Implantable medical device and method for treating a spinal disorder

Abstract

The invention discloses an implantable medical device for treating spinal disorders, comprising a superelastic corrective rod that can be attached to a set of pedicle spine screws, characterised in that the corrective rod defines a continuous longitudinal axis along which a set of aligned sections are arranged. The set of sections alternately comprises a contact section and a recessed section, which can be twisted. The set of screws comprises at least one locking screw comprising a closure on the head that can be configured to move between a locked position and a sliding position.

Description

[0001] DESCRIPTION

[0002] Implantable medical device and treatment procedure for a spinal condition

[0003] Technical field of the invention

[0004] The present invention falls within the field of healthcare. Specifically, it relates to an implantable medical device for the treatment of scoliosis.

[0005] Background of the invention

[0006] The spine is made up of a series of bones, the vertebrae, which are articulated with each other, with intervertebral discs between them. Besides supporting the body, it houses the spinal cord and allows for trunk movement. Under physiological conditions, the spine is straight when viewed from the front and curved in kyphosis and lordosis when viewed from the side. This physiological alignment can be lost, resulting in scoliosis. Scoliosis is defined as a three-dimensional deformity of the spine in the coronal, sagittal, and axial planes. That is, in a patient with scoliosis, the spine shows curvatures when viewed from the front, the physiological curves are altered when viewed from the side, and there is a rotation of the vertebrae in the axial plane. Idiopathic scoliosis is the most common form; 3% of the population has some degree of scoliosis, and it is eight times more common in females.The more severe the deformity, the lower its prevalence in the population. Its causes are not clearly determined.

[0007] The problem with scoliosis lies in its potential to progress or worsen as the patient grows. The two main risk factors are the severity of the curve and skeletal immaturity at diagnosis. Thus, the more severe the curve, the greater the likelihood of progression, and the more remaining growth the patient has, the greater the risk of progression. Severe forms of scoliosis are associated with increased early mortality due to cardiorespiratory complications. Mild forms are not life-threatening, but they are associated with aesthetic concerns and self-esteem issues, as well as a higher incidence of back pain and a decline in quality of life, especially in adulthood. Scoliosis treatment depends primarily on two factors: the severity of the curve and the patient's skeletal maturity.Generally speaking, mild curves of less than 20-25 degrees, given their low potential for progression, only require periodic monitoring to detect any worsening. Moderate cases of more than 25-30 degrees, in growing patients, are treated with a brace; and severe cases of more than 45-50 degrees are candidates for surgical treatment.

[0008] The gold standard surgical treatment for adolescent idiopathic scoliosis consists of posterior spinal fusion. A longitudinal incision is made down the center of the back to expose the vertebrae, and screws are implanted inside them as anchor points to apply corrective forces. With the aid of titanium or cobalt-chromium rods, and the application of translational, compression-distraction, and derotation forces, the deformity is corrected, fixing the entire operated spine and eliminating its mobility.

[0009] Classical goals of scoliosis treatment include:

[0010] 1. Achieve a three-dimensional correction of the deformity.

[0011] 2. To achieve a clinically balanced patient, that is, that the head is centered in the pelvis, fusing the fewest possible vertebrae.

[0012] 3. Achieve a solid fusion of the operated spine.

[0013] Achieving a solid spinal fusion aims to protect the surgery. When scoliosis is corrected but a bony block (fusion) between the operated vertebrae is not achieved, the metal implants used are subjected to repetitive cyclic forces / loads, which can lead to fatigue failure and breakage. This results in recurrence of the deformity and pain. Once spinal fusion is achieved, the metal implants are no longer subjected to these repetitive cyclic loads, and therefore there is no risk of fatigue failure.

[0014] However, spinal fusion, especially in the lumbar region, is associated with two problems. On the one hand, it results in a loss of mobility and the patient's ability to flex their trunk, leading to stiffness, loss of function, and altered spinal biomechanics. On the other hand, it causes functional overload in adjacent vertebral segments (by fusing a segment, we eliminate its mobility, and therefore transfer all the workload to the unfused segments), leading to their premature / accelerated degeneration. This translates into pain and functional limitations for the patient, with a decline in their quality of life. In an attempt to avoid these problems associated with the "gold standard" treatment for scoliosis, non-fusion correction techniques are being developed.

[0015] Basically, we have two alternative techniques to fusion:

[0016] 1. Apifix (https: / / apifix.com / es / ): This device is based on a self-elongating longitudinal brace anchored to the vertebrae at the upper and lower ends of the curvature on the concave side, using open surgery. This allows for elongation of the brace, but not shortening. By lengthening the brace, since it is implanted on the concave side of the curve, the curve is corrected. It has no direct effect on vertebral rotation and requires surgery (not minimally invasive) for implantation.

[0017] 2. “Vertebral Body Tethering”: This technique involves implanting screws into the vertebral bodies via an anterolateral approach, either through thoracoscopy or thoracotomy / lumbotomy. A flexible nylon cord is then attached to these screws under compression, shortening the convex side of the curve and thus straightening it. Currently, the theoretical benefits of this solution are being questioned. Numerous recent communications and publications demonstrate that no further correction beyond that achieved during the surgical procedure itself is obtained, that there is no modulation of vertebral growth, and that the implant failure / breakage rate is around 70%, with a re-surgery rate of 30% (58th SRS Annual Meeting Seattle 2023, 57th SRS Annual Meeting Stockholm 2022). (https: / / www.globusmedical.com / international / products / reflect-scoliosis-correcBon-system / ) (https: / / www.srs.org / Files / PaBent_NewTechnologies_VertebralBodyTethering.2022.pdf)

[0018] Therefore, the problems associated with the "gold standard" treatment of correction and subsequent fusion, along with the lack of truly effective treatment alternatives, require the search for solutions that meet the following objectives:

[0019] 1. To achieve a three-dimensional correction of scoliosis, gradual and progressive over time, acting primarily on vertebral rotation and secondarily on vertebral translation

[0020] 2. To prevent fusion or rigidity of the spine in order to preserve its biomechanics and physiology.

