WO2010065545A1 - Intervertebral disc space sizing tools and methods - Google Patents

Abstract

A method and apparatus for making a size measurement within an intervertebral space by placing an expandable and contractible device into the intervertebral space, expanding the device, measuring a size characteristic of the space, contracting the device and then removing it. The measurement may be accomplished by an external x-ray or other imaging device imaging the expanded device in situ or by mechanically operated devices. An apparatus and method is provided for the measuring of the intervertebral space at a controlled distraction force. The apparatus includes an expandable device for providing a measurement within the intervertebral space and facilitating the measurement of the angulations of the lordotic curve of the intervertebral space.

Description

INTERVERTEBRAL DISC SPACE SIZING TOOLS AND METHODS

[0001] This application is a continuation of U.S. Patent Application No.

12/368,964 filed February 10, 2009, and claims the benefit of U.S. Provisional Patent Application No. 61/118,904, filed December 1, 2008, and U.S. Patent Application No. 12/368,964, filed February 10, 2009, both of which are incorporated herein by reference in their entirety.

Field of The Invention

[0002] The present invention relates to sizing tools used to measure the space between vertebrae for placement of artificial implants therebetween, and in particular, to sizing tools that can expand within an intervertebral space and methods for their use.

Background Of The Invention

[0003] The most common orthopedic condition for which professional medical treatment is sought is lower back pain. Although many factors may be responsible for causing lower back pain, a principal factor is damage or degeneration of an intervertebral spinal disc resulting in impingement on the nerve system, specifically the spinal cord, located within the spine. Such impingement may result in, for instance, loss of mobility, urinary and fecal incontinence, and sciatica or pain experienced in the extremities.

[0004] Damage to or degeneration of a spinal disc can result from a number of factors such as abuse or age. The disc itself is composed primarily of an annulus and a nucleus contained therein. The annulus is a fibrous annular piece that connects to the adjacent vertebrae and contains the nucleus, which is in turn a gel-like viscous material capable of shock absorption and flowable to permit poly-axial rotation and resilient compression of the vertebrae and spine. Most frequently, disc degeneration results from damage occurring to the annulus such that the flowable nucleus material may leak or seep out of the annulus. Disc degeneration also can occur in other ways, such as by being deprived of nutrient flow leading to a dried disc susceptible to damage. Because the nuclear material is flowable, extensive damage to the annulus is not necessary for leakage to occur.

[0005] Currently, approaches to treatment of spinal problems directly affecting the spinal cord are numerous. For instance, immobilization and high doses of corticosteroids may be employed. The dominant surgical procedures for treatment of these problems are spinal fusion and discectomy. Fusion is a method where adjacent vertebrae are immobilized so that they permanently secure to each other by having bone growth between and to the vertebrae, while discectomy involves removal of a portion or an entirety of a spinal disc.

[0006] However, the current practice of each of these procedures typically has certain limitations. With fusion, making a portion of the spine generally rigid produces a reduction in mobility, and drastically alters normal load distribution along the spinal column. Due to these factors, the non-fused portions of the spine experience stress and strain that are significantly increased over normal physiological motions. The increased stress and strain on the non-fused portions may lead to accelerated disc degeneration of the non-fused portions, particularly the adjacent levels of the spine.

[0007] Discectomy is effective for relieving sciatic pain by removing the damaged or herniated disc tissue compressing the spinal nerves. However, current discectomy often may lead to a reduction of the disc space between adjacent vertebrae, as well as instability in the affected portion of the spine. Such long-term effects with current discectomy often result in further surgery several years after the initial discectomy surgery.

[0008] In an alternative spinal surgery, a disc arthroplasty restores or reconstructs the disc using a prosthesis to replace a portion or entirety of the damaged disc. The primary objective of disc arthroplasty is to restore or maintain the normal disc anatomy and functions, while addressing and treating the causes of the pain. However, prosthetic disc implants have problems due to the complexity of the natural disc structure and biomechanical properties of a natural spinal disc. As used herein, the term natural refers to normal tissue including portions of the spine and the disc.

[0009] Two types of prostheses for disc arthroplasty are currently believed to merit further development by medical science and research. One type is a total disc prosthesis, or TDP, where the entire spinal disc is replaced after radical discectomy. A typical TDP includes structures that attempt to together mimic the properties of a natural disc.

[0010] The other type is a disc nucleus prosthesis, or DNP, that is used to replace only the nucleus of a spinal disc after a nucleotomy while retaining the annulus of the disc and, possibly, the endplates intact. As discussed above, failure of the natural disc does not require extensive damage to the annulus. An undamaged annulus, however, would often be capable of retaining a non-flowing prosthetic nucleus. Implantation of a DNP involves making a small incision in the annulus, clearing of the natural nucleus from the annulus through the procedure known as nucleotomy, and inserting the DNP through, and then within, the annulus. Accordingly, DNPs are typically smaller and require less extensive surgery than TDPs while still mimicking some of the biomechanical properties of a natural intervertebral disc.

[0011] Implantation of most DNPs with pre-formed dimensions requires a 5-6 mm, or larger, incision in the annulus for implantation and uses minimal disc tissue resection. Moreover, recovery and post-surgical pain are minimal due to the minimal invasiveness of the procedure, and interbody fusion remains a viable revision surgery. In addition, the incision in the annulus is kept as small as possible to minimize the potential for the implant to back out through the incision. The annulus itself is used to at least aid in maintaining the implant within the nuclear space. This permits the DNP to sit in the intervertebral space without anchors that violate the endplates of the vertebrae. As the annulus does not heal well and suturing the annulus is difficult due to its tissue properties, once the incision is too large, the ability of the annulus to retain the implant is diminished if not eliminated. [0012] The risk of enlarging the incision on the annulus in the DNP procedure is increased because sizing tools are typically also placed through the incision. The size of the implant should match the size of the natural disc and/ or nuclear cavity (i.e. the height of the space between adjacent vertebrae and the width and length dimensions or the footprint of the space within the annulus). If the implant is too large or too small, the implant may cause damage to the spine or pain to the patient. In order to determine the size of the nuclear cavity, conventional sizing tools such as a set of trial spacers disclosed by U.S. Patent No. 6,478,801 are used. Each spacer has a different size and is sequentially inserted in the nuclear space in trial and error fashion until the trial spacer fits the nuclear space which indicates the correct size of implant that should be used. Moving trial spacers in and out of the nuclear cavity numerous times, however, creates further risk of enlarging the incision or damaging the annulus, vertebral endplates and/ or even other tissue around the spine whether or not the annulus is present. Also with this procedure, the surgeon wastes time by choosing and obtaining a different trial spacer multiple times and then inserting each trial spacer into the nuclear space. Thus, a need exists for a sizing tool that need not be inserted into a nuclear space multiple times in order to obtain the dimensions of the nuclear space.

