Abstract
A well designed constrained liner does not have a “hood” nor a wide poly brim that extends beyond the metal shell because these cause impingement. The failure of a good design is almost always technique.
Size the liner so the poly is press fit against the metal rim of the cup. Cement thickness does not matter. Remove any derotation tabs on metal rim with a carbide burr so there is a firm press fit with no toggle. Do NOT angle the poly to change the anteversion.
Use the carbide burr to scratch the inner surface of the cup and a soft tissue burr to scratch the backside of the poly.
Cement must be liquid enough to fully seat the poly against the metal rim. If cement too doughy it resists full seating.
Put metal ring in groove during implantation and cementing to prevent cement into the groove.
If this is a primary cup use screws with the cup or cement the poly into the acetabular bone.
Dry the head and inner surface of the poly to facilitated reduction. Align the head concentrically into the mouth of the poly and push simultaneously on the knee and over the greater trochanter.
