Intervertebral cage with porosity gradient

An intervertebral cage with an outer frame, an open inner core region and a porosity gradient within the outer frame is provided. The outer frame includes a posterior wall, an anterior wall, a pair of side walls extending between the posterior wall and the anterior wall and the porosity gradient may comprise at least one of: a decreasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; an increasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; a decreasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls; and an increasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls.

TECHNICAL FIELD

The present disclosure generally relates to interbody implants, and particularly, to intervertebral cages.

BACKGROUND

Implantable interbody bone grafts such as spinal fusion devices are known and used by surgeons to keep and maintain adjacent vertebrae in a desired spatial relationship, provide weight-bearing support between adjacent vertebral bodies, and promote interbody bone ingrowth and fusion after surgery on a patient. Such spinal fusion devices, sometimes referred to as intervertebral cages, may be used for spine surgical procedures to treat degenerative disk disease, discogenic low back pain, spondylolisthesis, and the like.

Intervertebral cages are formed from a pair of side walls, a posterior wall, and an anterior wall so as to define an open interior for which allograft (donor) or autograft (patient) bone material can be placed to promote the interbody bone ingrowth and fusion. Some intervertebral cages are made from nonporous materials that prevent interbody bone ingrowth and fusion in the wall portions of the cage. Other intervertebral cages have a solid interior made from a porous material, but the porous material in the interior of the cage prevents allograft or autograft bone material from being placed therein and thereby be used to promote bone ingrowth and fusion. Accordingly, an improved intervertebral cage with an open interior and a porous structure that provides weight-bearing support between adjacent vertebral bones and aids in bone ingrowth and fusion would be desirable.

SUMMARY

In one embodiment, an intervertebral cage includes an outer frame with an open inner core region and a porosity gradient within the outer frame. The outer frame includes a posterior wall, an anterior wall, a pair of side walls extending between the posterior wall and the anterior wall, and the porosity gradient may extend through at least one of the pair of side walls of the outer frame. The porosity gradient may comprise a decreasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls or an increasing average pore diameter in a direction from the outer surface to the inner surface of the at least one of the pair of side walls. In the alternative, or in addition to, the porosity gradient may comprise a decreasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls or an increasing average pore diameter in a direction from the upper surface to the lower surface of the at least one of the side walls. Also, the porosity gradient may comprise a decreasing average pore diameter in a direction from the posterior wall to the anterior wall of the outer frame or an increasing average pore diameter in a direction from the posterior wall to the anterior wall of the outer frame.

In some embodiments, the intervertebral cage may have a porosity gradient with an increasing average pore diameter in a direction from the posterior wall to a central portion of at least one of the pair of side walls and in a direction from the anterior wall to the central portion of at least one of the pair of side walls. In other embodiments, the porosity gradient may comprise a decreasing average pore diameter in a direction from the posterior wall to a central portion of at least one of the pair of side walls and in a direction from the anterior wall to the central portion of at least one of the pair of side walls.

The porosity gradient within the intervertebral cage may include a first portion with porosity within a range of about 5% by volume to about 30% by volume and a second portion within a range of about 30% by volume to about 90% by volume. Also, the porosity gradient may include a first portion with porosity with an average diameter between about 5 μm and about 100μ and a second portion with porosity with an average diameter between about 100 μm and 1000 μm.

In another embodiment, an intervertebral cage comprises an outer frame with a posterior wall, an anterior wall and a pair of side walls extending between the anterior wall and the posterior wall. An open inner core region is between the posterior wall, the anterior wall and the pair of side walls, and a porosity gradient is within at least one of the posterior wall, the anterior wall and the pair of side walls comprises a porosity gradient. The porosity gradient promotes bone ingrowth and fusion between adjacent vertebrae when the intervertebral cage is inserted between a pair of vertebra during a spine surgery. The porosity gradient may include a first portion with porosity within a range of about 5% by volume to about 30% by volume and a second portion within a range of about 30% by volume to about 90% by volume. In the alternative, or in addition to, the porosity gradient may include a first portion with porosity with an average diameter between about 5 μm and about 100μ and a second portion with porosity with an average diameter between about 100 μm and 1000 μm. Also the porosity gradient may comprise at least one of: a decreasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; an increasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; a decreasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls; and an increasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls.

