Method and apparatus for spinal stabilization

A method and apparatus of limiting at least one degree of movement between a superior vertebral body, an inferior vertebral body, and an intermediate vertebral body that is disposed between the superior and inferior vertebral bodies of a patient. The method can comprise: advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body; positioning a proximal portion of the stabilization device such that the proximal portion limits at least one degree of movement between the superior vertebral body and the intermediate vertebral body by contacting a surface of the superior vertebral body; and advancing a distal end of a fixation device into a facet of the intermediate vertebral body and into a facet or pedicle of the inferior vertebral body for stabilizing the intermediate vertebral body and the inferior vertebral body.

BACKGROUND

1. Field of the Inventions

The present inventions relate to medical devices and, more particularly, to methods and apparatuses for dynamic spinal stabilization.

2. Description of the Related Art

The human spine is a flexible weight bearing column formed from a plurality of bones called vertebrae. There are thirty three vertebrae, which can be grouped into one of five regions (cervical, thoracic, lumbar, sacral, and coccygeal). Moving down the spine, there are generally seven cervical vertebra, twelve thoracic vertebra, five lumbar vertebra, five sacral vertebra, and four coccygeal vertebra. The vertebra of the cervical, thoracic, and lumbar regions of the spine are typically separate throughout the life of an individual. In contrast, the vertebra of the sacral and coccygeal regions in an adult are fused to form two bones, the five sacral vertebra which form the sacrum and the four coccygeal vertebra which form the coccyx.

In general, each vertebra contains an anterior, solid segment or body and a posterior segment or arch. The arch is generally formed of two pedicles and two laminae, supporting seven processes—four articular, two transverse, and one spinous. There are exceptions to these general characteristics of a vertebra. For example, the first cervical vertebra (atlas vertebra) has neither a body nor spinous process. In addition, the second cervical vertebra (axis vertebra) has an odontoid process, which is a strong, prominent process, shaped like a tooth, rising perpendicularly from the upper surface of the body of the axis vertebra. Further details regarding the construction of the spine may be found in such common references as Gray's Anatomy, Crown Publishers, Inc., 1977, pp. 33-54, which is herein incorporated by reference.

The human vertebrae and associated connective elements are subjected to a variety of diseases and conditions which cause pain and disability. Among these diseases and conditions are spondylosis, spondylolisthesis, vertebral instability, spinal stenosis and degenerated, herniated, or degenerated and herniated intervertebral discs. Additionally, the vertebrae and associated connective elements are subject to injuries, including fractures and torn ligaments and surgical manipulations, including laminectomies.

The pain and disability related to the diseases and conditions often result from the displacement of all or part of a vertebra from the remainder of the vertebral column. Over the past two decades, a variety of methods have been developed to restore the displaced vertebra to their normal position and to fix them within the vertebral column. Spinal fusion is one such method. In spinal fusion, one or more of the vertebra of the spine are united together (“fused”) so that motion no longer occurs between them. The vertebra may be united with various types of fixation systems. These fixation systems may include a variety of longitudinal elements such as rods or plates that span two or more vertebrae and are affixed to the vertebrae by various fixation elements such as wires, staples, and screws (often inserted through the pedicles of the vertebrae). These systems may be affixed to either the posterior or the anterior side of the spine. In other applications, one or more bone screws may be inserted through adjacent vertebrae to provide stabilization.

Although spinal fusion is a highly documented and proven form of treatment in many patients, there is currently a great interest in surgical techniques that provide stabilization of the spine while allowing for some degree of movement. In this manner, the natural motion of the spine can be preserved, especially for those patients with mild or moderate disc conditions. In certain types of these techniques, flexible materials are used as fixation rods to stabilize the spine while permitting a limited degree of movement.

SUMMARY

Notwithstanding the variety of efforts in the prior art described above, these techniques are associated with a variety of disadvantages. In particular, these techniques typically involve an open surgical procedure, which results higher cost, lengthy in-patient hospital stays and the pain associated with open procedures.

Therefore, there remains a need for improved techniques and systems for stabilizing the spine. For example, the devices can be implantable through a minimally invasive procedure.

Accordingly, one embodiment of the present inventions comprises a method of limiting at least one degree of movement between a superior vertebral body, an intermediate vertebral body, and an inferior vertebral body of a patient. In accordance with an embodiment of the method, a distal end of a stabilization device can be advanced into a pedicle of the intermediate vertebral body. A proximal portion of the stabilization device can be positioned such that the proximal portion limits at least one degree of movement between a superior vertebral body and the intermediate vertebral body by contacting a surface of the superior vertebral body. Further, the method can further comprise advancing a distal end of a fixation device into a facet of the intermediate vertebral body and into a facet of the inferior vertebral body for stabilizing the intermediate vertebral body and the inferior vertebral body.

Some implementations of the embodiment of the method described above can be modified such that the step of positioning a proximal portion of the stabilization device can comprise advancing a proximal anchor distally over an elongated body of the stabilization device. Further, the step of advancing a proximal anchor distally over an elongated body of the stabilization device can comprise proximally retracting the elongated body with respect to the proximal anchor. Additionally, the step of advancing a proximal anchor distally over an elongated body of the stabilization device can comprise applying a distal force to the proximal anchor.

In other implementations, the method can further comprise maintaining the patient in a face down position during the step of advancing a distal end of a stabilization device into the pedicle of the intermediate vertebral body. The step of advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body can comprise advancing the distal end of the stabilization device through the pars of the intermediate vertebral body. The steps of advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body and positioning a proximal portion of the stabilization device can be accomplished through a minimally invasive surgical approach.

Further, the step of advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body can comprise rotating the distal end of the stabilization device. Furthermore, advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body can further comprise advancing the stabilization device over a guidewire. In addition, advancing a distal end of a stabilization device into a pedicle of the intermediate vertebral body can further comprise advancing the stabilization device through an expanded tissue tract.

Another embodiment comprises a method of limiting at least one degree of movement between a superior vertebral body and an intermediate vertebral body of a patient. According to such an embodiment, a distal end of a first stabilization device can be advanced into a pedicle of the intermediate vertebral body. A proximal portion of the first stabilization device can be positioned such that the proximal portion abuts against a surface of an intermediate articular process of the superior adjacent vertebral body to limit at least one degree of movement between a superior vertebral body and an intermediate vertebral body. A distal end of a second stabilization device can be advanced into a pedicle of the intermediate vertebral body such that it is positioned with bilateral symmetry with respect to the first stabilization device. A proximal portion of the second stabilization device can be positioned such that the proximal portion abuts, with bilateral symmetry with respect to the first stabilization device, against a surface of a second intermediate articular process of the superior adjacent vertebral body to limit at least one degree of movement between the superior vertebral body and the intermediate vertebral body. Further, the method can also comprise advancing a distal end of a fixation device into a facet of the intermediate vertebral body and into a facet of the inferior vertebral body for stabilizing the intermediate vertebral body and the inferior vertebral body.

In some implementations of the method, the first and second stabilization devices can be used to limit extension and/or flexion between the superior vertebral body and the intermediate vertebral body. Further, the first and second stabilization devices can be used to limit lateral movement between the superior vertebral body and the intermediate vertebral body.

In accordance with yet another embodiment, a kit is provided for dynamic spinal stabilization. The kit can comprise one or more spinal stabilization devices and one or more orthopedic fixation devices. Each spinal stabilization device can comprise an elongate body, a distal anchor, a retention structure, a proximal anchor, and at least one complementary retention structure. The elongate body can have a proximal end and a distal end. The distal anchor can be disposed on the distal end of the elongate body. The retention structure can be disposed on the body, proximal to the distal anchor. The proximal anchor can be moveably carried by the body, and the proximal anchor can have an outer surface, and at least a portion of the outer surface can be elastic. The at least one complementary retention structure can be disposed on the proximal anchor and can be configured for permitting proximal movement of the body with respect to the proximal anchor but resisting distal movement of the body with respect the proximal anchor.

The orthopedic fixation device can comprise an elongate body, a distal anchor, a retention structure, a proximal anchor, at least one complementary retention structure, and a washer. The elongate body can have a proximal end and a distal end. The distal anchor can be disposed on the distal end. The retention structure can be disposed on the elongate body, proximal to the anchor. The proximal anchor can be moveably carried by the elongate body, and the proximal anchor can comprise a tubular sleeve and a radially outward extending head. The at least one complementary retention structure can be disposed on the proximal anchor and can be configured for permitting proximal movement of the elongate body with respect to the proximal anchor but resisting distal movement of the elongate body with respect the proximal anchor. The washer can be angularly moveable with respect to the longitudinal axis of the tubular sleeve. The washer can have an aperture that is elongated with respect to a first axis such that the washer permits greater angular movement with respect to the longitudinal axis of the tubular sleeve in a plane containing the first axis.

In some embodiments, the kit can be configured such that the distal anchor of each stabilization device comprises a helical flange. The retention structure on the body and the at least one complementary retention structure on the proximal anchor of each stabilization device can also comprise a series of ridges and grooves. For example, the at least one complementary retention structure on the proximal anchor of each stabilization device can comprise an annular ring positioned within a recess formed between the proximal anchor and the elongate pin.

Further, the proximal anchor of each stabilization device can also include a distally facing surface. The distally facing surface can include at least one bone engagement feature. The aperture of each orthopedic fixation device can circumscribe a channel having a width in a first direction and a height in a second direction that is perpendicular to the first direction. The width can be smaller than the maximum diameter of the head and the height can be greater than the width. In addition, the distal anchor of each orthopedic fixation device can comprise a helical flange. In some implementations, the distal anchor of each orthopedic fixation device can be moveable from an axial orientation for distal insertion through a bore to an incline orientation to resist axial movement through the bore.

In other embodiments, the retention structures of the elongate body and the proximal anchor of each orthopedic fixation device can permit proximal movement of the elongate body with respect to the proximal anchor without rotation. The washer of each orthopedic fixation device can include a bottom wall, a side wall and a lip for retaining the head of the proximal anchor within the washer. The elongated body of each orthopedic fixation device can comprise a first portion and a second portion that are detachably coupled together at a junction. The first portion of each orthopedic fixation device can include an anti-rotation structure and the proximal anchor of each orthopedic fixation device includes a complementary anti-rotation structure to prevent rotation between the first portion and the proximal anchor.

In yet another embodiment, a kit is provided for dynamic spinal stabilization, and can comprise one or more spinal stabilization devices and one or more orthopedic fixation devices. The spinal stabilization device can be used for limiting at least one degree of movement between a superior vertebral body and an inferior vertebral body of a patient, and can comprise an elongate body, a distal anchor, a retention structure, a proximal anchor, and at least one complementary retention structure. The elongate body can have a proximal end and a distal end. The distal anchor can be disposed on the distal end of the elongate body. The retention structure can be disposed on the body, proximal to the distal anchor. The proximal anchor can be moveably carried by the body and can include at least one flat surface configured to abut against a surface of an inferior articular process of the superior adjacent vertebral body when the stabilization device is inserted into the inferior adjacent vertebral body. Finally, the at least one complementary retention structure can be disposed on the proximal anchor and can be configured for permitting proximal movement of the body with respect to the proximal anchor but resisting distal movement of the body with respect the proximal anchor.

