Friday, July 26, 2013

What’s the Biochemical Basis for the Success of Continuous Passive Motion?

When it comes to dealing with knee pain, I believe strongly in the beneficial effects of motion. I often prefer the word “motion” to “exercise,” as the latter conjures up images of fitness buffs doing strenuous activities that may not be good for bad knees. Move, move, move (in the proper amounts, in the proper ways).

For those recovering from surgery (or maybe even for those who just have really bad knees), I think continuous passive motion can be a great idea. In Saving My Knees, I mention the experiments on rabbits that Robert Salter performed more than three decades ago. Salter discovered that the cartilage fell apart in rabbit knees that were immobilized, while the tissue improved in knees that were constantly flexed using a CPM device.

So continuous passive motion works. But why?

Well, one advantage of having a blog that’s read by lots of smart, well-informed people is that I’m constantly being alerted to interesting studies. Like this one from 2005: "Anti-Inflammatory Effects of Continuous Passive Motion on Meniscal Fibrocartilage." It’s another rabbit study, and one of the researchers is Salter.

Arthritis was induced in all the rabbits’ knees. It appears that the knees of half the animals received CPM for 24 or 48 hours, while the joints of the others were immobilized.

While rabbits certainly aren’t people, one “advantage” of experimenting on them (or disadvantage, if you’re one of the rabbits) is that their cartilage can be “harvested” for close-up, thorough inspection at the study's end because they’re generally euthanized.

What the researchers discovered were changes that may shed light on the biochemical reasons that CPM works (caveat: again, I’m reduced to summarizing an abstract because the full study lies behind a paywall).

Even after a timeframe as short as a day or two, the study noted significant differences between the knees that moved all the time and those that didn’t move at all.

The immobilized knees:

* Showed “marked GAG degradation.” GAGs, of course, are glycosaminoglycans, which contribute to the strength and resiliency of cartilage (Saving My Knees explains in more depth why glycosaminoglycans are important).

* Had higher levels of three different molecules that contribute to inflammation.

Knees that underwent continuous passive motion exhibited the converse of both these trends: there was a “rapid and sustained decrease” in glycosaminoglycan breakdown, and fewer molecules involved in inflammation were found. What’s more, CPM led to synthesis of an anti-inflammatory molecule.

The researchers conclude:
These studies explain the molecular basis of the beneficial effects of CPM observed on articular cartilage and suggest that CPM suppresses the inflammatory process of arthritis more efficiently than immobilization.
Now here’s my hunch:

Those molecular-level benefits of continuous passive motion will be found, in future studies, to apply to motion more broadly, and to knees more broadly (not just the ones that are post-surgery or arthritic). And that would be pretty good news for people battling chronic knee pain who are looking for a way out of the trap they’re in.


  1. My last post here I wrote briefly about ideas I have (and apparently other people had before me) regarding immune response and cartilage degeneration and suggested taking a high quality probiotic to reconfigure the "gut," as the gut is where the bulk of immune function occurs. Here's a link that describes, in part, the relationship between probiotics, gut and immune function:
    I'm a little lazy and probably could have found a more appropriate article, but it's basic and you can search for more info/studies about probiotics on your own.

    Also, I forgot to mention, that in adjunct to a probiotic, I have had much success (anecdotal, yes) with a supplement called UC11 (undenatured collagen type 2). Here's a link to a study done at UC Davis awhile ago about the efficacy of UC 2 compared with some more well known knee supplements:

    In the section "discussion" it say's something about the mechanism of action as unknown, but more recent studies have shown that UC11 is a very effective anti inflammatory, as well as potentially having more intuitive benefits, as it's the stuff your cartilage is built of.

    Good luck to everyone trying to heal their cartilage/knees.

    1. Wanted to add: Dumping a bunch of supplements into your system, thinking it will allow you continue your bad habits/overuse, etc., is not a good idea. I have followed much of Richards advice in his book over the last year plus and use supplements in addition to a ever evolving solution based approach to what works to "save my (own) knees."

    2. Racer X

      Can you elaborate on your solution based approach? For example, you used to cycle, do you still do that?

      The UC-11 sounds interesting, I may give that a try.

      cheers, TriAgain

  2. TriAgain,

    It's embarrassing for me to write this (how could I have been so stupid?), but the day before my elective surgery, I had gone on a fast-paced 80 mile ride with a group of like fit types. That was 17 months ago and my last words to them were, "See you in a few weeks!" At that time my road bike had a 53 x 42 front chain ring combo and a 27-11 rear cassette. The 27 was a bailout gear and rarely used.

    I have implemented too many behavior and equipment modifications to list here, in the effort to give you a glimpse of the roadmap to my still incomplete recovery... and have tested too many ideas to recollect...

    But a small cross-section of solutions: For 6 months post-op my conditioned worsened (traditional PT, bad riding habits) then I read R.B.'s book and began riding mostly on the flats (yes, I am stubborn and kept trying to climb more than I should have) in sneakers. I graduated to my Speedplays about 5 months ago and ride my road bike at least twice a week wearing them. My road bike now has a compact crank system with a 34 x 50 front and I use the 34 a lot and concentrate on spinning. I also focus on using my hamstrings to pull up when I pedal, as this seems to take stress off my patella. Because I am stubborn I do still climb, but less and my knee(s) continue to improve. That's the important point: improvement. If an activity is detrimental to my recovery I don't do it.

