Method and apparatus for stereotactic impleantation

A method of determining the appropriate size of a prosthesis to be implanted into an intervertebral disc space comprising:

• (a) making an image of the endplates of the vertebral bodies adjacent said target disc space;
• (b) determining the endplate with the smaller surface area from said image;
• (c) placing a template over the image of the smaller endplate, wherein said template comprises images of a plurality of prostheses sizes that are scaled to correspond to the magnification resulting from creation of the image of the endplates;
• and
• (d) selecting a prosthesis size from said plurality of sizes shown on said template, wherein when said prosthesis size on the template is positioned such that its edge is substantially tangent to the image of the anterior margin of the anteriorly superior vertebral body, the posterior edge of the prosthesis is positioned at least 1 mm anterior to the posterior edge of the endplate.

A method of preparing an intervertebral disc space of a patient to receive a prosthesis, comprising:

• (a) positioning a patient;
• (b) immobilizing the patient's spine;
• (c) making a lateral image of the patient's spine in the area of the target intervertebral space with a direction indicator visible on the image;
• (d) locating a reference line on said image that approximates the preferred positioning of the prosthesis;
• (e) determining the angle between the direction indicator and the reference line;
• (f) using such angle to position an instrument relative to the target disc space or its adjacent vertebral body endplates;
• (g) using said instrument to prepare the target disc space to receive the prosthesis.

Apparatus for positioning a subject comprising:

• (a) a radiographic image producer;
• (b) a subject holding apparatus for positioning the subject within the field of view of the image producer;
• and
• (c) a gravity direction indicator removably mounted within the field of view of the image producer, wherein said gravity indicator comprises a weighted radio-opaque pendulum pivotably mounted within at least a partial housing such that the indicator's position within the housing will change as the orientation of the housing relative to gravity changes.

A method of implanting an intervertebral disc prosthesis into a patient's disc space defined by two opposing endplates, wherein said prosthesis comprises two opposing articulating members and said prosthesis has a neutral position defined by the midpoint of its range of motion, said method comprising:

• (a) determining the position of a first target endplate when the spine is in its neutral position;
• (b) securing the patient in position for implantation;
• (c) determining the position of said first endplate after the patient's position is secured;
• (d) forming a first cavity within said first target endplate, wherein said first cavity is positioned such that when one of the opposing articulating members is positioned within the first cavity the prosthesis substantially assumes its neutral position when the patient's spine assumes its neutral position.

A method of implanting an intervertebral disc prosthesis into a patient's disc space defined by first and second endplates, wherein said prosthesis comprises first and second articulating members, said method comprising:

• (a) determining a first angle (α) that is the angle of the first target endplate relative to a reference plane when the spine is in its neutral position;
• (b) securing the patient's position;
• (c) determining a second angle (β) that is the angle of said first target endplate relative to said reference plane after the patient's position is secured;
• (d) forming a first cavity within said first target endplate by inserting a machining element into the target disc space and bringing the machining element into contact with the first endplate, wherein the angle of the machining element upon insertion relative to the reference plane is equal to β−α+δ, wherein δ is equal to any rotation of the machining element that is needed to bring the machining element into contact with the first endplate;
• and
• (e) positioning said first articulating member within said first cavity.

A method of implanting an intervertebral disc prosthesis into a target disc space defined by first and second target endplates, wherein said prosthesis comprises first and second articulating members, said method comprising:

• (a) determining a first angle that is the angle of the first target endplate relative to a reference plane when the spine is in its neutral position;
• (b) determining a second angle that is the angle of the second target endplate relative to said reference plane when the spine is in its neutral position;
• (c) forming a first cavity within said first target endplate;
• (d) forming a second cavity within said second target endplate;
• and
• (e) positioning said first articulating member within said first cavity and positioning said second articulating member within said second cavity such that the angle of said first articulating member relative to the reference plane is equal to said first angle and the angle of said second articulating member relative to said reference plane is equal to said second angle.