[0013] Other improvements specifically for the DNP procedure would be desirable. As mentioned above, a DNP requires less extensive surgery than for a TDP since it replaces only part of the disc. Implantation of most known DNPs with preformed dimensions generally requires a 5-6 mm, or larger, incision in the annulus for implantation. The incision, however, should be kept as small as possible to hold the DNP within the annulus without using anchors on the DNP that extend into the endplates of the vertebrae for securing the DNP. The minimal invasiveness of the procedure results in minimal recovery and post-surgical pain, and interbody fusion remains a viable revision surgery. Thus, maintaining a small incision and keeping damage to the annulus to a minimum is a high priority. Therefore, it would be desirable to provide a DNP and trial spacer that does not require an enlarged incision and does not significantly damage the annulus or other tissue during insertion and placement of the DNP.

[0014] Other problems relate to the geometry of the intervertebral nuclear space. A natural nuclear space within the annulus has a length in the lateral direction (orthogonal to the anterior-posterior direction) that is longer than the width of the space in the anterior-posterior direction. Since it would be desirable to have the sizing tool as well as the implant match the shape of the nuclear space, some conventional sizing tools or implants are generally rectangular, oval or obround with a length greater than its width in order to more closely fit the nuclear space. In this case, the short or narrow side of the sizing tool or implant is presented as the leading edge for insertion (i.e. it faces the incision) in order to maintain a reduced incision on the annulus. This frequently requires an anterior-lateral approach to the surgical site which requires a general surgeon's service, typically in conjunction with an orthopedic surgeon or neurosurgeon, or both, which then raises the costs of the procedure.

[0015] A posterior or posterior-lateral approach, while less costly, does not typically permit the access required for inserting sizing tools, removal of the natural disc and implantation of the prosthetic device because the geometry and structure of the spine blocks or fills the path to the nuclear space that is needed for the approach. This is especially true for a sizing tool as described where the sizing tool's long side would need to be presented first for insertion and extraction from a posterior approach. Therefore, a need exists for a sizing tool that is not limited to particular surgical approaches.

[0016] Some implants utilize an inflatable bladder or balloon-like structure as disclosed by U.S. Patent Publication No. 2004/0133280. These inflated structures, however, are not configured to be deflated in any controlled manner. Uncontrolled collapse of an inflated body within an annulus may result in a deflated structure that is too large or irregularly shaped to be retracted through the incision without enlarging the incision or damaging the annulus or other tissue.

[0017] Another problem occurs when the top or bottom end of a sizing tool does not match the geometry of the endplates on the opposing vertebrae which may be slanted to align with the lordotic or kyphotic curve of the spine. When a mismatch occurs, such as when the top plate of a sizing tool remains horizontal while the endplate of a vertebrae it faces is slanted, measurement readings of the height of the nuclear space may be inaccurate.

Summary of the Invention

[0018] In accordance with the embodiments illustrated herein, an intervertebral space sizing method and apparatus for measuring within the intervertebral space comprises placing an expandable and contractible device into the intervertebral space and measuring a characteristic of the space using an expandable device in an expanded size and then contracting the device to a contracted size and removing it from the intervertebral space. Preferably, the expandable, contractible device is shifted to an expanded size or position, e.g., in the superior-inferior direction relative to the intervertebral space, so that the device abuts adjacent vertebrae in order to determine the distance from one vertebra to the other. In accordance with a further aspect, the expandable device is configured to measure the width or footprint of the intervertebral space or an angle of the endplate of a vertebra. The device is contracted after the measuring operation to a smaller size to be removed to lessen any damage during the withdrawal operation. A holder or support for the device is held by the surgeon to insert and remove the device. Although the intervertebral space being measured may be with or without an annulus forming a nuclear space within the annulus, the device is particularly useful for being inserted and removed through a small incision in the annulus used to remove the disc. [0019] In accordance with one aspect of the present invention, an apparatus and method are disclosed for sizing an implantable space within a patient. The implantable space in a preferred form is an intervertebral space. Preferably, a measuring instrument is implemented in the form of an expandable intervertebral sizing instrument. Many features of the expandable intervertebral sizing instrument are applicable to surgical instruments in general, but in a preferred form, the intervertebral sizing instrument according to the present invention is particularly suited for determining the size and lordotic angle at a set distraction force of an intervertebral space to appropriately size spinal implants such as spinal cages, VBR/IBFs, and motion preservation implants such as TDPs, or DNPs. [0020] The expandable sizing instrument has a mechanism in the form of a measuring head configured to expand within an intervertebral space, i.e. the space between vertebrae of the spine, with a controlled amount of force or pressure to measure the space within the intervertebral space. In a preferred form, the force exerted on the vertebrae adjacent the intervertebral space is held constant throughout the range of motion of the measuring head. The measuring head includes a spacer mechanism which preferably includes a pair of pads that can toggle or pivot to effectively conform to the configuration of the vertebral surfaces including the lordotic angles thereof to facilitate accurate measurement of the space between the vertebrae. Furthermore, the pads may be radio-opaque, which allows the exact angle of the vertebral surfaces to be determined via fluoroscopy or x-ray imaging while the pads are positioned within the intervertebral space in an expanded configuration. [0021] In one form, the expandable sizing instrument has a thin curved outer shaft to reach within the narrow confines of the intervertebral space from a variety of surgical approaches, i.e. angles of entry. However, the outer shaft could also be straight for conventional surgical approaches. Inside the outer shaft is the drive mechanism that drives the spacer mechanism by applying force thereto. The outer shaft also preferably includes an indicator mechanism that displays a visual indication of the amount of space or height within the intervertebral space, which corresponds to the distance between the outer surfaces of the pads, which abut the inner surfaces of the adjacent vertebrae when the measuring head is in an expanded configuration.

[0022] Preferably, the expandable sizing instrument has a handle mechanism which has an adjustable force-setting mechanism including a compressible spring that creates the amount of force used to distract the vertebrae, i.e. the distraction force. The amount of force is controlled by the force adjustment mechanism in the form of a knob which can set the desired amount of distraction force via rotation thereof. A certain amount of distraction force is required to slightly distract the adjacent vertebrae so that when the implant is inserted, there is sufficient compressive force exerted on the implant by the vertebrae to keep the implant from slipping out of place. Using an inadequate amount of distraction force while sizing the intervertebral space can result in undersizing the implant, because the implant will not fit snugly between the vertebrae. Using an excessive amount of force can result in excessive distraction of the vertebrae, which may cause the selection of an implant that is too large for the space, and can damage the vertebral surfaces, endplates, or connective tissues in and around the spinal joint. Thus, via the adjustable force-setting mechanism, a user may reliably set the distraction force of the sizing instrument and thereby avoid excessive risk of inaccurately sizing the implant or causing injury to the patient.