In such an embodiment, the orthopedic fixation device can comprise an elongate pin, at least one distal anchor, a proximal anchor, and an anti-rotational structure. The elongate pin can have a proximal end, a distal end, and a first retention structure. The at least one distal anchor can be carried by the elongate pin. The proximal anchor can be axially moveable with respect to the elongate pin and can comprise a split ring positioned within an annular recess formed within the proximal anchor. The split ring can have at least one gap formed between two ends and can be moveable between a first position and a second position. The second position can be located closer to the longitudinal axis of the elongate pin as compared to the first portion so as to engage the first retention structure and prevent proximal movement of the proximal anchor with respect to the elongated pin while the first position allows distal movement of the proximal anchor with respect to the pin. The anti-rotational structure can prevent rotation of the split ring about the longitudinal axis of the elongate pin.

Some embodiments of the kit can be configured such that the elongate pin of each orthopedic fixation device includes at least one anti-rotational feature configured to engage a complementary anti-rotational feature of the proximal anchor. In such an embodiment, the anti-rotational structure of each orthopedic fixation device can position the gap of the split ring such that it is positioned over the anti-rotational feature of the elongate pin. Further, the anti-rotational feature of the elongate pin of each orthopedic fixation device can comprise at least one flat side. The anti-rotational feature of each orthopedic fixation device can also comprise includes a pair of tabs that extend inwardly from the tubular body toward the longitudinal axis of the tubular body and positioned between the gap of the split ring.

In additional embodiments of the kit, the distal anchor of each orthopedic fixation device can comprise a helical flange. Further, the distal anchor of each orthopedic fixation device can be moveable from an axial orientation for distal insertion through a bore to an incline orientation to resist axial movement through the bore. The elongate pin of each orthopedic fixation device can also comprise a first portion and a second portion that are detachably coupled together at a junction. Further, the first portion of each orthopedic fixation device can include an anti-rotation structure and the proximal anchor of each orthopedic fixation device can include a complementary anti-rotation structure to prevent rotation between the first portion and the proximal anchor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although embodiments of the present inventions will be disclosed primarily in the context of a spinal stabilization procedure, the methods and structures disclosed herein are intended for application in any of a variety medical applications, as will be apparent to those of skill in the art in view of the disclosure herein. For example, certain features and aspects of bone stabilization device and techniques described herein may be applicable to proximal fractures of the femur and a wide variety of fractures and osteotomies, the hand, such as interphalangeal and metacarpophalangeal arthrodesis, transverse phalangeal and metacarpal fracture fixation, spiral phalangeal and metacarpal fracture fixation, oblique phalangeal and metacarpal fracture fixation, intercondylar phalangeal and metacarpal fracture fixation, phalangeal and metacarpal osteotomy fixation as well as others known in the art. See e.g., U.S. Pat. No. 6,511,481, which is hereby incorporated by reference herein. A wide variety of phalangeal and metatarsal osteotomies and fractures of the foot may also be stabilized using the bone fixation devices described herein. These include, among others, distal metaphyseal osteotomies such as those described by Austin and Reverdin-Laird, base wedge osteotomies, oblique diaphyseal, digital arthrodesis as well as a wide variety of others that will be known to those of skill in the art. Fractures of the fibular and tibial malleoli, pilon fractures and other fractures of the bones of the leg may be fixated and stabilized with these bone fixation devices with or without the use of plates, both absorbable or non-absorbing types, and with alternate embodiments of the current inventions. The stabilization devices may also be used to attach tissue or structure to the bone, such as in ligament reattachment and other soft tissue attachment procedures. Plates and washers, with or without tissue spikes for soft tissue attachment, and other implants may also be attached to bone, using either resorbable or nonresorbable fixation devices depending upon the implant and procedure. The stabilization devices may also be used to attach sutures to the bone, such as in any of a variety of tissue suspension procedures. The bone stabilization device described herein may be used with or without plate(s) or washer(s), all of which can be either permanent, absorbable, or combinations.

FIGS. 1A and 1Bare side and rear elevational views of a dynamic stabilization device12positioned within a body structure10aof a spine.FIGS. 1D and 1Eare side and rear elevational views of two pair of bone stabilization devices, such as the dynamic stabilization device12and a fixation device800, positioned within body structures10a,10bof the spine. As will be explained in detail below, the dynamic stabilization device12and the fixation device800may be used in a variety of techniques to stabilize the spine. It should also be understood that the dynamic stabilization device12and the fixation device800may refer to more than one dynamic stabilization device12(such as a pair of dynamic stabilization devices12a,12b) and more than one fixation device800(such as a pair of fixation devices800a,800b).

As discussed further herein, in some embodiments, the dynamic stabilization device(s)12can include an outer surface of a proximal anchor that has a smooth or spherical shape. As will be explained below, the outer surface of the proximal anchor can be configured to abut against the inferior facet of the superior adjacent vertebrae. In this manner, motion between the adjacent vertebrae may be limited and/or constrained. When combined with the fixation device(s)800, the devices (12,800) can be implanted to result in beneficial dynamic stabilization of a desired portion of the spine.

In one embodiment, the dynamic stabilization device12can be attached (e.g., inserted or screwed into) and/or coupled to a respective body structures and limit motion of another respective body structure. In the another embodiment, the dynamic stabilization device12can limit extension in the spine by being attached and/or coupled to a respective inferior body structure and limiting motion of an adjacent respective superior body structure. As described herein, the superior and inferior body structures can refer to adjacent structures along the spine. When discussing the superior body structure, it will be presumed that when the dynamic stabilization device12and the fixation device800shown inFIGS. 1D and 1Eare both used, the devices12can be inserted into an intermediate body structure immediately below the superior body structure.

Further, the fixation device800can be inserted into the intermediate and the inferior body structures to secure said body structures together and to promote fusion between the body structures. Thus, the three body structures may be described as superior, intermediate, and inferior when the dynamic stabilization device12and the fixation device800are discussed together, or as simply superior and inferior when the dynamic stabilization device12and the fixation device800are being discussed individually. “Body structure” as used herein is the anterior solid segment and the posterior segment of any vertebrae of the five regions (cervical, thoracic, lumbar, sacral, and coccygeal) of the spine. In some embodiments, the dynamic stabilization device12can limit motion by contacting, abutting against and/or wedging against the adjacent body structure and/or a device coupled to the adjacent body structure. The fixation device800can be positioned below (or above in other embodiments) the stabilization device12and can be used to promote spinal fusion below the spinal level at which motion is limited by the dynamic stabilization device. In such an embodiment, the dynamic stabilization device can provide adjacent level support as an adjunct to fusion therapy. In one embodiment, the fusion therapy involves the fixation device800, which will be described in detail below.

With reference to the illustrated embodiment ofFIGS. 1A and 1B, the distal end of the dynamic bone stabilization device12is inserted into the pedicle of the inferior vertebrae, preferably through the pars (i.e., the region between the lamina and the superior articular processes). The proximal end of the device12extends above the pars such that it limits motion of a superior adjacent vertebra10bwith respect to the inferior adjacent vertebrae10b. In one embodiment, the proximal end of the device limits motion by abutting and/or wedging against a surface of the superior adjacent vertebrae as the superior adjacent vertebrae moves relative to the inferior adjacent vertebrae. In this manner, at least one degree of motion between the inferior and superior vertebrae may be limited. For example, the spine generally has six (6) degrees of motion which include flexion, extension, left and right lateral bending and axial rotation or torsion. In the illustrated embodiment, extension of the spine is limited. Embodiments in which the devices are inserted with bilateral symmetry can be used to limit left and right lateral bending.

In the illustrated embodiment, motion of the spine is limited when the proximal end of the device contacts, abuts, and/or wedges against the inferior articular process of the superior adjacent vertebra10b. In this application, it should be appreciated that one or more intermediate member(s) (e.g., plates, platforms, coatings, cement, and/or adhesives) can be can be coupled to the superior adjacent vertebra10bor other portions of the spine that the device contacts, abuts, and/or wedges against. Thus, in this application, when reference is made to the device contacting, abutting and/or wedging against a portion of the spine it should be appreciated that this includes embodiments in which the device contacts, abuts and/or wedges against one or more intermediate members that are coupled to the spine unless otherwise noted.

As explained below, the bone stabilization devices12may be used after laminectomy, discectomy, artificial disc replacement, microdiscectomy, laminotomy and other applications for providing temporary or permanent stability in the spinal column. For example, lateral or central spinal stenosis may be treated with the bone fixation devices12and techniques described below. In such procedures, the bone fixation devices12and techniques may be used alone or in combination with laminectomy, discectomy, artificial disc replacement, and/or other applications for relieving pain and/or providing stability.

An embodiment of the stabilization device12will now be described in detail with initial reference toFIGS. 2-4. The stabilization device12comprises a body28that extends between a proximal end30and a distal end32. The length, diameter and construction materials of the body28can be varied, depending upon the intended clinical application. In embodiments optimized for spinal stabilization in an adult human population, the body28will generally be within the range of from about 20-90 mm in length and within the range of from about 3.0-8.5 mm in maximum diameter. The length of the helical anchor, discussed below, may be about 8-80 millimeters. Of course, it is understood that these dimensions are illustrative and that they may be varied as required for a particular patient or procedure.

In one embodiment, the body28comprises titanium. However, as will be described in more detail below, other metals, or bioabsorbable or nonabsorbable polymeric materials may be utilized, depending upon the dimensions and desired structural integrity of the finished stabilization device12.

The distal end32of the body28is provided with a cancellous bone anchor and/or distal cortical bone anchor34. Generally, for spinal stabilization, the distal bone anchor34is adapted to be rotationally inserted into a portion (e.g., the pars or pedicle) of a first vertebra. In the illustrated embodiment, the distal anchor34comprises a helical locking structure72for engaging cancellous and/or distal cortical bone. In the illustrated embodiment, the locking structure72comprises a flange that is wrapped around a central core73, which in the illustrated embodiment is generally cylindrical in shape. The flange72extends through at least one and generally from about two to about 50 or more full revolutions depending upon the axial length of the distal anchor34and intended application. The flange will generally complete from about 2 to about 60 revolutions. The helical flange72is preferably provided with a pitch and an axial spacing to optimize the retention force within cancellous bone. While the helical locking structure72is generally preferred for the distal anchor, it should be appreciated that the distal anchor could comprise other structures configured to secure the device in the cancellous bone anchor and/or distal cortical bone, such as, for example, various combinations and sub-combinations of hooks, prongs, expandable flanges, etc. See also e.g., U.S. Pat. No. 6,648,890, the entirety of which is hereby incorporated by reference herein.

The helical flange72of the illustrated embodiment has a generally triangular cross-sectional shape (seeFIG. 3B). However, it should be appreciated that the helical flange72can have any of a variety of cross sectional shapes, such as rectangular, oval or other as deemed desirable for a particular application through routine experimentation in view of the disclosure herein. For example, in one modified embodiment, the flange72has a triangular cross-sectional shape with a blunted or square apex. One particularly advantageous cross-sectional shape of the flange are the blunted or square type shapes. Such shapes can reduce cutting into the bone as the proximal end of the device is activated against causing a windshield wiper effect that can loosen the device12. The outer edge of the helical flange72defines an outer boundary. The ratio of the diameter of the outer boundary to the diameter of the central core73can be optimized with respect to the desired retention force within the cancellous bone and giving due consideration to the structural integrity and strength of the distal anchor34. Another aspect of the distal anchor34that can be optimized is the shape of the outer boundary and the central core73, which in the illustrated embodiment are generally cylindrical.