A method of implanting an intervertebral disc prosthesis into a target disc space defined by first and second target endplates, wherein said prosthesis comprises first and second opposing articulating members, said method comprising:

• (a) determining a first angle (α) that is the angle of the first target endplate relative to a reference plane when the spine is in its neutral position;
• (b) determining a second angle (α′) that is the angle of the second target endplate relative to said reference plane when the spine is in its neutral position prior to positioning the patient for surgery;
• (c) securing the patient in position for implantation;
• (d) determining a third angle (β) that is the angle of said first target endplate relative to said reference plane after the patient's position is secured;
• (e) determining a fourth angle (β′) that is the angle of the second target endplate relative to said reference plane following securing the patient's position;
• (f) forming a first cavity within said first endplate by inserting a machining element into the target disc space and bringing the machining element into contact with the first endplate, wherein the angle of the machining element upon insertion relative to the reference plane is equal to β−α+δ, wherein δ is equal to any rotation of the machining element that occurs in bringing the machining element into contact with the first endplate, whereby the angle of said first cavity relative to said reference plane is equal to said first angle;
• (g) forming a second cavity within said second endplate by inserting a machining element into the target disc space and bringing the machining element into contact with the second endplate, wherein the angle of the machining element upon insertion relative to the reference plane is equal to β′−α′+δ′, wherein δ′ is equal to any rotation of the machining element that occurs in bringing the machining element into contact with the second endplate, whereby the angle of said second cavity relative to said reference plane is equal to said second angle;
• and
• (h) positioning said first articulating member within said first cavity and positioning said second articulating member within said second cavity.

A method of implanting a intervertebral disc prosthesis into a target disc space defined by first and second target endplates, wherein said prosthesis comprises first and second articulating members, said method comprising:

• (a) forming a first cavity within said first target endplate by inserting a machining element into the target disc space and bringing the machining element into contact with the first endplate, wherein the angle of the machining element upon insertion relative to the target disc space is between about 0° and about 13°;
• (b) forming a second cavity within said second target endplate by inserting a machining element into the target disc space and bringing the machining element into contact with the second endplate, wherein the angle of the machining element upon insertion relative to the target disc space is between about 0° and about 13°;
• and
• (c) inserting the first articulating member into said first cavity and inserting the second articulating member into said second cavity.

A method of implanting a intervertebral disc prosthesis into defined by first and second target endplates, wherein said prosthesis comprises first and second articulating members, said method comprising:

• (a) forming a first cavity within said first target endplate, wherein said first cavity is positioned substantially at a first angle relative to the target disc space of between about 0° and about 10°;
• (b) forming a second cavity within said second target endplate, wherein said second cavity is positioned substantially at a second angle relative to the target disc space of between about 0° and about 10°;
• and
• (c) inserting the first articulating member into said first cavity and inserting the second articulating member into said second cavity.

A system for positioning and stabilizing surgical instruments, comprising:

• (a) a substantially horizontal rectangular open frame adapted to be positioned over an operating area and to support surgical instruments, having two substantially horizontal lateral side portions, a substantially horizontal cephalad portion, and a substantially horizontal caudal portion;
• (b) two laterally extending side arms, each having a proximal end adapted to connect to at least one side of the open frame and a distal end adapted to connect to a vertically extending rod;
• (c) two vertically extending rods, each having a proximal end adapted to connect to one distal end of a side arm, and a distal end adapted to be engaged by a clamp;
• (d) two clamps, each adapted to releasably engage one distal end of a vertically extending rod and releasably engaging a rail or rail extension of an operating table.

An adjustable frame assembly comprising:

• (a) a substantially rigid frame having an instrument support section adapted for substantially rigid connection to surgical instruments;
• (b) first and second substantially rigid supports extending at their proximal ends from said rigid frame;
• (c) first and second side rail extensions that comprise table clamps adapted to attach said side rail extensions to the rails of a table and to lock the position of said side rail extensions relative to the table rails;
• and
• (d) support clamps that connect the distal ends of said first and second supports to said first and second side rail extensions, respectively, such that the position of each of said supports relative to its respective said side rail extension can be changed and locked substantially along both the axis of said support and the axis of said side rail extension.

