FR2717068A1 - Intersomatic cage insertable between two vertebral bodies - Google Patents

Abstract

The intersomatic cage (1a) for fitting between two adjacent vertebrae consists of two parallel branches (11a,12a) and a bridge (13a) between the rear ends (131a,132a,134a) of the branches, with a movable component (15a,16a) which can adjust the spacing between the forward ends (141a,144a) of the two branches once the cage is in position. The inner faces of the branches have thrust surfaces forming the sides of a V which points towards the bridge and which are in sliding contact with the spacer (15a), which is adjusted by a screw (16a).

Description

vertebral interbody fusion cage
The present invention relates to an interbody cage intended to be inserted between the vertebral bodies of two vertebrae, in particular lumbar vertebrae, as well as ancillary equipment for implanting the cage. Such a cage allows the fusion of the vertebral bodies after discectomy while maintaining the intervertebral distance.

 A lumbar interbody fusion cage according to the prior art comprises a hollow cylindrical body terminated by an anterior hemispherical end and closed by a screwed posterior plug. Longilinear windows are also provided longitudinally in the cylindrical body. The body is previously filled with bone "grafts", called "allograft", and the cap is screwed and blocked on the body. At least one such cage is introduced between two vertebral bodies using appropriate ancillary equipment.

 The dimensions of the cage are generally selected from a choice of a few sizes to adapt to the anatomical conditions of the patient.

However, the cage once chosen has fixed dimensions. However, it is generally desirable during the surgical intervention to adjust the relative position of the two vertebrae which are going to be "joined" by fusion of the vertebral bodies through the grafts, in particular their angular position in the anteroposterior plane or angle of lordosis. This intraoperative adjustment cannot be achieved with such an interbody cage.

 In addition, if most of the surgical procedures to set up such a cage are performed posteriorly, there are cases where intervention by the anterior route is preferable.

 The present invention aims to provide a vertebral interbody cage which allows intraoperative adjustment of the relative angular position of two vertebrae in particular lumbar in the anteroposterior plane, that is to say which contributes to impose a determined lordosis angle, while being adapted to be inserted anteriorly between the vertebral bodies of two vertebrae.

 To this end, an interbody cage intended to be inserted between two vertebral bodies is characterized in that it comprises two substantially parallel branches to be introduced between said vertebral bodies, a bridge connecting posterior ends of the branches, and a means operable from anterior ends of the branches for angularly spreading the anterior ends of the branches after insertion of the cage between the vertebral bodies.

 In practice, the bridge includes a clevis joint. The angular spacing of the anterior ends of the branches allows the surgeon to choose the angle of lordosis most appropriate to the anatomophysiological needs of the patient.

 Cooperation between the means for spreading and the branches has been sought so as to control the desired spacing by the anterior end of the cage, which is only accessible after implantation of the cage by the anterior route. The following features contribute to this goal.

 The internal faces of the branches have facing bearing surfaces which form the sides of a vee whose top is oriented towards the bridge and which are in sliding contact with the means for spreading.

 In order to impose a predetermined lordosis angle, the angular spacing of the branches can be limited on the one hand by abutment of the anterior ends of the branches against one another, on the other hand by abutment of the posterior ends of the branches l one against the other.

 According to a preferred embodiment, the means for spreading comprises a screw screwed into the anterior end of one of the branches and extending between the branches, and a spacer in contact with bearing surfaces facing the faces internal branches and integral at least in axial direction with a rear end of the screw. For this preferred embodiment, a predetermined lordosis angle can be imposed by means of end-of-travel stops for the spacer consisting of projecting front and rear ends of one of the branches. More precisely, these end-of-travel stops can be on the sides of at least one recess formed parallel to the screw in the branch where the screw enters to guide the spacer.

 Preferably, a rear end of the screw comprises a stop means, such as a ring, washer or collar, for axially immobilizing the spacer around the screw and thus allowing the free rotation of the threaded rod of the screw in the spacer while avoiding undesirable disassembly of the screw and the spacer.

