Patent pending n° EP13187799
Title: apparatus for orienting and positioning surgical instruments and implant prosthesis in a bone seat
The purpose of this system is to guide the surgeon during a prosthetic hip intervention and in particularly during the positioning of the shell into the acetabulum cup; producing real-time directions on reaching a predetermined target.
A more in depth look at the systems currently on the market can be found in appendix A.
The system is capable of compensating for three different types of errors:
1) Errors related to the incorrect positioning of the patient.
2) Errors related to the patient moving during the operation.
3) Errors related to the compensation of the pelvic tilt angle.
The methodology and system are furthermore compatible with different surgical positioning and different tilt angle compensation techniques.
The use of this invention does not change the operation performed by the surgeon.
The system is based on the individualization of only two anatomical points (during the intervention), which are the only points that can guarantee a simple identification with little influence from the morphology of the patient.
The system does not require measuring anatomical distance; instead its functionality is entirely based on its survey of angles.
The system is made up of the devices shown in Fig. 19 and the methodology of how they are used is summarized in Fig 21.
2101 Definition of the Target and Ideal position
2102 Calibration of the devices and positioning of the PIN
2103 Static correction of the Initial Position
2104 Dynamic correction to reach the target
2105 Generation of directions to reach the Target.
2) Introductory Concepts
The purpose of the invention is to support the surgeon during the insertion of the acetabulum cup (2003)inside the acetabulum (2002)during total or partial prosthetic hip interventions.
The incorrect positioning of an acetabulum cup can cause a series of complications that can compromise the entire implant (see appendix B).
The correct positioning can be found through the identification of two angles measured with respect to the two anatomical references of the pelvis: “the symmetry hip plane” and the “zero tilt plane” also called “the tilt plane” (2305).
Figure 23 shows how these two planes (2305 and 2307) are perpendicular to one another.
The “tilt plane” (201) is the imaginary plane that passes through the two iliac crests and the two superior points of the pubic symphysis (204 and 205).
For convenience the plane can be moved downwards (2306, 301) until it passes through the two acetabulums (2308, 306), which make up the insertion objectives of the acetabulum cup (2003).
Figures 3, 4, 5 show the ideal (307, 404, 507) direction that consists of the target for the correct position of the acetabulum cup (2003).
The ideal anatomic direction for the insertion of the acetabulum cup can be defined unambiguously through the identification of the anatomic angle of incline (309, 405) and the anatomic anteversion angle (311, 509).
The anatomic angle of inclination (309,405) is the angle between the projection of the ideal direction on the tilt plane (310,404) and the web of intersection between the symmetric plane and the tilt plane (308,402).
The anatomic anteversion angle (311, 509) is the angle between the ideal direction (307,507) and the tilt plane (301, 501).
Figure 5 shows how easily the anteversion angle (509) can theoretically be measure through a section of the pelvis parallel to the tilt plane and inclined with respect to the symmetric plane of an angle equal to the inclination angle. This prospective is shown from the direction 407 in Figure 4.
When the patient is positioned supine on a flat surface (for example on an x-ray bed or on an operating table) (Figure 7) the position the pelvis assumes is such that the tilt plane (702) cuts the reference plane (701) forming what is generally called “the angle of tilt.” (703).
During the intervention it is impossible to observe the tilt plane with precision and it is therefore difficult for the surgeon to use the incline angle and anatomic antiversion as references for the correct positioning of the acetabulum cup.
It is therefore necessary to transform the two anatomic angles into two different angles (called “operating angles” in the document), these angles use the operating table as a reference system.
Figure 8 shows how this transformation clearly influences the tilt angle (809).
The above image in Figure. 24 (missing) shows how a pair of anatomic angles leave space for incline and antiversion operating angles, which vary depending on the angle of tilt.
The tilt angle is dependent on:
1) Anatomic factors (morphology of the pelvis, patient’s build)
2) Position assumed by the patient
3) The type of surface contact.
