gms | German Medical Science

Objectives: In THR it is essential to achieve a primary stability to guaranty good long-term results. Especially for the increasing amount of old patients who receive a hip endoprosthesis due to a fracture of the femoral neck, it is a necessary to generate a postoperative full weight bearing situation. An alternative to the conventional uncemented press-fit technique as well as to the use of PMMA, is a novel locking screw hip stem, that achieves primary stability by 5 mono-cortical locking screws. The aim of this study was to investigate the loading behavior and the ability to generate primary stability of these three different methods.

Methods: Twelve pairs of embalmed human cadaveric femora, originating from donors aged 72-85 were used. Randomly the specimen-pairs were assigned to 2 study groups (n=6) with similar BMD. In one group an equal amount of right and left femora were assigned to be implanted with a cemented straight stem whereas the contralateral femur of each pair was implanted with a locking screw hip stem. In the other group the uncemented press-fit stem was compared to the locking screw hip stem in the same manner. The specimen-prosthesis construct was tested in a biomechanical setup under progressively increasing axial loading until catastrophic failure. Axial construct stiffness, failure load and cycles to failure were detected and statistically evaluated at a level of significance p=0.05.

Results and Conclusion: All parameters of interest are normally distributed in each of the study groups (Shapiro-Wilk Test) and with homogeneity of variances among the 4 groups (Levene Test). The cemented straight stem group showed the highest stability in terms of axial loading (5,9kN±1,6kN) bud did not differ significantly to the locking screw hip stem group (4,9kN±1,1kN), whereas the uncemented press-fit group (3,2kN±1,0kN) showed a significant lower primary stability.We conclude that the cemented stem and the Locking srew hip stem is primary stable.The uncemented stem is significant less stable than the other two techniques.This might influence decision making choosing the best fixation technique in an osteoporotic bone.