WO2012076005A2 - Dynamic bone-anchoring device - Google Patents

Abstract

The invention relates to an implant system consisting of a bone anchor and a connecting rod for dynamic stabilization of joints, in particular of segments of the spinal column. The implant system is characterized in that it permits a translatory relative movement between bone anchor and connecting rod, without limitation, but at the same time substantially prevents a relative movement of the angle between these components.

Description

 title

 DYNAMIC BONE ANCHORING DEVICE

description

 [001.] The invention relates to an anchoring device which can preferably be implanted for stabilization of the spine and has dynamic properties for maintaining a residual mobility. The dynamic is due to the special design of the

Anchoring element allows, this being designed so that the physiological

Center of rotation is obtained in the thus treated joint.

State of the art

 [002] For surgical treatment, especially for the stabilization of

Spine diseases using pedicle screw-rod constructs, a variety of implants is known. Due to the problems of increased movement and concomitant accelerated degeneration of adjacent spinal segments as a result of a stiffening surgery implant systems have been developed, which instead of a rigid

Stiffening allow dynamic stabilization. In addition to dynamic rod systems where flexibility is created in the rod, some approaches are based on allowing flexibility through articulations on or in the pedicle screws. From the patent (DE4110002C1, 1991) a pedicle screw is known which has a rotary

Degree of freedom and thus allows rotation between the screw head and screw shaft. The idea of a joint in the screw head was taken up again in (WO2008085369A1, 2006) and extended to a biaxial version in (WO0167973 A2, 2000). These versions have in common that the movements of the components unhindered and without

stabilizing effect in the axes of movement can take place.

 From a biomechanical point of view, it may be useful to maintain the segment mobility not rotationally but translationally upright. From (WO9505783A1, 1995) a fixation system is known, which allows a linear displacement of the pedicle screw along a fixation rod and spring elements for generating a restoring force requires. Out

(WO2010019791 A3, 2010), the combination of a ball joint and a linear guide within a connecting element is known. The disadvantage here is the large space requirement between the pedicle screws. Due to the ball joint no angular stabilization is possible. From (WO0217803A2, 2002) a pedicle screw with integrated linear guide is known. However, the design takes into account not only the translation but also different degrees of rotational freedom, which eliminates a stabilizing effect.

[004.] From (WO2008100944A1, 2008) a spinal implant is known, which allows a translation via a sliding sleeve along a rod. A disadvantage of this design is the limitation of the translation path through buffer (leads to high implant loading) as well as the reduction of the rod diameter in the region of the sliding sleeve (starting point for fatigue fractures observed in practice). From (WO2008094891A3, 2008) a similar implant is known. The essential, (obvious) distinguishing feature is a variation of the bore diameter, which increases in diameter in the region of the inlet and outlet of the sliding sleeve to allow the storage of a bent rod. The disadvantage here is the resulting angular play between the rod and the bone anchor, which counteracts stabilization. The latter two versions also show no provision for an angle adjustability of the sliding sleeve, so that in both variants placement errors of pedicle screws can not be compensated. This leads to a high load on the rod and the sliding sleeve, with negative effects on abrasion and fatigue strength.

task

 [005] The object of the present invention is to provide a

Bone anchor for the spine, on the one hand allows the translational movement along a connecting rod without restricting it to a certain way, and on the other hand fixes the angle position between bone anchor and connecting rod. To compensate for tolerances in the placement of the bone anchor an angle adjustability is desirable, but this should be able to be locked after the adjustment. The connecting rod should have a high fatigue strength. A certain bending elasticity of the

Connecting rod or bone anchor also appears to be advantageous for reducing the forces on the bone anchor.

solution

 [006] The problem is solved in that at least one bone anchor with a

Linear bearing is fitted, in which the connecting rod is mounted translationally. The linear bearing can be configured as a sliding or roller bearing (eg a ball-and-roller unit). The angular adjustability is achieved by the combination with a ball or hinge joint. The angular stiff translation of the rod is characterized by a constant in cross section Realized opening within a sliding element. A high fatigue strength is achieved by avoiding cross-sectional changes within the load bearing area of the

