The over extended knee, genu recurvatum. Watch your kids.

In 2011, in our infancy here at The Gait Guys, we were at the airport. And we saw this . . . .

What do you see here in this young lady ? What you should see here matters. They are just visual things, and lead to visual hypotheses, but it is your job to prove or disprove them. If you like to play these kinds of mental gymnastic games, this is valuable work. This is the work that sets you up to move skillfully, quickly and confidently in the exam and treatment room.
Join us for a rewind, back to 2011.

A young lady with knee recurvatum. Even at the airport you are not safe from The Gait Guys !

Standing waiting for my parents luggage I had to do a double take when i saw this excessive genu recurvatum of the knees. Of course it was much worse in person because of the added dimension that a photo cannot give.  This poor gal probably doesn’t even know she needs us. 

What do we see here and what assumptions can we extrapolate (assumptions from mere standing of course)  ?:

We are going to keep it to things from pelvis down or we will be here all day.

1. Anterior pelvis tilt. She appears to be sitting back into her pelvis so to speak, doing so we can see an increased lumbar lordosis pressing the pelvis anterior.  Combine this with suspect weak lower abdominals and the pelvis drops in the front. This position is often met with isometric contraction of the gluteals helping to maintain the forward/anterior shifted pelvis.
2. The above, will create an abnormal (possibly increased) tensile load on the hamstrings since the ischeal tuberosities are being drawn cephalad (up). This can create a net posterior shift of the knee joint since she is in relative hip extennsion.
3. The knees are likely locked into hyperextension. This will create meniscal tensions and certainly cause increased patellofemoral pressures.  This can also create the rarely diagnosed, but often present, anteriormeniscofemoral impingement syndrome. In this type of presentation the anterior compressive forces are so great compared to what should be balanced forces around the entire joint that the superior leading edge of the anterior mensicus (can affect medial or lateral menisci) begins to become impinged and irritated as the femur rolls and translates too far anterior. You have to know it exists to make the diagnosis.
4. She will be in relative ankle plantarflexion instead of balancing the tibia neutrally over the talus.  Relative constant plantarflexion means shorter posterior compartment (gastroc-soleus) and usually weak anterior compartment (tibialis anterior and long extensors of toes).  If she is a runner we bet shin splints were on her holiday list of things to resolve. This gal will likely have problems controlling pronation we suspect because of such assumed imbalances.

These are just the sagittal plane flaws we can assume. There are more but this is plenty to think about right now. I was going to walk behind to take a pic so we could make some assumptions about the frontal plane, but people all around were already getting suspicious of me snap photos of so many of them. 

Remember, these are just assumptions from a single static photo. Like in video analysis, anything you pic up on film is just a compensation. It does not tell you what you have wrong until you can test them for neuromuscular integrity and motor pattern assessments.  Do not hang your hat on photos or video analysis. Do the extra work that is required.  After all, you know where ASSUMPTIONS get us.

Oh, and we must not forget to once again thank Mr. UGG boot for helping add another dimension of challenge to this lovely lady ! Although this assumption would be better made off of a frontal plane photo.

Beware of geeks in the airport and shopping malls snapping photos and video. It is likely us, The Gait Guys.

Shawn and Ivo

rewind: https://thegaitguys.tumblr.com/post/14809328401/a-young-lady-with-knee-recurvatum-even-at-the

Varus Thrust Gait, Trampoline ankle Part 2: When ankle rocker is lost.

In several previous case videos we have shown a case of traumatic ankle injury causing ankle rocker loss and subsequent knee hyperextension during sagittal gait progression, and we have shown a case of a classic Varus Thrust gait (search our site).

Today, I will shows you a case where the 2 phenomenon are connected. If you know your normal anatomy, you should be able to put this together.

