Science and myths about knee pain problems, especially iliotibial band syndrome and patellofemoral pain. (And occasionally shin splints. And plantar fasciitis.)

Recently a reader wrote to me to point out that, in his opinion, recent scientific evidence has begun to support the “conventional wisdom” about chronic anterior knee pain (a.k.a. patellofemoral pain syndrome, or PFPS). That would make my e-book on the topic look bad. I pretty much roll my eyes at the conventional wisdom from the first word to the last.

I would be delighted to be wrong. Being wrong is good. I have an ego, but it’s invested in my intellectual integrity, not the position I held in 2009. (Just this Monday I cheerfully admitted some major wrongness about icing and heating therapy.)

So I went looking for recent papers that might embarrass me.

Super quick review of the conventional wisdom

The conventional wisdom is that PFPS is caused by biomechanical dysfunctions, and that they can be treated primarily with therapeutic exercise. The classic example: in patellar tracking syndrome, the kneecap slides unevenly, allegedly placing greater strain on the knee, which thus leads to pain; but the tracking problem can be fixed by selectively strengthening one side of the quadriceps muscle group.

My wisdom is that the conventional wisdom has resoundingly failed to help patients. Biomechanical problems are real but minor factors and largely untreatable in any case, and the characteristically stubborn character of PFPS is mainly due to a simple but vicious cycle: knees are extremely difficult anatomical structures to rest, with or without minor biomechanical dysfunctions, and once they have been aggravated by over-use they simply have a hard time calming down.

Correlations, schmorrelations

The paper the reader cited was “Concentric and eccentric torque of the hip musculature in individuals with and without patellofemoral pain”, which I was already familiar with. It didn’t change my mind before, and it still doesn’t.

Yes, Boling presented some data in 2009 showing a modest association between PFPS and hip weakness, but it was hardly a smoking gun! The weakness could be either a symptom of knee pain and/or a cause of it. Having a painful knee probably has an impact on how you use your whole leg, and might well cause hip weakness. The literature is overflowing with studies like this, and they collectively produce no clear signal. This one doesn’t change the basic (confused) picture, and they continue to be blatantly contradicted by other studies. For instance …

One of the recent studies that I found when I went looking states that “factors related to physical impairments did not associate to function or pain.” They present a long list of the usual biomechanical suspects, including hip strength just like the Bolgla, but they found no correlation at all with chronic anterior knee pain.

(Interestingly, they did find that “psychologic factors were the only associates of function and pain in patients with PFPS.” Now that’s odd, isn’t it? I’ll have to write an article just about that!)

Not-so-conventional conventional wisdom

Here’s another interesting point: Boling doesn’t particularly support “the conventional wisdom,” but rather a new variation on it. Their evidence (vaguely, weakly) suggests that it’s all in the hips. They found “weakness in eccentric hip abduction and hip external rotation.” This is certainly conventional wisdom in spirit (i.e. some biomechanical problem is to blame). But it’s also a whole new biomechanical bogeyman, not one of the usual suspects. This new fascination with hip function is a bit of a fad, an attempt to replace the old usual suspects. Many authors are claiming that there is an “emerging body of evidence” that hip function is critical to knee health. Bollocks. This is highly debatable, especially because most of that alleged “body of evidence” is emerging from one researcher’s public relations efforts: he loves doing press conferences and interviews for glossy running mags, but has yet to actually produce any evidence that any kind of runner’s knee pain is caused by hip weakness. I have criticized the hip strength thing quite strongly and thoroughly.

If the hip-weakness hypothesis is eventually proven — which is possible, despite my objections — it will result in therapists prescribing something new (hip exercises), and not something old (quadriceps exercises). That would really be validation of the conventional wisdom. But I’m not holding my breath.

Gait retraining results are significantly insignificant. Or something.

Also in the not-so-conventional wisdom category is “gait retraining.” If PFPS is all in the hips, then maybe learning to walk again will help your knees? A brand-spanking new study, not even in print yet, offers the closest thing I found to a surprising clash with my previous beliefs. I would not have expected these results:

Gait retraining in individuals with PFPS resulted in a significant improvement of hip mechanics that was associated with a reduction in pain and improvements in function.

