Neurosurgical protractor

Abstract

FIELD: medical equipment.SUBSTANCE: invention relates to medical equipment, specifically to a neurosurgical protractor for installing tubular neurosurgical devices in the intracranial space. The neurosurgical protractor for installing tubular neurosurgical devices in the intracranial space comprises two mutually perpendicular plates and a fold line between them. Each plate has three free edges: an upper edge, a lower edge, and a side edge. The upper edge is shaped like an arc of a circle with its center located on the lower edge of the fold line, and it includes an angle scale. The lower edge is shaped like an arc that corresponds to the curvature of the skull vault. The lateral edge connects the upper and lower edges. The fold line represents the normal to the skull vault and contains a straight-line scale.EFFECT: use of this invention allows for the precise installation of tubular neurosurgical devices in the intracranial space at the desired angle and depth.3 cl, 3 dwg

Description

[0001] Field of technology to which the invention relates

[0002] The invention relates to neurosurgery, namely to devices for determining the trajectory and depth of installation of tubular neurosurgical devices in the intracranial space.

[0003] Technology Level

[0004] Installation of tubular devices into the intracranial space is a common neurosurgical task - drainage of the lateral ventricles, installation of a ventricular catheter of a shunt system, etc.

[0005] Let's consider a geometric model of drainage of the anterior horn of the lateral ventricle - imagine it as a triangle. The apex of this triangle is the burr hole in the cranial vault (Kocher's point), the insertion site of the ventricular catheter. The second apex is the interventricular foramen of Monro - a target landmark, the optimal location for the tip of the ventricular catheter. The third apex is the actual location of the tip of the ventricular catheter. In this problem, we are interested in the relationship between the distance between the second and third apexes and the magnitude of the surgeon's angular error during catheter insertion. The distance between Kocher's point and the foramen of Monro in an adult is approximately 6 cm - this is the depth of catheter insertion. Let's imagine that this triangle is equilateral, with sides 6 cm long. Opposite each 60° angle lies a side equal to 60 mm. Each degree at the apex of the triangle corresponds to 1 mm at its base.

[0006] Thus, taking into account this model, at a target depth of 6 cm, each degree of angular error causes the catheter tip to shift by 1 mm from the target. Experience shows that a surgeon can make angular errors of up to 15-20° when inserting a catheter by eye, which leads to a tip shift of 1.5-2 cm. Potential clinical consequences of such a shift include missing the ventricle (the drainage system is not functional), erroneous placement into the white matter or subcortical nuclei, and penetration of cerebral vessels (risk of bleeding and functional deficit). Errors in determining the insertion depth are also common, which manifests itself in inserting the catheter into the third and fourth ventricles and basal cisterns. According to the literature, the incidence of malposition of ventricular catheters during their manual insertion is 12-45% of cases [1].

[0007] To reduce these errors, neurosurgeons use various devices to determine the angle and depth of insertion of the tubular device.

[0008] The Ghajar guide [2] is a well-known device. It is a hollow cylindrical guide element corresponding to the diameter of a tubular neurosurgical device (in particular, a ventricular catheter), mounted on three equally spaced legs of equal length. The guide allows for easy determination of a perpendicular trajectory: the surgeon places the legs of the guide on the cranial vault near the burr hole and inserts the catheter through the guide element. This device has several drawbacks.

[0009] Firstly, the guidewire is not universal, as it allows only one insertion angle—normal to the skull surface. If the target is offset from the normal due to anatomical variability or displacement by an intracranial pathological process, the device will be ineffective.

[0010] Secondly, after inserting the catheter, the surgeon must remove the guidewire with a reverse motion, guiding it along the entire diameter of the catheter, surrounded by the guide element. This action could potentially lead to catheter displacement.

[0011] Thirdly, the guide element has a fixed diameter and may not fit a particular catheter.

[0012] The Thomale guidewire [2] is known, comprising a round base with three awl-shaped legs, a graduated goniometric scale, a lock that fixes the required angle, and a hollow cylindrical guide element. The surgeon places the guidewire in the area of ​​the burr hole at Kocher's point so that the goniometric scale is located in the coronal plane, sets the guide element at the required pre-calculated angle using the goniometric scale, fixes the angle with the lock, and inserts the catheter through the guide element. This device has the following disadvantages.

[0013] Firstly, the guidewire allows for the determination of a custom angle only in the coronal plane, making it suitable only for lateral ventricular drainage through the Kocher point. Other locations are unavailable.

