Abstract:
A surgical instrument support is provided having an articulated arm with first structure on a proximal end of the arm. A lockable target ball is rotatably mounted on a distal end of the articulated arm, and the lockable ball has a diametric hole therein for receiving and supporting a surgical instrument. A mount has second structure that receives and secures the proximal end of the articulated arm. The first structure on the articulated arm cooperates with the second structure on the mount to automatically align the proximal end of the articulated arm with the mount in a repeatable relationship. The mount is adapted to be releasably attached to a fixed structure. Thus, after establishing a desired alignment of the lockable ball to a patient, the articulated arm can be removed from the fixed structure and then subsequently remounted therein without losing the desired alignment of the lockable ball with the patient.

Description:
FIELD OF THE INVENTION 
     This invention relates to neurosurgical apparatus generally, and more particularly, to an improved surgical instrument support. 
     BACKGROUND OF THE INVENTION 
     It is known to define and correlate the position of single or multiple points within the cranium with preoperative imaging by using frameless stereotactic systems such as the MAYFIELD/ACCISS Stereotactic Workstation which is commercially available from the assignee of this application. Frameless systems provide constant intraoperative navigational information, which permits a surgeon to identify precisely the spacial position of a probe in the surgical field with CT or MRI scan data shown on a high definition display monitor. 
     With a frameless stereotactic system, an intracranial target point is accessed by advancing a probe along a predetermined linear path or trajectory to the target point within the patient&#39;s skull. To provide the necessary stabilization of tooling during its advance along the linear trajectory, a surgical instrument support is used. The surgical instrument support is comprised of an articulated arm having a proximal end mounted on a patient support or other fixed structure and a lockable tool socket rotatably mounted on a distal end of the arm. The surgical instrument support allows a surgical instrument to be moved to the intracranial target point along a stable and fixed linear trajectory. By fixing the trajectory on the intracranial target point, the risk of misdirection or drift associated with freehand procedures is eliminated. 
     One example of a known surgical instrument support is the “EASYGUIDE” navigator system commercially available from Phillips Medical Systems N.A. Inc. of Shelton, Connecticut. Another example of a surgical instrument support is commercially available from the assignee of the present invention. Other examples of known surgical instrument supports are shown in U.S. Pat. Nos. 5,695,501 and 5,810,712, which are assigned to the assignee of this invention and hereby expressly incorporated by reference herein. All of these devices include a lockable ball rotatably mounted in a tool holder on the end of an articulated arm as described above. The ball has a diametric hole that receives an instrument. In a known manner, a known locating probe is inserted into the ball with the tip of the probe normally being positioned substantially at the center of the ball. The probe presents a linear image on a display monitor that is also displaying CT or MRI scan data of the patient. Thus, as the probe is moved, a path between the tip of the probe and a selected target point displayed with the scan data can be tracked. By moving the distal end of the articulated arm, the probe and ball are first located at a desired position with respect to the skull that defines a desired trajectory between the tip of the probe and the target point. The articulated arm is then locked, thereby locking the ball at the desired position. Next, the probe and ball are rotated to align a centerline of the hole in the ball with the desired trajectory, so that an instrument inserted through the hole in the ball follows the desired trajectory and intersects the target point. The ball is then locked in place, so that it cannot rotate with respect to the tool holder on the distal end of the articulated arm; and hence the orientation of the probe or other tool within the ball is fixed with respect to the target point. With the ball thus aligned, the probe is removed and other surgical instruments inserted into the ball are automatically aligned with the intracranial target point. 
     While these prior art devices have proved suitable for their intended purposes, they all have one particular disadvantage. In the above described process, after the surgeon has established the desired trajectory by locking the articulated arm and ball in place, the articulated arm and ball can interfere with procedures that are being conducted within the surgical field that do not require the presence of the articulated arm and ball. Thus, it is often desirable and sometimes necessary to move the articulated arm and ball from the surgical field. With known devices, any attempt to move the articulated arm and ball results in a loss of the desired trajectory that had been previously determined, thus requiring that the surgeon repeat the alignment process by which the desired trajectory was originally determined. 
     Therefore, there is a need for an improved surgical instrument support that can be moved from the surgical field and subsequently returned to its initial position without losing a previously established desired trajectory with respect to an intracranial target point. 
