Patent Publication Number: US-2020289278-A1

Title: Directional locking reverse shoulder prostheses and systems

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 15/248,868, filed Aug. 26, 2016, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/210,600, filed Aug. 27, 2015, the contents of each of which is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to prosthesis systems comprising trays and liners, including trays and liners having a locking mechanism. 
     BACKGROUND 
     This section provides background information related to the present disclosure, which is not necessarily prior art. 
     Reverse Shoulder Arthroplasty (RSA) is an alternative to traditional shoulder arthroplasty that is often indicated for use in elderly patients with deficient rotator cuffs. With advancements in RSA designs and simple surgical techniques, the use of RSA has spread to patients that are younger or who do not have rotator cuff deficiency. Traditional reverse shoulder liner locking mechanisms are symmetrical about an axis and therefore have the same strength in any loading orientation, but are limited by a snap lock feature that is deformed during insertion of the articular surface into the humeral stem or tray. The snaps are usually tabs that must be compressed beyond a rigid metal lip or ring. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present inventors have recognized, among other things, that a problem to be solved is that current RSA techniques often times result in the undesirable effects of scapular notching and limited range of motion. Currently practiced solutions to these undesirable effects employ a steeper humeral implant angle and, additionally or alternatively, a lateralized center of rotation. However, a result of these currently practiced solutions is an increased load applied to the liner locking mechanism that can result in liner dissociation. Accordingly, the present teachings provide for systems comprising trays and liners having an asymmetrical locking mechanism to bias the strength of the liner to resist loading forces and associated methods. 
     In one aspect, a prosthesis system for a joint can comprise a tray and a liner. The tray can have a lateral groove disposed in an inner surface of a lateral circumferential portion of the tray. The tray can also have a medial groove disposed in an inner surface of a medial circumferential portion of the tray. The liner can have an upper segment and a lower segment. At least the lower segment can comprise a locking portion for lockingly engaging the tray. The locking portion can comprise a lateral toe positioned generally diametrically opposite a plurality of resiliently deformable medial fingers defined in the locking portion. The liner and the tray can be engageable in a lateral-to-medial direction so that the plurality of medial fingers can resiliently deform to engage the medial groove subsequent to engagement of the lateral toe within the lateral groove. Upon implantation, the tray and the liner can be selectively rotationally oriented with respect to each other such that the lateral toe of the liner can be engaged within a middle portion of the lateral groove of the tray to resist disassociation of the liner from the tray when the prosthesis is subjected to physiological loading conditions. The medial circumferential portion of the tray can further comprise a medial tab that can extend from an upper surface thereof, and wherein a lower surface of the upper segment of the liner can define a female receptacle for matingly receiving the medial tab of the tray. The lower surface of the upper segment of the liner can define a plurality of female receptacles for receiving the medial tab. Each of the plurality of female receptacles can correspond to a unique angular rotational position between the liner and the tray. 
     In one aspect, a liner can have an upper segment and a lower segment. At least the lower segment can comprise a locking portion for lockingly engaging a tray. The locking portion can comprise a lateral toe positioned generally diametrically opposite a plurality of resiliently deformable medial fingers defined therein. The tray and the liner can be engageable in a lateral-to-medial direction so that the plurality of medial fingers can resiliently deform to engage a medial groove disposed in an inner surface of a medial circumferential portion of the tray subsequent to engagement of the lateral toe within the lateral groove. Upon implantation, the liner can be selectively rotationally oriented with respect to the tray such that the lateral toe of the liner can be engaged within a middle portion of a lateral groove of the tray to resist disassociation of the liner from the tray when the prosthesis is subjected to physiological loading conditions. The lower surface of the upper segment of the liner can define one or a plurality of female receptacles for matingly receiving a medial tab extending from an upper surface of the medial circumferential portion of the tray. Each of the plurality of female receptacles can correspond to a unique angular rotational position between the liner and the tray. 
