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Congruence Index App

Congruence is present when the center of the femoral head (ball) and that of the acetabulum (socket) coincide. Lack of hip congruence between the femoral head and the acetabulum leads to increased local contact stresses, degeneration and consequently to premature arthritis. Although corrective hip osteotomies for the realignment of the dysplastic acetabulum is the main goal of treatment strategies, if the joint space congruency remain fair this end up in failure. Joint congruency can be rated subjectively according to the surgeons experience but according to international literature, evaluation and monitoring hip joint congruency is crucial to judge and predict the outcome of treatment.


The App measures objectively the congruence and gives values as percentage  (Congruence Index)  which can be used for evaluation or comparisons of treatments modalities like acetabular osteotomies in developmental dysplasia or Legg-Calve-Perthes disease of the hip. 

 The CongruenceIndexApp is medical software aimed for orthopaedic surgeons, providing tools that allow doctors to:
-Securely import medical images directly from the camera or stored photos 
-Offers a very convenient and most accurate possibly way to determine joint space congruency with two methods. With transparent circular template-Moses template- you try to find the best-fitted circle superimposed over the femoral head, you mark the femoral head center and with the same manner you locate the acetabular center of the weight bearing zone. When the center of the best-fitted circle of the acetabulum coincide with the center of the femoral head, the concruency of the joint is considered normal (CnI =100%).The app calculates automatically the congruency index. The results are printed as a percentage of congruency of the hip joint and the hip is categorized as normal or abnormal. 
    -Save the planned images, for later review or consultation.
 The software is a class II medical device in the FDA. All information received from the software output must be clinically reviewed regarding its plausibility before patient treatment!  Congruence Index App indicated for assisting healthcare professionals. Clinical judgment and experience are required to properly use the software. The software is not for primary image interpretation. 
   In a busy everyday practice measuring in X-rays in clinical settings it is time consuming and cumbersome. Accessory instruments like protractors, goniometers, well sharped pencils, rulers or even transparent papers must be available. The app offers  a very convenient and accurate way to measure the value of congruence  by clicking  points, right over your iPhone or iPad and help decide what could be considered normal or pathologic.
The app is not a simple goniometer, is an enhanced product which help to monitor objectively during the course of the treatment how much hip joint concruency is achieved. This App is particular useful especially in clinical settings where you need a quick results. Please see tutorial videos at the developer’s web site. www.orthopractis.com


1. Hartig-Andreasen C, Troelsen A, Thillemann TM, Søballe K. What factors predict failure 4 to 12 years after periacetabular osteotomy? Clin Orthop Relat Res. 2012 Nov;470(11):2978-87

2. Okano K, Enomoto H, Osaki M, Shindo H. Joint congruency as an indication for rotational acetabular osteotomy. Clin Orthop Relat Res. 2009;467:894–900.

3. Matheney Travis,  Kim Young-jo,  Zurakowski David,  Matero Catherine, BA; Millis Michael. Intermediate To Long-term Results Following The Bernese Periacetabular Osteotomy And Predictors Of Clinical Outcome.The Journal Of Bone & Joint Surgery - Scientific Articles: 01 September 2009 - Volume 91 - Issue 9 - p. 2113-2123

4.Murphy S, Deshmukh R. Periacetabular osteotomy: preoperative radiographic predictors of outcome. Clin Orthop Relat Res. 2002; 405:168–174.



The app offers a very convenient way to measure Congruence. The first thing is to load one image from your photo library or capture a photo from x-rays photos of a patient. The app offers two ways to measure the simple method (Button ‘S.’) or the extended (Button ‘Ex’). By default the S button is highlighted which means the simple method is chosen

The following procedure is common for both methods and below is explained in more details.

The transparent circular template -Moses template- that consisted of several concentric circles appears. First you aim to locate the center of the femoral head by moving the template over the femoral head, trying to fit to a best-fit circle to the contour of femoral head circumference. Once you find the best-fitted circle superimposed over the femoral head then you click the button ‘point’ and the center of the femoral head is marked and the first point of measurement (C1) is marked. 

Next a dynamic red circle appears with the C1 center point marked over the screen. The radius of the circle is changed dynamically and by moving the attached finger, you try again to find the best fit circle to the contour of the femoral head circumference. Once you found the best fit you press the ‘point’ button and the whole femoral head is marked by the red the circle. If the button S, is highlighted you choose the simple method of measuring the congruence then you have to follow the method as explained below. With the transparent circular template you aim at the best-fitted circle of the acetabulum circumference with the same above mentioned manner. Aiming this time the best-fit circle to acetabulum, towards the weight bearing area of the acetabulum namely the sclerotic roof. Usually you have to focus the next larger circle of the transparent template and in the main time holding the center of the template inside to the former red circle of femoral head. Clicking the button ‘point’ you mark the centre of the acetabulum (C2). When the center of the best-fitted circle of the acetabulum coincide with the center of the femoral head, the concruency of the joint is considered 100% (normal).Values according to the mechanics less that 83% are abnormal. The results are printed over the screen.

If the button ‘Ex.’ is highlighted then you have chosen the extended method of measuring the congruence and you have to follow the next. First you aim first towards the weight bearing area of the acetabulum namely the sclerotic roof and by clicking the button ‘point’  you try to mark  three points one after another following the imaginary best fitted circumference of the acetabulum. By clicking the point ‘button’ the A1, A2, A3 are printed respectively. After the A3 point a red circle is printed, passing over the A1, A2, and A3 points and automatically the centre of acetabulum C2 is printed. The app calculates the congruency and the results are printed as a percentage of congruency and printed as normal or abnormal as mentioned above. Please see tutorial videos at the developer’s web site.

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