An adjustable frame assembly comprising:

• (a) a substantially rigid frame having an instrument support section adapted for substantially rigid connection to surgical instruments, wherein said frame defines a first plane;
• (b) first and second substantially rigid supports extending at their proximal ends from said rigid frame, and including an axial offset along its length;
• (c) first and second side rail extensions that comprise table clamps adapted to attach said side rail extensions to the rails of a table and to lock the position of said side rail extensions relative to the table rails, wherein said table defines a second plane that is substantially parallel to said first plane;
• and
• (d) support clamps that connect the distal ends of said first and second supports to said first and second side rail extensions, respectively, such that the position of each of said supports relative to its respective said side rail extension can be changed and locked in directions substantially parallel to substantially perpendicular to said first and second planes.

A clamp for securing an instrument to a support, comprising:

• (a) a main body comprising:
• (1) an upper side and a lower side, and two lateral sides;
• (2) a first aperture extending between the two lateral sides and adapted to receive an instrument holder;
• (3) a channel extending from the first aperture to the edge of the body along the lateral sides, and separating the main body into a first portion and a second portion;
• (4) a groove in the lower side adapted to receive a support and a securing block;
• (5) a second aperture extending between the upper and lower sides and adapted to receive a throughpin;
• (b) a securing block positioned in the groove and comprising a threaded opening and a beveled side, wherein the beveled side of the securing block forms a support channel in the groove;
• (c) a throughpin, rotatably disposed in the second aperture of the main body, comprising a threaded portion corresponding to and engaging the threaded opening of the securing block;
• (d) an instrument holder, rotatably disposed in the first aperture, comprising an opening adapted to receive an instrument and a slot extending from the opening to the external surface of the instrument holder;
• (e) wherein, when the throughpin is rotated in one direction, its threads urge the securing block against the lower side of the main body, simultaneously compressing the channel and constricting the first aperture, which in turn compresses the slot and constricts the opening of the instrument holder, and narrows the support channel.

A method for positioning surgical instruments relative to a reference line within a target location in a patient, comprising:

• (a) determining the position of the reference line relative to a gravitational vector;
• (b) determining a first point relative to a first plane intersecting the target location;
• (c) using the first point to position an instrument that is adapted to locate a second plane intersecting the target location;
• (d) positioning a fixture relative to the instrument;
• (e) using a position locating device to align the fixture along the intersection of the first and second planes, wherein such intersection is substantially congruent with the reference line;
• (f) securing the fixture in place;
• and
• (g) using the fixture the position other instruments within the target location relative to the reference line.

A system for positioning instruments within a patient's intervertebral disc space relative to a reference line, comprising:

• (a) a first instrument for locating and marking a transverse center of the disc space;
• (b) a second instrument for determining a sagittal center of the disc space that intersects with the transverse center;
• (c) an angle orienting instrument for adjusting the second instrument to be collinear with the reference line, which is positioned at a predetermined angle relative to a gravitational vector;
• and
• (d) a machining fixture that is positioned with the second instrument relative to the reference line, and which is adapted to position additional instruments relative to the reference line.

An instrument adapted to orient a fixture relative a skeletal joint, comprising:

• (a) a handle having first and second ends;
• (b) a nose at the first end adapted to be inserted into the joint;
• (c) an interfacing structure adapted to cooperate with a corresponding interfacing structure of a machining fixture;
• and
• (d) a leveling device at the second end.

An orienting device that is adapted to interface with and assist with the proper positioning of a surgical instrument relative to a gravitational vector, comprising:

• (a) a measuring component having indicia marked thereon that corresponds to various positions relative to the gravitational vector;
• (b) a connecting component that allows the orienting device to cooperate with the instrument when the instrument is positioned within a surgical site;
• and
• (c) a leveling device associated therewith for determining the orienting device's position relative to the gravitational vector.

A system for guiding site preparation instruments to a surgical site during spinal surgery, comprising:

• (a) a set of locating instruments for locating a specific position of the surgical site into which a site preparation instrument is to be guided;
• (b) a guiding structure adapted to be temporarily affixed to vertebral bodies to define the specific position located by the set of locating instruments, the guiding structure having a first set of features adapted to receive and guide a site preparation instrument;
• and
• (c) a corresponding site preparation instrument having a second set of corresponding features, wherein the first set of features can be aligned with the second set of corresponding features in order to guide a site preparation instrument to the surgical site.

