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Femur Osteotomy THR  App

         An App that merges computer assisted orthopaedic surgery (CAOS) features with augmented reality and  helps orthopaedic  surgeon to navigate and position the Blade of the Saw accurate in Space  by adjusting in real time.

         The App developed for augmented reality helping the surgeon during operation to navigate and position the blade saw properly. The App increase the accuracy, during bone cutting.

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Description

   The surgeon during Total Hip Replacement usually performs by free hand technique femur neck resection  with Orthopaedic bone saw tool, which is a bone cutter with reciprocating blade. This delicate procedure deserves good surgeon’s visual assessment of planes, hand craftsmanship and experience to perform the resection optimal namely in plane and length. The resection level is usually adjusted intra operatively manually by seeing a ruler or only by surgeons experience. The level of femoral neck resection is marked on bone with the electrocautery and with the  reciprocating blade of  bone saw the femoral head is cut. The plane of cutting should be perpendicular to the neck shaft Axis. Computer-assisted navigation system is proven that they improve  the precision and have been used in orthopaedic surgeries and they  offer superior accuracy compared to free hand techniques. The sites of intended osteotomies are identified by the navigational system and osteotomies are then performed manually, with the orientation of the  navigated  saw blade  guided by the navigational systems the required equipment are  costly and laborious to handle  intra operatively.

The  application take advantage of Augmented reality and merges it with Computer Assisted Orthopaedic Surgery (CAOS) techniques and principles in effort to help an orthopaedic  surgeon during operation without the need of expensive CAOS equipment. The App offers a cost-effective and promising alternative to navigation systems, offering  superior accuracy compared to free hand techniques.The app offers a navigated saw namely with the orientation of the saw blade guided by the App in Space.

           The App is medical App software aimed for orthopaedic surgeons, providing a tool that allows the surgeon to expedite the stage of femur neck resection during hip replacement surgery  effortlessly by adjusting  intra operatively the femoral neck resection level according to preoperative measurements thus allowing  accurate cutting of femur neck. The app works by offering:

-A red hazy plane appear perpendicular to yellow cylinder depicting the femoral neck the point of intersection between the planes, by pressing the + or - Button  you can adjust  intra operative in augmented reality the exact resection level of the femoral neck you plan and see simultaneously where resection level should be - depicted by the moving red plane in real time  -  The red plane intersect the distance from centrum of femur head to trochanter minor, the osteotomy length value is printed in real time continuously in screen and adjusted according to preoperative desired femur neck resection distance  in mm.

- Three perpendicular planes around the saw blade  appear with different hazy transparent colours (sagittal-blue, coronal-red, transverse-green) in augmented reality (AR ) over the tip of the bone saw blades extending to the  end over the blade  left-right span dimension.

-Over the screen in real time three angles corresponding to the direction of saw blade are depicted. Manipulating the Oscillating Bone Saw Cutting Machine Orthopedic Power Tool in real time the surgeon, values of all above mentioned angles change respectively, obtaining  positional information and direction with accuracy in real time in augmented reality by observing the screen of the i-phone. Angle values in real time are printed in  different colours in screen, whenever the values fall outside the normal ranges.

-The surgeon can be directed by augmenting his vision reality by taking into account the readings  and calculations and  perform resection osteotomy of femoral the neck accurate, without  being mislead, simultaneously adjusting intra operatively in real time the osteotomy depth and distance objectively, aiming always to measured preoperatively planed osteotomy features.

-By monitoring live the depth of the cut the surgeon can’t be mislead by wrong perceptions, so can predict where to stop cutting during handling with the  reciprocating oscillating saw without  accidentally injuring  neuromuscular structures.
 

   Missing anatomical reference points due to limited access and view are common problems during  joint replacement surgery accuracy in these surgeries is of paramount importance. Now the surgeon can obtain positional information more accurately in real time in augmented reality (AR) of the  blade saw by observing also the plane of the intended bone cut at femoral neck in mm ,eliminating the need for cumbersome, implant-specific mechanical jigs makes the app easily applicable. The App helps for  accurate, smooth, controllable, in line with planes without edges or off planes bone cuts compared to free hand techniques, a cost-effective and promising alternative to navigation systems used in orthopaedic surgeries. The combination of Augmented reality environment and real surgery with planes and rulers  appearing in operative field intra operatively, aiding the ability of surgeon to perform precise osteotomies brings a new dimension in operational surgery. The ability to integrate live accurate measurements of distances and angles and also  simultaneously estimating the range of depth cut before the actual cutting in augmented reality makes the app particularly useful especially in  minimal invasive operational settings where by default the vision of structures is sacrificed.

