Dislocation
Incidence:
- 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).
Etiology
- 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
![](images/t350/152-0Loose-rotated-cup-w-di.jpg)
Dislocated femoral component secondary to loose acetabular cup
with reverse acetabular inclination
![](images/t350/153-0dislocation(bipolar-he.jpg) ![](images/t350/dislocbipolar.jpg)
Dislocated bipolar hemiarthroplasties in 2 different patients.
![](images/t350/155-0D-L-hip-steep-angle-.jpg) ![](images/t350/155-1D-L-hip-steep-angle.jpg)
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
![](images/t350/156-0Recurrent-THR-disloc-p.jpg) ![](images/t350/156-1Recurrent-THR-disloc-p.jpg)
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.
![](images/t350/155-2Dislocated-hip-and-cup.jpg)
Dislocated acetabular cup and femoral component
![](images/t350/158-1Dislocated-cup-CT-pilo.jpg) ![](images/t350/158-2Dislocated-cup-CT.jpg)
![](images/t350/158-3Dislocated-cup-CT-guid.jpg)
Dislocated femoral component and acetabular cup in grossly
loose arthroplasty. CT guided aspiration to rule out infection.
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