Hip mobility issues in basketball players- why the lack of internal rotation?

Posted on August 3, 2015


I have a post On structural adaptation limitations (of the hip). At the end of the post I referenced research on whether hip “abnormalities” are genetic or an adaptation. This post will discuss that. It is effectively part two. 

I‘ll be using the following research paper:

The Cam-type Deformity of the Proximal Femur Arises in Childhood in Response to Vigorous Sporting Activity

The femoral neck is enlarged in a Cam “deformity.”

femoral neck

Thinking Camshaft may help. (CAM or Cam are commonly used. I’ll be using Cam, as CAM comes across as if it’s an acronym, which it’s not.)

This study looked at hip differences for 1) presence of Cam 2) internal rotation range of motion at 90 degrees hip flexion; between non-athletes and basketball players 9-25 years of age. It didn’t follow players for that time period; it looked at different age groups and compared them.

How many say, 9-12 year old basketball players have a Cam, compared to 25 year olds? Does the rate increase with age? If so, does it increase more than the control (non-athlete) group?

Per the title, The Cam-type Deformity of the Proximal Femur Arises in Childhood in Response to Vigorous Sporting Activity, you can guess what they found. Yes, playing basketball can influence Cam presence.

-> While this may seem pedantic, I think it’s important to note this study only looked at basketball players and non-athletes. The “in response to vigorous sporting activity” of the title is a bit misplaced, as is many references to “athletes” in the paper (such as the tables below). I’d bet a lot of us would read “sporting activity” or “athlete” and assume a bunch of different sports fit under this umbrella. “in response to vigorous basketball activity” is more accurate. I will get into specifics of basketball movement later on, which will show why this matters.

These weren’t small differences.

athletes compared to controls femoral neck

Notice the “Alpha angle” and the “o’clocks” above-

Alpha angle is a measurement for Cam “deformity.” Bigger the angle, the more of a Cam presence, or the larger the femoral neck, depending on how you want to look at it.

Alpha Angle with Cam lettering

The o’clock is a representation of the femur. What we want to keep in mind is the smaller numbers represent the front of the femur, while the bigger numbers are the back.

Femoral neck clock

Let’s call from 12 to 3 our “first quadrant.”

Femoral neck clock first quadrant

We see a big jump in differences between the basketball players and non-athletes in this first quadrant:

athletes compared to controls femoral neck first quadrant

  • For 9, 10, and 11 o’clock, the differences are
    • 1.5
    • 3.9 and
    • 0.2 respectively.
  • For 12, 1, 2, and 3 o’clock, the differences are
    • 8.3
    • 13.1
    • 11.7 and
    • 12.5 respectively.

Over time this difference grows much more amongst basketball players than the non-athletes:

athletes compared to controls and age femoral neck

Open is before growth plates close; closed is after. Let’s pull one example, the 1 o’clock.

  • Basketball players-
    • Open (young): 53.7 degrees
    • Closed (older): 64.3 degrees
  • Non-athletes-
    • Open (young): 47.5 degrees
    • Closed (older): 47.4 degrees

As I said, these are noticeable differences to start with, and they get bigger with age. At 9 years old there are likely already some adaptations to playing basketball, and these adaptations get more pronounced throughout the lifespan. This is where we can make a reasonable assumption most of these changes are environment oriented, not genetic.

-> The possible debate here would be those who played basketball throughout their lives somehow had hips that were already going to make these changes. I don’t think this is a worthy debate.

A consequence of a Cam “deformity” can be…

A loss of internal rotation range of motion of the hip. Which is what the authors found in the basketball players:

basketball players compared to controls internal rotation range of motion

As the subjects get older, the basketball players lose 21.8 degrees of internal rotation range of motion, where the non-athletes lose only 9.3 degrees. (It’s common to lose internal range of motion from our youth to young adulthood.)

Because this study started at only 9 years of age, these differences are likely underestimates. Again, by 9 years old, after what is for many 4 years of playing basketball (many start at 5 years old), there are likely already adaptations. Because the control subjects already had ~3 degrees more of internal rotation by 9-12 years of age, it’s conceivable the basketball players, by 9-12 years of age, had already lost that much. Meaning the basketball players may lose more like ~25 degrees as they age. (21.8 degrees + ~3 degrees = ~25 degrees.)