Reached connecting rod. By appropriate choice of diameter and material of the rod or an elastic connection of the linear bearing to the bone anchor, the demand for a certain bending elasticity can be achieved.

advantages

 [007.] It is advantageous in the present invention that they are simple

Connecting rod between the vertebrae can be used and thus no additional dynamic rod systems are required. While improving the

Biomechanical properties and the simplification of the implantation, this allows the implantation in areas with a small pedicle distance and reduced due to the simple design, the cost of such an implant system. The implant according to the invention stabilizes the segment to be treated, whereby a residual mobility is obtained. This is a prerequisite for preventing further progressive degeneration of already degeneratively altered spinal segments. Due to the pure translational

Movement along the rod can be undertaken with these system corrective spinal procedures, which often can not be performed with other dynamic rod systems because of their low shear stiffness. Movements (translations in anterior, posterior and lateral directions) are prevented so that, for example, the facet joints can be relieved and the position of the vertebrae corrected. Another advantage is that the stiffness differences between treated and untreated segments are low, thereby suggesting a reduction in terminal segment degeneration compared to treatment with other dynamic stabilization systems or fusion systems.

Preferred details and embodiments

 [008] The technical solutions are described below by way of example. This should be understood as a means of explaining the underlying idea and should not be construed as limited to the particular concrete representation.

 [009] A motion segment (1, Fig. 1) is the smallest biomechanical unit of the

Spine and defined as consisting of (1) two adjacent vertebrae (10 and 11) and one intervertebral disc (12). At the bone anchor (4), also called pedicle screw in the following description, a connecting rod (3) is mounted, which either a dynamic stabilization or with conventional Pedicle screws (2) can be combined for spondylodesis.

 [010.] The pedicle screw (4) according to the invention can be implanted in a vertebra (11) (FIG. 1) and has at least one non-fixed linear guide, which allows a translation relative to the connecting element (3). By the linear guide the movement path of the superior vertebral body (10) is forced to the physiological center of rotation (13). The pedicle screw (4, Fig. 2) consists of at least one screw shank (41), a

Screw head (42) or head portion (50) with locking means (46, 56) and at least one sliding element (43). Depending on the design variant contains the

Pedicle screw according to the invention additionally an angle adjustable and lockable joint (44, 412) and / or an angle adjustable sliding element (53b) or ball element (545) with a spherical surface. An optional connecting element (45) serves to fix the linear guide within the head. The head (42) serves to receive the aforementioned components and allows the receptacle of the connecting rod (3) via an opening (4243). The connecting rod may have a round (31) or rectangular cross-section (32). The pedicle screw is varied in the following versions to show various preferred connection and storage variants. On the function and design of the screw head (42) and its fixing components (44, 45, 46) is in the following

Description received only as an example. In principle, the combination of the linear guide with a non-angle adjustable (monoaxial) pedicle screw is to be regarded as an advantageous variant, which will not be discussed in more detail below.

[011.] In a first embodiment (4a, Fig. 2), the pedicle screw consists of a

Screw shank (41) which merges to the proximal screw shank (412) and with the screw head (42) is connected (Fig. 2). The spherical shaft head (412) allows articulated, polyaxial adjustment of the screw head (42) with respect to the screw shaft (41). In the screw head is in this variant, a fixing component (44), at least one sliding element (43), and optionally a releasable connecting element (45) for fixing the linear bearing. With a fixing element (46) (for example, a grub screw) all components are fixed within the screw head. The fixation component (44) has the function of permanently fixing the stem head (412) in a defined angular position, when the pedicle screw (4a) is fixed, e.g. is clamped with the fixing element (46). In the arrangement shown in Fig. 4a, the connecting element (45) has the task of the

Fixing element (46) generated clamping force on the sliding member (43) and the

Transfer fixing (44). During clamping, further form and / or frictional connections on the surface (4345) between the sliding element (43), the Connecting element (45) and the fixing component (44) generates, which fix the sliding element (43) in position and orientation. The sliding element may also have a contour or a collar (433) for fixing, which slipping of the sliding element (43) in

Prevented longitudinal direction. In the sliding member (43) is a bore (431) in which a round connecting rod (31) is mounted. The sliding element (43) is preferably made of a material which is optimized in terms of tribological properties and at the same time biocompatible. In particular, plastics, e.g. PEEK, PEKK, high strength, hidden polyethylene, PAI, PTFE, polyphenylene, PPSU, PSU, with or without

Fiber reinforcement, coated titanium alloys, chrome-cobalt alloys and ceramics.