Sounds straightforward and good, and they have my attention.

On the down side, the abstract is painfully vague (and buying the whole article would be a bit expensive), and I suspect some hanky panky. In particular, I’m troubled by the fact that their findings about two of their three “variables of interest” were not found to be statistically significant (which they admit), and then they don’t mention the third! Translation: “We measured three important things, and two of measurements were not stastically significant.” And the third? “No comment.”

But then they conclude with “significant improvement of hip mechanics!” What gives? Eh? What was significant?

They don’t say.

Another red flag is the curious statement (very unusual for an abstract) that one measure of improvement was “very close to significant.” This is an abuse of statistics. That phrasing tries to put a positive spin on bad news: there was actually a fairly high chance that the result was just a coincidence. It’s kind of bad form to say “almost” statistically significant instead of “not” statistically significant. I do not think that this word “significant” means what they think it means!

All of this pretty much reeks of researchers who really wanted a pro-gait-training result, and they did some mental gymnastics to make it sound like they got it.

Perception of knee pain is everything

Another experiment which had the potential to make me wrong was a comparison of “supervised exercise” versus “usual care.” I would never recommend supervised exercise, which is very much in the conventional wisdom camp, and a total waste of time in my opinion. But, at first glance, this paper looks like it’s displaying a fat thumbs up for supervised exercise: “Supervised exercise therapy improved patients’ pain at rest and during activity, and self-reported function improved faster than with no supervised intervention.”

Wow! Goody gumpdrops! Get me some supervised exercise for my knee pain, stat!

But wait, read the next sentence:

“The patients’ perception of recovery from patellofemoral pain syndrome was not greater among the supervised exercise group.” My emphasis.

Er … what? “Perception of recovery”? “Not greater”? Isn’t that kind of, um, a total letdown?

You bet it is! Simply put, you can measure as many “functional” improvements as you like, and while it might be interesting to the lads in lab coats, it doesn’t matter a tinker’s damn to the patient if they aren’t improved enough to feel better. You can’t say that a treatment “works” when the patient doesn’t perceive recovery. Basically what these patients said was “sure, maybe it’s better in a couple ways, but basically I still have a @!&^$% frustrating case of knee pain.” Patients who can’t preceive recovery regard the therapy as total bollocks.

So in some ways this study showed that (supervised) exercise is good for PFPS. But mostly it showed that it doesn’t do anything that matters. And when you consider the cost of hiring a physical therapist to supervise your exercise …!

Conclusion

Nope, my face is not red. I do not feel embarrassed by my anti-conventional-wisdom position on patellofemoral pain syndrome. It’s not time to change my mind on this yet. And, of course, even if I did change my mind I wouldn’t actually be embarrassed by it.

Perhaps of note is that the polite, constructive criticism that inspired all of this has not amounted to much. A reader raised a concern, but cited only a single example of relevant science (the Boling), and has not responded to my request for additional examples. This is what I would call a “hit and run” criticism: a perfectly good criticism in spirit, but where’s the beef?

But I still took it seriously. I always respond to such criticisms with an earnest spasm of self-doubt: what if I’m wrong? What if I’m publishing something incorrect? It was a good exercise to go trolling through the recent research looking for evidence that I might be wrong about knee pain.

Alas, not this time.

References

• Boling et al. Concentric and eccentric torque of the hip musculature in individuals with and without patellofemoral pain. Journal of Athletic Training. 2009.
• Hart. Supervised exercise versus usual care for patellofemoral pain syndrome. Clin J Sport Med. 2010.
• Noehren et al. The effect of real-time gait retraining on hip kinematics, pain and function in subjects with patellofemoral pain syndrome. British Journal of Sports Medicine. 2010.
• Piva et al. Associates of physical function and pain in patients with patellofemoral pain syndrome. Archives of Physical Medicine & Rehabilitation. 2009.