Clamps with shape memory

[0002] This patent application is a divisional of U.S. patent application Ser. No. 09/462,862, filed Jan. 14, 2000. Now U.S. Pat. No. 6,268,589.

[0003] The present invention generally relates to shape memory clamps which can be closed using a device for heating and closing heat-retractable shape memory clamps, and which are particularly well suited for use in surgery applications.

[0004] More particularly, the present invention relates to shape memory clamps which can be closed using a device for heating and closing nickel/titanium alloy clamps, including clamps of the type referred to in the industry as “hot staples”. Shape memory clamps are initially open at ambient temperature, for purposes of placement. A quantity of heat is then provided to close the positioned clamp and thus provide tissue support.

[0005] In practice, the ergonomic and economic standardization of surgical constraints requires such clamps to be manufactured to extremely restrictive specifications.

[0006] In this context, it is important for the device to be able to close all types of heated clamps, whether they be monocortical or bicortical, bipode or quadripode clamps, and irrespective of their section. It is also important for the device to include a reliable and effective safety system to prevent accidental bone necroses due to the heat applied by the device. It is also important for the device to have a heating cord that can be sterilized in an autoclave or disinfected in a bath.

[0007] Such goals are achieved in accordance with the present invention by providing shape memory clamps, of the type generally know as “hot staples”, which can be closed using a device for heating and closing heat-retractable shape memory clamps used in surgery applications and which is generally comprised of a unit which contains an electronic power and control circuit and a heating unit.

[0008] The electronic power and control circuit is preferably comprised of a current supply, a controller and an adjustment circuit which combine to deliver several predetermined quantities of heat, each corresponding to a given size of clamp.

[0009] Primarily for purposes of safety, the adjustment circuit is configured (calculated) so that the amount of heat delivered to a given clamp does not cause the temperature of the clamp to exceed a maximum value, such as 55° C. Also for purposes of safety, the electronic circuit further includes an automatic cut-out circuit for discontinuing the application of heating current at the end of a predetermined maximum time, such as 5 seconds, and a sound signalling circuit for emitting a first sound as a signal during the application of heat to the clamp (the heating time) and a second sound which differs from the first sound as a signal that the maximum heating time has been exceeded.

[0010] The heating unit is preferably constructed as a sterilizable unit. One end of the heating unit has a plug which can be plugged into a corresponding outlet of the device and the other end of the heating unit has a sleeve which includes a pair of heating electrodes and a control switch. The sterilizable unit is fully sealed and the several elements which comprise the sterilizable unit are selected to withstand the conditions of an autoclave. In its preferred embodiment, the control switch is provided with pressure-sensitive contacts.

[0011] Any of a variety of heat-retractable shape memory clamps of the type generally referred to in the industry as “hot staples” may be employed with the above-described heating device. Preferred staples will advantageously comprise a quantity of a nickel-titanium alloy which varies between 0.8 g and 2.8 g. The electronic power and control circuit of the device includes a selection knob having settings which are matched to the type and size of the clamp being used so that the prongs of the clamp are closed both automatically and without the danger of accidental bone necroses. For example, a variety of monocortical and bicortical bipodes can be employed, with the selection knob set at one of a number of relatively low power settings (e.g., the settings 1 to 5, of 10). A variety of epiphysial bipodes and quadripodes can also be employed, with the selection knob set at one of a number of relatively high power settings (e.g., the settings 5 to 10, of 10).

[0012] The present invention shall be more readily understood from the following description, with reference to the accompanying drawings.

[0013] FIG. 1 is an isometric view of a device for heating and closing the shape memory clamps of the present invention.

[0014] FIG. 2 is a block diagram of the electronic circuit of the device of FIG. 1.

[0015] FIG. 3 is a circuit diagram of the electronic circuit.

[0016] FIG. 4 is a cross-sectional view of the sleeve for the device.

[0017] FIG. 5 is an elevational view of the front face of the device.

[0018] FIG. 1 shows a preferred embodiment device for heating the shape memory clamps of the present invention, which is generally comprised of a box (1) containing an electronic power and control circuit (to be described below), a main power supply cord (2) for connecting the box (1) to a power source (i.e., line current), and a sterilizable unit (3). The sterilizable unit (3) is formed as a linking cord (4), one end of which has a plug (5) which can be plugged into an outlet (14) of the box (1) and the other end of which has a sleeve (6) which includes two heating electrodes (7) and a control switch (8).

[0019] Referring to FIG. 5, the front face of the box (1) is equipped with a main switch (9), a luminous defect indicator light (10), a luminous “on” signal indicator light (11), a heat quantity adjustment (potentiometer) knob (12), an indicator light (13) for signalling heating of the electrodes (7) and the outlet plug (14) for receiving the sterilizable unit (3). The rear face (not shown) of the box (1) is conventionally equipped with a signalling plate and an outlet for the supply cord (2).

