DESC:FIELD OF THE INVENTION:
This invention relates to the field of medical engineering.

Particularly, this invention relates to pre-surgical planning by using non-invasive imaging techniques.

More particularly, this invention relates to a system and method for development of a patient specific path guidance tool for human cervical, thoracic and lumbar vertebrae in Minimum Invasive Spine Surgery (MISS).

Specifically, this invention relates to a system and method for development of a patient specific path guidance tool for vertebrae in Minimum Invasive Spine Surgery.

BACKGROUND OF INVENTION:
Minimally invasive spine surgery (MISS) was first performed in the 1980s, but has recently seen rapid advances. Figure 1 shows human spine. Technological advances have enabled spine surgeons to expand patient selection and treat an evolving array of spinal disorders, such as degenerative disc disease, herniated disc, fractures, tumors, infections, instability and deformity. MISS was developed to treat disorders of the spine with less disruption to the muscles as shown in fig. 18. This can result in quicker recovery, decrease operative blood loss, and speed patient return to normal function. In some MISS approaches, also called "keyhole surgeries," surgeons use a tiny endoscope with a camera on the end, which is inserted through a small incision in the skin. The camera provides surgeons with an inside view, enabling surgical access to the affected area of the spine.

In prior art, through a small keyhole tubular retractor placed and rested on vertebra of interest. Through tubular retractor, small wire drill passed and advanced on human vertebra. The path is continuously monitored through C arm X ray machine. Generally, 20~30 X rays are required to check path of drill. If satisfactory, then instrument passed through retractor and hole enlarged and pedicle screw placed in position.

As with all non-emergency spinal surgeries, the patient should undergo an appropriate period of conservative treatment, such as physical therapy, pain medication, or bracing, without showing improvement, before surgery is considered. The time period of this varies depending on the specific condition and procedure, but is generally six weeks to six months. The benefits of surgery should always be weighed carefully against its risks. Although a large percentage of patients report significant symptom and pain relief, there is no guarantee that surgery will help every individual. Many MISS procedures can be performed on an outpatient basis. In some cases, the surgeon may require a hospital stay, typically less than 24 hours to 2 days, depending on the procedure.
MISS procedures are used to treat spinal disorders such asSpinal deformities such as Scoliosis (Stair Case Effect), Degenerative Disc Disease, Herniated Disc, Vertebral compression fractures, Tumors, Spinal infections, Spinal instability, etc.

Problems associated with such procedures are enlisted below:
• Highly skilled surgery technique
• Takes usually long time e.g. 4-24 hrs
• During each step requires confirmation of position of tool by C arm X-ray usually more than 40 exposures per surgery
• increases risk to Surgeon and Assistants of X ray exposure

Potential benefits of MISS comprise:
• Smaller incisions
• Smaller scars/less scar tissue
• Reduced blood loss
• Less pain
• Less soft tissue damage
• Reduced muscle retraction
• Decreased postoperative narcotics
• Shorter hospital stay
• Possibility of performing on outpatient basis
• Faster recovery
• Quicker return to work and activities

Surgery Risks associated with MISS comprise:
• Dissatisfactory Instrumentation Placement; may require re-operation
• Incision problems
• Death
• Spinal fluid leakage
• Paralysis
• Bleeding, Blood vessel damage, Blood clots, Bruising
• Pain or discomfort
• Allergic reaction, Anesthesia reaction, Headache
• Infection
• Pneumonia
• Stroke

OBJECTS OF THE INVENTION:
An object of the invention is to design and develop a Patient Specific guidance fixture to minimize risk of dissatisfactory location of instrument.

Another object of the invention is to provide a 3-dimensional model to help surgeon to visualize bone structure and deformity in spinal structure.

An additional object of the invention is to extract negative surfaces.

Yet an additional object of the invention is to develop guidance fixture to minimize risk of dissatisfactory location of instrument which will assist Surgeon to reduce Surgery time, thus saving OT costs as well as protecting staff of X-ray exposures.

SUMMARY OF THE INVENTION:
According to this invention, there is provided a system for development of a patient specific path guidance tool for surgeries pertaining to vertebrae, said tool comprises:
- a left hand side piece which interlocks with a right hand side piece, said left hand side piece comprising a downward facing lateral side elongate channel configured to allow a guide wire to pass through it and said right hand side piece comprises a downward facing lateral side elongate channel configured to allow a guide wire to pass through it; and
- an interlocking mechanism, at its operative posterior side, provides a profile which matches a resting surface on a pedicle of a bone, characterised in that, said interlocking mechanism comprising modular interlocking geometry such that said left hand side piece and said right hand side piece can be locked with respect to each other such that allows said elongate channels to have different angles with respect to a medial axis, thereby enabling said tool to assume a plurality of angular deviations, thereby configuring it, for use, towards a variety of patients with a variety of bone geometry.

