Patent Abstract:
the invention concerns a device for adjusting the position of a screw that is able to move a part of a surgical instrument , said device comprising : — a stem comprising a tip suited to the head of the screw , — an actuated system for driving said stem in rotation , — communication means to communicate with a control unit , such that the control unit transmits to the actuated system the number of turns to apply to the stem to reach the target position of the screw . the invention also concerns a surgical system for alignment of surgical guide means , comprising : — a positioning unit comprising a fixed part and a mobile part supporting the surgical guide means , the position of said mobile part being adjustable with respect to the fixed part by screws , — a referencing unit for detecting the position of the positioning unit with respect to a target position of the surgical guide means , — a control unit for computing the target position of screws , — said device for adjusting the positions of the screws .

Detailed Description:
as represented on fig2 , the adjustment device 4 according to the invention is an actuated screwdriver that comprises a body or handle 40 , a stem 41 , a tip 42 , an optional button 43 that is activated by the user , and an encapsulated battery that brings enough power to rotate the screwdriver . in a preferred embodiment , the actuation of the screwdriver is done by a motor . in a preferred embodiment the motor is a brushless motor which directly provides feedback on number of turns performed using its internal coding system . but alternatively many other solutions of actuators can be used to rotate a screw , such as piezoelectric actuators . the screw can be replaced by any non reversible linear motion mechanism , such as hydraulic or pneumatic mechanism , and the actuator can be any device that provides a linear motion of said mechanism . as better seen on fig3 a , the stem 41 is rotating with respect to the device body 40 thanks to a rolling system 44 . the rotation is controlled by a motorized system 45 . it must be noted that the devices illustrated on fig4 to 7 also comprise said rolling and motorized systems , although these features are not shown on these figures . the device is controlled by the control unit 21 of the navigation system or by the control unit of the imaging system , depending on the way the position of the instrument is determined . the controlled parameters are : turn direction , number of turns , turn speed , turn acceleration and stop . the number of turns and the direction are parameters given by the computer and transmitted through the wireless protocol to the device . the device communicates with the computer through a wireless protocol , such as wifi or bluetooth or zigbee . in one preferred embodiment , the wireless communication is based on the bluetooth communication protocol . optionally , the communication can be also performed by standard wires with a standard wire and communication protocol such as usb , ethernet , ieee 1394 , rs232 , or a proprietary wire and communication protocol , and in that case the power supply is also brought by a cable . in a simple embodiment of the invention , the computer display indicates to the user the screw in which the screwdriver must be placed . when the user has placed the screwdriver in the head of the screw indicated on the screen , the user presses a button and the screwdriver moves the screw to the target position . the operation is repeated for each screw . if the user misses one screw the computer display shows which screw must be readjusted until the final position of the guide matches the target . for instance , the screw that has the most important number of turns to be accomplished is suggested to the user . or the screw are always adjusted in the same order , starting by screw 1 , then 2 , until screw n and the process is iterated by skipping screws that already reached the target position with a predefined limit . depending on the kinematic structure ( e . g . containing singularities ) some screws will have to be adjusted more than once in a defined order . in the case of the adjustment of a drill guide ( see fig1 , 12 , 16 ), the calculated data are transferred to the device 4 . using a rfid identifier , a single screw ( corresponding to one degree of freedom ) can now be adjusted in a defined way with the adjustment device in the positioning unit . once all degrees of freedom are adjusted this way , the drill guide 15 is aligned optimally to a target defined on images and a defined drilling can be carried out . fig2 b shows additionally a possible type of coding . using the identifiers 46 the correct device 4 or the corresponding correct stem 41 and tip 42 for the device 4 can be determined . this stem 41 engages in the screw head 130 . the tip 42 engages into the screw head cavity 131 which comprises a mechanical resistor element 133 . the coding is established by the shape of the screw head cavity 131 ( see fig3 b ). the term screwdriver is used without loss of generality . it means an external