 The screw is headless and includes, for example, a slot or a cross, or a hexagon socket to allow the screw to be operated by an appropriate screwdriver.

 On the other hand, the cage is substantially parallelepipedic and thus offers flat bearing surfaces on the vertebral bodies.

 These bearing surfaces are external faces of the branches comprising transverse anchoring means for anchoring the branches in the vertebral bodies with which the external faces are in intimate contact. Preferably, the anchoring means are teeth.

 At least one of the branches includes at least one lumen to fill the cage with bone fragments for good bone recovery between the vertebral bodies.

 According to an alternative embodiment, the cage has substantially cylindrical lateral sides for good anatomical adaptation.

 The invention also relates to a cage holder for removable connection with a cage according to the invention. One face of the front end of at least one of the branches comprises a means of connection with the portecage, preferably a dovetail or tee stud and the cage holder comprises a groove with variable width for pinching the connecting means, such as a tenon, of the cage. The surgeon adjusts the width of the groove by means, such as an operating head, to link the cage and the cage holder in order to insert the cage between the vertebral bodies, then to separate the cage and the cage holder when the cage is well positioned between the vertebral bodies.

According to a preferred embodiment, the cage holder comprises
a hollow cylindrical body,
a rod slidingly mounted in a transverse conduit of the body and resiliently biased towards a flared posterior end of the conduit,
an operating head screwed to an anterior threaded end of the rod and resiliently biased against an anterior end of the body, and
two jaws containing said variable groove & width blocked in axial translation around a rear end of the rod and applied elastically in transverse opposition and sliding against the flared rear end of the duct.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which
- Figure 1 is a perspective view of a cage according to a first embodiment of the invention;
- Figure 2 is an exploded perspective view of the cage according to the first embodiment;
- Figure 3 is a longitudinal top view of the cage according to the first embodiment;
- Figure 4 is a first view in antero-posterior longitudinal section of the cage according to the first embodiment;
- Figure 5 is a second view in antero-posterior longitudinal section of the cage according to the first embodiment, with branches separated;
- Figure 6 is a perspective view of a cage according to a second embodiment of the invention;
- Figure 7 is an exploded perspective view of the cage according to the second embodiment;
- Figure 8 is a front front view of the cage according to the second embodiment;
- Figure 9 is a top view in partial section of the cage according to the second embodiment
- Figure 10 is a first longitudinal anteroposterior view of the cage according to the second embodiment;
- Figure 11 is a second longitudinal anteroposterior view of the cage according to the second embodiment, with branches apart;
- Figure 12 is a longitudinal view partially in axial section of a cage holder according to the invention
- Figure 13 is a cross-sectional view of the cage holder, along the line XIII-XIII in Figure 12;
- Figure 14 is a longitudinal view of a jaw of the cage holder; and
- Figure 15 is a longitudinal view of the portecage linked to the cage according to the second embodiment.

 The intersomatic cage and the cage-carrying tool according to the invention are made of a biocompatible material, for example titanium or titanium-based alloy.

 With reference to FIGS. 1 to 5, an intervertebral cage 1 according to a first embodiment of the invention is of substantially parallelepiped shape and is symmetrical with respect to an anteroposterior longitudinal plane of trace A-P and perpendicular to FIG. 3.

 Two longitudinal branches 11 and 12 of the cage are connected by a rear connecting bridge 13 transverse to the axis A-P. The connecting bridge includes a cylindrical fork joint. Two yoke branches 131 and 132 are drawn parallel to the anteroposterior plane at the rear end of the branch 12 and are crossed by coaxial cylindrical bores 133 perpendicular to the axis A-P.

The yoke branches 131 and 132 form a longitudinal groove 133f transverse to the bore 133 and suitable for receiving a sliding stud 134 projecting at the rear end of the other branch 11. The stud 134 has a cylindrical bore 135 having a diameter substantially greater than that of the hole 133. A cylindrical pivot pivot 136 is inserted substantially by force into the holes 133 and freely into the central hole 135 to link the branches 11 and 12 while allowing free rotation of the branch 11 around pivot 136.

