Recently some of my high level female soccer players have undergone biomechanical analysis in their 5th month post-op ACL reconstruction. Despite demonstrating good control and depth on box drops, squats (double, split and single leg stances) step downs, deceleration, running gait and jumping mechanics (double, split and single leg), there was one common fault. During their lateral cutting task, the stance foot was positioned in the direction they were cutting towards, instead of straight forward. This positioning results in excessive knee valgus and lateral moment arms which are dangerous to knee joint health, post-op or otherwise. To fix this problem I continued with the current neuromuscular training and general strength building plan, while adding some focused external rotation and abduction exercises and a variety of cutting and deceleration drills to teach forward facing foot placement. I emphasized increased hip, knee and ankle flexion angles during weight acceptance. This helps keep a lower center of mass, optimal kinetic alignment and maximizes muscle activation, leading to a greater distribution of forces. To get to this conclusion, I looked to the research and found a few studies, but the work by Sigward et al, and Kristianslund et al specifically addressed this issue.
In this study 61 female soccer players participated in a three dimensional kinematic and ground reaction force analysis. Based off their frontal plane kinematic measurements, subjects were placed into normal or excessive valgus groups. Of the 61 subjects 38 were found to be normal and 23 demonstrated excessive valgus moments. The authors found that the athletes with excessive valgus moments demonstrated greater laterally directed ground reaction forces, increased hip abduction, increased hip internal rotation and a more internally rotated foot progression angle at the point of initial change of direction loading.
The authors analyzed whole body kinematics, knee joint kinetics and the ground reaction forces of 123 female handball players. The athletes were directed to perform three lateral cuts from a forward run. What I liked about this study was that a ball was thrown to the subjects just prior to making a lateral cut in front of a stationary defender. This was as close to a reactive environment as I have seen in a clinical study. It was found that hip abduction angle, cut width, leg internal rotation, trunk lateral flexion and trunk rotation all added to aligning the knee medial to the stance foot. Additionally the authors found that landing on the toe helped to align their lower extremity to reduce the abduction moment arm. While this study did look at foot rotation position, the authors did not find it to add to knee abduction moments. However, foot internal rotation progression angle can also be due to an internally rotated leg, which does increase detrimental knee forces.
Included above are photos of one my athletes during their biomechanical analysis, and you can see all of these faults in action. The first photo is at 5 months post-op, the second is after 2 months of additional rehab. It’s clear that in the second photo, the athlete has a much stronger planting foot and optimal ankle, knee and hip alignment as well as good pelvic and trunk control. The position of the ground reaction force vector gives a good visual of where the knee forces are, the further outside the knee it gets the more dangerous it becomes. Additionally, this strengthens the recent notion to delay return to high level reactive sporting activities for youth athletes from 6-9 months to 9-12 months. Often times athletes and their parents want to return to sport as soon as possible, or when they see a normal high speed running gait, normal SL squat, box drop/jump or acceptable performance values on other non-reactive controlled tests. But as technology advances and more high quality biomechanical research comes out that analyzes athletes in high speed, and hopefully, reactive environments, it will become clear that ACL rehab requires a long, active recovery time. This is because the most dangerous tasks occur in unexpected split second situations, that require coordinated reflexive activation of multiple muscle groups, joint alignment and body mass control. From my experience this coordinated, whole body, multi-system response takes a long time to integrate and is the last phase of rehab.
Finally, analyzing the leg posture during a lateral cutting task is something that should be included in return to sport, and prevention programs. If youre a coach, trainer or PT, each athlete under your care should at least be analyzed visually, if not by cameras or biomechanical software, to prevent injury or reinjury. If the athlete demonstrates any of the detrimental postures mentioned in the studies during a controlled drill, it will only get worse in a reactive situation. This feedback can then dictate the direction of additional training or exercise they should focus on to stay healthy.