the following detailed description is of the best mode or modes of the invention presently contemplated . such description is not intended to be understood in a limiting sense , but to be an example of the invention presented solely for illustration thereof , and by reference to which in connection with the following description and the accompanying drawings one skilled in the art may be advised of the advantages and construction of the invention . in the various views of the drawings , like reference characters designate like or similar parts . with reference to fig1 , depicted in surgical instrument 100 having proximal end 102 and distal end 104 . distal end 104 has cylindrical tube 106 affixed to the edge of the surgical instrument 100 for accommodating a guidewire . as shown , cylindrical tube 106 is affixed to the top edge of the surgical instrument 100 . however , cylindrical tube 106 may be affixed to any side ( e . g ., sides or bottom ) depending upon the intended use of surgical instrument 100 . proximal end 102 preferably comprises a handle to allow a user to operate surgical device 100 . in a preferred embodiment , surgical instrument 100 is a scalpel having cutting edge 108 for cutting a skin surface . cutting edge 108 may comprise a cap or cover in order to protect a user and prevent cutting edge 108 from dulling . cylindrical tube 106 is affixed close to tip 110 of surgical instrument 100 to minimize the distance between tip 110 and the edge and a guidewire inserted through cylindrical tube 106 . to use surgical instrument 100 , guidewire 112 is threaded through cylindrical tube 106 as depicted in fig2 . surgical instrument 100 can then be advanced over guidewire 112 to a skin surface ( not shown ). an incision can then be made using cutting edge 108 . the incision is precise because cylindrical tube 106 limits the range of movement of surgical instrument 100 , thereby avoiding any inadvertent skin nicks to the skin surface . additionally , the cylindrical tube 106 allows for precise movement of surgical instrument 100 , thereby eliminating residual skin tags after incision that may prevent smooth advancement of catheters or devices over the guidewire 112 . an alternate embodiment of surgical instrument 100 is depicted in fig3 - 5 . as shown , surgical instrument 100 can be encased in sheath 200 . sheath 200 has a first channel 202 for accommodating the connection between button 204 and surgical instrument 100 . button 204 is used to move surgical instrument 100 from a closed position ( fig4 ) to an open position ( fig3 ). in some embodiments , the surgical instrument is maintained in the open and / or closed position by a locking mechanism , similar to that of a utility knife . sheath 200 further comprises a second channel 206 for accommodating cylindrical tube 106 when surgical instrument 100 is in a closed position . sheath 200 protects an operator from lacerations while threading guidewire 106 through cylindrical tube 106 . for example , during threading , surgical instrument 100 remains in a closed position ( fig4 ). surgical instrument 100 can then be advanced to an open position ( fig3 ) when surgical instrument 100 is close to the desired incision location . while the present invention has been described at some length and with some particularity with respect to the several described embodiments , it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment , but it is to be construed to provide the broadest possible interpretation of such claims in view of the prior art and , therefore , to effectively encompass the intended scope of the invention . furthermore , the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available , notwithstanding that insubstantial modifications of the invention , not presently foreseen , may nonetheless represent equivalents thereto .
disclosed herein is a surgical instrument having a cylindrical tube affixed thereto . the axis of the cylindrical tube is aligned with a central axis of the surgical instrument so it can be advanced along a guidewire .