Case background, video #1:  *Impaired ankle rocker (severe) in action. This was a case of ankle talus dislocation while trampoline'ing :) No surgery, but ankle was bagged up for 6 weeks. This is a TIGHT and blocked ankle rocker now, better for it to be more stable than unstable since every ligament was torn completely. These are his first steps in 6 weeks. 90 ankle dorsiflexion on the table, which is insufficient for anyone to have normal gait. Here is a great view of what happens when there is insufficient ankle rocker, one scenario at least (there are several ways around an insufficient ankle rocker). Here you can see the knee hyperextension strategy at the moment the body mass attempts to pass over the ankle, the ankle says "Nope, not today bud, try throwing the knee into extension to get over me.". And so, that is what happens here. Imagine what message the hip and glutes get from that strategy ! So, you won't see this every day, but imagine all the cases of minor ankle rocker impairment you do get in a few of your clients, and the micro knee extension strategies you can't see, that are fiddling with optimal mechanics. If you do not look, you will not find. It is why I mentioned the case last week of the ankle ROM looking normal on the exam table, but it not being used during gait. Again, not everyone needs more ankle rocker, often they need more S.E.S. (skill, endurance, strength). Skill includes, proprio, balance, coordination, motor patterning, etc. Make no mistake, this fella needs more ankle rocker !

in the sagittal video below, and more obviously in a separate video further below to more clearly demonstrate a more classic Varus Thrust gait, one should be able to see the knee undergoing a sudden abrupt varus (lateral) shift during the gait loading response.  The tib-femoral joint is a sagittal hinge, not a frontal-lateral plane hinge, so this is clearly pathomechanical movement. This knee will likely undergo premature knee cartilage and meniscal degeneration if the phenomenon is not resolved.
The cause of this issue is likely more simple than complicated however there may also be multiple factors coming together in a perfect storm. However, make no mistake, in order to understand a varus thrust gait, one has to understand the why and how of the gait presentation. Additionally, one must have a clinical knowledge of the restraining systems of the knee, both active and passive, and have a high degree of clinical suspicion and working knowledge of how to assess for these types of problems. It this immediate case below, with the severe ankle rocker loss (see in the first video) the client hits the loss of ankle rocker/dorsiflexion and must attempt to move forward. In video #1 we see knee hyperextension, but what you need to see on the video below is knee varus thrust. This is a soft case, it is not a TRUE varus thrust, but the mechanism is there. It is there on that left leg/knee if you know what to look for, and is in part because he is supinating the foot excessively, while moving through neutral knee and into terminal knee extension, to try and find some kind of lateral frontal plane strategy to get around the blocked ankle rocker. Remember, there is lots of medial and lateral joint play at neutral zero degree extension, and very little if any in terminal knee extension lock out. So the shift occurs mostly around the zero degree range and then is thrusted into terminal extension giving it that "sudden abrupt" appearance. Remember the knee is not a frontal plane hinge, but it does have some frontal plane wiggle room at zero degrees, test it out for yourself !  Why does this phenomenon occur in this client with zero posterolateral corner knee injury ? Well, it is simple anatomy. The medial condyle is longer and deeper than the lateral (see xray photo below showing this relationship) and with such far lateral foot supination combined with terminal knee extension, he is likely only bearing weight on the medial condyle and the joint pivots and shifts in this zero degree extension through to hyperextension lock out (not a true instability pivot-shift but the mechanism remains present) until the LCL (lateral collateral ligament) complex and iliotibial band and other lateral structures engage. Because there is no true lateral laxity, there is only a subtle lateral shift,  unlike the 3rd video below of the lady walking on tiles. So, this is a case of knee hyperextension and mild varus thrust gait from a blocked ankle rocker motion joint. 

Below are some thoughts from a prior video on Varus Thrust gait (see video to the right). You must understand all of these components to help these clients fully. 

Things to consider:  
- old ACL/PCL and posterolateral corner damage (search our site for articles we have composed)
When the posterolateral corner complex of the knee is torn up from a blow to the knee or a torsional loading failure, the 3 components of the posterolateral corner (the lateral collateral ligament (LCL), the popliteal tendon, and the popliteo-fibular ligament complex). This complex attaches just in front of the origin of the lateral gastrocnemius tendon off the lateral femoral epicondyle. This complex can be blown out from either a PCL or ACL injury mechanism, these big player ligaments are rarely torn in isolation.
- is there a Pivot Shift phenomenon, likely.  A positive Pivot Shift test will be present. One must know how to perform this test to confirm its presence, it can be a tricky test if one does not know the load vectors to apply and what the shift feels like and where it occurs during the test. This can be a very subtle positive test, again, first hand experience is everything. 
- one must find this before surgery occurs for the ACL or PCL. Failure to find and address this damaged complex will likely result in rotational stability problems once return to play occurs. IT will not likely be noted in the initial post-operative months as the aggressive loading response will not be performed early on. Failure to address this problem will likely put ACL-PCL reconstruction success at a high risk.

