US20200261233A1

US20200261233A1 - Reverse shoulder arthroplasty system

Info

Publication number: US20200261233A1
Application number: US16/796,538
Authority: US
Inventors: Robert Patrick Stchur; John D. Kuczynski
Original assignee: Sure Orthopedics LLC
Current assignee: Sure Orthopedics LLC
Priority date: 2019-02-20
Filing date: 2020-02-20
Publication date: 2020-08-20
Also published as: US20200261209A1; US20200261247A1; US11813171B2

Abstract

An orthopedic medical device assembly that includes a first bearing for attachment to an implant and a second bearing for attachment to an implant, such as a glenosphere.

Description

BACKGROUND OF THE DISCLOSURE

The exemplary embodiments of the subject disclosure relate generally to a reverse shoulder arthroplasty (RSA) system.
RSA restores a fulcrum on the glenoid so that the deltoid can then rotate the arm upward. This is accomplished by taking an unconstrained joint (i.e., a large ball on a small socket) and converting it to a constrained joint (i.e., introducing a large socket to replace the ball and a small ball to replace the socket). This constraining of the joint is a reason why RSA outcomes are predictably good, as the constrained implant does all the work and does not rely on soft tissue to achieve stability and function. These advantages have allowed RSA surgeries to gain prominence, now being used for more indications to treat a wider domain of subjects.
Nevertheless, RSA still has room for improvement. One drawback with RSA is the appearance of the shoulder after the surgery, i.e., the dropped shoulder deformity. This is particularly problematic in thin female subjects. In some cases, for example, subjects who have undergone RSA cannot maintain the thin straps of dresses or bras on their shoulders. While RSA can provide a desirable functional outcome for the subject, retaining the native appearance of the shoulder would improve the subjects' overall experience with the surgery.
Accordingly, there remains a need to improve upon shoulder cosmesis and avoid “distalization” of the humeral implant, in which the humerus is moved inferior to its native location. There also remains a need to increase the strength of a surgically replaced shoulder.

