Mechanical stability of polyethylene liners cemented into acetabular shells.

Revision of well-fixed, metal-backed acetabular components for dislocation or polyethylene failure requires consideration of removing the entire construct or replacing the polyethylene liner only. For non-modular or first-generation modular components with poor locking mechanisms, one option is to cement undersized liners into well-fixed shells. The purpose of this study was to measure the stability of undersized liners cemented into metal acetabular shells and compare the results with those of modular components. Hooded polyethylene liners measuring 28 x 50 mm and 28 x 56 mm were cemented into 66-mm acetabular shells (Smith & Nephew, Inc., Memphis, TN) with Simplex-P polymethylmethacrylate cement (Howmedica, Inc., Rutherford, NJ) giving 4- and 2-mm cement mantles, respectively. The force required to lever-out the liners from the shells was measured using the protocol described by Tradonsky et al. Assemblies with 4-mm mantles dissociated at an average of 322 +/- 47 in-lbf.; however, the assemblies with 2-mm mantles would not dissociate before the polyethylene yielded at torques as high as 600 in-lbf. These results compare favorably with the previously reported range (43 to 684 in-lbf) for modular acetabular components. These results suggest that undersized polyethylene liners can be cemented into well-fixed acetabular shells and expected to be stable.