Other critical factors to consider in the Varus Thrust Gait:
- is there medial knee osteoarthritis ?
- what is the foot type and what are the mechanics ?  ie. Forefoot varus, Forefoot supinatus, rearfoot variances
- does the patient have excessive pronation challenges that create massive internal spin into the tibia ?
- is the hip frontal and rotation plane stable?  Can the patient adequately control rotation at the hip level ?
- is there a Cross Over gait phenomenon with narrow based step width ? (search our blog and youtube for  "gait guys crossover gait").  A narrow step width will create an "unstacked" limb and promote more rotational risk into the limb, often playing out at the least tolerable joint to rotation . . . the knee.
- Does the client have Tibial Varum ? Genu Varum, Genu Valgum ? These can promote and complicate the Varus Thrust gait.
- Does the client have Tibial torsion or Femoral Torsion variants ? These can promote and complicate the Varus Thrust gait.

- is there weakness of the lateral gastrocnemius or biceps femoris (to name just two the directly cross over this posterolateral interval and can offer joint compression/stability ? What about weaknesses in the medial leg ? Not that these are anywhere sufficient to offset a PLRI (posterolateral rotatory instability), but, they are secondary helpers/restraints.

One should clearly see now that the Varus Thrust gait is potentially complicated and multifactorial. One MUST understand:
1. many components of normal gait and normal anatomy from foot to pelvis, at least.
2. be able to assess for aberrant mechanics and pathologies within all joints of the lower limb
3. be able to assess for post operative rotational stability and laxity (*even a healed, yet partially attenuated, Posterolateral corner complex that was not noted or addressed in the ACL-PCL reconstruction can come back to haunt even the best reconstruction. Those little rotational instabiliites will build over the years and render attenuation of the other secondary posterior restraints in the knee. Like a Lisfranc injury, sometimes things take a few years to brew and blossom before the "career ender" instability shows up. Trust us, we have seen it enough times.  

Rule: if one does not know it exists, one will miss it. If one does not know how to assess it, one will miss it. If one does not know normal anatomy, torsional variants, foot types and gait types, one is likely to be lost and left fumbling.  Our clients deserve more. 

Clinical pearl: if you are radiographically sharp, you should have noted the Pellegrini-Stieda lesion at the medial tibial epicondyle (this is not a radiograph for this case, it was used to show the longer medial condyle reach). These are ossified post-traumatic lesions near the medial femoral collateral ligament attachment. This avulsion injury of the medial collateral ligament can calcificy after a few post-trauma weeks. 

- Dr. Shawn Allen, the other gait guy

Podcast 109: A clinical case of a total knee replacement and achilles tendonopathy.

Great open clinical discussions today on things we see in the clinic. We start with a great case that opens up the dialogue, a case of a total knee replacement and achilles tendonitis.  Hope you will join us on this clinical journey today.

Interested in our store ? Want to buy some of our lectures or our National Shoe Fit program? Click here (thegaitguys.tumblr.com) and you will come to our blog. In the left tab, you will find tabs for STORE, SEMIANRS, BOOK etc. We also lecture every 3rd Wednesday of the month on onlineCE.com. We have an extensive catalogued library of our courses there, you can take them any time for a nominal fee (~$20). 

A. Podcast links:

http://traffic.libsyn.com/thegaitguys/pod_109f.mp3

http://thegaitguys.libsyn.com/podcast-109-a-clinical-case-of-a-total-knee-replacement-and-achilles-tendonopathy

B. iTunes link:
https://itunes.apple.com/us/podcast/the-gait-guys-podcast/id559864138

C. Gait Guys online /download store (National Shoe Fit Certification & more !)
http://store.payloadz.com/results/results.aspx?m=80204

D. other web based Gait Guys lectures:
Monthly lectures at : www.onlinece.com type in Dr. Waerlop or Dr. Allen, ”Biomechanics”

-Our Book: Pedographs and Gait Analysis and Clinical Case Studies
Electronic copies available here:

