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      An App that merges computer assisted orthopaedic surgery (CAOS) features with augmented reality and  helps orthopaedic  surgeon to navigate and position the  acetabular cup properly by adjusting in real time the anteversion and Inclination of the cup.
      The App developed for augmented reality helping the surgeon during operation to navigate and position the acetabular cup properly.The App increase the accuracy, during reaming, inserting and  impacting the cup. 


 Good surgical technique and accurate implantation of the acetabular cup component improve the longevity and function of Total Hip Arthroplasty (THA). Malposition, outside safe zone increases the risk of complications namely decreased range of movements, increased rates of impingement, increased wear rates, recurrent dislocations, osteolysis, ‘squeaking’, leg-length discrepancy, and early failure rates. 
        Placement of the acetabular cup during surgery can be performed by using  free hand technique and or by alignment support frames on the Inserter. The  surgeon try to navigate by taking into account the position of the frames relatively with surgical  bed plane. Acetabular cup orientation based on surgeon’s visual assessment and experience could result in an inaccurate placement. Computer-assisted navigation system is proven that they improve  the precision in cup position. Apple developed and popularised (AR) Augmented Reality technology readily available for its devices. 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 is medical App software aimed for orthopaedic surgeons, providing a tool that allows the surgeon to expedite the procedure of cup positioning effortlessly by following below these steps 

-by registering, with the tip of iPhone-Case-Probe instrument certain anatomical  landmarks, to see in Augmented Reality all 3D planes with different transparent colours (sagittal-blue, coronal-red  transverse-green),  
a transparent sphere appears inside the real acetabulum centred over the centre of hip rotation and also in augmented reality the  bony pelvis  appears over the screen.  
-by attaching the Case-Probe to certain clamp and attaching to the reamer or later to inserter, the surgeon can be oriented by observing  in real time over the phones screen, six angles, Operative Anteversion (OA) and Inclination (OI), Radiographic Anteversion (RA) and Inclination (RI), Anatomical  Anteversion (AA) and Inclination (AI) respectively .
-by observing in real time all angles, changing the direction of the reamer or inserter the surgeon can adjust the position of the cup respectively, aiming the final Implant orientation to be inside the new redefined safe zone- adjusted by patient-specific pelvic tilt-(Operative inclination (OI) 43°±12°, anteversion (OA) 31°± 8°). During surgery, as long as the measured values of OI and OA are inside the above mentioned normal range, the printed colour in screen remains green, otherwise are printed in red colour.
 -According to Lewinnek’s safe zone the surgeon should place the cup in 40°±10° degrees of Radiographic inclination (RI) and in 15°±10° degrees of Radiographic anteversion (RA). During surgery, as long as the measured values of RI and RA are between the above mentioned normal range, the printed colour in screen remains green, otherwise  are printed in red colour.
-Pelvic tilt is measured as anterior pelvic plane (APP) Angle and printed over screen. Its value is used for the calculation of anteversion and inclination of above mentioned angles and respectively adjusted.
Acetabular dimension is also printed in mm allowing the surgeon to decide in advance the size of starting reamer.
-Powerful undo feature gives the user the freedom to make corrections without resetting. Simply by clicking the undo button the measurement returns to last chosen point and you are ready to choose the same point again, without reseting and starting again from the beginning.

-QR-code Image attached over Passive Sensor acts as a dynamic reference base, by accidental change of pelvis position intra-operatively the app updates  the position of  registered points in AR  according to the  new position of patient pelvis respectively without to reregister.
-Positional landmarks are easily missed during operation, the operative field is repeatedly changing by sequential reaming where eccentric position is frequent error due to poor vision. Surgeon can be guided easily by observing screen indications of inclination and anteversion in real time in augmented reality and direct the reaming- to avoid eccentric positioning or the impacting of the cup in not optimal position.

     The App is a software develop for augmented reality helping the surgeon to navigate and position the acetabular cup properly. In  surgical navigation the advent of augmented reality by the app help adjust objectively the anteversion and inclination of the cup either during sequently reaming or during final impaction of the cup.
    The app offers the potential to adjust the operating technique, decrease intraoperative errors and optimize the surgical result in real time. Assisting the placement of acetabular component especially in difficult cases is a major advantage .
    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.