     In another aspect, a tray can have a lateral groove disposed in an inner surface of a lateral circumferential portion of the tray. The tray can also have a medial groove disposed in an inner surface of a medial circumferential portion of the tray. The tray can be engageable with a liner that can have an upper segment and a lower segment. At least the lower segment of the liner can comprise a locking portion for lockingly engaging the tray. The locking portion can comprise a lateral toe positioned generally diametrically opposite a plurality of resiliently deformable medial fingers defined therein. The tray and the liner can be engageable in a lateral-to-medial direction so that the plurality of medial fingers can resiliently deform to engage the medial groove subsequent to engagement of the lateral toe within the lateral groove. Upon implantation, the tray can be selectively rotationally oriented with respect to the liner such that the lateral toe of the liner can be engaged within a middle portion of the lateral groove of the tray to resist disassociation of the liner from the tray when the prosthesis is subjected to physiological loading conditions. The medial circumferential portion of the tray can further comprise a medial tab that can extend from an upper surface thereof for matingly receiving a medial female receptacle defined in the upper segment of the liner. The lateral circumferential portion of the tray can further comprise a lateral tab that can extend from an upper surface thereof for matingly receiving a lateral female receptacle defined in at least a portion of the upper segment of the liner. 
     In another aspect, the present teachings provide for a method that can comprise the steps of selectively rotationally orienting a tray and a liner with respect to each other such that a lateral toe of a lower segment of a liner can be aligned with a middle portion of a lateral groove disposed in an inner surface of a lateral circumferential portion of the tray; and engaging the lateral toe of the liner in the lateral groove of the tray; engaging a plurality of resiliently deformable medial fingers defined in the lower segment of the liner within a medial groove disposed in an inner surface of a medial circumferential portion of a tray, wherein the medial fingers are disposed generally diametrically opposite the lateral toe; wherein the lateral toe resists disassociation of the liner from the tray when the prosthesis is subjected to physiological loading conditions in use. The method can comprise engaging a medial tab extending from an upper surface of the medial circumferential portion of the tray with a female receptacle defined in the upper segment of the liner. Additionally or alternatively, the method can comprise engaging a lateral tab extending from an upper surface of the lateral circumferential portion of the tray with a lateral female receptacle defined in at least a portion of the upper segment of the liner. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  illustrates exemplary loading conditions of a reverse shoulder arthroplasty prosthesis; 
         FIG. 2  illustrates a cross-sectional side view of an exemplary prosthesis system according to the present disclosure; 
         FIG. 3  illustrates a top perspective view of an exemplary liner according to the present disclosure; 
         FIG. 4  illustrates a side view of the liner of  FIG. 3 ; 
         FIG. 5  illustrates a top view of the liner of  FIG. 3 ; 
         FIG. 6  illustrates a top perspective view of an exemplary tray according to the present invention; 
         FIGS. 7A-7D  illustrate cross-sectional views of an exemplary prosthesis system during the lateral-to-medial engagement of the liner and the tray; and 
         FIG. 8  illustrates a front view of an exemplary prosthesis system during engagement of the liner and the tray. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     The present teachings provide for systems comprising trays and liners having an asymmetrical locking mechanism to bias the strength of the liner to resist physiological loading forces and associated methods. In a reverse shoulder arthroplasty (RSA) configuration, a metal glenosphere attached to the scapula articulates against a liner attached to the humeral component. Current RSA systems and techniques can result in the undesirable effects of scapular notching and limited range of motion. Currently practiced solutions to these undesirable effects typically employ a steeper humeral implant angle and, additionally or alternatively, a lateralized center of rotation. Biomechanically derived loading for the humeral component can be estimated based on the muscle activation direction, here, the deltoid muscle, with lack of rotator cuff muscle contribution. This estimation can be fully understood by reference to A. Terrier et al.,  Simulated joint and muscle forces in reversed and anatomic shoulder prostheses . Journal of Bone &amp; Joint Surgery, British Volume, 90(6) 751-756 (08). As shown in  FIG. 1 , the primary joint reaction force  102  is in the direction of the humeral axis, combining a compressive load vector  103  and a medial shear load vector  108  on the humeral articular surface. Therefore steeper humeral implant angles can lead to higher shear (or lever-out) forces  103  experienced by the liner, challenging the liner/tray locking mechanism. Further, lateralization of the center of rotation increases the joint reaction forces necessary to move the arm, which can also challenge the locking mechanism. The instant systems, liners, trays, and associated methods seek to reduce or eliminate these adverse effects by disposing the most robust portion of the locking mechanism laterally to resist the primary load direction. The inventors have found through physical and empirical testing that the asymmetrical locking mechanism can maintain approximately 60% higher shear loading than a conventional circumferential lock mechanism. 