    All information received from the software output must be clinically reviewed regarding its plausibility before patient treatment! The App indicated for assisting during operation the Operator. Judgment and experience are required to properly use the App. The software is not for primary image interpretation. Any influence the operators in making decisions during operation remains Surgeons own responsibility and experience. A surgeon must always rely on his or her own professional clinical judgement when deciding whether to use a particular technique when treating a particular patient. App does not dispense medical advice. It is recommended that surgeons must be trained in the use before using it in real surgery. 

 Reference 

1. Kevin L. Garvin MD,  et al  Total Knee Arthroplasty With a Computer-navigated Saw A Pilot Study Clin Orthop Relat Res (2013) 471:155–161.

2. Nobuhiko Sugano Computer Assisted Orthopaedic Surgery for Hip and Knee Current State of the Art in Clinical Application and Basic Research-Book- Spinger Publication. (2019)

3.Jess H. Lonner  Robotics in Knee and Hip Arthroplasty Current Concepts, Techniques and Emerging Uses- Book- Springer Nature Switzerland publication (2019)
4. Guoyan Zheng Shuo Li  Lecture Notes in Computational Visionand Biomechanics 

Editors Computational Radiology for Orthopaedic Interventions Book- Springer Nature Switzerland publication (2019)

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        How can I use this  App

 

    For successful accurate bone saw blade placement during instrument with the aid of App two physical devices: (a) the  Case i-Phone - Probe tool (CIPT) and (b) the Clamp tool (CT) have to be 3D-printed according to surgeon preference material (Stainless Steel, ULTEM or Peek which can be sterized according to manufacturer own specification and guidelines) - (STL or OBJ files can  be downloaded for free from our web site http://www.orthopractis.com/augmentedreality-apps ). 

These devices have concrete dimensions, are  calibrated for the app and are necessary for  landmark registration and real time  positional guidance. 

    The unsterilized i-Phone should be placed in a sterilized waterproof sealable bag. This is common practice in surgical fields where non sterile parts are usually placed in sterile bags like arthroscopes, cameras, optical wires, tools etc. Sterile bags are readily available in operation rooms, taking always in to account bag manufacturer specification and guidelines. Plastic coverage should be transparent and not blur the iPhone cameras.

The surgeon should placed the iPhone in the case place of the Case i-Phone -Probe tool (CIPT)  which is previous  sterilised according to manufacture guidelines for the 3D printed material specification used.

 

In details:

A. A Case i-Phone - Probe tool (CiPT). This device is dedicated for surface registration and the same instrument combined with the next instrument the clamp works as position detector. The tool consist of the case, in which the iPhone sits and the rod. Rod has predefined length ( 32 cm) and it is attached perpendicular to the phones case, at the point where factory defined the centrum of the iPhone. This point is by default the origin in 3D dimensions namely 0,0,0 in XYZ axis. The other side of the rod is the side that acts as pointer tip location (z dimension). 

In the  Case i-Phone - Probe tool (CIPT)  the case should be according to the dimensions of iPhone model used. 

B. The Clamp tool (CT). This tool is a simple clamp attached to the handle of the inserter or reamer that has a slot designed to receive perpendicular the pointer tip side of the case i-Phone-probe tool (CiPT). The clamp tool must be positioned at 17.6 cm away from the tip of the inserter or reamer. For this distance the app is calibrated in order to calculate and work properly.

This default values are for Iphone 11 Max Pro. 

 

How it works. Method-technique.

 

First the Case i-Phone - Probe tool (CiPT) - a device dedicated for surface registration -  should be 3D printed after downloading the appropriate 3D files according to user’s iPhone model from developers site. The device consist of the case, in which the iPhone sits and the rod. Rod has a predefined length ( 32cm) and it is attached perpendicular to the phones case. The other side of the rod is the side that acts as mechanical pointer tip location. The pointer tip sphere in augmented reality (AR) by the app should coincide with the mechanical pointer tip location of the rod in order to measure accurate.  

Calibration is achieved by simply pressing the directions buttons (+,-) over the screen, the position (XYZ) of pointer tip sphere in augmented reality (red sphere) is adjusted accordingly. The user aim the pointer tip sphere in AR to be aligned in all dimensions and coincide over the mechanical pointer tip location of the rod of the  i-phone in Case.

More specifically:

-by pressing the + or - button in the upper row, the (z) distance is adjusted respectively - it is recommended, first to measure manually the distance from tip-pointer to case, by default this is 32 cm, and calibrate first the Z distance - real distance from the case to tip of the pointer. The following x y calibration procedure are in two dimension over the screens phone (x,y), aiming to bring the presented red sphere to coincide optically with actual pointer tip.

-in the intermediate row the + - button adjust the (x) distance of Point tip to red sphere.

