HK40023303A - Self-identifying surgical clamp, fiducial element for use with such a clamp, and kits comprising such clamps and fiducials - Google Patents

Description

Self-identifying surgical forceps, reference element for use with the forceps, and kit including such forceps and reference element

Technical Field

The present invention relates to surgical devices, and more particularly, to surgical clamps for use in navigation systems or robotic systems.

Background

Computer Assisted Surgery (CAS) systems have been developed to improve safety and reduce risks in existing procedures, and have enabled new surgical methods, such as minimally invasive surgery, to be implemented. The CAS system includes a navigator to guide the surgeon during the intervention, such as the one proposed in US 6351659B 1. The navigator is typically based on an optical tracking system that continuously determines the position and orientation of the patient and certain surgical instruments relative to a fixed coordinate system. This information is matched with a virtual representation of the patient's anatomy to give visual feedback to the surgeon. The surgeon may then observe the trajectory of the surgical instrument relative to certain anatomical locations that would not otherwise be visible, for example, due to being covered by soft tissue. Another type of CAS system is a robotic-assisted device based on an optical tracker or a mechanical tracker. Robotic aids, such as the one described in US2014/0350571 a1, propose to provide physical guidance for the trajectory of the surgical instrument to the pre-planned anatomical site. All of these systems are based on fixing a reference element as part of a tracking mechanism on the anatomy of the patient.

In some spinal surgeries, for example, to perform Surgery on several vertebral body segments, more than one anatomical site must be tracked during the intervention, as described in ughwaogho et al in 2010 (e.ughwaogho, j.m. flynn, "Current Navigation Modalities in Spine Surgery," University of Pennsylvania orthopaedics Journal, volume 20, pages 65 to 69, month 5 2010). In such interventions, the different zones can be sequentially operated on using a single clamp by fixing the clamp on the target vertebra when one zone is to be intervened, and then releasing the clamp to move to the next zone. Another option is to simultaneously secure more than one clamp on different areas and have the system track one of the clamps. In both cases, the surgeon must inform the system: where or which reference array the tracker is mounted to be visible to correlate the pre-operative image of the patient with the current position of the clamp. This procedure presents some risks because human error may cause the system to believe that the tracker is associated with a surgical site that does not correspond to the true physical location. In such a case, the trajectory of the virtual representation relative to the patient presented to the surgeon will not correspond to the physical location due to the risks posed by this. In the current art, there is no system that describes an automatic identification mechanism to let the system know where the tracker is installed.

Disclosure of Invention

The present invention provides a reference clamp provided with a unique identifier in the form of a passive circuit having a predetermined impedance value that can be automatically identified by a tracking device. In a kit comprising a plurality of jaws, the identifier is automatically associated with different anatomical sites at the beginning of an intervention, during a patient registration procedure. The invention also comprises a reference piece complementary to the clip and a set of reference elements, each provided with a different configuration of radiopaque spheres.

Drawings

For the purpose of providing a thorough understanding of the present invention, there is provided in the art a set of drawings. The drawings illustrate a preferred embodiment of the invention and should not be construed as limiting the scope of the invention but merely as an example of how the invention may be practiced.

Figure 1 shows a clamp and a registration reference element according to the invention.

Figure 2 shows a set of three clamps attached to the spine of a patient according to the present invention.

Fig. 3 shows the same three clamps with registration reference elements attached to them.

Fig. 4 shows the same three grippers with a mechanical tracker and robotic assistance mounted on one of the grippers.

Fig. 5 shows two examples of automatic identification circuits.

Detailed Description

The present invention proposes surgical clamps to accurately locate and track a pre-planned surgical site in an operating room. Thanks to the invention, the navigated surgery or the robot-assisted surgery is performed in a minimally invasive manner with high accuracy. The procedure aimed at is the insertion of pedicle screws into the vertebrae, but can also be extended to other types of procedures. The precise location of the screws may be planned from preoperative images of the patient before the patient enters the operating room, or may be planned during surgery with the ability to use an intraoperative three-dimensional imaging device, typically a computed tomography system (CT). Planning the procedure includes defining the size, location, and orientation of pedicle screws in the target vertebra.

A three-dimensional image of the anatomical site may be acquired before the patient enters the operating room. In this example, the anatomical region corresponds to a portion of a spine of the patient. The surgeon plans the procedure based on the preoperative image. It should be noted that this step may be performed several days before the procedure is scheduled. When a patient enters an operating room and in order to perform a procedure with a navigation system or a robotic assistance device, the relative position and orientation of the tracking device with respect to the anatomical site must be established. This is achieved by a two step process. First, the relative position and orientation of the target vertebra with respect to a reference object rigidly fixed to the bone is registered. The clamp (1) of the invention as shown in figure 1 is rigidly fixed to the bone and serves as a reference. To complete the registration step, once the clamp is fastened to the spinal spinous process of a vertebra by means of the two jaws (3) of the clamp, an element (1') of known geometry is temporarily mounted on the clamp. This element is referred to in the literature as the registration reference element. When the registration step is completed, the registration reference elements are removed from the jaws. It should be noted that the clamp is still attached to the bone. The relative position and orientation of the jaws is then tracked during the procedure by mechanical or optical tracking means. The lower part (3) of the reference clamp is rigidly fixed to the bone by means of the jaws of the reference clamp, while the upper part (2) has a dynamic coupling mechanism (4, 5). The dynamic linkage is prepared to receive one end of the tracking device or registration fiducial elements with various markings.

