"System and method for aligning intramedullary nails"

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The present invention relates to a system for aligning intramedullary nails.

The present invention relates also to a method for aligning intramedullary nails.

As is known, intramedullary nails are used, in particular in the case of breakage of the long bones, to stabilize in the correct position the separate stumps of a fractured bone. An intramedullary nail normally comprises an elongated internally hollow body with a predetermined rigidity, the shape of which depends on the type of bone to which the nail is intended. The elongated body is also provided with proximal and distal holes for the fixing.

These holes are formed at the end of the nail, namely in the regions located respectively in the closest and farthest area respect to the patient's heart, once the nail has been implanted. The nail is directly inserted inside the medullary canal of the bone and locked by inserting, through bony portions, screws into the proximal and distal holes, in order to prevent any relative movement of the bone stumps. By way of example, the figure 1 shows an intramedullary nail 1 inserted in a bone 2 by means of two screws 3 inserted in distal holes 4.

The retrieval of the distal holes is often very difficult. In fact, although the intramedullary nails are substantially rigid, they must be somehow elastic and, in almost all cases, they deform more or less significantly during implantation. In particular, the nails can flex in the anterior-posterior and medium-lateral direction and, in addition, the nails can be subjected to torsion (internal rotation or external rotation) . Because of the deformation, the distal holes do not occupy the desired position and should, therefore, be localized by means of complex procedures based on the use of a high number of radiographic images. Consequently, the patient and, above all, the health personnel are exposed to very dangerous radiation .

The known nails guiding systems comprise a bar, an adapter to connect the bar to a proximal portion of the nail, so that the bar has a predetermined direction, and a mask hinged at the distal end of the nail, so as to rotate in a plane. The mask is provided with guide holes which reproduce the configuration of the distal holes. The guidance systems known are arranged to be calibrated before the installation of the nail. In other words, the bar is initially connected to the nail by means of the adapter, and then, the position of the mask is adjusted by sliding the bar with respect to the adapter and rotating the mask itself with respect to the bar, so that the guide holes match the distal holes of the nail. The bar is then separated from the nail and reconnected to it after implantation .

However, these known systems are effective only if the deformation of the nail during implantation is minimal. In many cases, in fact, the displacement of the distal holes with respect to the not deformed configuration of the nail is such that the guide holes are still unusable. In particular, rotation or twisting of the nail is critical. Furthermore, the inaccuracies in the alignment of the distal holes of the nail and of the guide holes cause the stress of the guide system in order to introduce the fixing screws. Therefore, the screws, due to imperfect alignment of the distal holes of the nail with the guide holes of the mask, must be able to withstand even considerable efforts during the insertion and, for this reason, they are made of metal alloys. This problem doesn't allow to use screws in polymeric materials absorbable by the organism, which does not require subsequent removal interventions. Purpose of the present invention is to provide a system and a method for aligning intramedullary nails which allow the use of screws not necessarily made of metallic material but made of polymeric material absorbable by the body and to overcome the limits of alignment inaccuracy and dangerousness of the operating conditions which still affect the systems and methods of alignment of intramedullary nails previously described with reference to the known technique.

According to the present invention, a system for aligning intramedullary nails is provided, as defined in claim 1.

According to the present invention, a method for aligning intramedullary nails is provided, as defined in claim 6.

For a better understanding of the present invention a preferred embodiment is now described, purely as non- limiting example, with reference to the accompanying drawings, in which:

- Figure 1 shows an image of an intramedullary nail inserted in a bone, according to the prior art;

- Figure 2 shows a schematic view of system for aligning intramedullary nails, according to the invention; - Figure 3 shows a schematic view of a drill of the system for aligning intramedullary nails, according to the invention;

- Figure 4 shows a schematic view of a longitudinal section of the intramedullary nail inserted through the system for aligning intramedullary nails, according to the invention .

With reference to these figures, and in particular to Figure 2, a system 10 for aligning intramedullary nails is shown, according to the invention. The system 10 comprises an intramedullary nail 11 suitably modified, and comprises two distal holes 14, having axes of symmetry Y'Y' and Y' 'Y' ', able to accomodate screws 13 to be inserted and to be aligned respectively to the axis Y'Y' and Y' 'Y' ' . The intramedullary nail 11 comprises, in its internal thickness

15, in correspondence of the two distal holes 14, two coils

16, shown in transparency in figure 2. Starting from the distal holes 14, as best shown in Figure 4, the nail 11 is provided along its extension of two longitudinal slots 17 that run from the point where the two coils 16 are positioned up to a distal end of the nail 11. Two pairs of electrical wires 18 and 19 respectively flow along the slots 17. Each of these pairs of electrical wires 18 and 19 connects each of the two coils 16 to two external meters, namely to instruments external to the nail 11, able to measure the voltage induced on the two coils 16. Moreover, the two pairs of wires 18 and 19 protrude from the nail 11 so as to arrive on the contacts 20 and 21 of a board 22 which acts as a support base. The system 10 also comprises an apparatus 23 configured for processing the electrical signals coming from the coils 16, trough the board 22, so as to insert screws 13 in the distal holes 14 of the intramedullary nail 11 in a aligned way.

