Biomechanical evaluation of proximal tibia behaviour with the use of femoral stems in revision TKA: An in vitro and finite element analysis A. Completo a, * , A. Rego a , F. Fonseca b , A. Ramos a , C. Relvas a , J.A. Simões a a Departamento de Engenharia Mecânica, Universidade de Aveiro, 3810-193 Aveiro, Portugal b Faculdade de Medicina da Universidade de Coimbra, Hospitais da Universidade de Coimbra, 3004-504 Coimbra, Portugal article info Article history: Received 19 May 2009 Accepted 21 October 2009 Keywords: Revision total knee arthroplasty Femur Tibia Press-fit stem Cemented stem Experimental strains abstract Background: Recognized failure mechanisms after revision total knee arthroplasty include failure of fix- ation, instability and loosening. Thus, extended stems have been used to improve fixation and stability. In clinical cases where the stem is only applied in the femur, a question concerning the structural aspect of tibia may arise: Does a stemmed femur changes the structural behaviour of proximal tibia? It seems, that question has not yet been fully answered and the use of stems in the opposite bone structure requires further analysis. Methods: Proximal cortex strains were measured with tri-axial strain gauges in synthetic tibias for three different types of implanted femurs, with two constrained implants. To assess the strains at the cancel- lous bone under the tibial tray, it was considered a closest physiological load condition with the use of finite element models. Findings: No significant differences of the mean of the tibial cortex strains for the stemmed femur rela- tively to the stemless femur were observed. The R 2 and slopes values of the linear regressions between experimental and finite element strains were close to one indicating good correlations. The strain behav- iour of cancellous bone under the tibial tray is not completely immune to the use of femoral stem exten- sions. However, the level of this alteration is relatively small when compared with the strain magnitudes. Interpretation: The main insight given by the present study could probably lie in the fact that the use of femoral stems does not contribute to an increase of the risk of failure of the tibia. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Several studies describe an important decrease in postoperative bone mineral density, closest to the implants, after total knee arthroplasty (TKA) (Li and Nilsson, 2000; Soininvaara et al., 2004). The restoration of lost bone and joint stability are important challenges in revision TKA among others such as proper limb align- ment and ligament balance (Bono and Scott, 2005; Mabry and Hanssen, 2007). Bone lost is generally categorized as contained or segmental. Contained defects are surrounded by intact bone, whereas segmental defects have no remaining cortex (Hoeffel and Rubash, 2000). Several clinical options for each bone deficiency category are available for revision surgery. Cement with or without screws, modular or custom augments, and morsellized or struc- tural graft have all been advocated for certain bone deficiencies (Peters et al., 1992; Howling et al., 2001). Morsellized allograft is ideal for smaller contained defects and has been successful in lar- ger defects as long as the component achieves stability on host rim bone (Whiteside and Bicalho, 1998). Structural allograft should be considered in large contained, segmental and combined defects (Clatworthy et al., 2001). Alone, neither of these techniques can give the initial support and stability to the implants in revision TKA. To improve fixation of components, stability and load-share, implants with extended stems have been used in revision TKA (Jaz- rawi et al., 2001; Rawlinson et al., 2005; van Loon et al., 2000). Revisions TKA are commonly made with posterior-stabilized im- plants (semiconstrained) when patients present good collateral lig- amentous stability (Bono and Scott, 2005) or in the cases where knee stability is not achieved, more constrained devices such as varus–valgus constrained designs are used (Bono and Scott, 2005). Failure mechanisms after revision TKA include collapse of fixation, subsidence, loosening and fracture (Rand et al., 1986). The need of reoperation after revision TKA is approximately 15%, of which nearly 44% may require two or more additional surgeries (Sierra et al., 2003). At revision TKA the fixation of the tibial tray is at risk because of increased bending and torsional loads acting on the implant (Albrektsson et al., 1990; Sharkey et al., 2002). Failure of the supporting cancellous bone in compression is the greatest risk for a well-cemented tibial tray (Burstein and Wright, 1994). Stem extensions can be used in the femur, tibia or in both bone structures simultaneously depending on the clinical evaluation 0268-0033/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2009.10.011 * Corresponding author. E-mail address: completo@ua.pt (A. Completo). Clinical Biomechanics 25 (2010) 159–165 Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech