RU2726399C1 - Method of posterior-transforaminal interbody spinal fusion accompanied by decompressor-stabilizing operations on lumbar spine - Google Patents

Abstract

FIELD: medicine.SUBSTANCE: invention refers to medicine, namely to spinal surgery, and can be used for posterior-transforaminal interbody fusion accompanied by decompression-stabilizing surgical interventions on the lumbar spine. Non-invasive examination of the injured vertebral-motor segment is performed. Possible sizes of planned for implant installation in given anatomical conditions are estimated. Bone screws of the transpedicular fixation system are implanted in the vertebrae, decompression is provided. In an oblique direction – at an angle to the sagittal plane – a corridor is formed, which is intended for further introduction of the implant into the interbody body. That is ensured by facetectomy, resection of the arch of the upper fixable vertebra to the base of the spinous process, resection of the yellow ligament throughout the segment to the contralateral side, mobilization of the dural sac. After imaging, medially at value from 1/3 to 1/2 of the width of the spinal canal, an opening is made in an interbody spacing, a posterior longitudinal ligament and a fibrous ring. Discectomy is performed with treatment of vertebral closing plates. Autobone resulting from vertebral processing is preserved and used as an osteoconductive material. Implant is formed. For this purpose, the cage is filled with autobone, the implant is inserted into the interbody space, implant is brought along a corridor with due allowance for a skewed trajectory of introduction; transpedicular helical fixation of vertebras is performed by mounting elements of a metal structure of a transpedicular system in a compression mode. Non-invasive examination of the injured vertebral-motor segment is performed by multi-helical computed tomography. Transpedicular helical fixation is performed on the opposite side from the side of the implant installation, performing the implantation of bone screws and erection of the metal structure with supporting compression. Cage is used with width of 16 to 22 mm and length of 30 to 35 mm, height of 10 to 12 mm, made by additive technology, by selective layer-by-layer laser melting of titanium powder BT-6, made personally for a specific patient. When forming a corridor intended for insertion of an implant, a volume of intervertebral disc larger than that of the implant is removed, during implantation, the implant is turned, placing its long side in the frontal plane, filling the cavities with autobone. Access is performed through median incision or paravertebrally by Wiltse to perform skeletonization of posterior structures of stabilized vertebras.EFFECT: method provides fusion of vertebrae with reduced risk of developing pseudoarthrosis, reduced time of surgical intervention and reduced aggressiveness of surgical intervention by increasing the area of contact of the implant and reducing tissue injuries.7 cl, 12 dwg

Description

Technical field

The invention relates to medicine, to spinal surgery, and can be used for posterior-transforaminal interbody fusion during decompression and stabilization surgery on the lumbar spine.

State of the art

Spondylodesis (fusion of the vertebrae) on the lumbar spine is used for degenerative diseases or injuries, for this the intervertebral disc is removed in whole or in part and an implant is placed in the vacated disc space, replacing the disc and stabilizing the adjacent vertebrae.

The known method of posterior interbody fusion (source [1]: patent RU 2614219), including a linear incision of soft tissues, the allocation of arches and interstitial spaces on both sides of the spinous processes, interlaminectomy, facetectomy, microsurgical decompression of the roots of the spinal cord, discectomy and disc curettage, channels in the interbody space, the formation of an autograft and sequential introduction into the channels of an autograft and an implant from porous titanium nickelide. The canals in the interbody space are formed while maintaining the integrity of the endplates of the adjacent vertebral bodies. An autograft is formed from bone chips formed during interlaminectomy, facetectomy and decompression of the spinal roots by squeezing the liquid fraction of the bone mass and pressing until a supportable bone column of a given size is obtained, and the porous titanium nickelide implant is installed in the support channel in such a way as to ensure the preservation autograft.

Known unilateral transforaminal access for performing interbody fusion TLIF TLIF (Transforaminal Lumbar Interbody Fusion) (transforaminal interbody fusion) (source [2]: Internet page on the Abromed website, section “treatment methods”, “spinal neurosurgery”, “spinal fusion”: access mode: http://abromed.ru/methods/spine-surgery/fusion/tlif/), in which surgical intervention is performed through an incision in the lumbar back, through a median unilateral approach. During the operation, rods and bolts are attached to the back of the vertebra, after which a spacer is inserted into the disc space on one side of the spine. Various cages are used for the operation. In the interbody space, the surgeon places a bone implant, the tissue for which is taken from the patient's pelvic bone. As the implant takes root, two adjacent vertebrae fuse together, which provides immobility between them. When accessing the vertebra posteriorly, special stem-shaped screws are inserted into its body, after which the affected disc is removed. A bone fragment is taken from the patient's pelvic bone. Next, a cage filled with a bone fragment is placed in place of the disc. The screws in the adjacent vertebrae are held together with rods or plates, after which the wound is closed.

