Patent Application
20140163624
The present invention generally relates to apparatus and methods for anchoring elements such as screws and, more particularly, to apparatus and methods for a screw, such as a bone screw, with a deflectable portion to increase the pullout resistance of the screw and its resistance to loosening. The anchoring elements of the present invention may also be useful for other medical and non-medical applications.
The elderly are increasing their share in the overall number of orthopedic and particularly spinal surgical procedures. As incidence of osteoporosis increases with age it presents a challenge when pedicle screw fixation is considered.
Conventional screws have a given pullout strength. In a conventional bone screw, the advancing screw displaces trabecular bone, and the displaced spongy bone forms a thickened bony envelope around the shaft of the positioned screw. This condensed spongy bone concentration around the screw shaft is forced between the coils of the thread. The pull out strength depends on this concentration of the bone tissue on one hand, and on the resisting surface of the helical thread on the other.
The thread of the screw projecting from its core is a cumulative surface which faces and resists forces of pullout.
There is a compelling need for a screw (or other anchoring element) design and method that improves the pullout resistance of the screw, reduces the risk of undesired screw loosening and overcomes other disadvantages of the prior art.
One aspect of the present invention is an anchoring element, comprising a shaft having a core and a longitudinal channel, the shaft also having a distal portion and having threading along at least a portion of a length of the shaft; an elongated element movable within the channel, the elongated element being (i) a tensioning element or (ii) a rigid element or (iii) a tensioning element and a rigid element; one or more lateral cut-outs in the core at the distal portion or at a central portion of the shaft, each cut-out backed by an effective hinge, the channel traversing at least one side of one of the cut-outs, the elongated element and distal portion configured such that upon axial movement of the elongated element, the distal portion deflects to an angle from a longitudinal axis of the shaft.
A further aspect of the present invention is a method of inserting an anchoring element into an object, comprising taking an anchoring element, the anchoring element configured with a shaft that has a core and a longitudinal channel, the shaft also having a distal portion and having threading along at least a portion of a length of the shaft, the anchoring element having an elongated element configured to move within the channel, the core configured with one or more lateral cut-outs at the distal portion or at a central portion of the shaft such that each cut-out is backed by an effective hinge and such that the channel traverses at least one side of one of the cut-outs, inserting the anchoring element into the object; and moving the elongated element axially so that the distal portion deflects away from a longitudinal axis of the shaft.
A still further aspect of the present invention is a method of inserting an anchoring element into an object, comprising taking an anchoring element that is pre-biased to assume a deflected form such that a distal portion of a shaft of the anchoring element is at an angle to a longitudinal axis of the shaft, the shaft also having threading along at least a portion of a length of the shaft, the anchoring element configuring with a longitudinal channel housing a rigid elongated reinforcing element configured to move within the channel, the core having one or more lateral cut-outs at the distal portion or at a central portion of the shaft, each cut-put backed by an effective hinge, the channel traversing at least one side of one of the cut-outs; inserting the anchoring element into the object with the longitudinal channel housing a rigid elongated reinforcing element that temporarily holds the anchoring element in a straightened configuration; and moving the rigid elongated reinforcing element axially through the channel sufficient to release the anchoring element to the pre-biased deflected form.
A yet still further aspect of the present invention is a method of inserting an anchoring element into an object, comprising taking an anchoring element, the anchoring element configured with a shaft that has a core and a longitudinal channel, the shaft also having a distal portion and having threading along at least a portion of a length of the shaft, the anchoring element having an elongated element configured to move within the channel, the core configured with one or more lateral slits at the distal portion or at a central portion of the shaft such that each lateral slit is backed by an effective hinge and such that the channel traverses at least one of the slits, inserting the anchoring element into the object; and moving the elongated element axially toward a distal tip of the shaft so that the slits open and the distal portion deflects away from a longitudinal axis of the shaft.
