FIELD OF THE INVENTION

The present invention relates to a partial endoprosthesis device for a cervical intervertebral joint.

The device is suitable for treating patients suffering from a painful condition due to an early facet or disc degeneration with incipient foraminal stenosis, while preserving the relative movement of two adjacent vertebrae.

BACKGROUND OF THE INVENTION

As well known, most vertebral painful conditions are caused by the state of a joint, i.e. they depend on a relative motion deficit of the articular facets. This is case, in particular, for most neck pains.

The existing devices for treating these vertebral painful conditions can briefly classified into fusion devices for two or more adjacent vertebrae suppressing the relative motion thereof and, on the other hand, devices conceived to maintain the relative motion. Normally, the devices for preserving the relative motion are intersomatic devices, in particular they comprise disc replacement elements. In practice, only intersomatic devices exist for treating cervical spine painful conditions, of course, apart from the vertebral fusion devices.

In the case of the cervical vertebrae, the only currently available motion preservation intersomatic devices are implanted via anterior approaches. In fact, an intersomatic space cannot be reached via a posterior or lateral approach without running the risks of damaging nerve plexuses, which has severe neurological consequences for the patient. These risks are less important for non-cervical spinal levels and, therefore, rear approaches to the intersomatic space are preferred in those cases.

However, risks of neurological injuries and serious postoperative consequences are in any case involved if an anterior approach is used, which is required for implanting an intersomatic device at the cervical level.

US2011/288556 describes a partial endoprosthesis of an intervertebral joint, comprising a plate for introduction between the articular facets of two adjacent vertebrae. In order to maintain the device in the implant location before it becomes integrated with the bone, i.e. in order to primarily stabilize the device, screws are provided to fasten the device to the external surfaces of the laminae. This solution can damage and weaken the articular processes, in particular in the case of a cervical vertebra, since they are thin.

WO2014/042388 describes a device for spacing two adjacent vertebrae, configured to rigidly connect the vertebral bodies of two adjacent vertebrae to each other. In an embodiment, the device comprises a sawtooth-shaped primary stabilization means. This device is conceived for introduction between vertebral bodies, and is not suitable either for fixing two cervical facets to each other, or for preserving their relative movement, due to the sawtooth-shaped primary stabilization means, and would be also detrimental for the stability of the facets same.

WO2007/070785 describes a spacer device for restoring a physiologic distance between two articular facets of respective adjacent vertebrae, comprising a section, indicated as the intermediate section, whose size is suitable for introduction between the facets, and preferably also comprising a fastening portion configured to receive a mounting member like a screw for connection to the vertebral body. In an exemplary embodiment, the device is configured for connection to a single vertebral body of the two adjacent vertebrae. Even this device provides screws as the primary stabilization means, and involves therefore the above-mentioned drawbacks.

Further devices for at least partially preserving the relative movement of adjacent vertebrae and, in particular, of adjacent cervical vertebrae, are described in US 2013/274882 A1, US 2011/288556 A1, US 2005/159746 A1, US 2007/055373 A1.

SUMMARY OF THE INVENTION

It is therefore a feature of the present invention to provide a partial endoprosthesis of a cervical intervertebral joint, i.e. a device for implant in an articular process to functionally replace an articular facet of a cervical or cervical-adjacent vertebra, which provides a reliable primary stabilization before the device becomes integrated with the articular process.

It is also a feature of the invention to provide such a device that preserves the stability of the thin articular processes in which it becomes integrated, thus overcoming the problems of the above-cited prior art.

It is a particular feature of the invention to provide such a device that can be implanted by a relatively easy and not modestly invasive procedure.

It is also a feature of the invention to provide such a device and system that is easy and quick to be manufactured.

These and other objects are achieved by a partial endoprosthesis device as defined by independent claim No.1. Exemplary specific embodiments of the invention are defined by the claims depending thereon.

