Hip internal rotation is almost a buzz word these days. I see it so frequently on social media that I wonder if anyone cares about hip external rotation, anymore? Do we still care about flexion and extension of the hip, too?
First off, what is hip internal rotation?
Also called hip medial rotation, or femur medial rotation, the action happens about the hip joint. In other words, hip internal rotation is when the femur of the leg rotates towards the centre-line of the body in the acetabulum joint of the hip.
In our assessments, we use this to measure people's hip internal rotation from the comfort of their homes:
On this particular client, for reference, it looks like this:
Illustrated from three different angles, hip internal rotation, shown another few ways on video, looks like this:
According to Kapron et at (2012), in the population of football players they studied,
Although 95% of the hips had at least 1 radiographic sign of femoral acetabular impingement (FAI), pain was reported in only 8.5% and 2.3% during the impingement and FABER tests, respectively.
The FABER test is a test of hip external rotation, although, when people get an acetabular impingement, it is because of a decrease internal OR external rotation range of motion causing the impingement (Kapron, 2012).
If any one of my athletes started training with me, and started to experience pain in their hips, they might surmise that it was "because" of the training that their hips started hurting. But, based on those statistics, most people walking around have some sort of problematic change in the hip that is detectable on a radiographic scan, yet they might not develop pain. So, development of pain, in and of itself, should not be thought of as too worrisome, as it is not indicative of damage, most times.
Other studies, like the meta-analysis by Boutris et al (2018), found that:
[There is a] significant association between ACL tear and both limited hip rotation and radiographic FAI (femoral acetabular impingement)
On one hand, healthy hips that have enough hip internal rotation range to move through many activities, for example, the squat. Delp et al (1999) studied the degrees of internal rotation and how they change throughout different ranges of hip flexion (more hip flexion = deeper squat), and found that:
The experimental results and the computer model showed that the internal rotation moment arms of some muscles increase with flexion
So, it appears there is an association with limited hip internal rotation and potential for injuries. In practice, we find that when athletes or clients lack internal rotation in their hips, they often start to report pain or tightness in surrounding areas, like low back, knees, and groin. Especially those with athletic endeavours, or looking to do specific strength movements in the gym, like a deep squat.
You can probably tell, based on this image of a step up in one of our clients, that the hip with the excessive hip internal rotation upon movement, also caused the worse back position:
Counter-intuitively, although it looks like the right leg has more internal rotation than the left leg, you would be wrong in thinking so. Proof:
While both of these hips display limited hip internal rotation (normal is 30-45 degrees), neither is more or less mobile than the other. So, while we could improve the range of motion bilaterally - can you see why the spine is coming along for the ride on the right side?
Part 2 of this hip internal rotation series will be out soon! Feel free to subscribe to our site by hitting "Login" at the top of the page - this will make you a member and keep you in-the-loop when new blog posts come out!
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