An exploratory study of the use of ultrasound in the measurement of anterior tibial translation under gastrocnemius muscle stimulation.

Gastrocnemius' role as an agonist or antagonist of the anterior cruciate ligament (ACL) is not well understood. This study explored the use of ultrasound imaging to investigate how gastrocnemius stimulation levels influenced anterior tibial translation. The gastrocnemii of 10 participants were stimulated to four different levels using electrical muscle stimulation. The quadriceps were co-activated at a fixed level. Anterior tibial translation was determined using ultrasound imaging. Intraclass correlation coefficient [ICC (2,1)] was used to assess the intra-rater reliability over two sessions. Intra-rater reliability was good at rest and under most muscle stimulation levels (ICC = 0.84 to 0.92), and moderate with the lowest (ICC = 0.71) and highest stimulation (ICC = 0.61). While anterior tibial translation was not significantly different across simulation levels, ultrasound imaging recorded the anterior movement of the tibia as the gastrocnemius was activated, thus supporting gastrocnemius' role as an antagonist of the ACL.