In still another embodiment, a method for promoting bone ingrowth and fusion between adjacent vertebrae comprises inserting an intervertebral cage between a pair of adjacent vertebrae during a spine surgical procedure. The intervertebral cage includes an outer frame with a posterior wall, an anterior wall and a pair of side walls extending between the anterior wall and the posterior wall. An open inner core region is between the posterior wall, the anterior wall and the pair of side walls, and a porosity gradient is within at least one of the posterior wall, the anterior wall and the pair of side walls comprises a porosity gradient. The porosity gradient enhances flow of bodily fluids and bone material into the intervertebral cage and promotes bone ingrowth and fusion between adjacent vertebrae. The porosity gradient mat comprise at least of: a decreasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; an increasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; a decreasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls; and an increasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls. In some embodiments, the method includes placing allograft or autograft bone material within the open inner core region.

DETAILED DESCRIPTION

According to one or more embodiments described herein, an intervertebral cage may generally comprise a pair of side walls, a posterior wall, an interior wall, an open inner core region, and a porosity gradient within at least one of the pair of side walls, posterior wall, and interior wall. The porosity gradient may include porosity at a first location or position within the one of the side walls, posterior wall, and/or interior wall with a first average pore diameter and porosity at a second location or position within the one of the side walls, posterior wall, and/or interior wall with a second average pore diameter that is different than the first average pore diameter. In the alternative, the porosity gradient may include porosity at the first location or position within the one of the side walls, posterior wall, and/or interior wall with a first average pore diameter and porosity at the second location or position within the one of the side walls, posterior wall, and/or interior wall with the same average pore diameter as the first average pore diameter, however the number or density of pores at the second location or position is different than the number or density of pores at the first location. Various embodiments of intervertebral cages will be described in further detail herein with specific reference to the appended drawings.

FIG. 1generally depicts one embodiment of an intervertebral cage10with an outer frame12with a pair of side walls100, a posterior wall110, and an anterior wall120. An open inner core region140is provided within the outer frame12. The intervertebral cage10has an upper surface102(+Y direction), a lower surface104(−Y direction), a posterior end112, and an anterior end122. Also, each of the side walls100have an outer surface106distal to the open inner core region140and an inner surface108proximal to the open inner core region140.

At least one of the side walls100, posterior wall110and/or anterior wall120has a porosity gradient (not shown inFIG. 1) that assists in bone ingrowth and fusion when the intervertebral cage10is used and placed between adjacent vertebrae of a patient during a surgical procedure. As used herein, the term “porosity” refers to void space in volume percent within a matrix of material used to form the intervertebral cage10and the phrase “porosity gradient” refers to a change in porosity as a function of distance (e.g., thickness, width, and/or length) within the intervertebral cage10. Also, allograft or autograft bone material may be placed within the open inner core region140to promote bone ingrowth and fusion. In some embodiments, at least one of the side walls100includes one or more apertures101through which allograft or autograft bone material can be placed into the open inner core region140to promote bone ingrowth and fusion. Accordingly, the intervertebral cage10without allograft or autograft bone material within the open inner core region140may be positioned between a pair of adjacent vertebra during spine surgery, and then the open inner core region140may be filled with allograft or autograft bone material utilizing the one or more apertures101. In the alternative, the intervertebral cage10with allograft or autograft bone material within the open inner core region140may be positioned between a pair of adjacent vertebra during spine surgery, and additional allograft or autograft bone material may optionally be inserted into the open inner core region140.