According to the invention, a partial endoprosthesis device is provided for preserving the motion of a vertebral joint, for implant into a spinal segment comprising two adjacent vertebrae, wherein at least one of the two adjacent vertebrae is a cervical vertebra, the adjacent vertebrae comprising a lower vertebra having a couple of upper articular processes with respective upper articular facets and an upper vertebra having a couple of lower articular processes with respective lower articular facets, each upper articular facet of the lower vertebra articulated with a corresponding lower articular facet of the upper vertebra, the device comprising:an elongated articular portion extending along a longitudinal axis between a first end and a second end axially opposite to each other, the articular portion having a first face and a second face opposite to the first face, wherein the first face comprises a central protrusion having a height, with respect to the face, set between 0.5 mm and 3 mm, preferably between 1.5 and 2.5 mm, and having a surface made of an osteointegrable material;wherein the second face has a surface roughness Ra lower than 0.2 μm, wherein the first face has a plurality of primary stabilization elements,a shoulder portion adjacent to the first end and arranged at an angle with respect to the articular portion at a side opposite to the second face;
such that, by implanting the device:with the articular portion inserted between an upper articular facet of the upper articular facets of the lower vertebra and a corresponding lower articular facet of the upper vertebra, andwith the first face in contact with a first articular facet selected between the upper articular facet and the lower articular facet, andwith the second face in contact with a second articular facet selected between the lower articular facet and the upper articular facet, according to whether the upper articular facet or the lower articular facet is selected as the first articular facet, respectively,
it is obtained that the articular portion, with its first face, finally becomes integral with the first articular facet by osteointegration and, with its second face, slidingly engages with the second articular facet so as to preserve the motion thereof, thus providing the partial endoprosthesis,
wherein the main features of the device are that:the articular portion has a thickness increasing from the first end going towards an own second end,the primary stabilization elements are elongated and flexible elements;the stabilization elements extend laterally with respect to the protrusion, between an own first connection end for connecting with the protrusion, and an own free end, and form an acute angle with the direction of the longitudinal axis, said angle oriented towards the first end of the articular portion.

Therefore, a primary stabilization means is provided that does not have the drawbacks described in the cited prior art, first of all it doesn't waken the structure of the thin articular processes of the cervical vertebrae, and the structure of the vertebral arch, which occurs, on the contrary, if screws are used.

This way, the primary stabilization elements provided as elongated and flexible elements, and oriented at an acute angle, due to their elongated shape and to their flexibility, can become closer to the protrusion while the device is being introduced into the articular space between the articular facets, and this way they do not hinder this introduction. Moreover, the elongated and flexible elements, once the device has been positioned, are fastened to the articular process like hooks, and resist against expulsion of the device from the articular space. In this fastening process, the thickness increase of the articular portion from the first end towards the second end cooperates with those elements, which creates a positive engagement between the articular portion and the articular facets engaged with one another. This active cooperation between the increasing thickness of the articular portion and the flexible primary stabilization means effectively restricts any possibility for the articular portion to be expelled from the space between the articular facets, in particular, during the implantation and the primary stabilization, before the articular process becomes integrated with the protrusion and the first face by osteosynthesis.

More in detail, the device is arranged with the protrusion comprising the osteointegrable surface in a recess suitably created by the surgeon in the first facet, which is the one to be functionally replaced. This recess is deep enough to allow the protrusion of the device to come into contact with a bleeding bone portion of the corresponding articular process, or in any case with a bone portion close to the trabecular portion, so as to assist the integration between the device and the bone. The protrusion is high enough to reach this inner portion of the articular process. On the other hand, the face opposite to the one bearing the protrusion is completely smooth, and allows the device to physiologically slide on the second facet, facing the first one, as if this second face were the patient's natural bone joint surface.

Therefore, the invention provides a prosthesis device for a joint surface, i.e. a device that can functionally replace a damaged bone joint surface of one of two adjacent vertebrae, at one cervical level or at a level adjacent thereto, and that solves the primary stabilization problems affecting the prior art. In other words, a device is obtained that provides a slidable prosthesis of the articular processes of two adjacent vertebrae, so as to heal such a condition as articular cartilage degeneration, while preserving the physiologic motion of the vertebrae and also restoring the natural foramen height. Due to articular degeneration, the foramen height decreases, causing stenosis. Moreover, said device is free from the above-mentioned prior art primary stabilization problems.

Preferably, the acute angle formed between the stabilization elements and the direction of the longitudinal axis of the articular portion, in a undeformed configuration, is set between 30° and 60°. Such an angle allows a good trade-off between a relative ease of insertion of the device into the articular space, and a grip of the primary stabilization means strong enough to effectively contrast the expulsion of the device from its implant location.