Method [2] requires additional surgical intervention to extract the bone fragment from the pelvic bone.

The known method of posterior spinal fusion (source [3]: patent RU 2076654), related to the surgical treatment of injuries of the spine, mainly its lower thoracic and lumbar regions. The method uses a means of tightening a group of vertebrae to be immobilized, and supporting implants. The method includes skeletonizing from one side of the spinous processes and facet joints of damaged and adjacent vertebrae, forming a round hole between each adjacent of the said spinous processes in the area of their bases, introducing into each hole of said supporting cylindrical implant, repositioning the spinal column and fixing the means contractions on the spinous processes. The bed for the implant-plate is formed by removing the cortical layer from the arches and facet joints of the said vertebrae and introducing the plate into the bed, as a means of tightening the group of vertebrae using a bracket made of a material with thermomechanical shape memory, and these supporting implants are made of porous superelastic artificial material.

The main disadvantage of analogs [1, 2, 3] is the trauma of surgical interventions, high blood loss, the use of redundant fixing devices that tighten the group of vertebrae.

The known method of transforaminal interbody fusion (source [4]: Step-by-step guide: the main stages of the MIS TLIF procedure. The AOSPINE Osteosynthesis Association "Step-by-Step Guide: Key Steps in a MIS TLIF procedure", prepared by: Dr. Roger Härtl ) and Daniel Gelb), which consists in performing access to the operated spinal segment, separating the half-arches and the interstitial space between them from the side of the compressed nerve, performing unilateral resection of hypertrophied articular processes of the facet joint, entering the spinal canal and partial decompression the roots of the spinal cord, the resected bone tissue is preserved and crushed, the compressed root is shifted in the medial direction, the disc herniation and osteochondral growths are resected, in the fibrous ring of the intervertebral disc that has opened after the displacement of the root, a window is cut out with a scalpel and curettage is performed through it. disc, the end plates of the adjacent vertebrae are cleaned until the appearance of "blood dew", the interbody space is stretched, the implant is installed, for this the titanium cage is stuffed with autobone crumb and the resulting implant is inserted into the interbody space in the oblique direction.

This method [4] of interbody fusion is less traumatic. In this method, the resection of the posterior supporting bone structures is performed only from one "diseased" side, i.e. from the side of the compressed nerve, stability in the operated segment suffers to a lesser extent. Resection of the yellow ligament (posterior wall of the spinal canal) is also performed on one side, the dura mater and roots (contents of the spinal canal) are in contact with the paravertebral muscles only from the side of the compressed nerve, cicatricial adhesive process only on the "sick" side. Traction of the root and dural sac from the diseased side eliminates the risk of root trauma and the appearance of neurological symptoms on the “healthy” side.

The disadvantage of this method [4] is the high probability of the formation of pseudoarthrosis, subsidence of the implant, due to the small area of contact between the implant and the bone, as well as its longitudinal location. The supporting surface of the used implant causes a concentration of mechanical stresses on the surface of the vertebral body and the implant pushes the bone tissue, losing stability and not providing stabilization of the vertebrae. The implant used does not take into account the individual characteristics of the patient, the personal anatomical parameters of the vertebrae.

A known system and method for spinal fusion (source [5]: patent US8608804B2). Contains an implant connected to an insertion instrument with the ability to remove. The implant does not contain autologous bone, is made of a polymer composition (for example, polyetheretherketone (PEEK) and / or polyetheretherketone (PEKK)), or ceramic, or metal, or a combination of these materials. The implant is placed in the space between the first vertebra and the second vertebra. For fusion in the lumbar spine, the implant has a predetermined width in the range from 9 to 18 mm, a height from 8 to 16 mm and a length from 25 to 45 mm. The implant contains holes between the upper and lower surfaces. The upper and lower surfaces in contact with the vertebrae have a serrated surface.

