OR THE FIXATION OF PORTIONS OF AUTOLOGOUS OR PROSTHESIS BONE TYPE, E.G. PORTIONS
The present invention relates to a device for the fixation of portions of autologous or prosthesis bone type.
In particular, the invention relates to a device for the fixation of portions of autologous or prosthesis bone type, preferably cranial portions.
The fixation of bone portions with particular reference to cranial fixation, is a procedure that in neurosurgery is carried out on a daily basis on patients subject to craniotomy following traumatic events or intracranial pathologies but also in the presence of a structural or morphological defect of the cranium that could be a surgical indication. Such procedure allows the anchoring to the skull cap of both portions of autologous bone type explanted in advance, and of prostheses capable of making up any bony lacunas.
The fixation technique must ensure a suitable morphological integration between the implanted bone (or cranial prosthesis) and the receiving bone. Modern fixation techniques provide for the use of different types of materials and technical solutions such as titanium alloy mini plates, which are used with
suitable screws made both of the same type of material and of polymeric material fully reabsorbable.
Prosthesis fixation devices of the above types, used in osteosynthesis of both the braincase and in orthopaedic operations are known from U.S. Patents No. 5.372.598,
No. 5.413.577 and No. 5.578.036
According to the teachings of the above patents, the mini plates are fixed by screws to the bone portion, leaving the outer anchoring holes free, which allow anchoring to the skull cap by screws.
Even though the small plates according to the known art mentioned above allow a safe anchoring of the bone portions, they imply some operating disadvantages.
A first disadvantage is in the need of having to make holes on the skull cap for fixing the small plate by screws.
Another disadvantage is related to the following alignment to be carried out between the holes made in the skull cap and the small plate anchoring holes.
A different fixation device is known from EP-A-1224911, wherein however even though there are no screws, the fixation is carried out by a clip effect of the device which therefore does not prevent undesired sliding of the held portion.
The general object of the present invention therefore is to provide a device for the fixation of portions of
autologous or prosthesis bone type.
Another object of the present invention is to provide a device for the fixation of portions of autologous or prosthesis bone type especially suitable for cranial bones.
Moreover, the objects of the present invention also include that of providing a device which should be easy to make, simple and quick to install, and which should be minimally invasive for the patient.
In view of the above objects, according to the present invention, a device has been realised for the fixation of portions of autologous or prosthesis bone type, in particular cranial portions, having the features described in the annexed claims.
The structural and functional features of the present invention and its advantages as compared to the known art will appear more clearly from an analysis of the following description, made with reference to the annexed drawings, which show a fixation device obtained according to the innovative principles of the invention itself.
In the drawings: figure 1 is a plan view of a device according to the invention in an intermediate condition of realisation; figure 2 is a plan view of the device of figure 1,
completed; figure 3 is a perspective view of the device of figure 2; figure 4 is a front elevation view of the device of figure 2; figure 5 is a side elevation view of the device of figure 2.
With reference to the figures, a fixation device 10 of a portion of autologous or prosthesis bone type, in particular of a cranial portion, is obtained in the form of a shaped element adapted for engaging by- clipping receiving bone portions with autologous bone portions explanted in advance, or prostheses capable of making up any bone lacunas, for properly fixing them. In general, device 10 according to the invention comprises: at least one engagement element adapted for clipping an autologous or prosthesis bone portion for suitably fixing it working in pseudo-elastic regimen; - a mobile engagement element that takes the locking configuration using the shape memory effect so as to not engage the bone portion to be fixed prior to the full recovery; a union element between said two elements which can adjust to any geometry of the separation region between the elements to be fixed.
In the device according to the present invention, of which a purely exemplifying embodiment is illustrated and described, the problem has been coped with and solved in order to ensure a suitable fixation allowing the positioning of the prosthesis (or bone portion) without the need of making holes with the consequent a1ignment prob1ems.
The device, obtained from alloys generally exhibiting the so-called "shape memory", preferably nickel- titanium alloys (Ni-Ti) or composition alloys obtained by ternary modifications with copper, iron, vanadium, niobium, tungsten and tantalum (Cu, Fe, V, Nb, W and Ta) or copper based alloys, for allowing the fixation of bone portions and in particular cranial portions without any type of screw, using the intrinsic properties of the shape memory alloys. In general, shape memory materials exhibit as fundamental feature, the possibility of varying their shape when subject to temperature variations, to recover their original shape afterwards at the end of the material heating step. Shape memory alloys used for making the devices according to the present invention are selected so as to allow at low temperatures to be shaped for the various application requirements, and afterwards when brought to the body temperature, to retake their original shape.
Anchoring to the cap is thus ensured by a substantially clip-like clipping system which uses the pseudo-elastic behaviour of the material while engagement elements, suitably shaped, are deformed to allow housing the bone portion in engagement.
Afterwards, the deformation imposed to such engagement elements is recovered using the shape memory effect ensuring the clipping of the device to each bone portion and the fixation between receiving bone and explanted bone, or prosthesis.
The absence of holes and screws and the elimination of an accurate alignment procedure, allow a quicker and less invasive intervention making the technique very efficient.
In fact, it should be noted that the device according to the present invention engages the bone portion in a pseudo-elastic manner, but then ensures recovery without causing scraping on the bone. In fact, the tightening tab "pinches" the bone from top at the end of the recovery step unlike what the device according to the mentioned European patent EP 1224911 does, which closes the upper portion making it scrape against on the bone surface.
Moreover, the device subject of the present invention does not require the orthogonality of the surfaces to be fixed.
