Strengthening for painful knees performs poorly in a new trial

It’s routine for therapists to prescribe strengthening of the mighty quadriceps muscle group as the primary treatment for patellofemoral syndrome — pain in the joint between the kneecap and the femur, a common trouble spot, notoriously stubborn. There has been plenty of evidence over the years that patients do well with this approach, and it is sometimes held up as one of the few clear examples of good evidence-based rehab. Quoting from my book, before I updated it:

“The evidence to support exercise is good and growing, with numerous research reviews clearly indicating a favorable effect for most people, most of the time. Studies appear to consistently support exercise programs designed around knee strengthening, hip strengthening, or both.”

Sounds like good news. But there have always been some awkward questions about this, such as: How good, really? And does the strength of the quads really matter? Or is the active ingredient just methodical moderate stimulation? Maybe confidence-building activity over time?

To help sort this out, we have a biggish new trial in the British Journal of Sports Medicine. Researchers compared quads and hip strengthening, twelve weeks of either one or the other, in 200 people with aching kneecaps (a substantial sample size for once). I discuss the exact protocol in a detailed follow-up post. There were no meaningful differences between the two groups. And then there was this:

“…neither programme surpassed the minimal clinically important change threshold.”

Both kinds of rehab were ineffective. Both of them were distinctly underwhelming. In this apparently well-designed test.

This swings the evidence pendulum fairly strongly away from strengthening as a treatment for patellofemoral pain. It suggests that the biomechanical equation of the knee joint is probably not being optimized by stronger quads (e.g. via improved tracking), despite the fact that this is what so many professionals assume. And it suggests that there is no important “active ingredient” at all, because basically not much happened.

Maybe strengthening the quads and/or hips is nothing more than an exercise in “amusing the patient while nature cures the disease.”

Or perhaps it’s more a matter of herding the patient a little, keeping them from sabotaging nature’s cure: when people focus on a therapeutic exercise prescription, they are probably less likely to undermine their efforts with less controlled forms of exercise. I have long wondered if this is the boring, non-obvious reason that people seem to get any benefit from such prescriptions: it tends to have the effect of regulating their exercise dosage, minimizing loading spikes that would otherwise derail their recovery.

In other words, maybe strengthening the quads is really just a way of getting people to be a bit more consistent and careful with how they use their knees … allowing nature to take its course back to homeostasis.

Here’s how my book sums it up now:

“We must take the new evidence from Hansen et al quite seriously. It doesn’t prove that strengthening is ineffective, but it does substantially undermine its status as evidence-based rehab. At the very least, we must accept that the truth remains elusive, and embrace the usual uncertainty in this business.”