In hip arthroplasty, when is a constrained liner typically considered?

• A. Recurrent instability
• B. Deficient soft tissues
• C. Neuromuscular conditions
• D. Primary osteoarthritis with intact soft tissues

Answer: (A)

Constrained liners are used to prevent dislocation by mechanically securing the femoral head within the acetabular cup, providing greater constraint than a standard liner. They are considered when instability recurs—repeated dislocations after a hip replacement—because the added constraint helps resist dislocation when soft tissues or soft-tissue–radial balance are insufficient to maintain stability with conventional components. In a primary osteoarthritis case with intact soft tissues, there’s typically no dislocation risk to justify the extra constraint, since a standard liner allows adequate stability without the downsides of extra constraint such as limited range of motion or higher wear. While deficient soft tissues or neuromuscular conditions can contribute to instability and may lead to considering a constrained design, the scenario that most clearly prompts use of a constrained liner is recurrent instability.