FR2852815A1 - Inter-vertebral connecting device for use in e.g. scoliosis, has two pedicle screws, coupled by rod, including V-shaped head with two branches, where branches are tightened to turn rod by ninety degrees - Google Patents

Abstract

The device has two pedicle screws (1), coupled by a rod (6), including a V-shaped head with two branches. The branches are tightened to turn the rod by 90 degrees. The branches are then released to enable them to regain a rest position. A spring effect of the branches exercises a tightening effort with the rod on two points of each branch, to generate a butting on the branches based on a traction effort on the rod.

Description

The present invention relates to an intervertebral connection device

implantable

  allowing to join the vertebrae and thus maintain their spacing.

  The maintenance of the vertebrae should be as close as possible to normal; this use applies in particular in the case of: Compaction of the vertebrae (discs crushed by wear) - Scoliosis exaggerated Lordosis - Cyphosis (exaggerated convexity of the dorsal part of the spine;) Brief in the case of instability or reduction of the intervertebral space The process consists in joining together the vertebrae to correct their position or limit their movement.

  The devices commonly used for this type of intervention are produced according to the principle of connection between pedicle screws implanted in the vertebrae and connected together by preformed rods secured by screws acting by direct compression of the rod on the head of the screw or by means of a collar or a ball joint element.

  The principle always sought consists in ensuring a connection between a pedicle screw and a rod which is often approximately perpendicular to it.

  This manipulation very often requires the installation of separate mechanical elements (in addition to the pedicle screws and the rods) for example washers, stirrups or nuts which are delicate to handle (correct engagement of the nut thread or fitting a washer).

  All these manipulations of mechanical elements increase the duration of the intervention and oblige the operator to count the parts in order to avoid losses as well as the risk of errors.

  Mechanically, some systems use pressure screws, the end of which presses directly on the rod or systems tightening a stirrup on the rod.

  The forces generated by the movements of the patient create significant forces on the assembly which result in phenomena of matting of one or both elements which leads to the sliding of the assembly and to its ineffectiveness.

  The loosening of the elements frequently requires re-operative interventions on the patient to resume the connections; the latter being most often made of titanium alloy, a particularly ductile material.

  The present invention aims to overcome these various defects by proposing an implantable intervertebral connection device capable of automatically making up for the play due to the mating or to any other cause without requiring any intervention; this device consists of a minimum number of parts limiting the loss of elements and guaranteeing an extremely short installation time.

  The materials used (Spring steel such as that known under the brand "Phynox" or shape memory material) allow the assembly a certain flexibility which generates a role of shock absorber providing greater comfort and greater durability of the assembly.

  To this end the invention relates to an implantable intervertebral connection device comprising at least two pedicle screws and a connecting rod, the object of the invention based on the design of the gripping head of the pedicle screw.

  The head of the pedicle screw (1) consists of two elastic branches (2) and (5) integral with the screw (1); (the material constituting the screw must be bio-compatible and preferably made of a spring steel such as that known under the brand "Phynox" or a material with shape memory, or any material having sufficient elastic characteristics); the branches forming a V between them fig 3 and each of these branches (5) and (2) having several machining operations essential to the invention.

  The upper part of the branches (5) and (2) fig3 must be machined so that it can receive the connecting rod (6) and prevent it from moving.

  The end of the branches (5) and (2) is machined so as to form a sloping entry or a gentle ramp for the rod (6) fig5, making it easier to set up the mechanism by rotating the screw on the rod, the end of the branch (7) can strike the rod and this sloping machining will facilitate the rise of the branch on the rod.

  Machining in the form of teeth, (3) and (3 ') at the lower part, (4) and (4') at the upper part, are practiced so as to provide specific supports and to concentrate on these supports the efforts due with the spring effect of the branches (2) and (S). The two branches (2) and (5) go through these supports to pinch the rod and create on each branch of the V a bracing (joint greenhouse effect) with the rod.

  Other characteristics and advantages will emerge from the description of a preferred embodiment of the device of the invention; description given by way of example and with reference to the appended drawings.

  Figl is a side elevational view of a vertebrae connecting device according to the invention.

  Figure 2 is a detailed view of a pedicle screw head showing its installation ancillary.

  Fig 3 details the support points on the rod, the very principle of the invention. Figure 4 is a block diagram of the placement of the connecting rod.

  Figure 5 is an end view of the device mounted on its rod. Figure 6 is an embodiment with the V-shaped part attached to the screw and rotating axially around the latter.

  In Figure (1), there is shown the connection between two pedicle screws according to the invention, the upper part of the screw (1) being machined so that its head forms 2 branches (2) and (5) fig (3); these two branches form in the view shown in fig (3) a V whose angle (x) at rest (screw without rod, in the free state) is greater than the angle (y), 5 angle generated by the presence of the rod (6) on which the two arms (2) and (5) are supported which generates on the rod a force corresponding to the elasticity stress of the branches (angle Y fig 3).

  Therefore, whatever the bending of the rod, the two branches (2) and (5) will deform more or less and maintain good contact (3) (4) (3 ') (4') with the rod permanently ensuring the bracing.

  In the event of tensile forces on the rod towards F fig 3 the points (4 ') and (3') fig3 become slippery and the points (4) and (3) form an arch on the rod. The combination of the two opposite branches therefore constitutes a mechanical device which does not allow the displacement of the rod regardless of the direction of the force exerted on the rod (force towards F or towards G).

  The greater the tensile force exerted on the rod, the more the arcboutement 20 (resistant force) will increase; the tooth shapes (4 ′) and (4) and (3 ′) and (3) produced in a steel of hardness greater than the rod which can go as far as penetrating the rod.

