Abstract
Recurrent dislocation following total hip arthroplasty (THA) is a complex, multifactorial problem that has been shown to be the most common indication for revision THA. At our center, we have tried to approach the unstable hip by identifying the primary cause of instability and correcting that at the time of revision surgery.
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Type 1:
Malposition of the acetabular component treated with revision of the acetabular component and upsizing the femoral head.
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Type 2:
Malposition of the femoral component treated with revision of the femur and upsizing the femoral head.
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Type 3:
Abductor deficiency treated with a constrained liner or dual mobility bearing.
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Type 4:
Soft tissue or bony impingement treated with removal of impingement sources and upsizing the femoral head.
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Type 5:
Late wear of the bearing treated with bearing surface exchange and upsizing the femoral head.
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Type 6:
Unclear etiology treated with a constrained liner or dual mobility articulation. These may be patients with abnormal spino-pelvic motion.
The most common etiologies of instability in our experience include cup malposition (Type 1) and abductor deficiency (Type 3).
We reviewed 75 hips revised for instability and at a mean 35.3 months 11 re-dislocations occurred (14.6%). Acetabular revisions were protective against re-dislocation (p<0.02). The number of previous operations (p=0.04) and previously failed constrained liners (p<0.02) were risk factors for failure. The highest risk of failure was in patients with abductor insufficiency with revisions for other etiologies having a success rate of 90%.
Although instability can be multifactorial, by identifying the primary cause of instability, a rational approach to treatment can be formulated. In general the poorest results were seen in patients with abductor deficiency. Given the high rate of failure of constrained liners (9 of the 11 failures were constrained), we currently are exploring alternatives such as dual mobility articulations. Our early experience with dual mobility suggests improved results when compared to constrained liners.
