The Effects of Pad Placement and Angular Velocity on Tibial Displacement during Isokinetic Exercise

Kevin E. Wilk, James R. Andrews

Presented at the Sports Physical Therapy Section Team Concept Meeting, December 1992, Newport Beach, CA.

The purpose of this study was to compare the effects of proximal single resistance pad placement (PSPP) and distal single pad placement (DSPP) on tibial displacement during isokinetic exercise on anterior cruciate ligament (ACL)-deficient knees. This study is important to the clinician because it documents tibial displacement during open chain isokinetic knee extension exercise at various isokinetic speeds. In addition, this study documents the range of motion where the greatest amount of anterior tibial displacement occurs. The anterior displacement of the tibia was recorded by a computerized knee laxity testing device during isokinetic exercise. Data were collected from 12 ACL-deficient knees. Each subject was tested on an OSI Knee Signature System for quantifiable tibial displacement during a Lachman's test, anterior drawer test, and active vs. passive knee extension. Following this, each subject was tested on a Biodex isokinetic dynamometer at isokinetic velocities of 60, 180, and 300°/sec with the computerized knee laxity testing device in place. Pad placement consisted of distal single pad placement, which is 1 inch proximal to the medial malleolus, and proximal single pad placement, which is 3 inches proximal to the DSPP location. The testing procedure was standardized, and peak torque was monitored to ensure consistent maximal effort throughout the study. The results indicated that PSPP resulted in less anterior tibial displacement at all three test speeds. The peak anterior tibial displacement occurred in a range from 30 to 15° of knee flexion at both pad placements and all three test speeds. Lastly, the greatest amount of anterior tibial displacement occurred at the 60°/sec isokinetic velocity, whereas less displacement occurred at 180 and 300°/sec, respectively. This study documents that high-speed isokinetics result in less anterior tibial displacement than low-speed isokinetics, and if ACL graft strength or maturation is questionable, a 30° extension block or a proximal resistance pad may be used.

J Orthop Sports Phys Ther 1993;17(1):24-30.

Key Words: anterior cruciate ligament, tibial displacement, resistive exercise

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