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      Acetabular Cup Position: How to perform

      Last updated on July 6 2022

       

      Description

      Hip dislocation is among the most common complications following total hip arthroplasty (THA) and it can be caused by an inappropriate cup placement. Early cup loosening often presents as limited range of motion (ROM) or hip pain and increases the need for revision surgeries.

      A measuring instrument is required in which the anteversion of acetabular cups that have already been inserted can be measured, the Acetabular Cup Position (ACP) procedure.  With this procedure, the inclination and anteversion of the cup can be calculated. Radiographic landmarks play an important role and include 3 points on the acetabular cup and 2 points on the teardrops. The method used by the procedure for the anteversion calculation is Liaw’s method which uses the ellipse of the Acetabular cup.

      This procedure allows knowing the main measurements needed to detect an inappropriate cup positioning and avoid its complications.

      Measurements

      The measurement made by the procedure is displayed in the image:

      • Inclination (INC): the angle formed between the major axis of the acetabular cup and the Hilgenreiner’s line;
      • Cup Anteversion (Liaw) (CA): arc sin (tan Bp) where: Βp:  the angle formed between the major axis of the acetabular cup and a line connecting the endpoints of the major and minor axis of the ellipse formed by the acetabular cup.

      acp_1

      Auxiliary references

      To show this procedure, PeekMed® needs additional references:

      • Hilgenreiner’s line: a horizontal line through the teardrops (or triradiate cartilage in children) of the acetabulum;
      • Major axis of the acetabular cup: a line from the left to right endpoints of the acetabular cup;
      • Βp:  the angle formed between the major axis of the acetabular cup and a line connecting the endpoints of the major and minor axis of the ellipse formed by the acetabular cup;
      • Acetabular Cup Ellipse:  an ellipse that is defined by the borders of the Acetabular Cup.

      How to perform

      After selecting this procedure in the sidebar, you must mark the points to conclude it. To see the caption of each point you need to click on this button .

      Beware: you can change the position of the points at this stage or later. To do this, simply click on each handle with the left mouse button and move them to the most suitable position.

      This procedure has no advanced configuration.