In high-risk hip arthroplasty patients, what is the therapeutic purpose of using a constrained liner?

• A. To increase range of motion beyond normal
• B. To enhance stability and reduce dislocation risk
• C. To simplify surgery
• D. To decrease wear

Answer: (B)

A constrained liner is used to prevent dislocation by mechanically locking the femoral head within the acetabular liner, providing extra stability for hips at high risk of instability (such as those with abductor deficiency, neuromuscular problems, or a previous dislocation). This design reduces the chances of the joint dislocating during movement or activities that would normally provoke instability.

However, this comes with trade-offs: the range of motion is more limited because the head is held more tightly inside the liner, and there can be increased stresses at the components that might lead to wear or loosening over time. It’s not intended to increase motion or simplify the operation, and it may not reduce wear in general, given the altered mechanics.

So the best choice is that it enhances stability and reduces dislocation risk.