[0021] 3. Reduce the morbidity of the surgical procedure by performing minimally invasive surgeries.

[0022] On the other hand, the use of shape memory alloys for scoliosis correction is well known. Shape memory alloys (SMAs) are functional materials that exhibit a reversible thermoelastic martensitic phase transformation, which can be associated with a significant macroscopic shape change of up to 10%.

[0023] This transformation essentially consists of a shearing of the atomic structure of the crystal lattice of the high-temperature phase, called austenite, which transforms into the low-temperature phase, called martensite. During cooling from the austenite phase, martensite appears at the Ms temperature (martensite start), and when the Mf temperature (martensite finish) is reached, the entire material is in the martensite phase. Conversely, if the martensite phase is heated, the reverse transformation occurs: austenite reappears at the As temperature (austenite start), and upon reaching the Af temperature (austenite finish), the entire material returns to the austenite phase.

[0024] - Shape memory effect. Starting with a piece in austenite with shape A, the piece can be cooled, transforming the austenite phase into martensite. When the material is in the martensitic phase, it is easily deformable due to the mobility of the interfaces between the martensite vanes, and it can be given a different shape M (with a local deformation that varies between 4% and 10% depending on the alloy type). When the piece is heated, the initial phase is recovered, transforming completely back to austenite upon reaching shape A at temperature Af. This is called the "shape memory effect." During this heating transformation, the piece exhibits a restoring force associated with shape memory, which can be used for the treatment of scoliosis and has been employed in various studies, as described later.

[0025] - Superelastic effect. Starting with a piece of austenite with shape A, a force can be applied (at a constant temperature greater than Af) to induce a martensitic transformation under stress, producing a significant shape change S (with a local deformation varying between 4% and 10% depending on the alloy type). However, in this situation, the material will be under a permanent (almost constant) force attempting to return to its shape A. This stress-induced transformation is known as the “superelastic effect,” and in this proposal, it is the condition used for scoliosis correction in the implantable medical device that is the subject of this patent.

[0026] There are several publications on the use of shape memory metal alloys in the correction of scoliosis, among which the following should be mentioned:

[0027] The document "Clinical outcomes of nitinol staples for preventing curve progression in idiopathic scoliosis" (Lavelle WF, Sandami AF, Cahil PJ, Betz RR. J Pediatr Orthop. 2011 Jan-Feb;31(1 Suppl):S107-13) describes nitinol staples implanted in the lateral area of ​​the vertebral bodies, bridging the intervertebral discs, on the convex side of the curve. When heated, the staples, due to the shape memory effect, shorten and exert a compressive force on the vertebral growth plate. These compressive forces would slow vertebral growth, theoretically correcting the curve. However, the results were poor, especially in curves greater than 35°. e .

[0028] The document "Temporary use of shape memory spinal rod in the treatment of scoliosis. Wang Y, Zheng G, Zhang X, Zhang Y, Xiao S, Wang Z. Eur Spine J (2011) 20:118-122" refers to a 6 mm round nitinol rod. This rod was cooled to less than 4 e C to work with the easily malleable martensitic-phase metal alloy. This facilitates the insertion of the bar into the heads of the screws previously implanted on the concave side of the patient's spine. Once the bar was anchored to the screws, warm saline solution at 40°C was applied. eC to activate the shape memory effect of these alloys, so the bar recovered its original shape in the austenitic phase, and therefore exerted translational corrective forces on the vertebrae, without affecting vertebral rotation. Subsequently, a conventional bar (titanium or cobalt-chromium) was placed on the contralateral side, and the nitinol bar was replaced with another conventional one. That is, a nitinol bar is used as an intraoperative correction tool, which is then replaced during the same surgery with a conventional bar. Therefore, this technique does not offer better results than conventional scoliosis correction techniques.

[0029] A randomized, double-blinded clinical trial to evaluate the safety and efficacy of a novel superelastic nickel-titanium spinal rod in adolescent idiopathic scoliosis: 5-year follow-up. Cheung JPY, Samartzis D, Yeung K, To M, Luk KDK, Cheung KM. Eur Spine J. 2018 Feb;27(2):327-339 describes a comparison of the outcomes of adolescent idiopathic scoliosis correction using a conventional titanium rod versus a nitinol shape-memory rod. The surgical procedure is similar regardless of the type of rod used. This second type of rod has a cylindrical cross-section of 6 mm and is cooled to below 20°C. e C to work in the martensitic phase and facilitate its insertion, and that, when implanted in humans, upon reaching a body temperature of 37 eIt activates and transforms into its austenitic phase, recovering the original shape in which it was manufactured and therefore exerting corrective forces on the spine. This same group published two years later a biomechanical laboratory analysis of nitinol rods of 5.5 and 6 mm in diameter, to compare it with titanium or cobalt-chromium rods (A novel scoliosis instrumentation using special superelastic nickel-titanium shape rods: a biomechanical analysis using a calibrated computer model and data from a clinical trial. Wang X, Yeung K, Cheung JPY, Lau JYN, Qi W, Cheung KMC, Aubin CE. Spine Deformity (2020) 8:369-379).

