Abstract:
A surgical headframe for maintaining a stereotactic system reference frame relative to a patient&#39;s head. The headframe includes a frame body, first and second arms, a plurality of contact pads, and a strap. The first and second arms extend from opposing sides of the frame body, respectively. The plurality of contact pads are coupled to the frame body and are each adapted to engage a patient&#39;s head. The strap is selectively connectible to the first and second arms. In this regard, the strap is adapted for wrapping about a back of a patient&#39;s head. The surgical headframe is capable of precisely positioning and fixating the reference frame to the patient&#39;s head during these stereotactic procedures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit, and incorporates by reference the entirety of, U.S. Provisional Application Ser. No. 60/235,215, filed Sep. 4, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a headframe for use with a stereotactic system. More particularly, it relates to a surgical headframe for accurate, non-traumatic (non-invasive) positioning (fixation) of a reference frame to a patient as part of a stereotactic system, especially a tandem optical stereotactic device. 
     Stereotactic surgical systems provide surgeons with visual guidance information of surgical instruments/probes relative to an enclosed anatomical position, especially within the cranium or head. Basically, a stereotactic surgical system provides a quantitative determination of an anatomical position based upon a scanned image, such as a CAT scan, MRI scan, PET scan, etc. This scanned information is processed by a computer to produce a displayable image of the head. Subsequently, during a surgical procedure, the stereotactic system relates a position of a surgical instrument otherwise deployed within the anatomical body of interest (e.g., the head) relative to the previously-generated scanned information in visual form. 
     Stereotactic devices are highly useful in the field of neurosurgery, and more recently ENT procedures requiring instrument deployment in close proximity to the optic nerve, carotid artery, skull base, facial nerve, internal auditory canal, etc. A more recent stereotactic system is optical or camera based in which two cameras are employed to visualize special instruments in a surgical field, digitize the viewed information from the camera and relate it via computer graphics to image data generated by the above-described image scanning techniques. The relationship of the optical camera(s) view and the image data will then make quantitative the anatomy seen in the camera view and also make quantitative the position of surgical instruments such as probes, microscopes, or space pointers, etc., relative to the anatomy via registration of the camera view to the image data. An example of such a tandem optical, stereotactic device is available under the trade name Landmar™ ENT Image Guidance System, from Medtronic-Xomed of Jacksonville, Fla. 
     Regardless of the exact stereotactic configuration, a stereotactic or dynamic reference frame must be fixed to the patient&#39;s head to provide accurate positioning information. A wide variety of headframes or headframes have been developed to facilitate fixation of the reference frame to the patient&#39;s head. In this regard, important constraints relating to the headframe design include precise positioning of the reference frame relative to the patient&#39;s head, relatively long-term fixation, and allowing for movement of the patient&#39;s head without deviation of a position of the reference frame relative to the head during the surgical procedure. In light of these constraints, many of the available stereotactic headframes incorporate one or more bone screws or bone pins to physically secure the headframe to the skull. Obviously, this is highly invasive, and contrary to the minimally invasive nature of intended procedures. Alternatively, other stereotactic headframes are tightly clamped to the patient&#39;s head. Due to the possibility of headframe movement along the patient&#39;s skin, the clamping device(s) is typically very rigid, again causing discomfort to the patient under extended usage. 
     Surgical stereotactic systems continue to rapidly evolve with improvements to imaging and display components. However, the headframe apparatus has essentially remained unchanged, and is unacceptably bulky and invasive or traumatic. Therefore, a need exists for an improved surgical headframe for use with a stereotactic system. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a surgical headframe for maintaining a stereotactic system reference frame relative to a patient&#39;s head. The headframe includes a frame body, first and second arms, a plurality of contact pads, and a strap. The first and second arms extend from opposing sides of the frame body, respectively. The plurality of contact pads are coupled to the frame body and are each adapted to engage a patient&#39;s head. Finally, the strap is selectively connectible to the first and second arms. In this regard, the strap is adapted for wrapping about a back of a patient&#39;s head. With this construction, the surgical headframe is capable of precisely positioning and fixating the reference frame to the patient&#39;s head during a stereotactic procedure, without requiring bone screws, bone pins or clamps. In one preferred embodiment, three contact pads are provided, and are arranged in a tripod-like fashion. In a further preferred embodiment, the contact pads are pivotally coupled to the frame body, and are co-planer. With this preferred construction, the headframe is highly stable when applied to the patient&#39;s head. In yet another preferred embodiment, a control pad is mounted to the frame body. 