The disadvantage of an implant [5] for fusion is the absence of autobone material, which reduces its ability to fuse with the vertebrae and create a reliable fusion of the vertebrae. In addition, the size of the implant does not provide an optimal distribution of the load on the surface of the closed vertebrae, so that the minimum specific pressure on the bone tissue is ensured. The use of a smooth toothed structure on the upper and lower surfaces does not provide adhesion of bone cells and does little to promote long-term integration of the implant with the vertebra. The implant does not take into account the individual anatomical features of the patient, i.e. is not personal. In addition, the disadvantages of the pusher for installing the implant include the impossibility of moving the implant in the direction perpendicular to the axis of the pusher, the implant is installed across the axis of the pusher and it is not possible to apply it using the TLIF technology [4].

Thus, the problem of the known methods of spinal fusion lies in the high trauma of access and the lack of taking into account personal anatomical features, which leads to a high risk of vertebral nonunion and the development of instability in the postoperative period.

The essence of the technical solution

The problem to be solved by the claimed invention is to increase the efficiency of performing posterior interbody fusion by increasing the contact area of the implant and reducing tissue trauma.

The technical result consists in ensuring the fusion of the vertebrae in the lumbar spine, while reducing the risk of developing pseudoarthrosis, reducing the time of surgery and reducing the aggressiveness of the surgical intervention.

The technical result is achieved by the fact that in the method of posterior transforaminal interbody fusion during decompression-stabilizing surgical interventions on the lumbar spine, in which a non-invasive examination of the damaged spinal motion segment is performed, the possible sizes of the planned implant for installation in these anatomical conditions are estimated, implantation into the vertebrae is performed bone screws of the transpedicular fixation system, provide decompression, in an oblique direction - at an angle to the sittal plane, a corridor is formed intended for the subsequent introduction of the implant into the interbody space, for this a facetectomy is performed, the arch of the upper fixed vertebra is resected to the base of the spinous process, the yellow ligament is resected throughout along the segment to the contralateral side, the dural sac is mobilized, after its visualization, medially by an amount from 1/3 to 1/2 of the width of the spinal canal, A window is inserted in the interbody space, in the posterior longitudinal ligament and in the annulus fibrosus, discectomy is performed with the processing of the vertebral endplates, the autobone formed during the processing of the vertebrae is preserved and used as an osteoconductive material, an implant is formed, for this the cage is filled with autobone, the implant is installed in the interbody space , the implant is inserted along the corridor, taking into account the oblique trajectory of insertion, transpedicular screw fixation of the vertebrae is performed by mounting the elements of the transpedicular system metal in the compression mode.

After the described resection of the posterior structures of the vertebrae and the intervertebral disc, the formed corridor allows the introduction of an implant up to 22 mm wide and up to 35 mm long, which is confirmed by the performed anthropometric calculations (according to MSCT data).

The use of a special implant made of a titanium alloy of the proposed design, using individual sizes or an individual standard size range, and manufactured using additive technology, by selective layer-by-layer laser melting of VT-6 titanium powder placed in the implant of an osteoconductive material in combination with the technique of its installation provides reliable spinal fusion with minimal aggression of interference. Due to the possibility of safe insertion of a significantly larger implant, the likelihood of the formation of a bone block (interbody fusion) increases, and, as a consequence, the effectiveness of stabilizing surgical interventions. Changing (expanding) the zone (total facetectomy, resection of the arc with the base of the spinous process) and the sequence of resection of the posterior structures (first, a full decompression of the nerve roots in the spinal canal and foramenally) makes it possible to form a wide "corridor" for the safe introduction of the implant into the interbody space.

The method makes it possible to install an implant more than 2 times larger in area than implants in analogues. On the one hand, this makes it possible to provide sufficient primary stability, on the other hand, the contact area of the osteoconductive material with the treated endplates increases significantly, which ultimately significantly increases the likelihood of interbody fusion. In fact, the area of support and contact approaches in its absolute values the values of LLIF (lateral lumbar interbody fusion - lateral lumbar interbody fusion). At the same time, no separate access and expensive instrumentation for implant insertion is required, which will facilitate wide clinical implementation of the method among surgeons who are skilled in inserting implants from the posterior approach.