     SUMMARY OF INVENTION 
     The present invention provides an improved surgical instrument support that offers more flexibility than known instrument holders. The surgical instrument support of the present invention permits difficult surgical procedures to be performed in less time and with less stress, that is, more efficiently, and without any loss in accuracy or precision. The surgical instrument support of the present invention has the advantage of being able to automatically re-establish a desired alignment of the instrument support after it has been removed from its fixed mount. The invention is especially useful in those situations where after aligning the instrument support with a patient, it is necessary to perform procedures in the surgical field that do not require the surgical instrument support. With the surgical instrument support of the present invention, once its desired position and orientation are precisely aligned with the patient, it can be removed from the surgical field and then, upon being placed back into its mount, the desired position and orientation are automatically re-established without repeating the original alignment process. 
     In accordance with the principles of the present invention and the described embodiments, a surgical instrument support is provided having an articulated arm with a first structure on a proximal end of the arm. A lockable target ball is rotatably mounted on a distal end of the articulated arm. The lockable ball has a diametric hole therein for receiving and supporting a surgical instrument. A mount has a second structure that receives and secures the proximal end of the articulated arm. The first structure on the articulated arm cooperates with the second structure on the mount to automatically align the proximal end of the articulated arm with the mount in a repeatable relationship. The mount is adapted to be releasably attached to a fixed structure. 
     In one aspect of the invention, the proximal end of the articulated arm has a cross-sectional profile, and the mount has a hole with a cross-sectional profile that receives the proximal end of the articulated arm in a repeatable relationship. The mount further has a clamp for securing the proximal end of the articulated arm in the hole in the mount. In a further aspect of the invention, the cross-sectional profiles of the first and second structures are noncircular profiles. Thus, the surgical instrument support of the present invention permits removal and remounting of the articulated arm without losing the desired position and orientation of the lockable target ball with respect to a patient. 
     In another embodiment, the present invention includes a method of performing a surgical procedure that includes first moving a distal end of an articulated arm having a target ball rotatably mounted therein to a desired position. The joints of the articulated arm are locked to maintain the target ball at the desired position. Next, the target ball is rotated to a desired orientation, and the target ball is locked at the desired orientation. The proximal end of the articulated arm is then unclamped from a mount attached to a fixed structure. The proximal end of the articulated arm has a desired relationship with respect to the mount, and the proximal end of the articulated arm is removed from the mount. The articulated arm is then inserted into the mount such that first structure on the articulated arm cooperates with second structure on the mount to automatically align the proximal end of the articulated arm with the mount in the desired relationship. Thus, the target ball is automatically placed at the desired position and the desired orientation. 
     Various additional advantages, objects and features of the invention will become more readily apparent to those of ordinary skill in the art upon consideration of the following detailed description of the presently described embodiments taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a surgical instrument support in a first application in accordance with the principles of the present invention. 
     FIG. 2 is a partial cross-sectional view of the mount taken generally along the line  2 — 2  of FIG.  1 . 
     FIG. 3 is a partial cross-sectional view of the mount taken generally along the line  3 — 3  of FIG.  2 . 
     FIG. 4 is a partial perspective view illustrating the coupling between the proximal end of the articulated arm and the mount of FIG.  1 . 
     FIG. 5 is a perspective view of the invention in a second application in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a surgical instrument support  20  is mounted on a surgical skull clamp  22  that is supporting the head  24  of a patient. The skull clamp  22  is mounted at the end of a patient support, for example, an operating table, (not shown) in a known manner. The surgical tool support  20  includes an articulated arm  28  having a distal end  30  connected to a tool holder  32  and a proximal end  34  connected to a mount  36 . The articulated arm  28  is comprised of two links  38 ,  40  that have ends rotatably connected together to form a pivot joint  42 . An opposite end of the link  38  is connected to an end of a shaft  44  of the tool holder  32  via a ball and socket joint  46  such that the end of the shaft  44  can rotationally swivel with respect to the end of the shaft  38 . Similarly, the opposite end of the second link  40  is connected by a ball and socket joint  48  to the proximal end  34 , thereby permitting the articulated arm  28  to rotationally swivel with respect to the proximal end  34 . The pivot joint  42  and swivel joints  46 ,  48  are clamped and unclamped by rotating a knob  50 . The assembly of the pivoting links  38 ,  40  with the swivel joints  46 ,  48  is commercially available as a tool holder from J&amp;L Industrial Supply of Plainview, N.Y. The tool holder  32  with shaft  44  is commercially available as an “ACCUPOINT” tool holder from Ohio Medical Instrument Company of Cincinnati, Ohio. For this invention, the end of the shaft  44  of the ACCUPOINT tool holder has been fitted with a ball (not shown) which is assembled into the swivel joint  46  in a known manner; and the proximal end  34  has a ball (not shown) which is assembled into the swivel joint  48  in a known manner. 