[0030] On the other hand, other surgical techniques for scoliosis correction are known, such as Vertebral Body Tethering, which uses a cord on the convex side of the curve via an anterior approach. In this technique, the cord is the element that generates the force acting on the patient's spine. Alternatively, a procedure known as posterior tethering has been proposed, where the activating cord is introduced posteriorly to minimize the surgical trauma involved in anterior implantation. This alternative technique has limitations, such as the possible generation of thoracic hypokyphosis, which have been addressed with various solutions.

[0031] An example of this type of solution is US patent 2016310170 A1, which describes a spinal assembly consisting of two complementary members: a first member, or tether, configured for attachment to a first portion of vertebral tissue, defining a longitudinal axis; and a second, bar-shaped member configured for attachment to a second portion of vertebral tissue, such that the second portion is axially movable relative to the second member, and resists and / or prevents sagittal movement of the second member relative to the second portion. This type of solution requires the use of a stabilizing bar as a complement to the tether on the concave side.In this sense, the first member or tether is the force generator and responsible for the displacement of the spine, while the stabilizing bar has the objective of reducing or avoiding the development of adverse effects during this tether treatment, such as thoracic hypokyphosis.

[0032] Therefore, it is necessary to develop a solution that allows for the improvement of current surgical treatment systems for scoliosis, according to the criteria described above, acting primarily on vertebral rotation and translation.

[0033] Brief description of the invention

[0034] The present invention describes an implantable medical device for the treatment of spinal disorders in a patient. These disorders include scoliosis, lordosis, and pathological kyphosis. This medical device comprises a superelastic correction bar (i.e., in a superelastic state) connected to a set of spinal pedicle screws.

[0035] Thus, the correction bars have two clearly differentiated working modes depending on whether the surgical working temperature (Tw) or the normal patient temperature (Tp) is below or above the transformation temperature to austenite Af:

[0036] - If Tw and Tp are less than Af, the material works in "shape memory" mode, and both the shape change MA and the recovery force it exerts take place during heating the material up to above Af, that is, heating up to Tp. The correction bar is said to be in shape memory state.

[0037] - If Tw and Tp are greater than Af, the material operates in a “superelastic” mode, and both the shape change MA and the recovery force it exerts occur at a constant temperature. The correction bar is said to be in a superelastic state.

[0038] For the material to behave in a certain way, its transformation temperatures (which are inherent to the material) must be designed to meet the specified conditions regarding Tw and Tp. This is achieved through the metallurgical design of the alloy composition and its prior thermal and mechanical treatments. Consequently, when selecting a material for surgical use, the supplier is required to ensure the metallurgical quality of the bar at Tw (standard 22) meets the specified requirements. e C) either in a "shape memory state" or in a "superelastic state". Obviously, it cannot have both states at the same time at temperature Tw, so it is necessary to make a choice that excludes the other.

[0039] Specifically, the correction bar defines a continuous longitudinal axis. Along this longitudinal axis, a set of segments are arranged, aligned at their center. The set of segments alternately comprises:

[0040] - a contact section, and

[0041] - a torsional recessed section, with a cross-section smaller than the contact section.

[0042] The contact section of the correction bar has a conjugate contact surface, mechanically linked in use to the lower surface of the pedicle screw cover. The screw assembly comprises at least one locking screw with a head lock configurable between a locked position and a sliding position.

[0043] In the locked position, the lock prevents the bar from sliding longitudinally. In contrast, in the sliding position, the superelastic correction bar can be isothermally displaced longitudinally from a tensioned position—where the recessed section has been twisted—to a target position.

[0044] During the superelastic recovery movement of the correction bar, forces are generated in the rest of the medical device that can be used to correct scoliosis. Specifically, the movement of the correction bar applies primarily defeatory forces, and secondarily translational forces, to at least one segment of the spine. In this regard, the recessed section of the correction bar is particularly relevant. This recessed section allows for the controlled application of a torsional force to a contact section, partially deforming the bar with minimal alteration to the remaining contact sections.

[0045] The twisting of the recessed section allows for the definition of an initial or untwisted position and a twisted position, resulting from the surgeon's actions. Since this twisting is defined by the surgeon, the recessed section can be readjusted as many times as necessary, according to the surgeon's needs.

[0046] This feature represents a substantial improvement over shape memory-based bars, which are predefined during manufacturing and cannot be readjusted later.

[0047] On the other hand, unlike other previous solutions, such as stabilization bars, the correction bar (100) is configured to apply defeat and translation forces on the pedicle screw assembly (200), when the recessed section (B, D) is in a twisted position, as many times as the surgeon deems appropriate.

[0048] The presence of a contact surface on the device's correction bar enables the application of defeat forces to the spine by twisting the bar during placement. Due to the bar's superelasticity, it will return to its original shape / twist once implanted. Specifically, during the bar's superelastic displacement, the contact surface, conjugate to the underside of the pedicle screw cap, applies a defeat force to the pedicle screw head. Once the pedicle screw's polyaxiality is blocked, either by its inherent nature (non-polyaxial screw) or by a locking mechanism (polyaxial screw), the force is transmitted to the vertebra where the pedicle screw has been implanted.

[0049] In conclusion, the medical device described in the present invention is capable of being used during a scoliosis treatment procedure, the correction bar itself being the generator of a force, readjustable according to the surgeon's interest, which allows the displacement and movement of the patient's spine.