     With reference to  FIGS. 2-8 , a prosthesis system  200  for a joint can comprise a tray  202  and a liner  204 . As illustrated in  FIG. 2 , the tray  202  can have a lateral groove  206  disposed in an inner surface of a lateral circumferential portion  210  of a circumferential lip of the tray  202 . The tray  202  can also have a medial groove  208  disposed in an inner surface of a medial circumferential portion  212  of the circumferential lip of the tray  202 . The lateral groove  206  and the medial groove  208  can comprise different portions of a single groove extending the circumference of the inner surface of the tray  202 . The liner  204  can have an upper segment  214  and a lower segment  216 . At least the lower segment  216  can comprise a locking portion for lockingly engaging the tray  202 . The locking portion can comprise a lateral toe  218  positioned generally diametrically opposite a plurality of resiliently deformable medial fingers  220  defined therein. The liner  204  and the tray  202  can be engageable in a lateral-to-medial direction so that the plurality of medial fingers  220  can resiliently deform to engage the medial groove  208  subsequent to engagement of the lateral toe  218  within the lateral groove  206 . The plurality of medial fingers  220  can comprise from about 2 to about 6 medial fingers. The lateral toe  218  of the liner  204  can remain substantially undeformed during and subsequent to engagement within the lateral groove  206 . Upon implantation, the tray  202  and the liner  204  can be selectively rotationally oriented with respect to each other such that the lateral toe  218  of the liner  204  can be engaged within a middle portion of the lateral groove  206  of the tray  202  to resist disassociation of the liner  204  from the tray  202  when the prosthesis is subjected to physiological loading conditions. 
     In one aspect, the lateral groove  206  of the tray  202  can further comprise a lateral locking lip  222  projecting radially inward from the inner surface of the lateral circumferential portion  210 . The lateral toe  218  and the lateral locking lip  222  can cooperate to at least partially secure the liner  204  within the tray  202 . In a further aspect, the lateral toe  218  and the lateral locking lip  222  can cooperate to serve as the primary locking feature of the locking mechanism. 
     In another aspect, the superior surface of the medial groove  208  of the tray  202  is formed by a medial locking lip  224  projecting radially inward from the inner surface of the medial circumferential portion  212  of the tray  202 . A medial lead-in ramp  226  can extend from a point above the top surface of the medial locking lip  224  to the top surface of the medial locking lip  224 . The medial lead-in ramp  226  provides a surface to guide the one or more resiliently deformable medial fingers  220  over the medial locking lip  224 . In another aspect, the plurality of medial fingers  220  can further comprise a snap lip  228  projecting outward from the distal end of each of the plurality of medial fingers  220 . The medial fingers  220  can resiliently deform when passing over the medial lead-in ramp  226  and return to a neutral position, for example, once the snap lips  228  pass the medial locking lip  224 . The locking lip of the medial groove  208  and the snap lip  228  of each of the plurality of medial fingers  220  cooperate to at least partially secure the liner  204  within the tray  202 . In a further aspect, the plurality of medial fingers  220  and the snap lip  228  can serve as a secondary locking feature of the locking mechanism. 