The distal end32and/or the outer edges of the helical flange72may be atraumatic (e.g., blunt or soft). This inhibits the tendency of the stabilization device12to migrate anatomically distally and potentially out of the vertebrae after implantation. Distal migration is also inhibited by the dimensions and presence of a proximal anchor50, which will be described below. In the spinal column, distal migration is particularly disadvantageous because the distal anchor34may harm the tissue, nerves, blood vessels and/or spinal cord which lie within and/or surround the spine. Such features also reduce the tendency of the distal anchor to cut into the bone during the “window-wiper effect” that is caused by cyclic loading of the device as will be described. In other embodiments, the distal end32and/or the outer edges of the helical flange72may be sharp and/or configured such that the distal anchor34is self tapping and/or self drilling.

A variety of other embodiments for the distal anchor32can also be used. For example, the various distal anchors described in U.S. Pat. No. 6,908,465, issued Jun. 21, 2005 can be incorporated into the stabilization device12described herein. The entire contents of this application are hereby expressly incorporated by reference. In particular, the distal anchor32may comprise a single helical thread surrounding a lumen, much as in a conventional corkscrew. Alternatively, a double helical thread may be utilized, with the distal end of the first thread rotationally offset from the distal end of the second thread. The use of a double helical thread can enable a greater axial travel for a given degree of rotation and greater retention force than a corresponding single helical thread. Specific distal anchor designs can be optimized for the intended use, taking into account desired performance characteristics, the integrity of the distal bone, and whether the distal anchor is intended to engage exclusively cancellous bone or will also engage cortical bone. In still other embodiments, the distal anchor34may be formed without a helical flange. For example, various embodiments of levers, prongs, hooks and/or radially expandable devices may also be used. See e.g., U.S. Pat. No. 6,648,890, which is hereby expressly incorporated by reference in its entirety.

As shown inFIG. 3B, the body28is cannulated forming a central lumen42to accommodate installation over a placement wire as is understood in the art. The cross section of the illustrated central lumen is circular but in other embodiments may be non circular, e.g., hexagonal, to accommodate a corresponding male tool for installation or removal of the body28as explained below. In other embodiments, the body28may be partially or wholly solid.

With continued reference toFIGS. 2-4, the proximal end30of the body28is provided with a rotational coupling70, for allowing the body28to be rotated. Rotation of the rotational coupling70can be utilized to rotationally drive the distal anchor32into the bone. In such embodiments, any of a variety of rotation devices may be utilized, such as electric drills or hand tools, which allow the clinician to manually rotate the proximal end30of the body28. Thus, the rotational coupling70may have any of a variety of cross sectional configurations, such as one or more curved faces, flats, or splines. In the illustrated embodiment, the rotational coupling70is a male element in the form of a hexagonal projection. However, in other embodiments, the rotational coupling70may be in the form of a female component, machined, milled or attached to the proximal end30of the body28. For example, in one such embodiment, the rotational coupling70comprises an axial recess with a polygonal cross section, such as a hexagonal cross section. As explained above, the axial recess may be provided as part of the central lumen42.

The proximal end30of the fixation device is also provided with a proximal anchor50. The proximal anchor50comprises a housing52, which forms a lumen53(seeFIG. 5) configured such that the body28may extend, at least partially, through the proximal anchor50. The proximal anchor50is axially distally moveable along the body28such that the proximal anchor50can be properly placed with respect to the inferior vertebra and superior vertebra. As will be explained below, complimentary locking structures such as threads, levers, split rings, and/or ratchet like structures between the proximal anchor50and the body28resist proximal movement of the anchor50with respect to the body28under normal use conditions. The proximal anchor50preferably can be axially advanced along the body28with and/or without rotation as will be apparent from the disclosure herein.

With particular reference toFIGS. 4-6, in the illustrated embodiment, the complementary structure of the proximal anchor50is formed by an annular ring51, which is positioned within an annular recess55formed along the lumen53. As will be explained below, the ring51comprises surface structures54which interact with complimentary surface structures58on the body28. In the illustrated embodiment, the complimentary surface structures58comprise a series of annular ridges or grooves60formed on the surface of the body28. The surface structures54and complementary surface structures58permit distal axial travel of the proximal anchor50with respect to the body28, but resist proximal travel of the proximal anchor50with respect to the body28as explained below.

As shown inFIG. 6, the annular ring51is split (i.e., has a least one gap) and is interposed between the body28and the recess55of the proximal anchor50(seeFIG. 5). In the illustrated embodiment, the ring51comprises a tubular housing57(seeFIG. 6), which defines a gap or space59. In one embodiment, the gap59is defined by a pair of edges61a,61b, that are generally straight and parallel to each other. Although not illustrated, it should be appreciated that in modified embodiments, the ring51can be formed without a gap. When the ring51is positioned along the body28, the ring51preferably surrounds a substantial portion of the body28. The ring51can be configured so that the ring51can flex or move radially outwardly in response to an axial force so that the ring51can be moved relative to the body28, as described below.

In the illustrated embodiment, the tubular housing57includes at least one and in the illustrated embodiment ten teeth or flanges63, which are configured to engage the complementary surface structures58on the body28in a ratchet-like motion. In the illustrated embodiment (seeFIG. 5), the teeth or flanges include a first surface65that lies generally perpendicular to the longitudinal axis of the anchor and generally faces the proximal direction (i.e., the direction labeled “P” inFIG. 5) and a second surface67that is inclined with respect to the longitudinal axis of the anchor and that faces distal direction (i.e., the direction labeled “D” inFIG. 5). It should be noted that the proximal and directions inFIG. 5are reversed with respect toFIG. 4.

With continued reference toFIG. 5, the recess55is sized and dimensioned such that as the proximal anchor50is advanced distally over the body, the second surface67of the annular ring51can slide along and over the complementary retention structures58of the body28. That is, the recess55provides a space for the annular ring to move radially away from the body28as the proximal anchor50is advanced distally.

A distal portion69of the recess55is sized and dimensioned such that after the proximal anchor50is appropriately advanced, proximal motion of the proximal anchor50is resisted as the annular ring51becomes wedged between the body28and an angled engagement surface71of the distal portion69. In this manner, proximal movement of the proximal anchor50under normal use conditions may be prevented. In modified embodiments, the annular ring51can be sized and dimensioned such that the ring51is biased inwardly to engage the retention structures58on the body28. The bias of the annular ring51can result in a more effective engagement between the complementary retention structures58of the body and the retention structures54of the ring51.

In certain embodiments, it is advantageous for the outer surface49of the proximal anchor50to rotate with respect to the body28. This arrangement advantageously reduces the tendency of the body28to rotate and/or move within the superior articular process of the inferior vertebrae10aas the outer surface49contacts, abuts or wedges against the inferior articular process of the superior vertebrae10b. In the illustrated embodiment, rotation of the outer surface49is provided by configuring the lumen53and annular recess55such that the anchor50can rotate about the body28and ring51. Preferably, as the anchor50rotates the axial position of the anchor50with respect to the body28remains fixed. That is, the annular ring51resists proximal travel of the proximal anchor50with respect to the body28while the anchor50is permitted to rotate about the body28and ring51. Of course those of skill in the art will recognize other configurations and mechanisms (e.g., bearings, rollers, slip rings, etc.) for providing rotation of the outer surface49with respect to the body28. In a modified embodiment, the proximal anchor50can be configured such that it does not rotate with respect to the body28. In such an embodiment, a key or one or more anti-rotational features (e.g., splines, grooves, flat sides, etc.) can be provided between the proximal anchor50, the ring51and/or the body51to limit or prevent rotation of the proximal anchor50with respect to the body28.

As mentioned above, it is contemplated that various other retention structures54and complementary retention structures58may be used between the body28and the proximal anchor50to permit distal axial travel of the proximal anchor50with respect to the body28, but resist proximal travel of the proximal anchor50with respect to the body28. Examples of such structures can be found in U.S. Pat. No. 6,685,706, entitled “PROXIMAL ANCHORS FOR BONE FIXATION SYSTEM.” The entire contents of U.S. Pat. No. 6,685,706 are hereby expressly incorporated by reference herein. In such embodiments, the structures54and complementary retention structures58can be configured to allow the proximal anchor to be advanced with or without rotation with respect to the body28.

As mentioned above, the complimentary surface structures58on the body28comprise threads, and/or a series of annular ridges or grooves60. These retention structures58are spaced axially apart along the body28, between a proximal limit62and a distal limit64. SeeFIG. 4. The axial distance between proximal limit62and distal limit64is related to the desired axial working range of the proximal anchor50, and thus the range of functional sizes of the stabilization device12. Thus, the stabilization device12of the example embodiment can provide accurate placement between the distal anchor34and the proximal anchor50throughout a range of motion following the placement of the distal anchor in a vertebra. That is, the distal anchor34may be positioned within the cancellous and/or distal cortical bone of a vertebra, and the proximal anchor may be distally advanced with respect to the distal anchor throughout a range to provide accurate placement of the proximal anchor50with respect to the vertebra without needing to relocate the distal anchor34and without needing to initially locate the distal anchor34in a precise position with respect to the proximal side of the bone or another vertebra. The arrangement also allows the compression between the distal anchor34and the proximal anchor50to be adjusted. Providing a working range throughout which positioning of the proximal anchor50is independent from setting the distal anchor34allows a single device to be useful for a wide variety of different anatomies, as well as eliminates or reduces the need for accurate device measurement. In addition, this arrangement allows the clinician to adjust the compression force during the procedure without adjusting the position of the distal anchor. In this manner, the clinician may focus on positioning the distal anchor sufficiently within the vertebra to avoid or reduce the potential for distal migration out of the vertebra, which may damage the particularly delicate tissue, blood vessels, nerves and/or spinal cord surrounding or within the spinal column. In addition or alternative, the above described arrangement allows the clinician to adjust the positioning of the proximal anchor50with respect to the inferior articular process of the superior adjacent vertebrae. In this manner, the clinician may adjust the position of the proximal anchor50without adjusting the position of the distal anchor such that the anchor50is configured to wedge or abut against inferior articular process of the superior adjacent vertebrae. In a modified embodiment, the position of the proximal anchor50with respect to the surrounding vertebra can be adjusted by rotating the device12and advancing the distal anchor and the proximal anchor carried by the body.

In the embodiment ofFIGS. 4-6, the proximal anchor50can be distally advanced over the body28without rotating the proximal anchor50with respect to the body28. In one embodiment, the ring51and the proximal anchor50are rotationally linked by, for example, providing inter-engaging structures (e.g., tabs, ridges and the like). In such an embodiment, the proximal anchor50can be advanced without rotating the proximal anchor50and be removed and/or the position adjusted in a proximal or distal direction by rotating the proximal anchor with respect to the body28. This can allow the surgeon to remove an proximal anchor and use a different sized or configured proximal anchor50if the first proximal anchor is determined to be inadequate. In such an embodiment, the proximal anchor50is preferably provided with one or more engagement structures (e.g., slots, hexes, recesses, protrusions, etc.) configured to engage a rotational and/or gripping device (e.g., slots, hexes, recesses, protrusions, etc.). Thus, in some embodiments, the proximal anchor50can be pulled and/or rotated such that the anchor50is removed from the body.

In many applications, the working range is at least about 10% of the overall length of the device, and may be as much as 20% or 50% or more of the overall device length. In the context of a spinal application, working ranges of up to about 10 mm or more may be provided, since estimates within that range can normally be readily accomplished within the clinical setting. The embodiments disclosed herein can be scaled to have a greater or a lesser working range, as will be apparent to those of skill in the art in view of the disclosure herein.

In embodiments optimized for spinal stabilization in an adult human population, the anchor50will have a diameter within the range of from about 1 to 1/16 of an inch in another embodiment the proximal anchor proximal anchor50within the range from about 0.5 to ⅛ of an inch in another embodiment.

