Disengagement of a locking screw from a modular stem in revision total knee arthroplasty. A report of three cases.

Abstract

Use of modular components in either primary or revision total knee arthroplasty allows the surgeon to achieve intraoperative customization, optimum kinematics, and improved fixation1-8,11,13,15. Modularity in total knee arthroplasty includes augmentation of the femoral component with distal or posterior metallic blocks, or both, and augmentation of the tibial component with metallic wedges or blocks. In addition, fixation of the intramedullary stems is possible, and this allows stress relief and load-sharing with the host bone1,6-8,11,12. Although such elaborate configurations are unnecessary for most primary total knee arthroplasties, many surgeons routinely use intraoperative customization in revision procedures and frequently this customization involves the stem1,2,4-8,12,14. Concerns with respect to modularity in total knee arthroplasty have arisen because of the many junctions of modular components. Issues relating to metallic wear, fretting, and corrosion between the body of the prosthesis and the various modular components require the surgeon to understand the potential long-term problems2 and to proceed with caution. In addition, loosening of screws used to secure blocks, wedges, or the intramedullary stems can be a problem. Dissociation of modular components after implantation is quite rare; however, surgeons must be aware of the complication and be prepared to correct it2. We present the cases of three patients who had disengagement of a locking screw from a modular stem that had been implanted in a revision total knee arthroplasty. In each instance, a screw had been used to reinforce the Morse taper junction between an intramedullary stem and the femoral component, as recommended by the manufacturer. Months after implantation, the screw disengaged from the femoral component and became an intra-articular loose …