Length of clinically proven cemented hip stems: State of the art or subject to improvement?
Hamadouche, M., Jahnke, A., Scemama, C. et al.Hip
Purpose
The purpose of this study was to identify the shortest possible length of an established cemented hip stem in order to reduce stress shielding and optimise its bending behaviour.
Methods
Twenty-five prototypes from the same batch (five for each stem length) were included. Lengths resulted from the original length (100 %) and four distal shortenings to 94, 88, 83 and 78 % of original length. For standardised implantations, synthetic femurs were prepared. Relative movements under axial torque and stem bending under varus–valgus torque applications were investigated consecutively. Analyses of variance (ANOVA) were applied to detect differences between lengths.
Results
The maximum torque transfer occurred at the level of the lesser trochanter (p < 0.01). In particular, for the 78 % version, relative motion of the stem tip increased significantly compared with all other lengths (p = 0.02-0.04). Comparable findings were made for mean overall movements. In regards to varus–valgus torque, both the distal tip and the proximal shoulder always bent in the same direction following the femoral deflection. For the 83 % version bending of stem’s shoulder was increased compared with the other length (p = 0.01 – 0.02), whereas tip bending was always comparable (p = 0.45-0.91).
Conclusions
Our data show that the intention to preclinically optimise the mechanical behaviour of cemented stems by modifying their length seems to be a reasonable option. Advantages are decreased inner bone stiffening to reduce stress shielding and a lower cement volume, which is involved in cellular interactions.
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