In embodiments, at least one of the side walls100, posterior wall110and/or anterior wall120of the intervertebral cage10has one or more portions with porosity within the range of about 10% to about 80% by volume with open pores distributed throughout. For example, the at least one of the side walls100, posterior wall110and/or anterior wall120of the intervertebral cage10may have one or more portions with porosity within the range of about 10% to about 80% by volume with open pores distributed throughout. In some embodiments, at least one of the side walls100, posterior wall110and/or anterior wall120of the intervertebral cage10has a first portion with a porosity within the range of about 5% to about 30% by volume, for example within the range of about 5% to about 10% by volume, and a second portion with a porosity within the range of about 30% to about 90% by volume, for example within the range of about 75% to about 90% by volume. The average pore diameter of the porosity may range from about 1 micron to about 1500 microns. For example, the average pore diameter of the porosity may range from about 1 micron to about 500 microns. In another example, the average pore diameter of the porosity may range from about 5 microns to about 500 microns. As used herein, the phrase “average pore diameter” refers to an average of the diameters of at least ten (10) pores on a selected plane along a thickness, width or length of the intervertebral cage10and the term “diameter” refers to an average diameter of a pore obtained by an average of at least two diameter measurements of the pore.

In some embodiments, the intervertebral cage10has a first portion with a first average pore diameter and a second portion with a second average pore diameter that is different than the first average pore diameter such that the porosity of the first portion is different than the porosity of the second portion. In other embodiments, the intervertebral cage10has a first portion with a first average pore diameter and a second portion with a second average pore diameter that is the same as the first average pore diameter, however the number of pores in the second portion is different than the number of pores in the first portion such that the porosity of the first portion is different than the porosity of the second portion.

Referring now toFIGS. 2A-2B, an embodiment of a porosity gradient along a thickness (Y direction) of the side walls100is schematically depicted. Particularly, an end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 2Aand a side cross-sectional view depicted by section II-II inFIG. 1is schematically depicted inFIG. 2B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1and a second portion105with porosity having a second average pore diameter d2that is greater than the first average pore diameter d1(i.e., d2>d1). As depicted inFIGS. 2A-2B, the first portion103may extend from the upper surface102towards the lower surface104and the second portion105is positioned below (−Y direction) the first portion103. In embodiments, each of the side walls100comprises an upper (+Y direction) first portion103extending from the upper surface102towards the lower surface104, a lower (−Y direction) first portion103extending from the lower surface104towards the upper surface102, and a second portion105positioned between the upper and lower first portions103. Accordingly, a porosity gradient is provided along the thickness (Y direction) of the side walls100with the second portion105with porosity having the second average pore diameter d2sandwiched between the upper and lower first portions103with porosity having the first average pore diameter d1that is less than the second average pore diameter d2. In some embodiments, the first portion103, and other first portions described herein, may have a porosity within the range of about 5% to about 30% by volume, for example within the range of about 5% to about 10% by volume, and the second portion105, and other second portions described herein, may have a porosity within the range of about 30% to about 90% by volume, for example within the range of about 75% to about 90% by volume. Also, whileFIGS. 2A-2Bschematically depict three separate porosity portions, i.e., two first portions103and one second portion105, it should be understood that the porosity gradient along the thickness of the side walls100may be formed from only two separate porosity portions, i.e., only one first portion103and one second portion105, more than three separate porosity portions, or a single porosity portion with a pores comprising a gradual or continuous change in pore diameter as a function of thickness of the side walls100.

Referring now toFIGS. 3A-3B, another embodiment of a porosity gradient along a thickness (Y direction) of the side walls100is schematically depicted. Particularly, the end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 3Aand the side cross-sectional view depicted by section II-II inFIG. 1is schematically depicted inFIG. 3B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A) and a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1. As depicted inFIGS. 3A-3B, the second portion105may extend from the upper surface102towards the lower surface104. Also, the first portion103is positioned below (−Y direction) the second portion105. In embodiments, each of the side walls100comprises an upper (+Y direction) second portion105extending from the upper surface102towards the lower surface104, a lower (−Y direction) second portion105extending from the lower surface104towards the upper surface102, and a first portion103positioned between the upper and lower second portions105. Accordingly, a porosity gradient is provided along the thickness (Y direction) of the side walls100with a first portion103with porosity having the first average pore diameter d1sandwiched between upper and lower second portions105with porosity having the second average pore diameter d2that is greater than the first average pore diameter d1.