A still further aspect of the present invention is an anchoring element, comprising a shaft having a core and a longitudinal channel, the shaft also having a distal portion and having threading along at least a portion of a length of the shaft; an elongated element movable within the channel, the elongated element being flexible enough to bend during deflection but sufficiently rigid to effectuate the deflection; one or more lateral cut-outs in the core at the distal portion or at a central portion of the shaft, each cut-out backed by an effective hinge, the channel traversing at least one side of one of the cut-outs, the elongated element and distal portion configured such that upon axial movement of the elongated element, the distal portion deflects to an angle from a longitudinal axis of the shaft.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, descriptions and claims.
Various embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein:
FIG. 13C1 and FIG. 13C2 isometric views of a locking mechanism for maintaining deflection of the distal portion, in accordance with one embodiment of the present invention;
FIG. 15AA is an isometric view similar to
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
The present invention generally provides a method and apparatus for an anchoring element, such as a bone screw, with a deflectable portion to increase the pullout resistance of the anchoring element and/or its resistance to loosening. The anchoring element may initially assume a straight configuration in which it behaves as a conventional anchoring element, for example a screw being inserted by a normal threaded insertion method in which the helical thread engages the bone tissue (if it is a bone screw) and the screw advances. The shaft may have threading along at least a portion of its length and may have a core with at least one longitudinal channel for housing an elongated element that may be a tensioning element or a rigid reinforcing element or both. The longitudinal channel may be displaced off center in at least one dimension (vertically or horizontally) along a plane perpendicular to the longitudinal axis of the shaft. The elongated element may traverse at least one of the one or more lateral cut-outs (or at least one side of one of the cut-outs) in the core of the shaft, which may be located at the distal portion of the shaft, or in some embodiments at the central portion of the shaft. The cut-outs may be backed by an effective hinge, which may be an integral hinge. The elongated element and the distal portion may be configured such that upon axial movement of the elongated element through the channel toward the proximal end of the shaft (or toward the distal tip of the shaft in other embodiments), the distal portion may deflect to an angle from the longitudinal axis. If the elongated element is a tensioning element it may be affixed to the distal portion. If the anchoring element is pre-biased to deflect, the elongated element may be rigid non-tensioning element that when moved axially allows the anchoring element to leave its straightened configuration and deflect. In another version, the elongated element may be pushed through a non-straight or curved or contoured longitudinal channel to straighten the channel and thereby effectuate the deflection of the distal portion of the shaft. After the anchoring element has been fully inserted, upon axial movement of the elongated element, a bend or other deflected shape may be formed, preferably at or near the distal portion, such as a distal tip, of the anchoring element. Non-limiting medical applications include a bone screw used in sacro-iliac joint fixation, fixation for ALIF implants, lateral approach implants, femoral neck fixation and percutaneous humeral head fixation. A non-limiting example of a valuable non-medical mechanical application includes passing a screw through a sheet of material, such as a hollow wall structure, and then deflecting the distal portion in order to improve anchoring of the screw.