[0050] With proper adjustment of the elements described in the present invention, it is even possible to achieve scoliosis treatment with minimally invasive surgery, where pedicle screws are the elements that are introduced and implanted in the patient to contact at least one segment of the spine to be treated, which would reduce morbidity during the surgical procedure.

[0051] Unlike previous solutions, the recessed section used is a torsionally superelastic section, meaning it can rotate on its own axis to apply a defeat force to the screw assembly linked by the contact section (and indirectly to the spine) once actively twisted by a user. The superelastic displacement of the bar in this device allows for a gradual and progressive three-dimensional correction of scoliosis over time, acting primarily on vertebral rotation and secondarily on vertebral translation.

[0052] On the other hand, the readjustable torsion used in each of the recessed sections allows the surgeon to correct the desired force a second time, thus adapting the force generated by the correction bar on the spine. This readjustable recessed section capability according to the present invention cannot be used in correction bars that employ a thermal differential based on a pretreatment during their manufacture. In this sense, the present invention, by using torsion and its elastic recovery as the basis for force generation, allows the same correction bar to be used for multiple adjustments of the patient's spine.

[0053] Additionally, it prevents spinal fusion, preserving the spine's biomechanics and physiology. This device is not intended for use only during the surgical procedure, such as for intraoperative corrections. It can be removed once the patient's growth has ceased and imaging tests show signs of skeletal maturity, thus facilitating spinal flexibility.

[0054] The following elements are described in the figures

[0055] 1. Medical device

[0056] 100 Correction bar

[0057] 101 Contact surface

[0058] A, C, E Contact section

[0059] B, D Lowering section

[0060] DA Transverse diameter

[0061] D B Vertical diameter

[0062] L Side of the quadrangular section

[0063] 200 Pedicle screw

[0064] 201 Stem

[0065] 202 Head

[0066] 203 Lid

[0067] Description of the figures

[0068] Figure 1 shows a perspective view of a particular embodiment of an implantable correction bar according to the present invention intended for use in a lumbar curve.

[0069] Figure 2 shows the larger circular segment section of a particular embodiment of the contact section (A, C and E) of the bar.

[0070] Figure 3 shows the substantially quadrangular section of a particular embodiment of the recess section (B and D) of the correction bar.

[0071] Figure 4 shows a perspective view of a particular embodiment of an implantable correction bar according to the present invention intended for use in a thoracic spine for a curvature of the correction bar between 20 e and 60e Figure 5 shows a side view of the particular embodiment of the correction bar shown in Figure 4.

[0072] Figure 6 shows a schematic of a medical device according to the present invention, where the connection between a correction bar and a pedicle screw is shown, comprising a stem and a capped head.

[0073] Detailed description of the invention

[0074] The present invention describes an implantable medical device (1) for the treatment of spinal disorders in patients. Among the spinal disorders to be treated using the medical device (1) according to the present invention are scoliosis, lordosis, and pathological kyphosis. In particular, it is suitable for patients diagnosed with idiopathic or syndromic scoliosis, and those with incomplete growth, or moderate scoliosis between 30 and 60 degrees. 2 Cobb angle. On curves less than 30e It could also be applied based on the risk of progression.

[0075] The medical device (1) according to the present invention comprises a correction bar (100), made of a superelastic material, connectable to a set of spinal pedicle screws. Each pedicle screw (200) comprises a shank (201), penetrating the bone of a vertebra, and a head (202) with a cap (203) defining an opening into which the correction bar (100) can be inserted. Depending on the model used, it may include other commercially available features, such as protrusions or openings to facilitate the operation of the pedicle screw (200).

[0076] Specifically, the correction bar (100) of the medical device (1) defines a continuous longitudinal axis, with a curvature adjusted according to the location of the ailment in the spine.

[0077] As can be seen in Figure 1, which shows a particular embodiment of the correction bar (100) for a lumbar curve, for a curvature of the correction bar (100) between 20 e and 60 e Along the longitudinal axis, a series of sections are arranged. These sections are aligned around their center. Additionally, the series of sections consists of two types, arranged alternately:

[0078] - a set of contact sections (A, C, E), and a set of torsionable recessed sections (B, D), with a section smaller than the section of the set of contact sections (A, C, E).

[0079] The contact section (A, C, E) of the correction bar (100) is insertable into the head (202) of a pedicle screw (200), so that the contact surface (101) of the contact section (A, C, E), preferably located dorsally, is facing a cover (203) of the pedicle screws (200).

[0080] The contact surface (101) is a surface conjugate to the lower surface of the lid (203) so that the fit of both components at their contact is adequate. In a particular embodiment, the contact surface is preferably a flat surface, complementary to a flat lower surface of the lid (203), as shown in Figure 1.

[0081] Alternatively, the contact surface (101) may have other configurations with polyhedral shapes, either indentations or protrusions relative to the cross-section of the contact section (A, C, E). The combination of these polyhedral shapes with the lower surface of the cover (203) ensures the transmission of the torsional forces generated by the correction bar (100) to the screw (200), and therefore to the patient's spine.

[0082] Consequently, the lower surface of the cover (203) is designed so that both surfaces, the contact surface (101) and the lower surface of the cover (203), remain complementary, providing conjugate contact. Thus, regardless of the configuration of the contact surface (101) in use, a good fit is achieved between the contact surface (101) of the correction bar (100) and the lower surface of the cover (203), so that the force generated by the correction bar (100) can be correctly transmitted to the patient's vertebrae.

