Home Up Materials Radiography Arthrography CT and MRI References


Prosthesis Types
 Total Hip 
Baseline Exam
 -Acetab. Position
 -Center of Rotation
 -Femoral Stem 
 -Leg Length Discr.
 Intra-op- Fractures 
 Cement Herniation
Follow-up Study
 Bony Abnormalities
 Heterotopic Bone
 Non Union
 Hardware Failure
 -Polyethylene Wear
CT and MRI



  • 1-3% for primary total hip arthroplasties (Ali Khan, Lewinnek)
  • 16% for revision arthroplasties (Manaster)
  • Usually occurs early in convalescence
  • Patients must avoid hip flexion greater than 90 degrees (shoes and socks must be put on with adaptive equipment, and any hip adduction (no crossing of legs).


  • Inadequate adjustment of soft tissue tension at time of surgery leading to instability
  • Loss of abductor mechanism, usually due to detachment of the greater trochanter
  • Shortening of limb with short femoral neck and high acetabular component
  • Malpositioned prosthetic components
    • Optimal acetabular component positioning
      • Anteversion 15 +/- 10 degrees
      • Lateral inclination 40 +/- 10 degrees. 
    • Malpositioned acetabular component
      • Steep lateral inclination is associated with superior dislocation
      • Retroverted cup is associated with posterior dislocation (Coventry)
      • Anteverted cup is associated with anterior dislocation (Lewinnek)


Dislocated total hip replacement

Dislocated femoral component secondary to loose acetabular cup with reverse acetabular inclination

Dislocated bipolar hemiarthroplasties in 2 different patients.


Dislocated femoral component secondary to steep acetabular cup inclination, pre and post revision. Note constraining ring about femoral head, which helps maintain head in cup

Dislocated femoral component related to non union of greater trochanteric osteotomy. Post operative radiograph with constraining ring about femoral head, which helps maintain head in cup. Greater trochanter resected.

Dislocated acetabular cup and femoral component

Dislocated femoral component and acetabular cup in grossly loose arthroplasty. CT guided aspiration to rule out infection.



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