Initial stability of uncemented hip stems: an in-vitro protocol to measure torsional interface motion

M. K. Harman, A. Toni, L. Cristofolini, M. Viceconti

Research output: Contribution to journalArticlepeer-review


The difficulty in quantitatively assessing the inherent variables of surgical stem insertion and interfemur differences continues to be a problem in experimental methodologies which assess hip stem stability. An in-vitro torsional stability protocol was developed which limited the mechanical testing variability and provided a reproducible micromotion measurement of an uncemented stem in synthetic composite femurs. Using a controlled mechanical stem insertion resulted in less interfemur variability within each group with the coefficient of variation being reduced from 35% overall to less than 20%. Femurs with shallow stem insertion depths had significantly larger micromotion than femurs having deep stem insertion depths. The sensitivity of the experimental protocol and the synthetic composite femurs to the varied functional behaviour of three different stem designs was demonstrated. The stem with a hollowed anterior-to-posterior proximal section experienced significantly more motion than the two stems with full proximal sections, reinforcing the need for proximal contact to ensure minimal micromotion in torsional loading.

Original languageEnglish
Pages (from-to)163-171
Number of pages9
JournalMedical Engineering and Physics
Issue number3
Publication statusPublished - Apr 1995


  • biomechanics
  • hip
  • micromotion
  • stability
  • stem
  • THR
  • torsion
  • Uncemented

ASJC Scopus subject areas

  • Biomedical Engineering
  • Biophysics
  • Orthopedics and Sports Medicine
  • Psychology(all)


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