By the early/mid-twenties, basketball players have ~15 degrees less internal rotation range of motion.

Visualizing why

In the first post on hip structure adaptation, I used this GIF detailing the femur banging into the acetabulum sooner when retroversion is present:

Normal and Retroverted Internal Rotation GIF

With a Cam, both hips may have the same starting position, but the consequence of the Cam is the same as with retroversion.

Cam Internal Rotation GIF

A thicker femoral neck hits the acetabulum sooner, decreasing the space available for hip internal rotation range of motion.

Why do basketball players acquire a Cam “deformity?”

“The pathomechanism for the increase in alpha angles in the athletes during the growth period is unknown. Vigorous exercise may trigger the deformity, as high skeletal stresses have been associated with a pathologic skeletal growth pattern and morphologic alterations in gymnasts and baseball players [5, 6]. We speculate the cumulative effect of high stresses and perhaps more or less subtle differences in the direction of loading on the proximal femur during growth may modulate growth toward an abnormal shape.”

This is too vague for me. Perhaps the authors didn’t want to get into this, or aren’t sure, but I’m happy to put forth a more specific reason why I think basketball players acquire this skeletal structure.

Bone is amazingly intricate, yet fairly simple at the same time. Load it regularly, and it grows. It’s very, very specific where this growth occurs => exactly where it’s loaded.

Femoral neck clock first quadrant

This first quadrant is where the basketball players have extra bone. This first quadrant is where the basketball players must be incurring extra loading. (In the fourth quadrant, the non-athletes actually have more bone. Note the specificity going on here.) Now an athlete’s entire body is going to be dealing with extra loading compared to a control. But with basketball players, this first quadrant must be disproportionally more loaded. How?

The most obvious thing basketball players do compared to not only non-athletes, but other athletes, is jump a ton. Jump, and land a ton.

Let’s look at pillow man Dwight Howard.

dwight howard about to rebound

Notice the hips flexed some. Having someone draped on top of you is a common position in basketball, loading you(r bones) ever more.

He jumps:

Dwight Howard Rebound 2

Dwight Howard rebounding 1

And will then land with the hips a bit flexed. The legs will go from where they are to more of where the yellow line is:

Dwight Howard rebounding 1 with line

steph curry rebound dwight howard

And Steph Curry will box him out.

steph curry rebound dwight howard with line

Hips a little flexed on left; then straight (extended) in middle; then flexed again on right.

When a person lands, the force of their entire body -and in basketball, often the force of another person- comes down on these somewhat flexed femurs.

Pelvis AnatomyFemur AnatomyFemoral neck anatomyAcetabulum anatomy

Above images from this video .

When the leg is straight, or a bit extended, when Dwight Howard is straight up in the air, the forces of gravity will go as such:

Femur and acetabulum GIF

Femur and pelvis with gravity GIF

Other hip images from this video.

In this case, the top part of the femoral neck is being stressed. This would be our 12 o’clock. It’s getting pulled down, so it needs to resist that load.

Femoral neck clock with gravity line

12 o’clock is one location basketball players clearly had a Cam going on. But in a basketball player, there is a lot of loading going on with the femur in this flexed position of landing.

Femoral neck gravity GIF

Hip flexed, with orange representing femoral neck getting stressed downward.

The top part of the femur in this scenario is our first quadrant. Our entire clock rotates when landing from a jump, so our first quadrant is receiving more of that downward stress.

Hip flexion femoral clock GIF

Our new clock:

Femoral neck clocks Rotated

1) The first quadrant gets significantly stressed when in this hip flexion position

Femoral neck clocks Rotated with gravity line

2) What I bet goes on here is that acetabulum and femur, and everything in between them, compress significantly together. Not every time, but in the midst of playing basketball, enough. Something like this:

Hip Flexion compression

This is a bit more flexed than would normally happen, but the red is still roughly our first quadrant.

The top part of the femur (first quadrant when in some hip flexion), the part that’s being stressed / compressed, responds by getting bigger. This is our “1 o’clock.” Or, “antero-superior aspect of the femoral head.” (The forward and upward part.)