[0020] FIGS. 2 and 3 show the electronic power and control circuit, which is generally comprised of a current (power) supply A, an adjustment circuit B, a control circuit C and an automatic cut-out circuit D. The electronic circuit can further include an optical and sound signalling circuit E, which will be discussed below.

[0021] The current (power) supply A comprises two transformers TR1 and TR2. The primaries of the transformers TR1 and TR2 are connected to the power source. The transformer TR1 is of a type having plates resistant to short-circuits. The secondary of the transformer TR1 delivers a voltage of 12V to the control circuit C, the cut-out circuit D and the signalling circuit E. The transformer TR2 is a toric transformer with a screen effect. The secondary of the transformer TR2 delivers a current of 20A under 4V and is used to feed the heating electrodes (7).

[0022] The transformers TR1 and TR2 are charged by operating a main power switch (the switch SW3 of FIG. 3) which corresponds to the main switch (9) of FIG. 1. In addition to their power supplying function, the transformers TR1 and TR2 also fulfil a safety function; that being the isolation of patients and the main power supply.

[0023] The adjustment circuit B is coupled with the power supply A (phase feed) and is connected to the primary of the transformer TR2. The adjustment circuit B is generally comprised of a triac TH1, a diac TH2 and a quadrature circuit R11, C10. The triac TH1 switches from 0 to a maximum value on each cycle of the current in an extremely short period of time. This period (the “locking time”) is adjusted by the diac TH2 and the potentiometer R13, which is operated responsive to the adjustment knob (12). The knob (12) is calibrated from 1 to 10, with each graduation corresponding to a predetermined amount of current for a given size of clamp.

[0024] By way of example, for a charge between electrodes of 0.1 W and 50 W and a nominal current of 1A, the respective voltage measurements on positions 1, 5 and 10 of the knob (12) are:

[0025] Position 1: 0.9V±20%;

[0026] Position 5: 1.4V±20%; and

[0027] Position 10: 2.0V±20%.

[0028] The positions 1 to 5 are primarily used for a range of monocortical and bicortical clamps of different sizes, having an alloy content of between 0.8 g and 1.7 g. The positions 5 to 10 are primarily used for a range of epiphysial and quadripode clamps having an alloy content of up to 2.8 g.

[0029] The control circuit C operates to co-ordinate the various functions of the device. Heating of the clamp is triggered by the control switch (8), which drives the relay K2. The contact k_2.1, of the relay K2 puts the capacitor C7 at zero volts. At the same time, the contact k_2.2of the relay K2 puts the clock U3 at +12V.

[0030] Primarily for purposes of safety, the automatic cut-out circuit D operates to automatically cut off excessive heating (i.e., heating which has exceeded a predetermined period), thus limiting the amount of heat delivered to the clamp. In this way, any risk of necrosis is avoided, even if, for example, the surgeon forgets to turn off the switch (8).

[0031] The clock U3 is the main element of the circuit D. Operating times are adjusted (e.g., from 0 to 17s) by the counter (U3) and the variable resistor R17. A positive voltage is applied to the clock input so that when completed, the output (S3) of the clock has a potential and the relay K1 is released. The contact k_2.1of the relay K2 then provides the desired timing sequence. The relay K1 is attracted and is released when the specific time has elapsed.

[0032] The optical and sound signalling circuit E includes the indicator light (11), the indicator light (13) and an acoustic signalling device LA1. The indicator (11) is illuminated to signal charging upon closure of the contacts SW3. The indicator (13), which is implemented with a LED (electroluminescent diode) D6, and the acoustic signalling device LA1 indicate the operating state for the device. To this end, the indicator (13) is illuminated when the control switch (8) is closed. At the same time, a voltage is established on the relay contact k_2.2of the modulator U2. The modulator U2 is then activated, inducing modulation pulses in the sound signalling device LA1. The modulation pulses are sent, via gates U4, to the base of a transistor Q2 at intervals raised to 0 volts. If the control switch (8) is kept pressed when the prescribed time has elapsed, the indicator light (13) remains lit and the sound signalling device LA1 emits a continuous sound.

[0033] The electronic circuit is comprised of components which can be readily assembled by the skilled artisan.

[0034] FIG. 4 shows a sectional view of the electrode carrier sleeve. As an example, the sleeve (6) shown in FIG. 4 has a hollow cylindrical shape. However, any other ergonomic shape which will facilitate handling of the device by the surgeon can be used.

[0035] Two conductor wires (15, 16) are connected to two contact zones (8a, 8b) of a light touch switch (8). The switch (8) is in turn connected to two heating electrodes (7a, 7b). The electrodes (7a, 7b) are kept parallel at the extremity of the sleeve (6), and are conventionally insulated by a non-conducting bush (17). A central conductor (18) is provided to ensure proper grounding.