[0023] In a preferred form, the expandable sizing instrument is operated by adjusting the force adjustment mechanism, and positioning or placing the tip of the inserter within the intervertebral space. An actuator mechanism, such as a trigger or lever operably connected to the spacer mechanism, is operable to cause the spacer mechanism to expand or contract. When the actuator mechanism is moved to a first position, the spacer mechanism expands and the indicator mechanism indicates the size of the intervertebral space corresponding with the expanded size of the spacer mechanism. The spacer mechanism may be contracted by moving the actuator mechanism to a second position, which corresponds to an insertion or removal configuration of the measuring head.

[0024] One advantage of the expandable sizing instrument is the ability to eliminate multiple insertions of different sized trial spacers to determine the correct size implant. The elimination of multiple insertions into the narrow confines of the intervertebral space reduces the time required for the surgery and amount of time the patient is under anesthetic. The reduction of time under anesthetic correspondingly reduces the health risk and the recovery time of patients due to the surgery and anesthetic.

[0025] Another advantage of the expandable sizing instrument is the ability to reduce the potential of tissue damage to the remaining annulus fibrosus or disc during the implantation of a disc nucleus prosthesis, or DNP. The repeated insertion and removal of static trial spacers can cause damage to the annulus, because the remaining annulus is generally stretched each time a spacer is inserted or removed. By eliminating the need for repeated insertion and removal of trial spacers, the expandable sizing instrument has the advantage of minimizing tissue damage to the annulus.

[0026] Finally, an additional advantage of the expandable sizing instrument is the ability to improve consistency and reliability of the insertion of spinal implants such as spinal cages, VBR/IBFs, TDPs, or DNPs. The expandable sizing instrument allows the accurate and consistent sizing of intervertebral implants in an objective measurable way. The precise measurement of the intervertebral space reduces reliance upon the subjective manner in which surgeons determine the correct implant size based on the subjective "feel" of the fit of a trial spacer and hence reduces human error. The objective measurement provided by an expandable sizing instrument according to the present invention allows for more consistency and reliability in the implantation of correctly sized spinal implants. Moreover, the expandable sizing instrument saves labor because there is less training required to size implants and a lessened likelihood of subsequent revision surgeries. [0027] Additional advantages and features of the invention will become apparent from the following description and attached claims taken in combination with the accompanying drawings.

Brief Description of the Drawings

[0028] FIG. 1 is a perspective view of an expandable sizing instrument in accordance with the present invention showing a pair of pad members of a measuring head in an open configuration thereof.

[0029] FIG. 2 is an exploded perspective view of the expandable sizing instrument of FIG. 1.

[0030] FIG. 3 is a side elevational view of the expandable sizing instrument showing the pad members in a closed configuration thereof, with the actuator in the forward orientation, which corresponds with an insertion and removal configuration of the sizing instrument.

[0031] FIG. 4 is a side elevational view of the expandable sizing instrument showing the pad members in an opened configuration thereof, with the actuator in an intermediate rearward orientation, which corresponds with an opened configuration of the sizing instrument.

[0032] FIG. 5 is a cross-sectional view of the expandable sizing instrument of

FIG. 4, showing the biasing member in the form of a coil spring and a force adjustment mechanism disposed in the handle portion of the instrument.

[0033] FIG. 6 is an enlarged, fragmentary cross-sectional view of the expandable sizing instrument measuring head in the opened configuration, showing upper and lower link members connecting the upper and lower pad members to the distal drive member via pin connections.

[0034] FIG. 7 is an enlarged, fragmentary cross-sectional view of a drive mechanism of the expandable sizing instrument, showing the connection of the inner shaft to the distal drive member via a linkage member. [0035] FIG. 8 is an enlarged, fragmentary cross-sectional view of the indicator and force applicator mechanism of the expandable sizing instrument, with the actuator in a forward position corresponding with a closed configuration of the measuring head.

[0036] FIG. 9 is an enlarged, fragmentary cross-sectional view of the force applicator mechanism of the expandable sizing instrument, and particularly the force adjustment mechanism thereof, which is operable to adjust the amount of distraction force transmitted to the vertebrae via the pad members.

[0037] FIGS. 10 and 11 are elevational views of the measuring head of the expandable sizing instrument in the respective closed and opened configurations.

[0038] FIG. 12 is an enlarged, fragmentary cross-sectional view of the pads in the opened configuration, showing the pivotable bearing system with pins disposed in the throughbores of the upper and lower linkages having central narrow portions and outer portions having expanded configurations, which allow the pad members to pivot in a plurality of directions.

[0039] FIG. 13 is a plan view of the expandable sizing instrument showing the distraction force indicator disposed on the handle thereof.

[0040] FIG. 14 is a plan view of the expandable sizing instrument measuring head in the open configuration.

[0041] FIG. 15 is a top sectional view of the expandable sizing instrument measuring head in the opened configuration as shown in FIG. 13.

[0042] FIG. 16 is an enlarged, fragmentary cross-sectional view of the expandable sizing instrument measuring head in the opened configuration.

[0043] FIG. 17 is an enlarged, fragmentary cross-sectional view of the expandable sizing instrument in the opened configuration.

[0044] FIG. 18 is an enlarged, fragmentary cross-sectional view of the expandable sizing instrument showing the indicator mechanism and actuator mechanism. [0045] FIG. 19 is an enlarged, fragmentary cross-sectional view of the force adjustment mechanism.

[0046] FIGS. 20 and 21 are rear views of the expandable sizing instrument in respective closed and opened configurations thereof showing the adjustment knob disposed on the handle.

[0047] FIG. 22 is a rear cross-sectional view of the force adjustment member, the orientation plug, and the biasing member disposed within the handle.

[0048] FIG. 23 is a perspective view of the expandable sizing instrument operating in the intervertebral space from a generally anterior insertion orientation, with the measuring head in the measuring configuration.

[0049] FIG. 24 is an enlarged, fragmentary perspective view of the sizing indicator for the expandable sizing instrument.

[0050] FIG. 25 is an enlarged, fragmentary side view of the sizing indicator for the expandable sizing instrument showing a measurement of 11 mm, corresponding with an opened position of the measuring head.

