NL2019711B1 - A spinal implant - Google Patents

Abstract

The invention is directed to a spinal implant comprising of a chain of at least two interconnected segments comprising a first and last segment at both ends of the chain, wherein the segments of the chain are interconnected such that the chain can bend in a plane as present between two vertebral endplates of adjacent vertebra of a spinal column to form a ring.

Description

A SPINAL IMPLANT

The invention is directed to a spinal implant comprising of a chain of interconnected segments comprising a first and last segment at both ends of the chain. US2009/0182431 describes a spinal implant which consists of a chain of three segments which is used for implantation between a pair of adjacent vertebrae. The disc between vertebrae of a human spine is sometimes damaged due to disease or injury, or may simply deteriorate due to age, disease, injury or congenital effect. A spinal implant is used to provide proper spacing between adjacent vertebrae. Such implants are also used to promote fusion between the vertebrae. Such implants are also referred to as an interbody fusion cage. In this publication a chain is described consisting of three segments which are interconnected by means of a pivot connection. US8882841 describes a spinal implant which consists of a chain of two segments. The two segments are interconnected by means of a hinge. The spinal implant can have a straightened shape and a crescent shape. The chain is introduced in its straightened shape into an anterior central position within the intervertebral disc space and once in place have it assume its crescent shape.

Typical commercially applied spinal implants do not have the above described chain design and are more like the spinal implant described in US2016193055, WO16148923, US20150018956, US2012265306, WO16130878, US2008097610, US7326251 and US2006241760.

The known spinal implants have the disadvantage that they are relatively large which increases the risk of damaging nerve roots, or the innervation of the psoas muscle. However, in order to have better bone ingrowth and reduce the chance of implant dislocation during the fusion time, a certain surface contact between a spinal implant and the vertebras endplate is needed. The aim of the present invention is to provide a spinal implant which on the one hand is relatively small but at the same time provides sufficient surface contact between the implant and the vertebras endplate.

This is achieved by the following spinal implant. A spinal implant comprising of a chain of interconnected segments comprising a first and last segment at both ends of the chain, wherein the segments of the chain are interconnected such that the chain can bend in a plane as present between two vertebral endplates of adjacent vertebra of a spinal column to form a ring.

Applicants found that when the spinal implant is designed as a chain which can form a ring a slimmer design is possible which at the same time provides a sufficient surface area when positioned between the two vertebral endplates of adjacent vertebra. The invention, its preferred options and further advantages shall be described below in more detail.

In this description the invention will be described using terms as upper and lower. These terms are in no manner intended to limit the scope of protection and are merely used to describe the spinal implant in a configuration in which it would normally be used when placed in an intervertebral disc space.

The minimum number of segments in the chain should be is at least 4 and more preferably 4. The maximum number of segments will be limited by what is mechanically possible.

When the chain is capable of forming a ring it is preferred that the first and last segment are provided with a closure suited to connect the first and last segment when the chain is in its ring shape. This reduces the risk of dislocation of the spinal implant once it is placed between the adjacent vertebrae. The closure should be such that it can be easily closed once the implant is placed. An example of such a closure is a magnetic closure.

The segments may be connected in any manner which allows the segments to position themselves in a ring shape relative to each other. Preferably the segments are interconnected by means of a pivot connection. The chain preferably has a straight position or nearly straight position and a curved position in the shape of a ring. In the straight position the chain will be, in use, introduced in an intervertebral disc space. This may be performed using a posterior interbody fusion (PLIF) approach or a transverse lumbar interbody fusion (TLIF) approach. Once arrived in the intervertebral disc space the chain is allowed to curve into its final ring shape. Once a final ring shape is arrived at the first and last segment may be connected using the closure. The chain may be allowed to curve into its ring shape by means of springs connecting two adjacent segments. Preferably the segments are interconnected by means of a pivot connection comprising a hinge made of a shape memory alloy. This allows one by locally increasing or lowering the temperature slightly to alloy the hinge to move into its other position. A suitably shape memory alloy is Nintinol.

The segments may comprise an upper surface which in use faces a vertebral endplate of a vertebra of a spinal column and a lower surface which in use faces the vertebral endplate of the lower adjacent vertebra of the spinal column. The upper and lower surface are spaced away defining the body of the segment. The segments have an exterior side and an interior side wherein interior and exterior are here defined by the ring shape of the spinal implant as viewed in use in its superior view.

Preferably the body of the segments comprises a solid and curved exterior side wall. This solid exterior side wall provides the strength required to cope with the compressive load of the spine. Suitably the segment further comprises a solid part for supporting a pivot connection at two ends of the body. Suitably the segment is further provided with a porous part extending from the upper surface to the lower surface of the segment. Such a porous part is advantageous because it provides the segment with mechanical properties similar to the vertebrae. Furthermore the porous structure of the implant would be similar to bone. Also the porous structure will enhance bone ingrowth into its pores which eventually, results in a stronger and faster fusion. Preferably part or all of the interior side wall has a porous structure. A preferred segment comprises an interconnected solid part and porous part made of the same material.