  In a preferred version of the invention, the rod (6) can receive machining (knurling thread, etc.) making it possible to increase the coefficient of adhesion between the teeth (4) and (4 ') and ( 3) and (3 ') and the rod (6).

  On the branches 2 and 5 fig 3 will be made imprints (preferably in the highest part of the branches 2 and 5. These imprints will receive a tool (pliers) 10 and 11 (fig 2) to bring the two branches l 'from one another and thus increase the space between the teeth (3) and (4), (3') and (4 ').

  This space thus obtained (maximum when points (3) and (4), (3 ') and (4') are aligned parallel to the axis of the pedicle screw) allows, by rotation of 90 of the head of the pedicle screw, introduction or release of the rod (6).

  The reader will find the description of the installation of the device which is the subject of the invention in FIG. 4 in the form of a block diagram.

  After having conventionally screwed the pedicle screws into the vertebrae, the operator will align the screw heads so that the heads (branches 2 and 5 are parallel to the rod as shown in fig 4 (A).

  After the rod (6) has been formed by the surgeon to adapt it to the shape of the patient's back, the latter will be introduced into the heads of the screws (forming a V) fig 4 (B) the angle formed by the two branches being maximum (X fig 3) since the rod is not present to limit it.

  Once the rod is placed in the screw heads, the operator tightens the two branches using the appropriate ancillary (10) and (11) fig 2 until they are brought back substantially parallel so that the space reserved for the rod between the teeth (3) and (4), (3 ') and (4'), thus being brought to its maximum fig 4 (C).

  This operation carried out, the operator, using his ancillary, will turn the head of the screw by 900 so that the rod is introduced into the branches fig 4 (D); it will only have to reopen the ancillary so that the spring effect of the branches brings the latter under pressure on the rod (6) and creates at the point of contact of the teeth a bracing with the rod fig 4 (E ).

  The compulsory use of spring effect metals for this invention allows flexibility of all of the pedicle screws by deformation of the assembly of the screw branch connection; this deformation can be adjusted by varying the cross-section of the material and its shape (zone H fig 2) until the desired flexibility is obtained.

  This flexibility of the assembly between the screw and the rod can make it possible to absorb shocks and thus play a role of shock absorber which will increase the resistance of the vertebrae screw connection, a particularly fragile area especially in the case where the quality of the 'bone is very degraded.

  This cushioning effect will also increase patient comfort (transmission of shocks).

  In a preferred version of the invention, the head made up of its elastic V which is the subject of the invention can be attached to the screw and be secured to the latter by screwing (the screw can be threaded at its end.) Or by stamping from the end of the screw (8 fig 6), the V (9) fig 6 while being held axially can rotate around the axis of the screw, which will allow it, during the quarter turn necessary for its setting in place on the rod (6), not to drive the screw into the vertebra with a value corresponding to a quarter turn of the latter's pitch.

35 In all cases of construction, the hardness of the material constituting the teeth of the head must be greater than the hardness of the rod (6).

Claims (8)

  1) Implantable intervertebral connection device comprising at least 2 pedicle screws, connected by a rod (6). The pedicle screws, conventional in their lower parts (1), are characterized by their heads forming an elastic V made up of two branches (2) and (5) preferably made of a biocompatible spring steel, these two branches being internally machined from so that once tightened on themselves by an appropriate tool (10) and (11), they allow by a rotation of 90 to surround a rod (6) and when the tool (10) and (11) have released the branches (2) and (5) forming the V these will tend to return to their rest position and by spring effect they will exert on the rod 15 (6) a clamping force at two points for each of the branches, these points (3), (4), (3 '), (4') machined in the shape of teeth, generating with the rod (6) a bracing (greenhouse effect joint) on one or the other of the two branches V according to the direction of the tensile force (F or G) on the rod (6) (Figure 3).   2) Device according to claim 1 characterized in that the branches of the V (2) and (5) in their upper part have imprints (Figures 2 and 3) allowing the adaptation of an ancillary (10), (11) ensuring the tightening of the two branches forming the V and thus creating a sufficient space between the teeth (3) and (4), (3 ') and (4'), before performing a quarter turn and thus enclose the rod (6) in the space created.   3) Device according to claim lou 2 characterized in that the branches of the V are machined at their end (7) so as to form a sloping entry or a gentle ramp and provide support on the rod (6) and thus facilitate the end of rotation and ensure the positioning of the Vs on the rod (6) (Figure 5).   4) Device according to one of claims 1 to 3 characterized in that the support points of the branches of the V (2) and (5) on the rod are obtained by the machining of tooth shapes (4) and ( 3), (4 ') and (3') in order to guarantee maximum pressure due to the spring effect of the branches and to increase the bracing of the branches on the rod (6).   5) Device according to one of claims 1 to 4 characterized in that the rod (6) comprises machining in the form of threading or knurling or any other aspect having the role of increasing the surface roughness and therefore its resistance to sliding (Figures 2 and 3).   6) Device according to one of claims from 1 to 5 characterized in that the V-shaped head is secured to the pedicle screw (1) (Figures 1 to 5).   7) Device according to one of claims 1 to 5 characterized in that the V-shaped head is attached to the pedicle screw (1) by a mechanical assembly such as a masting or a screwing allowing or not the rotation of the screw relative to head 10 (Figure 6).   8) Device according to one of claims 1 to 7 characterized in that the branches of the V (2) and (5) are made flexible by adjusting the metal sections at the connection with the rod (6).