[0051] FIGS. 26 and 27 are respective side elevational and enlarged, fragmentary cross-sectional views of the expandable sizing instrument in the locked open configuration.

Description of the Preferred Embodiments

[0052] A system for replacing a spinal disc from an intervertebral space between adjacent, superior and inferior vertebrae includes a number of alternative sizing tools described herein and used for determining the size of the intervertebral space. After the size is determined using the sizing tools described herein, an artificial disc implant with an appropriate size that fits the measured space can be implanted so that the relatively complicated procedure for implanting the disc does not need to be repeated. The sizing tools may be used for implantation of either a disc nucleus prosthesis (DNP) or a total disc prosthesis (TDP).

[0053] The sizing tool described herein has a holder with a distal end connected to an expandable device that is placed within the intervertebral or nuclear space. The illustrated expandable device has a superior portion that can be shifted closer to or farther from an inferior portion by an expansion mechanism connected to the expandable device. The expansion mechanism is provided on the sizing tool for expanding the expandable device in a superior-inferior direction and within the intervertebral space so that the expandable device abuts both vertebrae forming the space to determine the distance or height from one vertebra to the other. It should be noted that wherever the term intervertebral space is mentioned it includes the space with or without an annulus forming a nuclear space.

[0054] The following location and direction convention will be used throughout the description of the sizing instrument 1001 of FIGS. 1-27. The term "proximal" refers to a direction of the instrument away from the patient and towards the user while the term "distal" refers to a direction of the instrument towards the patient and away from the user. Typically, and as shown in FIG. 1, the "proximal end" of the expandable sizing instrument 1001 is shown on the top right of the figure shown as direction A. The "proximal direction" is referring to any motion toward the user and in FIG. 1 is toward the top right in direction A. The "distal end" of the inserter 1001 is shown on the bottom left of FIG. 1. The "distal direction" is referring to any motion toward the patient and in FIG. 1 is toward the bottom left shown as direction B in FIG. 1.

[0055] The expandable sizing instrument 1001 allows a precise amount of distraction force to be set by the force adjustment mechanism 1801 and the amount of intervertebral space 2101 can be measured by the spacer mechanism 1101, as shown in FIG. 1. The pads 1103 of measuring head 1100 of the inserter 1001 allow for measurement of varying angulations of endplates 2401 due anatomical differences of patients as shown in Fig. 12 and Fig. 23. All external surfaces of the inserter 1001 preferably are electropolished to improve the efficiency of cleaning and sterilization. [0056] The spacer mechanism 1101 is operable to measure the height of the intervertebral space 2101. The spacer mechanism 1101 expands from a closed position shown in FIG. 3 to an expanded open configuration shown in FIG. 4. The distance between the pads 1103 increases as the lever 1503 of the actuator mechanism 1501 is pulled in direction C. In a preferred form, the spacer mechanism 1101 has a height of 7 mm in a closed configuration and a maximum height of 11.5 mm in a fully open configuration. As shown in FIG. 6, the pads 1103 are connected to the inside linkage 1105 and outside linkage 1107 by the pad pins 1109.

[0057] As shown in FIG. 12, the pads 1103 are able to pivot on the inside linkage 1105 and outside linkage 1107 utilizing a pivotable bearing system 1114. The pivotable bearing system 1114 allow the pads 1103 to conform to the varying angulations of the inner endplate surfaces of adjacent vertebrae, which facilitates precise measurement of the intervertebral space. Further, because the pads 1103 can conform more closely to the inner endplate surfaces, the pads 1103 distribute distraction forces more evenly on the endplate surfaces. Consequently, the endplates are less likely to be damaged by the pads 1103 during distraction of the vertebrae and measurement of the intervertebral space.

[0058] The pivotable bearing system 1114 allows the pads 1103 to tilt about a plurality of different axes such that the pads have two degrees of freedom. The pads 1103 may tilt forwards and backwards about the longitudinal axis of pad pins 1109, as well as laterally from side to side as shown in FIG. 12. The pads 1103 may tilt forwards or backwards and simultaneously to one side or the other such that pads 1103 may tilt in any direction. This poly axial articulation of the pads 1103 allows the pads to conform with the configuration of the endplates, regardless of surgical approach made with the tool. For example, the configuration of the endplates along an anterior approach will likely vary from the configuration of the endplates along a lateral approach. A sizing tool according to the present invention thus allows the surgeon to accurately measure the invertebral space from a plurality of different surgical approaches.

[0059] The poly axial articulation of the pads 1103 is made possible through the configuration of the throughbores through which the pad pins 1109 are disposed and the bearing surfaces 1107a, 1107b, 1105a, 1105b of the upper and lower linkages 1107 and 1105. The pads 1103 rest on the inside bearing surfaces 1105a and the outside bearing surfaces 1107a when in a non-tilted orientation. However, should the endplates of the vertebrae be tilted at a lordotic angle β, which is typically the case, the pad bearing surfaces 1103a can tilt at the lordotic angle β so that the pads 1103 can conform closely to the contour of the endplates. Conforming to the contour of the endplates enables more accurate measurement of the intervertebral space. The inner bearing surfaces of the pads 1103c and the pad pins 1109 engage with the inside and outside bearing surfaces 1105b and 1107b, which are angled with respect to the non-tilted orientation of the pads 1103. The lordotic angle β can vary depending on the anatomy of the patient's vertebrae 2201. In a preferred form, the pads 1103 are configured to toggle independently to tilt at a minimum angle of 11 degrees in any direction when the pads 1103 are in an open configuration corresponding with a measurement of 8 mm. The pads 1103 may be tilted a greater amount when the pads 1103 are opened further than 8 mm, because the pad members 1103 do not interfere with one another when distracted further apart. In addition, the pads 1103 preferably do not toggle when positioned in a closed configuration. [0060] The top pad 1102a and the bottom pad 1102b also pivot independently so that the top pad 1102a can have a lordotic angle which is different from the bottom pad 1102b. The spacer mechanism 1101 may be used to determine the lordotic angle because the pads 1103 tilt or pivot to conform to the lordotic angle of the endplates 2401 and an x-ray or fluoroscopy will clearly indicate the lordotic angle since the radio-opaque pads 1103 will be readily visible on the x-ray or fluoroscopy films. The ability to measure different lordotic angles is especially important because the shape of the implant required will depend on the surgical approach taken by the surgeon, i.e. a posterior, anterior, or lateral approach. Preferably, the pads 1103 may pivot in any direction to conform to the lordotic angle of the vertebrae no matter what insertion approach is taken by the user. The pads 1103 may be pivotable to the same angle β in each direction, or the angle may vary in some directions. For example, in the embodiment shown in FIG. 6, the distal ends of pads 1103 may be pivoted towards one another at a greater angle than β so that the proximal ends of the pads are distracted far enough apart to allow access to the components of spacer mechanism 1101 for easier cleaning.

