Anterior Tibial Translation During Squatting with Tip Toe Weight Bearing: An Arthrometric and Eletromyographic Analysis

Abstract

Rehabilitation programs for patients after anterior cruciate ligament (ACL) reconstruction have generally focused on redeveloping functional strength of the knee musculature through a combination of closed kinetic chain (CKCE) and open kinetic chain exercises, although closed kinetic chain exercise has been more popular. Previous studies have demonstrated increased anterior tibial translation with open chain compared to CKCE. Normal static squat is generally one of the most popular CKCE. Basically, this exercise is hamstring and gluteus muscle exercise. The most important rehabilitation program after ACL reconstruction is quadriceps exercise. However, no studies have been published documenting the differences in tibial translation with trunk flexion and examining the effects of quadriceps contraction. The purpose of this study is to compare the electromyographic variables and anterior tibial translation when squatting on both legs in two different weight bearing positions and to examine the influence in the change in the trunk flexion angle.
Maximal sagittal plane knee translation during squatting was investigated in 10 healthy subjects without any previous history of knee joint trauma using an electrogoniometer system (CA-4000, OS Inc., Hayward CA, USA). The CA-4000 was also used to measure tibial translation with two methods squatting at the variable trunk flexion. For each condition, angle of maximum translation were recorded and compared between the two conditions. The two exercises, normal squatting and tip toe weight bearing squatting, were simulated by adjusting tibial anterior translation across the knee at each flexion angle. The subjects then performed five bilateral squatting movement with no external load. Anterior tibial displacement was measured at every five degrees of knee flexion from 0 to 90 degrees. The electromyograms (surface EMG, Universal Ltd.) were monitored via telemetry for the vastus medialis, biceps femoris of the right leg. Surface EMG data were normalized to the percentage of the maximum voluntary contraction, the third highest surface EMG activity.
The trunk flexion angle increased, and anterior drawer displacement decreased with normal squatting. As the trunk flextion angle increased, anterior drawer displacement did not increase with tip toe weight bearing squatting. Upon full extension of the trunk, anterior drawer displacement showed no significant differences between the two squatting methods. The amplitude observed on the electromyograms of the hamstrings increased as the trunk flexion angle increased, and the amplitude on the quadriceps increased with tip toe weight bearing squatting.