Of course, the femur gets loaded some in flexion when running too. 68% of male (50% of women) soccer players have been found to have a Cam “deformity.” Basketball players run on a harder surface, but don’t run as much in total, as soccer players. 89% of basketball players were found to have a Cam, a good amount more than soccer. So, I think there is more going on here than only the running. This is why I brought up the point earlier of not merely throwing this away as “vigorous sporting activity.” Specific movements cause specific adaptations.

Meaning this is not “deformity.” This is not abnormal. This is not random. This is response to stimulus.

On limitations again

You may have noticed I’ve been putting deformity in quotations. Deformity depends on your point of view.

The authors mention an alpha angle greater than 55 degrees is considered abnormal.

“In athletes, we found an alpha angle of 55° or greater in 41 (89%) of 46 hips in the anterosuperior head quadrant, which represents a nearly 10-fold increase in the athlete hips.”

When 90% of the population has the abnormality, can you say it’s abnormal anymore? Sure, compared to everyone else, basketball players have an abnormal height. But we don’t consider it abnormal in the way we use the word. It’s not derogatory. We don’t consider it a deformity. We consider it beneficial.

Whether it’s my theory above or something else, clearly, something is going on here that the body is finding the need to adapt to basketball through a thicker femoral neck. More than likely, this ends up being a femoral neck more suited to play basketball. A thicker femoral neck is less likely to break, for instance.

Concurrently, this ends up being a femoral neck, and hip, less conducive to engaging in activities necessitating a good amount of hip internal range of motion, and probably anything with deep hip flexion. This ends up being a femoral neck more likely to bang into the acetabulum, increasing the odds of impingement and arthritis down the road. The authors mention repeatedly how athletes have a greater risk of hip arthritis.

You can’t have it both ways. You can’t have it all.

When you get good at one thing, you invariably get worse at something else. For professional athletes, this doesn’t matter much. (Until they’re not athletes anymore, which is the majority of their life.) A basketball player isn’t all of a sudden going to try and be a hockey goalie, olympic weightlifter, gymnast, or someone requiring incredible hip mobility. For everyday people though, this matters.

If you have an extensive basketball background, then there is a good possibility you need to forever be concerned with not doing activities putting your hips in certain positions. You spent a good portion of your life getting good at something, and there are consequences to that. Consequences you may never encounter, but some you may.

-> Bone atrophies once a stimulus is gone. However, there are adaptations that never go away with bone. Height being an obvious one. I banged up two of my fingers a decade ago from football. They’re still thicker than my others, despite the stimulus being gone.

Formerly dislocated on right.

Formerly dislocated on right.

The body seems to like keeping adaptations from youth. If you grew up throwing a ball, you’ll probably always be able to throw a ball. If you never grew up throwing a ball, it may forever be tough to throw one. Think the expression “Throw like a girl.” It’s not that girls can’t throw; it’s so many of them used to grow up not throwing, that past a certain age, their bones couldn’t adapt to get into this position:

Humeral retroversion. (From: http://sph.sagepub.com/content/1/4/314/T1/embed/inline-graphic-3.gif)

Humeral retroversion.

This is where getting surgery for things of this nature is shortsighted. I’ve mentioned previously there is no telling the bone won’t come right back. (This isn’t a nose job. A nose isn’t loaded where a femur is.) Especially if you’re a basketball player getting this surgery to help your hip mobility for basketball. You may be shaving down, getting rid of, an adaptation. We don’t tell basketball players “you’re abnormally tall, we need to perform surgery to shorten you and make you more like the general population.” We probably shouldn’t be telling them “you have abnormal hips, we need to make them look more like the general population.”

But say you get surgery because you want to have fun playing goalie in your rec hockey league. What about basketball though? By shaving down your femoral neck you must be lessening the ability of your hips to handle basketball, no? Shave that femoral neck down, then all of a sudden go play basketball like you used to, and who knows how much greater risk you’re at to break that femoral neck.

You can’t be good at everything.

However good you are at X, you’re proportionally bad at Y, likely because of how good you are at X. This is not a matter of hard work, or being innovative enough, or lack of technology. No. This is a matter of nature. “You don’t like it? Go somewhere else! To another universe. Where the rules are simpler. Philosophically more pleasing. More psychologically easy. I can’t help it…Because it’s the way nature works!

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