Referring now toFIGS. 4A-4B, yet another embodiment of a porosity gradient along a thickness (Y direction) of the side walls100is schematically depicted. Particularly, the end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 4Aand the side cross-sectional view depicted by section II-II inFIG. 1is schematically depicted inFIG. 4B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A), a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1, and a third portion107with porosity having a third average pore diameter d3that is greater than the first average pore diameter d1and less than the second average pore diameter d2(i.e., d1<d3<d2). In some embodiments, the third portion107, and other third portions described herein, may have porosity between the range of porosity of the first portion103and the range of porosity of the second portion105. For example, the third portion may have porosity within the range of about 5% to about 90% by volume, for example within the range of about 10% to about 75% by volume. In embodiments, where the first portion103has porosity within the range of about 5% to about 10% by volume and the second portion105has porosity within the range of about 75% to about 90% by volume, the third portion107may have porosity within the range of about 10% to about 75% by volume.

Still referring toFIGS. 4A-4B, the first portion103may extend from the upper surface102towards the lower surface104, the second portion105may extend from the lower surface104towards the upper surface102, and the third portion107is positioned between the first portion103and the second portion105. Accordingly, a porosity gradient is provided along the thickness (Y direction) of the side walls100with a third portion107with porosity having the third average pore diameter d3sandwiched between a first portion with porosity having the first average pore diameter d1that is less than the third average pore diameter d3(i.e., d1<d3) and a second portion with porosity having the second average pore diameter d2that is greater than the third average pore diameter d3(i.e., d2>d3).

Referring now toFIGS. 5A-5B, still yet another embodiment of a porosity gradient along a thickness (Y direction) of the side walls100is schematically depicted. Particularly, the end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 5Aand the side cross-sectional view depicted by section II-II inFIG. 1is schematically depicted inFIG. 5B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A), a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1, and a third portion107with porosity having a third average pore diameter d3(FIG. 4A) that is greater than the first average pore diameter d1and less than the second average pore diameter d2(i.e., d1<d3<d2). As depicted inFIGS. 5A-5B, the second portion105may extend from the upper surface102towards the lower surface104, the first portion103may extend from the lower surface104towards the upper surface102, and the third portion107is positioned between the second portion105and the first portion103. Accordingly, a porosity gradient is provided along the thickness (Y direction) of the side walls100with a third portion107with porosity having the third average pore diameter d3sandwiched between a second portion105with porosity having the second average pore diameter d2that is greater than the third average pore diameter d3(i.e., d2>d3) and a first portion103with porosity having the first average pore diameter d1that is less than the third average pore diameter d3(i.e., d1<d3).

Referring now toFIGS. 6A-6B, an embodiment of a porosity gradient along a width (Z direction) of the side walls100is schematically depicted. Particularly, an end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 6Aand a top cross-sectional view depicted by section inFIG. 1is schematically depicted inFIG. 6B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A) and a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1(i.e., d2>d1). As depicted inFIGS. 6A-6B, the first portion103may extend from the outer surface106towards the inner surface108and the second portion105may be positioned inwardly toward the open inner core region140from the first portion103. In embodiments, each of the side walls100comprises an outer first portion103extending from the outer surface106towards the inner surface108, an inner first portion103extending from the inner surface108towards the outer surface106, and a second portion105positioned between the outer and inner first portions103. Accordingly, a porosity gradient is provided along the width (Z direction) of the side walls100with the second portion105with porosity having the second average pore diameter d2sandwiched between the outer and inner first portions103with porosity having the first average pore diameter d1that is less than the second average pore diameter d2.