[0083] In turn, two sections can be distinguished: outer contact sections, designed to connect with screws (200) implantable at the first or second end of the spine corresponding to the upper and lower limit vertebrae, and an inner section, designed to connect with a pedicle screw (200) implantable at the apex or apical vertebra, and optionally, with a screw (200) implantable in at least one vertebra adjacent to the apical vertebra. In Figure 1, sections A and E correspond to outer contact sections, while section C corresponds to an inner section. The recessed section (B, D) has a smaller cross-section than the contact section (A, C, E). This smaller cross-section improves the torsional capacity of the correction bar (100).Torsion can be applied by the user using specific clamps or wrenches in the direction of the scoliosis rotation, fixing the outer sections (A, E) of the correction bar (100) while applying the torsion to the inner sections (C) of the correction bar (100).

[0084] The screw assembly (200) comprises at least one locking mechanism disposed on an implantable screw (200), preferably in the apical vertebra or apex, thus defining a locking screw. The locking mechanism of this screw is configurable from a locked position to a sliding position.

[0085] In the locked position: the correction bar (100) is locked longitudinally

[0086] In the sliding position of the closure: the correction bar (100) can slide as a result of the superelastic recovery displacement, doing so isothermally from a tension position to a target position.

[0087] An example of a locking screw is a torque-sensitive lock. This lock allows the longitudinal movement of the screws (202) (200) to be blocked and, if necessary, the polyaxial movement of the screws.

[0088] The superelastic displacement of the correction bar (100) generates forces in the rest of the medical device (1) that can be used for the correction of the spinal condition.

[0089] In use, following the implantation of the medical device (1), there is a post-operative period during which the superelastic correction bar (100) continues to exert a restoring force. Furthermore, it allows the patient a degree of mobility in both coronal and sagittal flexion, as well as some axial rotation, thus avoiding immobilization of the musculoskeletal structure and the harmful side effects associated with immobilization, as occurs with current solutions.

[0090] In other words, unlike other solutions, a corrective effect on the spine is achieved by applying a sustained force over time, providing a degree of mobility or flexibility to the spinal segment included in the surgery, thus preventing ankylosis or rigidity of the spine. To this end, the superelastic correction bar (100) can have varying thicknesses in the recessed section (B, D), allowing the restoring forces to be adjusted according to the patient's anthropometric parameters (weight, height, etc.) and their condition (magnitude of the curve and rigidity of the scoliosis).

[0091] Specifically, in the particular embodiment shown in Figure 1, the correction bar (100) comprises a set of five sections: three contact sections (A, C, E), with a larger circular segment cross-section, and two recess sections (B, D) with a substantially quadrangular cross-section. Recess section B connects contact sections A and C, while recess section D connects contact sections C and E.

[0092] In an embodiment with three contact sections (A, C, E) as shown in Figure 1, contact sections A and E, or outer sections, are fitted with screws (200) to be implanted at the ends of the affected area, the upper and lower border vertebrae, while contact section C, the inner section, corresponds to the screw (200) implanted in the apical vertebra. In one particular embodiment, contact sections A and E may have a length of 5 cm, while contact section C has a length of 4.5 cm. The recess sections B and D share a length of 2 cm.

[0093] In one particular embodiment, the anchoring arrangement of the correction bar (100) is carried out by means of screws (200) implanted in the vertebrae at L4-L2-L1-T11, leaving T12 and L3 free. In another particular embodiment, the screws (200) would be implanted in each of the vertebrae from T11 to L4, without leaving any vertebra free, so that the recessed sections (B, D) would correspond to the space between vertebrae, particularly between T12-L1 and L2-L3.

[0094] Additionally, in a particular embodiment, the correction bar (100) may have a straight shape in the coronal plane, and curvatures in thoracic kyphosis and lumbar lordosis in the sagittal plane.

[0095] Figure 2 shows the cross-section of the larger circular segment of a particular embodiment of a contact section (100). This cross-section of the larger circular segment may have a transverse diameter (DA) and a vertical diameter (D). B), particularly in this embodiment of 5.5 mm and 4.5 mm, respectively. Alternatively, the cross-section of a contact section (A, C, E) may have other configurations. Thus, the curve of the circular segment may be replaced by a polygonal perimeter if manufacturing conditions so require.

[0096] In summary, regardless of the chosen perimeter, the contact bar (100) can be inserted along the heads (202) of a set of pedicle screws (200), so that the contact surface (101), whether flat or polyhedral in shape, is conjugately facing the lower surface of the cover (203).

[0097] Figure 3 shows the substantially quadrangular section of a particular embodiment of the recessed sections (B, D). In this embodiment, a substantially quadrangular section refers to a square section where the vertices have been slightly rounded. In this particular embodiment, the side (L) of the square has a dimension of 3.5 mm. Thus, a quadrangular solution can be interpreted within the definition of substantially quadrangular, although this may present certain drawbacks in its interaction with the patient.

[0098] However, in another particular embodiment, the section of the recessed sections (B, D) may have the shape of a larger circular segment (same as Fig.2), the diameter of this circular segment being smaller than the diameter of the section of the contact sections (A, C, E).

[0099] Thanks to any of these configurations, by maintaining a cross-section of the recessed sections (B, D) smaller than the contact sections (A, C, E), controlled torsion points are defined. This allows a surgeon to define the torsion applied to the bar intraoperatively, and consequently the force generated by the correction bar (100) on the patient's spine. The choice of one configuration over another may be determined by its ease of manufacture.

