Return to Play After an Anterior Cruciate Ligament Injury: Prioritizing Neurological and Psychological Factors of the Decision-Making Algorithm

ANTERIOR CRUCIATE LIGAMENT RISK POTENTIAL IN SOCCER PLAYERS

If a comprehensive neuromotor rehabilitation program is to be used effectively with soccer athletes, then the first priority is to define how the players should move, so that they can demonstrate protective kinematics with all soccer-specific tasks and minimize stress to the ACL. As the ideal movement pattern becomes autonomous, then it should be trained within the context of a dynamic environment; remembering that environmental changes have a large impact on the final movement pattern selected by the individual. Brophy et al⁸⁹ evaluated videos of non-contact ACL injuries in male and female soccer players and determined that 45% occurred while cutting, 25% while landing, and 16% during deceleration. These 3 patterns represent 86% of the ACL injuries observed and offer an opportunity for evaluation and treatment with specific central neuromotor rehabilitation techniques.

The foundational movement patterns for the soccer player should focus on producing leverage that minimizes stress to the ACL during the 3 primary tasks outlined above. To achieve this, it is necessary to reduce posterior ground reaction forces at the hip and knee joint during these movements. There is a high correlation between the magnitude of the posterior ground reaction force, and anterior tibial shear, and subsequent displacement.^90,91 This stress can be reduced by increasing the hip and knee flexion angles during soccer-specific movements that involve pivoting, decelerating, and landing from a jump in a unipedal stance.⁹²

This phenomenon can be explained by observing changes in the ACL elevation angle, hamstring insertion angle, and patella tendon-tibial tuberosity insertion angle. As the knee moves into flexion, the ACL takes on a more parallel orientation to the tibia, and its fibers are better able to resist elastic deformation accompanied by a posterior ground reaction force.^93,94 The quadriceps will produce less anterior translation on the tibia because the patella tendon insertion angle is reduced relative to the longitudinal axis of the tibia, and the mechanical advantage of the quadriceps is decreased.⁹⁵ Lastly, the hamstrings will be able to provide better leverage posteriorly because the resultant force trends toward a more parallel orientation to the tibial plateau, which enables the player to counter, more effectively, the posterior ground reaction force and the anterior pull directed by the quadriceps.⁹⁵

This theory is supported by the work of Li and colleagues,⁹⁶ who showed that there is an inverse relationship between knee flexion angle and ACL loading. In their study, they applied a constant quadriceps force of 200 N at 15°, 30°, and 60° angles. The anterior shear force was obviously the highest at 15° and reduced by 20% at 30° and 60% at 60°. When hamstrings co-contraction was added, there was an additional 30% reduction in anterior shear at 15° and 50% at 30° and 60°. From a more flexed position, the hamstrings can increase joint compression and reduce the anterior translation by allowing the concave medial tibial plateau to limit the anterior drawer effect and absorb the forces that occur with excessive anterior shear, internal rotation, and valgus loads.⁹⁷ As the knee flexion angle approximates 60°, the hamstring leverage is increased, and the quadriceps leverage is diminished to the point where its ability to produce anterior tibial translation is neutralized.⁹⁸ Daniel and colleagues98 referred to this as the quadriceps neutral angle.

For soccer-specific movements that are potentially injurious to the ACL, it may then be beneficial to create a default movement pattern at the knee that approximates this value. In keeping with the information presented in this paper, it will be important to have the player reproduce this angle consistently during activities that involve pivoting, decelerating, and landing from a jump within the context of match play. This will certainly require that segments located both proximal and distal to the knee are able to function within specific parameters so that a cohesive protective synergy is produced throughout the lower quarter which minimizes posterior ground reaction forces and is protective of the ACL. This is where structured neuromotor training that is able to modulate networks within the CNS may be beneficial.

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