Review Question - QID 3192

The radiograph demonstrates a dislocated total hip arthroplasty that remains unstable following reduction. Medializing the acetabulum decreases the lever arm of the abductors resulting in reduced soft tissue tensioning, greater laxity, and thus decreased stability.

Conversely, stability can be increased in the following ways: Revising to an extended offset femoral component and advancing the trochanter increases the lever arm of the abductors increasing soft tissue tension. Increasing the head to neck ratio (choice 5) increases the range of motion to impingement. Constrained liners increase the functional depth of the cup. This increases the jumping distance from impingement to excursion at the cost of greater contact stresses at the acetabular bone, cup, and liner interfaces.

Soong et al discusses the evaluation and management of dislocation following total hip arthroplasty in this review article. The basis of treatment is multi-factorial including chronicity since implantation, mechanism of dislocation, position of the implants, and the age, health, and expectations of the patient. Interventions include bracing, soft tissue management, and component revision depending upon the etiology of the instability.

Parvizi et al reviews surgical techniques of revision hip arthroplasty in this instructional course lecture.

Illustration A provides a visual example of the importance the head to neck ratio plays in stability.