Catastrophic failure of tripolar constrained liners due to backside wear: a novel failure mode.

Constrained acetabular liners have been developed for patients who are at high risk for dislocation or who are undergoing revision surgery for recurrent dislocations. We report on 2 cases of failure of tripolar constrained liners due to severe backside polyethylene wear after dissociation of the outer polyethylene liner without dislocation, a mode of failure not previously reported. The backside of the inserts suffered severe polyethylene deformation, wear, and scratching due to dissociation from the locking mechanism. In patients with tripolar constrained liners, radiographic evidence of eccentric wear should be considered as possible occult dissociation of the polyethylene liner within the shell. Conversion to a modular dual mobility liner appears to be a viable solution in this setting.