[0036] The unit including the linking cord (4), the sleeve (6) and the plug (5) is made of materials which can be sterilized in an autoclave, withstanding temperatures of up to 134° C. The unit further includes a gasket (19) adjacent to the linking cord (4) to further allow for sterilization of the unit by immersion, if desired. A reinforcement piece (20) is provided at the outlet for the linking cord (4) to avoid kinking and to protect the conductor wires (15, 16, 18).

[0037] In use, the placement of a clamp by the surgeon proceeds as follows. The bone fragments to be joined are appropriately prepared and positioned. Drilling guides are then placed on both sides of the fracture and holes for receiving the clamps are drilled. The clamps are then placed, one after the other, in the drilled holes. The heating device is then charged, by turning on the main switch (9), and the position for the adjustment knob (12) is selected (according to the clamp which is being used). The sleeve of the device is then pressed on the clamp which is to be closed, and heating is initiated by depressing the switch (8) once the proper current has been established. An intermittent sound (signal) is then made by the device.

[0038] The electronic power and control circuit then operates to automatically determine and regulate the suitable amount of heat which is to be applied to each clamp, responsive to the position selected for the adjustment knob (12). The applied current can be interrupted by the surgeon on closing of the clamp, or in default (e.g., at the end of five seconds), by the automatic cut-out circuit D. A continuous sound (signal) is then made by the device to warn the surgeon.

[0039] The above-described heating device provides a variety of improvements. For example, any type of heated clamp (i.e., the clamp S shown in FIG. 1) can be used. To this end, the spacing of the electrodes (7a, 7b) is set (e.g., at 15 mm) to allow the dorsal parts of the smaller and average-sized clamps, such as monocortical and bicortical bipodes having an alloy content of from 0.8 g to 1.7 g, to be heated (from the back) in a single application. For the larger clamps, such as epiphysial bipodes and quadripode clamps having an alloy content of up to 2.8 g, dorsal parts of the clamp at two opposing angles are first heated (from the back), followed by the heating (from the back) of remaining dorsal parts of the clamp, at opposing angles, which has the effect of successively folding the prongs of the clamp. These operations c an be repeated, as needed, to effectuate plural impulses. In any event, the amount of heat delivered to the clamp is automatically limited. In particular, the amount of heat delivered to the clamp is limited so that the temperature reached by the alloy of the clamp is limited to 55° C. The period for applying heat to the clamp is also automatically limited. The sleeve is totally impervious to liquids, and there is no risk of explosion because the electrical contacts used do not create any electric arcs.

[0040] As previously indicated, the above-described heating device can be used with any of a variety of heat-retractable shape memory clamps S used in surgery, which are generally referred to in the industry as “hot staples”. However, the above-described heating device is most favorably used with staples which are specially designed to be closed using the above-described heating device. Such staples will preferably comprise a quantity of a nickel-titanium alloy which varies between 0.8 g and 2.8 g.

[0041] A typical monocortical bipode can have a size of 11 mm×8 mm, with a section of 1.0 mm×1.0 mm, and is preferably closed using a device with the knob (12) set to a position from 1 to 5, operating at one impulse. Alternative monocortical bipodes can have sizes of 11 mm×10 mm, 13 mm×10 mm and 15 mm×1 mm, each with a section of 1.5 mm×1.5 mm, and which are in each case preferably closed using a device with the knob (12) set to a position from 1 to 5, operating at two impulses.

[0042] Typical bicortical bipodes can have sizes of 11 mm×15 mm×13 mm, 11 mm×17 mm×15 mm and 11 mm×19 mm×17 mm, each with a section of 1.5 mm×1.5 mm, and which are in each case preferably closed using a device with the knob (12) set to a position from 1 to 5, operating at two impulses.

[0043] Typical epiphysial bipodes can have sizes of 20 mm×20 mm, 25 mm×22 mm and 30 mm×30 mm, each with a section of 3.0 mm×2.0 mm, and which are in each case preferably closed using a device with the knob (12) set to a position from 5 to 10, operating at three impulses.

[0044] Typical quadripodes can have an entreax (span) of 9 mm or 15 mm, combined with prongs having a length of 6 mm, or an entreax (span) of 15 mm, combined with prongs having a length of 8 mm or 10 mm, in each case having a section of 1.5 mm×1.2 mm. As previously indicated, such quadripodes are advantageously closed using a device with the knob (12) set to a position from 5 to 10.

[0045] The quadripodes are advantageously used to increase the stability of a number of osteosynthesis, having the advantages of a miniplaque, without the use of screws. The use of quadripodes is particularly recommended when secondary displacements are of concern because the stability of the osteosynthesis is ensured in all directions. Quadripodes are also well suited to foot surgery indications, as well as maxilo-facial surgery (e.g., mandibular osteosynthesis in the symphysis and para-symphysis region, and osteosynthesis of Lefort 1 type osteotomies) and cranioplasty.

[0046] It will be understood that various changes in the details, materials and arrangement of parts which have been herein described and illustrated in order to explain the nature of this invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the following claims.