Preferably between 10 and 90% and more preferably between 30 and 80% of the area of the upper surface and lower surface is comprised of a porous surface of the porous part. This percentage allows a sufficient area for bone ingrowth on the one hand leaves a sufficient area of solid part for achieving a desired mechanical strength. The porous part may have the design of an open cell foam. The pores in the porous part and thus the openings in the outer surface of the porous part preferably have a diameter of between 0.5 and 0.7 mm.

The segment may be made of a bio-compatible material such as for example biocompatible polymer, like PEEK, PEKK, ceramics, like for example zirconia and metals, like for example titanium, CoCr alloys, Magnesium and Tantalum. Such a segment may be made by using a mould, by subtractive manufacturing, like milling and turning and/or by additive manufacturing like 3D printing and sintering. Combinations of manufacturing techniques are often required to make the complex structures. If the segment comprises a body having a combination of porous and solid parts it may be advantageous to manufacture such a segment using a hybrid manufacturing involving additive manufacturing such as 3D printing and subtractive manufacturing techniques such as CNC machine (milling or turning machine) for finishing. Additive manufacturing of spinal implants may be performed as described in EP3045151. Or for example US2016193055 which describes a manufacturing process to make the porous parts. Spinal implants made in this manner are preferably made from titanium or titanium alloys. Examples of suitable titanium alloys are TÏ-6AI-4V (Grade 5) and the more pure Ti-6AI-4V Eli (Grade 23).

The invention shall be illustrated by the following figures.

Figure 1 shows a spinal implant (1) comprising of a chain (2) of four interconnected segments (3). The chain (2) has a first segment (4) and a last segment (5) at both ends (6,7) of the chain (2). The segments (3) are interconnected by means of pivots (8). The pivots (8) enable the chain to curve into a ring shape as shown in Figure 2. The first segment (4) is provided with a bore (9) that allows the use of a tool (not shown). The segment (3) is provided with two ends (10,11), a solid part (12) and a porous part (13). The porous part (13) runs from the upper surface (14) to the lower surface (15) (not shown) of a segment (3). The first segment (4) is provided with an opening (16) in which a pin (not shown) of the last segment (5) fits to form a closure.

Figure 2 shows the spinal implant (1) of Figure 1 in its ring shape.

Figure 3 shows the spinal implant (1) in its ring shape between two vertebral endplates (17,18) of adjacent vertebra (19,20) of a spinal column (21). This space is also referred to as the intervertebral disc space.

Figure 4 shows another spinal implant (30) according to the invention. The spinal implant (30) comprising of a chain (31) of four interconnected segments (33). The chain (31) has a first segment (34) and a last segment (35) at both ends (36,37) of the chain (31). The segments (33) are interconnected by means of pivots (38). The pivots (38) enable the chain to curve into a ring shape as shown in Figure 5. The segment (33) is provided with two ends (40, 41), a solid part (42) and a porous part (43). The porous part (43) runs from the upper surface (44) to the lower surface (not shown) of a segment (33). At the pivots (38) a spring (39) is provided which forces the chain to form a ring shape when it is introduced in an intervertebral disc space.

Figure 5 shows the spinal implant (30) of Figure 4 in its ring shape when viewed from above wherein first segment (34) and last segment (35) are connected by means of a closure (45).

Figure 6 shows the spinal implant (30) of Figure 4 in its ring shape when viewed from above and located on a vertebral endplate (46) of a vertebra (47) of a spinal column (48) as seen in a superior view. In the space (48) formed by the interior of the ring shaped spinal implant bone graft may be placed to further enhance the desired fusion between the adjacent vertebrae. Because of the enclosed ring shape such bone graft cannot easily escape the intervertebral disc space which will further enhance fusion.

Claims (11)

A spinal implant, comprising a chain of interconnected segments, with a first and last segment at both ends of the chain, the segments of the chain being interconnected in such a way that the chain can bend in a plane such as the one present is between two vertebral end plates of adjacent vertebrae of a vertebral column, to form a ring. The spinal implant of claim 1, wherein the first and last segments are provided with a closure suitable for connecting the first and the last segment. The spinal implant of claim 2, wherein the number of segments is at least 4. The spinal implant of claim 3, wherein the number of segments is 4. The spinal implant of any one of claims 1 to 4, wherein the segments are interconnected by means of a rotatable connection. A spinal implant as claimed in any one of claims 1 to 5, wherein the segments comprise an upper surface that, during use, is directed to a vertebral end plate of a vertebral vertebra, as well as a lower surface that, during use, is directed toward the vertebral end plate of the lower adjacent vertebra of the vertebral column, the upper and lower surfaces being spaced apart and defining the body of the segment, and wherein the segments comprise an outer side and an inner side defined by the annular shape of the spinal implant, as seen in top view during use. The spinal implant of claim 6, wherein the body of the segments has a fixed and curved outer side wall, a fixed part to support a rotating connection at two ends of the body, and a porous part extending from the upper surface to the lower surface of the segment. The spinal implant of claim 7, wherein part or all of the inner inner wall has a porous structure. The spinal implant of claim 7 or claim 8, wherein the body of the segments is made by using an additive manufacturing method. The spinal implant of claim 9, wherein the body of the segments is made of titanium or a titanium alloy. The spinal implant of any one of claims 5 to 10, wherein the pivotal connection comprises a hinge made from a shape-memory alloy.