[0014] Secondly, the conductor includes 4 parts, which complicates production and operation.

[0015] Thirdly, the guide element is removable (diameters of 2.6; 3.1 and 3.6 mm are available in the catalogue), which makes it necessary to check that its diameter matches the diameter of the catheter.

[0016] Fourth, the guide element completely covers the catheter, which may lead to displacement of the catheter during the removal of the guidewire.

[0017] Disclosure of invention

[0018] The technical result of the invention is the creation of a simple instrument enabling the insertion of tubular neurosurgical devices (ventricular catheters, etc.) into the intracranial space at the desired angle and depth, with high precision. The instrument should indicate the normal to the cranial vault, as well as angles other than a right angle. The instrument should be compact and consist of a single component, radically simplifying and increasing the reliability of the design. The instrument should not completely enclose the tubular neurosurgical device.

[0019] To achieve the specified technical result, a neurosurgical protractor has been developed, which includes two mutually perpendicular plates and a fold line between them; each plate has three free edges - upper, lower and lateral; the upper edge has the shape of an arc of a circle, the center of which is located at the lower edge of the fold line, and contains a goniometric scale; the lower edge has the shape of an arc corresponding to the curvature of the cranial vault; the lateral edge connects the upper and lower edges; the fold line is normal to the cranial vault and contains a rectilinear scale.

[0020] The top edge of the plates can be shaped like a 60° arc with a radius of 5 cm and notches every 10 degrees. The bottom edge of the plates can be shaped like an arc with a radius of 10 cm and a length of 2 cm. The fold line can be 5 cm long and have holes every 1 cm. The protractor can be made of 1 mm thick metal sheet.

[0021] The protractor is made from two plates bent at right angles, which allows it to be manufactured as a single part using a minimum number of technological operations - for example, by laser cutting and bending metal sheets, which significantly reduces the cost of production and simplifies operation, increasing the reliability of the product.

[0022] Two plates bent at right angles to each other represent two mutually perpendicular planes of the head - for example, sagittal and coronal, which allows for accurate planning of the trajectory of insertion of a tubular neurosurgical device based on preoperative CT or MRI images and reproducing it during surgery by measuring the corresponding angle on each plate.

[0023] The fold line between the plates serves a triple purpose: as a guide (the tubular neurosurgical device is not fixed within it along its entire diameter); as a reference point for selecting the desired angle (the lower edge of the fold line is the zero point of the protractor); and as a ruler for selecting the insertion depth of the tubular device if it does not contain index marks. The neurosurgeon can insert tubular devices either perpendicular to the cranial vault or at an angle other than right angles, marking the planned angle along the goniometric scale on the upper edge of the desired plate.

[0024] The lower edge of each plate is shaped like an arc, matching the curvature of the cranial vault. This allows the protractor to be positioned so that the fold line is normal to the cranial vault in any area. Simply set the average cranial vault curvature (the average radius of an adult cranial vault is 10 cm) and lengthen the lower edges of the plates to ensure a stable position on the cranial vault (e.g., 2 cm). This ensures the protractor's versatility in terms of conformity to the cranial vault of individual patients in the vast majority of cases.

[0025] Description of drawings

[0026] Fig. 1. Neurosurgical protractor, general view.

[0027] Fig. 2. Neurosurgical protractor, side view.

[0028] Fig. 3. Neurosurgical protractor, top view.

[0029] Implementation of the invention

[0030] The neurosurgical protractor includes two mutually perpendicular plates and a fold line between them; each plate has three free edges - upper, lower and lateral; the upper edge has the shape of an arc of a circle, the center of which is located at the lower edge of the fold line, and contains a goniometric scale; the lower edge has the shape of an arc corresponding to the curvature of the cranial vault; the lateral edge connects the upper and lower edges; the fold line is normal to the cranial vault and contains a rectilinear scale.

[0031] In this particular case, the protractor is made of a metal sheet (stainless steel or other) with a thickness of 1 mm; the upper edge of the plates has the shape of an arc of 60°, a radius of 5 cm, and contains notches every 10 degrees; the lower edge of the plates has the shape of an arc with a radius of 10 cm and a length of 2 cm; the fold line has a length of 5 cm and contains holes every 1 cm.

[0032] The neurosurgical protractor is designed for the placement of tubular neurosurgical devices into the intracranial space. Specifically, it can be used in procedures such as external ventricular drainage and ventriculoperitoneal shunting.