-in the last row by pressing the + or - button the (y) distance from the Point tip to red sphere is adjusted likewise.

 

Operative set up:

The patient is in decubitus position or lateral position for total hip replacement surgery. The surgeon continues by conventional usual fashion, the app is applicable at certain stage of the procedure namely at preparation of the femur before the insertion of the stem prostheses - the osteotomy phase.

Before proceeding to the Osteotomy phase a default registration procedure is  mandated for accurate outcome patient.

 

Registration phase. 

 

General guidelines - technique of point registration: 

A green coloured marking sphere appears by touching any point over the screen in augmented reality during registration. By touching physically the tip pointer of the Case-Iphone-Probe Tool over the anatomical Point of interest and by touching the screen of iPhone simultaneously each time a green sphere appears in augmented reality. The powerful undo feature gives the user the freedom to make corrections without resetting the whole procedure. Simply by clicking the undo button the measurement returns to previous chosen point and thus registering once again the same anatomical landmark, without reseting the whole procedure and avoid starting over again.

 

Femoral Registration.

 

Following surgical exposure and once the surgeon has finally approached patients femoral head which is dislocated from the acetabulum, registration is followed by the above mention technique. 

 

A. Registration of Femoral Head and femoral neck.

Four anatomical points at marginal circumference of femur head should be selected - aiming preferably to the most distant from each other, poles of the femoral head - north, south, east, west - (C1,C2,C3,C4).  Each time by pressing the screen during registration green spheres appears at pointer tip in AR. By the registration of the last point (C4) a magenta sphere appears inside a blue sphere which overlay over the circumference of  femur head, depicting the center of femoral head, or the center of rotation of femoral head (C point).

With the same manner, aiming preferably at the marginal circumference of femur neck head, at the most distant part of the neck four points (N5, N6, N7, N8) are selected and registered by pressing the screen during each time. A yellow cylinder appears overlaying the real femur neck.

 

B. Registration of trochanters Major and minor of the femur.

By touching the probe over the anatomic geometry of points of interest and registrating three point instead one, improves the accuracy of registration. By touching with the probe around the ridges of each trochanter - first the major and then the minor, T and t points are registered. Registering three points around the trochanter major namely T9,T10,T11 in circumferential manner, a magenta sphere appear in the centroid of these (T point). By repeating the same technique, t12, t13, t14 are selected for trochanter minor with the same manner, t point is depicted also as magenta sphere in the centroid of these.

By selecting one point at the lateral aspect of femur epicondyle and one at the medial aspect medial femur epicondyle registration is complete. 

A colourful cylinder appears (Ct) starting from the centre of  femoral head  (C point) to the trochanter minor (t point). The Ct distance is depicted numerically in mm  as LL (leg length) over the screen. The alternate colour is helpful and act as a ruler in augmented reality, each colour represent certain distance in mm. The interval between two overhanging blue discs corresponds to the actual 10 mm distance, between blue and green disc 5 mm, and between smaller disks in tandem fashion between different colour 1mm respectively.

A red hazy plane appear perpendicular to yellow cylinder depicting in the femoral neck the point of intersection between the planes. By pressing the + or - button you can adjust intraoperative in augmented reality the exact resection level of the femoral neck you plan and see simultaneously where resection level should be - depicted by the moving red plane in real time -. The red plane intersect the cylinder - (leg length) - distance from femur head (C) to trochanter minor (t) and a value is printed in screen which represent the desired femur neck resection distance in mm (Osteotomy length) - distance from trochanter minor to the intersection of Leg length to red osteotomy plane. By pressing the button - or + the osteotomy length can be adjusted in realtime with the measured osteotomy length in preoperative planning accordingly. By default the osteotomy length distance begins with 0 starting from trochanter minor - t point. In screen, Head diameter of femoral head in mm, Neck diameter of femur neck in mm, Leg length in mm, femoral offset in mm, Femoral anteversion in mm, Osteotomy length mm, and Cut Depth in mm are shown.

 

Bone Saw cut navigation. 

Once the position of the coronal plane of femoral neck resection is defined and a red hazy transparent osteotomy plane is depicted (coronal) passing through the femoral neck constantly in augmented reality. By pressing the <go> button three perpendicular planes around the saw blade appeared with different hazy transparent colours (sagittal-blue, coronal-red, transverse-green) in augmented reality over the tip of the bone saw blades extent ending over the blade span dimension. The coronal plane - red hazy transparent plane is depicted passing through two reds spheres constantly in augmented reality which are extending at the edges of the blade. A green transparent plane (transverse plane) passing through the green spheres, perpendicular to previous transparent red plane (coronal) is depicted in augmented reality. Likewise transparent blue plane appears (saggital plane) passing through two blue sphere, perpendicular to previously planes.