mechanism to turn a screw in a given direction . it is also possible to use several mechanisms to grab the screw head by friction or pressure only when a go button is pushed so that the screw cannot be turned manually when the device comes in contact with the screw head , which eliminates parasite motions of the screw . it is also possible to design a motorized screwdriver such that the handle contains only the stator part and the screw head contains the rotor part , or vice versa . in such mechanism , the handle of the screwdriver can be purely made of coils and it is easily covered by a sterile drape since it has no turning part . in this case , the screw head is a set of miniature coils . there exist many other adjustment devices principles that can be used to turn the screw with a handy device . advantageously , the adjustment device comprises detection means for determining the identification ( or code ) of the screw the tip is in contact with . depending on the various embodiments disclosed below , each screw possesses within the navigation system identification ( id ) means to distinguish it from the others . in one preferred embodiment , illustrated on fig3 , the adjustment device detects which screw the tip is in contact with by a mechanical solution . to that end , a thin rigid mechanical stem 50 is sliding inside the device stem 41 . by using the rigid mechanical link between the stem 50 , the body 54 , and the position cursor 51 , the contact between the sliding stem 50 and the screw &# 39 ; s head cavity 131 determines the value of the position sensor 52 . when the tip is not inserted into the screw &# 39 ; s head 130 , a spring 53 places the position sensor 52 at its default position . when the tip is in the screw &# 39 ; s head 130 , the position sensor 52 measures the depth d of the screw &# 39 ; s head cavity 131 . this depth is measured and transmitted to the control unit of the navigation system 2 by the wireless communication . each screw &# 39 ; s head cavity 131 has a different depth d , so that the position sensor delivers a different value for each screw , allowing the control unit of the navigation system to know which screw the device is about to activate . in another embodiment , illustrated on fig4 , the adjustment device detects which screw the tip is in contact with by an electrical solution . in this case , a resistance 60 is inserted into the screw &# 39 ; s head 130 linked by two electrical wires 61 , 62 respectively to two connectors 63 , 64 that are on the bottom surface of the screw &# 39 ; s head . in the device stem and tip are inserted two electrical wires 65 , 66 that are respectively connected to two connectors 67 and 68 that are on the extremity of the device tip . when the tip is in the screw &# 39 ; s head 130 , the connectors 63 and 67 are in contact , as well as the connectors 64 and 68 . it allows the device to measure the tension thanks to an ohmmeter 69 . this tension is measured and transmitted to the control unit of the navigation system by the wireless communication . each screw &# 39 ; s head has a different resistance value r , so that the ohmmeter 69 delivers a different value for each screw , allowing the control unit of the navigation system to know which screw the device is about to activate . in another embodiment , shown on fig5 , the adjustment device detects which screw the tip is in contact with by a magnetic solution . a magnet 70 is inserted into the screw &# 39 ; s head 130 . a “ hall effect ” sensor 71 is inserted into the device tip that delivers a tension that is dependent of the distance between the magnet 70 and the sensor 71 . this tension is measured and transmitted to the control unit of the navigation system by the wireless communication . each screw &# 39 ; s head has the same magnet but inserted at a different depth d , so that the sensor 71 delivers a different tension for each screw , allowing the control unit of the navigation system to know which screw the device is about to activate . in another embodiment , illustrated on fig6 , the adjustment device detects which screw the tip is in contact with by an optical solution . to that end , a cavity 131 is inserted into the screw &# 39 ; s head 130 . the bottom 132 of the cavity 131 is painted with a uniform color or with a pattern such as a bar code . a first optical fiber 80 carries light 81 from the device stem to the cavity 131 , in order to light the cavity 131 . a second optical fiber 81 carries the light 83 from the cavity to the device stem and then to an optical sensor such as a micro camera ( not shown ). the image delivered by the second optical fiber 82 is transmitted to the control unit of the navigation system by the wireless communication . each bottom 132 of screw &# 39 ; s head cavity 131 has a different color or different pattern , allowing the control unit of the navigation system to know which screw the device is about to activate . in another embodiment , shown on fig7 , the adjustment device detects which screw the tip is in contact with by a tracking solution . a tracker 90 is rigidly