Biomechanical assessment of a lunge deceleration maneuver: Implications of the non-contact mechanism of anterior cruciate ligament injury
Podraza, Jeffery T.
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Injury of the anterior cruciate ligament (ACL) within the knee joint is a common occurrence among male and female athletes of all age groups. Non-contact deceleration movements are considered the most common mode of injury. Strain of the ACL from excessive anterior tibial translation as a result of quadriceps overload is thought to be the major cause. This study utilized kinematic, kinetic and EMG measures of a lunge deceleration movement to identify where risk of ACL injury is most and least likely to occur. Ten subjects performed deceleration trials landing within the range of 0-25, 25-50 or 50-75 degrees of knee flexion. Knee flexion at landing was varied in order to quantify changes in loading variables and the relative role of the different lower extremity musculature that may alter ACL strain. Significant differences between conditions were noted in vertical as well as posteriorly directed ground reaction forces, knee extensor moments, anterior tangential tibial acceleration, the co-contraction index and the stabilization index. Ground reaction forces decreased with increasing knee flexion whereas knee extensor moment and tibial tangential acceleration increased. EMG increased for all muscles when landing with increased knee flexion; however, an EMG-to-torque model predicted increased torque for quadriceps and decreased torque for hamstrings. Gastrocnemius EMG and torque values changed very little across conditions while the soleus muscle EMG and torque output increased. Overall, the co-contraction and stabilization indices decreased indicating that the knee extensors dominate with greater knee flexion at landing. Presumably, larger knee extensor moments and less co-contraction will result in greater anterior tibial translation thereby increasing the risk of ACL injury. Most non-contact deceleration ACL injuries occur when the knee is extended and have been attributed to quadriceps overload. The results from the present study suggest that quadriceps overload is greatest when the knee is flexed while landing as opposed to extended. As a result of these findings, current theories that implicate quadriceps overload as the main cause of ACL injury during non-contact injuries require further investigation. Also, the results bring into question current hypotheses about the role of hamstrings as joint stabilizers when the extensor muscle moments increase. Soleus may play a much larger role in preventing ACL injury due to its action on the tibia when the foot is planted. The mechanism for non-contact ACL injury may be more complex and not strictly related to quadriceps overload or antagonist-agonist force imbalances.