With reference back toFIGS. 2-4, in the illustrated embodiment, the outer surface49of the proximal anchor50has a smooth or spherical shape. As will be explained below, the outer surface49of the proximal anchor50is configured to abut against the inferior facet of the superior adjacent vertebrae. In this manner, motion between the adjacent vertebrae may be limited and/or constrained.

FIG. 7Aillustrates an embodiment in which the body28comprises a first portion36and a second portion38that are coupled together at a junction40. In the illustrated embodiment, the first portion36carries the distal anchor34(shown without a central core) while the second portion38forms the proximal end30of the body28. As will be explained in more detail below, in certain embodiments, the second portion38may be used to pull the body28and therefore will sometimes be referred to as a “pull-pin.” The first and second portions36,38are preferably detachably coupled to each other at the junction40. In the illustrated embodiment, the first and second portions36,38are detachably coupled to each other via interlocking threads.

Specifically, as best seen inFIG. 7B, the body28includes an inner surface41, which defines a central lumen42that preferably extends from the proximal end30to the distal end32throughout the body28. At the proximal end of the first portion36, the inner surface41includes a first threaded portion44. The first threaded portion44is configured to mate with a second threaded portion46, which is located on the outer surface45of the second portion38. The interlocking annular threads of the first and second threaded portions44,46allow the first and second portions36,38to be detachably coupled to each other. In one modified embodiment, the orientation of the first and second threaded portions44,46can be reversed. That is, the first threaded portion44can be located on the outer surface of the first portion36and the second threaded portion46can be located on the inner surface41at the distal end of the second portion38. Any of a variety of other releasable complementary engagement structures may also be used, to allow removal of second portion38following implantation, as is discussed below.

In a modified arrangement, the second portion38can comprise any of a variety of tensioning elements for permitting proximal tension to be placed on the distal anchor34while the proximal anchor is advanced distally. For example, any of a variety of tubes or wires can be removably attached to the first portion36and extend proximally to the proximal handpiece. In one such arrangement, the first portion36can include a releasable connector in the form of a latching element, such as an eye or hook. The second portion38can include a complementary releasable connector (e.g., a complementary hook) for engaging the first portion36. In this manner, the second portion38can be detachably coupled to the first portion36such proximal traction can be applied to the first portion36through the second portion as will be explained below. Alternatively, the second portion48may be provided with an eye or hook, or transverse bar, around which or through which a suture or wire may be advanced, both ends of which are retained at the proximal end of the device. Following proximal tension on the tensioning element during the compression and/or positioning step, one end of the suture or wire is released, and the other end may be pulled free of the device. Alternate releasable proximal tensioning structures may be devised by those of skill in the art in view of the disclosure herein.

In a final position, the distal end of the proximal anchor50preferably extends distally past the junction40between the first portion36and the second portion38. As explained above, the proximal anchor50is provided with one or more surface structures54for cooperating with complementary surface structures58on the first portion36of the body28.

In this embodiment, the stabilization device12may include an antirotation lock (not shown) between the first portion36of the body28and the proximal collar50. For example, the first portion36may include one or more of flat sides (not shown), which interact with corresponding flat structures in the proximal collar50. As such, rotation of the proximal collar50is transmitted to the first portion36and distal anchor34of the body28. Of course, those of skill in the art will recognize various other types of splines or other interfit structures can be used to prevent relative rotation of the proximal anchor and the first portion36of the body28. To rotate the proximal anchor50, the housing52may be provided with a gripping structure (not shown) to permit an insertion tool to rotate the flange proximal anchor50. Any of a variety of gripping structures may be provided, such as one or more slots, recesses, protrusions, flats, bores or the like. In one embodiment, the proximal end of the proximal anchor50is provided with a polygonal, and, in particular, a pentagonal or hexagonal recess or protrusion.

Methods implanting stabilization devices described above as part of a spinal stabilization procedure will now be described. Although certain aspects and features of the methods and instruments described herein can be utilized in an open surgical procedure, the disclosed methods and instruments are optimized in the context of a percutaneous or minimally invasive approach in which the procedure is done through one or more percutaneous small openings. Thus, the method steps which follow and those disclosed are intended for use in a trans-tissue approach. However, to simplify the illustrations, the soft tissue adjacent the treatment site have not been illustrated in the drawings.

In one embodiment of use, a patient with a spinal instability is identified. The patient is preferably positioned face down on an operating table, placing the spinal column into a normal or flexed position. A trocar optionally may then be inserted through a tissue tract and advanced towards a first vertebra. In another embodiment, biopsy needle (e.g., Jamshidi™) device can be used. A guidewire may then be advanced through the trocar (or directly through the tissue, for example, in an open surgical procedure) and into the first vertebrae. With reference to FIG. ID, the guide wire110is preferably inserted into the pedicle of the vertebrae preferably through the pars (i.e. the region of the lamina between the superior and inferior articular processes).

With reference toFIG. 1E, a suitable expandable access sheath or dilator112can then be inserted over the guidewire and expanded (FIG. 1F) to enlarge the tissue tract and provide an access lumen for performing the methods described below in a minimally invasive manner. In a modified embodiment, a suitable tissue expander (e.g., a balloon expanded catheter or a series of radially enlarged sheaths) can be inserted over the guidewire and expanded to enlarge the tissue tract. A surgical sheath can then be advanced over the expanded tissue expander. The tissue expander can then be removed such that the surgical sheath provides an enlarged access lumen. Any of a variety of expandable access sheaths or tissue expanders can be used, such as, for example, a balloon expanded catheter, a series of radially enlarged sheaths inserted over each other, and/or the dilation introducer described in U.S. patent application Ser. No. 11/038,784, filed Jan. 19, 2005 (Publication No. 2005/0256525), the entirety of which is hereby incorporated by reference herein.

A drill with a rotatable tip may be advanced over the guidewire and through the sheath. The drill may be used to drill an opening in the vertebrae. The opening may be configured for (i) for insertion of the body28of the bone stabilization device12, (ii) tapering and/or (iii) providing a counter sink for the proximal anchor50. In other embodiments, the step of drilling may be omitted. In such embodiments, the distal anchor34is preferably self-tapping and self drilling. In embodiments, in which an opening is formed, a wire or other instrument may be inserted into the opening and used to measure the desired length of the body28of the device12.

The body28of the fixation device may be advanced over the guidewire and through the sheath until it engages the vertebrae. The body28may be coupled to a suitable insertion tool prior to the step of engaging the fixation device12with the vertebrae. The insertion tool may be configured to engage the coupling70on the proximal end of the body28such that insertion tool may be used to rotate the body28. In such an embodiment, the fixation device12is preferably configured such that it can also be advanced over the guidewire.

The insertion tool may be used to rotate the body28thereby driving the distal anchor34to the desired depth within the pedicle of the vertebra. The proximal anchor50may be carried by the fixation device prior to advancing the body28into the vertebra, or may be attached and/or coupled to the body28following placement (partially or fully) of the body28within the vertebrae. In another embodiment, the anchor50may be pre-attached and/or coupled to the body28.

In one embodiment, the clinician will have access to an array of devices12, having, for example, different diameters, axial lengths, configurations and/or shapes. The clinician will assess the position of the body28with respect to the superior vertebrae and choose the device12from the array, which best fits the patient anatomy to achieve the desired clinical result. In another embodiment, the clinician will have access to an array of devices12, having, for example, bodies28of different diameters, axial lengths. The clinician will also have an array of proximal anchors50, having, for example, different configurations and/or shapes. The clinician will choose the appropriate body28and then assess the position of the body28with respect to the superior vertebrae and choose the proximal anchor50from the array, which best fits the patient anatomy to achieve the desired clinical result. In such an embodiment, the proximal anchor50is advantageously coupled to body28after the body28is partially or fully inserted into the vertebrae.

Once the distal anchor34is in the desired location, the proximal anchor50is preferably advanced over the body28until it reaches its desired position. This may be accomplished by pushing on the proximal anchor50or by applying a distal force to the proximal anchor50. In another embodiment, the proximal anchor50is advanced by applying a proximal retraction force to the proximal end30of body28, such as by conventional hemostats, pliers or a calibrated loading device, while distal force is applied to the proximal anchor50. In this manner, the proximal anchor50is advanced distally with respect to the body28until the proximal anchor50is in its proper position (e.g., positioned snugly against the outer surface of the vertebra). Appropriate tensioning of the stabilization device12can be accomplished by tactile feedback or through the use of a calibration device for applying a predetermined load on the stabilization device12. As explained above, one advantage of the structure of the illustrated embodiments is the ability to adjust the compression and/or the position of the proximal anchor50independently of the setting of the distal anchor34within the vertebra. For example, the positioning of the distal anchor34within the vertebra can be decoupled from the positioning of the proximal anchor50with respect to the superior vertebra.

In one embodiment, the proximal anchor50is pushed over the body28by tapping the device with a slap hammer or similar device that can be used over a guidewire. In this manner, the distal end of the device12is advantageously minimally disturbed, which prevents (or minimizes) the threads in the bore from being stripped.

Following appropriate tensioning of the proximal anchor50, the proximal portion of the body28extending proximally from the proximal anchor50can be removed. In one embodiment, this may involve cutting the proximal end of the body28. For example, the proximal end of the body may be separated by a cutting instrument or by cauterizing. Cauterizing may fuse the proximal anchor50to the distal end32of the body28thereby adding to the retention force between the proximal anchor50and the body28. Such fusion between the proximal anchor and the body may be particularly advantageous if the pin and the proximal anchor are made from a polymeric or plastic material. In this manner, as the material of the proximal anchor and/or the pin is absorbed or degrades, the fusion caused by the cauterizing continues to provide retention force between the proximal anchor and the body. In another embodiment, the body comprises a first and a second portion36,38as described above. In such an embodiment, the second portion38may detached from the first portion36and removed. In the illustrated embodiment, this involves rotating the second portion38with respect to the first portion via the coupling70. In still other embodiments, the proximal end of the body28may remain attached to the body28.

The access site may be closed and dressed in accordance with conventional wound closure techniques and the steps described above may be repeated on the other side of the vertebrae for substantial bilateral symmetry as shown inFIGS. 1A and 1B. The bone stabilization devices12may be used alone or in combination with other surgical procedures such as laminectomy, discectomy, artificial disc replacement, and/or other applications for relieving pain and/or providing stability.

As will be described in detail below, the dynamic stabilization device12can provide adjacent level support as an adjunct to fusion therapy. In one embodiment, the fusion therapy involves the fixation device800, which will be described in detail below. The fixation device800can be positioned below (or above in other embodiments) the stabilization device12and can be used to promote spinal fusion below the spinal level at which motion is limited by the dynamic stabilization device. In other embodiments, fusion can be promoted using other devices.

As will be explained below, the superior body structure (e.g., the superior vertebrae10b) can be conformed to the device by providing a complementary surface or interface. In one embodiment, the superior vertebrae can be modified using a separate drill or reamer that is also used to form the countersink200described above. In other embodiments, the drill that is used to form an opening in the inferior body can be provided with a countersink portion that is also used to modify the shape of the superior vertebrae10b. In still other embodiments, the shape of the superior vertebrae10bcan be modified using files, burrs and other bone cutting or resurfacing devices to form a complementary surface or interface for the proximal anchor50.