With reference to fig. 3, the registration reference element (1 ') is a rigid body made of radiolucent material having several radiopaque spheres (8') arranged in a known geometry. The radiopaque spheres are easily identified in two-dimensional radiographs or three-dimensional computed tomography imaging because they exhibit high contrast with respect to the rest of the body that makes up the registration reference elements. An intra-operative image of the region is acquired while the reference clamp is secured to the target bone and the registration fiducial element is mounted on the clamp. It is desirable to use a three-dimensional intraoperative acquisition device to achieve higher accuracy. If such a device is not available, at least two-dimensional radiographs must be acquired in different orientations in order to be able to accurately locate the position of the reference element in space from the two-dimensional projection of the sphere. In the present invention, multiple grippers with unique identifiers can be used, and each gripper has an associated reference element with a unique ball configuration. These different configurations of radiopaque spheres allow for unambiguous identification of the clip during the registration process. Thus, when the registration process is completed, the system knows exactly which clip is fixed in the different anatomical sites where the surgery is to be performed.

The accuracy of the registration process depends to a large extent on the distance between the sphere of the reference element and the target region. Therefore, in order to improve accuracy, it is desirable to place the sphere as close to the target as possible. In this embodiment, the target area is the pedicle of the vertebra, and the element of the system closer to this area is the reference clamp. In the present invention, the reference clip may further comprise a radiopaque ball (8) at the upper portion, the ball (8) being used in the registration process. This makes the registration process more reliable, thereby improving the accuracy of the overall system and reducing the risks inherent to intervention.

First, the registration process establishes the exact position of the reference clamp. This can be done due to the fact that: the radiopaque spheres are easily detected in the intra-operative image and are known with reference to the geometry of the jaws and the fiducial elements. As mentioned previously, the intraoperative image may be a three-dimensional reconstruction of a region of interest or several two-dimensional radiographs. In the case of a three-dimensional intraoperative acquisition, the position of the reference clip is easily established by finding a radiopaque sphere in the three-dimensional volume. If the registration is performed using two-dimensional radiographs, the position of the sphere is obtained by: the positions of the spheres are back projected from the two dimensional image and the position of the spheres in three dimensional space is found by triangulating the various projections of each sphere.

The position and orientation of the vertebrae in the three-dimensional preoperative image is then matched to the intraoperative image of the vertebrae. This is performed using a standard gray-based registration algorithm that solves for the transformation that relates the two geometries together. At this point, the surgical site defined on the pre-operative image of the vertebra may be identified in the operating room relative to the reference clamp. It is important to note that the reference clamp is rigidly fixed to the bone, so there is no relative movement between the clamp and the bone. Thus, the registration fiducial element may be removed, leaving the reference clamp fixed to the bone. In this regard, the position and orientation of the vertebrae are accurately tracked during surgery by tracking the position and orientation of the reference clamps. The registration fiducial element can be easily removed from the reference clamp due to the coupling mechanism described below.

The coupling mechanism (fig. 1) is based on a magnetically dynamic coupling system, advantageously but not necessarily comprising two parts, each part comprising magnets (5, 5') having opposite polarities, such that they cooperate with each other to form the coupling portion. The mountable element may be a registration reference element or a tracker device. Preferably, three V-shaped grooves (4) on the clamp part and three balls (4') on the other part (reference element or tracker) provide the magnet coupling together with the magnet. This coupling forms a precise and repeatable interface between the two rigid bodies. The system provides six points of contact-two for each sphere-to ensure that the coupling mechanism constrains the six degrees of freedom (three degrees of freedom with respect to position and three other degrees of freedom with respect to rotation) of the relative motion between the jaws and the tip of the tracker. A magnet (5, 5') located in the centre of each part provides the strength required to avoid any relative movement between the clamp and the tip of the tracker by holding the two parts together. The force exerted by the magnet is such that it ensures the connection between the clamp and the tracker during an intervention. However, this force makes the connection releasable by a human operator to allow easy removal of the system at any time. When the three V-shaped grooves form an angle of 120 °, the most stable dynamic coupling portion will be obtained. However, for the present invention, it is preferred that the three V-shaped grooves form three angles so that the coupling mechanism can only be engaged in a single position. For example, angles of 110 °, 110 ° and 140 ° ensure that the coupling mechanism is engaged in a unique position. For this purpose, at least one of these angles must be different from the other two angles.

