Bone preserving level of osteotomy in short-stem total hip arthroplasty does
not influence stress shielding dimensions – a comparing finite elements
analysis
Background The main objective of every new development in total hip
arthroplasty (THA) is the longest possible survival of the implant.
Periprosthetic stress shielding is a scientifically proven phenomenon which
leads to inadvertent bone loss. So far, many studies have analysed whether
implanting different hip stem prostheses result in significant preservation of
bone stock. The aim of this preclinical study was to investigate design-
depended differences of the stress shielding effect after implantation of a
selection of short-stem THA-prostheses that are currently available. Methods
Based on computerised tomography (CT), a finite elements (FE) model was
generated and a virtual THA was performed with different stem designs of the
implant. Stems were chosen by osteotomy level at the femoral neck (collum,
partial collum, trochanter sparing, trochanter harming). Analyses were
performed with previously validated FE models to identify changes in the
strain energy density (SED). Results In the trochanteric region, only the
collum-type stem demonstrated a biomechanical behaviour similar to the native
femur. In contrast, no difference in biomechanical behaviour was found between
partial collum, trochanter harming and trochanter sparing models. All of the
short stem-prostheses showed lower stress-shielding than a standard stem.
Conclusion Based on the results of this study, we cannot confirm that the
design of current short stem THA-implants leads to a different stress
shielding effect with regard to the level of osteotomy. Somehow unexpected, we
found a bone stock protection in metadiaphyseal bone by simulating a more
distal approach for osteotomy. Further clinical and biomechanical research
including long-term results is needed to understand the influence of short-
stem THA on bone remodelling and to find the optimal stem-design for a
reduction of the stress shielding effect