In contrast to prior art anchoring elements such as bone screws, in which the pullout strength of a screw and its resistance to loosening are limited by the fact that the shaft of the screw is straight, the present invention may have an increased pullout strength and resistance to loosening. The deflected part of the anchoring element may greatly increase the effective area resisting axial withdrawal (“pullout”) of the anchoring element. In addition, the risk of undesirable loosening or failure of the anchoring element may be reduced due to the decreased cyclic and/or static loading on the deflected part. The “loosening” that the present invention may inhibit is one or both of the following: (a) reduced fixation to the tissue (i.e. the anchor or screw can wiggle) and (b) the anchor, i.e. screw, unthreads from the tissue by rotating along the long axis to the point where it ‘backs out’ of the tissue. In further contrast to the prior art bone anchoring elements, such as bone screws, which may have a straight shaft, the anchoring element of the present invention may have a distal portion, such as a distal tip, that is bent in relation to a longitudinal axis of the shaft of the anchoring element. In further contrast to methods of the prior art, in which anchoring elements such as bone screws are inserted into tissue, and their shape is not altered, a method of the present invention, may in some preferred embodiments include deflecting a distal portion, such as a distal tip, of the bone screw after it has been inserted. In some preferred embodiments, the method the present invention may include straightening out the bent distal portion of the anchoring element prior to removal of the anchoring element. In still further contrast to prior art anchoring elements such as bone screws, in which the core of the shaft may be solid, the core of the shaft of the anchoring element of the present invention may have cut-out portions, especially lateral cut-out portions. The cut-out portions may be backed by an effective hinge that may be an integral hinge. The effective hinge may be displaced from the longitudinal axis to improve leverage. The cut-out portions may have associated transverse slits to facilitate deflection. These cut-out portions may be V-shaped, U-shaped or of another shape in cross-section and may be more proximal than the distal tip. In still further contrast to certain prior art anchoring elements, in which slots may be formed longitudinally in the anchoring element, the anchoring element of the present invention, may, in one preferred embodiment, have cut-outs that may be lateral cut-outs in the core of the anchoring element. In yet still further contrast to the prior art, in which an expansion of a portion of an anchoring element may be such that the expansion is symmetrical and/or may involve a plurality of segments expanding outward symmetrically, the anchoring element and method of the present invention, in one preferred embodiment, may involve a deflectable portion or deflectable distal end, or a deflectable distal tip, that may comprise an asymmetric deflection, for example in that an end view of the anchoring element in its already deflected configuration may be asymmetric. In further contrast to the prior art, in which an expansion of an anchoring element may involve a plurality of separated portions of the anchoring element connected to a common base and expanding identically and simultaneously, the anchoring element and method of the present invention may, in one preferred embodiment, involve successive deflection of segments of one distal portion of the anchoring element such that a particular segment of the deflected portion, taken alone, may be positioned at a different deflection angle to the longitudinal axis than that of another segment of the deflected portion. In further contrast to the prior art, in which the shaft of the anchoring element is solid, the shaft of the bone screw of the present invention may have one or more longitudinal channels. The channel(s) may be on a surface of the shaft or may be entirely within the core of the shaft. The channel may be off center from a longitudinal axis of the shaft. In still further contrast with the prior art anchoring elements such as bone screws, the method and anchoring element of the present invention may utilize an elongated element, that may be a tensioning element, affixed to a distal portion, such as a distal tip, of the anchoring element. The elongated tensioning element may be pulled or pushed to deflect the distal portion of the anchoring element at an angle that in some preferred embodiments is between 10 and 180 degrees (or in other preferred embodiments between about 70 and about 110 degrees) from the longitudinal axis of the shaft. In contrast to prior art methods, in which the bone screw displaces trabecular bone and the displaced spongy bone forms a thickened bony envelope around the shaft of the bone screw, the method of the present invention may, after deflection of the distal tip, yield an area adjacent the distal tip that is void or of reduced or very low bone density on one side of the distal tip. This may reduce cyclic loading on the deflected part and reduce the risk of the screw loosening and/or failing. In contrast to the prior art screws and methods, the deflected tip may also yield an area of increased concentration adjacent the deflected distal tip on an opposite side of the distal tip. In still further contrast to the prior art, a method of the present invention may, in some preferred embodiments, include resiliently pre-biasing the anchoring element to assume the deflected form and then using a rigid reinforcing element to hold the anchoring element straight until removal of the rigid reinforcing element. This may be useful where additional rigidity is required during threaded insertion of a screw into a bone. In further contrast to the prior art, in some preferred embodiments, the anchor or screw, or in other preferred embodiments, the hinges alone, may be made of a material that is a shape memory alloy (i.e. Nitinol or another such alloy) such that the deflectable portion is provided in a default deflected state. In that case, a rigid element positioned in the core of the screw may hold the deflectable portion in a straight configuration for insertion into the bone. After positioning, the rigid element may be removed and the deflectable portion (with or without the aid of an elongated element (tensioning or rigid reinforcing) being pulled) may deflect to its bent configuration. In still further contrast to prior art anchoring elements, in which a channel may be static, the present invention, in some preferred embodiments, utilizes a longitudinal channel that before axial movement of the elongated element may be in a contoured or non-straight configuration whereas the channel may be straight after axial movement of the elongated element.