SUMMARY OF THE DISCLOSURE

In an exemplary embodiment, the subject disclosure provides an orthopedic medical device assembly that includes a first bearing for attachment to an implant. The first bearing includes a first substantially planar base, a first recess adapted to receive an implant component. The first recess includes a first minimum point of inflection, in which a position normal to the first minimum point of inflection along the first substantially planar base is spaced from a lateral side of the first substantially planar base a first distance along the substantially planar base. The first bearing further includes a first thickness defined by a distance from the first substantially planar base to the first minimum point of inflection. The orthopedic medical device assembly further includes a second bearing for attachment to the implant. The second bearing includes a second substantially planar base having an overall size and shape the same as the first substantially planar base, and a second recess adapted to receive an implant component, in which the second recess has a radius of curvature the same as the first recess and includes a second minimum point of inflection. A position normal to the second minimum point of inflection along the second substantially planar base is spaced from a lateral side of the second substantially planar base a second distance greater than the first distance. The second bearing further includes a second thickness defined by a distance from the second substantially planar base to the second minimum point of inflection, wherein the second thickness is greater than the first thickness.
In another exemplary embodiment, the orthopedic medical device assembly further includes a third bearing for attachment to the implant. The third bearing includes a third substantially planar base having an overall size and shape the same as the first substantially planar base, a third recess adapted to receive an implant component, in which the third recess has a radius of curvature the same as the first recess and includes a third minimum point of inflection. A position normal to the third minimum point of inflection along the third substantially planar base is spaced from a lateral side of the third substantially planar base a third distance greater than the second distance. The third bearing further includes a third thickness defined by a distance from the third substantially planar base to the third minimum point of inflection, wherein the third thickness is greater than the second thickness.
In another exemplary embodiment, the first and second recesses are concave shaped. In an exemplary embodiment, the first bearing has a cross-sectional profile along its midline that includes a first trapezoid having sides at a first angle, and the second bearing has a cross-sectional profile along its midline of a second trapezoid having sides at a corresponding second angle that differs from the first angle.
In an exemplary embodiment, the first and second bearings comprise a polymer, such as an ultra-high molecular weight polyethylene.
In an exemplary embodiment, the second distance is greater than the first distance by about 1 to 5 mm. In another exemplary embodiment, the second thickness is at least 2 mm, or at least 5 mm, or at least 8 mm.
Another exemplary embodiment of the subject disclosure provides a reverse shoulder implant assembly that includes a humeral stem having a tray and a distal end; and a first bearing for attachment to the humeral stem. The first bearing includes a first recess that includes a first minimum point of inflection. When the first bearing is attached to the tray, the first minimum point of inflection is spaced from an inferior plane defined by the distal end of the humeral stem a predetermined distance along a longitudinal direction of the humeral stem. The first bearing further includes a first thickness defined by a minimum distance from the tray to the first minimum point of inflection. The reverse shoulder implant assembly further includes a second bearing. The second bearing includes a second recess that includes a second minimum point of inflection. When the second bearing is attached to the tray, the second minimum point of inflection is spaced from the inferior plane defined by the distal end of the humeral stem the predetermined distance along the longitudinal direction of the humeral stem. The second bearing further includes a second thickness defined by a minimum distance from the tray to the second minimum point of inflection. The second thickness is greater than the first thickness.
In an embodiment, the predetermined distance is from about 50.8 mm to about 76.2 mm (i.e., 2 inches to about 3 inches). In another embodiment, the tray includes a plane at an angle from about 135° to about 155° from a longitudinal axis of a stem of the humeral stem. In an embodiment, the second thickness is at least 9 mm.
Another embodiment of the subject disclosure provides a reverse shoulder assembly kit. The kit includes a humeral stem having a tray and a proximal end. The kit further includes a first bearing for attachment to the humeral stem. The first bearing includes a first recess that includes a first minimum point of inflection. When the first bearing is attached to the tray, the first minimum point of inflection is spaced from a superior plane defined by the proximal end of the humeral stem a predetermined distance along a longitudinal direction of the humeral stem. The first bearing further includes a first thickness defined by a minimum distance from the tray to the first minimum point of inflection of about 3 mm.
The kit further includes a second bearing. The second bearing includes a second recess that includes a second minimum point of inflection. When the second bearing is attached to the tray, the second minimum point of inflection is spaced from the superior plane defined by the proximal end of the humeral stem the predetermined distance along the longitudinal direction of the humeral stem. The second bearing further includes a second thickness defined by a minimum distance from the tray to the second minimum point of inflection of about 6 mm.
In an exemplary embodiment, the kit further includes a third recess that includes a third minimum point of inflection. When the third bearing is attached to the tray, the third minimum point of inflection is spaced from the superior plane defined by the proximal end of the humeral stem the predetermined distance along the longitudinal direction of the humeral stem. The third bearing further includes a third thickness of about 9 mm defined by a minimum distance from the tray to the second minimum point of inflection.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of the exemplary embodiments of the subject disclosure will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, there is shown in the drawings exemplary embodiments. It should be understood, however, that the subject application is not limited to the precise arrangements and instrumentalities shown.

FIGS. 1A-C are cross-sectional views of an orthopedic medical device assembly in accordance with an exemplary embodiment of the subject disclosure;

FIGS. 2A-C are cross-sectional views of the orthopedic medical device assembly of FIGS. 1A-C, described in accordance with an exemplary embodiment of the subject disclosure;

FIGS. 3A-C are cross-sectional views of a plurality of bearing components in accordance with an exemplary embodiment of the subject disclosure;

FIG. 4 is a perspective view of a humeral implant stem according to an alternative embodiment of the subject disclosure; and

FIG. 5 is an anterior view of the humeral implant of FIG. 4.