     In one aspect, the medial circumferential portion  212  of the tray  202  can further comprise a medial tab  230  that can extend from an upper surface thereof. A lower surface of the upper segment  214  of the liner  204  can define a medial female receptacle  234  for matingly receiving the medial tab  230  of the tray  202  in order to prevent rotation of the liner  204  relative to the tray  202  when engaged. The lower surface of the upper segment  214  of the liner  204  can further define a plurality of medial female receptacles  234  for receiving the medial tab  230 . The liner  204  can have at least three medial female receptacles  234 . Each of the plurality of female receptacles can correspond to a unique angular rotational position between the liner  204  and the tray  202 . Each of the plurality of medial female receptacles  234  can have a center-to-center angular rotational measurement of from about 10 degrees to about 60 degrees. In one example, each of the plurality of medial female receptacles  234  can have a center-to-center angular rotational measurement of about 30 degrees. Adjusting the angular rotational position between the liner  204  and the tray  202  can provide for either or both of customizable balancing and customized constraint of the joint that can, for example, enable a surgeon to maximize joint stability. 
     In another aspect, the lateral circumferential portion  210  of the tray  202  can further comprise a lateral tab  232  that can extend from an upper surface thereof. At least a portion of the upper segment  214  of the liner  204  proximate the lateral toe  218  can define a lateral female receptacle  236  for matingly receiving the lateral tab  232  of the tray  202  in order to prevent rotation of the liner  204  relative to the tray  202  when engaged. At least a portion of the upper segment  214  of the liner  204  proximate the lateral toe  218  can further define a plurality of lateral female receptacles  236 , wherein each of the plurality of female receptacles corresponds to a unique angular rotational position between the liner  204  and the tray  202 . The liner  204  can have at least three lateral female receptacles  236 . Each of the plurality of lateral female receptacles  236  can have a center-to-center angular rotational measurement of from about 10 degrees to about 60 degrees. In one example, each of the plurality of lateral female receptacles  236  can have a center-to-center angular rotational measurement of about 30 degrees. 
     In another aspect, the tray  202  can have an outside diameter of from about 30 mm to about 50 mm. In one example, the tray  202  can have an outside diameter of about 40 mm. 
     In one aspect, the tray  202  can have a central through-hole  242  disposed therein. The center through-hole  242  can facilitate, for example, conversion assembly and tray removal. In one example, a tool can be inserted or threaded into the through-hole to lift the tray out of the stem. 
     In another aspect, an upper segment  214  of the liner  204  can define a face  244  that comprises an articulating surface. The face  244  can have a diameter D a  of from about 30 mm to about 50 mm. In one example, the face  244  can have a diameter of from about 35 mm to about 50 mm. Some exemplary face diameters can include 36 mm, 40 mm, and 42 mm. In another aspect, the face can have a face angle  246  measured between a stem axis A s  and an axis A f  normal to the face of less than about 150 degrees. In another aspect, the face can have a face angle  246  of from about 135 degrees to about 155 degrees. 
     In one aspect, the liner  204  can comprise polyethylene. The polyethylene can comprise ultra high molecular weight polyethylene. The liner  204  can further comprise vitamin E. In additional or alternative aspects, the liner  204  can be monolithic such that the upper segment  214  and the lower segment  216  are continuous or the upper segment  214  and the lower segment  216  can be joined to form the liner  204 . 
       FIGS. 7A-7D  illustrate an exemplary method of assembling the liner  204  into the tray  202 . A tray  202  and a liner  204  can be selectively rotationally oriented with respect to each other such that a lateral toe  218  of a lower segment  216  of a liner  204  can be aligned with a middle portion of a lateral groove  206  disposed in an inner surface of a lateral circumferential portion  210  of the tray  202 . As shown in  FIG. 7A , the lateral toe  218  of the liner  204  can be engaged in the lateral groove  206  of the tray  202  while the lateral tab  232  of the tray  202  can be disposed in a selected one of the plurality of lateral female receptacles  236  of the liner  204 . As shown in  FIGS. 7B and 7C , a plurality of resiliently deformable medial fingers  220  can be deformed as they are urged into contact with the medial lead-in ramp  226  while the medial tab  232  can be disposed in a selected one of the plurality of medial female receptacles  234 . As shown in  FIG. 7D , the medial fingers  220  can return to a neutral position, for example, once the snap lips  228  pass the medial locking lip  224 . The medial fingers  220  are disposed generally diametrically opposite the lateral toe  218  and the lateral toe  218  resists disassociation of the liner  204  from the tray  202  when the prosthesis is subjected to physiological loading conditions. 
