AF/IR describes the movement of the AF joint, which is the intersection of the acetabulum and the femur. “Acetabulum on Femur” Internal Rotation. A quick review of anatomy: you have a pelvis. The pelvis is a ring consisting of four bones: the left innominate, the pubic bone in front, the right innominate, and the sacrum in the back. Each innominate consists of an upper part and a lower part. The top part is called the illium and the bottom part is called the ischium. Keep in mind they are the same bone.

Your femur (upper leg bone) connects to the ischium at a particular location called the acetabulum, usually known as the hip socket. In the picture below, you are looking at a right acetabulum and a right femur.

This point of intersection, commonly referred to as the hip joint, in PRI speak, is often given two names: AF- Acetabular/Femoral Joint. FA- Femoral/Acetabular Joint. Remember, the AF joint and the FA joint are the same joint. There are two different names given so as to separate the movements that occur at this important joint articulation.

The fact that a femur moves inside the acetabulum is well established. As you walk, run, kick, jump, and squat, your femurs will move on/inside the acetabulum. What is rarely considered, but what is one of the main cornerstones of PRI, is that the acetabulum also moves on top of the femur. It’s not a one directional system. Both bones move on each other all the time. And in PRI thinking, the movement of an Acetabulum on a Femur (A on F or simply AF) plays a more critical role in explaining movement dysfunction than how the femur moves inside the acetabulum (F on A, or FA)

The Left AIC pattern is identified by the Postural Restoration Institute as a neuromuscular pattern that is inherent in all humans due to the structural and functional asymmetries built into the human body that biases us to favor the right side of our body. This pattern of neuromuscular activation puts us in a particular position that leads to us losing full tri-planar motion in our pelvis.

For example, in a pure Left AIC position, you will not be able to fully adduct or extend your left leg due to the position of the pelvis. In a left AIC pattern, your left pelvis will be in AF/ER.

Restoring true tri-planar movement will necessitate regaining AF/IR. In this post I hope to explain what AF/ER really is. In the typical Left AIC pattern, the left ilium moves forward on the femur.

This positions the left hip into a state of flexion. That is what you are seeing above, the left ilium is forward compared to the right ilium.

This also has the effect of orienting our entire pelvis, and our lower spine, to the right.

Not only that, since all pelvic movement occurs in three planes of motion, the illium (upper part of the innominate) also moves away (abduction in the frontal plane) and rotates away from the midline of our body (external rotation).

So the resting state of our left ilium becomes one of “ER”: flexion, abduction, external rotation.

Since the pelvis is a ring, when something occurs on one side, the opposite movement has to occur on the other side. In this case, as the left ilium moves forward, the right ilium moves backwards into extension, moves closer to the body (adduction) and rotates towards the midline of the body (transverse).

The right ilium is doing the exact opposite movements. The resting state of our right ilium becomes one of “IR”: extension, adduction, internal rotation

The problem occurs when this particular pelvic position, a left ilium forward and in “ER” and a right ilium back and in “IR” becomes our default pattern.

This position should only occur when standing on your right foot. It should not be our pelvic pattern when our weight shifts to the left leg.

The pelvic position should switch so that our right ilium moves forward and into Right AF/ER” and our left ilium moves back and into Left AF/IR when we stand on our left foot.

But in the Left AIC pattern it doesn’t. It says as is.

Removing all the biomechanical lingo, let me express the idea in another way.

Let’s say you have two possible pelvic positions: Position #1 and Position #2. Alternating between these two positions enable you to walk properly.

When your weight is on your left foot, your pelvis should be in Position #1.

When your weight is on your right foot, your pelvis should be in Position #2.

However, in the Left AIC pattern, your pelvis is in Position #2 even when you are on your left foot.

Remember, on your left foot you should be in Position #1.

To move and walk like a human being should, you must shift into Position #1 when your weight is on your left foot. But that’s not happening.

Now, obviously your pelvis does move (otherwise you couldn’t walk), but it doesn’t completely move into the opposite pattern, so you are essentially stuck in one pelvic position since you can’t be in two different patterns at the same time.

You are either in Position #1 or Position #2.

Even while you are transitioning from Position #1 to Position #2 or from Position #2 to Position #1, you are still in one position until the point that the positions change.

Even when standing on two feet with our weight seemingly evenly distributed, it’s likely that our pelvis is still in the position of a left illium forward and the right ilium back at least to a minimal degree, even if we have gone through PRI programs. What we want, what is desirable, is for our pelvis to alternate positions like this

This alternating sequence of pelvic motion is called “walking”. In the Left AIC pattern, our pelvis is not alternating its movements like in the pictures above and instead our walking sequence becomes this:

As you can see, I gave you the same picture four times. That’s because in the Left AIC, your pelvic position isn’t changing, it’s not alternating between Position #1 and Position #2. It’s stuck in Position #2.

When your pelvis stops alternating its position as you walk, you are no longer walking like a human should walk.

Don’t get me wrong, you will walk, but you will have to walk by using compensation patterns.

And that is where the trouble begins.

When you compensate, you substitute incorrect movement patterns in other parts of your body e.g, your feet, legs, spine, ribs, shoulders, neck, and even cranium, to gain movements that are limited due to the fact that your pelvis is no longer alternating its patterns.

Quite simply, you can’t limit movement in one area of the body and not have it affect other areas.

Here is a list of pain that I experienced in my adult life prior to PRI, likely due to compensational movement patterns that occured in response to my pelvis losing the ability to move fully in three planes of motion.

1. Plantar Fasciitis in both feet
2. Shin Splints
3. Hip Impingement
4. SI joint pain on both sides
5. Generalized lower back pain
6. “between the ribs pain”
7. Upper back and neck spasms that originated between the shoulder blades
8. Upper trap/neck tension and discomfort

This is why everything PRI does first starts at the left pelvis to restore its ability to get into Left AF/IR.

Your left ilium has to move out of its flexed and ERd position and into an extended and IRd position.

The iliums must alternate between “IR” and “ER” to eliminate deleterious compensational movement patterns that can build up and cause pain, instability, and muscle weaknesses.

For more information about Left AF/IR and how to strengthen it, check this post out.