DETAILED DESCRIPTION OF THE DISCLOSURE

Reference will now be made in detail to exemplary embodiments of the subject disclosure illustrated in the accompanying drawings. Wherever possible, the same or like reference numbers will be used throughout the drawings to refer to the same or like features. It should be noted that the drawings are in simplified form and are not drawn to precise scale. In reference to the disclosure herein, for purposes of convenience and clarity only, directional terms such as upper, lower, top, bottom, above, below and diagonal, are used with respect to the accompanying drawings. Such directional terms used in conjunction with the following description of the drawings should not be construed to limit the scope of the subject disclosure in any manner not explicitly set forth. Additionally, the term “a,” as used in the specification, means “at least one.” The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import.
“About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, or ±0.1% from the specified value, as such variations are appropriate.
“Substantially” as used herein shall mean considerable in extent, largely but not wholly that which is specified, or an appropriate variation therefrom as is acceptable within the field of art.
As used herein, the term “adjacent” refers to being near or adjoining. Adjacent components (which can be integral or separate) can be spaced apart from one another, or can be in actual or direct contact with one another (i.e., directly adjacent).
Throughout the subject application, various aspects thereof can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the subject disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.
Furthermore, the described features, advantages and characteristics of the exemplary embodiments of the subject disclosure may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the subject disclosure can be practiced without one or more of the specific features or advantages of a particular exemplary embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all exemplary embodiments of the present disclosure.
Referring now to the drawings, FIGS. 1-5 illustrate an orthopedic medical device assembly 100 according to an exemplary embodiment of the subject disclosure. The assembly 100 includes a first bearing 101, a second bearing 201, and a third bearing 301 for engagement with a glenosphere implant 402. Each bearing includes a substantially planar base 103, 203, 303 that are each sized and shaped the same and a recess 104, 204, 304. The substantially planar bases 103, 203, 303 are each adapted to be seated on a tray 512 of a humeral stem implant 511 having a distal end 513. Certain embodiments of the subject disclosure, however, are not necessarily limited to the particular design of the implant to which the instantly disclosed bearings can be applied.
The recesses 104, 204, 304 are concave shaped, all having the same radius of curvature and are each adapted to engage the glenosphere implant 402. In one exemplary embodiment, the recess 104, 204, 304 each have a radius of curvature suitable to operatively receive a glenosphere having a diameter of from about 34 mm to about 42 mm (e.g., a 36, 38, or 40 mm diameter glenosphere).
Each recess includes a minimum point of inflection 105, 205, 305 and has a thickness defined by the distance from the minimum point of inflection to its substantially planar base. In other words, a position normal 106, 206, 306 to the minimum point of inflection 105, 205, 305 to the minimum point of inflection 105, 205, 305 defines the thickness of a respective bearing.
In this exemplary embodiment, bearing 101 has a thickness 109 of about 1-3 mm and preferably 3 mm, bearing 201 has a thickness 209 of about 3-6 mm and preferably 6 mm, and bearing 301 has a thickness 309 of about 6-9 mm, and preferably 9 mm. In one exemplary embodiment, a bearing (101, 201, 301) has a thickness of at least 2 mm, or at least 5 mm, or at least 8 mm. Bearings of other thicknesses can be provided in accordance with exemplary embodiments of the disclosed subject matter.
A distance from the center 420 of the glenosphere to a shaft 519 of the humeral implant e.g., a longitudinal axis of the stem defines a lever arm (121, 221, 321) and substantially corresponds to the distance from the acromion to the deltoid muscle of the subject. A longer lever arm (121, 221, 321) provides a higher torque and facilitates abduction. Lever arm 321 is longer than lever 221 and lever arm 221 is longer than lever arm 121. The associated larger lever arm is provided by the use of a thicker bearing on the humeral implant while maintaining a fixed position of the minimum point of inflection in relation to a distal or proximal end of the implant.
As shown in FIGS. 1A-1C, the position normal 106, 206, 306 to the first minimum point of inflection 105, 205, 305 along the substantially planar base 103, 203, 303, is spaced from a lateral side 107, 207, 307 of the substantially planar base a distance 108, 208, 308, along the substantially planar base 103, 203, 303. The third distance 308 is greater than the second distance 208 and the second distance 208 is greater than the first distance 108. In an embodiment, the second distance (e.g., 208) is greater than the first distance (e.g. 108) by about 1 to 5 mm, e.g. 1, 2, 3, 4, or 5 mm.
Stated differently, the presently disclosed bearings allow the implant to maintain its medial orientation with respect to the glenosphere as the thickness of the bearing is increased. Prior bearings do not maintain its location of the minimum point of inflection with respect to the glenosphere when the bearings are increased in thickness, causing the humeral implant to distalize (inferiorize). Accordingly, increases in the lever arm can be attained with a thicker bearing without an attendant drop in the shoulder. In other words, a thicker bearing according to the subject disclosure lateralizes the humerus, without distalizing the humerus.
FIGS. 2A-C also illustrate bearings 101, 201, 301 attached to a tray 512 of a humeral stem 511. The humeral stem has a distal end 513, which defines an inferior plane 514. The inferior plane is perpendicular or substantially perpendicular to the longitudinal axis 516 of the humeral stem. When the bearing 101, 201, 301 is attached to the tray 512, the minimum point of inflection 105, 205, 305 is spaced from the inferior plane 514 defined by the distal end 513 of the humeral stem 511 a predetermined distance 516. This predetermined distance 516 is the same for each of the bearings 101, 201, 301. A superior plane 523 is defined about a proximal end of the humeral stem 511. The superior plane 523 is also perpendicular or substantially perpendicular to the longitudinal axis 516 of the humeral stem.
