Impending spontaneous head neck dissociation caused by anteverted cup: A case report on reverse bottle opener effect and review of literature.

Modularity in total hip arthroplasty (THA) not only allows adjustments of leg length and offset but also simplifies the revision. It allows limited revision of various components and decreases surgical morbidity of complete revision. Despite benefits, modularity is associated with risks like corrosion and component dissociation. Dissociation between head and neck taper is rare and the cause is attributed to taper corrosion, revision, stem subsidence, pumping phenomenon, injury and closed reduction of dislocated THA. We report a case of late-onset impending head-neck dissociation in a THA caused by a well-fixed anteverted cup with polyethylene liner wear by "reverse bottle opener effect." To our knowledge, this is the most late-onset reported case of head-neck dissociation, occurring after 13yrs of index surgery.