[012.] In a second preferred variant (4b, Fig. 3), the sliding element (43) has a rectangular recess (432) for receiving a connecting rod with also

rectangular cross-section (32). This has the advantage that the bending stiffness of the rod can be adjusted by different edge dimensions to the physiological requirements for each direction of movement. There is also the possibility of a rotation-stable

Connection of the guide (43) to the screw head (42) to transmit torsional moments along the rod. Through a different game between staff and leadership in the two

Cross-sectional directions (height / width) is another possibility of targeted

Influencing the stabilization properties.

 [013.] In a third variant, the pedicle screw (4c, Fig. 4) consists of a

Screw shaft (41) with shaft head (412), a screw head (42), at least one linear bearing (43), a fixing component (44), a connecting element (45) and a fixing element (46). To optimize the wear resistance of the linear bearing, the use of at least one linear bearing (43) with rolling bodies is proposed in this embodiment. The linear bearing (43) thus serves in the narrower sense as a cage for rolling elements, which can be configured as ball, roller or needle roller bearings. Fig. 4 shows the embodiment with balls (4381) and needles / rollers (4382) as rolling elements.

 [014.] An embodiment (4d) with needle or roller bearings is shown in FIG.

[015.] For larger translational distances, the use of rotating rolling elements is recommended, either within ball bearings or through a circulation guide of the rolling elements. Due to the cramped installation conditions, there is also a guided

Roller bearing, as shown in (4e) (Fig. 6). To protect the rolling elements and the surrounding tissue is proposed to embed the rolling elements by a cuff, a scraper or a corresponding design of the head in this and thus separate the rolling elements of the body tissue. [016.] In a further embodiment variant of the pedicle screw (5a, FIG. 7), the polyaxial alignment is achieved via a substantially cylindrical or prismatic sliding element (53a) and a surrounding ball element (545). The fixation via a bracket (56), which is biased during assembly in the longitudinal direction of the screw. The bracket has this purpose a suitable locking mechanism, for example in the form of hooks and edges (562, 564). The bracket can also be performed flexurally elastic and include a plurality of locking positions, so that a reliable bias can be achieved. These

Embodiment (5a) has the advantage that no ver to screw ver components are required for mounting or bracing. The embodiment (5a) essentially has a screw shaft (51), a screw head (50), a ball element (545), a sliding element (53a) and a fixing element (56). The screw head (50) and the fixing element (56) have convex, congruent to the ball element surfaces (5053, 5653), which produce a positive and non-positive connection with the ball member (545) and thus the

Permanently fix sliding element (53a) in a previously set position and orientation. To improve the transmission of the clamping force on the sliding member (53 a), the

Ball element (545) with slots (543) be provided. In this example, the slider is shown as being able to receive a round implant rod (31) (531). Alternatively, the rod may have a rectangular cross-section (32). In a further variant, the sliding element and the ball element (545) can be made in one piece (53b) in order to reduce the number of components.

 [017.] In a further embodiment (5b, FIG. 8) there is a spherical one

Sliding element (53b) in a pedicle screw head (52) which is mounted in a hinge-like manner via a pin (5121) (FIG. 8). The sliding element (53b) is adjustable in angle and can be locked via a fixing device (56). The pin (5121) runs largely parallel to the rod (31) and establishes a hinge-joint connection between the screw shank (51, 512) and the screw head (52). This hinge joint allows the compensation of lateral misalignment or dynamic, lateral movements between rod (3) and Pedikelschraubenschaft (2, 4) by the head (52) can tilt about this axis (5121). The combination of the spherical sliding element (53b) with a hinge joint results in the advantage of an enlarged Winkeleinstellbereichs in the lateral direction, with a fixed angle position in all other planes.

