Patent Publication Number: US-2006015114-A1

Title: Robotizable system of motorized guide for operative instrumentations

Description:
The present invention concerns a system of motorized guide for surgical instrumentations, especially for arthroplasty and more particularly for knee surgery. In a very advantageous and therefore preferred embodiment of the invention, the guide system comprises an apparatus with at least four axes of linear moviment and at least a further rotational axis, said axes bringing about a system with six freedom degrees by exploiting the parallel kinematics.  
     PRIOR ART  
      In general the usual knee operations are carried out by utilizing a classic mechanical instrumentation which is manually piloted by the surgeon with the risk of imprecisions relative to the pre-operative planning (RX, plates).  
      At least two inconveniences can be encountered: 1)—the operative planning is per se little precise and therefore scarsely reliable; 2)—to this intrinsic imprecision of the operative planning must be added the imprecision of the instrumentation positioning. To obviate the first inconvenience, the use of a surgical navigator is being experienced, which should allow a planning in the course of the intervention (called pre-operative) through a kinematic analysis of the limb to be surgically operated. This corresponds to a passage from a static analysis to a kinematic analysis. The use of the (virtual) kinematic planning risks to loose its beneficial effects as long as a surgical instrumentation not-automatically (f.i; manually or half-manually) positionable is being used.  
      In addition to their imprecision susceptibility, the manual operations shows the further inconvenience of requiring very long times of execution.  
      International Patent Publication WO 98/40037 (corresp. To U.S. Pat. No. 6,385,475) describes a process and device for the preoperative determination of the positioning data of endoprosthetic parts in which a respective outer articular point is determinated by way of movement of the bones about a respective outer joint located at the end of the said bones facing away from the central joint.  
      According to an other Publication (WO 02/36031) the position of a knee prosthesis is determinated with a system comprising means for determining:—the shape of the tibia;—its position relative to the ankle joint;—a high point of the tibial plateau:—the position of the ankle;—the orientation and size of the tibial prosthesis etc. by taking into account several parameters such as the perpendicular to the section plane passing through the centers of the prosthesis and of the ankle joint.  
      EP 1079756 concerns an interactive computer-assisted surgical system using three-dimensional models of anatomical structures whose positions relative to a surgical tool are registered in real time.  
      Moreover the Prior Art cited in the European Search Report of the corresponding (not yet published) EP n° 04001424 consists of the four following references (classified A, i.e. technological background): U.S. Pat. No. 5,690,635 and U.S. Pat. No. 5,171,244, WO89/09570 and EP 0104732.  
      U.S. Pat. No. 5,690,635 describes system comprising bone immobilization and a robot including a base, a mounting member and a manipulator.  
      PCT-WO89/09570 describes an arrangement comprising:—an alignment instrument;—a first fixture for the trunk;—a second fixture for fixing the knee-joint and the tibia; and—a unit to control the measuring and cutting instruments.  
      U.S. Pat. No. 5,171,244 is concerned with a method of arthroscopic prosthesis knee replacement.  
      EP n° 0104732 describes an orthopedic bone cutting device to provide a surgeon with three freedom degrees of movement of said cutter.  
      The first object of the present invention is to provide a system which eliminates the Prior Art drawbacks.  
      An other object of the invention is to provide a system which is particularly efficient at least in terms of precision and duration, for the passage from the virtual planning (surgical navigator) to the relevant execution of the operative intervention.  
      A further object of the invention is a robot which incorporates in a very compact form, the system components and the relevant means of command and control f.i. by microprocessor. 
    
    
      The main characteristics of the invention will clearely appear from the embodiments represented in the accompanying drawings in which:  
       FIGS. 1 and 2 ′ are perspective views of the robotizable system according to the invention;  
       FIG. 2  is a side view of  FIG. 1 ; and  
       FIG. 3  is a cross section view with a plane having as a trace the line X-X in  FIG. 1 . 
    