The pliers comprise two rigid halves, each half having a jaw with a tip at its lower part (3). The tip of each jaw penetrates the surface of the bone to ensure that the clamp is firmly secured to the bone during the intervention. The upper part (2) of one of the halves has a base of the dynamic coupling mechanism with three V-shaped grooves. The other half has a rounded tip at its upper portion to facilitate clamping of the clamp by an auxiliary tool. The tool is adapted to clamp the current clamp. The jaws have a ratchet-tooth mechanism to allow the jaws to be clamped against the bone and to prevent the jaws from being released from the bone during an intervention. The ratchet clamping mechanism has teeth at both halves of the clamp to allow movement only in the clamping direction.

The clamp and tracker (fig. 4) have a detection mechanism that informs the system when the tracker is attached to the clamp. The detection mechanism is an electrical circuit connected to a processing unit that is able to identify when a connection has been established. The clamp portion of the coupling mechanism at the upper portion of the clamp has a passive circuit, and the tracker portion of the coupling mechanism at the tip of the tracker connects the base portion to the processing unit. The processing unit applies a small voltage, so when the connection is established, the circuit is closed and a current is detected.

The ball of the previously described dynamic coupling mechanism is made of an electrically conductive material and is connected to the processing unit. The V-shaped groove has a conductive portion with which the ball makes contact to establish an electrical connection between the top portion and the base portion. Fig. 5a and 5b are two examples of circuits implementing the detection mechanism. In both cases, two impedances of value Z are used between the different contacts. In a first example, if a voltage V is applied by the processing unit, the value of the current through the circuit is I-2V/Z. In a second example, if a voltage V is applied by the processing unit, the value of the current through the circuit is I ═ V/2Z.

Other configurations of passive circuits include one or more resistors, capacitors, coils, or any combination of coils. This concept extends to the automatic detection of different clamps in the present invention. The number of vertebrae that must be intervened depends on the type of operation and may range from only two to more than ten. In this context, the surgeon can fix several clamps at different vertebrae to obtain a reliable reference at different positions. The robotic system will then indicate the trajectory of the screws that must be inserted at each vertebra. To achieve this, it is essential that the system always knows the vertebrae to which the tracker is fixed, since the trajectory of the screws varies from one vertebra to the other. In order to enable the system to automatically detect different clamps, each clamp presents a different impedance Z in the detection circuit. Thus, the processing unit can identify to which clamp the tracker is connected by measuring the current flowing through the clamp. Different clamps have an identifier associated with them.

A clamp with a different identifier has a different registration reference element associated with the clamp to also identify the clamp during the registration process. Different registration reference elements have the same body made of radiolucent material, but the radiopaque spheres have different configurations. The different configurations of the spheres make it possible to identify the clamps during the registration step and, therefore, which clamp is fixed to which vertebra. Thus, the system can associate the vertebrae to the clamp identifier, and when the tracker is connected to the clamp, the system can immediately identify in which vertebra the tracker is installed.

The clamps are rigidly fixed to the bone during intervention and, therefore, the clamps must be made of a hard and biocompatible material. Titanium is the metal of choice in many medical applications, since it satisfies both properties. The titanium alloy Ti6Al4V is commonly used for prostheses or appliances, and is therefore the preferred material for clamps. Stainless steel is also suitable for such applications. Alternatively, the clamps may be made of a carbon fiber reinforced ceramic material which has the advantage of being radiolucent.

Claims (7)

1. Surgical clamp (1) comprising two halves, each half having an upper portion (2) and a lower portion (3) forming two jaws (3) adapted to be brought into contact with a surgical site, characterized in that one of the upper portions (2) is provided with a dynamic coupling mechanism (4, 5) and a passive electrical circuit having a predetermined impedance value.

2. The surgical clamp (1) according to claim 1, wherein the dynamic coupling mechanism comprises a magnet (5) and three V-shaped grooves (4), each groove having at least one conductive portion, the grooves forming three angles, wherein at least one of the angles is different from the other two angles.

3. The surgical clip (1) according to any one of the preceding claims, further comprising a radiopaque ball at the upper portion (2).

4. A kit formed from a plurality of tongs according to any one of the preceding claims 1 to 3, wherein each tong has a different impedance.

5. A registration reference element (1 ') for use with a forceps according to any of the preceding claims, the registration reference element (1') comprising a radiolucent material and being provided with dynamic coupling means (4 ', 5') matching the coupling of the forceps (1).

6. The registration fiducial element of claim 5, comprising a predetermined configuration of radiopaque spheres at a top portion.

7. A kit of registration fiducial elements as in claim 5 or 6, each fiducial having a different configuration of radiopaque spheres.