[0033] Before surgery, CT or MRI images of the patient's head are opened on the computer. Preoperative planning of the depth and trajectory of insertion of the tubular neurosurgical device is performed using one of two options.

[0034] The first option is used when the insertion site of the tubular neurosurgical device is known, but its trajectory is unknown. The location of the burr hole (e.g., Kocher's point) is determined. A normal to the skull surface passing through the proposed burr hole is constructed in two mutually perpendicular planes (e.g., sagittal and coronal). In each plane, the angle by which the insertion trajectory of the tubular neurosurgical device must be deviated from the normal is calculated to ensure its tip is in the target area. The insertion depth of the tubular neurosurgical device is calculated.

[0035] The second option is used when the insertion trajectory of the tubular neurosurgical device is known (e.g., along the normal to the cranial vault), but the insertion site is unknown. A normal to the cranial surface is constructed in two mutually perpendicular planes (e.g., sagittal and coronal), passing through the target location of the tubular neurosurgical device tip. The location of the burr hole is determined—where the normal intersects the cranial vault. The insertion depth of the tubular neurosurgical device is calculated.

[0036] During surgery, after shaving the head, securing it with a clamp, marking the access area, treating the skin with an antiseptic solution, and draping the surgical field, an incision is made in the area where the burr hole will be placed. The periosteum is retracted with a rasp. The burr hole is created using a brace, drill, or other tool. The dura mater is finely incised with a scalpel, and the cerebral cortex is coagulated at the planned insertion site of the tubular neurosurgical device.

[0037] Take a neurosurgical protractor. Using the rectilinear scale on the fold line, measure the required length of the tubular neurosurgical device, based on the previously calculated insertion depth (if the device has depth markings, this is not necessary). Position the protractor plates in two mutually perpendicular planes, in which the preoperative calculation was made. The lower edges of the plates are placed against the bone near the burr hole, with the fold line of the protractor normal to the cranial vault. Alternatively, the lower edges of the plates can be placed against the skin, pre-positioned congruently with the cranial vault.

[0038] If the insertion trajectory of the tubular neurosurgical device is normal, it is simply inserted along the fold line of the protractor to the desired depth. If a change in trajectory is necessary, the tubular neurosurgical device is tilted away from the fold line at the required angle, using the lower edge of the fold line and the goniometric scale of the corresponding plate as a guide. After ensuring that the tubular neurosurgical device is correctly positioned (no CSF ​​leakage when entering the ventricle, etc.), the protractor is removed.

[0039] List of references

[0040] 1. Pathak SM, Licata JP, Graves EKM, Gerstenhaber JA, Erkmen K. Development of an adjustable patient-specific rigid guide to improve the accuracy of external ventricular catheter placement. J Neurosurg. 2024 May 10; 141(4):1079-1087. doi: 10.3171 / 2024.2.JNS232137.

[0041] 2. Ghajar JBG. Apparatus for guiding catheter into cerebral ventricle. Patent for invention EP0229105 B1. Application 28.05.1986. Publication 22.07.1987.

[0042] 3. Thomale UW, Knitter T, Schaumann A, Ahmadi SA, Ziegler P, Schulz M, Miethke C. Smartphone-assisted guide for the placement of ventricular catheters. Childs Nerv Syst. 2013 Jan; 29(1):131-9. doi: 10.1007 / s00381-012-1943-1.

Claims

1. A neurosurgical protractor for installing tubular neurosurgical devices in the intracranial space, comprising two mutually perpendicular plates and a fold line between them, wherein each plate contains three free edges - upper, lower and lateral, the upper edge has the shape of an arc of a circle, the center of which is located on the lower edge of the fold line, and contains a goniometric scale, the lower edge has the shape of an arc corresponding to the curvature of the cranial vault, the lateral edge connects the upper and lower edges, the fold line represents the normal to the cranial vault and contains a rectilinear scale.

2. A neurosurgical protractor according to claim 1, characterized in that the upper edge of the plates has the shape of an arc of 60°, with a radius of 5 cm, and contains notches every 10 degrees, the lower edge of the plates has the shape of an arc with a radius of 10 cm and a length of 2 cm, the fold line has a length of 5 cm and contains holes every 1 cm.

3. A neurosurgical transporter according to paragraph 1, characterized in that it is made from a metal sheet 1 mm thick.

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