Advantageously according to the invention, the apparatus 23 comprises a powered drill used for the insertion of the screws 13 in the intramedullary nail 11. As an example, Figure 3 shows the drill 24 comprised in the apparatus 23, equipped with a support 25 for a solenoid 27. The drill tip 26 is attached to the spindle of the drill 24, not shown in the figure. The drill 24 is used from time to time to insert first one and then the other screw 13 to be inserted in a distal hole 14.

In particular, the system 10 is based on the electromagnetic interaction between the coils 16 and the solenoid 27 wound on the support 25 of the drill 24, in order to align each screw 13 to the axes Y' and Y' ' . In fact, when the apparatus 23 is connected to the power and is turned on, the solenoid 27 sends a variable magnetic field directed toward the coils 16. The coils 16 comprised in the intramedullary nail 11 receive the variable magnetic field and, for electromagnetic induction of the law Lenz, generate a potential difference having an intensity proportional to the variation of the magnetic flux that invests them. The two receiving coils 16 are aligned to the axes Y'Y' and Y' 'Y' ', being in the holes 14 of the nail 11 in which the fixing screw 13 must be inserted. The condition of alignment between the holes 14 of the nail 11 and the solenoid 27 is obtained when the electromagnetic induction is maximal, this condition being signaled to the operator so that to be sure of the optimal condition for the insertion of fixing screws 13 in the nail 11.

The system 10 for alignment of intramedullary nails is used after the predetermination of the best initial condition from which to start for searching the alignment, that is the condition in which the holes 14 of a nail 11 are when the nail has been inserted without undergoing deformation .

Subsequently, rather than perform the search of the alignment position by means of offsets of the apparatus 23 with respect to the three spatial reference axes X, Y and Z, and by means of rotations around them, that are very long and difficult operations to perform either manually or by means of an automatic control system, the Applicant use the knowledge of the deformation of the intramedullary nail after its insertion. Such deformations are formed by anterior-posterior and medium-lateral bending and by internal or external twists. Therefore, as described above, executing movements that follow the bending anterior- posterior and medium-lateral bending and the internal or external twists, it's possible to provide an automatic positioning sysetm which find the alignment in a simple and safe way.

In this configuration, the apparatus 23 is movable so as to be able to translate along the three reference axes XYZ and to rotate with respect to them. The maximum potential difference in reception can be obtained when the transmission solenoid and the receiving coils are aligned with each other, or when the reference axis Y coincides with the axis of symmetry Y'Y' or Y' 'Y' ' .

The system 10 may also comprise, within the apparatus 23, a signaling device of the achieved alignment, not shown in the figure. In particular, since the apparatus 23 receives the measures of the induced electromotive force, can incorporate a calculation unit that stores all the values of the induced voltage and find the value correspondent to the occurrence of the condition of maximum induction .

Advantageously according to the invention, the system 10 comprises a robotized control device which finds the alignment through a series of displacements and rotations indicating at the end the point and the direction where to insert the screw 13 to fix the intramedullary nail 11.

As already explained, the present application also relates to a method for aligning intramedullary nails.

The method comprises the steps of:

- Positioning the apparatus 23 in an initial condition;

- Executing the scans according to the anterior- posterior and medium-lateral bending deformation of the nail 11 to find the maximum of electromagnetic induction;

- Executing the scans according to the internal and external twist deformation of the nail 11 to find the maximum of electromagnetic induction;

- Signaling the achieved alignment.

Therefore, with the system and method for aligning of intramedullary nails according to the invention it is possible to accurately identify both the point and the direction of insertion of the fixing screw of the nail, thus allowing, for fixing of the nail, the use screws not necessarily made of metal material but made of polymeric material absorbable by the body.

Additionally, with the system and method for aligning of intramedullary nails according to the invention it's possible to actually increase the speed for retrieving the point and the direction of insertion of the screw in the intramedullary nail, due also to the possibility to implement the method with an automatic control device.

Moreover, with the system and with the method for aligning of intramedullary nails according to the invention, the errors relative to the initial positioning of the instrumentation used for retrieving the point and the direction of insertion of the fixing screw in the intramedullary nail become irrelevant because they can be compensated.

Finally, with the system and method for aligning intramedullary nails according to the invention, frequencies of used electromagnetic fields are extremely lower than those of x-rays and make the exposure of operators and patients harmless during the operation of the equipment .

Finally it is clear that the system and method for aligning intramedullary nails described and illustrated here can be modified and varied without departing from the protective scope of the present invention, as defined in the appended claims.