When the bearing 101, 201, 301 is attached to the tray 512, the minimum point of inflection 105, 205, 305 is spaced from the inferior plane 514 defined by the distal end 513 of the humeral stem 511 a predetermined distance 516. Also, when the bearing 101, 201, 301 is attached to the tray 512, the minimum point of inflection 105, 205, 305 is spaced from the superior plane 523 a second predetermined distance 524. In other words, as the bearings get thicker, the distal end of implant stem does not distalize (inferiorize). The predetermined distance 516 remains the same regardless of the bearing thickness. Similarly, the proximal end of the implant does move proximally (or distally) as the thickness is changed, the second predetermined distance 524 also remaining the same regardless of the bearing thickness. The bearing 101, 201, 301 is medialized on the glenosphere 402 as the thickness of the bearing is modified.
In certain exemplary embodiments, the predetermined distance is from about 1 inch to about 4 inches, or from about 1.5 inches to about 3.5 inches, or from about 2 inches to about 3 inches.
As shown best in FIGS. 3A-3C, bearings 101, 201, 301, when a cross-section is taken along its midline has a section that along with plane 122 defines a trapezoid having sides at a first angle 117, 217, 317 and sides at a second angle 118, 218, 318. Angles 117, 217 and 317 can be different from each other and angles 118, 218 and 318 can be different from each other.
In certain embodiments, the bearing 101, 201, 301 includes a polymer, such as a polyethylene polymer. In this exemplary embodiment, the polymer is an ultra-high molecular weight (UHMWPE) polyethylene polymer (e.g., a polyethylene polymer having a molecular weight between 2-6 million with a degree of polymerization between 71,000-214,000). In other embodiments, the bearing 101, 201, 301 comprises a polymer or component (e.g., a primary polymer or component) besides polyethylene.
As noted, the bearings 101, 201, 301 can be used in conjunction with a variety of humeral stems. FIGS. 6-7 depict a humeral stem 611 according to an exemplary embodiment of the subject disclosure. The humeral stem 611, includes a tray 612 located adjacent to a proximal end 642 of the implant. The tray 612 is configured as best shown in FIG. 6. The tray includes a circular plane 648 for receiving a bearing (e.g., bearing 101, 201 or 301) and a circular ring 652 about a perimeter of the plane. The circular plane 648 includes a plurality of recesses 644 adapted to receive complementary features of a bearing (e.g., bearing 101, 201, 301) for engagement thereto. A plurality of suture holes 646 are provided around the perimeter of the tray to provide an anchor for suturing procedures (e.g., suturing involving the greater tuberosity). Notches, detents or a similar retaining mechanism 654 are provided circumferentially about the circular ring 652 to assist in securing the bearing 101, 201, 301 to the tray 612.
In the particular embodiment shown in FIGS. 6-7, the tray 612 is integrally formed with a shaft 634. The tray includes a plane 671 at an angle from about 135° to about 155° from a longitudinal axis 638 of a stem of the humeral stem.
The shaft 634 extends in the longitudinal direction 638 from the proximal end 642 of the humeral stem 611. As shown best in FIG. 7, shaft 634 includes a proximal section 656 adjacent the tray 612. The proximal section 656 of the shaft 634 further includes a threaded hole 662 adapted to receive a threaded shaft (not shown).
A middle section 658 of the shaft proceeds from the proximal section 556. The middle section 658 has a narrowing profile as it proceeds from the proximal section 656, the profile being the widest along the proximal section where it forms a seat for an inferior portion 673 of the tray 612. The inferior portion 673 of the tray 612 further includes an overhanging portion 675 that is not supported by the shaft 634 and that can serve as an engaging surface for engagement with the humerus. A distal portion 669 of the stem extends from the middle section 658 where the stem is defined by a circular or oval cross-sectional shaped shaft 660 (FIG. 4).
As shown in FIG. 5, the proximal section 656, the middle section 658 and a portion of the distal section 669 can be provided with a porous or textured surface 668 to promote bone attachment, as represented by the diamond cross-hatching. In certain embodiments, the porous or textured surface does not extend an entire length of the shaft 634 (e.g., there is an untextured portion of the distal section 669) so as to prevent the stem from being fractured when attempting to extract the implant during implant revision surgery. The amount of surface textured relative to an untextured portion of the stem can vary.
The total length of the stem 611 can also vary. In certain embodiments, the total length of the stem 611 is from about 2 inches to about 5 inches, or from about 2.5 inches to about 4.5 inches. In one embodiment, the stem 611 has a total length of about 3 inches.
In certain embodiments, a second perimeter wall section 672 of the implant and a third perimeter wall section 674 of the implant extend from a first perimeter wall section 570 at an angle of about 125° to about 135°, or from about 128° to about 132° (e.g., 130°). Alternatively, the second perimeter wall section 672 and/or the third perimeter wall section 674 can extend from the first perimeter wall section 670, at an angle from about 90° to about 180°, or from about 110° to about 150° (e.g., 110°, 111°, 112°, 113°, 114°, 115°, 116°, 117°, 118°, 119°, 120°, 121°, 122°, 123°, 124°, 125°, 126°, 127°, 128°, 129°, 130°, 131°, 132°, 133°, 134°, 135°, 136°, 137°, 138°, 139°, 140°, 141°, 142°, 143°, 144°, 145°, 146°, 147°, 148°, 149°, or 150°).
It will be appreciated by those skilled in the art that changes could be made to the exemplary embodiments described above without departing from the broad inventive concept thereof. It is to be understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the subject disclosure as defined by the appended claims.