A machining fixture to position instruments relative to a surgical site, comprising:

• (a) a base having at least one aperture adapted to receive a fixation device for securing the machining fixture in place;
• (b) a torso extending from said base and having at least one slot therein adapted to cooperate with one or more structures on an instrument in order to control the positioning of the instrument relative to the surgical site;
• and
• (c) an entryway adapted to receive the instrument.

A machining fixture to position instruments relative to a surgical site, comprising:

• (a) a base;
• (b) a torso extending from said base;
• (c) an entryway adapted to receive the instrument;
• and
• (d) an adjustable bushing movably positioned in an aperture in the base such that the bushing can be positioned in an extended position or a retracted position to facilitate the stable positioning of the fixture relative to the surgical site.

A machining fixture to position instruments relative to a surgical site, comprising:

• (a) a base;
• (b) a torso extending from said base;
• (c) an entryway adapted to receive an instrument;
• and
• (d) a rotation facilitation section adapted to be secured to a brace to align the machining fixture in an angled position with respect to the surgical site.

A machining fixture to position instruments relative to a surgical site, comprising:

• (a) a base;
• (b) a torso extending from said base;
• (c) an entryway adapted to receive the instrument;
• and
• (d) an adjustable mounting device located near the base for positioning and locking the machining fixture with respect to a fixation device.

A method of adjusting the position of a machining fixture relative to a gravitational vector in order to prepare vertebral bodies to receive an implant within the intervertebral disc space therebetween, comprising:

• (a) determining the position of anatomical features of the vertebral bodies or the intervertebral space relative to a gravitational vector;
• (b) inserting a first end of a positioning instrument into the intervertebral disc space such that a second end of the instrument extends outside the intervertebral disc space;
• (c) positioning the machining fixture over the second end of the instrument;
• and
• (d) adjusting the position of the fixture based on the position of the anatomical features relative to the gravitational vector.

A method for preparing a target space within a patient to receive a prosthesis, comprising:

• (a) positioning the patient on a surface;
• (b) locating an angled relation of the target space relative to the surface;
• (c) providing a reference frame assembly on the surface;
• (d) determining the approximate center of the target space in at least two dimensions;
• comprising:
• i) locating the approximate transverse center of the target space;
• ii) locating the approximate sagittal center of the target space;
• and
• iii) marking the intersection of the transverse and sagittal centers;
• and
• (e) positioning and securing a site preparation fixture relative to the intersection, wherein the fixture is adapted to receive site preparation instruments.

A method for locating a preferred implant location for a spinal intervertebral disc prosthesis and for preparing the spinal disc space for receiving the prosthesis, comprising:

• (a) determining an angle that defines the relation of the disc space relative to a gravitational vector;
• (b) stabilizing a frame over a general area of the disc space using an operating room table as a fixed base;
• (c) determining a preferred transverse position for locating the prosthesis within the disc space using a transverse positioning tool;
• (d) marking the preferred transverse position of the disc space;
• (e) determining the preferred sagittal position for locating the prosthesis within the disc space, comprising:
• (1) aligning a sagittal positioning tool with respect to the marked transverse position;
• (2) determining the preferred location of the sagittal positioning tool, which is the location at which an axis of the sagittal positioning tool is at an angle relative to the gravitational vector that is substantially equal to the angle that defines the relation of the disc space relative to a gravitational vector;
• (f) orienting a guide with respect to the preferred location of the sagittal positioning tool such that an axis of the guide is substantially parallel to said axis of the sagittal positioning tool;
• (g) anchoring the guide to the frame and to the vertebral bodies bordering the disc space;
• and
• (h) inserting site preparation tools through the guide to prepare the disc space for receiving a prosthesis, wherein the guide interfaces with the site preparation tools to control their position relative to the disc space and the adjacent vertebral bodies.

A method for positioning surgical instruments within a target location in a patient, comprising:

• (a) using a leveling device in association with an instrument inserted into the target location to locate first and second points relative to the target location, wherein said first and second points define a reference line;
• (b) positioning a fixture relative to the reference line;
• and
• (c) using the fixture to position surgical instruments within the target location.

A method for confirming a correct position of a machining fixture relative to a patient's vertebral bodies during spinal surgery, comprising:

• (a) aligning an alignment block with respect to the fixture, the alignment block having at least one centering aperture;
• (b) inserting a gauge having a pre-determined marking through said centering aperture wherein one end of the gauge contacts a vertebral body and another end of the gauge extends from the centering aperture;
• and
• (c) ensuring that the marking is properly oriented in relation to the centering aperture.