     Yet another aspect of the present invention relates to a method of securing a reference frame to a patient&#39;s head as part of a surgical procedure. The method includes providing a surgical headframe having a frame body, first and second arms, a plurality of contact pads, and a strap. The first and second arms extend from opposing sides of the frame body. The contact pads are coupled to the frame body. Finally, the strap is selectively securable to the first and second arms. With this in mind, the reference frame is mounted to the headframe. The headframe is then positioned at the patient&#39;s head such that the contact pads contact the patient&#39;s head. The strap is then wrapped behind the patient&#39;s head. Finally, the strap is secured to the first and second arms. In one preferred embodiment, the first and second arms are rotatably mounted to the frame body, thereby reducing moment forces generated by extension of the strap about the patient&#39;s head from being transmitted to the patient&#39;s forehead and serve to increase user comfort. 
     Yet another aspect of the present invention relates to a method of manufacturing a surgical headframe for use in a stereotactic procedure. The method includes providing a frame body having a central portion and opposing sides. First and second arms are extended from the opposing sides of the frame body, respectively. A plurality of contact pads are coupled to the frame body. In this regard, each of the contact pads are adapted to engage a patient&#39;s head. Finally, a strap is selectively secured to the first and second arms opposite the frame body. To this end, the strap is adapted for wrapping about a back of a patient&#39;s head. Upon final assembly, the headframe is adapted to receive and maintain a stereotactic reference frame. In one preferred embodiment, a first contact pad is coupled to the central portion of the frame body, and the second and third contact pads are positioned opposite one another relative to the first contact pad. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a surgical headframe in accordance with the present invention applied to a patient; 
     FIGS. 2A-2C illustrate a frame body of the headframe of FIG. 1; 
     FIGS. 3A-3B illustrate a swivel arm portion of the headframe of FIG. 1; 
     FIG. 4 illustrates a strap portion of the headframe of FIG. 1; 
     FIG. 5 is a cross-sectional view of a contact pad; 
     FIGS. 6 illustrates contact pads assembled to the frame body; 
     FIG. 7 illustrates assembly of the swivel arms to the frame body; and 
     FIG. 8 illustrates auxiliary components assembled to the headframe of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of a surgical headframe  10  is provided in FIG. 1 as applied to a patient  11 . Although not illustrated, it will be understood that the surgical headframe  10  is for use with a stereotactic image guidance system (not shown), an example of which is available under the trade name LandmarX® from Medtronic-Xomed. With this in mind, the headframe  10  includes a head frame body  12 , swivel arms  14 , a strap  16 , and contact pads  18   a - 18   c . Details on the various components are provided below. In general terms, however, the head frame body  12  is configured for placement about a patient&#39;s skull. The swivel arms  14  extend from opposite sides of the frame body  12 , respectively. The strap  16  is connected to, and extends between, the swivel arms  14   a ,  14   b . Finally, the contact pads  18   a - 18   c  are secured to the frame body  12  as shown, positioned to precisely fixate the headframe  10  relative to the patient&#39;s skull. As a point of reference, and as described elsewhere, the surgical headframe  10  is preferably configured to receive and rigidly maintain a dynamic reference frame (not shown), such as at a post or lug  20  otherwise formed by the frame body  12 . 
