If you have seen a physiotherapist for knee, hip, lower back, or maybe even neck issues, you would have probably done some work on strengthening your glutes before, so why is it that this muscle group often needs work? And why is this important in Total Knee Replacements (TKR)?
The gluteus maximus, more commonly known as ‘glute’ is a powerful extensor of the hip (moves the leg behind and away from the body). Anatomically it connects to the pelvis, the sacrum and the coccyx (tailbone). It also has important connections with the Thoracolumbar Fascia and important ligaments such as the sacrotuberous ligament. It inserts into the iliotibial band – a large, strong piece of connective tissue along the outside of the thigh, and into the Tensor Fascia Lata (TLF) muscle.
Functionally when the gluteus maximus takes its fixed point from the pelvis, it extends the acetabulofemoral joint and brings the bent thigh into a line with the body. Taking its fixed point from below, it acts upon the pelvis, supporting it and the trunk upon the head of the femur; this is particularly obvious in standing on one leg.
Its most powerful action is to cause the body to regain the erect position after stooping, by drawing the pelvis backward, being assisted in this action by the biceps femoris (long head), semitendinosus, semimembranosus, and adductor magnus.
The gluteus maximus is a tensor of the fascia lata, and by its connection with the iliotibial band steadies the femur on the articular surfaces of the tibia during standing, when the extensor muscles are relaxed. The lower part of the muscle also acts as an adductor and external rotator of the limb. The upper fibres act as abductors of the hip joints.
As you can see it does quite a lot of important stuff, is there more of a reason for why it is important following a TKR? Any why are consultants particularly keen for you to ‘strengthen your glutes’?
In the ‘normally’ aligned knee, 75% of the load passes through the medial compartment (inside aspect) of the knee. Following some pain and inflammation from an episode of osteoarthritis, this will commonly result in a slight alteration in a person’s gait (walking pattern). This slight change, or varus shift, which visually speaking you can think of a bow leg) increases the load further through the inside aspect of the knee. This creates a rather unfortunate vicious cycle…
A person has a bit of knee pain so they unconsciously adjust their walking pattern to ease the pain, but this change actually exacerbates the load on the part of the knee already taking a high level of load, which can lead to more pain and irritation. The person then adjusts a little bit more, which further increases the load through the inside of the knee, and so on and so forth.
This is why there is a much higher chance of the cartilage wearing away on the inside of the knee.
How is this relevant to the glutes?
Well, research has shown that by strengthening the gluteus maximus, and the TFL, this decreases the varus shift, bringing the hip/knee/ankle complex closer to an anatomical ‘optimum’, which therefore reduces the load from the inside of the knee, protecting the joint, and improving function. When the mechanical axis is shifted 4 degrees valgus, the load becomes symmetric between the medial and lateral joint compartments (50:50).
To summarise, if you have osteoarthritis and you are currently experiencing medial knee joint pain, working with a therapist to strengthen your glutes and TFL can improve the loading forces going through the knee and may improve symptoms and help protect your knee.
If you have had a TKR, then strengthening the glutes and the TFL will maintain good loading forces and help improve your walking pattern, reducing load through the prosthesis and enhancing your TKR experience.