[0061] As shown in FIGS. 6 and 16, the spacer mechanism 1101 is shiftably connected to the distal drive member 1303 by the inside linkage 1105, and the outside linkage 1107. The opener pin 1111 connected to the outer shaft 1201 causes the inside linkage 1105, and the outside linkage 1107 to distract apart from each other when the distal drive member 1303 moves in the distal direction B because the inside linkage opening cam surface 1111a and the outside linkage opening cam surface 1111b slide along the stationary opener pin 1111. The opener pin 1111 effectively allows the spacer mechanism 1101 to be expandable within the intervertebral space 2101. [0062] Similarly, when the distal drive member 1303 moves in the proximal direction A, the closer pin 1113 connected to the outer shaft 1201 closes the inside linkage 1105, and the outside linkage 1107. Closing cam surfaces 1113a, 1113b in the linkages 1105, 1107 provide a guide path that allows the linkages to slide along the closer pin 1113. As the linkages 1105, 1107 are retracted proximally, the stationary closer pin 1113 acts on the sloped closing cam surfaces 1113a, 1113b, providing the linkages 1105 with a closing force which causes the pads 1103 to retract and come together. The closer pin 1113 effectively allows the spacer mechanism 1101 to be collapsible within the intervertebral space 2101 as well as for allowing adjustments of position and removal of the inserter 1001.

[0063] One benefit from the arrangement of the opener pin 1111 and closer pin

1113 and linkages 1105, 1107 is to maintain a substantially constant force distribution on the pads 1103. Once the desired distraction force is set by the knob 1805 of the force adjustment mechanism 1801, the pads are operable to provide the set distraction force to the adjacent vertebral bodies with which they are engaged. To provide a constant distraction force over the entire displacement range of the pads 1103, several factors are considered including spring choice, cam geometry, and pad size. Given a known surface area of the pads, the necessary distraction force for a given cam surface geometry may be calculated using known methods, such as three dimensional modeling software.

[0064] First, the force vectors, which are perpendicular to the closing cam surface 1111a, 1111b at the contact point between the opener pin 1111 and the closing cam surface 1111a, 1111b, are calculated. Next, the necessary input force is calculated for the initial closed configuration of the pads 1103. Once the input force for the initial closed configuration is determined, additional calculations for the input force at the halfway open configuration and fully open configuration of the pads 1103 are calculated. Based on the input forces at the three points, the spring constant needed at each point can be calculated based on the known displacement of the linkages 1105, 1007 in the proximal-distal direction. Once the spring constants are known for each of the three positions, the geometry of the closing cam surface 1111a and 1111b may be modified to obtain substantially identical spring constants for each of the three points. In a preferred form, the closing cam surfaces 1111a, 1111b have a generally sinusoidal contour along the portion thereof that the opener pin 1111 travels. The appropriate spring is then chosen based on the calculated spring constant. In a preferred form, the spring 1703 has a diameter of 0.975 inches and a length of 4 inches. The return spring 1511 preferably has a diameter of 0.281 inches and a length of 0.75 inches, with a spring constant of 9.2. Different springs may be used depending on the desired range of distraction force or pressure and the size of the pads 1103. For instance, if larger pads are used, larger or stronger springs may be used to maintain the desired amount of pressure to be exerted on the vertebral endplates, because the larger the surface area of the pads, the greater the exerted force must be to maintain a constant pressure. The amount of distraction force is adjustable to a set level through rotation of the knob 1805 of the force adjustment mechanism 1801, which is operable to selectively compress or allow expansion of spring 1703.

[0065] In a preferred form, the adjustable distraction force ranges from 20 PSI to 70 PSI and the pads 1103 have a surface area between 0.133 to 0.307 square inches. Different sized and shaped pad members may be used, depending on user preference, vertebral size, implant size or shape, insertion approach, and other factors. For instance, racetrack-shaped pad members may be used for sizing the intervertebral space for a similarly-shaped nuclear implant. In other forms, pads 1103 with a round configuration may preferable for use over pads with an elongate configuration, depending on the surgical approach used. For instance, pads with an elongate configuration may be better suited for lateral approaches, because a smaller incision may be made in the annulus to fit the narrow profile of the pads. [0066] The spacer mechanism 1101 is preferably made of stainless steel. In its preferred embodiment, the inside linkage 1105 and the outside linkage 1107 are 440 stainless steel and provided with a low friction coating to allow smooth cam action by the opener pin 1111 and closer pin 1113 on the linkages 1105 and 1107. In a preferred form, the linkages 1105, 1107 are coated with chrome.

[0067] The outer shaft 1201 provides structural support for both the mechanical operation of the spacer mechanism 1101 previously described and for the drive mechanism 1301 as shown in FIG. 5. The outer shaft 1201 has a small diameter tubular configuration so that it has a narrow circular profile as shown in FIGS. 10 and 11. The narrow profile is desirable to fit within the narrow confines of the intervertebral space 2101 as shown in FIG. 23.

[0068] As shown in FIGS. 14 and 15, the outer shaft 1201 has a curve at angle α which is shown at approximately 10 degrees in the preferred embodiment. The curve at angle α of the outer shaft 1201 is configured to allow the inserter 1001 to reach the center of the vertebral body 2201 when the inserter 1001 is used from a posterior approach. Alternatively, the outer shaft 1201 could have a curve at angle α of zero or be straight for a conventional surgical approach.

[0069] The outer shaft 1201 also provides structural support to mechanically guide the drive mechanism 1301 as shown in FIGS. 5 and 15. The outer shaft 1201 constrains the distal drive member 1303 and linkage 1305 to move in the proximal and distal directions A and B upon actuation of the actuator mechanism 1501. The outer shaft 1201 also provides the structural connection by joining the spacer mechanism 1101 to the rest of the inserter 1001. The outer shaft 1201 is made of stainless steel in its preferred embodiment

[0070] The drive mechanism 1301 provides mechanical linkage for the inserter

1001 apparatus and is the mechanism to transmit force from the actuator mechanism 1501 to the spacer mechanism 1101 as shown in FIGS. 5 and 15. The drive mechanism 1301 is mounted within the outer shaft 1201 to drive the spacer mechanism 1101. [0071] The drive mechanism 1301 is composed of three shiftable shafts: distal drive member 1303, linkage 1305 and inner shaft 1307. The distal drive member 1303, linkage 1305 and inner shaft 1307 are mechanically connected by pins 1309 (shown in FIGS. 7 and 17) in order to provide force in the proximal and distal directions A and B at angle α (shown in FIGS. 13 and 14). The drive mechanism 1301 is made of stainless steel in its preferred embodiment.

