There are tons of different reasons for knee pain and naturally, if you have some pathological issues, like an ACL tear, you need to get professional help. Nevertheless, there are also countless situations where we feel pain/discomfort / decreased stability around the knee joint, even though nothing is “broken”. In this article, we are going to tackle two common issues that are heavily related to the Pelvic girdle and the positioning of the pelvis and they can both be related to knee pain, low back pain etc.
ER – IR – ER
No, that was not me falling asleep on my keyboard. Those refer to External Rotation(ER) and Internal Rotation(IR). Whenever we move on our legs, like walking or squatting, our hip joint go through these motions, because human movement generally moves from a position of external rotation to internal rotation and back to external rotation. This is also called Hip Flexion Movement Arc, which we will come back little later.
Before we go any further, we need to understand what shock absorption is. Shock absorption is the process of absorbing a force when you, for example walk, lift a weight, or shift your weight from one leg to the other. The foot, leg, pelvis, and spine participate in absorbing the force. In the foot, you would call it a pronation/supination, in the spine, lordosis/kyphosis, and in the SI- joint, nutation/counternutation.
With this in mind, you can think of nutation to be the motion that occurs when force (weight) is absorbed by the sacroiliac joint (SI joint) and occurs in the direction of gravitational forces (toward the ground). Counternutation would be the body’s response, lifting the joint up against gravity.(Ground Reaction Force)
At the sacroiliac joint, it is the movement of the sacrum, which is very little(about 2°). Nutation occurs when the sacrum absorbs shock; it moves down, forward, and rotates to the opposite side. In counternutation(extension) the sacrum would move up, backward, and rotate to the same side that absorbs the force. A good example is the gait cycle.
During those motions, the ilium (other body structure in the SI joint) would rotate in the opposite direction because body weight causes the sacrum to move down and forward, while forces from the ground, coming up through the legs, cause the ilium to move down and backward (I am leaving out the rotational aspect). So you can think that these two opposite forces meet at the sacroiliac joint and force it into nutation. At the bottom point of nutation, the ligaments would momentarily absorb the full weight, which would make the sacrum and ilium reverse direction – rebound into counternutation.
But as I said, the movement itself is almost invisible, but nevertheless, there is a joint and any joint in the body needs to work correctly. Ok, let’s move on from the SI joint, but if you are having some issues in the SI joint, you should address that in the first place.
Hip Flexion Movement Arc
When you walk or squat down, the early flexion phase is ER-biased. Which means that the position is more externally rotated. This would be when you stand straight (o°) to about 60° of hip flexion. During this phase, there should be external rotation in the hip joint and the sacrum would be biased to the counternutation, just like we just talked about. The foot is slightly supinated, the ankle is toward plantar flexion and there is more muscle activation toward abduction.
When you start going toward the second phase, you are experiencing more internal rotation from the hip joint, dorsiflexion of the ankle, and pronation of the foot. Sacrum is in nutated state. This phase is about from 60° to 110°. For some people, it starts and ends a bit earlier, some people later, so these are only approximations and general guidelines. There is more muscle activation toward adduction.
The last phase from 110° to 120° brings us back to the externally rotated state. The hip is externally rotated, the ankle is towards plantar flexion, and the foot is more supinated. There is more muscle activation toward abduction.
Primary muscles for external rotation
- Glute max
- Glute medius (posterior fibers)
- Hamstring – biceps femoris (lateral side)
- Adductors (proximal part)
Primary muscles for internal rotation
- Adductors (distal part)
- Tensor Fascia Latae
- Glute Medius (anterior fibers)
- Hamstring – semitendinous & semimembranosus (medial side)
What about the knee?
Ok, now we get down to business. As a general rule, whenever your femur (leg bone) is rotating externally, the tibia (shin bone) should also externally rotate. The same goes with internal rotation, they both move in the same direction.
If there is too much of anything happening, it might end up in a situation where the femur and tibia are starting to move in opposite directions relative to each other. As there is always the possibility where the pelvis is moving relative to the fixed femur or the femur moving relative to the fixed pelvis, anything that happens from the top down, or down up, must be taken into consideration.
Too much internal rotation
Let’s start with the Internal Rotation. People usually think only of situations, where the femur is internally rotating. This is of course super important, but it is rarely understood that there are actually FIVE ways for the internal rotation to happen! We are only gonna look at one example this time and it is by tilting the hip anteriorly(forward). This usually looks like overextension of the lower back. So while the pelvis is oriented toward anterior pelvic tilt, it creates relative internal rotation in the hip joint. Sometimes this is a good compensation strategy, sometimes it is not.
When there is a lack of external rotation of the hip, this might end up in a situation, where the tibia is starting to compensate for the situation by creating external rotation relative to the femur. So your femur is rotating internally, but your tibia is rotating externally. This will cause an extra load to the medial side of the knee (inside). This is usually called knee valgus and when it is problematic, there are usually either some issues with the hip, ankle/foot, or both. When everything is balanced matter, it’s all good and the mechanical model of the human body is slightly towards the knee valgus.
Too much external rotation
The opposite example of this would be the hip oriented toward the posterior pelvic tilt. This creates the hip joint to externally rotate. When the femur is rotating externally too much, it can actually change the angle of the femur. Now, the tibia can either rotate also externally or try to compensate by rotating internally. Usually, this ends up with some lateral knee issues (outside). This is called the knee varus.
What type of training will help?
If you find yourself in the latter example, you would probably need to focus on the internal mechanics of the pelvis and the femur. If you are already in the internally rotated position, then your job is to increase the external rotation. Most daily movements are unilateral, so this can really be a “one-side issue”, which means, you need to do different types of movements on each side.
But if you don’t know where you are right now, just do a little bit of all, and see how it feels. It is not bad for you for sure, but of course, eventually, you want to focus on things that are important to you. Because I give you general guidelines here, they cannot be specific and detailed instructions for every individual.