     Referring to FIG. 2, the mount  36  includes first and second blocks  52 ,  54  slidably mounted on a relieved or smooth portion  56  of a shaft  58 . A knob  59  is rigidly connected to one end of a shaft  58 , and a bearing washer  60  is located on the shaft  58  between the lower surface  62  of the knob  59  and an outer surface  64  of the block  54 . The block  52  is prevented from moving over the threaded portion  66  of the shaft  58  by a lock ring  67  mounted on the shaft  58  in a known manner. The smooth portion  56  of the shaft  58  has a length permitting the blocks  52 ,  54  to slide axially with respect to each other. A biasing element  68 , for example, a compression spring, is mounted over the shaft  58  between the blocks  52 ,  54  and biases the blocks away from each other such that a small gap is formed therebetween, for example, of approximately 0.100 inches. At least one guide pin  70  (FIG. 3) is pressed into one of the sliding blocks, for example, the block  54 , and slidingly engages a bore  72  in the other block  52 . The guide pin  70  and bore  72  function to prevent the blocks  52 ,  54  from rotating with respect to each other on the shaft  58 . Normally, a pair of guide pins  70  and bores  72  are used. The block  52  has a known annular toothed or starburst connector  74  on its outer end. Such a starburst connector is normally a circular structure in which the connector portion is an annular ring of adjacent, radially extending serrations or teeth. 
     Upon rotating the knob  59 , for example, clockwise, the threaded portion  66  of the shaft  58  is threaded into a center hole  81  of a starburst connector  82  mounted on a Kant Twist clamp  83 . The starburst connector  74  is brought into mating contact with the starburst connector  80 , thereby securing the mount  36  to the Kant Twist clamp  83 . The blocks  52 ,  54  have respective first and second structures  76 ,  78 , for example, opposed U-shaped channels, that together form a hole having a substantially square, cross-sectional profile or shape. The cross-sectional profile of the structures  76 ,  78  match and receive the structure  80  (FIG. 4) on the proximal end  34  of the articulated arm  28 . The structure  80  has a substantially square, cross-sectional profile or shape that slides into the combined structures  76 ,  78 . Further rotation of the knob  59  moves the block  54  toward the block  52 , thereby clamping the proximal end  34  of the articulated arm  28  between the blocks  52 ,  54 . As the knob  59  is rotated in an opposite direction, for example, counterclockwise, the block  54  is separated from the block  52  by the compression spring  68 , thereby releasing the proximal end  34  of the articulated arm  20  prior to the starburst connectors  74 ,  80  separating. Thus, the structure of the mount  36  permits the articulated arm  28  to be removed from the mount  36  without disturbing the mechanical connection of the mount  36  to a fixed element, for example, the Kant Twist clamp  83 . 
     In use, the mount  36  can be attached to a Kant Twist clamp  84  as illustrated in FIG. 1 or, alternatively, connected to a starburst connector  86  (FIG. 5) on the base of the skull clamp  22 . Next, rotating the knob  59 , the threaded portion of the shaft  58  is threaded into a center hole (not shown) of one of the starburst connectors  82 ,  86  in a known manner. The knob  59  is rotated until the starburst connector  74  on the mount  36  is engaged with its mating starburst connector  82 ,  86  in the desired manner. This is achieved by rotating the knob  50  until the starburst connectors are brought together. At this point, the compression spring  68  continues to hold the blocks  52 ,  54  apart, thereby facilitating the insertion of the square shaft  80  (FIG. 4) of the distal end  34  of the articulated arm  28  into the hole formed by the structure  76 ,  78  of the blocks  52 ,  54 . 
     The distal end  34  of the articulated arm  28  is properly seated in the mount  36  when a locating surface  90  (FIG. 4) on the proximal end  34  of the articulated arm  28  contacts a stop surface  92  on the mount  36 . The locating surface  90  is a generally annular surface surrounding the structure  80  and is located in a plane substantially perpendicular to a longitudinal centerline  93  of the structure  80 . Similarly, two substantially coplanar and flat surfaces  93  on each of the blocks  52 ,  54  form the generally annular stop surface  92  that surrounds the structure  76 ,  78  of the respective blocks  52 ,  54 . With the proximal end  34  of the articulated arm  28  properly seated in the mount  36 , the knob  50  is again rotated to move the blocks  52 ,  54  together, thereby clamping the proximal end  34  of the articulated arm  28  to the mount  36 . 
     Thereafter, in a known manner, referring to FIG. 1, the articulated arm is manipulated to bring the tool holder  32  to a desired position with respect to the head  24 . The locking knob  50  is rotated to lock the pivot joint  42  and swivel joints  46 ,  48 , thereby locking the tool holder  32  in its desired position. The target ball  96  is then rotated until the desired trajectory with the intracranial target point is achieved, and the target ball is locked at its desired orientation by rotating the locking knob  98 . 
