Modulation of the relationship between external knee adduction moments and medial joint contact forces across subjects and activities

Trepczynski, Adam, Kutzner, Ines, Bergmann, Georg, Taylor, William R and Heller, Markus O. (2014) Modulation of the relationship between external knee adduction moments and medial joint contact forces across subjects and activities. Arthritis & Rheumatology. (doi:10.1002/art.38374). (PMID:24470261)

Abstract

Objective: The external knee adduction moment (EAM) is often considered a surrogate measure for the distribution of loads across the tibio-femoral joint during walking. The purpose of this study was to quantify the relationship between the EAM and directly measured medial tibiofemoral contact forces (Fmed) in a sample of subjects across a spectrum of activities.

Methods: The EAM for 9 total knee replacement patients was calculated using inverse dynamic analysis while their telemetric implants provided Fmed for multiple repetitions of 10 activities including walking, stair negotiation, sit-to-stand and squatting. The effects of the factors “subject” and “activity” on the relationships between Fmed and EAM were quantified using mixed-effect regression analyses in terms of the root mean squared error (RMSE) and the slope of the regression.

Results: Across subjects and activities a good correlation between peak EAM and Fmed was observed with an overall R² value of 0.88. However, the slope of the linear regressions varied between subjects by up to a factor of 2. At peak EAM and Fmed, the RMSE of the regression across all subjects was 35% body weight (BW), while the maximum error was 127%BW.

Conclusion: The relationship between EAM and Fmed is generally good, but varies considerably across subjects and activities. These findings emphasize the limitation in relying solely on the EAM to infer medial joint loading when excessive directed co-contraction of muscles exists, and call for further investigations into the soft tissue related mechanisms that modulate the internal forces at the knee.

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Contributors

Author: Markus O. Heller

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