fixed to the device 4 . one knows by design the device tip position in the device tracker 90 coordinates system . one knows by design the screw &# 39 ; s head position in the instrument tracker 10 coordinates system . then , once the device tip is inserted into a screw &# 39 ; s head , the control unit of the navigation system 2 can determine which screw &# 39 ; s head the device tip is inserted in , allowing the control unit of the navigation system to know which screw the device is about to activate . if the accuracy of the navigation system is not sufficient , it can be compensated by adding a simple mechanical contact sensor that detects that the tip is in contact with the screw head . in another embodiment ( not illustrated here ), the adjustment device detects which screw the tip is in contact with by a software solution : before the device activation , the navigation system records the position of the instrument , called the initial position . when the user presses the activation button , the device turns as first step the stem in a constant known direction ( e . g . clockwise ). the navigation system then tracks the movement of the mobile part of the instrument . by taking into account the design of the screw , the design of the instrument , the given rotation direction and the number of turns that were applied , one can determine the unique screw that brought the instrument to this current position . then , once the screw id is determined by this first stem actuation , the device can then rotate the stem in the correct rotation direction with the correct number of turns to reach the target position . in all that precedes the control unit of the navigation can be replaced by the control unit of the imaging system , if a medical imaging system is used instead of a navigation system to define the target of the positioning unit . in the example where a navigation system is used , the surgical procedure flow diagram for adjusting the position of a cutting plane as shown on fig8 is composed of steps [ a ], [ b ], [ c ], [ d ] and [ e ] that are described in fig1 . [ a ] the control unit 21 computes the current position of the mobile part 12 of the positioning unit with respect to the solid 3 thanks to the instrument tracker 10 , the solid tracker 30 , and the localizer system . [ b ] if the current position is the target position then the procedure exits . [ c ] if the target position is not reached , then for each screw 13 i , where i is equal to 1 , 2 or 3 , the computer computes the unique number of turns ti that needs to be applied on 13 i , so that the mobile part 12 reaches the target position . ti is positive if the rotation direction is clockwise and negative if the rotation direction is counter - clockwise . for that computation , the computers needs to know the target position of the instrument , which is selected by the surgeon , the screws parameters ( diameter , thread length , thread thickness ), which are known by design , the screws positions on the instrument , which are known by design . [ d ] the navigation system instructs the user which screw needs to be activated : i . in one preferred embodiment , the user is instructed to place the device tip 42 on a given screw &# 39 ; s head . the computer displays on the screen which screw &# 39 ; s head the device tip 42 must be placed on . in one preferred embodiment , each screw &# 39 ; s head has a unique color , and the computer displays the color of the screw on the screen . in another embodiment , each screw &# 39 ; s head is labeled with a unique number ( such as 1 , 2 , 3 ), and the computer displays the number of the screw on the screen . in another embodiment , each screw &# 39 ; s head is labeled with a unique letter ( such as a , b , c ), and the computer displays the letter of the screw on the screen . screws can be also differentiated simply by their position on the instrument or by their shape . the user needs to follow the screws order displayed by the computer . ii . in another preferred embodiment , the user is instructed to place the device tip 42 on a given screw &# 39 ; s head . each screw &# 39 ; s head has a unique characteristic such as color , or number , or letter as detailed in ( i ). the computer computes on which screw &# 39 ; s head the device tip 42 must be placed on . the information is then transferred from the computer to the device by the wireless communication protocol . the device then instructs the user by displaying the information on itself , preferably on the top of the handle of the screwdriver . it can be by lighting some colored leds if screws are identified by a color , by lighting a letter if screws are identified by a letter , or by lighting a number if screws are identified by a number . the user needs to follow the screws order displayed by the computer or displayed on the handle of the screwdriver . iii . in another preferred embodiment , the user is not instructed to place the device tip 42 on a particular screw &# 39 ; s head . the user can independently choose any screw &# 39 ; s head , whatever the order is . the