Typically, an operative posterior end of the elongate channel comprises a profile corresponding with a left-side transverse process pedicle so that said tool derives a stable left-hand-side support along with precision of guide wire entry.

Typically, an operative posterior end of the elongate channel comprises a profile corresponding with a right-side transverse process pedicle so that said tool derives a stable right-hand-side support along with precision of guide wire entry.

Typically, said tool comprises a left-side angled branch connects said left-side piece with said elongate channel.

Typically, said tool comprises a right-side angled branch connects said right-side piece with said elongate channel.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention is now described in relation to the accompanying drawings, in which:

Figure 1 shows human spine;

Figure 2 shows process of conversion process of non-invasive images viz. CT/MRI data into 3D model;
Figure 3 shows flow chart for design and development of Patient Specific Surgical Guide for MISS;

Figure 3A shows sample human vertebra with pedicles and transverse processes;

Figure 3B shows a method to establish correct pedicle axis;

Figure 3C shows fitted pedicle screw through same axes;

Figure 3D illustrates modeling of negative surface for tool / jig / surgical guide;

Figure 4 shows graphical representation of the process of construction of development of surgical guides;

Figures 5A and 5B illustrate various views of a surgical guide (100) of this invention;

Figure 6 shows details of design of this invention.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a system and method for development of a patient specific path guidance tool. The development of this patient specific path guidance tool is imperative in assistance of Minimally Invasive Spine Surgery (MISS) and Transforaminal Lumbar Interior Fusion (TLIF) surgeries by using BioCAD models retrieved from non-invasive imaging techniques and Reverse Engineering approach. The output of this system and method is a patient specific surgical guide for human vertebrae for MISS which is the crux of this invention.

According to this invention, therefore, there is provided a patient specific path guidance tool.

Figure 2 shows process of conversion process of non-invasive images viz. CT/MRI data into 3D model.

Imported raw data is segmented based on predefined threshold HU value. By using developed GUI, this segmented data is transformed to smooth surface and can be exported in as Point Cloud Data. By using conventional modelling mechanisms, this data is pre-processed for removal of unwanted data manually as well as automatic data reduction by using noise reduction techniques, etc. Under close observations and guidelines from an Orthopedic Surgeon, further strategy for surgery is decided. Identification of resting surfaces and locations are critical in this step. This refers to a previous patent filed by the current Applicant and current Inventor.

Figure 3 shows flow chart for design and development of Patient Specific Surgical Guide for MISS.

In accordance with an embodiment of this invention, a first determination mechanism is configured to determine axes for pedicle screws, using conventional CAD modelling environment.

Figure 3A shows sample human vertebra with pedicles and transverse processes. The objective of this step is to establish pedicle axes for correct fitment of pedicle screws. To establish correct axes, please refer Figures 3A, 3B, and 3C. In figure 3A, resting surface for surgical guide is highlighted and referenced by reference numerals 14a, 14b, and 14c, pedicle axes as well as elliptical cross section of pedicle. Cross Section A-A is elliptical cross section. One needs to fit pedicle screw with minimum same wall thickness on all sides of screw.

To establish correct pedicle axis, as shown in Figure 3B, a cylinder with average diameter is fitted through Point Cloud Data of pedicle region selected from point cloud data of vertebra estimated from the system and method of this invention.
By using techniques for fitting cylinder through selected point cloud data, the system can establish Cylindrical surface through pedicle point cloud data. This enables the system and method to establish correct pedicle axis (same as the fitted cylinder). Figure 3C shows fitted pedicle screw through same axes.

In accordance with another embodiment of this invention, a modelling computation engine is configured to model a resting surface.

Figure 3A shows resting surfaces for the surgical guides. These are well established landmarks on each vertebrae of human spine. In this system and method, point cloud is selected and fit with smooth surface through these points. This enables us to get negative profile for surgical guide. This is to be selected manually while designing jig as shown in figure 3D

Figure 3D illustrates modeling of negative surface for jig / surgical guide.

Figure 4 shows graphical representation of the process of construction of development of surgical guides.

1. Point Cloud Data estimated using the current system based on reverse engineering approach is used.
2. Pedicle Axes Selection: Land mark Point selection for pedicle region and cylindrical surface fitted through the points. Output will be diameter (which will enable to identify diameter of pedicle screw) and axes of pedicle screw can be identified and exported as numerical data to modelling mechanisms.
3. Resting surface: Points on resting surfaces selected and smooth surface fitted through it. These surface exported as an IGES file, in neutral file format.
4. CAD Environment: In CAD based environment, axes and surface modelled. By considering pedicle axes cylinders of pedicle size modelled. Hole of dia. 2.5~3 mm created for drilling. Both cylinders are connected together by modelled support structure. Modelled cylinders are cut/trimmed by imported negative surfaces.[refer figure 5 of accompanying drawings]
5. Data exported as *.stl file, which can be directly printed on RP machines.