Referring now toFIGS. 7A-7B, another embodiment of a porosity gradient along a width (Z direction) of the side walls100is schematically depicted. Particularly, an end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 7Aand a top cross-sectional view depicted by section inFIG. 1is schematically depicted inFIG. 7B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A) and a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1(i.e., d2>d1). As depicted inFIGS. 7A-7B, the second portion105may extend from the outer surface106towards the inner surface108and the first portion103may be positioned inwardly toward the open inner core region140from the second portion105. In embodiments, each of the side walls100comprises an outer second portion105extending from the outer surface106towards the inner surface108, an inner second portion105extending from the inner surface108towards the outer surface106, and a first portion103positioned between the outer and inner second portions105. Accordingly, a porosity gradient is provided along the width (Z direction) of the side walls100with the first portion103with porosity having the first average pore diameter d1sandwiched between the outer and inner second portions105with porosity having the second average pore diameter d2that is greater than the first average pore diameter d1.

Referring now toFIGS. 8A-8B, yet another embodiment of a porosity gradient along a width (Z direction) of the side walls100is schematically depicted. Particularly, the end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 8Aand the top cross-sectional view depicted by section inFIG. 1is schematically depicted inFIG. 8B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A), a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1, and a third portion107with porosity having a third average pore diameter d3(FIG. 4A) that is greater than the first average pore diameter d1and less than the second average pore diameter d2(i.e., d1<d3<d2). As depicted inFIGS. 8A-8B, the first portion103may extend from the outer surface106towards the inner surface108, the second portion105may extend from the inner surface108towards the outer surface106, and the third portion107may be positioned between the first portion103and the second portion105. Accordingly, a porosity gradient is provided along the width (Z direction) of the side walls100with the third portion107with porosity having the third average pore diameter d3sandwiched between the first portion with porosity having the first average pore diameter d1that is less than the third average pore diameter d3(i.e., d1<d3) and the second portion105with porosity having the second average pore diameter d2that is greater than the third average pore diameter d3(i.e., d2>d3).

Referring now toFIGS. 9A-9B, still yet another embodiment of a porosity gradient along a width (Z direction) of the side walls100is schematically depicted. Particularly, the end cross-sectional view depicted by section I-I inFIG. 1is schematically depicted inFIG. 9Aand the top cross-sectional view depicted by section inFIG. 1is schematically depicted inFIG. 9B. Each of the side walls100comprise a first portion103with porosity having a first average pore diameter d1(FIG. 2A), a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1, and a third portion107with porosity having a third average pore diameter d3(FIG. 4A) that is greater than the first average pore diameter d1and less than the second average pore diameter d2(i.e., d1<d3<d2). As depicted inFIGS. 9A-9B, the second portion105may extend from the outer surface106towards the inner surface108, the first portion103may extend from the inner surface108towards the outer surface106, and the third portion107may be positioned between the second portion105and the first portion103. Accordingly, a porosity gradient is provided along the width (Z direction) of the side walls100with the third portion107with porosity having the first average pore diameter d3sandwiched between the second portion105with porosity having the second average pore diameter d2that is greater than the third average pore diameter d3(i.e., d2>d3) and the first portion103with porosity having the second average pore diameter d1that is less than the third average pore diameter d3(i.e., d1<d3).

Referring now toFIGS. 10A-10B, an embodiment of a porosity gradient along a length (X direction) of the intervertebral cage10is schematically depicted. Particularly, a top cross-sectional view depicted by section inFIG. 1is schematically depicted inFIG. 10Aand a side cross-sectional view depicted by section II-II inFIG. 1is schematically depicted inFIG. 10B. A first portion103with porosity having a first average pore diameter d1(FIG. 2A) and a second portion105with porosity having a second average pore diameter d2(FIG. 2A) that is greater than the first average pore diameter d1(i.e., d2>d1) extend along a length of the intervertebral cage. As depicted inFIGS. 10A-10B, the first portion103may extend from the posterior end112towards the anterior end122. Also, the second portion105is positioned between the first portion and the anterior end122. In embodiments, the length of the intervertebral cage10comprises a posterior first portion103extending from the posterior end112towards the anterior end122, an anterior first portion103extending from the anterior end122towards the posterior end112, and a second portion105positioned between the posterior and anterior first portions103. Accordingly, a porosity gradient is provided along the length (X direction) of the intervertebral cage10with a second portion105with porosity having the second average pore diameter d2sandwiched between posterior and anterior first portions103with porosity having the first average pore diameter d1that is less than the second average pore diameter d2.

