Medial knee collapse, also known as knee valgus, is when the knee collapses or falls inward during any sort of weight bearing activity, like a squat, during gait, or during sport specific movements like cutting. Knee valgus is characterized by hip adduction and hip internal rotation in a flexed hip position. This position of the knee is most commonly associated with a non-contact mechanism of injury of the Anterior Cruciate Ligament (ACL), and occurs in the running or jumping athlete during the deceleration phase of a cutting movement.
ACL injury is the most common form of knee injury today in the United States, with estimates ranging from 100,000 to 200,000 per year. In addition to ACL loading, medial knee collapse also predisposes to lower extremity to a host of other orthopaedic issues such as: lateral hip pain, ITB stress, patellofemoral stress, MCL strain, and tibialis posterior stress.
How is The Gluteus Maximus Related to Medial Knee Collapse?
As mentioned above, medial knee collapse is characterized by excessive hip adduction and internal rotation. While the gluteus medius is the primary frontal plane hip abductor, and weakness of this muscle is clinically associated with knee valgus, one must not forget the important functional role of the gluteus maximus when considering impairments related to knee valgus. (We will devote our attention in this article to the gluteus maximus only, assuming the gluteus medius is functionally strong).
The gluteus maximus is the biggest of the gluteal muscles that form the large majority of your butt. The gluteus maximum is also known as a “tri-planar muscle”, meaning that it has the ability to move the hip joint in all three cardinal planes. The gluteus maximus can extend the hip in the sagittal plane, abduct the hip in the frontal plane, and externally rotate the hip in the transverse plane. All three of these muscle actions counteract the motions associated with medial knee collapse: hip adduction, internal rotation, and flexion.
As the gluteus maximus is the main hip extensor, the body will naturally recruit and use other hip extensors, namely the hamstrings and adductor magnus, to compensate for its weakness. While hamstring and adductor magnus compensation will help hip extension, the additional recruitment of these other hip extensors actually further exacerbate medial knee collapse due to secondary actions of the hamstrings and adductor magnus.
The hamstrings, while being a hip extensor, are also a hip adductor.
The adductor magnus, while being a hip extensor, is also a hip adductor
The combination of hamstring and adductor magnus overuse to compensate for gluteus maximus weakness drives the hip into more adduction, which will further exacerbate medial knee collapse! Of our body’s three primary hip extensors, two of the three actually adduct the hip instead of abduct the hip; thus, further emphasizing the importance of adequate gluteus maximus strength.
Interestingly enough, many individuals actually have more than adequate gluteus maximus strength, as evidenced by physical therapist assisted manual muscle testing, or the ability to squat/leg press a lot of weight. Yet they still demonstrate medial knee collapse in functional activities. Why ,you might ask?
These individuals lack proper neuromuscular control and the ability to adeuquately recruit their gluteus maximus.
The ability to properly recruit the correct muscles, in a sequential order, is something that we not only take for granted, but also seldom have to think about. When we walk, kick a soccer ball, or throw a football, we don’t think – we just do. Training your brain to turn on the right muscles can be a challenging process, but a quick fix might simply be adjusting your trunk angle! Leaning the trunk forward during squats, running, or sport specific movements effectively increases the hip flexion moment while decreasing the knee flexion moment. This results in a greater propensity to activate the hip extensors with a forward trunk lean. A 2010 study by Pollard et al. found that greater utilization of the hip extensors was associated with decreased valgus moments and angles. The findings of this study are in line with the emphasis we place on the importance of the gluteus maximus and its role in preventing medial knee collapse.
In summary, you must not forget to consider weakness or improper neuromuscular facilitation of the “tri-planar muscle”, the gluteus maximus, when addressing impairments potentially causing medial knee collapse!