The method is illustrated by drawings, which show:

FIG. 1 is a diagram of the vertebra in the axial plane, the lines of the corridor for the introduction of the implant are indicated;

FIG. 2 - diagram of the vertebra in the axial plane, shows the corridor for the implant installation, after resection of the posterior vertebral structures;

FIG. 3 is a diagram of a vertebra in the axial plane, an implant is shown installed in the interbody space, a variant with an oblique arrangement of the implant;

FIG. 4 - a diagram of a vertebra in the axial plane, shows an implant installed in the interbody space, a variant with a transverse arrangement of the implant;

FIG. 5 is a diagram, a view of the vertebrae from the back, in the frontal plane, a corridor (window) for the introduction of the implant is indicated;

FIG. 6 is a diagram, a view of the vertebrae from the back, in the frontal plane, the implant is shown;

FIG. 7 - diagram, cage;

FIG. 8 - diagram of the implant (cage filled with autologous bone);

FIG. 9 is a table with the dimensions of the cage.

FIG. 10 is a diagram of the vertebra in the axial plane, the corridor for the introduction of the implant is indicated;

FIG. 11 is a diagram, a view of the vertebrae from the back, in the frontal plane, shows the location of the window for the introduction of the implant;

FIG. 12 is a diagram of a vertebra in the axial plane, an implant in the intervertebral space is indicated;

The drawings indicate:

1 - vertebra, and 1b - upper vertebra, and 1n - lower vertebra;

2 - spinous process;

3 - corridor lines;

4 - corridor;

5 - implant;

6 - autologous bone.

The method is carried out as follows (see figure 1-12).

This method of interbody fusion is used to stabilize the L3-S1 segments.

In the method of posterior transforaminal interbody fusion during decompression and stabilizing surgical interventions on the lumbar spine, a non-invasive study of the injured spinal motion segment is performed using X-ray methods and computed tomography. Determine the dimensions of the vertebrae 1 planned for fusion (Fig. 1) of the upper 1c and lower 1n, the intervertebral disc, as well as the potentially possible safe dimensions of corridor 4 (lines of the corridor pos. 3) (Fig. 2; 3) for the installation of the implant 5. Determine the maximum the possible width of the corridor 4, and choose the cage of the maximum possible width and length, so that it can pass through the corridor and can be located within the outer contour of the intervertebral disc. Evaluate the possible and required dimensions of the planned for installation of the implant 5 (Fig. 7; 8; 9), taking into account the provision of the maximum possible width and length of the cage (Fig. 9) applicable in the given anatomical conditions. An interbody cage (Fig. 7) is produced, optimal in length, width and height, for connecting the vertebrae, and suitable for installation through corridor 4 with predetermined dimensions (Fig. 9) under the given anatomical conditions. Alternatively, the interbody cage is selected from pre-fabricated ones with the preferred dimensions for a given patient, taking into account the dimensions of the anatomical structures of the spinal motion segment on which the intervention is performed, from 30 to 35 mm in length, 16 to 22 mm in width, and 10 to 11 mm in height. Through a midline incision, or paravertebral according to Wiltse, skeletonization of the posterior structures of the stabilized vertebrae 1 is performed, 1 bone screws of the transpedicular fixation system are implanted into the vertebrae transpedicularly, and decompression of compressed structures is provided. Corridor 4 is formed (Fig. 2; 11; 12), intended for the subsequent introduction of the implant 5 (Fig. 8). For this, facetectomy is performed (resection of the intervertebral facet joints), the arch of the upper fixed vertebra 1c (Figs. 5, 10) is resected to the base of the spinous process 2 (Fig. 2), the yellow ligament is resected along the entire segment to the contralateral side. After visualization of the dural sac, it is mobilized medially by an amount from 1/3 to 1/2 of the width of the spinal canal. Using a scalpel, a wide window is cut (Fig. 5; 10) in the interbody space, in the posterior longitudinal ligament and in the annulus fibrosus, corresponding in size to the implant 5, so that it can pass through the window. Discectomy is performed with the processing of the endplates of the vertebrae 1. Autobone 6 (bone chips, particles of connective tissue, etc.), formed during the processing of the vertebrae, is preserved and used as an osteoconductive material. An implant 5 is formed, for this the cavity of the cage (Fig. 7) is filled with autologous bone 6. The cage (Fig. 6) is equipped with two through holes from the upper surface of the lower one, forming cavities intended for filling with autologous bone 6. The upper and lower surfaces of the cage have a rough structure ( uneven roughness Ra from 20 to 70 microns, formed when printing on a 3D printer from titanium powder Ti-6Al-4V using DMLS or SLS or EBM technology), which ensures cell adhesion and implant fixation between vertebrae 1n and 1c. The interbody implant 5 is installed (Fig. 3; 12) taking into account the oblique insertion trajectory (Fig. 3; 12) (at an angle to the sagittal plane and, if required, to the axial plane), the implant 5 is inserted into the interbody space (Fig. 6). Then transpedicular screw fixation is carried out by mounting the rod metal structure in the compression mode for jamming the implant 5 in the interbody space. The transpedicular screw fixation is performed on the opposite side from the side of the implant 5, the screws are implanted and the hardware is mounted with supportive compression.

