RU2642382C2 - Combined extractor for damaged bone screws - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: combined extractor contains handle to create the torque, rod adapter and the working head in the form of a cup with opened outwards conical cavity, surface which is equipped with helical ribs with a conic cross-sectional shape, forming the inner long-pitch multiple thread, that are placed axisymmetricly and are consistently interconnected. Radial grooves are made in the head from the side of conical cavities on the same angular distances from each other and from the helical projections, in which figured plate are installed with the ability to move axially, placed in the radial grooves at the end of cylindrical rod that is placed in central holes of the working head and tubular adaptor attached with the other end using elastic corrugated cylinder (bellows) to the handle and being the anchor of electromagnet (solenoid) of AC, stator of which is attached flange of tubular adaptor and contains radial cylindrical dowels, forming a bayonet connection with figured cuts in the cylindrical handle collar, covering on the outside generatrix the stator of electromagnet. Sides of figured plates, turned inside of conical cavity of working head, has angle of slope equal to the angle of slope of conical surface cavity, and equipped with cutting elements in form of teeth, similar to teeth of outer one-row spline broach, cross-sectional shape of which conforms to the cross-section shape of helical ribs.

EFFECT: reduced duration of surgery, avoidance of need to create large axial effort and moments needed for helical ribs cut in screws material with the aim of creating the indentations of required sizes, allowing to transmit torque to turn damaged screws without cutting used ribs.

10 dwg

Description

The invention relates to traumatology, orthopedics and vertebrology, and is intended to remove implants and their threaded fragments, deprived of structural elements that contribute to their capture and unscrewing with the help of known tools, damaged from bone tissue due to mechanical stress or fatigue failure of threaded elements (screws).

Modern systems for correcting and stabilizing the spine and other bone elements of the human skeleton that are damaged due to diseases or injuries are characterized by the presence of a large number of fastening threaded elements in the form of screws (about 20 types), differing in length and diameter, ensuring the fastening of system elements in the bone tissue and eliminating their spontaneous unscrewing from her. They have a diameter of 1.2 to 8.5 mm, a length of 2.5 to 140 mm and are equipped with heads of various shapes with structural elements (grooves, slots, polyhedral holes) for the tool, considered as an analogue, with which they are screwed into the bone tissue and are unscrewed from it in case of, for example, performing revision operations (Deformity Spinal Fixation System, www.Lanx.com .; Operative Technique, Stryker Spine, www.Stryker.Com/emea/index. Htm; GOST P 50582- 93; ISO 5835-91).

The most common damage inherent in screws is the separation of the head from the threaded part, and the separation plane can be in close proximity to the head and pass through the stress concentration zone formed by the transitional neck of the screw located outside the bone tissue, or pass through the cavity of the thread along the bone border tissue, or, which further exacerbates the problem of extraction, located inside the bone tissue. It follows that the outer ends of the threaded fragments of the screws located in the separation plane differ in diameter and do not have structural elements for their capture, which creates the problem of their extraction (unscrewing).

As analogues, we took tools for screwing / unscrewing whole (intact) screws, which are screwdrivers with heads equipped with special structural elements that mesh with the corresponding structural elements of the screws (Spine correction and stabilization systems. - Kharkov, IPPS named after Prof. M.I. Sitenko; ISO 8319-1; ISO 8319-2).

The main disadvantage of these tools is that none of them is equipped with hook elements for threaded fragments of damaged screws that can transmit them the torque necessary for unscrewing them from the bone tissue.

As a prototype, the extractor design for threaded fragments of transpedicular screws (Ukrainian patent No. 988224, Bull. No. 8 dated 04/25/2012) containing a head in the form of a cup with an open outward cavity in the form of a truncated cone, the surface of which is equipped with helical protrusions with a conical transverse shape, is taken sections connected by a rod adapter with a handle to create axial force and moment of turning out, with the aim of forming screw-shaped protrusions on threaded fragments by plastic deformation radial recesses (dents), which are then used to transmit a fragment of the moment of rotation (unscrewing).

The main disadvantage of this design of the extractor is the difficulty of forming on the bone tissue (or bone cement) threaded fragments of screws (or on damaged heads) recesses (dents) using helical protrusions necessary to transmit the moment of unscrewing. The formation of these indentations (dents) requires significant axial forces and moments applied to the handle of the extractor, which in most cases is unacceptable due to excessive deformation of the spinal column, the risk of damage to the intervertebral discs, nerve processes and closely located internal organs. This disadvantage will be crucial when reversing damaged screws related to implants installed in other places of the human skeleton.