Claims

1. An orthopedic medical device comprising:

a first bearing for attachment to an implant, the first bearing including:

a first substantially planar base,

a first recess adapted to receive an implant component, wherein the first recess includes a first minimum point of inflection, wherein a position normal to the first minimum point of inflection along the first substantially planar base is spaced from a lateral side of the first substantially planar base a first distance along the substantially planar base, and

a first thickness defined by a distance from the first substantially planar base to the first minimum point of inflection; and

a second bearing for attachment to the implant that includes:

a second substantially planar base having an overall size and shape the same as the first substantially planar base,

a second recess adapted to receive an implant component, wherein the second recess has a radius of curvature the same as the first recess and includes a second minimum point of inflection, wherein a position normal to the second minimum point of inflection along the second substantially planar base is spaced from a lateral side of the second substantially planar base a second distance greater than the first distance, and

a second thickness defined by a distance from the second substantially planar base to the second minimum point of inflection, wherein the second thickness is greater than the first thickness.

2. The orthopedic medical device of claim 1, further comprising a third bearing for attachment to the implant that includes:

a third substantially planar base having an overall size and shape the same as the first substantially planar base,

a third recess adapted to receive an implant component, wherein the third recess has a radius of curvature the same as the first recess and includes a third minimum point of inflection, wherein a position normal to the third minimum point of inflection along the third substantially planar base is spaced from a lateral side of the third substantially planar base a third distance greater than the second distance, and

a third thickness defined by a distance from the third substantially planar base to the third minimum point of inflection, wherein the third thickness is greater than the second thickness.