device detects when the tip is in contact or not of the screw &# 39 ; s head , and detects which screw it is in contact with , and communicates the screw id to the navigation system by the wireless communication protocol such that the adjustment necessary for that particular screw is known . alternatively , these parameters can be first stored in the driver . [ e ] then the user presses the button 43 to activate the adjustment device . if the device is used with automated detection of contact and identification of screw head , pressing a button is not necessary and the device is activated automatically . the device stem 41 then turns the given number of turns ti that was determined by the computer to reach the target position of the instrument . once the device stem 41 has turned the desired number of turns ti , the stem rotation stops , instructing the user that the target position for the screw 13 i has been reached . optionally , the navigation system 2 can check that the mobile part 12 has reached the desired position for that particular screw and if it is not the case , send an updated command to the screwdriver to add more portions of turn in order to adjust it accordingly and this process can be repeated until the position of the mobile part 12 has reached the desired position within a given arbitrary accuracy such as 0 . 2 mm for instance , which is done like a standard servoing mechanism . then the instrument position is updated and the process goes to step [ a ] for setting other screws to the desired positions . the global process is iterated until all screws have reached their desired position such that the mobile part is now in its final target position for all desired degrees of freedom . to reach a target screw position , there exist many possible methods to control the motors in order to optimize the speed of the process : a first method consists in measuring the position of the mobile part before the screw has reached its final position using the navigation system and iterating the command on the motors that take into account the measured position and the target position . standard control commands can be used to optimize the speed and convergence of such process , for instance using well known proportional integral derivative ( pid ) commands . another method consists in turning the motor in the right direction with an increasing speed and then decreasing speed when the motors reach the expected position and finally stopping the motor when it is very low speed so that the measurement taken with the navigation system can be done with averaging and the time delay to stop the device is compliant because of low speed . there exists many additional ways of optimizing the command by using the measurements of the final position of the mobile part using navigation system or by using the measurements of the motor controller that often provide the number of turns performed by the motor , with a division of such number by mechanical reduction . it is also possible to combine both measurements in real time in order to optimize and stabilize the convergence towards the target position . in some situations , the relationship between the screws is not independent , and it is therefore necessary to adjust some screws before adjusting other screws and coming back to the first screws to be able to reach the desired target . the system can easily predict those situations and optimize the paths between those maneuvers to limit the number of iterations . in a preferred embodiment , the positioning unit that is used in conjunction with ( a ) a navigation system or ( b ) a referencing unit and medical images uses a parallel mechanical architecture instead of a serial architecture . the advantage of a parallel architecture is the stiffness of the positioning unit such that the mobile part on which the guide or instrument is mounted has a stable relationship with respect to the anatomical structure for any position of the screws that activate individual degrees of freedom of the parallel architecture . a drawback of a parallel architecture is that it is usually difficult to adjust the screws manually and individually to reach a desired global position because each screw influences all parameters of the global position . degrees of freedom are strongly correlated together . however , using the adjustment device which positions automatically the screws to a defined position determined by the computer eliminates this drawback and only the advantageous aspects of this architecture remain . in a backup mode of functioning , the computer of the control unit simply displays to the user the number of turns to be applied on each screw . in a preferred embodiment , a ruler can be attached permanently or temporary to each screw to make it possible the adjustment of each screw without the adjustment device . the ruler can be integrated to the positioning unit ( see fig1 ) or can be provided directly on the screwdriver . according to a first advantageous embodiment of the invention , illustrated on fig9 - 12 , the adjustment device can be utilized in