The formation of depressions of insufficient depth leads to the cutting off of a part of the material of the threaded fragment (in this case, the thread) with screw-like protrusions when it is unscrewed, which is explained by the presence of a large moment of resistance due to the "blocking" of the threaded part in bone tissue or in special bone cement, and a small surface area formed recesses perceiving the torque applied to the handle. Cutting off part of the material of the thread of a screw fragment of a screw (or its damaged head) leads to an increase in the surface area (contact area) with which the helical protrusions of the head interact, and therefore, to repeat the procedure for the formation of new recesses, an even greater axial force and moment of rotation will be required for introducing helical protrusions into the material of screws or their threaded fragments, which will create even more uncomfortable conditions for the patient, increase the time of the operation and complicate its implementation.

The basis of the invention is the task of creating a tool (extractor) that can provide reliable capture and turning of damaged screws and their threaded fragments from bone tissue (or from special bone cement) without significant force effects on both bone structures and adjacent soft tissues of a person the patient.

The essence of the invention lies in the fact that in the proposed design of a combined extractor containing a handle placed axially symmetrically and sequentially connected to each other to create axial force and torque, a rod adapter and a working head in the form of a cup with an outwardly open cavity of a conical shape, the surface of which is provided with helical protrusions with a conical cross-sectional shape, forming an internal multi-thread with a large step, in the head from the side of the conical cavity radial grooves are placed at equal angular distances from each other and from helical protrusions, in which curly plates are placed with the possibility of movement in the axial direction, inserted into radial grooves at the end of a cylindrical rod mounted in the central holes of the working head and a tubular adapter attached to the other end with using an elastic corrugated cylinder (bellows) to the handle and being an anchor of an electromagnet (solenoid) of alternating current, the stator of which is mounted on a tubular flange the adapter also contains radial cylindrical keys that form a bayonet connection with curly cuts in the cylindrical collar of the handle, covering the electromagnet along the outer forming stator, the sides of the curved plates facing the inside of the conical cavity of the working head have an angle of inclination equal to the angle of inclination of the conical surface of the cavity and are equipped with cutting elements in the form of teeth similar to the teeth of an external single-row spline broach, the cross-sectional shape of which is similar to the shape of the transverse echeniya helical protrusions.

When comparing the prototype with the claimed technical solution it is clear that the latter is characterized by the following distinctive features.

Firstly, the creation of a combined extractor equipped with structural elements specially designed to form depressions on the surfaces of damaged screws or their threaded fragments for subsequent engagement of helical protrusions of the working head with them, reduces the duration of surgical intervention, since the use of other special tools is not required.

Secondly, the force loads on the bone elements and adjacent tissues of the patient are significantly reduced, since the process of forming depressions by cutting using for this purpose the cutting tools in the form of combined plates in the form of curly plates, which are external spline microtracts, is characterized by much smaller forces cutting than the process of forming depressions by plastic deformation using helical protrusions.

Thirdly, the presence of pre-formed recesses of the required size, used as guides for helical protrusions of the head, contributes to their further deepening when it is screwed up due to plastic deformation, but with much less effort, the material of the damaged bone screw (or its threaded fragment) and the transfer of the required in magnitude of the moment of unscrewing without the risk of cutting (rolling, smoothing) these recesses and the need to repeat the procedure of formation of new x recesses, instead of cut, but already on a larger contact area and with large axial forces and moments.

In FIG. 1 shows a sectional view of a combined extractor design; in FIG. 2 is a view along arrow A in FIG. one; in FIG. 3 is a section along BB in FIG. one; in FIG. 4 is a view along arrow B in FIG. one; in FIG. 5 - geometrical parameters of cutting teeth of figured plates, performing the functions of external slotted microwater; in FIG. 6 is a view along arrow D in FIG. 5; in FIG. 7 is a diagram of receiving slots (recesses) on a threaded fragment of a screw formed as a result of tearing off the head; in FIG. 8 is a view along arrow D in FIG. 7; in FIG. 9 is a diagram of the formation of slots on the spherical head of a damaged screw as a result of flaring (smoothing) of the faces of a polyhedral recess under a socket wrench; in FIG. 10 is a view along arrow E in FIG. 9.

Combined extractor (Fig. 1) is a rod system consisting of coaxially located in series and interconnected arms 1, an electromagnet of alternating current (solenoid) 2, a tubular adapter 3 and a working head 4.

The handle 1 is equipped with an annular collar 5, covering the cylindrical stator 6 of the electromagnet along the outer generatrix, equipped with radial cylindrical keys 7, which are placed in the figured slots 8 of the annular collar, forming a bayonet joint (Fig. 4). The stator is connected to the flange 9 of the tube adapter 3, at the opposite end of which is made an internal thread for connecting with the threaded shank 10 of the working head 4 in the form of a cup with an outwardly open cavity 11 in the form of a truncated cone, on the surface of which there are screw-shaped protrusions 12 (Fig. 2) having a conical cross-sectional shape, forming a multi-start (in this case, for example, three-way) conical thread with a large pitch, opposite in direction to the thread of the extracted screws or their fragments.

