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Chiari Osteotomy

(See also: Acetabular Osteotomies)

Discussion

  • a acetabular osteotomy salvage procedure which is indicated in patients without a concentrically reducible hip;
  • modified shelf osteotomy above acetabulum w/ medial displacement of acetabulum;
  • distal fragment is displaced medially and upward as osteotomy hinges on the symphysis pubis;
  • hip capsule is interposed between newly formed acetabular roof & femoral head;
    • relies on periarticular soft tissue metaplasia for coverage;
  • femoral head is placed beneath surface of bone & joint capsule & corrects pathologic lateral displacement of the femur;
  • medialization will reduce the lever arm and will reduce joint loading;
    • because the biomechanics of the hip are improved by displacing hip nearer the midline, a Trendelenburg limp is often elminated;
  • clinical results are mixed & are affected by patient age & degree of DJD;

Indications

  • for patients over 4 years of age;
  • recommended in cases w/ inadequate femoral head coverage, w/ moderate dysplasia and moderate subluxation
  • generally considered when other reconstructions are impossible;
  • when femoral head cannot be centered adequately in acetabulum by abduction and internal rotation;
  • symptomatic subluxated hips w/ early signs of OA;
  • for dislocations that have been reduced but have later become subluxations;
  • preoperative center-edge angle of at least minus 10 degrees are desirable selection criteria. 

Contra-indications

  • complete obliteration of the joint space;
    • labral tear:
      • tear usually leads to a poor result;
      • if torn labrum is found, it should be repaired or resected;
      • arthrogram will rule out labral tear;
      • bilateral Chiari osteotomies may be contraindicated in women because it may interfere with child rearing;

Technique

  • iliac osteotomy is angled from the sciatic notch to the ASIS (anterolateral distally to posteromedial proximally);
  • avoid placing iliac buttress into a horizontal position since this will cause a persistently unstable joint laterally;
  • following osteotomy, a triangular osseous defect anteriorly which is stabilized w/ curved plate of bone graft from iliac wing;
  • inadequate stabilization of anterior defect will result in anterior instability;
  • acetabulum is displaced medially;
  • acetabulum is abducted into a more vertical & medial position and replaces it w/ joint capsule supported by osseous buttress of  the iliac wing;
  • distal (acetabular) fragment is displaced medially and adducted;
  • proximal (iliac) fragment is not allowed to move laterally;
  • inferior surface of proximal fragment forms roof over femoral head;

Case Examples

Post Op

  • partial weight-bearing for at least three months to allow for capsule  metaplasia;

Complications

  • this procedure will shorten the affected leg