Referring now toFIGS. 11A-11B, another embodiment of a porosity gradient along a length (X direction) of the intervertebral cage10is schematically depicted. Particularly, a top cross-sectional view depicted by section inFIG. 1is schematically depicted inFIG. 11Aand a side cross-sectional view depicted by section II-II inFIG. 1is schematically depicted inFIG. 11B. A first portion103with porosity having a first average pore diameter d1and a second portion105with porosity having a second average pore diameter d2that is greater than the first average pore diameter d1(i.e., d2>d1) extend along a length of the intervertebral cage. As depicted inFIGS. 11A-11B, the second portion105may extend from the posterior end112towards the anterior end122. Also, the first portion103is positioned between the second portion105and the anterior end122. In embodiments, the length of the intervertebral cage10comprises a posterior second portion105extending from the posterior end112towards the anterior end122, an anterior second portion105extending from the anterior end122towards the posterior end112, and a first portion103positioned between the posterior and anterior second portions105. Accordingly, a porosity gradient is provided along the length (X direction) of the intervertebral cage10with a first portion103with porosity having the first average pore diameter d1sandwiched between posterior and anterior second portions105with porosity having the first average pore diameter d2that is greater than the second average pore diameter d1.

AlthoughFIGS. 2A-11Bonly depict a porosity gradient along a single direction of the intervertebral cage10, it is understood that the intervertebral cage may include a porosity gradient along multiple directions of the intervertebral cage10. For example and without limitation, the intervertebral cage10may have a porosity gradient along a thickness of at least one of the side walls100, posterior wall110and/or anterior wall120, and a porosity gradient along a length of the intervertebral cage10. In the alternative, the intervertebral cage10may have a porosity gradient along a thickness of at least one of the side walls100, posterior wall110and/or anterior wall120, and a porosity gradient along a width of the intervertebral cage10. In another alternative, the intervertebral cage10may have a porosity gradient along a length of the intervertebral cage10and along a width of the intervertebral cage10. In still another alternative, the intervertebral cage10may have a porosity gradient along a thickness of at least one of the side walls100, posterior wall110and/or anterior wall120, a porosity gradient along a length of the intervertebral cage10, and a porosity gradient along a width of the intervertebral cage10.

In use, the intervertebral cage10is implanted between a pair of adjacent vertebrae during a spine surgery operation. The open inner core region140may include allograft or autograft bone material before the intervertebral cage10is implanted between a pair of adjacent vertebrae. In the alternative, or in addition to, allograft or autograft bone material may be placed in the open inner core region140after the intervertebral cage10is implanted between a pair of adjacent vertebrae, e.g., by inserting the allograft or autograft bone material through at least one of the apertures101in the side walls100. The porosity gradient within the intervertebral cage10enhances the flow of bodily fluids and bone material into the intervertebral cage and promotes bone ingrowth and fusion between adjacent vertebrae. In some embodiments, the porosity gradient provides for porosity that may generally match or mimic porosity of bone material (i.e., the porosity in volume percent and/or average pore diameter) in contact with the intervertebral cage10. Particularly, the intervertebral cage10may include a first portion103with porosity that general match's porosity of osteon (compact) bone material in contact with the first portion103and a second portion105with porosity that general matches porosity of cancellous (spongy) bone material in contact with the second portion105. In this manner the intervertebral cage10provides portions with porosity that match different types of bone material thereby promoting bone ingrowth and fusion between adjacent vertebrae.