 During the manufacture of the cage, after assembly of the articulation, the pivot 136 can be blocked in translation by a conventional process not shown, such as crushing or welding or screwing at least one end of the pivot 136 to one yoke branches 131 and 132.

 However, according to another variant, the pivot 136 rotates freely in the holes 133 which are then wider than the hole 135, and is linked centrally to the hole 135 in the stud 134 by locking washer, flange, weld, thread or medium. similar.

 The travel of the branches 11 and 12 is limited between first and second extreme positions by rotation of the branch 11 around the pivot 136. The first extreme position is a "closed" position shown in FIGS. 1 and 4 in which external faces 111 and 121 of the branches 11 and 12 are substantially parallel. The second extreme position is an open position "shown in FIG. 5, in which the faces 111 and 121 form an angle AN of a few degrees.

 The anterior end of the cage is an anterior bridge 14 transverse to the axis A-P. The bridge 14 includes first and second parts 141 and 144 which are separate and facing each other.

 The first part of bridge 141 is monolithic with the anterior end of branch 12 and extends over approximately three quarters of the height of bridge 14.

The bridge part 141 is terminated opposite the branch 12 by a bearing surface 142 parallel to the face 121. A longitudinal threaded bore 143 is formed in the part 141 and centered on the axis A-P.

 The second bridge part 144 is monolithic with the front end of the branch 11. The part 144 comprises a bearing surface 145 opposite the bearing surface 142 and similar to the latter. When the cage 1 is in the closed position according to FIG. 4, the surfaces 142 and 145 are in abutment against one another.

When the cage 1 is in the fully open position, shoulders 11e of the branch 11 located on either side of the tenon 134 abut against upper corners 12e of the fork branches 131 and 132, and the bearing surfaces 142 and 145 are distant from each other.

The external face at the end of the bridge 14 comprises a removable connection means with a cage-carrying tool 2 detailed below. The connecting means is a dovetail tenon 146 formed continuously in the parts 141 and 144 of the anterior bridge 14. As a variant, the tenon is formed only on the highest bridge part 141, or is replaced by dovetail housing. According to other variants, the removable connection means is of the tenon type or housing with a cross section,
A spacer roller 15 has the shape of a cylinder cut by two planes orthogonal to each other and parallel to the axis of the cylinder to form two longitudinal flats 150 and 151. The flat 151 and the cylindrical surface 152 of the roller are surfaces bearing cooperating respectively with the internal faces 122 and 112 of the branches 12 and 11. The roller 15 further comprises in the middle of the flat 150 a transverse smooth hole 153 which receives the rear posterior end of a hexagon socket screw without head 16. The screw 16 is screwed into the hole 143 of the branch 12 and passes through it.

 The rear end of the screw turns freely in the hole 153 of the roller 15. The screw 16 is immobilized in translation in the roller hole 153 by an internal elastic O-ring forcibly embedded in two corresponding grooves respectively made in the hole and the 'rear end of the screw, or by two collars or stop washers 162 and 163 welded with argon around the screw 16 on either side of the roller 15 after insertion of the screw 16 into the hole 153.

 The internal faces 112 and 122 of the branches 11 and 12 extend between the rear and front bridges 13 and 14 and form a sliding path for the roller 15.

The internal face 122 of the branch 12 is planar and parallel to the external face 121. In the other branch 11, the face 112 is inclined at an angle AF relative to the external surface 111 in the anteroposterior plane.

Thus, the end of the internal face 122 near the posterior bridge 13 is permanently at a smaller distance from the opposite face 112 than is the end of the face 122 near the anterior bridge 14, whatever the closed or open position of branches II and 12.

