Patent Application
20160310178
The invention relates to a template for use in manufacturing an implant for spinal or other orthopaedic fixation and to a method of manufacturing such an implant. The template is capable of bending in response to a force and is capable of retaining a bent shape which is used to model the implant with a shape corresponding to the shape of the template.
It is known in the medical art to use spinal rod templates for modelling the shape of a permanent rod that is used for stabilizing the spine by means of a screw-rod system. The necessary shape and length of the spinal rod which is to be implanted into a patient is determined on the basis of the rod template which is a rod that is initially bent and measured to conform to the effected part of the patient's spine. The rod template is then utilized for the configuring of the permanent rod which is to be implanted into the patient and secured to a portion of the length of the spine. Such templates are, for example, known from U.S. Pat. No. 6,221,077 B1.
The rod templates are bent manually or with a tool in the operating room (OR). To permit bending in the OR, rod templates known in the art can be made of an aluminium alloy, for example AlMg—Si, having a relatively low strength. After use in the manufacture of the permanent rod implants, the rod templates are bent back and sterilized for using them a second time. This procedures may be repeated several times. However, the used rod templates may still have a remaining curvature. In addition, there may be a risk of breaking when the rod templates are bent and bent back several times.
US 2010/0063548 A1 describes a spinal correction template having a first configuration which substantially corresponds to an uncorrected shape of a spine. The spinal correction template can be activated such that the template achieves a second configuration to cause the spine to assume an orientation substantially corresponding to the second configuration of the spinal correction template. In one embodiment, the spinal correction template can be formed of a shape-memory alloy such as Nitinol. The step of activating occurs at a temperature in the range of about 28° C. to about 37° C. Hence, the template can have an austenite finish temperature (Af) that is below body temperature (about 37° C.). A spinal correction method using the template further includes attaching a primary spinal rod to at least a portion of a spine after the spine achieves a corrected orientation, and removing the spinal correction template. A secondary spinal rod may be inserted in place of the spinal correction template. In some embodiments, the spinal correction template can remain in the patient's body.
It is the object of the invention to provide a template for use in manufacturing an implant for spinal or other orthopaedic fixation that can be bent in the OR at about room temperature and that is reusable several times. Further, a method of manufacturing such a template and a method of manufacturing an implant with such a template shall be provided.
The object is solved by a template according to claim 1, a method for manufacturing the template according to claim 14 and a method for producing an implant using the template according to claim 15. Further developments are given in the dependent claims.
The template is configured to change its configuration between a first configuration, in which template is capable of bending in response to a force and is capable for retaining a bent shape, and a second configuration in which the template assumes a memorized shape in response to directing the temperature to a recovery level, and wherein the recovery level of the temperature is above body temperature. By body temperature, a temperature of around 37° C. is meant. Hence, the template is in the first configuration during its intended use of bending it in the OR outside or inside a patient's body.
With such a template, the curvature of the section of the spine that has to be corrected or the shape of a bone plate which is intended to bridge bone parts or bones to be immobilized can be reproduced by bending or contouring the template with low force in the OR, either manually or using a tool. The bending or contouring the implant can be performed before or while surgery takes place.
Afterwards the implant can be manufactured by duplicating the shape of the template using another material for the implant and applying higher forces, usually with a tool.
With the template, difficult shapes can be easily reproduced and an improved anatomical contour can be obtained.
The memorized shape of the template, such as a straight or even shape, can be easily achieved by heating the template to a temperature above the recovery level so that the template automatically assumes the memorized shape. A step of bending back is no longer necessary. After recovery of the memorized shape the template may be re-used for another procedure. The transformation from the first configuration to the second configuration and vice-versa is reversible. Therefore, the template can be re-used a great, even an infinite number of times. An active cooling step is not needed to achieve the first configuration. If the template is not kept at a temperature above the recovery level, the temperature of the template automatically decreases so that the template assumes the first configuration in which it is deformable.
Further, it is possible to revise the formed shape of the template through mild heating to a temperature below the recovery level.
The template may be, for example, a spinal rod or a bone plate. The rod template may be used for producing a spinal rod for correcting a deformity or misalignment in the spinal column caused by disorder such as, for example, scoliosis or caused by injuries. Templates for producing bone plates with a bent shape may be used, for example, in the case of fractures of the hand or the shoulder.
In one embodiment, the template is made of a nickel-titanium (NiTi) alloy with an austenite finish temperature (Af) which is above body temperature, in particular above 45° C., preferably above 50° C., more preferably above 60 C and most preferably about 70° C. to about 80° C. Hence, the second configuration which is the memorized shape, can be easily achieved by sterilizing the template with the usual procedure of sterilizing medical instruments, such as vapour sterilization or by immersing it in hot water. Thereby, the recovery level of the template to achieve the memorized shape is easily achieved. The NiTi alloy is biocompatible, therefore, the template is usable inside and outside the human body.
In one embodiment, the NiTi alloy comprises around 49.0 to 52.0 at.-% (atomic percent) nickel, more preferably 49.5-50.0 at. % nickel. The remainder is titanium. Hence, the alloy is a martensitic shape memory alloy that has a martensite finish temperature (Mf) that is above room temperature. By room temperature a temperature of around 23° C.±3° C. is meant.
The strength, in particular the bending stiffness of the template made of this material is less than that of conventional AlMgSi templates. Hence, the template can be bent with less force.
The template can be manufactured in a simple manner including conventional steps of hot drawing and annealing. Thereafter, the template may be cut to size and may be laser marked and finally cleaned.
During manufacturing, the template may obtain an oxide layer on the surface, in particular during a step of annealing. The oxide layer has a colour that differs from the colour of the surfaces of the implants. Therefore, the template can be easily distinguished from the implants. The oxide layer also allows laser marking and imprinting other markings, such as length scales etc.
