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PHYS THER
Vol. 85, No. 12, December 2005, pp. 1390-1391
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Corrections

Correction



   Introduction
 
In a research report published in Physical Therapy in 1993, Oatis1 calculated stiffness and damping coefficients of the knee joint, based on the moment of inertia of the leg and foot with respect to the center of mass of the leg-foot segment. She alerts Journal readers to an error in those calculations leading to the results presented in Table 3 of the article. Equations 1 and 2 should have used the moment of inertia with respect to the knee.

Oatis reanalyzed and recalculated the stiffness and damping coefficients (shown in Tabs. 1 and 2), using the moments of inertia with respect to the knee joint. As in the 1993 study, assessment of stiffness and damping coefficients demonstrated moderate to high reliability, with most intraclass correlation coefficients (ICCs) greater than .7 and 2 ICCs greater than .59.2 Oatis found that the revised stiffness and damping coefficients were larger than those reported in the 1993 study.


View this table:
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[in a new window] 		Table 1. Stiffness Coefficients (N·m/rad) Calculated from 2 Different Moments of Inertia: Stiffness Coefficients Calculated Using the Moment of Inertia With Respect to the Knee Joint (Corrected Values) Are Larger Than When Calculated Using the Moment of Inertia With Respect to the Center of Mass (Original Values)

 

View this table:
[in this window]
[in a new window] 		Table 2. Damping Coefficients (N·m/rad) Calculated from 2 Different Moments of Inertia: Damping Coefficients Calculated Using the Moment of Inertia With Respect to the Knee Joint (Corrected Values) Are Larger Than When Calculated Using the Moment of Inertia With Respect to the Center of Mass (Original Values)

 
The original study reported that both stiffness and damping coefficients were increased in the 45-degree test. In the reanalysis, damping coefficients were significantly increased in the test at 45 degrees compared with the test at 75 degrees, whereas the increase in the stiffness coefficients at the 45-degree test position was statistically insignificant. Effects of gender appeared to be similar to those reported in the original study, with increased stiffness and damping coefficients in male subjects at both test positions. Effects of age remain unclear. The 1993 study reported that stiffness at the 75-degree test position was increased in the 30- to 39-year-old group compared with the 70+ age group. The re-analysis also showed a statistically significant increased stiffness in the 30- to 39-year-old subjects compared with the 20- to 29-year-old group. These differences may reflect the significant structural differences in these joints or the differences in data collection, or both. No attempt was made in the reanalysis to identify any structural or functional differences among the different age groups.


   References
Top
 Introduction
 References
 

  1. Oatis CA. The use of a mechanical model to describe the stiffness and damping characteristics of the knee joint in healthy adults. Phys Ther.1993; 73:740–749.[Abstract/Free Full Text]
  2. Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice. 2nd ed. Upper Saddle River, NJ: Prentice Hall Health;2000 :565.




This Article
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