What Implications Does “Envelope of Function” Have for Designing a Plan to Beat Knee Pain?

Last week I described Scott F. Dye’s common-sensical idea of the “envelope of function.” He believes that patellofemoral pain patients should try to “maximize the range of painless loading for a given symptomatic joint (envelope of function) as safely and predictably as possible.” Such an idea is consistent with my own belief in slowly strengthening a damaged joint.

This week, I want to consider implications of the “envelope of function” perspective. In other words, how does it translate into practice?

At the end of this post, I’ll tell you what Dye himself recommends for treating achy knees.

Before that, I want to share my own observations about what “envelope of function” implies.

But even before that, it’s worth taking a few moments to examine which popular theories Dye rejects as insufficient to explain knee pain. Doing so helps explain what compelled him to develop his analytical framework in the first place.

Dye, a long-practicing orthopedic surgeon, surveys current approaches to handling patellofemoral pain with more than a touch of dismay. What he sees are theories that often lead to “corrective” surgery that is worse than ineffective; it actually harms the patient.

For one, some in his field are obsessed with cartilage to the point that they try to fix damaged tissue through chondroplasties and microfractures. (Note: here my thinking somewhat diverges from his, on the role of bad cartilage in contributing to knee pain, but that’s a long digression -- in any event, I think he’s right that much surgery is unnecessary).

As Dye observes, the level of pain a patient experiences doesn’t always correlate well with the degree of chondromalacia in the knee. You may have advanced chondromalacia and no symptoms, or articular cartilage that appears normal that’s associated with a very painful joint (all true, but I think the total picture is a bit more complex).

Dye also rejects the “malalignment” school of thinking (what I have often disparaged as “structuralism”), which commonly blames knee pain on an improperly tracking kneecap. He gives several reasons why this analysis doesn’t make sense.

If the presence of observable factors of malalignment is so important ... why does one find patients with bilaterally radiographically determined patellofemoral malalignment [that is, mistracking in both knees as indicated by X-ray], with only unilateral symptoms [that is, symptoms in only one knee]?

Or there’s this to ponder:

Why do more than 90% of patients with anterior knee pain who have a diagnosis of malalignment as the cause have a successful response to conservative therapy, even though there has been no documentation of long-term restoration or correction of the supposed causative underlying indicators of malalignment.

Finally, he points out:

The malalignment theory also does not explain the variability of patellofemoral symptoms in the same patient at different times, including the presence of sharp pain on occasion and then dull aching pain on another.

He does recognize that “some patients have clinically significant malalignment” that responds well to corrective treatments, such as a lateral release. “However,” he goes on to caution, “in my experience, the numbers of these patients are relatively few.”

Finding the blame-the-cartilage and blame-the-malalignment frameworks for understanding and dealing with knee pain wanting, he comes up with “envelope of function.” But what does this perspective imply, in practical terms, if you’re trying to fix a couple of bad knees?

Here are what I consider two interesting implications:

“Envelope of function” is kind of a big tent idea. That is, you can interpret it as being somewhat agnostic about the origin of knee pain. What matters, a believer could argue, is the fact that you have a certain degree of knee pain and, given that, what’s the best way to heal?

For example, I thought my pain stemmed from cartilage problems. Maybe I was right. Maybe I was wrong. Arguably, an “envelope of function” approach works in either case because, primarily, your concern is staying within the range of loading that your joint can tolerate.

Obviously, this concept wouldn’t make sense for a patient who has an important, identifiable contributor to knee pain that must be dealt with before healing can occur -- the equivalent of an iron spike sticking out of the joint that must be removed first. But I don’t think that describes the vast majority of patients who have chronic knee pain.

An “envelope of function” approach suggests it’s absolutely critical to determine that range of optimal loading for your bad knee. The best place to do this, in my opinion: at a doctor’s or physical therapist’s office, using machines/devices that can quantify exactly how much load your knee can safely tolerate.

Yet very few medical professionals attempt to do this. This is one reason I think we’re still in the Dark Ages on treating chronic knee pain. The American military can fire a cruise missile down a chimney 1,000 miles away, but the U.S. medical establishment can’t (or has no desire to, more significantly) measure how much force an individual can safely put on a bad knee joint, over the course of a 24-hour day.

Now, what does Dye himself recommend for patellofemoral pain patients, besides a “scrupulous adherence to load restriction within the patient’s reduced envelope of function”?

An anti-inflammatory program.

He appears to favor icing and medication, and approvingly cites a regimen of icing 15 to 20 minutes, two or three times daily.

Indeed, runaway chronic inflammation -- the undesirable kind -- is a problem among those who have constant knee pain. I’m a little leery of his solution though, as I usually associate icing and medication with people who use both to keep doing unhealthy things (such as running when their knees aren’t strong enough). Also, icing and medication interfere with the signaling you get from your knees that’s often telling you, “Stop doing that!” (sitting, standing, whatever)

Still, anti-inflammatories may be a good idea, if used smartly.

He also supports painless (his emphasis) muscle strengthening, stretching and patellofemoral taping.

My own opinion (as I’ve made clear on this blog): stretching isn’t of much use but if it feels good why not?, muscle strengthening should be put on the back burner completely in favor of “joint strengthening”, and as for taping -- sometimes it can offer relief, so why not try it as an interim measure?

“A period of 6 to 9 months of conservative therapy often is required” to improve an ailing joint, Dye informs us soberly, then warns: “The first pain-free day does not mean that the envelope of function has been fully restored but that healing is occurring.”

Getting to the right healing program isn’t easy, as Dye observes. “It is not unlike trying to find the numbers to a combination lock.” True, so true. However, when you succeed in finding the right sequence that springs that stubborn lock, and get squarely on the long-term path to getting better, it’s really a great feeling.