In the case of the NiTi template, the detection under X-rays is improved due to the higher density compared to the conventional AlMgSi templates.
Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. In the drawings:
Referring to
In a second configuration, shown in
The rod 10 includes a shape memory material that is characterized by having two distinct configurations and the ability to restore itself, for example by heating it to a temperature above the recovery level, to a memorized shape that has been pre-configured.
More specifically, the material of the rod 10 is a shape memory alloy and still more specifically a nickel-titanium alloy (NiTi alloy) exhibiting the shape memory effect. In the first configuration, the material is in the martensitic metallurgical state where the rod 10 is flexible and deformable and can be caused to assume any of a variety of shapes. Hence, the rod 10 can be bent by exerting a low force, for example manually, onto the rod 10 to cause the rod 10 to assume a bent shape. By directing the temperature above the recovery level, i.e. by heating the rod 10 to a temperature above the recovery level, the material assumes the austenitic metallurgical state wherein the rod 10 is rigid and assumes the memorized shape. The temperature at which the material begins to transform into the austenitic metallurgical state is the austenite start temperature (As) and the temperature at which the material has fully transformed into the austenitic metallurgical state is the austenite finish temperature (Af). In the case of the NiTi alloy, the recovery level can be defined as the austenite finish temperature (Af).
When the temperature of the rod 10 falls below the temperature of the recovery level, the material reaches the martensite start transformation temperature Ms at which temperature the austenitic metallurgical structure begins to transform into the martensitic metallurgical structure. At the martensite finish temperature Mf the alloy is completely converted into the martensitic state. When the rod is reheated, the transformation back to the austenitic structure begins at the austenite start temperature As and is completed at the austenite finish temperature Af. The transition temperatures Af, As, Mf and Ms are determined with a method according to ASTM F2082-06 that is a standard test method for determination of the transformation temperatures of nickel-titanium shape memory alloys by bend and free recovery.
In the preferred embodiment, the Af temperature is selected to be above body temperature, for example above 45° C., preferably above 50° C., more preferably above 60° C. and most preferably between about 70° C. to about 80° C. An upper limit of the Af temperature may be about 90° C. to about 100° C. The martensite finish temperature Mf is preferably above room temperature. It depends on the Af temperature of the alloy. For example, a template having an Af temperature of about 80° C. may have an As temperature of about 60° C., a Ms temperature of about 50° C. and a Mf temperature of about 40° C.
A particular example for shape memory alloy of the rod 10 according to the first embodiment is a so-called martensitic nickel titanium alloy with a nickel content that is less than that of nickel titanium alloys having superelastic properties, i.e. preferably less than about 50.6 to 51.0 at.-% nickel according to the standard ASTM F 2063. For example, the nickel content of the alloy according to an embodiment 49.0 to about 52.0 at. %—nickel, preferably about 49.5 to about 50.0 at.-% nickel. The remainder is titanium. Small portions of impurities may be present as listed in ASTM F 2063. An example of such an alloy is SM 495. This material can be deformed at room temperature and is transformed back to the austenitic metallurgical state at a temperature Af higher than body temperature.
The rod 10 may have on its surface an oxide layer that is obtained through annealing during a step of manufacturing the rod 10. The oxide layer may have a color that is darker than conventional oxide layers of permanent implants. This results from the fact that the oxide layer obtained through annealing is thicker than conventional oxide layers on implants that may be obtained by anodic oxidation. The oxide layer may represent a marking to distinguish the rod by its color from implants.
On the surface of the rod 10 markings (not shown) may be provided that are obtainable by laser marking. Such markings can include CE marking, LOT-number marking and/or other markings. For example, the rod 10 may have incremental distance markings.
A flexural strength of the rod 10 in the first configuration is, for example, around 100-150 N/mm2. The rod may have a diameter corresponding to usual diameters of spinal correction rods, for example, a diameter of 3.5 mm, 4.5 mm, 5.5 mm etc. The density of the material of the rod may be considerably higher than that of convention AlMgSi rods, for example, around 6 g/cm3 or higher. This causes improved detection through X-rays.
A method of manufacturing the template rod 10 includes steps of forming a pre-configured shape, memorizing the pre-configured shape such that the template has the pre-configured memorized shape in the austenitic metallurgical state. The manufacturing steps include hot drawing and annealing. Typical conditions for annealing are annealing at around 350° C. to around 800° C. for around 5 minutes to around 60 minutes. Suitable conditions may be selected dependent on the specific composition of the alloy. By the annealing, the oxide layer is obtained. The method may further include steps of cutting to size and/or of laser marking and/or of cleaning the template.
Turning now to
Turning now to
The method of manufacturing the bone plate 60 and the method of producing a permanent bone plate implant are the same as described for the first embodiment.
Further modifications of the above described embodiments may be contemplated. For example, instead of spinal rods or bone plates, any other orthopaedic components or implants may be manufactured using a correspondingly shaped template, such as bone nails or pegs or hooks.
Instead of a nickel titanium alloy, other shape memory alloys or shape memory polymers (SMPs) can be used. Such shape memory polymers may include linear block copolymers, for example shape memory polyurethane, thermoplastic polymers, for example polynorbornene, or chemically cross-linked SMPs. The recovery level is then defined as the temperature at which the material begins to transform into the first configuration to reach its memorized shape.
The memorized shape can be any shape. Hence, bending the template and the resulting bent shape of the template in the first configuration includes generating a deviation form the memorized shape.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15 164 551.2 | Apr 2015 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| 62150636 | Apr 2015 | US |
