Rate of force application during knee arthrometer testing affects stiffness but not displacement measurements.
METHODS
Repeated-measures counterbalanced design.


OBJECTIVE
To determine the effect of rate of force application on anterior tibial displacement and anterior tibial stiffness when measured with the KT-2000 knee arthrometer.


BACKGROUND
Clinicians and researchers frequently use the KT-2000 to quantify anterior tibial displacement and stiffness. While many factors (ie, tibial rotation, alignment of the arthrometer, etc) have been identified to affect KT-2000 measurements, the effect of the rate of force application has not been studied.


METHODS
Seventeen recreationally active males between the ages of 19 and 36 years (mean age +/- SD, 27.8 +/- 5.3 years) with no previous history of knee injury participated. With the knee in 25 degrees of flexion, the KT-2000 was applied to the participants' anterior tibia. While the distal femur was stabilized, the first author applied a posterior-to-anterior force at a fast and slow rate. Three trials for the slow and fast rates of force application were averaged and used for statistical analysis. Anterior tibial displacement (mm) was measured at 133 N and the related anterior tibial stiffness (N/mm) values were calculated between 89 and 133 N. Separate paired t tests with Bonferroni adjustment were used to determine if differences in displacement and stiffness between rates of force application were present.


RESULTS
Stiffness was significantly greater in the slow (mean +/- SD, 58 +/- 22 N/mm) as compared to the fast trials (mean +/- SD, 47 +/- 19 N/mm) (P = .005). Differences in displacement, however, were small and not significant (P = .132) between the slow (mean +/- SD, 3.9 +/- 1.5 mm) and fast (mean +/- SD, 4.0 +/- 1.6 mm) trials.


CONCLUSIONS
The rate of force application affects anterior tibial stiffness but not anterior tibial displacement when measured with the KT-2000. This suggests that to ensure reliable results when using the KT-2000, the rate of force application must be controlled when measuring stiffness between 89 and 133 N, but not when measuring anterior tibial displacement at 133 N.
Gross
Steven M
SM
St. John's University, Jamaica, NY, USA.
Carcia
Christopher R
CR
Gansneder
Bruce M
BM
Shultz
Sandra J
SJ
D000328:Adult; D016118:Anterior Cruciate Ligament / Q000502:physiology; D001696:Biomechanical Phenomena / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008023:Ligaments, Articular / Q000502:physiology*; D008297:Male; D009983:Orthopedic Equipment; D010329:Patella / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D013314:Stress, Mechanical; D013977:Tibia / Q000502:physiology*; D016474:Weight-Bearing