     The frame body  12  is shown in greater detail in FIGS. 2A-2C. The frame body  12  is preferably formed from a rigid, light-weight material, such as aluminum, and forms the post  20 , a central portion  30 , a first leg  32 , and a second leg  34 . The first and second legs  32 ,  34  extend in opposite directions from the central portion  30 , and are preferably identical in construction. In this regard, each of the arms  32 ,  34  includes a first section  36  and second section  38 . The first section  36  extends in an angular fashion from the central portion  30 . The second section  38  extends downwardly from the first section  36  (or rearwardly relative to the orientation of FIG. 2A) and defines an arm receiving region  40  and a pad receiving region  42 . The arm receiving region  40  is configured to receive a respective one of the swivel arms  14  (FIG. 1) at an engagement surface  58  via a lateral passage  44  formed therein. Similarly, the pad receiving region  42  is configured to receive a respective one of the contact pads  18  (FIG. 1) via a transverse bore  46  (best shown in FIG.  2 C). Notably, and as best shown in FIG. 2B, the central portion  30  similarly forms a transverse bore  48  for mounting of one of the contact pads  18  (FIG.  1 ). The frame body  12  is highly planar or flat at an inner surface  50  thereof. That is to say, regardless of how the legs  32 ,  34  are formed relative to the central portion  30 , the frame body  12  is, as a whole, planar at the inner surface  50 . This preferred configuration is illustrated in FIGS. 2B and 2C. As a result, the contact pads  18 , otherwise assembled to the respective passages  46 ,  48 , are similarly oriented in a planar fashion. Further, and returning to FIG. 2A, the transverse bores  46  are equidistantly spaced relative to the central portion  30 , and thus relative to the transverse bore  48  formed therein. This configuration effectively positions the subsequently assembled contact pads  18  in a triangular or tripod-type configuration relative to the frame body  12 . As described in greater detail below, this tripod configuration provides increased lateral stability when the headframe  10  is secured fixed to a patient. 
     In one preferred embodiment, the frame body  12  has an overall width (i.e., distance between the respective second sections  38  of the legs  32 ,  34 ) of 4.125 inches and a height (i.e., distance between pad receiving region  42  and central portion  30 ) of 2.25 inches. These preferred dimensions correspond generally with the spacing of an adult forehead. Alternatively, however, other dimensions are equally acceptable. Finally, the post  20  extends in a perpendicular fashion (relative to the inner surface  50 ) from an outer surface  52 . In one preferred embodiment, the post  20  includes an auxiliary frame receiving body  54  including a central passage  54  and a starburst or toothed surface  56 . 
     One of the swivel arms  14  is shown in greater detail in FIGS. 3A and 3B. The swivel arm  14  is preferably integrally formed from a rigid, light-weight material, such as aluminum, and is defined by a base  60 , an intermediate section  62 , and a leading end  64 . The base  60  is configured for mounting to the frame body  12  (FIG. 2) and defines an inner face  66  through which a passage  68  transversely extends. As best shown in FIG. 3B, the base  60  extends transversely relative to the intermediate section  62 . In other words, the inner face  66  is non-contiguous with a corresponding surface of the intermediate section  62  such that the inner face  66  is non-planar relative to the intermediate section  62 . In one preferred embodiment, relative to a plane defined by the intermediate section  62 , a plane of the inner face  66  extends at an angle of approximately 32°, although other dimensions are equally acceptable. Regardless, the inner face  66  is configured to abut a corresponding surface of a respective one of the arm receiving regions  40  (FIG. 2A) previously described, for example the engagement surface  58  (FIG.  2 A). The angular orientation of the inner face  66  relative to the intermediate section  62 , as well as the angular extension of the intermediate section  62  relative to the base  60 , facilitates extension of the swivel arm  14  along a side of a patient&#39;s head (not shown), as well as allowing the swivel arm  14  to rotate in the plane of the inner face  66 . 
     The intermediate section  62  is depicted in FIG. 3A as including opposing shoulders  70  which are provided to receive and maintain auxiliary components (not shown). Alternatively, where the auxiliary components are unnecessary or are secured to other portions of the headframe  10 , the shoulders  70  can be eliminated. Finally, the leading end  64  forms an opening  72  for receiving a pin (not shown) for securing the strap  16  (FIG. 1) to the swivel arm  14 . 
     The strap  16  is shown in greater detail in FIG.  4 . The strap  16  is preferably formed of an elastic material, preferably silicone, and includes strips  80   a ,  80   b  extending in an opposing fashion from a central region  82 . As described below, the strap  16  is preferably sized for wrapping about a patient&#39;s head (not shown), and preferably has an overall length on the order of 21 inches. Each of the strips  80  forms holes  84 , sized for coupling to a pin (not shown) otherwise mounted to a respective one of the swivel arms  14  (FIG.  3 ). The central region  82  preferably has an increased width relative to that of the strips  80 , and is sized for placement over, or to straddle, the occipital bone. Alternatively, other configurations are equally acceptable. 
     One of the contact pads  18  is shown in greater detail in FIG.  5 . The contact pad  18  is preferably formed from a soft, autoclavable material, such as silicone, and defines an inner surface  90 , a rim  92 , and a contact surface  94 . An opening  96  is formed through the inner surface  90  and is configured to receive a coupling device (not shown) for attachment to the frame body  12  (FIG.  2 A). As described below, a ball joint or ball and socket device (not shown) is preferably used to pivotally couple the contact pad  18  to the frame body  12 . In this regard, the opening  86  is sized to receive a portion of the coupling device in a manner that allows convenient disassembly therefrom, such that after use, the contact pad  18  can easily be removed and discarded or recycled, with the coupling device available for re-use following appropriate cleaning/sterilization. The rim  92  defines an outer diameter of the contact pad  18 , preferably approximately  2  inches in diameter, it being understood that a wide variety of other dimensions, either greater or smaller, are equally acceptable. The contact surface  94  extends in a generally concave fashion from the rim  92 . With this curved configuration, in conjunction with the durometer of the material selected for the contact pad  18 , optimal comfort is provided to the patient, while providing maximum stability. 
     Assembly of the contact pads  18  to the frame body  12  is best shown in FIG.  6 . As previously described, in a preferred embodiment three of the contact pads  18   a - 18   c  are provided and are secured to the central portion  30  and the opposing pad receiving regions  42 , respectively. For example, in one preferred embodiment, a ball joint (not shown) is employed to mount a respective one of the contact pads  18   a - 18   c  to the frame body  12 , with the ball portion being coupled to the transverse bores  46 ,  48  (FIG. 2C) otherwise formed by the frame body  12 . With this one preferred mounting technique, each of the contact pads  18   a - 18   c  can be maneuvered or swiveled relative to the frame body  12  so as to accommodate a particular patient&#39;s head shape. Regardless of the exact mounting technique, the contact pads  18   a - 18   c  are arranged in a triangular or “tripod” fashion, with the contact pads  18   a ,  18   c  being equidistantly spaced from the contact pad  18   b . This triangular arrangement of the contact pads  18   a - 18   c  provides greatly enhanced lateral stability relative to a two-pad design, thereby restricting overall motion of the individual contact pads  18 . 
     Assembly of the swivel arms  14  to the frame body  12  is shown in greater detail in FIG.  7 . In particular, each of the swivel arms  14  is mounted to the frame body  12  by a coupling device  100  including a threaded pin  102  and a head  104 . The pin  102  extends through the lateral passage  44  associated with the arm receiving region  40  of the frame body  12  and threadably engages the passage  68  formed in the base  60  of the respective swivel arm  14 . The head  104  is preferably configured to provide convenient grasping by a surgeon who rotates the head  104  to thread the pin  102  into the base  60 . Upon engagement by the coupling device  100 , the inner face  66  of the swivel arm  14  abuts the engagement surface  58  of the arm receiving region  40 . In this regard, the engagement surface  58  and the inner face  66  are preferably flat such that, where desired, the swivel arm  14  can freely rotate relative to the frame body  12  about the pin  102 . More particularly, the swivel arms  14   a ,  14   b  are preferably assembled to allow for 360° movement relative to the frame body  12 . During use, this preferred construction eliminates bending movements or forces from transferring from the step  16  (FIG. 1) through the respective pins  102  to the frame body  12  that might otherwise cause the headframe  10  (FIG. 1) to slip or move from a desired position. Finally, as a point of reference, the assembly of FIG. 7, depicts retention pins  110   a ,  110   b  extending from the leading ends  64  of the swivel arms  14   a ,  14   b , respectively. As described below, the retention pins  110   a ,  110   b  are available for receiving and maintaining the strap  16 . 
