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PreOp Planning for Arthrodesis

- Debridement:
 - all foreign material must be removed from the knee;
      - retained frags of cement can act as nidus for residual infection;
 - infected granulation tissue & scar tissue should be excised to provide healthy vascularized soft tissue surrounding the knee.
 - number of debridements needed before wound closure depends on surgeon's ability to remove all infected material and on whether or not 
      bone-grafting is to be performed.
 - at least two separate debridement procedures should be performed after implant removal, and there should be at least one negative culture,
      before bone-grafting is done;
 - removal of components & primary arthrodesis should be reserved for cases in which reimplantation is not considered possible & there
      is minimal arthritic involvement of adjacent joints.
 - intravenous antibiotics for 6 weeks after complete removal of an Infected Total Knee prosthesis;
- Knee Flexion:
 - optimum position for knee arthrodesis is slight flexion;
 - w/ minimum bone loss:
     - 10-20 deg of flexion allows foot to clear ground during swing phase of gait w/o circumduction of hip;
     - there should be slight valgus and 10 deg of external rotation;
 - w/ marked bone loss:
       - in instances of marked bone loss, position closer to full extension maintains as much length as possible.
       - in no instance should knee be placed in > 20 degrees of flexion;
- Bone Apposition:
 - most important factor for success of arthrodesis is bone apposition;
 - there must be vascular cancellous bone apposition.
 - resection of 1-2 mm of bone from distal aspect of femur & proximal aspect of tibia exposes vascular bone;
 - whenever possible, the interdigitation of bone ends should be done to improve stability and bone apposition.
 - large, hinged implants & implants w/ intramedullary stems necessitate sacrifice of more bone, and less bone is left for apposition than
      is left with resurfacing designs;
 - similarly, the knee with multiple revisions has less chance of a successful result than does a knee treated with primary operation.
- Bone Grafting:
 - is performed at time of arthrodesis for cases w/ extensive bone loss;
 - in presence of bone loss, cancellous bone-grafting, by incr surface available for bone apposition, can improve the chances of success;
 - bone graft should be placed about periphery of arthrodesis site to allow revascularization from surrounding soft tissues;
     - intramedullary circulation of the bone is usually compromised by prior implant and cement