spine surgery performed with medical imaging . fig9 shows a detail of a spine 3 with several vertebral bones . an attachment unit 11 ′, which can be seen on side and upper views , is an percutaneous support having a general h shape for supporting a positioning unit for a drill guide ( not shown here ). the pins 31 are used for attachment of the attachment unit 11 ′ to the spine 3 . thanks to the flanges 32 , different positions for the attachment of the positioning unit and / or the referencing unit ( not shown here ) are possible . at the same time the flanges 32 can be used as x - ray visible markers . optionally , four screws 33 are used as an additional stabilization for support on the skin , whereas the screws 33 can be likewise designed as markers . fig1 depicts an attachment unit 11 ′ in different views . the top view shows a referencing unit 34 that is attached orthogonally to the fixed part 11 . this orthogonal referencing unit 34 comprises among others also squared markers 32 . in the top and middle views it can be seen positioning points which are designed as markers 32 . the bottom view illustrates a x - ray image which shows the spine 3 and markers 32 . fig1 shows a surgical positioning unit which is located at spine 3 . the attachment unit 11 ′ with the referencing unit 34 including the corresponding markers is flange mounted to the vertebrae via pins 31 . the fixed part 11 of the positioning unit is mounted on the referencing unit 34 ( not shown here ). the actuator elements of the positioning unit are four screws 13 that can adjust the mobile part 12 and thus the drill guide 15 in a defined way . a lower pair of screws 13 at fixed level z 1 moves a ball and socket joint 12 in a small plane to a defined target ( x 1 , y 1 ) in a limited range that constitutes a first small two - degrees of freedom parallel architecture . an upper pair of screws 13 at fixed level z 2 moves a ball and socket joint 12 in a small plane to a defined target ( x 2 , y 2 ) in a limited range that constitutes a second small two - degrees of freedom parallel architecture . the upper and lower pairs of screws 13 are connected on their basis and constitute a four - degrees of freedom positioning unit . the drill guide 15 is passing through the two points ( x 1 , y 1 , z 1 ) and ( x 2 , y 2 , z 2 ) which define a linear trajectory . acting on ( x 1 , y 1 ) with the first pair of screws and on ( x 2 , y 2 ) using the second pair of screws makes it possible to reach any linear target in a limited range . to that end x - ray images are acquired for the entity shown in fig1 and transferred to the computer . based on the markers determination , the position of the drill guide 15 can be determined . for this the positioning unit ( in zero position ), the drill guide 15 , the attachment unit 11 ′ including referencing unit 34 with markers 32 and the displayed parts of the spine 3 have defined positions to each other . in the present embodiment the operator has positioned the positioning unit already at the patient in such a way that the drill guide 15 must be modified only slightly . using the x - ray images available in the computer and the corresponding coordinates the operator determines the trajectory of the boring in the vertebra . the computer computes the adjustments of the drill guide 15 using the coordinates such that the extension of the drill guide 15 coincides with the planned boring in the vertebrae . as shown on fig1 , the adjustment device 4 is then operated to turn the screws 13 by the appropriate number of turns . fig1 shows an x - ray image of the attachment unit 11 ′ and the planned drilling bore 16 . a second advantageous embodiment of the invention , illustrated on fig1 - 17 , the adjustment device can be utilized in hip surgery performed with medical imaging . for the use of the surgical instrument the positioning unit must be attached to the object being operated ( here , the femoral head ). as one can see from fig1 and 15 , this is achieved by a clamp mechanism which is implemented by the attachment unit 11 ′. the attachment unit 11 ′ is flange mounted to the femoral head 3 of the bone , such that there is an essentially rigid connection . as one can deduce from the x - ray image in fig1 , the referencing unit 34 is flange mounted to the attachment unit 11 ′. the referencing unit 34 comprises additionally x - ray visible markers 32 , whereby two x - ray images ( e . g . lateral view and frontal view ) allow determining the coordinates in space . there are further functions that can be implemented via the markers 32 in particular the flange mounting of a unit with screws . for that purpose a boring for example can act as an essentially x - ray invisible material . with this boring a flange mounting is possible with screws . with the computer program shown in fig1 , the operator can define the exact trajectory of a boring 16 inside the bone or correspondingly in the femoral head 3 . thanks to the coordinates of the referencing unit 34 , which is designed as attachment unit at the same time , and the planned boring 16 , the computer