Abstract
The well-fixed cemented femoral stem and surrounding cement can be challenging to remove. Success requires evaluation of the quality of the cement mantle (interface lucency), position of the stem, extent of cement below the tip of the stem and skill with the specialised instruments and techniques needed to remove the stem and cement without perforating the femur. Smooth surfaced stems can usually be easily removed from the surrounding cement mantle with a variety of stem extractors that attach to the trunnion or an extraction hole on the implant. Roughened stems can be freed from the surrounding cement mantle with osteotomes or a narrow high speed burr and then extracted with the above instruments. Following this, the well-fixed cement mantle needs to be removed.
Adequate exposure and visualization of the cement column is essential to remove the well-fixed cement without damage to the bone in the femur. This is important since fixation of a revision femoral component typically requires at least 4 cm of contact with supportive cortical bone, which can be difficult to obtain if the femur is perforated or if the isthmus damaged. Proximally, cement in the metaphyseal region can be thinned with a high speed burr, then split radially and removed piecemeal. It is essential to remember that both osteotomes and high speed burrs will cut thru bone easier than cement and use of these instruments poses a substantial risk of unintended bone removal and perforation of the femur if done improperly. These instruments should, as a result, be used under direct vision.
Removal of more distal cement in the femur typically requires use of an extended femoral osteotomy (ETO) to allow for adequate access to the well-fixed cement in the bowed femoral canal. An ETO also facilitates more efficient removal of cement in the proximal femur. The ETO should be carefully planned so that it is distal enough to allow for access to the end of the cement column and still allow for stable fixation of a new implant. Too short of an ETO increases the risk of femoral perforation since the straight cement removal instruments cannot negotiate the bowed femoral canal to access the end of the cement column without risk of perforation. An ETO that is too distal makes cement removal easier, but may not allow for sufficient fixation of a new revision femoral stem. Cement below the level of the ETO cannot be directly visualised and specialised instruments are necessary to safely remove this distal cement. Radiofrequency cement removal devices use high frequency (ultrasonic) radio waves to melt the cement within the canal. Although cement removal with these devices is time consuming and tedious, they do substantially reduce the chances of femoral perforation. These devices can, however, generate considerable heat locally and can result in thermal injury to the bone and surrounding tissues. Once the distal end of the cement mantle is penetrated, backbiting or hooked curettes can be use to remove any remaining cement from within the canal. It is important that all cement be removed from the femur since reamers used for preparation of the distal canal will be deflected by any retained cement, which could result in eccentric reaming and inadvertent perforation of the femur and make fixation of a new implant very challenging. An intra-operative x-ray can be very helpful to insure that all cement has been removed before reaming is initiated.
One should always plan for a possible femoral perforation and have cortical strut grafts and a stem available that will safely bypass the end of the cement column and the previous cement restrictor.