A system for machining the space between bones of a joint, comprising:

• (a) a milling tool, comprising:
• (1) a power source attachment located at a distal end of the milling tool;
• (2) a longitudinally extending barrel having first and second transverse guide blocks adapted to interact with a machining fixture to limit the longitudinal position and rotational or translational movement of the milling tool;
• and
• (3) a milling head located at the proximal end of the milling tool, adapted for at least partial insertion into the space between bones of a joint and adapted to contact the bones of the joint upon rotation about a pivot point or translation, the milling head comprising:
• (i) a cutting head drive adapted to rotate a cutting head around an axis substantially perpendicular to the axis of the longitudinally extending barrel;
• and
• (ii) a cutting blade disposed on the cutting head, comprising a base disk, a radially extending cutting flute, and at least one opening in the base disk adapted to allow cooling fluids to contact the bone and remove debris.

A milling depth gauge, comprising:

• (a) a shaft having a proximal end and a distal end;
• (b) a transverse saddle disposed on the shaft and adapted to receive a guide block of a milling tool and to cooperate with a stop of a machining fixture;
• (c) a rod movably associated with the shaft and extendable therefrom, said rod comprising a foot located at a proximal end of the rod, and a contacting portion disposed on the foot;
• and
• (d) an adjustable locking portion adapted to secure the degree of extension of the extendible rod.

A transverse burring system, comprising:

• (a) a burring block adapted to cooperate with a supporting instrument to limit the size and shape of tissue removed from a joint, comprising:
• (1) a distal threaded portion having an opening therein;
• and
• (2) a proximal portion having an anterior-posterior positioning stop adapted to position a burring tool in the anterior-posterior direction and a lateral positioning stop adapted to limit lateral movement of the burring tool;
• (b) a burring adjustment ring, comprising an opening surrounded by a threaded portion corresponding to the threaded portion of the burring block, and a proximal edge adapted to cooperate with the supporting instrument;
• (c) wherein when the burring adjustment ring is turned relative to the burring block, the burring block is raised or lowered relative to the supporting instrument.

A burring depth gauge, comprising:

• (a) a body having a proximal end and a distal end;
• (b) a positioning portion disposed on the body, comprising a positioning stop adapted to interact with an anterior-posterior positioning stop of a burring block;
• (c) a shaft movably associated with the body and extendable therefrom;
• and
• (d) an adjustable locking portion adapted to secure the degree of extension of the extendible shaft.

A system for separating and maintaining separation of the bones of a joint, comprising:

• (a) a distractor comprising a proximal end, a distal end, and an intermediate length, wherein:
• (1) the proximal end comprises:
• (i) a substantially blunt, substantially flat, longitudinally extending blade adapted for insertion into the joint, the blade comprising a leading edge, a first and second opposed face, and opposed lateral edges;
• and
• (ii) a laterally projecting stop located at a distal end of the blade and adapted to contact one or more joint surfaces and limit the penetration of the blade into the joint;
• (2) the distal end comprises:
• (i) a handle extending substantially orthogonal to the intermediate length, and adapted for gripping and turning;
• (b) wherein when the handle is turned, the opposed lateral edges of the blade bear against the bones of a joint and force them apart.

A profile-matching distractor comprising:

• (a) first and second discs;
• (b) a handle having a base portion and first and second extensions that extend from said base portion, wherein said first and second extensions are attached to said first and second discs, respectively, and said first and second discs comprise tapered cavities in their facing surfaces;
• (c) an actuating nut rotatably mounted on the base portion and having a threaded opening therein;
• (d) an actuating shaft having a conically tapered end and a threaded end, wherein the actuating shaft is positioned between said first and second extensions such that the threaded end is positioned within the threaded opening of the actuating nut and the tapered end is positioned within said tapered cavities of said first and second discs;
• (e) wherein as said actuating nut is rotated, the tapered end of the actuating shaft translates longitudinally, and as the enlarged portion of the taper moves out of the tapered cavities the first and second discs are pushed away from one another.