[018.] A simplified variant (5c) for the polyaxial adjustment of the rod (31) with a spherical sliding element (53b) is shown in FIG. Here, the spherical slider (53b) is inserted into an annular pedicle screw head (52) for mounting. An optional Groove (5054) can facilitate the assembly of the transversely aligned sliding element. After aligning the ring this can be locked with a fixing element (56) in the desired angle position. The fixing element (56) preferably has a concave surface on the side facing the sliding element, which faces the ball surface of the

Sliding element is largely congruent.

 [019.] In a further variant (6) is an example of an alternative polyaxial

Screw head design (62) shown (Fig. 10). The bracing is not carried out as previously shown by substantially inner fixing and connecting elements (44, 45, 46), but via external elements (651, 652, 66). The pedicle screw (6) has a clamping cage (64), at least one sleeve (651, 652), a sliding element (63) and a

Fixing element (66). With the aid of the fixing element (66), the sleeve (651) can be pushed onto the clamping cage (64) so that a clamping force is generated on the screw shaft head (612) due to the conically shaped clamping cage (64). For this purpose, the tensioning cage is preferably slotted in the region of the connection point with the shaft head (612); the inside has on the circumference a groove whose profile is designed such that the tensioning cage engages on the shaft head.

figure description

Fig. 1 shows the implantable invention for fixation of a vertebra.

Fig. 2 describes the first embodiment of the invention using the example of a braceable pedicle screw.

Fig. 3 shows a second embodiment possibility for the use of a square

Implant rod.

Fig. 4 shows another embodiment, which uses rolling bearings to reduce the abrasion.

Fig. 5 illustrates an alternative embodiment of the previous embodiment. Fig. 6 shows the use of ball bearings.

Fig. 7 illustrates another way of linearly supporting a rod for a polyaxial pedicle screw design. Fig. 8 shows the use of a spherical sliding element for the polyaxial adjustment of the rod. Furthermore, in this embodiment, a movable axis is provided, which can compensate medial-lateral movements of the spine.

Fig. 9 describes a simplified possibility of a polyaxially adjustable dynamic anchoring device for spinal columns.

Fig. 10 shows an alternative embodiment of the screw head with a

external clamping mechanism.

