Position Matters: How hip position changes hip rotation

The hip can be a complex and daunting joint to assess. There are lots of structures within and surrounding the hip that could be causing issues. On top of this, hip dysfunction has been shown to be a factor in low back dysfunction as well as knee pain. With the importance the hip plays in different pathologies, it’s also important to know and be able to interpret what you are assessing.  

Early on in my career, I’ve often caught myself assessing hip internal and external rotation range of motion and strength in supine because it was the most convenient position since I already had my patient/client lying supine. Turns out, I was only getting a part of the picture. 

Position Matters – Bone 

The position of the joint will affect the rotation of the hip. The hip is often thought of as a ball in a cup.  

But in reality, it’s not that simple. The acetabulum can be anteverted, retroverted, superiorly or inferiorly inclined, all of which will change hip rotation. Not to mention the depth of the acetabulum which will create overcoverage of the femoral head.  And femoral version which will change the transverse angle of the femoral neck.  The anatomical position of the acetabulum and the femur can lead to early bone contact and early impingement limiting hip range of motion. Kraeutler et al (2018) showed that range of motion of hips with a variety of femoral versions and abnormal morphology had significant differences in hip rotation. Although it was not analyzed, they also show the differences of measuring hip rotation in neutral and hip rotation at 90 degrees. This suggests that anatomical structure position leads to differences in bony limitations of the hip and bony limitations are different depending on the testing positions.  

Position Matters – Capsule and Ligaments 

The taughtness of the ligaments and capsule also changes depending on the position of the hip. The major ligaments of the hip – iliofemoral, pubofemoral and ischiofemoral – together are angled around the hip joint, creating almost a sling around the femoral head. This unique positioning allows them to provide stability against the high forces the pass through the hip joint. However, if we unravel the ligaments by changing the hip position, they allow for greater range of motion. van Arkle et al (2015) found that the hip has what they coined a “passive restraint envelop” which is a slack region of range of hip motion between 30-60 degrees where the ligaments provide very little passive resistance to hip rotation. Within this envelop the ligaments are slack and therefore will not limit hip rotation. Testing hip rotation in this range can give you a better idea of what the true joint motion is like and testing outside of this range can give you an idea of the quality of the ligaments. Although we typically test rotation in hip neutral or at 90 degrees of flexion, they show that both positions will have different rotational ligament restraints. They also found that, in general, the hip had greater internal rotation in extension and greater external rotation in flexion, again suggesting that testing position matters. 

Position Matters – Muscles

The eureka moment of how hip position matters for me came when I read this article by Delp et al (1999). This study estimated muscle moment arm of hip muscles at different angles of hip flexion. They found that when the hip is in 90 degrees of flexion, all portions of the glute med had a hip internal rotation moment arm. But when the hip was extended, the posterior fibers of the glute med had an external rotation moment arm.   

When they measured the glute max, all portions of the muscle had an external rotation moment arm when the hip was in extension. In hip flexion, the anterior portion of the glute max had an internal rotation moment arm.  

I think the results of this study provide a few important things to consider. 

1) Assess Range of Motion in Different Position

First, we should always assess range of motion in different positions. Even just in neutral and at 90 degrees of flexion can give you a better picture of how the hip moves. With the hip in flexion, hip IR will typically be limited by structural position of the acetabulum and femur which gives you some clues on femoral version, acetabular version and acetabular depth. Hip ER in flexion will restricted by the muscles and ligaments of the posterior hip, painting a picture of tissue restrictions of the posterior hip. In extension, hip IR will be checked by the the deep rotators of the hip as the ischiofemoral ligament and most of the other posterior hip muscles will be slackened in this position. Hip ER in extension will test the anterior ligaments and capsule, in particular the iliofemoral ligament as most muscles around the hip will be slackened to a certain extent in a neutral hip position. 

 2) Assess Hip Strength in Different Positions 

The first key takeaway is that we should consider hip position when assessing hip strength. When you are assessing the hip at 90 degrees of flexion, all fibers of the glute med and the anterior fibers of the glute max contribute to hip internal rotation, while the rest of the glute max contributes to hip external rotation. With the hip in extension or the person prone, all glute max fibers and the posterior glute med fibers have an external rotation moment arm while the anterior glute med fibers have an internal rotation moment arm. Testing hip strength in both positions will bias different areas of the muscle based on whether it internally or externally rotates the hip and could give different results.  

Interpreting the results of both test positions may seem confusing because now you must think about what fibers of what muscle are doing what movement. But I think this demonstrates the need to simplify your thought process. In general, not just at the hip, measure movement not muscles. Based on the results of this study, there is no one muscle that does one movement. So why do we try to blame one single muscle for a poor MMT result? The glute med is often blamed for hip issues, but it seems as though it might not just be the glute med. This study shows that muscles work together, not in isolation, to create motion. Therefore, we should focus on the movement, and not the muscle.  

3) Strengthen in Different Positions 

Another key takeaway from this study is that we need to strengthen in different positions. For example, when someone is weak in hip IR, one might give a seated hip IR with a band with the hip in 90 degrees of flexion. But what about when the hip is at 60 degrees of flexion? Or in extension? When a motion is weak, it is often weak in varying positions. And by biasing all the different muscles contributing to the motion, we can do a better job of improving strength.  

Here are some examples on how to work the hip in different positions: 

Hip IR

90/90 Hip IR

Reverse Clam

Seated Hip IR

Hip Adduction

Iso Adductor Squeeze @ 45 deg

Iso Adductor Squeeze @ 90 deg

Iso Adductor Squeeze @ 0 deg

Hip ER

Clamshell @ 60 deg

 Clamshell @ 0 deg

Bottom line, changing the position of the hip changes the passive restraints and function of some of the hip muscles. Taking that into consideration, it’s important to test the hip in different positions and also to work the hip in different positions.