Saturday, November 22, 2014

Old, Bad Beliefs Die Hard

I came across this Internet article on the VMO (vastus medialis oblique), one of the four muscles that, collectively, are known as the quadriceps. About halfway through, I noticed an interesting assertion:
... patellofemoral pain syndrome. A misaligned patella results in pain on the front of the knee, ultimately caused by a weak VMO.
My initial reaction was along the lines of “Whoa, back that truck up!” For one, if you read a lot of the literature on patellofemoral pain syndrome (PFPS) from informed sources (as I’ve tried to do), you’ll discover there’s much confusion about what indeed does cause PFPS. (Actually, to take a step back, it’s not even clear that this is a meaningful diagnosis in the first place.) So this article’s pat suggestion that your knee pain is caused by a misaligned patella that in turn is caused by a weak VMO is venturing way out on a limb.

For starters, the role of a mistracking kneecap in causing pain may have been oversold. This study (rather small but intriguing) found no relationship between the amount of patellar mistracking and reported knee pain.

Then there’s the problem of strengthening the VMO in isolation. That, by implication, is what someone with a weak VMO in this scenario needs to do. After all, if your problem is maltracking, and you strengthen all the muscles equally, then it seems you would have the same amount of maltracking, only with stronger muscles causing it.

So how do you strengthen the VMO in isolation?

Well, you can’t, as Doug Kelsey has observed a number of times, such as in this passage:
The VMO is one of four muscles which all share the same nerve: the femoral nerve. Muscles contract when nerves tell them to contract. Since the VMO has the same nerve as the other three thigh muscles, it will contract along with the others. You cannot make the VMO contract by itself.
Strengthening the VMO to correct a mistracking patella is a typical old school recommendation for treating chronic pain from achy knees. Tease the reasoning apart, bit by bit, and it falls to pieces. Yet the advice lives on in many corners of the Internet.


  1. That's exactly what the orthopedic surgeon told me on my first visit, to ask my physio to show me how to make the vmo strong...oh he also prescribed glucosamine which I'm still taking but every time I think 'placebo'. Anyhow I don't know why GP sent me to see a surgeon but anyway... In a month I've learned so much about cartilage, joints, muscles...that I'd like to come back to that surgeon again and explain how wrong he is.... It is really a myth the story of the vmo...

  2. Yup, virtually every medico I saw said strengthen the VMO - except the Sports Dr at a major Sydney NRL Club, who watched my VMO etc working when I jumped off a box and said it was fine (20+ years of cycling will do that!). He said to strengthen my glutes/hip muscles - which I did, but to no avail. And they still think you can do exercises that isolate the VMO, or make it switch on at the correct time. The only thing I've found that makes my VMO fire alone is cranking up the TENS machine.


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  4. I bought your book and have benefited from it but I think there may be some substance to what (some of) the structuralists are claiming.

    1. John Davis writes

    Additionally, Powers puts to rest the “patellar tracking” myth with a summary of some very clever MRI studies. Recall earlier that the prevailing opinion in orthopedic circles was that PFPS is a result of abnormal patellar tracking, and as such must be addressed by quadriceps strengthening and perhaps altering the firing patterns of the quadriceps muscles. Using dynamic MRI imaging, a technique which can capture real-time changes inside the body, Powers and his coworkers at UCLA demonstrated that, while the patella does indeed track abnormally in the patellar groove of the femur in patients with PFPS, this only occurs in non-weight bearing motions. When the patient does a weight-bearing motion, like a squat, the strong contraction of the quadriceps muscles essentially “locks” the patella in place. Instead, the femur rotates relative to the kneecap! So while on the outside it may appear that the patella is moving, in fact it’s the femur that’s moving!

    So the structuralists may be wrong about patellar tracking but they may be correct about the importance of hip strength and mobility. (I agree the VMO stuff is pretty much bunk).

    2. Related to that point, hip mobility and strength interventions are effective.

    Khayambashi et al conducted a RCT looking at isolated hip abductor and external rotator strengthening 3 times per week for 8 weeks with a 6 month follow-up. At the conclusion of the study, the exercise group’s VAS Pain Scale decreased from 7.9 to 1.4 and maintained at 1.7 at the 6 month follow-up. This group’s WOMAC score showed similar improvements with a baseline rating of 54 and post intervention scores of 10.7 (8 week) and 10.8 (6 month). Both of these outcomes showed significantly superior results in comparison to both baseline and the control group.

    I find this compelling. So I suspect that PFPS is multifactorial. Strength and mobility deficits can cause the femur to internally rotate, which increases pressure on the knees. And light activities such as walking and easy cycling can stimulate cartilage regrowth. But I'm curious on what you think about this.

    1. Ah, hip strength and knee pain! Well, I'm a skeptic. I'm always willing to concede I may be wrong, or perhaps hip strength is a factor for a minority of people, but when I looked into hip strength and knee pain, it inspired me to write these posts:

      I hypothesized at the time that it's more likely that hip weakness is a result of patellofemoral pain syndrome, not a cause of it. And sure enough a meta study came out (analyzing all the presumably high-quality hip-knee pain studies) that prompted this post:

      One of the researchers for the meta study in fact concluded:

      "Therefore, hip weakness may not be the cause of knee pain — in fact, it is more likely to be a result."

      That sounds about right to me.