Among the various alloys which can be used, Ni-Ti alloys belong to the class of innovative metal materials that in recent years have been subject to study thanks to their functional properties. Such alloys, in fact, can work in pseudo-elastic regimen and/or using the shape memory effect, thus being capable of being used for making devices with different functional properties strictly correlated to the use temperatures and to the thermo-mechanical processes undergone by the alloy.
The Ni-Ti device for cranial fixation is designed to obviate the anchoring problems of prostheses and bones exhibiting flute beak edge profiles although keeping its efficacy even in the cases of bones with flat profiles. The flute beak profile is that found in most craniotomy operations as it is connected to the use of manual cutting techniques of the bone portion which are highly more preferred, in the ordinary practice, than the use of craniotome.
The device subject of the present invention allows optimising the fixation and installation procedure avoiding the need of perforation and allowing the use of the device actually in any possible configuration. In fact, it is evident that with the device according to the present invention, it is not required for the cut to be perpendicular to the main surface of the bone
to be fixed.
The device is preferably made of a Ni-Ti shape memory- alloy with an atomic percentage composition of Ni comprised between 49 and 51 percent and preferably of 50.4%. The alloy used for making the device is optimised through suitable thermo-mechanical treatments that allow both a suitable mechanical response and a transformation temperature Af around the body temperature.
Such treatments to be carried out in the shaping step of the component comprise the plastic deformation of the component in suitably shaped dies and the performance of thermal treatments in inert atmosphere or vacuum for times comprised between 15 minutes and two hours based on the mechanical response required by the component.
Device 10 according to the exemplified embodiment of the invention is obtained starting from a sheet of said alloy preferably obtained by plastic deformation with a residual hardening value of not less than 15%. Device 10 comprises a sheet element shaped so as to exhibit a first and a second opposed ends 12 and 13 spaced apart to form for example a circle sector and connected to one another by a central segment 11. In the sheet in the proximity of each end 12 and 13, a tab is punched, respectively a first tab 14 in the
first end 12 and a second tab 15 in the second end 13.
Such tabs copy the profile of the ends of the sheet element and are partly cut and folded according to arrows F in figures 3 and 4.
Each tab is upturned in the direction of end 12, 13 opposed to that in which said tab is obtained.
In this way, a sort of articulation with a single degree of freedom is realised, defined by axes of rotation respectively z1 for the first tab 14 and z1 ' for the second tab 15 passing in any single articulation and normal to the front plane.
With particular reference to figures 4 and 5, the sheet element shows, moreover, the central segment (11) angled with respect to the two ends 12 and 13 that are situated on two different parallel planes.
Each upturned tab 14, 15, cooperating with an end 12,13 and with the central segment 11 of the sheet element allows to realize the clipping engagement of the bone portion profile.
The geometry such as set, allows a complete adaptability to different profiles either of the receiving bone or of the prosthesis, for instance the cranial prosthesis, assuring, by self-accommodation of the segments and of the tabs, the fixation of elements to the so called flute beak profiles.
In particular, the anchorage to the skull cap is
guaranteed by the mobile upper segment that takes advantage of the elasticity of the material while the opening of one of the tabs, through rotation around the axis passing in the union point with the central segment, allows the necessary space for the housing of the prosthesis.
The deformation of the tab is successively recovered, by heating, using the shape memory effect .
The device that works as a clip exhibits two types of configurations: the open configuration (a tab and the opposed end both raised) , and a closed configuration (a tab and the opposed end both closed) .
In the open configuration, the clip is anchored to the skull cap by clipping it for example with the first end
12 cooperating with the second tab 15 so as to respectively contact the upper and lower surface of the bone. On the other hand, the opening of the first tab
14 gives the necessary space for inserting the prosthesis.
Afterwards, heating the clip to values slightly higher than the body temperature induces the phase transformation of the shape memory material, allowing the transition of the device from the open configuration to the closed configuration.
In the closed configuration, the device clips to the bone portion (or prosthesis) similarly to the skull cap
portion it is clipped to.
During the transition from one configuration to the other, the device tends to recover the deformation imposed but the bone constraint prevents a complete recovery, allowing the clip to work in constrained shape recovery while the central segment 11 autonomously adjusts to the bone profile configuration. Since the constrained shape recovery allows expressing forces proportional to the recoverable deformation, the device has been pre-shaped with folded tabs relative to the central segment 11 with an angle comprised between 10 and 20 degrees allowing the fixation of bones with different surface bending radiuses.
Using the constrained shape recovery and the profile, the clip is capable of solving the problem of fixation of bones, and in particular cranial bones, in the presence of any morphological feature of the bone portions to be fixed and moreover it 'allows a minimally invasive operation without the use of screws and the need of holes made on both the skull cap and the prosthesis.
The annexed drawings are indicative only, as regards the concept of fixation by systems using shape recovery and pseudo-elastic properties.
The achievement of similar shapes with different geometry of the ends (for example with fixing tips or
systems adapted for minimising the sliding of the ends) and of the tabs (for example with different bends or larger or more narrow shapes) are to be regarded as fully equivalent to the system proposed.
From the description above made with reference to the figures, it is evident how a device for the fixation of bone prostheses and in particular of cranial prostheses according to the invention is especially useful and advantageous. The object mentioned in the specification preamble is thus achieved.
Of course, the shapes the device according to the invention can take may differ from those shown by way of a non-limiting example in the drawings.
The scope of protection of the invention therefore is defined by the annexed claims.