Effects of knee simulator loading and alignment variability on predicted implant mechanics: A probabilistic study

Peter J. Laz, Saikat Pal, Aaron Fields, Anthony J. Petrella, Paul J. Rullkoetter

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Inherent variability in total knee arthroplasty loading and alignment, present in vivo and in simulator testing, may ultimately influence polyethylene tibial insert wear and long-term performance. The effect of this variability was quantified on implant kinematics and contact mechanics during simulated gait loading conditions using semi-constrained and unconstrained fixed bearing, cruciate retaining implants. A probabilistic finite element model of the Stanmore knee wear simulator was utilized to estimate the envelope of anterior-posterior (AP) and internal-external (IE) position and contact pressure and to evaluate the variability in corresponding ranges of motion (ROM). Variability levels were represented by standard deviations of up to 10% of the maximum value for load inputs and 0.25 mm and 0.5° for component alignment inputs. Model predictions compared well with experimental simulator results for the semi-constrained implant, with predicted positional envelopes of up to 1.8 mm (AP) an 34° (IE) for the semi-constrained and upto 2.6 mm (AP) and 37° (IE) for the unconstrained implant at the variability levels evaluated. ROM varied by up to 22%, while peak contact pressure variations averaged less than 2 MPa for both designs. For each implant, loading variability was more influential during the swing phase of gait, while alignment variability affected kinematics more during stance. The relative rank of sensitivities showed differences between the two designs, providing insight into critical parameters affecting kinematics and contact characteristics.

Original languageEnglish (US)
Pages (from-to)2212-2221
Number of pages10
JournalJournal of Orthopaedic Research
Issue number12
StatePublished - Dec 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Orthopedics and Sports Medicine


  • Kinematics
  • Knee simulator
  • Sensitivity
  • Variability
  • Wear


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