After resection of the posterior structures of the vertebrae 1 and the intervertebral disc, the formed corridor 4 allows the introduction of the implant 5 up to 22 mm wide and up to 35 mm long, which is confirmed by the performed anthropometric calculations (according to MSCT data).

The implant 5 provides a reduction in mechanical stress in the area of the vertebral endplates. The load is distributed evenly over a large area.

Use of a special implant 5 with a titanium alloy cage of the described design, using individual sizes (when printing a cage for a specific patient) or an individual standard size range (when choosing a cage from pre-fabricated ones), and made using additive technology, by selective layer-by-layer laser melting of titanium powder VT-6, filled with osteoconductive material (autologous bone), in combination with the technique of its installation, provides reliable fusion with minimal invasiveness of intervention. Due to the possibility of safe insertion of the implant 5 of a significantly larger size than in analogues, the probability of the formation of a bone block (interbody fusion) increases, and, as a consequence, the effectiveness of stabilizing surgical interventions. Changing (expanding) the zone (total facetectomy, resection of the arch with the base of the spinous process) and the sequence of resection of the posterior structures (first, a full decompression of the nerve roots in the spinal canal and foramenally) makes it possible to form a wide "corridor" (Fig. 2; 11) for safe introduction implant 5 in the interbody space.

The method allows to install an implant more than twice as large in area as implants in similar methods. On the one hand, this makes it possible to provide sufficient primary stability, on the other, the contact area of the osteoconductive material with the treated vertebral endplates 1 n and 1c significantly increases, which ultimately significantly increases the likelihood of interbody fusion. In fact, the area of support and contact approaches in its absolute values the values of LLIF (lateral lumbar interbody fusion - lateral lumbar interbody fusion). This does not require a separate access and expensive instrumentation for the introduction of the implant 5, which will contribute to the widespread clinical implementation of the method among surgeons who are proficient in the introduction of implants from the posterior approach. The method provides for the fusion of the vertebrae in the lumbar spine, while reducing the risk of developing pseudoarthrosis, reducing the time of surgery and reducing the aggressiveness of the surgery.

Alternatively, the method can be performed as follows, further reducing the aggressiveness of the intervention and improving the stability of the connected vertebrae.