As mentioned above, a countersink can be provided for the proximal anchor50. With reference toFIG. 8, a pair of counter sinks200is shown formed in or near the pars of the inferior vertebrae10a. Each counter sink200is preferably configured to generally correspond to a distal facing portion49a(seeFIG. 4orFIG. 10A) of the proximal anchor50. In this manner, the proximal anchor50, in a final position, may be seated at least partially within the inferior vertebrae10a. In the illustrated embodiment, the countersink200has a generally spherical configuration that corresponds generally to the spherical shape of the distal portion49aof the proximal anchor50of the illustrated embodiment. In modified embodiments, the countersink200can have a modified shape (e.g., generally cylindrical, conical, rectangular, etc.) and/or generally configured to correspond to the distal portion of a proximal anchor50with a different shape than the proximal anchor illustrated inFIGS. 2-4.

The countersink200advantageously disperses the forces received by the proximal anchor50by the superior vertebrae10band transmits said forces to the inferior vertebrae10a. As will be explained in more detail below, the countersink200can be formed by a separate drilling instrument or by providing a counter sink portion on a surgical drill used to from a opening in the body10b.

In addition or in the alternative to creating the countersink200, the shape of the inferior articular process IAP (which can include the facet in certain embodiments) of the superior vertebrae10bmay be modified in order to also disperse the forces generated by the proximal anchor50contacting, abutting and/or wedging against the superior vertebrae10b. For example, as shown inFIG. 8, a portion204of the inferior articular process IAP of the superior vertebrae10bthat generally faces the proximal anchor50can be removed with the goal of dispersing and/or reducing the forces applied to the proximal anchor50. In the illustrated embodiment, the inferior articular process is provided with a generally rounded recess206that corresponds generally to the rounded outer surface49of the proximal anchor50. In modified embodiments, the inferior articular process IAP can be formed into other shapes in light of the general goal to reduce and/or disperse the forces applied to the proximal anchor50. For example, in certain embodiments, the inferior articular process IAP may be formed into a generally flat, blunt or curved shape. In other embodiments, the inferior articular process IAP may be configured to abut and/or wedge more efficiently with a proximal anchor50of a different shape (e.g., square, oval, etc.). In general, the countersink200and surface206provide for an increased contact surface between the superior vertebra and the proximal anchor50and the inferior vertebra and the proximal anchor50. This contact area reduces stress risers in the device and the associated contact areas of the vertebrae. In addition, the windshield wiper affect is reduced as the forces transmitted to the proximal anchor50from the superior vertebrae are transmitted through the area formed by the countersink200.

FIGS. 9A and 9Billustrate an exemplary embodiment of a device210that can be used to form the countersink200and/or the recess206described above. As shown, the device comprises a body212having a distal end214, a proximal end216and a guidewire lumen (not shown) extending therethrough. The proximal end216is configured to engage any of a variety of standard driving tools as is known in the art. The distal end214is provided with an outer surface220that generally corresponds to the outer surface49of the proximal anchor50. The outer surface220is also provided with one or more removal or cutting features218(e.g., flutes, sharp edges, etc.) so as to remove or cut bone as the device210is rotated. A pin221(shown in dashed lines inFIG. 9B) can be provided at the end of the device210. The pin221can be inserted into the hole formed in the vertebrae and helps to center and support the device221at it cuts the countersink200and/or recess206into the bone.

In use, the device210is advanced over a guidewire that is inserted into the inferior vertebrae10b. As the device210is advanced and rotated, the device210encounters the inferior process IAP (seeFIG. 8) of the superior vertebrae10band portions thereof are removed. Further advancement of the device210, forms the countersink200in the superior articular process of the inferior vertebrae10aand removes additional portions of the superior vertebrae10b. Accordingly, in this embodiment, the device210can be used to form both the countersink200and to change the shape of the inferior articular process IAP of the superior vertebrae10b.

FIGS. 9C-Eillustrate an insertion tool300that may be used to rotate and insert the body28as described above. As shown, the tool300generally comprises an elongated shaft302having a distal end304, a proximal end306and a guidewire lumen308extending there through. In the illustrated embodiment, the proximal end304includes a flat edge310and engagement feature312for engaging a driving tool (e.g., a drill). In modified embodiments, the proximal end306can include a handle such that the tool300can be rotated manually.

The distal end304of the tool306is provided with a distal sleeve portion314, which has an outer shape that preferably corresponds substantially to the outer surface shape of the proximal anchor used in the procedure. Within the distal sleeve portion314is a lumen316, which communicates with the guidewire lumen308and is configured to receive the proximal end of the body28. The lumen316includes a rotational region318configured to engage the coupling70on the proximal end of the body28. Distal to the rotational region318is a recess320in which an elastic or resilient member322(e.g., a silicon sleeve) can be placed. As shown inFIG. 9E, when the proximal end of the body28is inserted into the lumen316, the rotational region318engages the coupling70and the elastic or reslilent member322grips the body28to hold the body28in place within the tool300.

As described above, the insertion tool300may be used to rotate the body28thereby driving the distal anchor34to the desired depth within the pedicle of the vertebrae. The surgeon can stop rotating the body28before the distal end of the tool300contacts the bone. In embodiments, in which a countersink is formed, the tool300can be rotated until the distal end sits within the countersink at which point further rotation of the tool300will not cause the distal anchor to advance further as further advancement of the body28causes it to be released from the tool300. In this manner, over advancement of the distal anchor32into the vertebrae can be prevented or limited.

It should be appreciated that not all of the steps described above are critical to procedure. Accordingly, some of the described steps may be omitted or performed in an order different from that disclosed. Further, additional steps may be contemplated by those skilled in the art in view of the disclosure herein, without departing from the scope of the present inventions.

With reference toFIGS. 1A and 1B, the proximal anchors50of the devices12extend above the pars such that they abut against the inferior facet of the superior adjacent vertebrae. In this manner, the proximal anchor50forms a wedge between the vertebra limiting compression and/or extension of the spine as the facet of the superior adjacent vertebrae abuts against the proximal anchor50. In this manner, extension is limited while other motion is not. For example, flexion, lateral movement and/or torsion between the superior and inferior vertebra is not limited or constrained at least to the degree of the extension. In this manner, the natural motion of the spine can be preserved, especially for those patients with mild or moderate disc conditions. Preferably, the devices are implantable through a minimally invasive procedure and, more preferably, through the use of small percutaneous openings as described above. In this manner, the high cost, lengthy in-patient hospital stays and the pain associated with open procedures can be avoided and/or reduced. In one embodiment, the devices12may be removed and/or proximal anchors50may be removed in a subsequent procedure if the patient's condition improves. Once implanted, it should be appreciated that, depending upon the clinical situation, the proximal anchor50may be positioned such that it contacts surfaces of the adjacent vertebrae all of the time, most of the time or only when movement between the adjacent vertebrae exceeds a limit.

In some instances, the practitioner may decide to use a more aggressive spinal fixation or fusion procedure after an initial period of using the stabilization device12. In one particular embodiment, the bone stabilization device12or a portion thereof may be used as part of the spinal fixation or fusion procedure. In one such application, the proximal anchor50can be removed from the body28. The body28can remain in the spine and used to support a portion of a spinal fixation device. For example, the body28may be used to support a fixation rod that is coupled to a device implanted in a superior or inferior vertebrae. Examples of such fusion systems can be found in U.S. patent application Ser. No. 10/623,193, filed Jul. 18, 2003 (U.S. Patent Publication No. 2004/0127906), the entirety of which is hereby incorporated by reference herein. Such a device is also described below.

As mentioned above, in certain embodiments described above, it may be advantageous to allow the proximal anchor to rotate with respect to the body28thereby preventing the proximal anchor50from causing the distal anchor34from backing out of the pedicle. In another embodiment, engagement features (as described below) may be added to the proximal anchor50to prevent rotation of the proximal anchor50.

FIG. 1Cillustrates a modified embodiment in which the first and second fixation devices12a,12bare coupled together by a member5that extends generally around or above the spinous process of the superior vertebra10b. In this manner, the member5can be used to limit flexion of the spinal column. The member may comprise any of a variety of suitable structural members. In one embodiment, the member comprises a suture or wire that is tied to the proximal end of the bodies28or the proximal anchor. In certain embodiments, various hooks or eyelets can be provided on the body or proximal anchor to facilitate coupling the member to the devices12a,12b.

The fixation devices12described herein may be made from conventional non-absorbable, biocompatible materials including stainless steel, titanium, alloys thereof, polymers, composites and the like and equivalents thereof. In one embodiment, the distal anchor comprises a metal helix, while the body and the proximal anchor comprise a bioabsorbable material. Alternatively, the distal anchor comprises a bioabsorbable material, and the body and proximal anchor comprise either a bioabsorbable material or a non-absorbable material.

In one embodiment, the proximal anchor50is formed, at least in part, from an elastic and/or resilient material. In this manner, the shock and forces that are generated as the proximal anchor abuts or wedges against the inferior articular process of the superior adjacent vertebrae can be reduced or dissipated. In one such embodiment, the proximal anchor50is formed in part by a polycarbonate urethane or a hydrogel. In such embodiments, the elastic material may be positioned on the outer surfaces of the proximal anchor or the portions of the outer surfaces that abut against the surfaces of the inferior articular process of the superior adjacent vertebrae. In one embodiment, such an anchor has a modulus of elasticity that is lower than that of metal (e.g., titanium). In another embodiment, the modulus of elasticity can be substantially close to that of bone. In yet another embodiment, the modulus of elasticity can be less than that of bone. In this manner, the stress risers generated during cyclic loading can be reduced to thereby reduce the tendency of the inferior articular process and the inferior vertebrae to crack during cyclic loading.

For example,FIGS. 10A and 10Billustrate an embodiment of device12′ with a proximal anchor50′ that comprises an outer housing or shell402. The shell402may be formed or a resilient material such as, for example, a biocompatible polymer. The proximal anchor50′ also comprises an inner member404that comprises a tubular housing406and a proximal flange408. The inner member402is preferably formed of a harder more rugged material as compared to the shell402, such as, for example, titanium or another metallic material. The shell402is fitted or formed over the tubular housing406. When deployed, the shell402is held in place between the flange408and the surface of the vertebrae in which the body402is placed. In modified embodiments, the shell402may be coupled to the inner member404in a variety of other manners, such as, adhesives, fasteners, interlocking surfaces structures and the like. In the illustrated embodiment, the inner member404includes a locking ring51positioned within a recess55as described above. Of course, in modified embodiments, other retention structures54and complementary retention structures58may be used between the body28and the proximal anchor50′ to permit distal axial travel of the proximal anchor50′ with respect to the body28, but resist proximal travel of the proximal anchor50′ with respect to the body28.

In the illustrated embodiment ofFIGS. 10A and 10B, the distal anchor34is provided with atraumatic or blunt tip7. In addition, the flange72of the distal anchor34includes a square or blunt edges. These features reduce the tendency of the distal anchor to cut into the bone during the windshield-wiper effect that may be caused by cyclic loading of the device as described above.

In another embodiment, the proximal anchor50is provided with a mechanically resilient structure. Thus, as with the previous embodiment, the shock and forces that are generated as the proximal anchor abuts or wedges against the inferior articular process of the superior adjacent vertebrae can be reduced or dissipated. In one such embodiment, the proximal anchor50is provided with mechanical springs, lever arms and/or the like. In such embodiments, as the mechanically resilient structure is compressed or extended the shock and forces are reduced or dissipated.