1. Murphy AB  and & The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA William S. Clin Orthop Relat Res 2018; 476:325-335.
2. Ogawa H, et al. A Pilot Study of Augmented Reality Technology Applied to the Acetabular Cup Placement During Total Hip Arthroplasty.J Arthroplasty. (2018) Jun;33(6):1833-1837.
3. Anuwat Pongkunakorn et al. Use of smartphone to improve acetabular component positioning in total hip athroplasty: A comparative clinical study Journal of Orthopaedic Surgery.-2019; 27(1) 1–8 .
4. Kenji Kurosaka et al, Assessment of Accuracy and Reliability in Acetabular Cup Placement Using an iPhone/iPad System 
Orthopedics. (2016);39(4) :e621-6.
5 Jacob M. et al,The 2014 Frank Stinchfield Award The ‘Landing Zone’ for Wear and Stability in Total Hip Arthroplasty Is Smaller Than WThought: A Computational Analysis Clin Orthop Relat Res 2015; 473:441–452. 

How can I use this  App


    For successful accurate cup placement during THA with the aid of Navitoolhip 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 .

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. Default values are for Iphone 11 Max Pro
    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). 
    C. Passive sensor (PS). This device is dedicated to act as dynamic reference array during tracking. Once 3D printed and added the adhesive QR-image label over the dedicated surface  should be  placed in a sterilized waterproof sealable bag and then  it should firmly attached to proximal pelvic bone (i.e. proximal Anterior Superior Iliac Spine (ASIS) or other anatomical landmark by the use of preferably to Swanz screw or a body of mini external fixator.

How it works in details . Method-technique.


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 specific :

-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.

Passive sensor (PS). A built-in known dedicated QR-code Image should be exported from the app and printed in a common colour printer preferably as an adhesive label and  attached firmly to passive sensor dedicated surface plane. The dimension of  the printed adhesive QR-code Image Label should  be four by four in centimetres in order to match perfectly the passive sensor dedicated surface. The printed QR Image is intended to work as unique dedicated tracker and should be in visual proximity. The QR-code Image marker is captured and recognised continuously in real time by the App. Over the printed QR-code Image marker in augmented reality, a red sphere  and a green plane appear laying over the surface plane once the QR-code Image is recognised. The QR-code Image marker is constantly recognised and continuously tracked by the app as along as the top centred button is on - highlighted. The Passive Sensor (PS) should be firmly mounted on pelvic bone. The QR-code Image attached over PS acts as a dynamic reference base attached to the system. Prerequisite is visual contact through i-Phones screen of QR-code Image. The position of all future register points are updated continuously while the QR-code Image acts as a dynamic reference guide marker. In case the patient pelvis is placed in different position during surgery and the attached PS on patient pelvis move as a whole array. Accidental change  of pelvis position intraopratively is common and the app updates  the position of  registered points in AR  according to the  new position of patient pelvis respectively. Aiming the iPhones camera to the PS QR-code image the app recognise the above mentioned image, recalculates the position of the already registered points in AR and updates accordingly their position in the right place over the real patients pelvis in the new position without the need to reregistering the points.

Operative set up.

The patient pelvis is in decubitus position for classic lateral approach of the hip for total hip replacement surgery by conventional usual fashion and the default registration procedure is for patient in supine position . - In case you place the patient in lateral decubitus only first three registration points should be chosen  in sagittal plane instead by <<touching>> three points preferably at the surface of two back post of the patient.


Registration phase.


A.XYZ- pelvic registration.

   A green coloured marking sphere appears by touching any point over the screen in augmented reality during registration. By touching the tip pointer of the Case-Iphone-Probe Tool over the surgical bed and by touching the screen of iPhone simultaneously each time a green sphere appears in augmented reality. The surgeon selects sequentially three different  points  (P1,P2,P3) over the surgical bed in the same plane. Through the selected points the coronal plane is defined and a red hazy transparent plane is depicted (coronal) passing through the green spheres constantly in augmented reality.

