Wednesday, 20 November 2013

Improve runners' knee by decreasing variability of motion

Last weekend I went to a "Run Faster" conference put on by the Royal College of Chiropractic Sports Science.  Topics ranging from running technique and coaching to nutrition and injury management were discussed.

One presentation that was exceptionally interesting to me was put on by Dr. Reed Ferber from the University of Calgary.  He also has a website that is an amazing, evidence-based, resource for any runner- click here to check it out.

Patella femoral pain (PFP)

While Ferber researches an array of topics, one focus of his talk involved a new look at how to not only manage PFP, but how to THINK about PFP.

As many of you know, PFP is a condition that involves pain at the front of the knee, directly under the knee cap.  It typically kicks in early into runs, and progressively gets worse as we keep running.  It also often hurts to keep the knee in sustained flexion (i.e. sitting for long periods of time), and can be quite stiff when it comes time to straighten the knee out again.

The cause of this pain is thought to be an irritation to the soft tissues underneath the knee cap as we move.  If things are moving smoothly, the tissues don't become irritated, and pain does not occur.  However, if things are not moving well, then friction, tears, inflammation and irritation to those tissues can occur, and pain follows.

Why does this irritation occur?  It is suspected that, in many cases, this is happening because of a knee position known as genu valgum, or being knock kneed (see right).

If you imagine the knee cap normally sitting within two grooves when the knee is straight, it only make sense that genu valgum would cause issues.  Rather then the knee cap being centered every time we take a step, having genu valgum will cause the knee cap to be forced up against one side of those grooves, resulting in a pinching of the tissues underneath with every step.

So why does genu valgum happen?  There are a few causes.  Sometimes it is due to the shape of our bony anatomy, other times it may be due to a muscular deficiency.  One common area that therapists link PFP to is weakness of one of the main pelvic stabilizers: glut med (see right).

Glut med's job is hip abduction if you are lying on your side, but it functions to keep your hips from dropping as you run or walk.  Somebody with good glut med strength will be able to maintain level hips, while somebody who has a weaker glut med will tend to sway and drop their hips as they run.

For instance, look at the picture on the right.  Picture (a) shows a runner with good glut med strength and good pelvic stability.  Then, picture (b) shows somebody with weak glut med strength, which as a result, is causing the hip to swing out to the side.  You can see that as the hip swings out to the side, this is going to put a force on the knee that encourages genu valgum.

So, our injury sequence: weak glut med...hip drop...genu valgum...then PFP.

Correct the genu valgum, correct the PFP, RIGHT?  Maybe not...

Ferber's new look on PFP

In one of Ferber's studies, he took a group of runners with PFP to test the above.  He had them do exercises to strengthen their hip abduction (glut med) for 15 minutes/day.  The exercise was simple: attach a resistance band to your ankle, and move your leg to the side for 10 reps, 3 sets, daily, for 3 weeks.

Here are the results:

The great news:
  • Pain (red bar) went down by over 40% 
  • Strength of hip addiction (blue bar) went up almost 40%
The "bad" news:
  • Knee position/ peak knee angle (black bar) didn't really change AT ALL.
So these athletes had PFP, they had weak hip abduction, they corrected that weakness, their pain got better...but their knee position did not change.  This is where it gets interesting.  

Ferber's study also looked at another component of motion: variability.  In other words, when we take a step, our legs move around in subtle ranges of motion (i.e side to side, rotation) that we don't really realize.  So if a runner is settling into a genu valgum position at foot strike, there is a number of different ways the knee can get there.  

Ferber thinks is that if that variability in motion is reduced, this is what MAY explain the change in PFP they saw without changing the knee position/ peak angle.  This is what they found:

Each line on this graph represents a foot strike.  So as you can see, on the pre-rehab graph on the left, the lines are random, and going all over the place.  By comparison, the post-rehab lines are very consistent.  YES, the subjects' peak knee angles are the same, but the movement to get there is no longer variable and unpredictable.  The researchers believe that this drop in variability is what gives tissues the type of load during running they need to heal.

Practical Applications

The practical applications, in mind, are quite significant.  There are three major reasons I say this.

  • If you suffer from an anatomical genu valgum that just does not seem to be reversible, this research shows it just might not matter.  If you have genu valgum, and PFP, correcting your genu valgum does not necessarily need to be your focus.  If you work on pelvic stability in general, and your variability of motion goes down, it is quite possible to get ride of the pain without changing the angle of your knee.
  • This research does not change what therapists should prescribe from a rehab standpoint.  Even if you think you are correcting genu valgum, hip abduction strength work would be prescribed.  So it's the same intervention, just expectations and outcome measures must be changed.  Decreased pain, hip abduction strength and variability of motion (if you have the fancy equipment), must be valued over knee position since knee position seems like it CAN be independent of those who suffer from PFP.    
  • Finally, it also puts into question the specificity of exercise prescription.  If you are not correcting genu valgum with hip abduction strength worth, then why is it better than something else?  Couldn't other exercises and interventions decrease variability of motion just as much?  Well, that is something the Ferber lab is looking into (and already has with looking at quad exercises which achieved similar results).  More to come on this!
That's it for now, thanks for reading, and thanks to Dr. Ferber for presenting such interesting work.  

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