Combined knee loading states that generate high anterior cruciate ligament forces

Abstract

Injuries to the anterior cruciate ligament frequently occur under combined mechanisms of knee loading. This in vitro study was designed to measure levels of ligament force under dual combinations of individual loading states and to determine which combinations generated high force. Resultant force was recorded as the knee was extended passively from 90 degrees of flexion to 5 degrees of hyperextension under constant tibial loadings. The individual loading states were 100 N of anterior tibial force, 10 Nm of varus and valgus moment, and 10 Nm of internal and external tibial torque. Straight anterior tibial force was the most direct loading mechanisms; the mean ligament force was approximately equal to applied anterior tibial force near 30 degrees of flexion and to 150% of applied tibial force at full extension. The addition of internal tibial torque to a knee loaded by anterior tibial force produced dramatic increases of force at full extension and hyperextension. This loading combination produced the highest ligament forces recorded in the study and is the most dangerous in terms of potential injury to the ligament. In direct contrast, the addition of external tibial torque to a knee loaded by anterior tibial force decreased the force dramatically for flexed positions of the knee; at close to 90 degrees of flexion, the anterior cruciate ligament became completely unloaded. The addition of varus moment to a knee loaded by anterior tibial force increased the force in extension and hyperextension, whereas the addition of valgus moment increased the force at flexed positions. These states of combined loading also could present an increased risk for injury. Internal tibial torque is an important loading mechanism of the anterior cruciate ligament for an extended knee. The overall risk of injury to the ligament from varus or valgus moment applied in combination with internal tibial torque is similar to the risk from internal tibial torque alone. External tibial torque was a relatively unimportant mechanism for generating anterior cruciate ligament force.

Effects of a Knee Extension Constraint Brace on Lower Extremity Movements after ACL Reconstruction

“…Evaluation of the effects of the knee extension constraint brace on lower extremity kinematics and kinetics was focused on sagittal plane mechanisms in this study. Although one study on ACL loading showed sagittal plane biomechanics are the major contributors to ACL loading, knee valgus-varus and internal rotation moments also affect ACL loading [29]. Future studies should determine the effects of the knee extension constraint brace on nonsagittal plane biomechanics.…”

“…ACL loading decreases as knee flexion angle increases, especially when the knee flexion angle is less than 30° [29]. At a given knee flexion angle, ACL loading decreases as the anterior shear force applied on the proximal end of the tibia decreases [17,38].…”

“…Increasing knee flexion angle and decreasing peak posterior ground reaction force during landing may reduce the risk for noncontact ACL injuries [1,4,14,29,31,35,42]. Therefore, this knee extension constraint brace may have potential as a rehabilitation tool to alter lower extremity movement patterns for patients after ACL reconstruction to address the high reinjury rate.…”

Sagittal plane biomechanics cannot injure the ACL during sidestep cutting

“…Previous research has shown that valgus and internal rotation knee loads, both in isola tion and in combination, have a significant impact on ACL loading (Kanamori et al, 2000;Markolf et al, 1995). (Seering et al, 1980) have also shown that liga ment damage occurred in cadaveric knee joints within 125-210 Nm of valgus torque or 35-80 Nm of internal rotation torque.…”

Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads

“…Surgical reconstruction to replace the ACL restores the limit of anterior tibial translation closer to those for a knee with an intact ACL than if no reconstruction is performed [5,36]. However, under more complex rotatory motions, such as internal tibial rotation and valgus rotation, these reconstruction procedures are less successful [8,17,23]. In a cadaveric study, ACL replacement grafts could not replicate the function of the intact ACL under such a combined rotatory loading condition [36].…”