For example,FIGS. 11A-13Billustrate embodiments of a proximal anchor500, which comprises a tubular housing502, which includes a recess503for receiving a locking ring51as described above. The distal end504of the housing502forms a generally rounded, semi-spherical face that can be inserted into a corresponding counter sink200(seeFIG. 8) as describe above. Extending from the housings502are a plurality of lever arms or deflectable flanges510. Each arm510generally comprises a generally radially extending portion512and a generally circumferential extending portion514. In the illustrated embodiments, two (FIGS. 13A-B), three (FIGS. 12A-B) and five arms (FIGS. 11A-B) are shown. However, the anchor500can include different numbers of arms (e.g., one, four or greater than five arms). As the superior adjacent vertebrae10bmoves against the proximal anchor500the radially extending portion514deflects relative to the tubular housing502to absorb or disperse the forces generated by the contact.

As mentioned above, in the illustrated embodiment, the tubular member502includes a locking ring51positioned within a recess503as described above. Of course, in modified embodiments, other retention structures and complementary retention structures may be used between the body28and the proximal anchor500to permit distal axial travel of the proximal anchor500with respect to the body28, but resist proximal travel of the proximal anchor500with respect to the body28.

With reference toFIG. 14, in a modified embodiment, a distal end of a proximal anchor50′ may include one or more bone engagement features100, which in the illustrated embodiment comprises a one or more spikes102positioned on a contacting surface104of the proximal anchors. The spikes102provide additional gripping support especially when the proximal anchor50′ is positioned against, for example, uneven bone surfaces and/or soft tissue. In addition, the spikes102may limit rotation of the proximal anchor50′ with respect to the body28thereby preventing the proximal anchor50′ from backing off the body28. Other structures for the bone engagement feature100may also be used, such as, for example, ridges, serrations, etc.

FIGS. 15 and 16illustrate modified shapes of the proximal anchor which can be used alone or in combination with the elastic or resilient material described above. InFIG. 15, a proximal anchor50″ has a saddle shaped curved surface51″ that generally faces the inferior articular process of the superior adjacent vertebra. In this embodiment, the saddle shaped surface may limit compression and/or extension of the adjacent vertebra and limit side to side motion and/or torsion between the vertebrae.FIG. 16illustrates an embodiment in which a proximal anchor50′″ has a rectangular shape with a flat shaped surface51′″. In this embodiment, the flat shaped surface may limit compression and/or extension of the adjacent vertebra and limit side to side motion between the vertebrae. In the embodiments ofFIGS. 15 and 16, it may be advantageous to limit or eliminate any rotation of the proximal anchor50″ and50′″ with respect to the body28and/or the vertebra. As such, the proximal anchor50″ and50′″ can include the retention devices100described above with reference toFIG. 14.

As mentioned above, in certain embodiments, clinician will also have an array of proximal anchors50′,50″, and50′″, having, for example, different configurations and/or shapes. The clinician will choose the appropriate body28and then assess the position of the body28with respect to the superior vertebrae and chose a proximal anchor from the array, which best fits the patient anatomy to achieve the desired clinical result. In such an embodiment, the proximal anchor can be advantageously coupled to body28after the body28is partially or fully inserted into the vertebrae. The clinician may also be provided with an array of devices for forming differently sized or shaped countersinks corresponding to the different proximal anchors.

As described above, in one embodiment, the proximal anchor50(which can also refer to any or all of50′,50″, or50′″) is configured such that it can be removed after being coupled and advance over the body28. In this manner, if the clinician determines after advancing the proximal anchor that the proximal anchor50is not of the right or most appropriate configuration (e.g., size and/or shape), the clinician can remove the proximal anchor50and advance a different proximal anchor50over the body28. In such an embodiment, the proximal anchor50is preferably provided with one or more engagement structures (e.g., slots, hexes, recesses, protrusions, etc.) configured to engage a rotational and/or gripping device (e.g., slots, hexes, recesses, protrusions, etc.). Thus, in some embodiments, the proximal anchor50can be pulled and/or rotated such that the anchor50is removed from the body28.

FIGS. 17 and 18illustrate an embodiment of a tool600that can be used to insert a proximal anchor50that utilizes a locking ring51(as described above) onto a body28of the device12. In the illustrated embodiment, the tool600comprises an elongated body602having a distal end604and a proximal end606. The proximal end606is provided with a handle608for manipulating the tool600. The distal end604of the device is generally tubular and is coupled to or otherwise attached to a distal sleeve610. The distal sleeve defines a chamber611, which extends from the distal end604of the elongated body602to the distal end613of the sleeve610. A guidewire lumen612can extend through the tool600.

With particular reference toFIG. 18, a pin616is partially positioned within the chamber611. The pin616includes an enlarged proximal portion618, which is positioned in the chamber611. The pin616also includes a reduced diameter portion620, which extends outside the chamber611. A guidewire lumen622can also extend through the pin616such that the entire tool600can be inserted over a guidewire. A biasing member624is positioned between the distal end604of the tubular member602the proximal end618of the pin616. In this manner, the pin616is biased to the position shown inFIG. 18. Advantageously, the distal end620of the pin616has an outside diameter that is slightly larger than the inner diameter of the locking ring51(see e.g.,FIG. 10B). Accordingly, the distal end620of the pin616can be inserted into the proximal anchor through its proximal end. In one embodiment, the locking ring51grasps the distal end620of the pin616to couple the proximal anchor50to the pin616. In the loaded position, the proximal end of the proximal anchor50preferably contacts the distal end613of the distal sleeve610.

In use, the tool600is coupled to the proximal anchor as described above. After the body28is inserted into the vertebrae, the tool600can be used to position the proximal anchor50over the proximal end of the body28. The tool600is then advanced forward. As the tool600is advanced forward, the proximal anchor50is pushed onto the body28as the pin616retracts into the chamber611. In this manner, the pin616holds the locking ring51in an expanded position until it engages the body28. Once the pin616is fully retracted into the chamber611, the pin616is decoupled from the proximal anchor50and the proximal anchor50is fully coupled to the body28.

In another embodiment, a dimension of the proximal anchor is capable of being adjusted. For example,FIG. 19illustrates an embodiment of a proximal anchor700in which the proximal anchor700can be radially expanded such that the relationship between the anchor700and the adjacent vertebrae can be adjusted by the surgeon. In this embodiment, the anchor700comprises a wall702, which can be formed of an elastic material. The wall is coupled to an inner member704that comprises a tubular housing706and a proximal flange708, which can be arranged as described above with reference to FIG.10B. The wall702and the inner member704define a cavity710, which can be filled with an inflation material712, such as, for example, a gas, liquid, gel, and/or hardenable or semi-hardenable media (e.g., an polymer, epoxy or cement). One or more valves714(e.g., a duck bill valve) can be provided along the wall702. An inflation lumen716can extend through the valve such that the cavity710can be inflated with the inflation material712. After inflation, the lumen716is removed and the valve714seals the cavity710. One or more dividing walls718can be provided with the cavity710such that the anchor50can be inflated in discrete or semi-discrete sections.

In one embodiment of use, the body28and proximal anchor700are inserted into position as described herein. The cavity710is then inflated to expand the proximal anchor50and increases its diameter. In this manner, the surgeon can control the degree to which the proximal anchor50limits the motion of the spine. For example, in one embodiment, increasing the diameter of the proximal anchor50would increase the distance between the two vertebrae. In some embodiments, the inflation material712can also be removed such that the dimensions can be decreased during the same procedure in which the device12is inserted into the spine. In still other embodiments, the inflation material712can be added or removed in a subsequent, preferably, minimally invasive second procedure such that the degree which the proximal anchor50limits the motion of the spine can be adjusted in the second, subsequent procedure. In one embodiment, this is done by inserting a lumen through the valve and adding and/or removing the inflation media712.

FIGS. 20A-Dillustrates another embodiment of a proximal anchor750in which one or more dimensions of the anchor750can be adjusted. In this embodiment, the dimensions are adjusted using a mechanical mechanism. With reference to the illustrated embodiments, the anchor750can include a proximal member752and a distal member754, which can be moveably carried by the body28as described below. The proximal member752defines a proximal stop756and the distal member754defines a distal stop758. An expandable member760is positioned between the proximal and distal stops756,758. The expandable member760is configured to expand radially as the proximal and distal stops756,758are moved towards each other and the expandable member760is compressed therebetween. In one embodiment, the expandable member760comprises an elastic material that when compressed expands as shown inFIGS. 20A and 20B. In another embodiment, the expandable member760comprises a malleable material (e.g., a metal or metal alloy) that is provided with one or more slots. In such an embodiment, the slots allow the member760to expand as it is compressed between the proximal and distal stops756,758.

With reference toFIG. 20D, the proximal member752can be provided with a recess55and ring51as described above with reference toFIGS. 5 and 6. In this manner, the proximal member752can be advanced in the distal direction while proximal movement of the member752is resisted. Of course, other complementary retention structures can be used between the member752and the body28as described to permit distal movement while resisting proximal movement. The distal movement of the distal member754can be prevented by a distal stop762provided on the body28. As shown inFIG. 20D, the distal member754can be provided with a smooth bore764such that it can be advanced over the body28towards the distal stop762.

FIG. 21illustrates an embodiment of a proximal anchor770which is similar to the previous embodiment. In this embodiment, the proximal member752includes threads772such that the proximal member752can be distally advanced or proximal retracted by rotation.FIG. 22illustrates another embodiment of a proximal anchor780. In this embodiment, the proximal member752is configured as described with referenceFIG. 20D. However, the distal member754is provided with threads782such that the position of the distal member754on the body28can be adjusted.

The above described devices and techniques limit motion of the spine by providing an abutment or wedge surface on one vertebrae or body structure. The abutment surface contacts, abuts, and/or wedges against a portion of a second, adjacent vertebrae or body structure so as limit to at least one degree of motion/freedom between the two vertebra or body structure while permitting at least one other degree of motion. While the above described devices and techniques are generally preferred, certain features and aspects can be extended to modified embodiments for limiting motion between vertebrae. These modified embodiments will now be described.

In one embodiment, the proximal anchor50of the fixation device may be, coupled to, attached or integrally formed with the body28. In this manner, movement between the proximal anchor50and the body28is not permitted. Instead, the clinician may chose a fixation device of the proper length and advance the device into the vertebrae until the proximal anchor lies flush with the vertebrae or is otherwise positioned accordingly with respect to the vertebrae. In one particular, embodiment, the proximal anchor that is coupled to, attached or integrally formed with the body28is configured to have an outer surface which can rotate, preferably freely, with respect to the body28. This arrangement advantageously reduces the tendency of the device to rotate and/or move within the inferior vertebrae as the proximal anchor50contacts the superior vertebrae.

In another embodiment, the abutment surface may be attached to the vertebrae through the use of an adhesive, fasteners, staples, screws and the like. In still another embodiment, the abutment surface may formed on a distal end of a stabilization device that is inserted through the front side of the vertebrae.

In the embodiments described above, the device12is generally inserted into the spine from a posterior position such that a distal end of the device12is inserted into the first, inferior vertebrae and a proximal end of the device12contacts or wedges against the second, superior vertebrae. However, it is anticipated that certain features and aspects of the embodiments described herein can be applied to a procedure in which the device is inserted from a lateral or anterior site. In such an embodiment, the distal end or side portion of the device may contact or wedge against the second superior vertebrae. Such embodiments provide a contact or wedge surface which is supported by one body structure to limit of the motion of an adjacent body structure.

In the embodiments, described above, it is generally advantageous that the proximal anchor be radiopaque or otherwise configured such that in can be seen with visual aids used during surgery. In this manner, the surgeon can more accurately position the proximal anchor with respect to the superior and inferior vertebra.