3. The orthopedic medical device of claim 1, wherein the first and second recess is concave shaped.

4. The orthopedic medical device of claim 1, wherein the first bearing has a cross-sectional profile along its midline of a first trapezoid having a sides at a first angle, and wherein the second bearing has a cross-sectional profile along its midline of a second trapezoid having sides at a corresponding second angle that differs from the first angle.

5. The orthopedic medical device of claim 1, wherein the first and second bearings comprise a polymer.

6. The orthopedic medical device of claim 5, wherein the polymer is ultra-high molecular weight polyethylene.

7. The orthopedic medical device of claim 1, wherein the second distance is greater than the first distance by about 1 to 5 mm.

8. The orthopedic medical device of claim 1, wherein the second thickness is at least 2 mm.

9. The orthopedic medical device of claim 1, wherein the second thickness is at least 5 mm.

10. The orthopedic medical device of claim 1, wherein the second thickness is at least 8 mm.

11. A reverse shoulder implant assembly comprising:

a humeral stem having a tray and a distal end; and

a first bearing for attachment to the humeral stem, the first bearing including:

a first recess that includes a first minimum point of inflection, wherein when the first bearing is attached to the tray, the first minimum point of inflection is spaced from an inferior plane defined by the distal end of the humeral stem a predetermined distance along a longitudinal direction of the humeral stem, and

a first thickness defined by a minimum distance from the tray to the first minimum point of inflection, and

a second bearing that includes:

a second recess that includes a second minimum point of inflection, wherein when the second bearing is attached to the tray, the second minimum point of inflection is spaced from the inferior plane defined by the distal end of the humeral stem the predetermined distance along the longitudinal direction of the humeral stem, and

a second thickness defined by a minimum distance from the tray to the second minimum point of inflection, wherein the second thickness is greater than the first thickness.

12. The reverse shoulder implant of claim 11, wherein the first or second recess is concave shaped.

13. The reverse shoulder implant of claim 11, wherein the first bearing has a cross-sectional profile along its midline of a first trapezoid having a sides at a first angle, and wherein the second bearing has a cross-sectional profile along its midline of a second trapezoid having sides at a corresponding second angle that differs from the first angle.

14. The reverse shoulder implant of claim 11, wherein the first and second bearings comprise a polymer.

15. The reverse shoulder implant of claim 14, wherein the polymer is ultra-high molecular weight polyethylene.

16. The reverse shoulder implant of claim 11, wherein the predetermined distance is about 50.8 mm to about 76.2 mm.

17. The reverse shoulder implant of claim 11, wherein the tray includes a plane at an angle from about 135° to about 155° from a longitudinal axis of a stem of the humeral stem.

18. The reverse shoulder implant of claim 11, wherein the second thickness is at least 9 mm.

19. A reverse shoulder assembly kit comprising:

a humeral stem having a tray and a proximal end; and

a first recess that includes a first minimum point of inflection, wherein when the first bearing is attached to the tray, the first minimum point of inflection is spaced from a superior plane defined by the proximal end of the humeral stem a predetermined distance along a longitudinal direction of the humeral stem, and

a first thickness defined by a minimum distance from the tray to the first minimum point of inflection of about 3 mm, and

a second bearing that includes:

a second recess that includes a second minimum point of inflection, wherein when the second bearing is attached to the tray, the second minimum point of inflection is spaced from the superior plane defined by the proximal end of the humeral stem the predetermined distance along the longitudinal direction of the humeral stem, and

a second thickness of about 6 mm defined by a minimum distance from the tray to the second minimum point of inflection.

20. The reverse should assembly kit of claim 18, further comprising a third recess that includes

a third minimum point of inflection, wherein when the third bearing is attached to the tray, the third minimum point of inflection is spaced from the superior plane defined by the proximal end of the humeral stem the predetermined distance along the longitudinal direction of the humeral stem, and

a third thickness of about 9 mm defined by a minimum distance from the tray to the second minimum point of inflection