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Technique for Acetabular Cup Removal


- Discussion:
    - considerations:
           - removal of press fit components can often be complicated by heavy bone ingrowth, insertion of under-reamed
                  components, or insertion of oversized peripherally oversized cups;
    - acetabular exposure:
           - w/ hybrid THR, typically the femoral stem is first removed (to improve exposure) but the cement is left in place (to reduce blood loss);
           - if exposure is not optimal, then consider trochanteric osteotomy;
           - entire circumference of the acetabular component must be visualized;
           - polyethylene is then removed (may be performed w/ corkscrew or with insertion of 6.5 mm screw thru the polyethylene and against the metal cup);
           - if screws are present, these are removed;
           - references:
                  - A technique of revision of failed acetabular components leaving the femoral component in situ
    - polyethylene removal:
           - polyethylene can be efficient removed by drilling into the polyethylene slightly off center (3.5 mm drill), and then by inserting a 6.5 mm screw in the polyethylene;
           - as the screw is driven into the polyethylene the screw will hit the outer metalic shell, which then causes the polyethylene to be pulled away from the metal (until it disengages);
           - be sure to insert the drill slightly off center inorder to avoid the central shell hole;
    - screw removal:
           - obviously all screws need to be removed before the acetabular shell is removed;
           - note that acetabular screw heads will differ from company to company so be sure that the appropriately shaped screw driven is on the table before the case begins;
    - cup removal:
           - cautions: wedging out of the prosthesis before it is loose, may frx acetabulum or may removal a large piece of bone (along with the component);
           - number one "rookie" mistake is to attempt to remove acetabular component prior to meticulous division of the metal-bone interface with curved osteotomes;
           - osteotomes and gouges:
                  - using curved osteotomes and curve gouges help loosen the prosthesis with minimal bone damage;
                  - gouge is directed just external to the outer hemisphere of socket following curvature of the sphere;
                          - beaware of pegs and spikes in the acetabular component;
                          - always direct the cutting instrument slightly toward the prosthesis and away from the bone;
                          - grab one edge of the component w/ needle nose pliers and apply traction in order to allow a more advantageous position for gouge;
                  - as disruption of the bone metal interface proceeds, it will be necessary to use longer and longer gouges;
                  - the gouges are then cut in multiple directions;
           - rod impactor agains the peripheral edge:
                  - apply a rod impactor (bone tamp) to the bottom edge of the metalic cup and attempt to drive (hammer) the inferior edge of the component toward the center of the acetabulum;
                  - this will help break up remaining osseous and fibrous attachments and will cause the superior component edge to become uncovered (which allows it to be extracted);
           - rod impactor against the inner edge:
                  - stab incision is made over the postero-superior aspect of the ilium - at a point that will allow straight access to the posterosuperior aspect of the acetabulum;
                  - the abductor muscle is split, and a small drill and a drill sheath is inserted agains the posterosuperior edge of the acetabulum, at the "palpable flange" of the acetabulum;
                  - if a tungsten-carbide drill tip is used then the drill can be drilled through the acetabular shell inorder to
                  - a rod impactor is then introduced and is directed slightly anteriorly, and an attempt is made to impact the component out of the acetabulum;
                  - this technique is based on the observation that the anterosuperior aspect of the acetabulum is most important in
                          bearing weight during gait (posterosuperior region being less important);
           - other methods:
                  - some components have a central threaded hole which allows insertion of a slap hammer;
                          - this method can result in component removal with a large segment of bone;
                  - occasionally the metal cup must be split into segments and removed in pieces;
                  - w/ a cemented prosthesis all acetabular cement must be removed, including cement plugs, which often remain firmly fixed to bone

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