[0100] Figure 4 shows a perspective view of a particular embodiment of an implantable correction bar (100) according to the present invention intended for use in a thoracic curve, opposite to the lumbar curve, for a curvature of the correction bar (100) between 20 e and 60 e Figure 5 shows an elevation view of this correction bar (100).

[0101] Again, the correction bar (100) of this particular embodiment comprises a set of five sections: three contact sections (A, C, E) with a larger circular segment section having a transverse diameter (DA) of 5.5 mm and a vertical diameter (D B ) of 4.5 mm, and two recessed sections (B, D) with a substantially quadrangular section, with a side (L) of 3.5 mm. Unlike the previous particular embodiment, the contact section C has a length of 6 cm which allows for better correction for this particular ailment.

[0102] Regardless of the implementation used, the displacement of the correction bar (100) achieves the application of translational forces and, unlike other known solutions, also defeating forces to at least one segment of the spine.

[0103] In one particular embodiment, the spinal condition can be defined by three points: a first end or upper limit vertebra, a second end or lower limit vertebra, and the apex of the condition or apical vertebra. These three points are where the pedicle screws (200) used during the medical procedure are implanted, such that each of the contact segments (A, C, E) corresponds to at least one pedicle screw (200) implanted at these three points. As a result, three fixation points are present in the scoliotic spine, where a primary rotational force and a secondary translational force can be applied.

[0104] Consequently, the longitudinal dimensions of the set of sections of the correction bar (100) can be adjusted according to the nature of the ailment and the dimensions of the patient himself, so that the correction bar (100) extends several centimeters, between 1 and 5 cm, beyond the screws (200) implanted at the ends, upper and lower limit vertebrae, of the ailment.

[0105] In one particular embodiment, the anchoring arrangement of the correction bar (100) is carried out by means of screws implanted in the T4-T5, T7-T8-T9, T11-T12 vertebrae, leaving the T6 and T10 vertebrae without screws.

[0106] In another particular embodiment, the implantable medical device (1) can be configured for a condition with a double curve, both thoracic and lumbar. In this particular embodiment, the correction bar (100) can be of a length spanning the entire spine, such that the axis has a double curve. The contact sections (A, C, E) can be sized to be inserted into pedicle screws (200) located in the thoracic and lumbar vertebrae. In one particular embodiment, the screws (200) are located in the thoracic vertebrae T4-T5, T7-T8-T9, and T11, and the lumbar vertebrae L1-L2 and L4, leaving vertebrae T6, T10, T12, and L3 free, which correspond to recessed sections. This embodiment comprises a total of five contact sections, linked to one another by recessed sections (B, D).In this embodiment, two outer sections (A, E), corresponding to the upper and lower limit vertebrae, and three inner contact sections (C1, C2, C3) can be defined. The connection between the inner contact sections (C1, C2, C3) can be made using recessed sections F (F1, F2, F3, F4) similar to the recessed sections (B, D) described previously. In another specific embodiment, depending on the patient's condition, the arrangement of the screws (200) may be modified, requiring an alternative arrangement of the screws (200) where the recessed sections correspond to intervertebral spaces.

[0107] In use, the ends, or outer sections (A, E), of the correction bar (100) can be secured using specific clamps or wrenches. Once the ends of the correction bar (100) are secured, torsion is applied to the superelastic correction bar (100) at the apex, in the direction of the scoliosis rotation. The applied torsion can be equal to or greater than the magnitude of the scoliosis rotation.

[0108] Figure 6 shows a schematic of a medical device (1) according to the present invention, where the connection between the correction bar (100) and a pedicle screw (200) is shown, comprising a stem (201) and a head (202) with a cap (203).

[0109] When using polyaxial screws (200), it is necessary to lock the polyaxial orientation of the screw heads (202) in the desired position. When using a monoaxial or uniplanar screw (200), locking the polyaxial orientation is not necessary due to the inherent nature of the screw (200).

[0110] However, the use of polyaxial screws (200) allows the use of a correction bar (100) where the contact surface (101) of the circular segment forms a plane that is not twisted with respect to the longitudinal axis, since it is the head (202) of the screw (200) that allows the insertion of the screw (201) to be adjusted to the specific spinal condition of a patient. If a monoaxial or uniplanar screw (200) is used, the dorsal contact surface (101) must be adjusted so that it aligns with the direction of the screw (202) heads (200) along the spinal segment being treated. This adjustment may involve rotating the contact surface (101) along the length of the correction bar (100).That is, the use of polyaxial screws (200) can be associated with the use of a correction bar (100) with a purely dorsal contact surface (101), while the use of non-polyaxial screws (200) requires the use of a correction bar (100) where the contact surface (101) is slightly twisted, depending on the convergence of the implanted screw (200) according to the patient's condition. Releasing—for example, the cap (203)—of a screw (200) allows for the elastic displacement of the correction bar (100). Alternatively, a screw (200) can be used where the bar-screw sliding is permitted while the polyaxial nature of the head is locked. These screw (200) models can improve the durability of a device such as the one described in the present invention subjected to cyclic loading.

[0111] Thus, the sliding between the superelastic correction bar (100) and the screws occurs without losing the polyaxial locking mechanism, except for one of the screws (200) where the sliding is blocked. Specifically, it is recommended to maintain a fully tightened screw (200), preferably at the apical vertebra, to prevent migration of the correction bar (100). That is, a tightened screw (203) between the screw (200) cap and the correction bar (100), preferably at the central contact section C, prevents migration of the contact bar (100), while allowing the remaining screws (200), especially at contact sections A and E, to slide.