Advantageously, the primary stabilization elements, in an undeformed configuration, have a curvature with respect to a line between the connection end and the free end. Preferably, the primary stabilization elements have a convexity oriented towards the protrusion. Such a conformation improves the effectiveness of the primary stabilization elements, according to the invention, besides assisting bending during the introduction thereof.

In an exemplary embodiment, the primary stabilization elements are arranged symmetrically with respect to the longitudinal axis of the articular portion.

In particular, the surface roughness Ra of the second face is lower than 0.1 μm, more in particular, the surface roughness Ra is lower than 0.05 μm and, even more in particular, is lower than 0.025 μm.

Advantageously, the protrusion has a substantially uniform height over the first face.

The protrusion can have different forms along the longitudinal axis. In particular, it can have a semicylindrical shape, a prismatic shape or a combination thereof. The protrusion can also be manufactured in the form in more separate segments oriented along the longitudinal axis, in particular two or three segments can be provided. In particular, the protrusion can extend up to the shoulder portion.

In an exemplary embodiment, the protrusion can be hollow, i.e. it can a have a shell shape, like a cylindrical shell shape, or a box-like shape, these shapes defining a recess above a covered portion of the first face. This recess can be filled with bone material such as bank bone material, in order to assist osteointegration.

An osteointegrable material can also be arranged on portions of the first face different from the protrusion, besides the material arranged on the protrusion. In other words, the first face can comprise a further surface that has an osteointegrable material, this further surface adjacent to the protrusion. In particular, this further surface exposing osteointegrable material can extend to the whole first face, out of the protrusion. This way, further surface is provided for osteointegration of the device, which can take place at the side portions of the facets, provided these portions are prepared by removing the cartilage.

In order to assist osteointegration, the surface comprising the osteointegrable material of the first face can be a porous surface, or a corrugated surface, or in any case a surface having a surface roughness Ra higher than 0.2 μm.

Advantageously, the osteointegrable material is selected among titanium and titanium alloys. Preferably, the osteointegrable material comprises trabecular titanium, which is normally in a porous form.

The thickness of the articular portion is preferably set between 0.5 mm and 3.5 mm, more preferably between 1 mm and 3 mm and, in particular, between 1 mm and 2 mm, in order to be suitable for any specific size of the articular processes. Moreover, regardless of such values, the thickness of the articular portion at a maximum thickness portion is higher than the thickness at the first end by an amount set between 0.5 and 0.7 mm. The maximum thickness portion can be the second end portion or a zone adjacent or proximate thereto. This thickness difference is useful to cause the shape of the articular portion to better collaborate with the primary stabilization means.

The articular portion has a maximum length and a maximum width along and across the longitudinal axis, respectively, these dimensions preferably set between 8 mm and 15 mm, independently from each other, more preferably set between 10 mm and 14 mm, in particular between 10 mm and 12 mm. Even in this case, these size ranges make it possible to fit the device to any specific size of the articular processes and facets. In particular, the articular portion has a rectangular shape whose width and length are the above maximum sizes. As an alternative, the articular portion has a transversal side, at its second end portion, which can have a rounded shape, and/or can be tapered in height, between the second end and the maximum thickness portion, in order to assist the introduction into the articular space.

Advantageously, the articular portion has a width narrower than one half the width of the articular portion, preferably the width of the protrusion is set between 1/10 and 4/10 the width of the articular portion. This increases the mechanical stress physiologically arising in the articular process region at which the protrusion is inserted, which promotes osteointegration.

The second face comprises a material selected from the group consisting of:Titanium, or a Titanium alloy;a ceramic material;a glass material.

Accordingly, the second face of the articular portion exposes a material, in particular titanium or an alloy thereof, smooth enough to assist the articular portion to relatively slide, by the second face of the device, on the second facet, i.e. on the upper articular facet of the lower vertebra or on the lower articular facet of the upper vertebra, thus maintaining the relative twist motion of the two adjacent vertebrae, which is associated with this relative sliding. The primary stabilization portion is preferably configured to abut against an external portion of the vertebra surrounding the articular space.

Advantageously, the shoulder portion has fastening means for fastening a percutaneous positioning device. In particular, the fastening means can comprise a screw-threaded hole.

A posterior or posterolateral or lateral approach can be used so as to more easily implant the device than via an anterior approach, which must be used to safely implant the conventional prior art devices.

