Metaphyseal anchoring short stem hip arthroplasty provides a more physiological load transfer: a comparative finite element analysis study

Abstract

Background: Short stem total hip arthroplasty (SHA) preserves femoral bone stock and is supposed to provide a more natural load transfer compared to standard stem total hip arthroplasty (THA). As comparative biomechanical reference data are rare we used a finite element analysis (FEA) approach to compare cortical load transfer after implantations of a metaphyseal anchoring short and standard stem in native biomechanical femora.

Methods: The subject specific finite element models of biomechanical femora, one native and two with implanted metaphyseal anchoring SHA (Metha, B. Braun Aesculap) and standard THA (CLS, Zimmer-Biomet), were generated from computed tomography datasets. The loading configuration was performed with an axial force of 1400 N. Von Mises stress was used to investigate the change of cortical stress distribution.

Results: Compared to the native femur, a considerable reduction of cortical stress was recorded after implantation of SHA and standard THA. The SHA showed less reduction proximally with a significant higher metaphyseal cortical stress compared to standard THA. Moreover, the highest peak stresses were observed metaphyseal for the SHA stem while for the standard THA high stress pattern was observed more distally.

Conclusions: Both, short and standard THA, cause unloading of the proximal femur. However, the metaphyseal anchoring SHA features a clearly favorable pattern in terms of a lower reduction proximally and improved metaphyseal loading, while standard THA shows a higher proximal unloading and more distal load transfer. These load patterns implicate a reduced stress shielding proximally for metaphyseal anchoring SHA stems and might be able to translate in a better bone preservation.

Keywords: Finite element analysis; SHA; Stem; Stress shielding; Total hip arthroplasty.

Fig. 1

Femoral stems. a Cementless metaphyseal anchoring short stem (SHA: Metha Aesculap, B. Braun) and b cementless standard straight stem (THA: CLS, Zimmer-Biomet)

Fig. 2

Workflow for the generations of the homogenized FE models

Fig. 3

Coronal and transverse views of von Mises stress distribution patterns in the three FE models: a native bone, b short stem (SHA, Metha), and c standard stem (THA, CLS). Load transfer for the native bone is predominantly proximally at the cortex, while after short and standard stem insertion the load transfers in large parts via the implant. However, the short stem shows a clear metaphyseal load transfer while for the standard stem the load transfer is more distally

Fig. 4

Mean cortical stress distributions in the three FE models (front view): a native cortical bone, bone with implanted, b short stem (Metha), and c)standard stem (CLS). Clear reduction of the cortical stress after implantation of both stems in the proximal region, however, with better metaphyseal loading of the short stem

Fig. 5

Mean cortical stress distributions for the different FE models (Native, SHA and THA) in the proximal, metaphyseal and distal femoral regions. Asterisk (*) indicates significance to the CLS-primary (p < 0.05). Clear reduction of the cortical stress after SHA and THA with high unloading of the proximal region. Notable, SHA shows a significantly improved loading of femur and a clearly improved metaphyseal loading compared to THA

Fig. 6

Peak cortical stress distributions in the FE models (native, SHA, and THA) (post view): a native bone, bone with implanted, b short stem (Metha), and c standard stem (CLS). Higher cortical loading for the SHA in the proximal region 2–6, while the standard stem shows high peak stress in the distal region 16–19