The cylindrical tip pointer of the i-Phone Case Probe is inserted and fit into a specially designed cylindrical slot, which is situated over the back surface of the Oscillating Bone Saw Cutting Machine Orthopedic Power Tool and impacted securely which is attached at 16.5 cm away from the tip of the center of blade. Surgeon can view a grey cylinder between two red spheres (rod) image superimposed in the real surgical field through the iPhone display mimicking the length of the blade. The direction of the i-Phone case with the rod should be turned manually clockwise or counterclockwise and adjusted accordingly so the grey cylinder between two  spheres shown in AR should be aligned with the axis of blade saw in the middle. Βy pressing The + or -  Button at  L button, which appears after pressing the Go button, the length between the tip pointer of the i-Phone Case Probe at the  Bone Saw Cutting Machine Orthopedic Power and the tip of the center of blade can be adjusted. Now the surgeon can obtain positional information in real time in augmented reality of the blade saw and the direction of the intended bone cut at femoral neck.

 

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Over the screen in real time three angles corresponding to the direction of saw blade are depicted. For simplicity reason every colour of a plane corresponds certain direction more specifically:

The row with red tile by red tile represented the angle subtended by the coronal plane of the blade saw (red) and coronal osteotomy plane (red). 

The row with green tile by red tile represent the angle subtended by transverse plane of the blade saw (green) and the coronal osteotomy plane (red).

The row with blue tile by red tile represent angle subtended by sagittal plane (blue) of the blade saw and the coronal osteotomy plane (red).

Angle values in real time are printed in colours in screen, whenever the values fall outside the normal ranges, angle values are printed in red colour so the surgeon can be guided more easily, seeing screen indications in real time and directing by hand the bone saw blade accordingly more precise thus avoiding not optimally cuts of femoral neck resection in space. These angle are helpful for accurate navigation of the blade saw in ideal position.

Manipulating the Oscillating Bone Saw Cutting Machine Orthopedic Power Tool in real time the surgeon, values of all above mentioned angles change respectively, obtaining positional information and direction with accuracy in real time in augmented reality by observing the screen of the i-Phone.

-By monitoring live the depth of the cut the surgeon can’t be mislead by wrong perceptions, so can predict where to stop cutting during handling with the  reciprocating oscillating saw without  accidentally injuring  neuromuscular structures.

The surgeon can be directed by augmenting his vision reality by readings the apps calculation and perform resection osteotomy of femoral the neck accurate, without mislead by plain subjective plain vision and simultaneously also adjust intra-operatively in real time the osteotomy distance objectively, according to measured preoperatively planed osteotomy distance.

 

In quick view, you have to choose sequentially and manually the following certain anatomical landmarks - points, that should be registered one after another and are shown below with the correct order:

 

A.Registration

Femoral head circumference C1, C2, C3, C4, a magenta sphere appear over center of rotation of femoral head (C point)

Femoral neck circumference N5, N6, N7, N8 

Ridges of trochanter major T9, T10, T11, a magenta sphere appear over trochanter major (T point)

Ridges of trochanter minor t12, t13, t14, a magenta sphere appear over trochanter minor (t point)

One point at the lateral aspect of femur epicondyle and one at the medial aspect medial femur epicondyle

 

B. Screen readings Real time  

The row with red by red tiles, angle subtended by the coronal plane of the blade saw (red) and coronal osteotomy plane (red), real time angle value - green colour represent normal range 0°±3° otherwise red .

The row with green by red tiles, angle subtended by transverse plane of the blade saw (green) and the coronal osteotomy plane (red), real time angle value - green colour represent normal range 90°± 3° otherwise red.

The row with blue by red tiles, angle subtended by sagittal plane (blue) of the blade saw and the coronal osteotomy plane (red),real time angle value - green colour represent normal range 90°±3° otherwise red.

 

Head diameter in mm

Neck diameter in mm

Leg length distance in mm - center of femoral head to center of the trochanter minor.

Femoral Offset in mm

Femoral anteversion

Osteotomy length - distance from trochanter minor to the intersection of Leg length to red osteotomy plane.  

Cut Depth in mm

 

All information received from the software output must be clinically reviewed regarding its plausibility before patient treatment! The App indicated for assisting during operation the Operator. Judgment and experience are required to properly use the App. The software is not for primary image interpretation. Any influence the operators in making decisions during operation remains Surgeons own responsibility and experience. A surgeon must always rely on his or her own professional clinical judgement when deciding whether to use a particular technique when treating a particular patient. App does not dispense medical advice. It is recommended that surgeons must be trained in the use before using it in real surgery.