[0112] In a particular embodiment, the implantable medical device (1) has a first set of sections (A, C, E) with a transverse diameter (DA) between 3.5 - 7 mm and a vertical diameter (D BThe thickness (L) is between 3.5 and 6 mm, defining a flat surface. Additionally, the recessed section may include a side (L) between 3 and 5 mm. The dimensions of the correction bar (100) will be adjusted according to the force required for the patient's condition, preventing breakage.

[0113] Regarding the material used to manufacture the correction bar (100), it is necessary to use a material that is superelastic at both the surgical operating temperature (Tw) and the patient's normal temperature (Tp), without requiring temperature modification as is the case with some shape-memory materials. Therefore, the correction bar (100) can be made of various superelastic metal alloys, such as nickel-titanium, nickel-titanium-copper, or other nickel-titanium-based alloys; copper-aluminum-nickel or copper-aluminum-based alloys; iron-nickel-cobalt-aluminum or alloys based on this system; zinc-copper-gold alloys; and, in general, any shape-memory alloy that exhibits superelastic properties at temperatures Tw and Tp. In one particular embodiment, the superelastic material is a nickel-titanium alloy (nitinol), which, at temperatures Tw and Tp, is in a superelastic state.The need to use a superelastic material stems from its ability to apply defeat forces to the spine through the torsion of the correction bar (100) during its placement. That is, due to the superelasticity of the correction bar (100) material, the correction bar (100) will tend to return to its original shape or torsion, defined as the target position. During the displacement of the correction bar (100) from its initial or tension position to the target position, the medical device (1), unlike other solutions, is able to apply defeat forces to the spine through the torsion and recovery of the correction bar (100).

[0114] Therefore, unlike other rods used in the prior art, the correction rod (100) is in a superelastic state as described herein and is not in its shape memory state at temperature Tw. Although nitinol is a common material in this type of solution, the rods known in the prior art are in a shape memory state, only becoming reactive with a change in temperature.

[0115] The present solution differs substantially from these prior solutions by requiring that the correction bar (100) be in a superelastic state instead of its shape memory state. This entails a different choice in the production conditions of the bars (100) and, consequently, in their use in the medical device (1) according to the present invention.

[0116] The characteristics of the medical device (1) described above allow for the treatment of the patient's spinal condition through a procedure comprising the following stages:

[0117] - Place a pedicle screw (200) in at least one upper limit vertebra, one lower limit vertebra and one apical vertebra.

[0118] - Connect a correction bar (100) according to the present invention by passing it through the heads (202) of the previously implanted screws (200). The correction bar (100) is connected such that the outer contact sections (A, E) of the correction bar (100) extend several centimeters, between 1 and 5 cm, beyond the screws (200) located in the upper and lower vertebrae. Additionally, the contact surface (101) of the correction bar (100) faces the cap (203) of the implanted screws (200). - Apply torsion to the correction bar (100) at an inner contact section (C), which connects to the screw of the apical vertebra, in the direction of the scoliosis rotation, by twisting the recessed sections of the contact bar (100).

[0119] - Allow longitudinal sliding, due to superelastic recovery, of the correction bar (100) but blocking the displacement of the correction bar on at least one screw (200).

[0120] As previously stated, the operating conditions differ substantially from those employed in current solutions. Specifically, the steps of the present procedure are carried out such that the surgical working temperature (Tw) and the normal patient temperature (Tp) are higher than the austenite transformation temperature (Af) of the correction bar (100).

[0121] Optionally, the heads (202) of the screws (200) can be locked, limiting the polyaxial movement of the screws (200). This step will not be necessary if using uniaxial or uniplanar screws (200), whose unidirectional nature prevents polyaxial movement.

[0122] The superelastic sliding of the correction bar (100) relative to the screws (200) can be achieved by partially or completely opening the cap (203) of the screws (200) or by using screws in which tightening the cap allows for blocking polyaxial movement—if necessary—while simultaneously permitting sliding between the bar and the screw. Sliding of the correction bar (100) is permitted except at one of the screws (200). In this way, one screw (200) is kept locked to prevent migration of the bar, while allowing displacement of the remaining correction bar (100) that acts on the patient's spinal condition. In one particular embodiment, the screw (200) that remains fixed is the one implanted in the apical vertebra.

[0123] In contrast to what is described in the state of the art, the superelastic effect of this type of material can be used to apply a force, mainly rotational and secondarily translational, in a quasi-constant manner during the recovery process at constant temperature Tp.

[0124] The superelastic recovery force, at the constant operating temperature Tw, will partially correct the scoliosis in translation, lateral flexion, and rotation. The corrective forces applied by the medical device (1) act superelastically until the end of the surgical procedure and continue to act permanently in the patient, at their operating temperature Tp, until the implant can be removed when the scoliosis is considered corrected or the patient has reached skeletal maturity. It is important to note that the removal of the medical device (1) is carried out once the patient's growth has finished and they show signs of skeletal maturity, unlike some known solutions that use nitinol rods for temporary use during surgery.There is a post-operative period, where the "superelastic" correction bar (100) will continue to act with a recovery force, but, in addition, it allows the patient a certain mobility in both coronal and sagittal flexion, as well as a certain axial rotation, avoiding immobilization of the osteo-muscular structure and thus promoting faster rehabilitation and avoiding the harmful side effects derived from immobilization as happens in current solutions.