 The screwing of the screw 16 in the hole 143 of the bridge 14 positions the roller 15 on its sliding path and thus imposes an angle AN between the external faces 111 and 121 of the branches 11 and 12. The length of the threaded section of the screw 16 located outside the roller 15 and screwed into the threaded bore 143 of the branch 12, and the length of this threaded bore 143 are greater than the sliding stroke CG of the roller whose limits correspond to the open and closed positions of the cage . In the closed cage position, the diametrical flat 150 of the roller substantially abuts against the internal face of the bridge part 141, as shown in FIG. 4; the screw head 161 is substantially flush with the front face of the bridge part 141, so that the screw 16 is always included in the cage and does not attack the surrounding medium. In the maximum open cage position, the roller is located substantially halfway between the yoke 131-132 and the deck part 141, as shown in FIG. 5.

 The external faces 111 and 121 comprise means for anchoring in vertebral bodies CV1 and CV2 shown diagrammatically in FIG. 5. The anchoring means are transverse teeth over the entire surface of the faces 111 and 121. As a variant, the means anchors are pins.

 The rear faces of the fork legs 131 and 132 and of the post 134 are rounded in order to facilitate penetration of the cage between two vertebral bodies by the anterior route.

 Each of the two branches 11 and 12 is further pierced by a rectantular or oblong lumen 113, 123 to lighten the cage and, if necessary, fill the cage with bone grafts.

 In practice, two cages 1 are juxtaposed in the same intervertebral space; the cages are at an average distance of 10 to 15 mm approximately from each other, and converge substantially from 10 to 150 approximately towards the anterior direction.

 With reference to FIGS. 6 to 11, a second embodiment of the intervertebral cage 1a according to the invention differs from the cage 1 mainly by its shape.

The cage la is substantially parallelepipedic and symmetrical with respect to a plane longitudinal to the antero-posterior axis of trace AP and perpendicular to FIG. 9. The cage la has substantially the same length as the cage 1 along the axis AP and the same height as cage 1, but has a width greater than that of cage 1 in the frontal plane, typically greater than twice the width of cage 1. The width of the cage corresponds substantially to the width of a disc vertebral to replace. In practice, the surgeon implants a single cage la in an intervertebral space.

 Like the cage 1, the cage 1a comprises two branches 11a and 12a joined by a posterior connecting bridge 13a. The bridge 13a comprises a posterior cylindrical articulation in clevis having two clevis branches 131a and 132a projecting from the branch 12a and framing a stud 134a of the other branch 11a, and a cylindrical pivot of rotation 136a freely passing through a hole 135a of the stud 134a and by force in two holes 133a of the yoke branches.

 The cage 1a also comprises an anterior bridge 14a in two parts 141a and 144a, a connection means 146a with the cage-carrying tool 2 and a means for spreading the branches comprising a screw 16a and a roller 15a.

 Perpendicular to the internal face 122a of the highest branch 12a are formed two recesses in right rectangular dihedral opposite 124a between the rear bridge 13a and the front bridge portion 14a of the branch 12a. The recesses 124a have large posterior and anterior sides longitudinally framing the roller 15a and a bottom constituting a sliding path for the flat 151a of the roller 15a. The bottom of the recesses 124a ensures the rectilinear guidance of the roller 15a which thus remains well perpendicular to the axis A-P.

 The length Ca of the bottom of the recesses 124a can define the sliding stroke CGa of the roller 15a, although this stroke is in practice determined by the movement of the pivoting branch 11a around the pivot 136a, between a closed position (FIG. 10) at which bearing surfaces 142a and 145a abut one against the other, and an open position (FIG. 11) to which the surfaces 142a and 145a are distant and ilea shoulders of the branch 11 framing the tenon 134a abut against edges 12ea of yoke branches 131a and 132a.

 The lower branch 11a has two substantially identical oblong slots 113a on either side of the axis A-P and open in the posterior direction according to the illustrated embodiment. The highest branch 12a has two substantially identical oblong lights 123a located on either side of the axis A-P, according to the illustrated embodiment. The cage can be filled with bone grafts through the lumens 113a and 123a. As a variant, the branches 11a and 12a comprise a single oblong opening transverse to the axis A-P.

