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Joint mismatch or  another words  joint  incongruity  between  femur head (ball) and acetabulum (socket) of  the hip leads to altered mechanics, which can lead to premature degenerative osteoarthritis. Loss of congruity with the acetabulum is commom in patients with DDH.

Treatment of incongruity is paramount importance because you have to address it early and the treatment of choice are usually corrective hip osteotomies. In order-from one hand to avert the natural course to the progression of secondary osteoarthritis (OA) and from another hand to avoid- in developing skeleton -  to deteriorate more the hip dysplasia the congruity must be objectively and thoroughly evaluated especially at follow up of these procedures in both congruent and incongruent hips. Congruity between the femoral head and acetabulum is determined by the percentage of femoral head covered by the bony acetabulum. The congruity index (CI) is calculated (A/B- ratio converted to a percentage)  by diving the  (A) distance by the distance (B), where distace (A) is the distance between the teardrop to the lateral acetabular margin and (B) is the distance from the teardrop again to the lateral femoral head edge.

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 download congruity  app
mac download congruity  app

The Congruity Index App 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 way to determine the most accurate possibly way an objective value  of congruity. By cliking three point at the x-ray picture on your iphone screen and inserting the side the App calculates the congruity index (CI) which is the percentage of femoral head covered by the bony acetabulum. Congruity between the femoral head and acetabulum is expressed in percentage. Values of Coverage less than 75% is considered pathologic in another words the hip is incongruent

    -Save the planned images, for later review or consultation.

 All information received from the software  output must be clinically reviewed regarding its plausibility before patient treatment!  Concruiency 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 Congruity 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 the congruity  and evaluate the remodelling. This App is particular useful especially in clinical settings where you need a quick results without losing time. 


1.Cooperman DR, Wallensten R, Stulberg SD. Acetabular dysplasia in the adult. Clin Orthop 1983; 175: 79

2. Delaunay S, Dussault RG, Kaplan PA, Alford BA Review Radiographic measurements of dysplastic adult hips  Radiographic measurements of dysplastic adult hips. Skeletal Radiol. 1997 Feb;26(2):75-81..

 download congruity  app
mac download congruity  app

How to measure the Congruity Index


The app offers a very convenient way to measure Congruity Index. First you  select between right or left hip by highlighting the relevant button - don’t  forget in medical imaging by default what is left in the screen is right in reality, except it is otherwise by markings. After you have selected the side, the transparent circular template appears and you aim first 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 have found the best fit by clicking the “point” button the center of the femoral head is marked (C1). 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. Next with the transparent circular template you try to locate the teardrop (C2 Point) and try to mark by pressing the “point” button. Now you are ready to mark the t lateral acetabular border- third point (C3 point) – by pressing the ‘point’ option.

The app calculates that the Congruity Index. The values are expressed in percentage (% ) of femoral head covered by the bony acetabulum. Coverage of less than  75% is pathologic and in the screen is printed the percentage and the term  “hip is incongruent” otherwise  the term “normal” is printed over. Detailed Reference data according age or gender of the patient are missing in International literature

 download congruity  app
mac download congruity  app
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