Appendix C describes some patient positioning techniques that allow the angle of tilt to remain constant in the future positioning of the patient. These techniques are very useful because they can evaluate the patient’s initial angle of tilt in regards to the operating table, by means of an x-ray.
Estimating the angle of tilt with a simple x-ray (see appendix D) and knowing or estimating the anatomic target angles, makes it possible to calculate the “operating target angles,” in other words the incline angles and antiversion angles in regards to the reference plane which are to be used for the positioning of the acetabulum cup.
The initial position of the patient must be taken into consideration when calculating the operating angles, as the patient’s pelvis could be positioned incorrectly in regards to the reference plane (Fig. 12,13,14).
The operating angles can vary during the intervention as a result of pelvic movement subsequent to the initial position due to various types of access points for the prosthetic hip implant or voluntary or involuntary movements of the patient.
3) Image Descriptions Descrizioni immagini.
FIG.1- Side view of the pelvis leaning on a plane with an incline which has a pelvic tilt of zero degrees.
FIG.2- Perspective view of the pelvis leaning on a plane with an incline resulting in a pelvic tilt of zero degrees.
FIG.3- Side view of the pelvis placed at a zero degree tilt showing the correct position of the acetabulum cup in the pelvis(2003) according to the white zone (see attachment 1)
FIG.4- A view of the pelvis from above placed at a zero degree tilt that shows the angle of incline for the correct positioning of the acetabulum cup according to the white zone (See attachment 1).
FIG.5- A perspective view of the pelvis placed at a zero degree tilt with the perspective of the two imaginary lines that represent the incline and antiversion for the correct positioning in the acetabulum according to the white zone (see attachment 1).
FIG.6- A perspective view of the pelvis with a tilt other than zero degrees leaning on a plane.
FIG.7- Side view of the pelvis with a tilt different from zero degrees. A graphic representation of the tilt angle greater than zero calculated with the angle given by the intersection of the leaning plane and the plane called the Anterior Pelvic Tilt.
FIG.8a- Side view of the pelvis with a tilt angle equal to zero degrees, which also represents the Anterior Pelvic Plane parallel to the plane in order to represent a tilt equal to zero degrees. Furthermore the lines represent the correct positioning of the acetabulum cup (2003) according to the white zone (see attachment 1).
FIG.8b-lateral view of the pelvis with a tilt other than zero degrees representing the change in the positioning of the acetabulum cup in the white zone with the change of the pelvic tilt angle (802;803;810).
FIG.9- View of the pelvis from the perspective of the acetabulum (906) to underline the difference between the antiversion angle with a zero degree tilt and one with a tilt greater than zero degrees positioning the acetabulum cup (Fig…) according to the guide lines of the white zone (see attachment 1).
FIG.10-Perspective view to underline the difference between the antiversion angle with a tilt angle of zero degrees (1011) and with a tilt greater than zero degrees (1010) positioning the acetabulum cup (Fig….) according to the guide lines of the white zone (see attachment 1).
FIG.11- View of the pelvis from above with a tilt angle other than zero and representing the angle of inclination.
FIG.12 View of the pelvis on a plane with casual lateral repositioning and rotation with the graphic representation of some of the necessary parts of the described system.
FIG.13- View of the pelvis from above with repositioning and angular corrections by the described system.
FIG.14- Frontal view of the pelvis with casual repositioning and rotation and a graphic representation of the margin of error corrected by the described system.
FIG.15a- Frontal view of the single patient device of the described system.
FIG.15b- Perspective view of the single patient device of the described system.
FIG.16- Side view of the assembly of some parts of the described system.
FIG.17- Frontal view of a component of the described system
FIG.18- Perspective view of some components of the described system.
FIG.19- Perspective view of the example components of the device for the described system.
FIG.20- View from above of the positioning of the acetabulum cup inside the acetabulum.