    One more example. I read a study somewhere (I can't remember where, I think it was buried in a grad students massive dissertation on the possible causes of OA) about a correlation that he had discovered between people who were hypermobile and the absence of OA. Partly with that in mind, I began aggressively working on loosening my IT bands (tennis ball, roller, massage), as it seemed possible that a contributing factor to my PFPS flare-ups could be related to the fact that my quads/IT bands where/are unbalanced in their development and that this was pulling my patella(s) down causing increased wear. Just some wild ideas.

    An example of where I am at fitness wise: Friday I went on a 9 mile hike over varied terrain. Aches and pains, but little cartilage pain. I do have to walk slow (3mph). Saturday afternoon I rode my MTB (no clip in pedals), for a total on 2 hours with 2000' of climbing. Did a lot of spinning, with my "max" at about 65-70%, which is the place on the graph where my cardiovascular and cartilage systems meet in mostly pain-free harmony. If I go harder my cartilage hurts and the recovery goes backwards. Six months ago I was at a place on the graph where the intersection was at about 20-30 %.

    Finally, I don't have any ambition about regaining super-fitness nor am I motivated by the idea that I will race again (I may, who knows?). When someone passes me I smile and say hi and do not chase them. From time to time if I mis-step or pedal too hard I can feel deep chondral pain. If I do too much or try to squat I get cartilage irritation. My point is, I try to find fulfillment wherever I am on MY graph of cardiovascular and cartilage harmony. Corny and earnest, yes I know, but that's part of my solution too.

    Hope this helps, Racer-X

  3. Racer X

    Very interesting and many similarities to myself.

    I was doing Half-Ironman triathlon till my medial meniscus blew 15 mths ago, I had 1/3 removed, was back on the bike riding for an hour within 6 days (surgeon said I could do whatever I felt I could handle), but within 2-3 weeks had full-blown bilateral pain (I call it PFPS, but not sure if that is correct).

    I pushed on riding for 4 months, and started running a little 8 weeks post surgery, but it just got worse. I already had compact cranks on my Cervelo!

    I've really not ridden or run now for 10mths. Sometimes (like y'day) I wake up and my knees felt good (actually, the usually feel good first thing), so jumped on the bike and putted about for 25mins in the small chainring on the flat (AVS 20kmh), but within hours my kneecaps were burning. I try to engage hammies more so not mashing down on the pedals using my quads & loading up the knees - but even that does not work. Like Richard, I think my pattern of cartilage damage does not respond well to cycling.

    Strange thing is, 6 mths ago on holiday in NZ, my wife and I rented MTBs from the motel and did 2x1hr rides (in joggers, feet not clipped in) and that seemed OK?

    I can also cope with 2x5-7mins easy spinning on the recumbent bike in the gym (the power is pathetic - 80 watts - I used to do 100km TTs probably averaging 200-220 watts).

    I can walk for 4-5kms, but if i go too fast, or too hilly i pay for it. Squatting is definitely out for me too. Being an(ex???) triathlete, I can still swim, though have to limit my kicking. And swimming is a dull way to maintain cardio fitness.

    May also borrow an MTB & see if I can handle that in sandshoes.

    I'm still hoping to race again & finally do an IM, but it is a distant hope. I'd settle for being able to ride for an hour pain free with enough intensity to get a decent cardio workout.

    I'm going to track down some of the UC-II you mention. Not sure if it is available here in Oz, may have to order on-line from the States. In fact, your whole theory about immune response rings some big bells with me. I already had chondro damage on the back on my R knee, which played up a bit, but nothing like I have now. The meniscus surgery seems to have triggered some sort of deterioration of cartilage in both knees. I've read your own body can start attacking your cartilage (immune response) & wonder if that has happened to me? It's like a switch was suddenly flipped in my knees.

    cheers, TriAgain

  4. TriAgain,

    There's something to be said for not being clipped in and cycling if you have PFPS (whatever that is?). You can get a cheap set of platform pedals mail ordered from "Performance." That's what I use on my MTB.

    I don't think all UC11 is created equal. I like a product named "Joint Formula," it's manufactured by "Ultra Botanicals." You can find it online @ $23-30 for a month's worth at suggested doses, but I take an extra tablet at night with my probiotic before sleep. Also, for what it's worth, I try to avoid Advil, Aleve, etc., as I have a low opinion about their short and long-term side-effects.

    As for immune malfunction and cartilage gone bad, all I have is my wild theories and no way to test them except anecdotally : 0

    Correction: I walk @ 2-3 mph tops. Very slow but steady. Like Richard, walking is where I seem to find my biggest benefits.

    Good luck TRI & let me know how the UC2 experiment goes,

    1. Thanks R-X

      Ordered 2 mths supply of UC-II from Amazon UK (can't seem to source it in Oz), $48Aus (free post - weird but good), the 'Now Foods' brand. Label says it has 10mg of undenatured collagen per 40mg which is what the studies suggest is needed. Will see it goes. Will prob take 2-3 wks to arrive.

      Also discovered y'day quite a good treadmill session which my knees seem to cope with: 10mins warmup at 5.4kmh on incline 0.5 (basically flat) then 5x2 mins at 5.4kmh on incline 10 (max incline is 15) with 2min back on 0.5 between. The 5x2 min actually gives some aerobic impact. I was going to try this on a hill near the gym, but the treadmill gives much better control of the intensity.


    2. Meant to add, I rarely take painkillers/anti-inflammatories as they just mask the problem. Sometimes I resort to icing if I've really stuffed up and the knees are very burny/achy.


  5. Thank you for posting about the immunology & probiotic ideas. I will look into it.

  6. Hello! I think I have found a really nice sum up of science on cartilage rehabilitation on this site.