For establishment of process, variety of surgical templates had been developed for cervical and thoracic spine for scoliosis patients of age from 5 years to 74 years.

Figures 5A and 5B illustrate various views of a surgical guide (100) of this invention.

In at least an embodiment of this surgical guide, there is provided a left hand side piece (51) which interlocks with a right hand side piece (52). The interlocking mechanism (53), at its operative posterior side, provides a profile which matches a resting surface on a pedicle of a bone. Typically, the left hand side piece comprises a downward facing lateral side elongate channel (54) configured to allow a guide wire to pass through it. Typically, the operative posterior end of the elongate channel comprises a profile corresponding with a left-side transverse process pedicle so that the jig derives a stable left-hand-side support along with precision of guide wire entry. Typically, the right hand side piece comprises a downward facing lateral side elongate channel (55) configured to allow a guide wire to pass through it. Typically, the operative posterior end of the elongate channel comprises a profile corresponding with a right-side transverse process pedicle so that the jig derives a stable right-hand-side support along with precision of guide wire entry. The interlocking mechanism is a modular interlocking mechanism such that the two pieces can be locked with respect to each other such that it is plausible for the elongate channels to have different angles with respect to the medial axis. This enables the jig, of this invention, to assume a plurality of angular deviations, thereby configuring it, for use, towards a variety of patients which a variety of bone geometry. This, drastically, reduces inventory cost as also provides a highly stable and precise fit of the jig on to the bone, thereby accurately guiding the guide wires into the bone. A left-side angled branch (56) connects the left-side piece (51) with the elongate channel (54). A right-side angled branch (57) connects the right-side piece (52) with the elongate channel (55).

Further, a surgical trail was conducted with above mentioned drilling jig/template/surgical guide, following were the observations:
1. Fitment was tight may be due to shrinkage of material while cooling down or during 3D printing process.
2. Observed difficulty in fitment of jig due to soft tissues, etc. in vicinity of the vertebrae.
3. These templates need to be sterilized since these are coming directly contact with bones and tissues. During sterilization process, deformation observed in thin sections, so needed to have minimum thickness of at least 3 mm.
4. Also, removal of template is difficult after pedicle drilling. Guide wires are long and cannot be removed before removing jig. If removed holes gets filled with blood and soft tissue creating issues with axes establishment once again.

To avoid these problems, following changes are suggested in design of template.

Figure 6 shows details of design of this invention. It is proposed to split drill jig body or handle into two pieces with interlocking geometry to avoid bending or split under load condition. Part A and part B are assembled in body during surgery and bound together by means of rubber band or string. After drilling, guide wires placed in position and rubber band or string broken to separate two parts of drilling jig.

Once these drill jig parts are separated, guide wires in position, tubular retractor inserted through guide wire and placed in position. Afterwards, guide wires are removed and through tubular retractor instruments or pedicle screws are passed.

While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
,CLAIMS:WE CLAIM,

1. A system for development of a patient specific path guidance tool for surgeries pertaining to vertebrae, said tool comprising:
- a left hand side piece (51) which interlocks with a right hand side piece (52), said left hand side piece comprising a downward facing lateral side elongate channel (54) configured to allow a guide wire to pass through it and said right hand side piece comprises a downward facing lateral side elongate channel (55) configured to allow a guide wire to pass through it; and
- an interlocking mechanism (53), at its operative posterior side, provides a profile which matches a resting surface on a pedicle of a bone, characterised in that, said interlocking mechanism comprising modular interlocking geometry such that said left hand side piece and said right hand side piece can be locked with respect to each other such that allows said elongate channels to have different angles with respect to a medial axis, thereby enabling said tool to assume a plurality of angular deviations, thereby configuring it, for use, towards a variety of patients with a variety of bone geometry.

2. A system for development of a patient specific path guidance tool for surgeries pertaining to vertebrae as claimed in claim 1 wherein, an operative posterior end of the elongate channel comprising a profile corresponding with a left-side transverse process pedicle so that said tool derives a stable left-hand-side support along with precision of guide wire entry.

3. A system for development of a patient specific path guidance tool for surgeries pertaining to vertebrae as claimed in claim 1 wherein, an operative posterior end of the elongate channel comprising a profile corresponding with a right-side transverse process pedicle so that said tool derives a stable right-hand-side support along with precision of guide wire entry.

4. A system for development of a patient specific path guidance tool for surgeries pertaining to vertebrae as claimed in claim 1 wherein, said tool comprising a left-side angled branch (56) connects said left-side piece (51) with said elongate channel (54).

5. A system for development of a patient specific path guidance tool for surgeries pertaining to vertebrae as claimed in claim 1 wherein, said tool comprising a right-side angled branch (57) connects said right-side piece (52) with said elongate channel (55).

Dated this 10th December, 2017

CHIRAG TANNA
of INK IDEÉ
APPLICANT’S PATENT AGENT