     With the same manner during the registration phase certain stable epicutaneous, pre-defined, pelvic anatomical landmarks-obtained through the drapes, have to be registered. The points that should be acquired are first - commence from the more proximal to the operated side in case the operated hip is the right patient’s hip but in reverse order in case the operated hip is the left patient hip -  the Anterior Superior Iliac Spine (ASIS) (P4)  and second  - the more distal to the operated side in case the operated hip is the right patient’s hip -Anterior Superior Iliac Spine (ASIS)(P5), reverse selection in case the operated hip is the left patient hip namely this anatomical point should be registered first-(P4) point. By registering  both points a green transparent plane (transverse plane) passing through the green spheres, perpendicular to previous transparent red plane (coronal) is depicted in augmented reality. By repeating the same procedure and registering at last the symphysis pubis (P6), a transparent blue plane appears (saggital plane) passing through the sphere, perpendicular to previously planes. For every three points of registration - three green spheres appears and in the centroid position between these points in space a light blue sphere appears which represents the final registration point of interest. The method of selection the registration points of the Superior Iliac Spines (ASIS) (P4,P5) and symphysis pubis (P6), by selecting three points over the region of interest each time, is different, in an effort to reduce the  positional registration error by simply selecting only one point for each time respectively.

     The planes appears with different hazy transparent colours (sagittal-blue, coronal-red, transverse-green) in augmented reality.

—App works uneventfully also by placing the patient in lateral decubitus position. In this event only the first step of registration of  points over the surgical bed (P1,P2,P3) is changed namely instead of registering point in coronal plane over surgical bed you select the three points over the imaginary - perpendicular to surgical bed plane  - points from the back of the patient in saggital plane by surgical back post behind  (see tutorials video at


C. Screen readings, Real time Anteversion - Inclination Angles -  Pelvic tilt - Cup diameter. 

    At the reamer or inserter handle the clamp is attached.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 clamp tool and impacted securely. Surgeon can view a grey cylinder between two red spheres (rod) image superimposed in the real surgical field  through the iPhone display mimicking the reamer or inserter. By  pressing  + or -  at L button the grey cylinder ending to yellow sphere enlarge or reduce the length of cylinder in order to match the length with the actual shaft length of instrument used in AR namely the tip of the real instrument (reamer or inserter ) should coincide with the yellow sphere.
    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 red spheres shown in AR and  should be aligned with the axis of the reamer or inserter direction. 
Now the surgeon can obtain positional information in real time in augmented reality of the reamer or the inserter. 
Over the screen in real time  six pelvic tilt-adjusted angles, appear, Operative Inclination (OI), Operative Anteversion (OA), radiographic anteversion (RA) and inclination (RI) and anatomical inclination (AI), anteversion (AA), concurrently  also APP angle and D-Diameter of acetabulum. 
    Pelvic tilt is measured by APP angle can be either negative-indicating posterior pelvic tilt or positive-indicating anterior pelvic tilt.      Acetabular dimension D is  printed in mm allowing the surgeon to decide in advance the size of starting reamer and the anteroposterior, mediolateral, and craniocaudal positions.
    Static values of patient acetabulum axis of OI-Operative Inclination, OA-Operative Anteversion, RI-Radiographic Inclination, RA-Radiographic Anteversion AI-Anatomical Inclination AA-Anatomical Anteversion are measured and printed over the screen in parentheses before the dynamic values respectively.
    Manipulating the reamer or inserter in real time, values of all above mentioned angles change dynamically, obtaining  positional information and direction with accuracy in real time in augmented reality  intraoperatively over iPhones screen .
 The surgeon can be directed by App readings and place the cup to optimal, and biomechanically sound position according to redefined the safe zone which take into account patient-specific pelvic tilt. 
(Murphy AB  and & The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA William S. Clin Orthop Relat Res (2018) 476:325-335 ). 
      The App allows to estimate also the patient-specific pelvic tilt  (APP angle) feature which is  incorporate in measurements and all values in anteversion and inclination are pelvic tilt-adjusted.
         During surgery, as long as the measured values by the App of Operative Inclination (OI) and Operative Anteversion (OA) are between normal ranges respectively (inclination 43°±12° and  anteversion 31°±  8°), the printed colour of them in screen remains green, otherwise whenever the value falls outside the normal range-pelvic tilt adjusted values of OI and OA - are printed in red colour. By this surgeon can be guided easily, by seeing screen indications in real time and direct positioning or impacting the cup optimally.  
        Also according to Lewinnek’s safe zone, surgeon should place the cup in 40°±10° of Radiographic inclination (RI) and in 15°±10° of Radiographic anteversion (RA). During surgery, as long as the measured values of RI and RA are between the above mentioned normal ranges, the printed colour of values in screen remains green, otherwise whenever they fall outside the normal ranges, the values of RI and RA are printed in red colour respectively.

In quick view, you have to choose sequentially and manually the following certain anatomical landmarks - points, which are shown below with the correct order: