Knee adduction moment and medial contact force--facts about their correlation during gait

PLoS One. 2013 Dec 2;8(12):e81036. doi: 10.1371/journal.pone.0081036. eCollection 2013.


The external knee adduction moment is considered a surrogate measure for the medial tibiofemoral contact force and is commonly used to quantify the load reducing effect of orthopedic interventions. However, only limited and controversial data exist about the correlation between adduction moment and medial force. The objective of this study was to examine whether the adduction moment is indeed a strong predictor for the medial force by determining their correlation during gait. Instrumented knee implants with telemetric data transmission were used to measure tibiofemoral contact forces in nine subjects. Gait analyses were performed simultaneously to the joint load measurements. Skeletal kinematics, as well as the ground reaction forces and inertial parameters, were used as inputs in an inverse dynamics approach to calculate the external knee adduction moment. Linear regression analysis was used to analyze the correlation between adduction moment and medial force for the whole stance phase and separately for the early and late stance phase. Whereas only moderate correlations between adduction moment and medial force were observed throughout the whole stance phase (R(2) = 0.56) and during the late stance phase (R(2) = 0.51), a high correlation was observed at the early stance phase (R(2) = 0.76). Furthermore, the adduction moment was highly correlated to the medial force ratio throughout the whole stance phase (R(2) = 0.75). These results suggest that the adduction moment is a surrogate measure, well-suited to predicting the medial force ratio throughout the whole stance phase or medial force during the early stance phase. However, particularly during the late stance phase, moderate correlations and high inter-individual variations revealed that the predictive value of the adduction moment is limited. Further analyses are necessary to examine whether a combination of other kinematic, kinetic or neuromuscular factors may lead to a more reliable prediction of the force magnitude.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Female
  • Femur / physiopathology*
  • Gait*
  • Humans
  • Knee Prosthesis*
  • Male
  • Middle Aged
  • Stress, Mechanical*
  • Tibia / physiopathology*

Grants and funding

This study was funded by the German Research Foundation (DFG Be 804/18-1,, Zimmer GmbH (, Deutsche Arthrose-Hilfe e.V. ( and the European Union Seventh Framework Programme (FP7/2007-2013 ICT-2009.5.2 MXL 248693, The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Funding was received from Zimmer GmbH, Winterthur, Switzerland for the development of instrumented knee implants. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.