Preferably, the clinician will have access to an array of fixation devices12, having, for example, different diameters, axial lengths and, if applicable, angular relationships. These may be packaged one or more per package in sterile or non-sterile envelopes or peelable pouches, or in dispensing cartridges which may each hold a plurality of devices12. The clinician will assess the dimensions and load requirements, and select a fixation device from the array, which meets the desired specifications.

The fixation devices may also be made from conventional non-absorbable, biocompatible materials including stainless steel, titanium, alloys thereof, polymers, composites and the like and equivalents thereof. In one embodiment, the distal anchor comprises a metal helix, while the body and the proximal anchor comprise a bioabsorbable material. In another embodiment, the body is made of PEEK™ polymer or similar plastic material. Alternatively, the distal anchor comprises a bioabsorbable material, and the body and proximal anchor comprise either a bioabsorbable material or a non-absorbable material. As a further alternative, each of the distal anchor and the body comprise a non-absorbable material, connected by an absorbable link. This may be accomplished by providing a concentric fit between the distal anchor and the body, with a transverse absorbable pin extending therethrough. This embodiment will enable removal of the body following dissipation of the pin, while leaving the distal anchor within the bone.

The components of embodiments of the present inventions may be sterilized by any of the well known sterilization techniques, depending on the type of material. Suitable sterilization techniques include, but not limited to heat sterilization, radiation sterilization, such as cobalt 60 irradiation or electron beams, ethylene oxide sterilization, and the like.

The specific dimensions of any of the embodiments of the bone fixation devices of the present inventions can be readily varied depending upon the intended application, as will be apparent to those of skill in the art in view of the disclosure herein. Moreover, although the present inventions have been described in terms of certain preferred embodiments, other embodiments of the inventions including variations in dimensions, configuration and materials will be apparent to those of skill in the art in view of the disclosure herein. In addition, all features discussed in connection with any one embodiment herein can be readily adapted for use in other embodiments herein. The use of different terms or reference numerals for similar features in different embodiments does not imply differences other than those which may be expressly set forth. Accordingly, the present inventions are intended to be described solely by reference to the appended claims, and not limited to the embodiments disclosed herein.

As mentioned above, the dynamic stabilization device12can provide adjacent level support as an adjunct to fusion therapy. In one embodiment, the fusion therapy involves the fixation device800, which will be described in detail below. The fixation device800can be positioned below (or above in other embodiments) the stabilization device12and can be used to promote spinal fusion below the spinal level at which motion is limited by the dynamic stabilization device.

FIGS. 23A-Dillustrate an embodiment of the bone fixation device800having a body802and a proximal anchor804. In this embodiment, the body802comprises a first portion806and a second portion808that are coupled together at a junction810(FIG. 23D). In the illustrated embodiment, the first portion806carries a distal anchor812while the second portion808forms a proximal end814of the body802. The first and second portions806,808are preferably detachably coupled to each other at the junction810. In the illustrated embodiment, the first and second portions806,808are detachably coupled to each other via interlocking threads. Specifically, as best seen inFIG. 23D, the body802includes an inner surface816, which defines a central lumen818that preferably extends from the proximal end814to a distal end820throughout the body802. At the proximal end of the first portion806, the inner surface816includes a first threaded portion822. The first threaded portion822is configured to mate with a second threaded portion824, which is located on the outer surface826of the second portion808. The interlocking annular threads of the first and second threaded portions822,824allow the first and second portions806,808to be detachably coupled to each other. In one modified embodiment, the orientation of the first and second threaded portions822,824can be reversed. That is, the first threaded portion822can be located on the outer surface of the first portion806and the second threaded portion824can be located on the inner surface816at the distal end of the second portion808. Any of a variety of other releasable complementary engagement structures may also be used, to allow removal of second portion808following implantation, as is discussed below.

In a modified arrangement, the second portion808can comprise any of a variety of tensioning elements for permitting proximal tension to be placed on the distal anchor812while the proximal anchor804is advanced distally. For example, any of a variety of tubes or wires can be removably attached to the first portion806and extend proximally to the proximal handpiece. In one such arrangement, the first portion806can include a releasable connector in the form of a latching element, such as an eye or hook. The second portion808can include a complementary releasable connector (e.g., a complementary hook or eye) for engaging the first portion806. In this manner, the second portion808can be detachably coupled to the first portion806such that proximal traction can be applied to the first portion806through the second portion808as will be explained below. Alternatively, the second portion808may be provided with an eye or hook, or transverse bar, around which or through which a suture or wire may be advanced, both ends of which are retained at the proximal end of the device. Following proximal tension on the tensioning element during the compression step, one end of the suture or wire is released, and the other end may be pulled free of the device. Alternate releasable proximal tensioning structures may be devised by those of skill in the art in view of the disclosure herein.

With particular reference toFIGS. 23A-23D, the proximal end814of the body802may be provided with a rotational coupling828, for allowing the second portion808of the body802to be rotationally coupled to a rotation device. The proximal end814of the body808may be desirably rotated to accomplish one or two discrete functions. In one application of embodiments of the present inventions, the proximal end814is rotated to remove the second portion808of the body802following tensioning of the device to anchor an attachment to the bone. Rotation of the rotational coupling828may also be utilized to rotationally drive the distal anchor into the bone. Any of a variety of rotation devices may be utilized, such as electric drills or hand tools, which allow the clinician to manually rotate the proximal end814of the body802. Thus, the rotational coupling828may have any of a variety of cross sectional configurations, such as one or more flats or splines.

With particular reference toFIG. 23A, the fixation device may include an antirotation lock between the first portion806of the body802and the proximal anchor804. In the illustrated embodiment, the first portion806includes a pair of flat sides830, which interact with corresponding flat structures832in the proximal anchor804. One or three or more axially extending flats may also be used. As such, rotation of the proximal anchor804is transmitted to the first portion806and the distal anchor812of the body802. Of course, those of skill in the art will recognize various other types of splines or other interfit structures can be used to prevent relative rotation of the proximal anchor and the first portion806of the body802. For example, in one embodiment, the first portion806may include three flat sides, which interact with corresponding flat structures on the proximal anchor804.

To rotate the proximal anchor804, a flange834is preferably provided with a gripping structure to permit an insertion tool to rotate the flange834. Any of a variety of gripping structures may be provided, such as one or more slots, flats, bores or the like. In one embodiment, the flange834is provided with a polygonal, and, in particular, a pentagonal or hexagonal recess836. SeeFIG. 24A.

InFIGS. 23B and 23C, the proximal anchor804is shown in combination with a washer840that can be configured to interact with a head of the proximal anchor. The washer840can include a base and a side wall. The base and side wall can define a curved, semi-spherical or radiused surface that interacts with the corresponding curved, semi-spherical or radiused surface of the head. The surface surrounds an aperture formed in the base. This arrangement can allow the housing and/or body to extend through and pivot with respect to the washer. A detailed description of the washer840can be found in U.S. Pat. No. 6,951,561 issued on Oct. 4, 2005 entitled “PROXIMAL ANCHORS FOR BONE FIXATION SYSTEM,” the entirety of the contents of which are incorporated herein by reference.

FIGS. 24A-Fillustrate in more detail the proximal anchor804ofFIGS. 23A-C. This embodiment can include a tubular housing842. A detailed description of the tubular housing842can be found in U.S. Pat. No. 6,951,561 referred to above. In the illustrated embodiment, the tubular housing842can be attached to, coupled to, or integrally formed (partially or wholly) with a secondary tubular housing844, which includes one or more anti-rotational features846(e.g., flat sides) for engaging corresponding anti-rotational features formed on the pin, which can be similar to the first portion806(e.g., see description above). The flange or collar834is attached, coupled or integrally formed with the proximal end of the secondary tubular housing. Teeth or flanges848on bridges850may also be configured such that the proximal anchor may be distally advanced and/or removed with rotation. The illustrated embodiment also advantageously includes visual indicia852(e.g., marks, grooves, ridges etc.) on the tubular housing842for indicating the depth of the proximal anchor804within the bone.

In one embodiment of use, the fixation device800ofFIGS. 23A-Ccan have an axial length and outside diameter suitable for a hole drilled in the bone. The distal end820of the fixation device800is advanced distally into the hole until the distal anchor812reaches the distal end of the hole. The proximal anchor804may be carried by the fixation device800prior to advancing the body802into the hole, or may be attached following placement of the body802within the hole. Once the body802and proximal anchor804are in place, the clinician may use any of a variety of driving devices, such as electric drills or hand tools to rotate the proximal anchor804and thus cancellous bone anchor812into the head of the femur. In modified embodiments, the fixation device is configured to be self-drilling or self tapping such that a hole does not have to be formed before insertion into the bone.

Once the anchor812is in the desired location, proximal traction is applied to the proximal end814of body802, such as by conventional hemostats, pliers or a calibrated loading device, while distal force is applied to the proximal anchor804. In this manner, the proximal anchor804is advanced distally until the anchor804fits snugly against the outer surface of the bone. Appropriate tensioning of the fixation device800is accomplished by tactile feedback or through the use of a calibration device for applying a predetermined load on the implantation device. One advantage of the structure of certain embodiments is the ability to adjust compression independently of the setting of the distal anchor812.

Following appropriate tensioning of the proximal anchor804, the second portion808of the body802is preferably detached from the first portion806and removed. In the illustrated embodiment, this involves rotating the second portion808with respect to the first portion via the coupling828. Following removal of the second portion808of each body802, the access site may be closed and dressed in accordance with conventional wound closure techniques.

An advantage of certain embodiments of the fixation devices disclosed above is that the proximal anchor provides the device with a working range such that one device may accommodate varying distances between the distal anchor and the proximal anchor. In certain applications, this allows the technician to focus on the proper positioning of the distal anchor with the knowledge that the proximal anchor lies within the working range of the device. With the distal anchor positioned at the desired location, the proximal anchor may then be advanced along the body to compress the fracture and/or provide stability between bones. In a similar manner, the working range provides the technician with flexibility to adjust the depth of the proximal anchor. For example, in some circumstances, the bone may include voids, cysts, osteoporotic bone that impairs the stability of the distal anchor in the bone. Accordingly, in some circumstances, the technician may advance the distal anchor and then desire to retract the distal anchor such that it is better positioned in the bone. In another circumstance, the technician may inadvertently advance the distal tip through the bone into a joint space or other undesired area (e.g., spinal canal). In such circumstances, the working range of the device allows the technician to reverse and retract the anchor and recompress. Such adjustments are facilitated by the working range of the proximal anchor on the body.

Preferably, the clinician will have access to an array of fixation devices (e.g., fixation device800) having, for example, different diameters, axial lengths and angular relationships. These may be packaged one per package in sterile envelopes or peelable pouches, or in dispensing cartridges which may each hold a plurality of devices800. Upon encountering a use for which the use of a fixation device is deemed appropriate, the clinician will assess the dimensions and load requirements, and select a fixation device from the array which meets the desired specifications.

The fixation devices described above may be used in any of a wide variety of anatomical settings beside the spine as has been discussed. For example, lateral and medial malleolar fractures can be readily fixed using the device according to certain embodiments. For example, the fixation devices800can be used with the distal fibula and tibia. The fibula terminates distally in the lateral malleolus, and the tibia terminates distally in the medial malleolus. A fixation device800can extend through the lateral malleolus across the lateral malleolar fracture and into the fibula. The fixation device800can include a distal anchor for fixation within the fibula, an elongate body and a proximal anchor as has been discussed.