 The lateral side surfaces 18a and 19a of the cage 1a are cylindrical convex about a vertical axis for good anatomical adaptation and facilitate penetration of the cage between two vertebral bodies.

 As shown more particularly in FIGS. 10 and 11, the screwing of the screw 16a in the tapped hole 143a of the bridge 14a positions the long roller lSa on its sliding path CGa between the branches 11a and 12a.

The flat 15a and the cylindrical surface 152a of the roller are in sliding contact respectively against the bottom of the recesses 124a and the internal face 112a of the branches. The inner face 112a of the lower branch lla forms an angle AFa with the outer face alla.

Thus the angle ANa between the external face lîla of the branch 11a and the external face 121a of the branch 12a is adjusted by rotation of the screw 16a in the tapped hole 143a. Whatever the closed (Figure 10) or open (Figure 11) position of the cage 1a, the screw 16a is always embedded in the cage.

 With reference to FIGS. 12 to 14, a cage holder 2 comprises an elongate body 20 longitudinal to the anteroposterior axis A-P. The cage holder comprises at one of its ends, called the distal anterior end, an operating head 21 and at its other end, called the proximal posterior end, a connecting means 22 with the cage 1, la. The cage carrier 2 is symmetrical with respect to a longitudinal plane of trace A-P and perpendicular to FIG. 12. The length L of the carrier 2 is approximately 20 to 30 centimeters.

 The body 20 is pierced longitudinally by a long cylindrical transverse conduit 201. The conduit 201 opens at the distal anterior end by a smooth hole 202 of diameter smaller than the conduit 201 and forms with this hole 202 an internal shoulder 203. At the end proximal posterior, the duct 201 opens out by a conical flare 204 having an apex angle of a few degrees.

 Two threaded positioning lugs of the headless & hexagon type needle punch 23 and 24 are screwed into two tapped holes 205 and 206 radial and centered in a diametral plane common to the body 20. The tapped holes are substantially located in the middle of the body 20 along the 'axis AP and are spaced about 1 cm apart. Once screwed into the holes, the pins 23 and 24 are flush with the cylindrical external surface of the body 20 and project radially into the conduit 201 over a length of 1 to 2 millimeters.

 The outer surface of the body 20 comprises alternating cylindrical grooves and crowns 207 and 208 from the anterior end to about the middle of the body 20 along the axis A-P. The grooves and crowns promote good grip of the cage holder 2.

 An internal rod 25 with several cylindrical sections is slidably mounted in the duct 201. From the front end, the rod 25 comprises a threaded front end section 251, a long smooth intermediate section 252, a short wide smooth smooth grooved section 253 , a second long smooth intermediate section 255, a short smooth wide section 256, and a thin posterior end section 257.

 The threaded end section 251 slidably crosses the hole 202 of the body 20 and protrudes longitudinally from the body 20. The smooth intermediate section 252 extends from the section 251 over approximately one third of the length of the rod 25. The section 252 has substantially the same diameter as the threaded section 251 and the other intermediate section 255.

 From the section 252 and opposite the positioning lugs 23 and 24, the smooth section 253 has a larger diameter than the two sections 251 and 252 and corresponding substantially to the diameter of the conduit 201. In the section 253 is made a longitudinal groove 254 suitable for receiving the projecting ends of the positioning pins 23 and 24. The radial distance between the axis AP and the bottom of the groove 254 is at least equal to the diameter of the sections 251, 252 and 255.

 After the second smooth intermediate section 255, the short smooth section 256 is approximately two centimeters long and has a diameter corresponding substantially to the diameter of the conduit 201.

 At the posterior end of the rod, the cylindrical section 257 of small diameter comprises transversely a substantially parallelepipedal pin 258 having cylindrical sides 258c mounted to slide in the duct 201, as shown in FIGS. 12 and 13, to block in translation and in rotation the connecting means 22 which is now described.