     The surgical instrument support  20  is now at its desired position to perform a surgical procedure. However, prior to the procedure, or as a part of the procedure, it may be necessary to perform other procedures in the surgical field that do not require the presence of the surgical instrument support  20 . The surgical instrument support  20  often interferes with the performance of such procedures, and it is desirable and sometimes necessary to move the surgical instrument support  20  from its previously aligned position. With known systems, any attempt to move or remove the surgical instrument support  20  from the aligned position results in a loss of that alignment. However, with the present surgical instrument support, the clamping knob  59  is rotated in a direction to loosen or separate the blocks  52 ,  54 . As the knob  59  is rotated, for example, one revolution, the biasing element  68  separates the block  54  from the block  52  without permitting the starburst connector  74  to separate from a mating connector  82 ,  86 . Thus, the distal end  34  of the articulated arm is released from the mount  36  while the mount  36  remains connected to a fixed element. 
     The distal arm can then be removed from the clamp  36  for any desired period. When the distal arm  28  is again required, the structure  80  having the substantially square, cross-sectional profile is inserted into the structure  76 ,  78  forming the generally substantially square hole (FIG.  4 ). The substantially square, cross-sectional profiles of the structures  76 ,  78 ,  80  cause the proximal end  34  of the articulated arm  28  to automatically align with the mount  36  in a desired relationship that existed when the articulated arm  28  was removed from the clamp  36 . Further, the seating of the locating surface  90  onto the stop surface  92  further guarantees that the articulated arm  28  is exactly in the same relationship that it had with respect to the mount  36  before the articulated arm  28  was removed therefrom. The knob  59  is again tightened, thereby moving the block  54  toward the block  52  and clamping the distal end  34  of the articulated arm  28  in the mount  36 . As will be appreciated, such a capability would not be possible if the structure  80  and mating on the distal end  34  of the articulated arm  28  and the mating structure  76 ,  78  had only a circular, cross-sectional profile. 
     Thus, the present invention provides an improved surgical instrument support that offers more flexibility than known instrument holders. The surgical instrument support of the present invention permits difficult surgical procedures to be performed in less time and with less stress, that is, more efficiently, and without any loss in accuracy or precision. The invention is especially useful in those situations where after aligning the instrument support with a patient, it is necessary to perform procedures in the surgical field that do not require the surgical instrument support. With the surgical instrument support of the present invention, once it&#39;s desired position and orientation are precisely aligned with the patient, it can be removed from the surgical field and then, upon being placed back into its mount, the desired position and orientation are automatically re-established without repeating the original alignment process. 
     While the present invention has been illustrated by a description of various described embodiments and while these embodiments have been described in considerable detail in order to describe the best mode of practicing the invention, it is not the intention of Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the spirit and scope of the invention will readily appear to those skilled in the art. For example, in the described embodiment, the structure  76 ,  78  of the mount  36  and the mating structure  80  on the proximal end  34  of the articulated arm  28  have substantially square, cross-sectional profiles. As will be appreciated, the invention is effective if those components have structure with any cross-sectional profile that causes the proximal end of the articulated arm to automatically align in the desired relationship with the mount  36 . For example, other multi-lateral, cross-sectional profiles such as triangular, hexagonal, octagonal, etc., cross-sectional profiles are effective. Further, arcuate cross-sectional profiles that include a circular shaft with a key, spline or other angular positioning feature, may also be used. In addition, the cross-sectional profiles may be non-circular, for example, elliptical in nature. The features  76 ,  78  of the clamp  36 ,  80  of the distal end  34  of the articulated arm  28  may also taper axially. 
     As will be appreciated, it is also not necessary that the cross-sectional profiles of the feature  80  on the proximal end  34  of the articulated arm  28  be identical to the cross-sectional profile of the features  76 ,  78  of the mount  36 . For example, the cross-sectional profile of the feature  80  may be elliptical; and the cross-sectional profile of the features  76 ,  78  of the mount  36  may be multi-lateral, for example, rectangular. In the described embodiment, the features  76 ,  78  of the blocks  52 ,  54  fully surround the feature  80  on the distal end  34  of the articulated arm  28 . As will be appreciated, the features  76 ,  78  do not have to fully surround the feature  80  but merely contact the feature  80  sufficiently to provide the desired alignment and clamping features. 
     Therefore, the invention in its broadest aspects is not limited to the specific detail shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.