As mentioned above, the devices describe herein may also be used for spinal fixation. In embodiments optimized for spinal fixation in an adult human population, the body800can generally be within the range of from about 20-90 mm in length and within the range of from about 3.0-8.5 mm in maximum diameter. The length of the helical anchor, discussed above, may be about 8-80 millimeters. Of course, it is understood that these dimensions are illustrative and that they may be varied as required for a particular patient or procedure.

In spinal fixation applications, the fixation device800may be used as a trans-facet screw. That is, the fixation device extends through a facet of a first vertebra and into the facet of a second, typically inferior, vertebra, which vertebrae are referred to above as intermediate and inferior vertebral bodies. This procedure is typically (but not necessarily) performed with bilateral symmetry. Thus, even in the absence of a stabilizing bar tying pedicle screws to adjacent vertebrae or to the sacrum, and in the absence of translaminar screws that can extend through the spinous process, the fixation devices can be used to stabilize two vertebrae, such as L3 and L4 to each other pending the healing of a fusion. In one embodiment, the body802of fixation device800can have a length of approximately 10 mm-30 mm and the diameter of the body802can be approximately 3 mm to 5.5 mm.

The fixation device800may also be used as a trans-laminar facet screw. In this embodiment of use, the fixation device extends through the spinous process and facet of a first vertebra and into the facet of a second, typically inferior, vertebra. As with the previous embodiment, this procedure is typically (but not necessarily) performed with bilateral symmetry. In one embodiment, the body802of fixation device800can have a length of approximately 50 mm-90 mm and the diameter of the body is approximately 4 mm to 5.5 mm.

The fixation device may also be used is used as a facet-pedical screw (e.g., as used in the Boucher technique). In such an embodiment, the fixation device extends through the facet of a first vertebra and into the pedicle a second, typically inferior, vertebra. As with the previous embodiment, this procedure is typically (but not necessarily) performed with bilateral symmetry. In such an embodiment, the fixation device800and the body802can be approximately 20-40 millimeters in length and 3.0-5.5 millimeters in diameter.

FIGS. 25A-Dillustrate another embodiment of a proximal anchor860. In this embodiment, the proximal anchor860includes a recess862configured to receive a split ring864. As will be explained in detail below, the proximal anchor860can include an anti-rotation feature to limit or prevent rotation of the ring864within the proximal anchor860. In light of the disclosure herein, those of skill in the art will recognize various different configurations for limiting the rotation of the ring864. However, a particularly advantageous arrangement will be described below with reference to the illustrated embodiment.

In the illustrated embodiment, the proximal anchor860has a tubular housing868that can engage with a body802or a first portion806of the body802, as described above. With reference toFIGS. 25B and 25D, the tubular housing868comprises one or more anti-rotational features870in the form of a plurality of flat sides that are configured to mate corresponding anti-rotational features872or flat sides of the body802of the fixation device800. As shown inFIG. 25D, in the illustrated embodiment, the body802has three flat sides872. Disposed between the flat sides872are the portions of the body802which include the complementary locking structures such as threads or ratchet like structures as described above. The complementary locking structures interact with the ring864as described above to resist proximal movement of the anchor860under normal use conditions while permitting distal movement of the anchor860over the body802.

As mentioned above, the ring864is positioned within the recess862. In the illustrated embodiment, the recess862and ring864are positioned near to and proximal of the anti-rotational features870. However, the ring864can be located at any suitable position along the tubular housing868such that the ring864can interact with the retention features of the body802.

During operation, the ring864may rotate to a position such that the gap874between the ends876,878of the ring864lies above the complementary retention structures on the body802. When the ring865is in this position, there is a reduced contact area between the split ring864the complementary retention structures thereby reducing the locking strength between the proximal anchor860and the body802. In the illustrated embodiment, for example, the locking strength may be reduced by about ⅓ when the gap874over the complementary retention structures between flat sides872. As such, it is advantageous to position the gap874on the flat sides872of the body802that do not include complementary retention structures.

To achieve this goal, the illustrated embodiment includes a pair of tabs880,882that extend radially inward from the interior of the proximal anchor800. The tabs880,882are configured to limit or prevent rotational movement of the ring864relative to the housing804of the anchor800. In this manner, the gap874of the ring864may be positioned over the flattened sides872of the body802.

In the illustrated embodiment, the tabs880,882have a generally rectangular shape and have a generally uniform thickness. However, it is contemplated that the tabs880,882can be square, curved, or any other suitable shape for engaging with the ring864as described herein.

In the illustrated embodiment, the tabs880,882are formed by making an H-shaped cut884in the tubular housing860and bending the tabs880,882inwardly as shown inFIG. 25D. As shown inFIG. 25D, the tabs880,882(illustrated in phantom) are interposed between the edges876,878of the ring864. The edges876,878of the ring864can contact the tabs to limit the rotational movement of the ring864. Those skilled in the art will recognize that there are many suitable manners for forming the tabs880,882. In addition, in other embodiments, the tabs880,882may be replaced by a one or more elements or protrusions attached to or formed on the interior of the proximal anchor860.

For the embodiments discussed herein, the pin, together with the distal anchor, and other components, can be manufactured in accordance with any of a variety of techniques which are well known in the art, using any of a variety of medical-grade construction materials. For example, the pin body and other components can be injection-molded from a variety of medical-grade polymers including high or other density polyethylene, nylon and polypropylene. The distal anchor can be separately formed from the pin body and secured thereto in a post-molding operation, using any of a variety of securing techniques such as solvent bonding, thermal bonding, adhesives, interference fits, pivotable pin and aperture relationships, and others known in the art. Preferably, however, the distal anchor is integrally molded with the pin body, if the desired material has appropriate physical properties.

Retention structures can also be integrally molded with the pin body. Alternatively, retention structures can be machined or pressed into the pin body in a post-molding operation, or secured using other techniques depending upon the particular design. Further, as recited in U.S. Pat. No. 6,951,561 referred to above, a variety of polymers, such as bioabsorbable polymers, can be used to fabricate components of the embodiments disclosed herein.

As shown inFIG. 26, the fixation devices800a,800bmay be used to provide stability without additional hardware. In this example, the fixation devices800a,800bis used similarly to a trans-facet screw. That is, the fixation devices800a,800bextend through a facet of a first vertebra and into the facet of a second, typically inferior, vertebrae. As in the illustrated embodiment, this procedure is typically (but not necessarily) performed with bilateral symmetry. Thus, even in the absence of a stabilizing bar tying pedicle screws to adjacent vertebrae or to the sacrum, and in the absence of translaminar screws that can extend through the spinous process, the fixation devices800a,800bcan be used to stabilize two vertebrae, such as L3 and L4 to each other pending the healing of a fusion. In one embodiment, the body of fixation devices800a,800bcan have a length of approximately 10 mm-30 mm and the diameter of the body is approximately 3 mm to 5.5 mm.

In the embodiment ofFIG. 26, the flange of the proximal anchor is typically supported directly against the outer surface of a vertebra. Because the outer surface is typically non-planar and/or the insertion angle of the fixation device is not perpendicular to the outer surface, an angularly fixed flange may contact only a portion of the outer surface. That is, the contact surface of the flange may not sit flush on the outer surface of the vertebra. This may cause the vertebra to crack due to high stress concentrations. This can result in poor fusion rates.

As such, in these applications, angularly adjustable flanges can be particularly advantageous because the flange can rotate with respect to the body and thereby the bone contacting surface may be positioned more closely to the outer surface of the vertebra. This can result in more bone contacting surface being utilized and the stress supported by the fixation device is spread out over a larger area of the vertebra. These angularly adjustable flanges may also be used with the spinal cages and rods. In such embodiments, the angle of the body fixation device may be not be perpendicular to the contact surface of the fixation rod or plate. In such situations, the angularly adjustable flange allows the flange to rotate and sit flush against the fixation rod and plate.

In the above embodiments, it may be advantageous to drill a counter bore into the first vertebra for receiving a portion of the proximal anchor. In such embodiments, the counter bore will typically have a diameter that is slightly larger than the outer diameter of the proximal anchor so that the proximal anchor may sit at least partially below the outer surface of the vertebra.

In certain regions of the spine, the dimension transverse to a facet joint and through the adjacent facets is relatively small. In these circumstances, the fixation may desirably include a through bore, opening through the distal cortex of the distal facet. The fixation device described above may be utilized either in a blind hole application, which the distal anchor is buried within the bone, or a through bore application is which the distal helix extends into and potentially through the distal cortex. However, a through bore fixation device may also be used.

The fixation devices800are preferably installed using a percutaneous or minimally invasive approach in which the procedure is done through one or more percutaneous small openings in a manner similar to that described above with respect to the stabilization devices12. As mentioned above, the fixation device800can be positioned below (or above in other embodiments) the stabilization device12, which can be used to promote spinal fusion below the spinal level at which motion is limited by the dynamic stabilization device12. In such an embodiment, the dynamic stabilization device can provide adjacent level support as an adjunct to fusion therapy. An advantage of this system and technique is that both the stabilization device12and the fixation device800can be inserted into the spine utilizing a minimally invasive approach in which the procedure is done through one or more percutaneous small openings. In other embodiments, the fixation devices800can be replaced and/or supplemented with other fixation devices of the type known in the art such as, for example, pedicle screws and rod constructs, cages, etc.

FIGS. 27-28are rear and side elevational views of the cervical spine in accordance with another embodiment. The methods and devices disclosed herein can be used in various areas along the spinal column and can be combined with other methods and devices. For example,FIGS. 27-28illustrate that at least one of the dynamic stabilization device12and the fixation device800can be used in the cervical vertebrae area of the spine. As shown however, the dynamic stabilization device12is illustrated. In embodiments wherein the dynamic stabilization device12is used in the cervical spine, for example, it is contemplated that the configuration of the dynamic stabilization device12has a length from about 5 mm to about 25 mm when configured for the cervical spine. The dynamic stabilization device12can therefore be specifically configured for uses in various parts of the spine.

In addition, the components disclosed herein may be provided with any of a variety of structural modifications to accomplish various objectives, such as osteoincorporation, or more rapid or uniform absorption into the body. For example, osteoincorporation may be enhanced by providing a micropitted or otherwise textured surface on the components. Alternatively, capillary pathways may be provided throughout the pin and collar, such as by manufacturing the components from an open cell foam material, which produces tortuous pathways through the device. This construction increases the surface area of the device which is exposed to body fluids, thereby generally increasing the absorption rate. Capillary pathways may alternatively be provided by laser drilling or other technique, which will be understood by those of skill in the art in view of the disclosure herein. In general, the extent to which the component can be permeated by capillary pathways or open cell foam passageways may be determined by balancing the desired structural integrity of the device with the desired reabsorption time, taking into account the particular strength and absorption characteristics of the desired polymer.

The component of the embodiments disclosed herein may be sterilized by any of the well known sterilization techniques, depending on the type of material. Suitable sterilization techniques include heat sterilization, radiation sterilization, such as cobalt 60 irradiation or electron beams, ethylene oxide sterilization, and the like.

The specific dimensions of any of the components and bone fixation devices can be readily varied depending upon the intended application, as will be apparent to those of skill in the art in view of the disclosure herein. Moreover, the components and devices have been described in terms of certain preferred embodiments, other embodiments including variations in the number of parts, dimensions, configuration and materials will be apparent to those of skill in the art in view of the disclosure herein. In addition, all features discussed in connection with any one embodiment herein can be readily adapted for use in other embodiments herein to form various combinations and sub-combinations. The use of different terms or reference numerals for similar features in different embodiments does not imply differences other than those which may be expressly set forth. Accordingly, the present inventions are intended to be described solely by reference to the appended claims, and not limited to the preferred embodiments disclosed herein.