Comments on “Stair climbing is more critical than walking in pre-clinical assessment of primary stability in cementless THA in vitro” by Jean-Pierre Kassi, Markus O. Heller, Ulrich Stoeckle, Carsten Perka, Georg N. Duda, Published on J. Biomechanics 2005; 38: 1143–1154

[...]it has been shown that: (i) Inclusion of any of the muscle groups affects the stress in the cement mantle around a debonded stem by less than 11% (Stolk et al., 2001). (ii) A no-muscle-simulation leads to stress overestimation with respect to a full-muscle one (Pancanti and Viceconti, 2001; Stolk et al., 2001). (iii) In Pancanti et al. [...]it seems that the direction of the hip resultant force that was applied to simulate walking and stair climbing (Table 1 in Kassi et al., 2005) did not match the direction proposed by the same group of Authors in a different paper (Fig. 5 in Heller et al., 2005).