An instrument for inserting a skeletal joint prosthesis into a joint space, wherein said prosthesis comprises at least two holder openings, said instrument comprising:

• (a) a locking arm;
• (b) at least two fingers extending from a distal end of said locking arm, and adapted to cooperate with said holder openings in the prosthesis;
• and
• (c) an ejector movably mounted between said fingers having a pushing surface that can be positioned distal to said fingers and proximal to said fingers.

A method of inserting a prosthesis into a target intervertebral space comprising:

• (a) forming a first cavity within a first vertebral body endplate adjacent the disc space;
• (b) forming a second cavity within a second vertebral body endplate adjacent the disc space;
• (c) positioning a profile-matching distractor within said first and second cavities, wherein said profile-matching distractor comprises first and second discs, and said first disc has a segment whose geometry approximately matches the geometry of a portion of said first cavity, and said second disc has a segment whose geometry approximately matches the geometry of a portion of said second cavity;
• (d) positioning a tubular distractor on first and second anchors extending from the adjacent vertebral bodies, wherein said tubular distractor comprises:
• (1) first and second tubes adapted to receive said anchors,
• (2) a first arm having a distal end attached to said first tube and a second arm having a distal end attached to said second tube, wherein said first and second arms care movably connected to one another such said distal ends of said arms can be moved relative to each other, and
• (3) an adjuster that controls the movement of said first and second arms relative to each other.
• (e) removing said profile-matching distractor from the disc space;
• (f) inserting said prosthesis into the disc space;
• and
• (g) removing said tubular distractor.

A method of implanting an intervertebral disc prosthesis into an intervertebral disc space of a patient comprising:

• (1) determining the appropriate size prosthesis;
• (2) taking an orientation image of the spine in the area of the target intervertebral disc space with a gravity direction indicator visible in the image field;
• (3) quantifying the relationship between the orientation of the spine and a gravitational vector shown by the gravity direction indicator visible on the image;
• (4) distracting the target disc space;
• (5) using a transverse positioning tool to locate the preferred transverse position for the center of the prosthesis;
• (6) using the preferred transverse position to position a sagittal positioning tool;
• (7) aligning a fixture over the sagittal positioning tool 250;
• (8) using the quantified relationship between the orientation of the spine and the gravitational vector to adjust the position of the sagittal positioning tool and fixture to a preferred sagittal position for the center of the prosthesis;
• (9) securing fixture to the vertebral bodies;
• (10) using the fixture to position machining instruments and machining cavities into the endplates adjacent the target disc space;
• and
• (11) inserting the prosthesis into the machined cavities.

A method of implanting a spinal intervertebral disc prosthesis into an intervertebral disc space of a patient comprising:

• (1) determining the appropriate size prosthesis;
• (2) positioning the patient on the operating table such that the spine approximates its neutral position;
• (3) immobilizing the patient on the operating table;
• (4) taking a lateral image of the spine in the area of the target intervertebral space with gravity direction indicator visible in the image field;
• (5) quantifying the relationship between the orientation of the spine and a gravitational vector shown by the gravity direction indicator visible on the image, wherein the quantified relationship is a spine orientation angle that is equal to the angle between an anatomic reference line and the gravitational vector;
• (6) attaching an adjustable frame assembly 20 above the target disc space, wherein the frame is attached to the operating table;
• (7) retracting soft tissue surrounding the target space;
• (8) removing a portion of the target disc;
• (9) distracting the target disc space by using distractors 140 of increasing widths to distract the vertebral bodies adjacent the target disc space to expose the target space;
• (10) using a transverse positioning tool to locate the preferred transverse positioning for the center of the prosthesis;
• (11) marking the preferred transverse position on a vertebral body;
• (12) using the preferred transverse position to position a sagittal positioning tool;
• (13) aligning a fixture 300 over the sagittal positioning tool 250;
• (14) placing an alignment block over the fixture and sagittal positioning tool to align their positions relative to one another;
• (15) loosely bracing the fixture with a brace either before or after the placement of the alignment block;
• (16) positioning a protractor over the alignment block, fixture, and sagittal positioning tool combination, and using the protractor to position the fixture such that the angle of the sagittal positioning tool's axis relative to the gravitational vector is equal to the spine orientation angle;
• (17) securing the fixture to the vertebral bodies;
• (18) removing the sagittal positioning tool, protractor, and alignment block from the fixture;
• (19) determining and locating a preferred anterior-posterior position for the prosthesis which defines where cavities in the vertebral body endplates should be formed;
• (20) performing a preliminary machining operation comprising removing tissue from within the target disc space to provide a space therein for insertion of a cavity forming machining instrument;
• (21) machining the endplates to form said cavities therein;
• and
• (22) inserting the prosthesis into said cavities.

A method of implanting a intervertebral disc prosthesis into a patient's disc space defined by first and second endplates, wherein said prosthesis comprises first and second articulating members, said method comprising:

• (a) determining a first angle (α) that is the angle of the first target endplate relative to a reference plane when the spine is in its neutral position;
• (b) determining a second angle (β) that is the angle of said first target endplate relative to said reference plane;
• (c) forming a first cavity within said first target endplate by inserting a machining element into the target disc space and bringing the machining element into contact with the first endplate, wherein the angle of the machining element upon insertion relative to the reference plane is equal to β−α+δ, wherein δ is equal to any rotation of the machining element that is needed to bring the machining element into contact with the first endplate;
• and
• (d) positioning said first articulating member within said first cavity.

A method of implanting a first intervertebral disc prosthesis in a first intervertebral disc space of a patient and implanting a second intervertebral disc prosthesis in a second intervertebral disc space of the patient, wherein the first and second disc spaces are adjacent and are separated by a linking vertebral body, comprising:

• (1) positioning a first fixture relative to the first disc space;
• (2) securing the first fixture's position by attaching a fixation device to the first fixture and the linking vertebral body;
• (3) using the first fixture to position at least one instrument within the first disc space to prepare the first disc space to receive the first prosthesis;
• (4) detaching the first fixture from the fixation device while leaving the fixation device attached to the linking vertebral body;
• (5) positioning a second fixture relative to the second disc space;
• (6) securing the second fixture's position by attaching the fixation device to the second fixture;
• and
• (7) using the second fixture to position at least one instrument within the second disc space to prepare the second disc space to receive the second prosthesis.

A method of implanting a first intervertebral disc prosthesis in a first intervertebral disc space of a patient and implanting a second intervertebral disc prosthesis in a second intervertebral disc space of the patient, wherein the first and second disc spaces are adjacent and are separated by a linking vertebral body, comprising:

• (1) positioning a first fixture relative to the first disc space;
• (2) securing the first fixture's position by attaching a fixation device to the first fixture and the linking vertebral body, wherein the fixation device comprises a threaded lower portion that is threaded into the linking vertebral body and an upper portion adapted to extend through an aperture in the fixture and engage a locking mechanism;
• (3) using the first fixture to position at least one instrument within the first disc space to prepare the first disc space to receive the first prosthesis;
• (4) removing the first fixture from the upper portion of the fixation device, while leaving the lower portion of the fixation device threaded into the linking vertebral body;
• (5) positioning a second fixture relative to the second disc space, wherein said second fixture comprises a movable base having an open portion adapted to receive the upper portion of the fixation device;
• (6) securing the second fixture's position by moving the movable base to capture the upper portion of the fixation device in the open portion of the movable base and securing a locking mechanism to the fixation device;
• and
• (7) using the second fixture to position at least one instrument within the second disc space to prepare the second disc space to receive the second prosthesis.

A method of implanting a second intervertebral disc prosthesis in a second intervertebral disc space of a patient, wherein the second intervertebral disc space is adjacent to a first intervertebral disc space having a first prosthesis previously implanted therein, and said first and second disc spaces are separated by a linking vertebral body, comprising:

• (1) positioning a fixation device in an opening in the linking vertebral body, wherein said opening was initially formed to position an instrument for use in implanting the first prosthesis;
• (2) positioning a fixture relative to the second disc space, wherein said second fixture comprises a movable base having an open portion adapted to receive a portion of the fixation device;
• (3) securing the second fixture's position by moving the movable base to capture the fixation device in the open portion of the movable base and securing a locking mechanism to the fixation device;
• and
• (4) using the second fixture to position at least one instrument within the second disc space to prepare the second disc space to receive the second prosthesis.