**7. Intramedullary stems**

In revision total knee arthroplasty, the mechanical stability of the femoral and tibial components is increased by the addition of intramedullary stems. Whatever solution is indicating to compensate bone loss, the use of an extended femoral and tibial stems reduce the stress forces on the metaphyseal region and bone-implant interface. Stem extensions, with or without offset, can supplement fixation, decrease stress at the bone-implant interface, and help address asymmetric bone defects. Offset stems can assist with implant alignment on the metaphysis, reducing the incidence of coronal or sagittal components malalignment and helping balance the flexion and extension spaces by effectively translating the components.

The stem ability to protect the proximal tibia or distal femur has been demonstrated in a laboratory setting using finite element model and cadaver models. Brooks et al used stems in conjunction with various bone augmentation techniques for defect in the proximal tibia: they suggested that a 70-mm stem carried from 23% to 38% of the axial load (Brooks et al., 1984).

A finite element analysis has revealed that the predicted bone loss is even greater in stemmed components compared to stemless ones; this may have consequences to discouraged routine use of stems in revision TKA (van Lenthe et al., 2002). Nevertheless Stern and Insall (Stern & Insall, 1992) advocates routine use of stemmed components in revision TKA. Engh et al used femoral stems mainly to protect large structural grafts in revision TKA (Engh et al., 1997). Meneghini et al. advise the use of cemented stemmed extension to maximize early implant xation and allow for successful biologic ingrowth of the TM cones into the remaining part of the bone (Meneghini et al., 2008). We recommend to add stem extensions when using metal augments to decrease stress at the bone-implant interface.

Cemented stems allow for intraoperative adjustment with unusual anatomy and achieve fixation in large canals and osteopenic bone (Murray et al., 1994). The main disadvantages are that they are difficult to remove if revision is necessary and since they are not canal filling, they do not guarantee alignment (Parsley et al., 2003). Cementless press-fit stem extensions are easy to use and facilitate component alignment, and diaphyseal engaging stems ensure fixation (Radnay & Scuderi, 2006). In our practice with stemmed components of TKA, we prefer to use hybrid fixation in both femur and tibia, with proximal cementation just in the metaphyseal area as usual. In fact, Jazrawi et al. demonstrated in a cadaveric study that a press-fit modular cementless stem could achieve equivalent stability than a somewhat shorter fully cemented stem (Jazrawi et al., 2001), whereas Albrektsson et al. showed with radiostereogrammetic analysis that a long cementless stem provide optional stability (Albrektsson et al., 1990).