[0072] The indicator mechanism 1401 provides an objective, accurate measurement of the height of the intervertebral space 2101 because the indicator mechanism 1401 is calibrated to the amount of displacement of the drive mechanism 1301 which, in turn, causes a specific known amount of expansion or compression of the spacer mechanism 1101. As shown in FIGS. 5, 8, 15 and 18, the indicator mechanism 1401 is mounted within the outer shaft 1201 and through the inner shaft 1307.

[0073] As shown in Fig. 18, the gauge 1403 has a spherical gauge surface 1405 engaged by a compressed gauge spring 1407 biasing the gauge 1403 into position. The spring force is resisted by the gauge pin bearing surfaces 1411 within the inner shaft 1307. When the inner shaft 1307 moves with the expansion or contraction of the spacer mechanism 1101 then the gauge 1403 will pivot or rotate about the spherical gauge surface 1405 to cause the gauge tip 1413 to shift to provide an indication of the size of the intervertebral space 2101. The gauge tip 1413 is free to tilt about the spherical gauge surface 1405 through the outer shaft cutout 1205. As shown in Fig. 24 and 25, the gauge tip 1413 is visible to the operator, typically the surgeon. The indicator mechanism 1401 indicates with the gauge tip 1413 the amount of intervertebral space 2401 available for the implant, which corresponds to the vertical distance between the vertebrae 2501. The indicator mechanism 1401 is made of stainless steel in its preferred embodiment.

[0074] The actuator mechanism 1501 allows the operator to deploy the spacer mechanism 1101 from the compressed configuration shown in FIG. 3 to the expanded configuration shown in FIG. 4. As shown in FIG. 3, the operator expands the spacer mechanism 1101 by moving the lever 1503 generally upwardly away from shaft 1201 in direction C to measure the height of the intervertebral space 2101. As shown in FIG. 4, the operator compresses the spacer mechanism 1101 by moving the lever 1503 generally downwardly toward the shaft 1201 in direction D opposite to direction C in preparation for removing the inserter 1001 from an intervertebral space 2101. The lever 1503 is typically down, i.e. depressed in direction D, when inserting the inserter 1001 to provide the most compact configuration of the spacer mechanism 1101 possible during insertion into the narrow incision in the patient. The lever 1503 is mounted to the outer shaft 1201 by the shaft pin 1510. [0075] As shown in FIGS. 5, 8 and 18, the actuator in the form of lever 1503 is connected to the drive mechanism 1301 and force mechanism 1701 by a linkage 1507 with a lever pin 1509 and shaft pin 1510. The force on the drive mechanism 1301 created by the pressure of the patient's tissue on the spacer mechanism 1101 and the return spring 1511 is counterbalanced by the force created by the force mechanism 1701 as shown FIGS. 8 and 18. However, the lever 1503 can alter this balance as desired by the user. Finally, as shown in FIGS. 26 and 27, the lever 1503 can be locked open by depressing the lever 1503 until it reaches its locked position, which is caused by interference between the lever body 1503 and the linkage 1507, generally shown in FIG. 27. When the lever 1503 is in the locked open configuration, the spacer mechanism 1101 will be in the most expanded position. The actuator mechanism 1501 is made of stainless steel in its preferred embodiment.

[0076] The handle mechanism 1601 provides a handle grip 1609 for the operator and provides structural support when the inserter 1001 is grasped by the human hand. The handle mechanism 1601 provides increased distance for the operator especially while conducting x-rays or fluoroscopy. Direct radiation exposure can be minimized by the surgeon grasping the proximal end of the handle mechanism 1601.

[0077] As shown in FIGS. 8 and 18, the handle mechanism 1601 is connected to the outer shaft 1201 by the front handle cap 1605 and set screws 1607. The position of the outer shaft 1201 in relation to the force mechanism 1701 can be adjusted by the set screws 1607 to account for manufacturing error, i.e. stack up error, which occurs during the machining of the various parts. As shown in FIGS. 8, 9, 18 and 19, the front handle cap 1605, grip 1609, and end cap 1611 contains the force mechanism 1701 whose main component is a compression spring 1703. The end cap 1611 also provides a bushing for the adjustment shaft 1803.

[0078] The handle mechanism 1601 is made of stainless steel in its preferred embodiment. Alternatively, the handle mechanism 1601 can be made of Lexan or other clear strong plastics to allow visual feedback of the force mechanism 1701 which is contained within the handle mechanism 1601.

[0079] The force mechanism 1701 provides a generally constant distraction force through all phases of motion of the spacer mechanism 1101 during a sizing operation of the intervertebral space 2101 and does not require the operator to manually adjust the amount of force used. The force applicator mechanism 1701 automatically sets the distraction force without constant user intervention to maintain the distraction force at a set level.

[0080] The main component of the force mechanism 1701 is the large compression spring 1703 mounted within the handle mechanism 1601 and shown in FIGS. 5 and 15. As shown in FIGS. 8 and 18, the spring 1703 fits within and exerts a force on the adjustable fitting 1705. The adjustable fitting 1705 is threadably connected to the mechanical adaptor 1707 which in turn transmits a force (that varies with the compression of the spring 1703) to the connection pin 1709. The connection pin 1709 is then connected to the linkage 1507 of the actuator mechanism 1501 and the force exerted by the spring 1703 is transmitted all the way to the spacer mechanism 1101. Should the force exerted on the spacer mechanism 1101 by the vertebrae 2501 increase beyond the force of the spring 1703, then the pads 1103 and spring 1703 will collapse until an equilibrium is reached.

[0081] The distraction force exerted on the vertebrae by the force mechanism

1701 can be fixed or adjusted as shown in FIGS. 9, 19, and 22. The compression spring 1703 is proximally fixed by the orientation plug 1711. The orientation plug 1711 fits within the proximal coils 1703a of spring 1703 and the end cap 1611. The orientation plug 1711 has radial flanges 1711a which fit within slots of the end cap 1611 to prevent the plug 1711 from rotating. The plug 1711 is threadably connected to the adjustment shaft 1803. Rotation of the adjustment shaft 1803 adjusts the force level of the compression spring 1703 by advancing or retracting orientation plug 1711 to respectively increase or reduce compression of the spring 1703. The rotation of the shaft 1803 is carried by the bearing 1713 which is preferably made of Teflon PFE to reduce the friction during rotation and adjustment of the shaft 1803. Finally, the variable force of the spring 1703 is adjustable via the knob 1805 of the force adjustment mechanism 1801. The components of the force mechanism 1701 are made of stainless steel in its preferred embodiment.