The principles and operation of an apparatus and method for a bone screw with a deflectable portion according to the present invention may be better understood with reference to the drawings and the accompanying description.
As shown in
Longitudinal channel 32 may also be on the surface 21 of shaft 20. Although an example of this is shown in
As shown in
Lateral cut-outs 33, in one preferred embodiment, span 60 rotational degrees or less between an upper part 33a of a cut-out and a lower part 33b of the cut-out (as measured from a point of rotation at the deepest point of the cut-out 33). In other preferred embodiments, the rotational degrees spanned is 70 degrees or less or in other preferred embodiments 80 degrees or less or in other preferred embodiments 90 degrees or less. These amounts of rotational degrees are merely illustrative non-limiting examples.
Cut-outs 33 may be close to a distal portion, for example a distal tip 27a, of the shaft 20 (which is also the distal portion 27, for example the distal tip 27a, of the anchoring element 10 in general) and may be proximal in relation to the distal portion 27 of shaft 20 that may be subject to deflection. Cut-outs 33 may be symmetrical about a plane (not shown) that is at 90° to the longitudinal axis (or in some other preferred embodiments substantially symmetrical, i.e. plus or minus 15% from the plane, or in other preferred embodiments not symmetrical about such a plane). Cut-outs 33 may interrupt the helical thread 29 around the shaft 20, assuming the anchoring element 10 is a screw. Even if the cut-outs 33 form interruptions in the helical thread 29, the cut-outs 33 do not significantly impact function of the helical thread as a whole during insertion of the screw 10.
It should be understood that the present invention does not place limitations on the location or nature of any threading or other resisting surface that may appear on the anchoring element 10 or on its surface 21 (or whether there will necessarily be any threading). For example, any such threading 29 may be on the entire length or along one or more portions of the lengths of the shaft or excluding particular portions thereof (for example on the entire shaft other than the distal tip 27 or other than the distal end 22 or other than the deflectable portion). The threading 29, if any, may also have a variety of dimensions (in terms of pitch, tooth shape, tooth size or other dimensional features), may include a double thread, and further may have various (i.e. left or right) coil directions.
Each cut-out 33 may be backed by an effective hinge 31 comprising a connection arrangement between cut-outs 33 allowing a pivoting movement between one side of a cut-out (i.e. 33a) and the other side of that cut-out (i.e. 33b) in the substantially axial direction. The movement may pivot on a part of effective hinge 31 that has little longitudinal dimension as shown in
Each effective hinge 31 may have the associated relief slit 39. Accordingly, the effective hinge 31 may be the material between the slit 39 and the cut-out 33. These relief slits 39 may increase the flexibility of the shaft 20 structure in the direction of deflection. During deflection, as shown in
The longitudinal channel 32 in core 30 (see
The elongated element 40 may be a tensioning element 40 (best seen in
As shown in
As shown in
It should be understood that the terra lateral “cut-outs” 33 as used in this patent application does include lateral slits or other lateral openings even if no material has been removed from the core 30 to create the slit or opening and also includes lateral cut-outs where material has been removed. In some preferred embodiments of the version discussed in
As shown in
Deflection of the distal portion 27 of the anchoring element 10 may be performed in any direction. According to one particularly preferred option where the anchoring element is a bone screw, it may in some cases be advantageous to employ deflection downwards (in a caudal direction), since this may minimize the chance of normal axial loading of the screw 10 resulting in loading of the deflected tip portion. The deflection shown in
The angle of deflection from the longitudinal axis 25 may be between about 10 degrees (or less) and about 180 degrees or more. In some preferred embodiments, this angle is between about 15 and about 150 degrees, or in other preferred embodiments between about 50 and about 130 degrees or on still other preferred embodiments between about 70 degrees and about 110 degrees, or other combinations of these numbers (i.e. about 50 degrees and about 110 degrees). Although the drawings show a fully deflected configuration that turns through roughly 90 degrees, i.e., between about 70 degrees and about 110 degrees, alternative embodiments in which the deflected portion turns through smaller angles (e.g., 30-70 degrees) or larger angles (e.g., 110-180 degrees) also fall within the broad scope of the present invention. Depending upon the type of tissue involved and the geometry of deployment relative to the tissue, even smaller deflection angles, such as a 10 degree deflection, may be effective to achieve enhanced resistance to pullout and/or loosening of the device.
