In part 1 we looked at causes of PFPS and a few solutions. Next we look at striking the balance of increasing load on the knee without causing pain. This work from Scott Dye has been hugely helpful in treatment of PFPS. He describes the “envelope of function” which is a very useful way of looking at a knee with PFPS. In a nutshell it means what your knee is capable of. Work above this you'll get pain and inflammation, work within it and potentially that envelope will grow and you'll be able to do more. Here is my simplified version of it;

The area marked “manageable” is what Dye would describe as your envelope of function. Note that activities with a low load can be “excessive” if they have high frequency i.e. if you do them too much. Activities with high load can be excessive, even if you don't do them often. If we add that into the diagram.

Everyone's graph will look a little different and can be influenced by a lot of things. It changes dramatically when we are injured;

Sometimes what's manageable shrinks so much then normal activities of daily living (ADLs) become too much load for the knee;

Our aim with rehab and strength and conditioning is to expand it, maybe that's where the saying “push the envelope” comes from? Maybe not!

So, if ADLs are enough to aggravate pain then how do we strengthen without aggravating? Surely if going down a flight of stairs is too much going to the gym will be too much?! That's where a bit of clinical biomechanics comes in. Studies through the years have looked at something called patella joint reaction force what we called PF load in part 1. They found that PF load is low in certain positions and with certain exercises. If we strengthen the knee using these positions it's much less likely to aggravate pain. This is summarised nicely in McGinty et al. 2000 (p164),

“Both OKC (Open Kinetic Chain) and CKC (Closed Kinetic Chain) exercises can be utilised in the treatment of patients with patellofemoral pain if performed in a pain free range. CKC exercises may be better tolerated by the patellofemoral joint in the range of 0-45° of knee flexion. In this range, suggested exercises include step-ups, mini-squats, and leg presses. OKC exercises may be better tolerated by the patellofemoral joint in the ranges 90-50° and 20-0° of knee flexion. In these ranges, suggested exercises include short arc isotonics, multiple angle isometrics, straight leg raises and quadriceps sets. Performing CKC and OKC exercises in these specific ranges loads the quadriceps while minimising stress on the patella.”

To translate that into English…Open Kinetic Chain means an exercise where the foot is not fixed and is free to move e.g. Kicking a ball, leg curl, hamstring curl. Closed Kinetic Chain means an exercises where the foot is fixed and the body moves e.g. Squats, lunges, step ups. Running is composed of both open chain movement as the leg swings through the air and closed chain, as the foot strikes the ground. Obviously this all happens fairly quickly when we run.

0° knee flexion means the knee is straight (fully extended), then the range goes from there, 20° bend obviously being just a little bend, full knee flexion is about 130°. The easiest way to describe this and how to use it is with a few videos. Apologies if the quality is poor, I had to film them in my lounge, on my own on a wet Friday morning!…

…some good exercises to start activating quads with minimal PF load;

…closed chain exercises, again with low PF load;

We've mentioned the importance of Gluteus Medius too, again if we want to strengthen we aim to do so with a low PF load and little work of Tensor Fasciae Latae (as this attaches to the ITB and can cause this to tighten, increasing load on the PF joint). There are a host of exercises for glutes here, if I were to pick one I'd go for sidelying abduction reproduced from Distefano et al. 2009 (below). There is also a video although it doesn't work on the iPad.

For reps, again your going with as much as comfortable for the knee and remember you should feel this working in the glutes (in the buttock) and not down the side or front of the leg.

I've mentioned in the video doing all these exercises about twice per day. This is useful in the early stages, when things are sore, you do “little and often” as your reps increase you may want to do the exercises once per day, or even every other day. Nothing is set in stone with this, see what works for you. Continue the exercises until you can easily do 25-30 reps of each, then, if comfortable, progress into range or increase load (e.g. Holding hand weights). Progression will be discussed in more detail in part 3.

It's also worth noting that you can tape the knee to reduce PF load during these exercises too (video of this in Part 1)

Final thoughts: managing PFPS is about reducing load on the patellofemoral joint while strengthening the muscles that support it. A careful selection of exercises done in a pain free range can achieve this. But…as ever on RunningPhysio… if in doubt get it checked out!

In part 3 we'll look at progressing your rehab and returning to running