    
      In the European Patent Publication EP n° 1410762 Applicant has described a “System and Method of orthopedic operations with no additional invasivity”, comprising an instrumentation for anchorage to the bone brought about with the aid of a device comprising:—a bracket;—at least one intercondylar pin also of fixation; and—means for the stationary application of said instrumentation.  
      In this patent application it is only fleetingly hinted at the possibility of using a robot to move a surgical instrumentation in particular of a cutting guide.  
      In the continuation of his researches, Applicant has found and developed a highly performing robotizable system of automated movement.  
      For illustrative clarity scruple it is convenient to refer (without introducing limitations) to the system according to the above mentioned European Patent Publication EP n° 1410762 the description and drawings of which are considered herewith incorporated.  
      In the perspective view of  FIGS. 1 and 2 ′ and in the side view of  FIG. 2 , as well as in the view of  FIG. 3  which is a cross-section with a plane having as trace the line X-X in  FIG. 1 , are represented:—a femur K;—an instrumentation for the anchorage to said femur, consisting of:—at least a bracket ME;—at leasat a shovel or grip  20 ;—at least two arms BRA and BRA′ associated to at least a rod AF;—at least a cortical screw FO-FV. For the movement of the cutting means GT are utilized motors MO and MV (for the horizontal respectively vertical movements).  
      According to a first feature of the invention, a helicoidal screw VO-VO′, VV-VV′ is now associated to each motor MO-MO′, MV-MV′, which screws while rotating move a translation block BT associated to said helicoidal screws VV-VV′ rotated by motor MV (MV′). A cutting guide GT is associated at the ends of said helicoidal screws VV and VV′.  
      With this simple system consisting of only two couples of motors MO-MO′, MV-MV′ and relevant screws a kinematic parallel movement of the cutting guide GT with five liberty degrees is brought about.  
      According to an other to feature of the invention, in order to reach the six degrees of freedom, which allow the total free spatial movement of the guide GT, a fifth motor MGT is added which puts in rotation according to arrow R (without translation) said cutting guide that now reaches the desired six freedom degrees.  
      Up to now the systems of automated movements were represented as comprised between or selected from the group consisting of the anthromorphous system of the ABB Company (which by the way has had no users in the operative practice) and the system known under the name Galileo of the Pi System AG which comprised only two motors and allowed the movement with only two freedom degrees.  
      With the system according to the invention we succeed, with the simple addition of only three (compact, cheap and reliable) micro-motors to surprisingly realize the total automation of the cutting guide reproducing thereby, with the maximal precision, the execution of the intervention virtual planning. Therefore the system of the present invention is characterized by a parallel kinematics i.e. a linear movement along at least four axes which are two by two parallel, with the addition of a further movement of sole rotation centered on the operation means, so bringing about a total movement with six freedom degrees.  
      Said system comprises therefore a first couple of motors each acting on a helicoidal screw, which carry out the linear movement at parallel kinematics in a first plane;—a second couple of motors each acting on a helicoidal screw, which realize the linear movement with a parallel kinematics in a second plane perpendicular to said first plane; and a fifth motor which carries out the rotatory movement of the cutting guide around its own axis.  
      According to the invention, the first couple of motors MO-MO′ is not mobile because it is rigidly fixed to the limb to be operated whereas the second couple of motors MV-MV′ is free to linearly translate in two perpendicualr directions. In said system of the invention is present a double driving block BT-BT′, each one of which moves relatively to the relevant motor MO-MO′ stationary during the block rotation, and represents the stationary part in respect to the mobile motors MV-MV′.  
      Therefore each driving block is animated with (i.e. is put in) a linear movement by one of the stationary motors and on its turn, animates with (i.e. puts in) a linear movement the mobile motor MV-MV′ as well as the fifth motor MGT.  
      The system according to the invention is preferably embodied in form of a robot.  
      To simplify its structure and working, the invention has been described with particular reference to the anchorage system according to Applicant&#39;s European Patent Publication EP n° 1410762. However the invention is not restricted to said anchorage system and obviously comprises all the changes, substitutions, variants and the like which, being in the reach of the mean technician of this Art, fall naturally within the scope and spirit of the present invention. For instance, at least a portion of the motors and other mobile elements can be manually activated.