In certain preferred embodiments, as seen from FIG. 13C1 and FIG. 13C2, anchoring element 10 may further comprise a locking mechanism 69 for maintaining deflection of the distal portion 27, such as distal tip 27A. For example, elongated tensioning element 40 or elongated reinforcing element 40a may have a series of projections, such as inclined teeth 69A, that may correspond to and may get caught or stuck in cut-outs 33 in core 30 for locking engagement. This would prevent the segments (for example segments 20A, 20B) from returning to their initial state before deflection. In another version of locking mechanism 69, a projection (or recess) on channel 32 may catch a groove or recess (or projection) on elongated element 40 or 40a and prevent the elongated element (40 or 40a) from moving further once deflection of distal portion 27 occurs.
In a case where the anchoring element 10 is a screw, the screw typically has a “tulip” (tulip-shaped hollow connector 88 (see
As shown in
Longitudinal channel 32 may be considered longitudinal notwithstanding the fact that particular segments of channel 32 are not strictly longitudinal if the main overall direction of the channel is longitudinal. This may be particularly applicable to the case where channel 32 houses a non-rigid tensioning element 40, such as a drawstring. For example, a channel extending along a length of shaft 20 and configured as a wave or a flattened “W” or along a winding path would still be longitudinal since the main overall direction of the channel is longitudinal. In one preferred embodiment, the anchoring element 10 or method (100, 200) of the present invention may employ a channel 32 where the effective force of a tensioning element 40 such as a drawstring through the channel 32 is to exert a substantially longitudinal force on the deflecting distal portion 27 even though the shape of the channel 32 is not strictly longitudinal or not longitudinal.
The deflecting of the distal portion 27, such as distal tip 27A, may be so that the distal portion 27 is at an angle from the longitudinal axis of between about 10 degrees and about 180 degrees, or at any other angle described herein, such as between about 70 and about 110 degrees. Some versions of method 100 may also include a step of deflecting the distal portion 27 until the cut-outs close together. Some versions of method 100 include a step of straightening the deflected distal portion 27 by pushing the elongated element (40 or 40a) axially in a distal direction until the anchoring element returns to an original straight configuration. Alternatively, the straightening of the deflected distal portion 27 may be achieved by pushing a rigid rod into the cannula or longitudinal channel in the shaft and pushing the segments back into a straight configuration. Then, an expanded version of a method of inserting into and removing from an object and anchoring element may include a step of removing the anchoring element from the object.
As shown in
It is particularly significant to note in regard to an anchoring element that is a bone screw that, as shown in
In some preferred embodiments described in this document, the screw can be re-straightened for withdrawal if clinically necessary. For example, in some cases, reversing the tightening mechanism within the tulip preferably forcibly returns the screw to its original straight configuration, allowing removal of the screw in a conventional manner if required. Where a flexible drawstring is used, reversibility of the tip deflection may be ensured through the elastic property of the resilient material of the screw. More preferably, the “drawstring” is implemented as a semi-rigid rod which is effective to actively deflect the bent tip back to its straightened state.
