A new technique for removal of the total hip arthroplasty acetabular component

In revision total hip arthroplasty, an arthrographically loose or migrated cemented or porous ingrowth acetabular component may be found to be quite secure and difficult to remove. An acetabular component that is not loose may need to be removed because of infection or malposition. Based on a previous study of torque failure of cemented and uncemented acetabular components in vitro, a pneumatic impact wrench has been developed that delivers repetitive shear loads to the implant-cement or implant-bone interfaces. Eight acetabular components (three polyethylene, two metal backed, and three porous coated) were implanted with polymethylmethacrylate into fresh, unembalmed human anatomic specimen acetabuli. Seven components were easily removed using this new device at an average setting of 16 kg/m of torque. One polyethylene component could not be removed because the studs cut through polyethylene grooves. In one pelvis, a fracture occurred through a pubic anchoring hole when the driver was taken by error through a 40 degrees arc rather than the recommended 15 degrees arc. This device has been used in vivo in four cases, easily removing the components without damage to the surrounding bone.