The methodology can be sub-divided into five phases described in Fig. 21.
The first phase (2101) is pure planning: it can be performed before the intervention and foresees the definition of the operating angles, which will be the objective during the intervention. As previously mentioned this planning needs to take into account various information such as:
1) Anatomic reference angles
2) Compensation for the tilt (initial tilt)
Appendix E describes how this phase can differ depending on the various operating approaches. This invention is compatible with all the approaches described.
The result of this phase is the pairing of the operating angles (the operating incline angle and antiversion angle) presuming the patient assumes the ideal supine position and alignment with respect to the operating plane (Fig 7).
Such result can be obtained through the use of appropriate software or by directly inserting the information (anatomic incline, anatomic antiversion, and initial tilt angle) in the principle device (Fig. 15) using the buttons (1502-1505) and the display found on the front of the device (1501).
The second phase (2102) foresees the patient’s supine position and is aligned with respect to the operating table and the calibration of the principle device (1901) is given by the sensor that corrects for movement during the operation (1904).
The calibration of the two instruments consists of the positioning of both devices in a pre-defined position called “calibration position” in regards to the operating table and can be found under one of the selections using the buttons on the principle device (1502-1505).
Thanks to the calibration procedure, the principle device (1901) and the sensor (1904) can estimate the variation of the angular positioning on three axles in regards to the reference system
composed by the operating table. This system is possible thanks to the presence of electronic circuits dedicated to this purpose (gyroscopes, accelerometers and magnetometers) inside both devices.
The third phase (2103) has two main objectives:
1) The connection of the sensor to the pelvis to correct for movement during the operation (1904):
a surgical pin (1905) is inserted into the pelvis and is connected to the sensor which corrects for movement during the operation; in this way the sensor and the pin are joined to the hip and every rotation of the pelvis is recorded by the sensor and transmitted to the principle device (1901). It is not mandatory to insert the pin in a specific location.
2) Compensation for errors related to the imprecise positioning of the patient in regards to the reference system:
The compensation of the initial positioning errors is implemented by connecting the principle device (1901) to the compass device (1903) as shown in Fig 16, pointing the two extremes of the compass on the two iliac crests (Fig 14) and pressing one of the buttons on the principle device (1502-1505).
Thanks to the position sensors of the principle device and the initial calibration completed in phase 2, the system is capable of individualizing the two angles identifying the error committed while aligning the patient with the operating table as the reference system (1405, 1303); These angles are automatically compensated by the system during the later phases.
By pressing the button, the principle device also memorizes the angular position of the sensor which corrects for movement during the operation (1904): this position will serve as a reference during the next phase to evaluate the various pelvis positions in regards to its initial position.
In the fourth phase the principle devise (1901) is connected to the clamp device (1902) as shown in Fig 18.
The clamp is used to join the principle device with the instruments necessary during the intervention: in further detail it deals with a cutter and/or an impact machine.
The fourth phase (2104) is characterized by the identification of the principle device’s angular position in comparison to the operating angles, compensating for the initial positioning errors (1405, 1303) and eventual pelvis movements revealed by the sensor to correct for movements during the operation (1904).
In the fifth phase (2105) the principle device communicates to the surgeon the directions needed in order to reach the pre-established angular target at the start or shut down of the led (1506-1513) located on the front of the device (Fig. 15).
The 4 led in the form of an arrow (1510-1513) guide the surgeon in the rotations, while the purpose of the central led (1509) is to signal the correct alignment of the device to the surgeon.
The system is also capable of compensating for delicate rotations in the three axles of the pelvis, therefore guaranteeing the compatibility with interventions that consider the rotation of the patient from a supine to a lateral position.
The fourth and fifth phases (2104, 2105) alternate repeatedly for the duration of the intervention until the acetabulum cup is inserted into the acetabulum.
At the end of the implant it is possible to use the device to evaluate the final error in regards to the desired result.