It should be noted that the deflection of the screw may be performed elastically, or part or all of the motion may include plastic deformation. In the latter case, an additional step of plastic deformation will typically be required if the screw is to be returned to its straightened configuration for removal.
Optionally, where additional rigidity is required during threaded insertion of the screw into the bone, the screw may be formed with an inner passageway which temporarily houses a rigid reinforcing element such as a K-wire (not shown) during insertion of the screw. According to this option, the screw may optionally be resiliently pre-biased to assume its deflected form, and may be temporarily retained in its straightened configuration by the presence of the reinforcing element until after insertion.
Accordingly, as shown by
Step 220 of method 200 may involve inserting the anchoring element into the object with the longitudinal channel housing a rigid elongated reinforcing element 40a that temporarily holds the anchoring element in a straightened configuration. A further step 230 of method 200 may be moving the rigid elongated reinforcing element to release the anchoring element to the pre-biased deflected form. A further step may involve pushing the rigid elongated reinforcing element, which may be a rod, axially along the channel 32 so as to deflect the segments (areas of the screw 10 between successive cut-outs 33) back to the straight configurations.
Method 200 may in some preferred embodiments involve moving the rigid elongated reinforcing element through a channel that is on a surface of the shaft, for example as shown in
As shown in
A further step 320 may comprise inserting the anchoring element into the object. Step 330 may be moving (i.e. pushing) the elongated element 40a axially toward a distal tip 27a of the shaft so that the slits open (see
Although illustrated herein in a non-limiting preferred embodiment where the deflected portion is substantially at the distal tip of the screw, i.e., with the deflection beginning at a distance of no more than two core diameters from the tip, alternative embodiments in which flexing occurs at any other location along the screw (and with any number of hinges/joints) also fall within the scope of the present invention.
It should also be noted that the invention is not limited to simple forms of deflection as shown, and could alternatively be implemented using non-parallel effective hinges formed by cut-outs at different angles around the axis, thereby achieving helical or other geometrical forms.
The core of the screw may have a conical shape or a cylindrical shape. The thread projecting from the core of the screw may follow the shape of the core, so that the screw itself may assume a cylindrical or conical shape, or may have an external shape (the envelope of the outer edges of the thread) which differs from the shape of the core to provide any desired combination of thread and core shapes.
Finally, as illustrated in
In all cases, the bone screw of the present invention may be made from any biocompatible material with suitable mechanical properties, and sufficiently flexible or deformable to provide the required deflection. Finally, it is noted that the channel 32 of an anchoring element 10, for example a bone screw, may also be used to inject any biocompatible material, such as bone cement, into the tissue where the anchoring element 10 is inserted, for example the vertebra, of a subject.
The invention has been exemplified thus far in a particularly preferred set of embodiments as a bone screw. It should be noted however that the structure as defined herein may be used to advantage in a range of other human and non-human medical applications. Furthermore, the structure finds valuable applications in non-medical mechanical application.
Although described herein with reference to screws, it should be noted that some aspects of the present invention may be implemented to advantage in non-threaded anchoring elements, such as nails or rods which are driven into or otherwise inserted into bone (or some other body or object) in a straight state and subsequently some part of the distal half of the device is made to deflect in order to provide enhanced pullout resistance and/or resistance to loosening. The devices may have round, square or other cross-sectional shapes. The structure, function and advantages of such devices will be understood by analogy to the screw embodiments discussed above.
As used herein, the term “about” in reference to a quantitative amount means plus or minus five percent. Substantially parallel lines or axes are completely parallel or intersect (or would intersect if extended) at an angle of 10 rotational degrees or less.
While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. Therefore, the claimed invention as recited in the claims that follow is not limited to the embodiments described herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB12/53973 | 8/2/2012 | WO | 00 | 8/16/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61514068 | Aug 2011 | US |