     Returning to FIG. 1, upon final assembly the surgical headframe  10  is secured to a patient&#39;s head  120  (preferably the forehead) by first locating the contact pads  18  against the head  120 . As previously described, the concave nature of the contact pads  18  facilitates “gripping” of the contact pads  18  to the head  120 . In the secured position, and as illustrated in FIG. 1, the swivel arms  14  extend rearwardly relative to the patient&#39;s head  120 , substantially along the patient&#39;s temple, or slightly above the ears. The strap  16  is then wrapped behind the patient&#39;s head  120 , much like a diving mask, and secured to the retention pins  110   a ,  110   b  via the holes  84 . In one preferred embodiment, the central region  82  (FIG. 4) of the strap  16  is placed over the occilipate bone (not shown). Alternatively, other locations of the strap  16  relative to the patient&#39;s head  120  can be employed. Regardless, due to the elastic nature of the strap  16 , the surgical headframe  10  can be tightly positioned or forced against the patient&#39;s head  120 . 
     By employing ball joints  122  (shown partially in FIG. 1) to couple each of the contact pads  18  to the frame body  12 , the contact pads  18  can swivel slightly to match the contours of the patient&#39;s head  120 . Further, the triangular or tripod-like arrangement of the contact pads  18  renders the surgical headframe  10  highly stable relative to the patient&#39;s head  120 . That is to say, the triangular orientation provides stability in all planes, and specifically prevents “rocking” of the headframe  10  along any one axis. Additionally, the contact pad  18   b  associated with the central portion  30  of the frame body  12  is offset from the plane in which the strap  16  wraps about the patient&#39;s head  120 . As a result, the contact pad  18   b  effectively stretches the skin engaged by the contact pad  18   b , further enhancing overall stability. Finally, the triangular or tripod arrangement of the contact pads  18  prevents skin between each of the contact pads  18  from stretching. This phenomenon is often times found with other non-traumatic headframe designs, and presents a distinct opportunity for undesirable headframe movement. Thus, movement problems associated with skin stretch found with other devices is eliminated with the tripod-like configuration of the present invention. 
     Once secured to the patient&#39;s head  120 , the surgical headframe  10  is available for receiving and maintaining other components of the stereotactic system. In particular, a dynamic reference frame  130  and a touch pad  132  are preferably secured to the post  20  as shown in FIG.  8 . As is known in the art, the dynamic reference frame  130  maintains one or more optical emitters  134  (shown generally in FIG. 8) that are utilized by the stereotactic system during surgical procedures. In this regard, the dynamic reference frame  130  is rigidly secured to the surgical headframe  10  via the post  20 . As previously described, the surgical headframe  10  is fixed to the patient&#39;s head  120  (FIG.  1 ). Thus, the dynamic reference frame  130  is rigidly associated with the patient&#39;s head  120 , and establishes a consistent reference zone even with movement of the patient&#39;s head  120 . The touch pad  132  is an auxiliary device available to provide the surgeon with the ability to effectuate changes in the use/display of the stereotactic system. It should be understood, however, that the touch pad  132  is not a required element of the present invention, and can be secured to areas other than the post  20 . 
     The surgical headframe of the present invention provides a marked improvement over previous designs. Fixation of the surgical headframe to a patient&#39;s head is non-invasive as it does not entail the use of bone screws or other incisions through the patient&#39;s skin. Further, as compared to clamp-type headframe designs, use of soft contact pads against the patient&#39;s skin greatly reduces the opportunity for trauma. Finally, by preferably orientating three contact pads in a triangular or tripod configuration, the headframe is highly stable in all dimensions. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present invention. For example, while the surgical headframe has been described as preferably employing three contact pads, a two-contact pad design can also be employed. With this configuration, the head frame assumes a semi-circular arc conforming to a patient&#39;s forehead and includes a mounting lug for maintaining the dynamic reference frame. The head frame rests on the patient&#39;s forehead on the two-curved, swiveling pin-jointed contact pads and is held in place by way of an elastic strap. Further, while preferred dimensions have been ascribed to the various components, other dimensions, either greater or smaller, are equally acceptable. 
     Additionally, the frame body and swivel arms need not be made from aluminum. Instead, a wide variety of other materials are available. In fact, in accordance with an alternative embodiment, the frame body and swivel arms (as well as other components of the headframe) are formed of a non-magnetic material such as plastic, ceramic, or other composite such that the headframe is compatible with MRI, CT, X-ray and magnetic stereotactic devices/procedures.