The intervertebral cage10may be formed or manufactured using any technique, process, etc., used to form porous bodies including without limitation3D printing, electric discharge machining (EDM), mechanical machining, chemical etching, layer-by-layer processes, and the like. The intervertebral cage10may be formed from any material suitable for medical implants. Non-limiting examples include Non-limiting examples of suitable materials include metallic materials such as titanium, titanium alloys, tantalum, tantalum alloys, stainless steel alloys, and cobalt-chromium alloys, polymer materials such as polyethylene (PE) and polyether ether ketone (PEEK), and ceramic materials such as hydroxyapatite (HAP) Ca10(PO4)6(OH)2, tricalcium phosphate Ca3(PO4)2, and mixtures of hydroxyapatite and tricalcium phosphate.

The intervertebral cages described herein may be used to promote bone ingrowth and fusion between adjacent vertebrae during and after a spine surgical procedure. In some embodiments, the porosity gradient enhances the flow of fluids, nutrients, additives, etc., in the thickness direction (Y direction) of the side walls100. For example, the first average pore diameter d1and/or the second average pore diameter d2may be configured to wick fluids, nutrients additives, etc., from the upper surface102and the lower surface104through the upper and lower first portions103, respectively, towards the second portion105positioned between the upper and lower first portions103(FIGS. 2A-2B). In the alternative, the first average pore diameter d1and/or the second average pore diameter d2may be configured to wick fluids, nutrients additives, etc., from the upper surface102and the lower surface104through the upper and lower second portions105, respectively, towards the first portion103positioned between the upper and lower second portions105(FIGS. 3A-3B). Also, the first average pore diameter d1, the second average pore diameter d2and the third average pore diameter d3may be configured to wick fluids, nutrients additives, etc., from the lower surface104towards the upper surface102through the second portion105, third portion107and first portion103(FIGS. 4A-4B), or wick fluids, nutrients additives, etc., from the upper surface102towards the lower surface104through the second portion105, third portion107and first portion103(FIGS. 5A-5B).

In other embodiments, the porosity gradient enhances the flow of fluids, nutrients, additives, etc., through the width direction (Z direction) of the side walls100. For example, the first average pore diameter d1and/or the second average pore diameter d2may be configured to wick fluids, nutrients additives, etc., from the outer surface106and the inner surface108through the outer and inner first portions103, respectively, towards the second portion105positioned between the outer and inner first portions103(FIGS. 6A-6B). In the alternative, the first average pore diameter d1and/or the second average pore diameter d2may be configured to wick fluids, nutrients additives, etc., from the outer surface106and the inner surface108through the outer and inner second portions105, respectively, towards the first portion103positioned between the outer and inner second portions105(FIGS. 7A-7B). Also, the first average pore diameter d1, the second average pore diameter d2and the third average pore diameter d3may be configured to wick fluids, nutrients additives, etc., from the inner surface108towards the outer surface106through the second portion105, third portion107and first portion103(FIGS. 8A-8B), or wick fluids, nutrients additives, etc., from the outer surface106towards the inner surface108through the second portion105, third portion107and first portion103(FIGS. 9A-9B).

In still other embodiments, the porosity gradient enhances the flow of fluids, nutrients, additives, etc., through the length direction (X direction) of the outer frame12. For example, the first average pore diameter d1and/or the second average pore diameter d2may be configured to wick fluids, nutrients additives, etc., from the posterior end112and the anterior end122through the posterior and anterior first portions103, respectively, towards the second portion105positioned between the posterior and anterior first portions103(FIGS. 10A-10B). In the alternative, the first average pore diameter d1and/or the second average pore diameter d2may be configured to wick fluids, nutrients additives, etc., from the posterior end112and the anterior end122through the posterior and anterior second portions105, respectively, towards the first portion103positioned between the posterior and anterior second portions105(FIGS. 10A-10B).

The terms “upper” and “lower” refer to orientations depict in the drawings and are not meant to define exact orientations of intervertebral cages described herein. Also, the terms “generally” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.