 The connecting means 22 is in the form of a tweezer having two identical jaws 221 which are symmetrical with respect to the trace plane AP in FIG. 12. As shown in FIG. 14, each jaw 221 comprises a substantially semi-cylindrical portion 222 in which is formed a cross-shaped housing having a large axial branch 257b for receiving longitudinally approximately half of the thin cylindrical section 257 and a small diametrical branch with rectangular section 258b for receiving approximately half of the post 258. From the portion 222 and at least partially in contact with the conical flare 204 of the conduit 201, each jaw 221 comprises a first semi-conical portion 223 of dimensions corresponding to the flare 204. The jaw is terminated by a second semi-conical portion 224 whose large base is common with that of the first portion 223.

 Substantially perpendicular to the large base of the portions 223 and 224, the jaw 221 comprises a blind transverse cylindrical hole 225 suitable for receiving a jaw spacer spring 226.

 The proximal end of each jaw 221 includes a transverse dovetail half-groove to form with the half-groove in the other jaw a dovetail groove 227 of variable width when the jaws are brought together or apart.

 Finally, the head 21 comprises a tap hole 211 which is screwed onto the section 251 projecting from the body 20 through the hole 202. A helical spring 26 threaded around the intermediate section 252 is supported between the shoulder 203 and the section 253 in the leads 201.

The spring 26 permanently applies the operating head 21 against the distal anterior flat end of the body 20 and pushes the rod 25 in the posterior direction when the head is unscrewed.

 By screwing the head 21 on the section 251, the rod 25 slides longitudinally towards the front end and the spring 26 is compressed. The jaws 221 are then brought together against the spring 226 due to the taper of the portions 223 which "fit" into the flare 204 of the conduit 201, which has the effect of reducing the width of the dovetail groove 227.

 Thus, by first unscrewing the head 21 slightly, the surgeon gives the dovetail groove 227 the width sufficient to insert the dovetail pin 146, 146a of the cage 1, la. Then by screwing the head 21 again, the surgeon narrows the groove 227 to pinch the post of the cage. The cage 1, la is then linked to the cage holder 2 and the longitudinal axes A-P of the cage and the cage holder are merged. Preferably, the cage 1, la is closed, that is to say the branches 11 and 12, ila and 12a are substantially parallel.

After anterior discectomy to remove a deficient disc between two vertebral bodies CV1 and CV2 and grating of the intervertebral space between these vertebral bodies using appropriate tools to form a housing of dimensions similar to the cage, the surgeon then implants cage 1, the anterior way thus accessible between the vertebral bodies
CV1 and Cv2 by maintaining and positioning the cage thanks to the cage holder, as shown in Figure 15.

 When the cage 1, the in the intervertebral housing is in the location desired by the surgeon, after having struck on the operating head 21 if necessary, the latter unscrews the head 21 to widen the groove 227 in order to dissociate the holder - cage and cage then remove the cage holder.

 Then, a hexagonal bit of a screwdriver is introduced into the hexagon socket head 161, 161a of the screw 16, 16a to screw the screw into the threaded hole 143, 143a and move the roller 15, 15a in order to spread the branches 11 and 12, 11a and 12a by an angle AN, ANa desired as illustrated in FIGS. 1, 6 by the arrows 30 and 31, 30a and 3la.

 Although the invention has been described with reference to two preferred embodiments of a cage, these may be modified while remaining within the scope of the invention. For example, instead of a rear bridge 13, 13a with pivot articulation 136, 136a, there may be provided a flexible hinge means which monolithically connects the rear ends of the branches 11 and 12, ila and 12a, l 'Advance of the roller 15, 15a in the posterior direction causing opposite deflections of the branches 11 and 12, lîa and 12a.