     Experimental Results 
     In another aspect, evaluation of resistance to liner dissociation in an exemplary directional locking mechanism according to the present disclosure compared to a conventional circumferential locking mechanism using physical testing and Finite Element Analysis (FEA) was performed. Similar size ultrahigh molecular weight polyethylene (UHMWPE) liners, one with a conventional circumferential locking mechanism design and one with a directional locking mechanism, were assembled per surgical technique in a tray fixture and mounted horizontally in a DI water bath at 37 degrees C. in a testing assembly. A 40 mm load head was used to apply a constant compressive load of 500 N and the load head was translated medially with respect to the fixed liner at a constant rate of 50 mm/min until the liner dissociated from the spacer or tray. Horizontal displacement and shear load values were collected at 100 Hz. A t-test assuming equal variance, with the null hypothesis that there was no difference in peak shear load per design, was used to determine difference in shear load between the circumferential locking design and direction design. A p value of less than 0.05 indicates a significant result. FEA was performed with identical constraints as the physical test setup using Ansys Workbench version 15 (Ansys Inc., Canonsburg, Pa.). Models utilized linear elastic properties for Ti-6Al-4Vspacers and trays (modulus: 1.497 GPa poisons ratio: 0.3) and non-linear properties for UHMWPE determined from the literature up to a strain level of 1.64 [5]. Frictional contact between the two metal components and poly component was specified at 0.2. Results were compared to physical testing to validate the FEA model. 
     Physical testing indicated that the circumferential and directional lock mechanisms resisted peak shear forces of about 511±19 N and about 835±13 N, respectively, a statistically significant difference (p&lt;0.0005). FEA analysis predicted peak shear loads of about 480 N and about 878.6 N, an error of about 6% and about 5% from physical testing results. 
     Some numbered examples of the present disclosure follow. 
     Example 1 is a system that can comprise a tray having a circumferential lip forming a recess, the circumferential lip can include a lateral groove disposed in an inner surface of a lateral circumferential portion of the circumferential lip and a medial groove disposed in the inner surface of a medial circumferential portion of the circumferential lip; and a liner coupleable with the tray with a locking portion, wherein the locking portion can comprise a lateral toe configured to engage the lateral groove in the tray and a plurality of medial fingers resiliently deformable to engage the medial groove of the tray to lock the liner onto the tray. 
     In Example 2, the subject matter of Example 1 optionally includes wherein the liner can define a plurality of medial female receptacles for receiving the medial tab. 
     In Example 3, the subject matter of Example 2 optionally includes wherein each of the plurality of medial female receptacles can correspond to a unique angular rotational position between the liner and the tray. 
     In Example 4, the subject matter of any one or more of Examples 2-3 optionally include wherein each of the plurality of medial female receptacles can have a center to center angular rotational measurement of from about 10 degrees to about 60 degrees with respect to adjacent female receptacles. 
     In Example 5, the subject matter of any one or more of Examples 1-4 optionally include wherein the lateral circumferential portion of the tray can further comprise a lateral tab extending from an upper surface thereof, and wherein the liner proximate the lateral toe can define a lateral female receptacle for matingly receiving the lateral tab of the tray. 
     In Example 6, the subject matter of Example 5 optionally includes wherein the liner proximate the lateral toe can define a plurality of lateral female receptacles, wherein each of the plurality of female receptacles can correspond to a unique angular rotational position between the liner and the tray. 
     In Example 7, the subject matter of any one or more of Examples 1-6 optionally include wherein a superior surface of the medial groove can be formed by a medial locking lip projecting radially inward from the inner surface of the medial circumferential portion of the tray. 
     In Example 8, the subject matter of Example 7 optionally includes a medial lead-in ramp that can extend from a point above a top surface of the medial locking lip to the top surface of the medial locking lip. 
