Multicycle mechanical performance of titanium and stainless steel transpedicular spine implants

David Pienkowski, George C. Stephens, Thomas M. Doers, Doris M. Hamilton

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Study Design. This was a prospective in vitro study comparing titanium alloy and stainless steel alloy in transpedicular spine implants from two different manufacturers. Objective. To compare the multicycle mechanical performance of these two alloys used in each of two different implant designs. Summary of Background Data. Transpedicular spine implants primarily have been manufactured from stainless steel, but titanium alloy offering imaging advantages. However, the notch sensitivity of titanium alloy has caused concern regarding how implants made from this material will compare stiffness and fatigue life with implants made from stainless steel. Methods. Twenty-four implants (two alloys, two designs, six implants per group) were mounted in machined polyethylene wafers and repetitively, loaded (up to 1 million cycles) from 80 N to 800 N using a 5-Hertz sinusoidal waveform. Load and displacement data were automatically and periodically sampled throughout the entire test. Results. Implant stiffness increased with cycle load number, reached a steady state, then declined just before fatigue failure. Stiffness varied less in titanium transpedicular spine implant than in their stainless counterparts. All stainless steel implant types were stiffer (steady-state value, P < 0.0001) than their titanium alloy counterparts. One titanium implant design failed with fewer (P < 0.05) load cycles than its stainless steel counterpart, whereas a stainless steel. Implant of another design failed with fewer (P = 0.002) load cycles than its titanium counterpart. Overall, fatigue life, i.e., the total number of load cycles until failure, was related to implant type (P < 0.0001) but not to implant material. Conclusions. A transpedicular spine implant's fatigue lifetime depends on both the design and the material and cannot be judged on material alone. Stainless steel implants are stiffer than titanium alloy implants of equal design and size, however, for those designs in which the fatigue life of the titanium alloy version is superior enlargement of the implants components can compensate for titanium's lower modulus of elasticity and result in an implant equally stiff as its stainless steel in counterpart. Such an implant mae from titanium alloy would then be clinically preferable because of titanium's previously reported imaging advantages.

Original languageEnglish
Pages (from-to)782-788
Number of pages7
Issue number7
StatePublished - Apr 1 1998


  • Corpectomy model
  • Fatigue life
  • Flexure stiffness
  • Spine implants
  • Stainless steel
  • Titanium alloy
  • Transpedicular

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Clinical Neurology


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