which hosts the software program can determine the adjustment of surgical guide means ( not shown here ) using the mobile part ( not shown here ). fig1 shows a positioning unit 17 which comprises four degrees of freedom of adjustment for adjusting the surgical guide means ( which is here a drill guide 15 ). such a positioning unit 17 has a scale used to target positions in a defined manner that were computed before by the computer . the positioning unit 17 comprises a fixed part 11 that can be attached to the attachment unit , and a mobile part 12 that supports the drill guide 15 . the positioning unit 17 also comprises an upper plate 170 and a lower plate 171 and is provided with screws 13 that are able to move the mobile part 12 with respect to the fixed part 11 , thereby modifying the position and orientation of the drill guide 15 . in order to guaranty high accuracy , all four adjustments for the different degrees of freedom are reset to 0 . fig1 depicts the positioning unit 17 with the attachment unit 11 ′ as a detachable unit ( modular design ) which is hence directly flange mountable to the bone . a further embodiment of the attachment unit 11 ′ is shown in fig1 . a collar 110 embraces a femoral head 3 and is locked with three screws 111 . additionally the collar 110 comprises markers 32 for determination of the coordinates . using the attachments 112 the positioning unit can be connected to the attachment unit 11 ′. in another preferred embodiment , illustrated on fig7 and 8 , the surgical application is the total replacement of the knee joint ; the solid 3 is the patient &# 39 ; s tibia or the basis of the instrument fixed to the tibia , and the tracker 30 , rigidly fixed to the bone , allows the navigation system 2 to track the tibia ; the instrument 1 is a cutting block on which a cutting plane 14 must be aligned with the desired target plane selected by the surgeon ; the instrument mobile part position is adjustable by three screws ; the position of the three screws determine a unique position of the cutting block with respect to the fixed part 11 . the cutting plane position is defined by a slope angle , a varus / valgus angle , and a cut thickness with respect to the tibia . the target position is entered into the navigation system by the surgeon or set to default values with respect to anatomical landmarks digitized by the surgeon with the navigation system . the goal of the device is then to adjust the position of the cutting block to the target position . in one preferred embodiment , the surgical application is the total replacement of the knee joint ; the solid 3 is the patient &# 39 ; s femur or the basis of the instrument fixed to the femur , and the solid tracker 30 , rigidly fixed to the bone , allows the navigation system 2 to track the femur ; the instrument 1 is a cutting block on which a cutting plane 14 must be aligned with the desired target plane selected by the surgeon ; the instrument mobile part position is adjustable by three screws 13 ; the position of the three screws determine a unique position of the cutting block with respect to the fixed part 11 . the plane position is defined by a slope angle , a varus / valgus angle , and a cut thickness with respect to the femur . the target position is entered into the navigation system by the surgeon or set to default values with respect to anatomical landmarks digitized by the surgeon with the navigation system . the goal of the device 4 is then to adjust the position of the cutting block in the target position . in another preferred embodiment , not illustrated , the positioning unit is simply an adjustable spacer or distracter between two bones . a screw mechanism is used to move apart two parallel plates that generate a distance between two bones for ligament balancing check and optimization . for example , one plate is positioned in contact with the tibia and the other one is positioned in contact with the femur , and the distance between the plates is adjusted by one screw . alternatively , 2 pairs of plates are located on the external and on the internal parts of the knee , thus being adjusted by two screws . for adjusting quickly and precisely the spacer to a desired value , the actuated screwdriver is placed in the screw head and the number of turns is applied to obtain the desired distance . it must be noted that the referencing method ( navigation or medical imaging ) is independent from the surgical instrument and application . indeed , although knee surgery has been described with reference to a navigation system whereas hip resurfacing and spine surgery have been described with reference to an imaging system , the skilled person could practice knee surgery with an appropriate imaging system and hip resurfacing or spine surgery with a appropriate trackers of a navigation system . kosmopoulos v , schizas c ., pedicle screw placement accuracy : a meta - analysis , spine . 2007 ; 32 ( 3 ): e111 - 20 p . a . grützner , a . hebecker , h . waelti , b . vock , l .- p . nolte , a . wentzensen , 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