[0125] However, as previously stated, the present medical device (1) is configured for continuous use by the patient, not for temporary use during surgery, thus giving rise to the postoperative period. In other words, the superelastic correction bar (100) will continue to move and exert force after the surgery is completed. However, as with other implants (e.g., knee), metal-to-metal friction between the elements of the medical device (1) caused by movement could generate metal ion emissions. This emission could lead to complications such as metallosis. To avoid this problem, in a particular embodiment, the medical device (1) may include a surface treatment of the bar, either thermal, chemical, or plasma-based, that prevents or limits the emission of metal ions (e.g., Physical Vapor Deposition - PVD), or a coating.The coating is designed to prevent metal-to-metal friction between the components. Therefore, the coating can be made of a polymeric material suitable for implantation in a patient. Additionally, the coating can be configured to be placed on the head (202) of the screw (200), or alternatively, surrounding the correction bar (100).

[0126] In a particular embodiment of the coating, the coating may define an insert, i.e., an element interposed between the screw cap (203) and the correction bar (100). Thanks to the presence of this individual insert, improvements are achieved in the fit, congruity, and tribological properties between the cap and the correction bar (100) of the device. Thus, while the coating may be global across the correction bar (100), it is also acceptable to employ an individual coating or insert, which is arranged individually between the flat part of the correction bar (100) and the screw cap (203). The presence of an insert on the lower surface of the cap (203) is particularly relevant in embodiments where the contact surface (101) has a polyhedral shape, such as a protrusion or indentation, ensuring a proper bond between the two surfaces.

[0127] In conclusion, the present solution allows for a three-dimensional correction of scoliosis, gradual and progressive over time, acting primarily on vertebral rotation and secondarily on vertebral translation, avoiding fusion of the spine and preserving its biomechanics and physiology, as well as reducing the morbidity of the surgical procedure.

Claims

1. CLAIMS 1. An implantable medical device (1) for the treatment of spinal disorders in a patient comprising a superelastic correction bar (100) connectable to a set of spinal pedicle screws (200) comprising a stem (201) and a head (202) with a cap (203), characterized in that the correction bar (100) defines a continuous longitudinal axis where a set of sections are arranged in alignment, wherein the set of sections alternately comprises: - a contact section (A, C, E) insertable into the head (202) of the pedicle screw defining a contact surface (101) conjugate to the lower surface of the screw cap (203) (200), and - a torsionable recessed section (B, D), defining a non-torsioned position and a torsioned position, with a cross-section smaller than the cross-section of the contact section (A, C, E), wherein the correction bar (100) is configured to apply defeat forces on the pedicle screw assembly (200) when the recessed section (B, D) is in a torsioned position; and wherein the screw assembly (200) comprises at least one locking screw comprising a head closure (202) configurable between: - a locking position, where the correction bar (100) is locked longitudinally, and - a sliding position, wherein the superelastic correction bar (100) is isothermally displaceable longitudinally from a tension position to a target position, such that said correction bar (100) applies, during the displacement in use, defeat and translational forces to at least one segment of the spine.

2. The implantable medical device (1) according to claim 1, wherein the contact surface (101) of the contact section (A, C, E) is a flat surface.

3. The implantable medical device (1) according to claim 2, wherein the contact section (A, C, E) comprises a larger circular segment section.

4. The implantable medical device (1) according to claim 1, wherein the contact surface (101) of the contact section (A, C, E) further comprises a polyhedral shape.

5. The implantable medical device (1) according to claim 4, wherein the polyhedral shape is a projection of the contact section (A, C, E).

6. The implantable medical device (1) according to claim 4, wherein the polyhedral shape is a slit in the section of the contact segment (A, C, E).

7. The implantable medical device (1) according to claim 2, wherein the contact section (A, C, E) comprises a transverse diameter (DA) between 3.5 - 7 mm and a vertical diameter (D B ) between 3.5 and 6 mm.

8. The implantable medical device (1) according to claim 1, wherein the recessed section (B, D) comprises a substantially square section with side (L) between 3 - 5 mm.

9. The implantable medical device (1) according to claim 1, wherein the recessed section (B, D) comprises a larger circular segment section.

10. The implantable medical device (1) according to claim 1, wherein the correction bar (100) is made of nitinol or any other shape memory alloy in a superelastic state.

11. The implantable medical device (1) according to claim 1, wherein at least one pedicle screw (200) is a polyaxial screw.

12. A method for treating a spinal condition using the medical device (1) according to claim 1, characterized in that it comprises the following steps: - place a pedicle screw (200) in at least one upper limit vertebra, one lower limit vertebra and one apical vertebra; - connect a correction bar (100) passing through the heads (202) of the previously implanted screws (200), so that the outer contact sections (A, E) of the correction bar (100) extend 1-5 centimeters beyond the screws arranged in the upper and lower limit vertebrae and the contact surface (101) of the correction bar (100) faces the cap (203) of the implanted screws (200); - apply torsion to an inner contact section (C) connectable to the screw (200) of the apical vertebra, in the direction of the scoliosis rotation, twisting the recessed sections of the contact bar (100); and - allow longitudinal sliding of the correction bar (100) by blocking displacement on at least one screw (200), where the surgical working temperature (Tw) and the normal patient temperature (Tp) is higher than the transformation temperature to austenite (Af) of the correction bar (100).

13. The treatment procedure according to claim 6, wherein the step of blocking the displacement further comprises blocking the polyaxiality of the heads (202) of the screws (200).

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