Biomechanical Behavior of an Hydroxyapatite-Coated Traditional Hip Stem and a Short One of Similar Design: Comparative Study Using Finite Element Analysis.

ABSTRACT

BACKGROUND: The objective is to compare, by the means of finite elements analysis, the biomechanical behavior of a conventional stem of proven performance with a short stem based on the same fixation principles. METHODS: A 3D femur was modeled from CT scan data, and real bone density measures were incorporated into it. Load stresses were applied to that bone in 3 different scenarios without prosthesis, with the conventional stem, and with the short stem. Different bone loading patterns were compared by Gruen's zones both visually and statistically using Welch's test. RESULTS: The implantation of a stem generates a certain degree of stress shielding in the surrounding bone, but the pattern of the change is very similar in the compared stem models. Although there is statistical significance (P < 0.01) in the mean stress variation in most of the Gruen's zones, the magnitude of the difference is always under 2 MPa (range 0.01 - 1.74 MPa). CONCLUSIONS: The bone loading patterns of the traditional stem and the short stem are very similar. Although there is no evidence of a link between biomechanics and clinical outcomes, our results may suggest that theoretical advantages of short stems can be exploited without the fear of altering bone loading patterns.