Patent Application
20100318110
The invention relates to a cannula for liquid jet irrigation of bone according to the preamble of claim 1 and to a device for liquid jet irrigation of bone comprising such a cannula according to claim 13.
In orthopedic surgery implant cut-out after osteosynthesis, e.g. treatment of proximal femur fractures is a major complication often leading to severe and sometimes lethal complications. The rate of implant cut-out was significantly reduced in the past by changing from mostly rigid fixation principles to dynamically active devices such as e.g. the dynamic hip screw. However, the number of failed fixations remains high for comminuted fractures in osteoporotic proximal femurs. Therefore, an urgent need for improvement of implant fixation remains.
Especially in osteoporotic bone the application of a bone cement augmentation of the bone structure around an implant has proven to significantly enhance the performance of the fixation. Specific and controlled augmentation and bone cement distribution around an implant can be achieved with fat and bone marrow removal by irrigation of the bone structure surrounding the implant.
From arthroplasty surgeries e.g. hip joint replacement surgery it is known that irrigation of bone has been carried out for better interdigitation of bone cements with cortical or cancellous bone leading to a significantly better cement penetration.
A study concerning the effects of bone surface preparation on bone cement penetration has been published by: R. S. MAJKOWSKI et al. “Bone surface preparation in cemented joint replacement”, The Journal of Bone and Joint Surgery, Vol. 75-B, No. 3, May 1993. This document is related to bone surface preparation in cemented joint replacement. The disclosure particularly concerns the penetration depth of bone cement into the trabecular structure of a bone. The penetration of the applied bone cement into the trabecular structure depends on the extent of marrow removal from the bone interstices.
It has been found that a mean penetration depth of between 4,8 to 7,9 mm can be achieved by use of pressurized liquid jet lavage for a bone surface preparation compared to unprepared bone where a mean penetration depth of 0,2 mm can be achieved. A pressurized liquid jet lavage which is uniformly applied to the bone structure to be prepared results in an equal irrigation of areas with a sparse distribution of trabeculae and areas with a dense distribution of trabeculae.
A hand-held pulsating fluid jet lavage device for delivering a pulsating fluid to a surgical site is known from U.S. Pat. No. 4,583,531 MATTCHEN. Sterilized fluid is supplied from a pump to a rigid tubing terminating at a nozzle which may be pointed at the surgical site to be cleansed. At the axial end of the nozzle the central bore of the rigid tube is terminally closed. The nozzle comprises eight lateral openings connecting the central bore of the tube with the periphery of the nozzle. However, in trauma surgery where Kirschner-wires are crucial instruments for the surgeon as to maintain a reduction of fracture fragments this known device would have the disadvantage that a Kirschner-wire used for the reduction of bone fragments would have be removed during irrigation of e.g. a cavity where an implant is inserted and subsequently inserted again when a cannulated implant, e.g. hip screw or spiral blade is inserted by using the Kirschner-wire as a guide-wire.
It is an object of the invention to provide a cannula for liquid jet irrigation of bone which allows a precise control of the localization of the irrigation area by means of a guide wire during the irrigation process.
The invention solves the posed problem with a cannula comprising the features of claim 1 and with a device for liquid jet irrigation of bone including the features of claim 13 and comprising such a cannula.
One advantage of the cannula according to the invention is that the surgeon can carry out an irrigation of the bone structure around an in-situ k-wire. The k-wire has not to be removed for the irrigation procedure, hence assuring the later implant position and fracture reduction.
One further advantage of the cannula according to the invention is that—compared to very small diameter cannulas which would have to be used at the side of the pin to irrigate the entire or parts of the bone structure surrounding the cavity—a precise control of the localization of the irrigation area and region is possible.
Another advantage of the cannula according to the invention is that the liquid jet lavage at selected regions only of the bone structure surrounding a previously produced cavity in the bone allows a controlled penetration and distribution of the bone cement in regions of the bone structure where a reinforcement of the trabecular structure is desired. For example, this allows to augment the bone structure at desired regions in order to enhance purchase to an implant (prophylactic and/or traumatic).
In a preferred embodiment each perforation defines an inner orifice in the through channel and said contraction is located between the front most portion of said inner orifice and said front end.
In a further embodiment the at least two perforations are arranged circumferentially at essentially the same angular distance from each other.
In another embodiment the at least two perforations have a hole axis each and all perforations are located in such manner that their hole axes cut said central axis at the same distance from said front end.
In again a further embodiment said through channel has a diameter do outside of said contraction and wherein the ratio do/dl of said diameter do of said through channel relative to the diameter di of said contraction is greater than 1,3; preferably greater than 1,7.