[0082] The force adjustment mechanism 1801 provides the element for controlling the amount of distraction force exerted by the inserter 1001 and to allow adjustment of the distraction force to a range of set levels for the user, preferably between 20 and 70 psi. The ability to control the amount of distraction is beneficial because different amounts of force may be needed to achieve the desired amount of distraction, which may depend on the portion of the spine 2001 in which the implant is to be inserted due to anatomical differences, i.e. the cervical region of the spine versus the lumbar portion of the spine. For example, the cervical region may require less distraction force than the larger lumbar region. Similarly, the amount of distraction force required depends on the degree of disc 2301 removal required for the implant.

[0083] The force adjustment mechanism includes large knob 1805 mounted to the handle mechanism 1601 via the adjustment shaft 1803 shown in FIGS. 5 and 15. The knob 1805 is mounted on the most proximal end of the inserter 1001 as shown in FIGS. 20 and 21.

[0084] As shown in FIGS. 13 and 14, the force adjustment knob 1805 utilizes handle markings 1807 to indicate the amount of distraction force. Preferably, the knob 1805 is rotated until the plug marking 1809 reaches the desired handle marking 1807 which corresponds to a precise amount of distraction force. The plug marking 1809 is preferably a laser etching on the orientation plug 1711 shown in FIGS. 9 and 19. The plug marking is visible through an aperture 1811 in the handle grip 1609 as shown in FIGS. 13 and 14.

[0085] As shown in FIGS. 9 and 19, the rotation of the knob 1805 causes the adjustment shaft 1803 to rotate and compress the spring 1703 and thus causes adjustment of the amount of force generated by the force mechanism 1701, as described above. The force adjustment mechanism 1801 is made of stainless steel in its preferred embodiment. Alternatively, an internal scale within the handle mechanism 1601 could be used.

[0086] The inserter 1001 can be manufactured by standard turning, milling, and Electro Discharge Machining (EDM). Alternatively, the inserter 1001 can be made from any suitable, structurally strong materials. The inserter 1001 can be constructed of suitable materials which are compatible with the uses and environments into which the device will be utilized. Preferably, the inserter 1001 is constructed of metallic materials such as stainless steel or titanium. The best mode of sterilizing the expandable space inserter 1001 is by sterilization through autoclave, i.e. steam.

[0087] The surgical procedure begins with sterilizing the surgical field and inserter 1001. Once the patient is anesthetized, a surgical incision is made in the patient from one of three basic approaches based on the surgeon's preference: 1) an anterior approach, i.e. from the front of the patient, 2) laterally, i.e. from the side of the patient, or 3) posteriorly, i.e. from the back of the patient. Once the incision is made the surrounding tissue is distracted or moved out of the way using standard instruments and methodology.

[0088] The installation site of the implant is prepared by removing the damaged tissue of the intervertebral disc 2301, i.e. a discectomy. The discectomy can be either a complete discectomy in which the entire disc is removed or a partial discectomy where the nucleus pulposus is removed and the annulus fibrosus is punctured. A full discectomy is more typical for the implantation of a spinal cage, Vertebral Body Replacement (VBR), or Interbody Fusion Device (IDF). A partial discectomy is more typical for the implantation of a DNP. In either procedure, the disc material is removed with a ring curette which cuts out the disc. [0089] For the implantation of a DNP, the annulus fibrosus is punctured and the nucleus pulposus is removed. There typically is not surface preparation of the endplates 2401. For a VBR/ IDF, the endplates of the vertebra are typically roughened with the use of a rasp because of the need to remove all disc material and to encourage blood flow and healing in the intervertebral space 2101. The roughening of the endplates 2401 flattens the surface of the vertebrae 2401 to conform to the surface of the implant thus reducing the risk that the implant will shift out of position.

[0090] The expandable sizing instrument 1001 surgical instrument is then deployed to determine the height and angles of the endplates 2401 in the intervertebral space 2101. The first step comprises adjusting the force adjustment mechanism 1801 by rotating the knob 1805 and setting the desired amount of distraction force as shown in FIG. 23. The distal end of the spacer mechanism 1101 is then inserted and positioned within the intervertebral space 2101. The actuator mechanism 1501 is deployed by moving the lever 1503 to cause the spacer mechanism 1101 to expand in the intervertebral space 2101. The operator of the inserter 1001, typically the surgeon, will then read the amount of intervertebral space, i.e. the distance between the vertebrae 2501, by viewing the indicator mechanism 1401. Alternatively, the force adjustment mechanism 1801 can be adjusted by rotating the knob 1805 while the spacer mechanism 1101 is within an intervertebral space 2101. Fluoroscopy can then be performed by taking and developing an x-ray or fluoroscopy image while the inserter 1001 is in a fixed position to determine the lordotic angle of the vertebrae 2501. After the invertebral space has been measured, the pads 1103 are retracted by pushing the actuator 1501 distally and the measuring head 1100 is removed from the intervertebral space. A properly sized implant is then selected and inserted as known in the art. [0091] While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

Claims

WHAT WE CLAIM IS:

1. An instrument for measuring the size of an intervertebral space, comprising: a handle portion; an elongate shaft portion having a longitudinal axis operably connected to the handle portion; upper and lower pad members connected to the shaft and configured for movement between an unexpanded orientation with the upper and lower pad members adjacent one another and a distracted orientation with the upper and lower pad members distracted apart from one another for engaging with inner facing surfaces of adjacent vertebrae; a biasing member operably engaged with both of the upper and lower pad members that biases the members towards a distracted orientation with a predetermined amount of distraction force.

2. The instrument of claim 1, wherein the biasing member is disposed within the handle portion.

3. The instrument of claim 1, wherein the elongate shaft portion is disposed within an outer shaft portion connected to the handle portion.

4. The instrument of claim 2, wherein the biasing member is biased by a force adjustment member which is movable between a first position, wherein the force adjustment member causes a first distraction force to be exerted by the biasing member and a second position, wherein the force adjustment member causes a second distraction force to be exerted by the biasing member.

5. The instrument of claim 4, wherein the biasing member is a coil spring, and the force adjustment member is selectively movable to increase or decrease the distraction force by compressing or decompressing the spring.