Symmetrically to the protrusions 12 in the head from the side of the conical cavity 11, radial grooves 13 are made with the same angular pitch β, in which the curved plates 14 are mounted with the possibility of movement, fixed with the help of the protrusions 15 in them in the blind grooves at the end of the rod follower 16 (Fig. 3 ) installed in the central hole of the working head, the other end of which, which is the anchor of the electromagnet, is attached to the handle using an elastic corrugated cylinder (bellows) 17, providing a fixed location of the yak Shooting relative to the pole pieces of the electromagnet 2.

The sides of the figured plates 14 turned inward to the conical cavity of the head are made with an inclination angle α (Fig. 5) equal to the angle of inclination of the conical surface of the cavity and equipped with cutting elements in the form of teeth 18 arranged with a pitch t, with a rake angle γ and a height h similar to teeth external single-row spline broach, the cross-sectional shape of which corresponds to the cross-sectional shape of the helical protrusions 12 (Fig. 6).

All design elements of the extractor are made of stainless tool steel.

To increase the wear resistance, the surfaces of the helical protrusions and teeth of the figured plates are coated with titanium carbide (TiC) (Vereshchaka A.S., Tretyakov I.P. Cutting tools with wear-resistant coatings. - M .: Mashinostroenie, 1986. - 192 p.).

The process of extracting (turning out) from the bone tissue of damaged screws and their threaded fragments is shown in FIG. 7-10.

In the initial state of the combined extractor, curly plates with teeth are pulled into the head (Fig. 1).

The extraction (inversion) of the threaded fragment of the screw is implemented as follows (Fig. 7). When the handle 1 rotates around the stator 6 of the electromagnet 2, due to the interaction of the keys 7 with the figured slots 8, it is moved along the axis of the extractor by the amount S (Fig. 4) together with the corrugated cylinder (bellows) 17, the pusher 16 and the figured plates 14 into the working the position shown in FIG. 1 and 7), i.e. the ends of the figured plates are axially extended by a value of δ from the grooves 13 in the working head 4 to the outside. Then the extractor is installed coaxially to the threaded fragment, the contact of the teeth of the figured plates with the tops of the threads of the thread of the fragment is ensured, the axial force F _{о is} applied and the power of the electromagnet is turned on. The alternating current supplied to the winding of the electromagnet generates a pulsating electromagnetic force, which causes axial vibration of the pusher 16 and the shaped plates 14 with cutting teeth 18 with a frequency of ν and amplitude a, which leads to the insertion of the fragment threads into the material and forming slots (Fig. 8) (Granovsky GI, Granovsky VG Metal cutting: Textbook for high schools. - M.: Higher school., 1985. - S. 245-248).

After the formation of the slots of the required depth, which guarantees the turning of the threaded fragment from the bone tissue or from the bone cement without cutting the received recesses (splines), the electromagnet is de-energized, and by turning the handle 1 counterclockwise relative to the stator, it is returned to its original position. Then, screw-like protrusions 12 are inserted into the formed slots on the threaded fragment and, applying to the handle in the same direction a torque M _BP and an axial force F _о , screw the working head onto the threaded fragment using the formed slots of the support guides and causing plastic deformation of the fragment material with conical screw-shaped protrusions in the radial and axial direction, increase the size of the slots and the reliability of engagement. As the head is screwed up, the number of slots on the tops of the thread threads of the fragment increases, and therefore, the likelihood of cutting the tops of the thread (flaring) decreases with an increase in M _bp , overcoming the resistance to eversion.

In the same sequence, the procedure for removing (turning out), for example, screws with a spherical head, having damage in the form of flared (smoothed) faces of a polyhedral recess in the socket head and in the form of a winder (Fig. 9, 10), is followed.

Claims (1)

Combined extractor for damaged bone screws, containing an axisymmetrically arranged and serially connected handle for creating torque, a rod adapter and a working head in the form of a cup with a conical cavity open to the outside, the surface of which is provided with helical protrusions with a conical cross-sectional shape, forming an internal multi-pass thread with a large step, characterized in that in the head from the side of the conical cavity are made at the same angular races radial grooves from each other and from helical protrusions, in which curly plates are placed with the possibility of axial movement, mounted in radial grooves at the end of a cylindrical rod placed in the central holes of the working head and a tubular adapter attached to the other end by means of an elastic corrugated cylinder (bellows) to the handle and which is an anchor of an electromagnet (solenoid) of alternating current, the stator of which is fixed to the flange of the tubular adapter and contains a radial cylindrical dowels forming a bayonet connection with figured slots in the cylindrical collar of the handle, covering the electromagnet stator along the outer forming stator, the sides of the shaped plates facing the inside of the conical cavity of the working head have an inclination angle equal to the angle of inclination of the conical surface of the cavity and equipped with cutting elements in the form of teeth similar to the teeth of the outer single-row spline broach, the cross-sectional shape of which corresponds to the cross-sectional shape of helical protrusions pov.

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