     In Example 9, the subject matter of any one or more of Examples 1-8 optionally include wherein the tray can have a central through-hole disposed therein. 
     In Example 10, the subject matter of any one or more of Examples 1-9 optionally include wherein each of the plurality of medial fingers can further comprise a snap lip projecting radially outward from a distal end thereof. 
     In Example 11, the subject matter of any one or more of Examples 1-10 optionally include wherein the upper segment of the liner can define a face comprising articulating surface. 
     In Example 12, the subject matter of Example 11 optionally includes wherein the articulating surface can have a diameter of from about 35 mm to about 55 mm. 
     In Example 13, the subject matter of any one or more of Examples 1-12 optionally includes wherein the face can have a face angle of less than about 150 degrees as measured between a stem axis and an axis normal to the face. 
     In Example 14, the subject matter of any one or more of Examples 1-13 optionally include wherein the face can have a face angle of from about 135 degrees to about 155 degrees. 
     Example 15 is a method that can comprise selectively rotationally orienting a tray and a liner with respect to each other such that a lateral toe of a liner is aligned with a middle portion of a lateral groove disposed in an inner surface of a lateral circumferential portion of a circumferential lip of the tray; engaging the lateral toe of the liner in the lateral groove of the tray; and engaging a plurality of resiliently deformable medial fingers defined in the lower segment of the liner within a medial groove disposed in an inner surface of a medial circumferential portion of the circumferential lip, wherein the medial fingers are disposed generally diametrically opposite the lateral toe; wherein the lateral toe and the lateral groove cooperate to resist disassociation of the liner from the tray when the prosthesis is subjected to physiological loading conditions in use. 
     In Example 16, the subject matter of Example 15 optionally includes engaging a medial tab extending from an upper surface of the medial circumferential portion of the circumferential lip with a medial female receptacle defined in the upper segment of the liner. 
     In Example 17, the subject matter of Example 16 optionally includes engaging the medial tabs extending from an upper surface of the medial circumferential portion of the circumferential lip with a selected one of a plurality of uniquely angularly oriented medial female receptacle defined in the upper segment of the liner. 
     In Example 18, the subject matter of any one or more of Examples 15-17 optionally includes engaging a lateral tab extending from an upper surface of the lateral circumferential portion of the circumferential lip with a lateral female receptacle defined in at least a portion of the upper segment of the liner. 
     In Example 19, the subject matter of Example 18 optionally includes engaging the lateral tab extending from an upper surface of the lateral circumferential portion of the circumferential lip with a selected one of a plurality of uniquely angularly oriented lateral female receptacles defined in the upper segment of the liner. 
     In Example 20, the subject matter of Example 18 optionally includes engaging the lateral tab extending from an upper surface of the lateral circumferential portion of the circumferential lip with a selected one of a plurality of uniquely angularly oriented lateral female receptacles defined in the upper segment of the liner. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     Throughout this specification, plural instances may implement components, operations, or structures described as a single instance. Although individual operations of one or more methods are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. Structures and functionality presented as separate components in example configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements fall within the scope of the subject matter herein. 
     Although an overview of the inventive subject matter has been described with reference to specific example embodiments, various modifications and changes may be made to these embodiments without departing from the broader scope of embodiments of the present disclosure. Such embodiments of the inventive subject matter may be referred to herein, individually or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single disclosure or inventive concept if more than one is, in fact, disclosed. 
     The embodiments illustrated herein are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed. Other embodiments may be used and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. The Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. As used herein, the term “or” may be construed in either an inclusive or exclusive sense. Moreover, plural instances may be provided for resources, operations, or structures described herein as a single instance. Additionally, boundaries between various resources, operations, modules, engines, and data stores are somewhat arbitrary, and particular operations are illustrated in a context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within a scope of various embodiments of the present disclosure. In general, structures and functionality presented as separate resources in the example configurations may be implemented as a combined structure or resource. Similarly, structures and functionality presented as a single resource may be implemented as separate resources. These and other variations, modifications, additions, and improvements fall within a scope of embodiments of the present disclosure as represented by the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.