the device of the present invention maintains the desired insertion trajectory of medical instruments and dissipates the force imparted by these same medical instruments by dispersing it over a relatively large area at the patient &# 39 ; s skin surface . as is shown in fig1 , the device 10 comprises a base 20 and an interchangeable sheath component 24 attached to a freely positionable ball joint 18 . the sheath 24 may be attached to any mechanism which is freely positionable in infinite degrees of freedom . the base 20 may be constructed to conform to the contours of the patient &# 39 ; s body . the base 20 may be constructed of plastics , polymers , kevlar ® or any other suitable medical grade material . in a preferred embodiment , the base 20 is constructed of a polyetherimide , such as ultem ® plastic . the base 20 is positioned directly on the patient , providing safety benefits over conventional systems . because of the potential side effects of general anesthesia and other considerations , many orthopedic procedures are performed under monitored anesthesia care or “ mac .” mac anesthesia includes the use of local anesthesia such that the patient is numb at the surgical site . the patient is usually also given intravenous medication to calm and relax them during the procedure . the anesthetist or anesthesiologist then monitors the patient during the procedure . patients are awake during mac anesthesia , and thus the patients may inadvertently move during surgery . if , as in conventionally mounted systems , the working cannula 12 is secured to the operating table , relative movement between the patient and the cannula 12 may result in a loss of instrument alignment and stability . mounting the base 20 and the sheath 24 directly to the surface of the patient offers an important safety benefit over these conventional systems . if a patient moves during a procedure , the surgeon can simply let go of the instruments until such movement stops , all the while the instrument alignment and stability remains intact . similarly , relative movement under impact or pressure loads can occur along the axis of the working cannula 12 in a system which is not mounted to the patient . tamping which occurs through the working cannula 12 , for example , may push the patient &# 39 ; s bone away from its engagement point at the distal end of the working cannula 12 . when the tamping force or pressure is released and the patient &# 39 ; s bone returns or springs back to its starting position , the relative position of the working cannula 12 against the bone may be different , and may offer a risk of entrapping tissue between the end of the working cannula 12 and the bone . the patient - mounted base 20 and working cannula 12 of the present invention minimize the opportunity for significant relative motion to occur between the patient and any of the surgical instrumentation . the base 20 includes a patient contacting surface 22 . the patient contacting surface 22 may include an adhesive to aid in the positioning and stability of the base 20 . the patient contacting surface 22 may further include foam or other suitable cushioning material . when mechanical forces are imparted onto the medical instruments passing through the working cannula 12 , those forces are dissipated against the depth stop of the working cannula 12 and the sheath 24 and subsequently across the surface area of the base 20 . thus , the impact forces that reach the interior body regions are partially controlled and are targeted to the surgical site . in the absence of the force dissipation , the mechanical forces imparted by the medical instruments could cause severe damage to tissues and structures apart from the surgical site . a surgical access portal or working cannula 12 is positioned on the base 20 to guide the placement of the instruments into the desired interior body region . the working cannula 12 controls the depth and insertion trajectory for the instruments introduced within and through the cannula 12 into the surgical site . the working cannula 12 may be slidably received through the sheath 24 of the device with its freely positionable ball joint 18 . a locking mechanism may be employed to lock the working cannula 12 into a desired position relative to the base ( or interior body region ). in an embodiment of the present invention , the locking mechanism may comprise a split channel and collar system such that the access portal includes channels aligned parallel or slightly toward each other and a collar movable in a longitudinal direction such that the channels are moved apart thus locking the working cannula 12 in place . conversely , the channels can be brought together releasing the working cannula 12 . the working cannula 12 may include depth gauges , such as markings to indicate how deep the working cannula 12 is placed into the patient &# 39 ; s interior body region . the device 10 may further include a mechanism to adjust the length of the sheath 24 . such a mechanism may include interchangeable blocks of various heights that may be placed on the sheath 24 that allow the user to vary the length of the sheath 24 . the sheath 24 may also be telescoping to vary its length . in another embodiment the device 10 may include adjustable heads 14 and 16 to vary the length of the sheath 24 . the adjustable heads may include a spring loaded push button to slidably adjust the length of the sheath 24 . by adjusting the length of the sheath 24 , which acts as a depth stop for the cannula , the depth that the cannula is inserted into the surgical site may be varied . the preferred embodiment of the present invention will be described as it is used in the treatment of a vertebral body defect such as a compression fracture . the device 10 includes a base 20 , which may be constructed of any suitable medical grade material , such as plastic or kevlar . prior to placement of the device 10 , the surgical site is identified by placement of a conventional guide pin into the vertebral defect . the safe and proper position of this pin is selected using fluoroscopic guidance to permit visualization by the surgeon . following placement of the pin , a cannulated dilating device is placed . the cannulation of the dilator closely fits over the pin diameter . the body of the dilator serves to create a larger access path through the patient &# 39 ; s tissue by gently deflecting tissues in its path . placement of the dilator can , in one embodiment , aid in selecting the appropriate length and depth of the interchangeable sheath 24 . this sheath 24 selection can be accomplished by observing depth markings on the body of the dilator at the point where the dilator crosses the surface of the patient &# 39 ; s skin . the chosen sheath 24 with its freely positionable ball joint 18 may then be quickly assembled to the base 20 . the sheath 24 is guided over the dilator and the base 20 is carefully positioned on the patient &# 39 ; s skin at the resulting location . the cannula 12 is then placed over the dilator and through the sheath 24 , and advanced to its final docking position in bone . the base 20 may be secured , if needed , to the patient &# 39 ; s skin using foam , tape or similar adhesive and / or fixation means . once the base 20 is secured , the dilator and guide pin may be removed such that the working cannula 12 is positioned for the introduction and guidance of all subsequent instruments needed to complete the procedure . the working cannula 12 provides a safe , repeatable trajectory for the passage of all subsequent instruments . in an embodiment of the present invention , the instrument alignment mechanism may include the sheath 24 , its freely positionable ball joint 18 and the working cannula 12 . in procedures where the instruments used must be operated with some degree of force , the working cannula 12 and base 20 together serve to transfer a portion of the applied force to the outer surface of the patient &# 39 ; s body and to dissipate that force over a broader surface area , minimizing the contact loading against the patient &# 39 ; s body and body tissues . the localized contact loading is minimized because the base 20 provides a greater surface area than the end of the instruments themselves , thus decreasing the pounds of force transferred to the surface at any given square inch . as shown in fig6 , in an alternate embodiment of the present invention , the device may include more than one base 20 , in an outrigger configuration . preferably , this outrigger configuration may include at least 3 bases 20 placed on the patient &# 39 ; s body . each base may include an instrument alignment mechanism . the instrument alignment mechanism of each base is operably connected to each of the other instrument alignment mechanisms at least one juncture 26 outside the perimeter of the bases . the embodiments above are intended to be illustrative and not limiting . additional embodiments are within the claims . although the present invention has been described with reference to particular embodiments , workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention .
an anchorless non - invasive force dissipation device for orthopedic instrumentation including a base having a patient contacting surface , the patient contacting surface including a surface area adapted for external placement on a patient &# 39 ; s body , and an instrument alignment mechanism operably connected to and selectively positionable relative to the base , the instrument alignment mechanism adapted to interface with at least one orthopedic instrument , such that forces applied by the orthopedic instrument are dissipated across the surface area of the base with the device being unanchored externally of the patient .