A non-invasive study of the damaged spinal motion segment is performed by multispiral computed tomography. Evaluate the possible dimensions of the planned for installation of the implant 5 (figure 7). The cage is made (Fig. 6) on a 3D printer using additive technology, by selective layer-by-layer laser melting of VT-6 titanium powder. A cage is made with specified dimensions (Fig. 6; 9), with a width ranging from 16 to 22 mm, a length ranging from 30 to 35 mm, a height ranging from 10 to 12 mm, taking into account the provision of the maximum possible width and length of the cage (Fig. 9) applicable in the given anatomical conditions. Implantation of 1 bone screws of the transpedicular fixation system into the vertebrae is performed minimally invasively through punctures, percutaneously. Bone screws are connected with rods. Provide decompression. An incision is made on the side of the implant installation with a length of no more than 30, and a corridor 4 (Fig. 2) is formed for the subsequent introduction of the implant 5 into the interbody space. When forming the corridor 4, intended for the introduction of the implant 5, remove the volume of the intervertebral disc larger than the volume of the installed implant 5 (figure 4). To do this, facetectomy is performed, the arch of the upper fixed vertebra 1c is resected to the base of the spinous process, the yellow ligament is resected along the entire length of the segment to the contralateral side, after visualization of the dural sac, it is mobilized medially by an amount from 1/3 to 1/2 of the width of the spinal canal ... Using a scalpel, a wide window (Fig. 5) is cut out in the interbody space, in the posterior longitudinal ligament and in the annulus fibrosus, discectomy is performed with the processing of the vertebral endplates. Autobone 6, formed during the processing of vertebrae 1, is preserved and used as an osteoconductive material. An implant 5 is formed, for this the cage is filled with an autobone 6. The upper and lower surfaces of the cage have a rough structure (uneven roughness Ra from 20 to 70 μm formed when printing on a 3D printer from Ti-6Al-4V titanium powder using DMLS or SLS or EBM technology) providing cell adhesion and implant fixation between vertebrae 1n and 1c. The implant 5 is installed (Fig. 6; 4), taking into account the oblique insertion trajectory into the interbody space, the implant is inserted along the corridor 4. When installing, the implant 5 is rotated (Fig. 4) placing its long side in the frontal plane, filling the voids with autobone 6. Implant 5 it is installed in this way symmetrically, centered relative to the longitudinal axis of the spine, which ensures a balanced distribution of forces and reduces the concentration of mechanical stress in the area of the vertebral endplates. The load is distributed evenly. The transpedicular screw fixation of vertebrae 1n and 1c is performed by mounting the hardware in the compression mode. The transpedicular screw fixation is performed on the opposite side from the side of the implant installation 5.

By increasing the contact area of the implant 5 with the vertebrae 1n and 1b, the efficiency of posterior interbody fusion increases, the risk of pushing bone structures and the development of instability decreases. Due to the unilateral access, tissue trauma is reduced and the best conditions for blood supply are required for recovery. Thus, the fusion of the vertebrae in the lumbar spine is ensured.

The proposed method was obtained in the development and evaluation of the effectiveness of the use of patient-oriented implants in the surgery of the axial skeleton in the Ilizarov Center, Kurgan.

Claims (7)

1. The method of posterior transforaminal interbody fusion during decompression and stabilization surgical interventions on the lumbar spine, in which a non-invasive study of the damaged spinal motion segment is performed, the possible sizes of the planned implant for installation in these anatomical conditions are estimated, implantation of bone screws of the transpedicular system is performed in the vertebrae fixation, provide decompression, in an oblique direction - at an angle to the sagittal plane, a corridor is formed, intended for the subsequent introduction of the implant into the interbody space, for this a facetectomy is performed, the arch of the upper fixed vertebra is resected to the base of the spinous process, the yellow ligament is resected along the entire segment to on the contralateral side, the dural sac is mobilized, after its visualization, medially by an amount from 1/3 to 1/2 of the width of the spinal canal, a window is cut out in the interbody space, in the posterior her longitudinal ligament and annulus fibrosus, discectomy is performed with the processing of the vertebral endplates, the autobone formed during the processing of the vertebrae is preserved and used as an osteoconductive material, an implant is formed, for this the cage is filled with autobone, the implant is inserted into the interbody space, the implant is brought along the corridor taking into account the oblique insertion trajectory, transpedicular screw fixation of the vertebrae is performed by mounting the elements of the transpedicular system metal structure in the compression mode. 2. The method according to claim 1, characterized in that the non-invasive examination of the damaged spinal motion segment is performed by multispiral computed tomography. 3. The method according to claim 1, characterized in that the transpedicular screw fixation is performed on the opposite side from the side of the implant installation, bone screws are implanted and the metal structure is mounted with supportive compression. 4. The method according to claim 1, characterized in that a cage is used with a width of 16 to 22 mm and a length of 30 to 35 mm, a height of 10 to 12 mm. 5. The method according to claim 1, characterized in that a cage made according to additive technology is used, by selective layer-by-layer laser melting of VT-6 titanium powder, made personally for a particular patient. 6. The method according to claim 1, characterized in that during the formation of the corridor intended for the introduction of the implant, the volume of the intervertebral disc is removed, which is larger than the volume of the implant to be installed; during installation, the implant is rotated, placing its long side in the frontal plane, filling the voids with autologous bone. 7. The method according to claim 1, characterized in that the access is performed through a midline incision or paravertebral according to Wiltse, the posterior structures of the stabilized vertebrae are skeletonized.

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