Claims

claims An anchoring device for dynamic stabilization of the spine, comprising a bone anchor (41), a head (42, 52, 62) adjustable in angle by means of a joint (412, 512, 5121, 612) relative to the bone anchor (41), having an opening (4243 ), a locking device (46, 56, 66) and a connecting rod (31, 32) with a constant load-bearing cross-section, characterized in that the head comprises a sliding element (43, 53a, 53b, 63) which is suitable for the rod (31, 32) relative to  Anchoring device translationally displaceable and angular stable to store.  2. anchoring device according to claim 1, characterized in that the sliding element (43, 53 a, 53 b, 63) includes an opening (431, 432) having a substantially constant cross section.  3. anchoring device according to one of the preceding claims, characterized in that the opening (431, 432) has a rectangular cross-section.  4. anchoring device according to one of the preceding claims, characterized in that the sliding element (43, 53 a, 53 b, 63) includes an outer surface having a substantially spherical curvature.  5. Anchoring device according to one of the preceding claims, characterized in that the joint (412, 612) is designed as a ball joint.  6. anchoring device according to one of the preceding claims, characterized in that the joint (512, 5121) is designed as a hinge joint.  7. Anchoring device according to one of the preceding claims, characterized in that the connecting rod (31, 32) has a rectangular cross-section.  8. anchoring device for dynamic stabilization of the spine, consisting of a bone anchor (41), a head firmly connected thereto (50), one  Locking device (56), a connecting rod (31, 32) with a constant  load-bearing cross section and an angle adjustable sliding member (53b) with spherical outer surface, characterized in that the locking device (56) is adapted to fix the sliding member (53b) in its angular position and that the sliding member (53b) further has an opening (531) , which is adapted to the rod (31, 32) relative to the anchoring device in the otherwise fixed state to store translationally displaceable and angularly stable. 9. anchoring device for dynamic stabilization of the spine, consisting of a bone anchor (41), a thus firmly connected head (50), a Locking device (56), a connecting rod (31, 32) with a constant load-bearing cross-section, an angular adjustable ball element (543) with a spherical outer surface and a sliding element (53a) with a substantially cylindrical or prismatic outer surface, characterized in that the locking device (56) is suitable to fix the ball element (543) in its angular position, that the sliding element (53a) is inside the ball element (543), and the sliding element has an opening (531) suitable for relatively modifying the bar (31, 32) for anchoring device in the otherwise fixed state to store translationally displaceable and angular stable.  10. anchoring device according to claim 9, characterized in that the ball element (543) is slotted.  11. anchoring device according to claim 9 or 10, characterized in that the  Locking device (56) consists of a bracket with a latching mechanism (562, 564) at each end of the bracket, the inner surface of the bracket (5653) is designed spherically concave, and the latching mechanism is dimensioned with at least one latching step so that this after assembly a bias on the ball member (543) or  Slide member (53b) exerts.  12. An anchoring device for dynamic stabilization of the spine, comprising a bone anchor (41), an associated annular head (50), a locking device (56), a connecting rod (31, 32) with a constant  load-bearing cross-section and an angle-adjustable sliding member (53b) with spherical outer surface, characterized in that the locking means (56) is adapted to fix the sliding member (53b) in its angular position, and the sliding member further has an opening (531), which suitable is the rod (31, 32) relative to  Anchoring device in the otherwise fixed state translationally displaceable and angular stable to store.  13. Anchoring device according to claim 12, characterized in that the  Locking device (56) consists of a grub screw on the for  Screw center of the center facing side has a concave, spherical recess.  14 anchoring device for dynamic stabilization of the spine, consisting of a bone anchor (41), a means of a joint (412) relative to the bone anchor (41) angle adjustable head (42, 52, 62), a locking device (46) Fixing the angular position of the head and a connecting rod (31, 32) with a constant load-bearing cross-section, characterized in that the head (42) includes a sliding element or cage (43) which rolling elements in the form of balls, rollers or needles includes (4381, 4382) which are adapted to the rod (31, 32) relative to  Anchoring device translationally displaceable and angular stable to store.  15. anchoring device for dynamic stabilization of the spine, consisting of a bone anchor (41), one by means of a joint (412) relative to the bone anchor (41) angular adjustable head (42, 52, 62), a locking device (46) for  Fixing the angular position of the head and a connecting rod (31, 32) with a constant load-bearing cross section, characterized in that the head (42) includes rollers (4383) which are suitable for the rod (31, 32) relative to the anchoring device translationally displaceable and angularly stable to store.  16. anchoring device according to claim 14 or 15, characterized in that the  Rolling (4381, 4382) or the head (42) surrounds a largely closed, elastic sleeve.  17. Anchoring device according to claim 14 or 15, characterized in that the head (42) is formed so that the rolling elements (4381, 4382) are outwardly surrounded by the head (42).  18. anchoring device according to one of the preceding claims, characterized in that at least one of the elements connecting rod (31, 32), sliding member (43, 53 a, 53 b, 63) and / or head (42, 52, 62) made of a high-strength polymer, in particular PEEK, PEKK, PAI, or high-drawn PE, each with or without fiber reinforcement. 19. Anchoring device according to one of the preceding claims, characterized in that at least one of the elements connecting rod (31, 32) and / or sliding element (43, 53 a, 53 b, 63) are made of a titanium or cobalt-chromium alloy. 20. anchoring device according to one of the preceding claims, characterized in that at least one of the elements connecting rod (31, 32) and / or sliding member (43, 53 a, 53 b, 63) with a wear-reducing coating such as TiN, TiC, TiCN, TiAlN, CrN, DLC, ZrN, Al TiN, MoS ₂ , ta-C, aC: H are coated.