In another embodiment the ratio do/dl is greater than 2, preferably greater than 4.
In a further embodiment said at least two perforations have a hole axis each enclosing an angle a with said central axis measured in a quadrant directed towards the front end, the angle a being smaller than 90°, preferably smaller than 80°. This allows the advantage that the irrigating liquid is applied in the forward direction.
In another embodiment the front most portion of said inner orifice of the front most of said at least two perforations is arranged at a distance D from said front end, D being preferably between 0,5 to 10,0 mm, most preferably between 1,5 to 3,0 mm.
In a further embodiment said contraction of said through channel axially extends over a length I of 0,5 to 3,5 mm, preferably of 1,5 to 2,5 mm over said length L of said cannula.
In another embodiment said diameter di of said contraction has a nominal value of 0,6 mm or 0,8 mm or 1,25 mm or 1,6 mm or 1,8 mm or 2,0 mm or 2,5 mm or 2,8 mm or 3,0 mm or 3,2 mm and a permissible variation of between +0,05 mm and +0,5 mm to permit a positive allowance between said contraction and a standard Kirschner-wire. This allows the advantage of a sealing between the through channel of the cannula and the Kirschner-wire simply formed by tolerances of the nominal diameters of the interacting members. Customary Kirschner-wires can be used, e.g. SYNTHES® Kirschner-wires which are available with diameters in a range between 0,6 mm and 3,2 mm such allowing an application to differently sized bones in case of e.g. femoral fractures or fractures at the wrist.
In a further embodiment each of said at least two perforations has a diameter d between 0,1 mm and 3,0 mm, preferably between 0,3 and 2,0 mm.
In again another embodiment the diameter do amounts to di+0,5 mm ≦do≦di+10 mm outside of said contraction. Typically the diameters di and do amount to di=2,5 mm and do=5 mm.
In a preferred embodiment of the device according to the invention said contraction has a diameter di in a range of (dw+0,05 mm)≦di≦(dw+0,5 mm), wherein dw is the diameter of the wire.
The preferred embodiment of the invention will be described in the following by way of example and with reference to the accompanying drawings in which:
Said cannula 1 comprises a front end 3, a rear end 4 and a through channel 5 coaxially penetrating said cannula between said front end 3 and said rear end 4. In the embodiment illustrated in
The N perforations 8 are arranged circumferentially at the same angular distance from each other such that the hole axes 11 of each pair of perforations 8 enclose an angle of 360°/N. The N perforations 8 are located such that their hole axes 11 cut said central axis 2 at the same distance from said front end 3 and that their hole axes 11 each enclose an angle α of 70° with said central axis 2. The cannula 1 is bevelled at the front end 3 such that the outer orifices of the three perforations 8 are situated on the bevelled surface at the front end 3 of the cannula 1.
Further, the diameter do of the through channel 5 outside of the contraction 6 is greater than the diameter dl of said contraction 6. The diameter dl of the contraction 6 is dimensioned to permit a positive allowance between said contraction 6 and the wire 7, e.g. a standard Kirschner-wire.
Before using the cannula 1 during an irrigation process a cavity is drilled into a bone whereby the diameter of said cavity is greater than the external diameter of the cannula 1. Thus, during the irrigation process when the cannula 1 is inserted into the cavity in the bone the irrigating liquid together with the removed fat and bone marrow can simply “flow” out of the cavity in the bone. Also vacuum could be used and applied in the proximity of the bone surface. This allows the advantage of a simple design of the device and no necessity of providing the cannula with an additional through channel, i.e. a suction channel. However, the cannula might be provided with a suction channel as an additional embodiment.
The diameter of such a cavity in the bone is ca. 1-10 mm greater than the external diameter of the cannula 1. An embodiment having a diameter-difference less than 1 mm would require a suction of the irrigating liquid together with the removed fat and the bone marrow and would reduce the performance of pulsed liquid jet.
The diameter difference between the diameter dw of the guiding wire 7 and the diameter do of the through channel 5 outside of the contraction 6 of the cannula 1 is in the range between 0.5 mm and 10 mm. A diameter difference less than 0.5 mm would result in a reduced performance (low transport volume of irrigating liquid per time).
The inventive cannula 1 is preferably applied in dynamic hip screw (DHS) surgery and allows the advantage that irrigation might take place after tapping of the thread for the hip screw into the bone.
In various embodiments of the present invention the number of perforations 8 is between 2 and 24 while the diameter d of each perforation 8 is in a range between 0,1 mm and 3,0 mm, preferably between 0,3 mm and 2,0 mm.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CH08/00019 | 1/15/2008 | WO | 00 | 8/27/2010 |