6. The instrument of claim 5, wherein the force adjustment member is selectively movable via rotational motion thereof about the longitudinal axis of the instrument.

7. The instrument of claim 6, wherein the force adjustment member is disposed within the handle and is operably connected to a rotatable knob disposed on an end of the handle.

8. The instrument of claim 1, further comprising an opposing biasing member operably connected to the elongate shaft to provide an opposing force to the force created by the biasing member.

9. The instrument of claim 1, further comprising an actuator operably connected to the upper and lower pad members for selectively moving the pad members between unexpanded and distracted orientations.

10. The instrument of claim 1, further comprising an indicator operably connected to the elongate shaft for displaying the distance between outer surfaces of the upper and lower pads.

11. The instrument of claim 1, wherein the upper and lower pad members are each configured for tilting about the longitudinal axis and for tilting about an axis transverse to the longitudinal axis for conforming to the endplates of adjacent vertebrae.

12. The instrument of claim 1, wherein the elongate shaft is movable along the longitudinal axis such that movement in one direction along the axis causes the pads to distract apart from one another, and movement in the opposite direction along the axis causes the pads to come together.

13. A method of measuring space within an intervertebral space between superior and inferior vertebrae, the method comprising: selecting a distraction force of an expandable device from a plurality of available distraction forces; placing the expandable device into the intervertebral space; expanding the expandable device while in the intervertebral space to an expanded position with the selected distraction force; measuring a characteristic of the space using the expandable device; contracting the expandable device to a smaller size; and removing the contracted, smaller size of the expandable device from the intervertebral space.

14. The method of claim 13, wherein selecting a distraction force includes selectively biasing or unbiasing a biasing member.

15. The method of claim 14, wherein selecting a distraction force includes selectively adjusting a force adjustment member to selectively bias or unbias the biasing member.

16. The method of claim 15, wherein selectively biasing or unbiasing a biasing member includes compressing or decompressing a coil spring by advancing or retracting the force adjustment member.

17. The method of claim 13, wherein selecting a distraction force includes determining the amount of distraction of the vertebrae desired.

18. The method of claim 13, further comprising conforming a portion of the expandable device to the contour of facing surfaces of adjacent vertebrae.

19. The method of claim 13, further comprising: placing the expandable device into an intervertebral space from which the disc and annulus have been removed.

20. The method of claim 13, further comprising: providing a holder having an exterior portion extending outside a person's body and having an interior portion carrying the expandable device; and using the holder to place the expandable device into the intervertebral space and to remove the expandable device from the intervertebral space.

21. The method of claim 13, further comprising: measuring the distance between adjacent vertebral endplates of adjacent vertebrae.

22. The method of claim 13, further comprising: providing at least one inclined surface on the expandable device substantially matched to an incline of an endplate of an adjacent vertebra.

23. The method of claim 22, wherein providing at least one inclined surface on the expandable device includes providing superior and inferior pad members of the expandable device that may tilt with respect to one another when in the expanded position thereof to substantially match the inclines of endplates of adjacent vertebrae; and conforming the pad members to the endplates of adjacent vertebrae.

24. The method of claim 22, wherein providing at least one inclined surface on the expandable device includes providing a pad member that may tilt about a longitudinal and lateral axis thereof to provide for polyaxial articulation of the pad member to facilitate matching the incline of an endplate of an adjacent vertebra; and matching the incline of an endplate of an adjacent vertebra with the pad member.

25. The method of claim 13, further comprising measuring with an imaging device a size dimension of the expandable device in its expanded position within the intervertebral space.

26. The method of claim 25, wherein the step of measuring with an imagining device comprises the use of one of: a) an x-ray device; b) an MRI device; c) a fluoroscopic device.

27. The method of claim 13, wherein the step of contracting the expandable device comprises: contracting superior and inferior portions of the expandable device away from endplates of adjacent vertebrae to reduce the pressurized engagement therewith to assist in removal of the expandable device.

28. The method of claim 13, further comprising: providing the expandable device with a shifting mechanism configured to shift portions of the expandable device relative to one another; and positioning the shifting mechanism in the intervertebral space for shifting the portions away from one another.

29. The method of claim 13, further comprising: collapsing the expandable device into a predetermined collapsed configuration; and removing the collapsed, expandable device from the intervertebral space.

30. The method of claim 29, further comprising: inserting the expandable device while in its predetermined collapsed state through an incision in an annulus into a nuclear disc space and removing the expandable device from said space and through the incision while the expandable device is in its predetermined collapsed state.

31. An instrument for measuring the size of an intervertebral space, comprising: a handle portion; an elongate shaft portion having a longitudinal axis operably connected to the handle portion; and upper and lower pad members operably connected to the shaft and configured for movement between an unexpanded orientation with the upper and lower pad members adjacent one another and a distracted orientation with the upper and lower pad members distracted apart from one another, wherein the upper and lower pad members are each configured for tilting about the longitudinal axis and at least one other axis for conforming with the endplates of adjacent vertebrae.

32. The instrument of claim 31, wherein the at least one other axis is transverse to the longitudinal axis.

33. The instrument of claim 31, wherein the pad members are connected to the shaft with a pivotable bearing member having two degrees of freedom, such that the pad members may tilt forward and backward and side to side and in combinations thereof to conform with the endplates of adjacent vertebrae when the instrument is inserted into the intervertebral space at a plurality of approaches with respect thereto.

34. The instrument of claim 31, further comprising upper and lower link members operably connected to the upper and lower pad members via pin members, the link members being configured for moving the pad members between their unexpanded and distracted configurations.

35. The instrument of claim 34, wherein the pad members each comprise a throughbore having central narrow portion and outer wider portions through which each pin member is disposed for allowing opposite ends of the pin members to tilt about the central narrow portion for facilitating tilting of the pads.

36. The instrument of claim 31, wherein the pad members are sized and configured for insertion through an incision in an annulus when in the unexpanded configuration.

37. The instrument of claim 31, further comprising a biasing member in operable engagement with the upper and lower pad members which biases the members towards a distracted orientation with a predetermined amount of distraction force.

38. The instrument of claim 37, further comprising an adjustable tensioning member operably connected to the biasing member, wherein the predetermined amount of force is selectable via adjustment of the force adjustment member between a first position, wherein the force adjustment member causes a first distraction force to be exerted by the biasing member and a second position, wherein the force adjustment member causes a second distraction force to be exerted by the biasing member.

39. The instrument of claim 31, wherein the elongate shaft is movable along the longitudinal axis such that movement in one direction along the axis causes the pads to distract apart from one another, and movement in the opposite direction along the axis causes the pads to come together.