  54 , resulting from the process by which the outer reinforcement layer  50  was manufactured. For example, in some embodiments, the outer reinforcement layer  50  may be 3D (three dimensionally) printed to produce porosity in the walls  54 ,  56 . Still referring to  FIG. 1 , the acetabular liner  10  is sized and shaped to be fitted into an acetabular shell  70 , after the acetabular shell  70  has been inserted into a patient&#39;s surgically prepared acetabulum. The acetabular shell  70  may be embodied as a typical acetabular shell prosthesis and is illustratively semi-hemispherical and includes a rim  72 , a concave inner wall  74  that extends inwardly from the rim  72 , and a convex outer wall  76  opposite the inner wall  74 . 
     Referring now to  FIG. 2 , the acetabular shell liner  10  is shown in its manufactured form. As shown, the inner bearing layer  30  is mated with the outer reinforcement layer  50 . In the illustrative embodiment, the rim  32  of the inner bearing layer  30  extends past the rim  52  of the outer reinforcement layer  50 . In other words, in the illustrative embodiment, the outer reinforcement layer  50  does not encase the entire inner bearing layer  30 . The portion of the polymeric inner bearing layer  30  that extends past the rim  52  of the outer reinforcement layer  50  may act as a buffer that reduces the potential of metal-on-metal contact between the femoral prosthesis and the acetabular prosthesis  20  (e.g., the rims  52 ,  72 ), when the prosthetic joint is flexed. 
     Referring now to  FIGS. 3 and 4 , it can be seen that the diameter  84  of the rim  32  of the inner bearing layer  30  is slightly less than the diameter of the rim  52 . As mentioned above, the substantially cylindrical portion  58  of the outer reinforcement layer  50  is tapered from the rim edge  60  to the dome  64  by a predefined angle  86  (e.g., 10 degrees). The tapered shape enables the liner  10  to taper lock or otherwise be secured into the acetabular shell  70  when the liner  10  is pressed into the acetabular shell  70  (e.g., by a surgeon). In some embodiments, and as shown more clearly in  FIGS. 5 and 6 , the rim  32  may have a chamfer to provide clearance between the rim  32  and the rim  52  (e.g., to help the rim  52  lock into the acetabular shell  70 ). 
     Referring now to  FIG. 5 , a generally cross-sectional view of one embodiment  500  of the acetabular shell liner  10  taken along line  5 - 5  of  FIG. 3 , and rotated by 180 degrees, is shown. In the embodiment  500 , a thickness  510  of the inner bearing layer  30  near the rim  32  is less than a thickness  520  of the inner bearing layer  30  at the apex  46  of the dome  44 . In the illustrative embodiment, the change in thickness of the inner bearing layer  30  is gradual, to provide a smooth inner surface for the femoral head to bear against. The thickness  520  of the polymeric material at the apex  46 , in the embodiment  500 , is less than 4 millimeters (e.g., approximately 3.3 millimeters). The metal outer reinforcement layer  50 , by contrast, is much thinner than either of the thicknesses  510 ,  520 , at approximately 0.5 millimeters. 
     The thicknesses of the inner bearing layer  30  and the outer reinforcement layer  50 , taken together, result in a combined thickness that is significantly thinner than typical acetabular shell liners. As such, the embodiment  500  provides a cavity  540  that can accommodate a much larger femoral head for a given acetabular shell size than typical acetabular shell and liner assemblies, while providing the structural integrity afforded by much thicker acetabular shell and liner assemblies (which are unable to accommodate as large of a femoral head). In the embodiment  500 , the ratio of the acetabular shell diameter to femoral head diameter is approximately 46 millimeters to 36 millimeters (i.e., a differential of 10 millimeters). 
     Referring now to  FIG. 6 , a generally cross-sectional view along line  5 - 5  of  FIG. 3 , of another embodiment  600  of the acetabular shell liner  10  is shown. The embodiment  600  is similar to the embodiment  500 , in that the thickness of the inner bearing layer  30  increases from one thickness  610  near the rim  32  to another thickness  620  at the apex  46 . In the embodiment  600 , the thickness  620  is approximately 4.32 millimeters. Similar to the embodiment  500 , the thickness  630  of the outer reinforcement layer  50  in the embodiment  600  is approximately 0.5 millimeters. In the embodiment  600 , the ratio of the acetabular shell diameter to femoral head diameter is approximately 48 millimeters to 36 millimeters (i.e., a differential of 12 millimeters). 
     Referring now to  FIG. 7 , a method for using the modular acetabular prosthesis  20  in a hip arthroplasty procedure may begin with a surgeon inserting the acetabular shell  70  into a surgically prepared (e.g., by a surgical reamer) acetabulum of a patient. The surgeon may press fit the acetabular shell  70  into place using a driver tool. In some embodiments, the surgeon may additionally thread one or more screws through one or more bores in the acetabular shell  70  to further secure the shell  70  in the acetabulum. In yet other embodiments, the surgeon may utilize other techniques, such as use of bone cement, to insert the shell  70  into the acetabulum. 
     Referring now to  FIG. 8 , the surgeon may subsequently secure, into the acetabular shell  70  (which has been inserted into the acetabulum, as described above) a liner (e.g., the acetabular shell liner  10 ) that includes a polymeric semi-hemispherical inner layer (e.g., the inner bearing layer  30 ) that is at least partially encased in a metal semi-hemispherical outer reinforcement layer (e.g. the outer reinforcement layer  50 ). As described above, the liner  10 , in the illustrative embodiment, is shaped to lock into the acetabular shell  70  (e.g., due to the tapered cylindrical portion  58  of the outer reinforcement layer  50 ). Additionally or alternatively, in some embodiments, the liner  10  may be secured into the acetabular shell  70  using another mechanism (e.g., one or more mechanical locking mechanisms). 
     Referring now to  FIGS. 9 and 10 , with the acetabular shell  70  and acetabular shell liner  10  in the patient&#39;s acetabulum, the surgeon may fit a head  910  of a femoral prosthesis  900  into a cavity (e.g., the cavity  42 ) defined by the polymeric semi-hemispherical inner layer (e.g., the inner bearing layer  30 ) of the liner  10 . As described above, the head  910  of the femoral prosthesis  900  is larger (e.g., in diameter) than would be possible with typical acetabular shell and liner assemblies because the combined thickness of the polymeric semi-hemispherical inner layer (e.g., the inner bearing layer  30 ) and the metal semi-hemispherical outer reinforcement layer (e.g., the outer reinforcement layer  50 ) is thinner than typical liners while providing at least as much structural integrity as thicker liners. 
     In subsequent steps, the surgeon may test the fit and range of motion of the femoral head  910  in the modular acetabular prosthesis  20 . In some embodiments, the acetabular shell  70  and/or liner  10  may be trial components (e.g., instruments) that the surgeon may swap out with other trial acetabular shells and/or liners having the features described herein, before determining that a particular combination of acetabular shell and liner provides a satisfactory fit and range of motion. Afterwards, the surgeon may replace the trial components (e.g., instruments) with permanent implant versions of the components. 
     While certain illustrative embodiments have been described in detail in the drawings and the foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. 
     There are a plurality of advantages of the present disclosure arising from the various features of the method, apparatus, and system described herein. It will be noted that alternative embodiments of the method, apparatus, and system of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the method, apparatus, and system that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.