Claims (17)

CLAIM8  1 - Intersomatic cage (1; la) to be inserted between two vertebral bodies (CV1, CV2), characterized in that it comprises two substantially parallel branches (II, 12; lia, 12a) to be introduced between said vertebral bodies, a bridge (13; 13a) connecting posterior ends (131, 132, 134; 131a, 132a, 134a) of the branches, and a means (15, 16; 15a, 16a) maneuverable from anterior ends (141, 144; 141a, 144a) branches to angularly separate the anterior ends of the branches after insertion of the cage between the vertebral bodies.  2 - Cage according to claim 1, characterized in that the bridge (13, 13a) comprises a clevis joint (131, 132, 134; 131a, 132a, 134a).  3 - Cage according to claim 1 or 2, characterized in that the internal faces of the branches (11, 12; pila, 12a) have facing bearing surfaces (112, 122; 112a, 122a) which form the sides of a vee whose top is oriented towards the bridge (13, 13a) and which are in sliding contact with the means for spreading (15, 16; 15a, 16a).  4 - Cage according to any one of claims 1 to 3, wherein an angular spacing of the branches is limited on the one hand by stop (142, 145; 142a, 145a) of the anterior ends (141, 144; 141a, 144a ) of the branches one against the other, on the other hand by stop (island, 12e, ilea, 12ea) of the posterior ends (131, 132, 134; 131a, 132a, 134a) of the branches one against the other.  5 - A cage according to any one of claims 1 to 4, characterized in that the means for spreading comprises  a screw (16; 16a) screwed into the anterior end (141; 141a) of one (12; 12a) of the branches and extending between the branches (11, 12; 11a, 12a), and  a spacer (15; 15a) in contact with facing bearing surfaces (112, 122; 112a, 122a) of internal faces of the branches and secured at least in axial direction with a rear end of the screw.  6 - Cage according to claim 5, comprising end of travel stops for the spacer (15; 15a) constituted by projecting front and rear ends (141, 132, 133; 141a, 132a, 133a) of l 'one (12; 12a) of the branches.  7 - A cage according to claim 5 or 6, comprising a recess (124a) formed parallel to said screw (16a) in said one (12a) of the branches to guide the spacer (15a).  8 - Cage according to any one of claims 5 to 7, characterized in that a rear end of the screw (16) comprises a stop means (162, 163) for axially immobilizing the spacer (15) around the screw.  9 - A cage according to any one of claims 1 to 8, characterized in that it is substantially parallelepiped,  10 - A cage according to any one of claims 1 to 9, characterized in that it has substantially cylindrical lateral sides (18a, l9a).  11 - Cage according to any one of claims 1 to 10, characterized in that the external faces (111, 121; villa, 121a) of the branches comprise transverse anchoring means, preferably teeth.  12 - A cage according to any one of claims 1 to 11, characterized in that at least one of the branches comprises at least one lumen (113, 123; 113a, 123a).  13 - A cage according to any one of claims 1 to 12, characterized in that a face of the anterior end (141; 141a) of at least one (12 12a) of the branches comprises a connecting means (146; 146a) with a cage holder (2).  14 - Cage according to claim 13, characterized in that the connecting means is a dovetail tenon (146; 146jazz  15 - Cage holder (2) for removable connection with the cage according to claim 13 or 14, characterized in that it comprises a variable width groove (227) for pinching the connecting means (146; 146a) of the cage (1, la).  16 - Cage holder (2) according to claim 15, characterized in that it comprises means (21) for modifying the width of the groove (227).  17 - Cage carrier (2) according to claim 15 or 16, comprising  a hollow cylindrical body (20),  a rod (25) slidably mounted in a transverse conduit (201) of the body and resiliently biased towards a flared posterior end (204) of the conduit,  an operating head (21) screwed to an anterior threaded end (251) of the rod and resiliently biased against an anterior end of the body, and  two jaws (221) containing said variable width groove (227) locked in axial translation around a rear end (257, 258) of the rod and applied elastically in transverse opposition and sliding against the flared rear end (204) of the duct (201).