-Amazon/Kindle:
http://www.amazon.com/Pedographs-Gait-Analysis-Clinical-Studies-ebook/dp/B00AC18M3E

-Barnes and Noble / Nook Reader:
http://www.barnesandnoble.com/w/pedographs-and-gait-analysis-ivo-waerlop-and-shawn-allen/1112754833?ean=9781466953895

https://itunes.apple.com/us/book/pedographs-and-gait-analysis/id554516085?mt=11

-Hardcopy available from our publisher:
http://bookstore.trafford.com/Products/SKU-000155825/Pedographs-and-Gait-Analysis.aspx

Show Notes:

Loose dialogue  on Anterior pelvis tilt and training it out

https://www.t-nation.com/training/dont-be-like-donald-duck?utm_source=facebook&utm_medium=social&utm_campaign=article3173

Ivo put up 2 articles recently on “Why is your muscle tight” and “iliocapsularis” muscle.
Why training the upper body might help integrate arms into gait for sporthttp://thegaitguys.tumblr.com/post/141990433844/gait-and-climbing-and-dns-part-2-introducing

http://journals.lww.com/acsm-msse/Abstract/publishahead/Influence_of_Step_Rate_on_Shin_Injury_and_Anterior.97596.aspx
- cross over looked at ?- ankle rocker looked at ?  endurance of anteiror compt looked at ?

Knee hyperextension and delayed heel rise in an interesting sport, Racewalking.

If you have been in practice long enough, you should know by now that in order to truly help an athlete you have to know their sport, the subtleties and the specifics.  You have heard us talk about premature heel rise off an on for years. Today, you must consider the opposite, delayed heel rise and the bizarre loading responses that come into the kinetic chains from such a behavior.

Racewalking is a long-distance event requiring one foot to be in contact with the ground at all times. Stride length is thus reduced and so to achieve competitive speeds racewalkers must attain cadence rates comparable to those achieved by Olympic 800-meter runners for hours at a time. Most people cannot truly appreciate how fast these folks are going.

There are really only two rules that govern racewalking:

1-The first rules states that the athlete’s trailing foot’s toe cannot leave the ground until the heel of the leading foot has created contact. 

2-The second rule specifies that the supporting leg must straighten, essentially meaning knee extension (and for some, terminal extension, ie. negative 5-10 degrees !) from the point of contact with the ground and remain straightened until the body passes directly over it. Again, essentially meaning full range knee extension for the entire stance phase of gait (early, mid and late midstance phases). 

Delated heel rise ?

Clearly some folks are going to take knee extension a little more literally. Look at the fella in the red and yellow. Can you say knee HYPER extension ? This is right knee anteriormeniscofemoral impingement looming on the horizon, this is an anterior compression overload phenomenon via the quadriceps. This is often met in this sport with the delayed heel rise that the sport seems to often drive. Prolonging the foot ground contact phase, attempting to abide by Rule#2, “the support  leg must straighten”, can lead to knee hyperextension if one is not careful. This will put a longer stretch load into the achilles and posterior compartment mechanism and this prolonged stretch-contract load can eventually lead to local pathology let alone in combination with the anterior knee compression we just eluded to. These folks will also be at risk for more anterior pelvic tilt, distraction of the anterior hip capsule-labral interval, unique hip extension and gluteal integration, and even possibly altered hip extension motor patterning driving abnormal loads into the hamstrings and low back.  Just imagine the changes in the hip flexor strategies in this scenario. 

To help your athletes, know their sport, know your normal biomechanics and know the pathologies when the rules of clean biomechanics are broken.

Today, on Rewind Friday, we will repost a more in-depth, with video, piece we did a few years ago on Race Walking. You may learn more about normal and abnormal gait than you think, today we translate some of the rules of the sport of race walking into deeper thoughts on gait mechanics.

Here is the link to our more in-depth video assessment and dialogue on the fascinating sport of race walking. If you have never truly looked at this sport before, you should enjoy this Rewind Post. (link).

- Dr. Shawn Allen

This is apparently a growing thing, INTERVAL walking. Oy. We are not particular fans at this point, nothing exciting or earth shattering at this point (other than the concerns we hi light below) but we will look into it more.
What you need to see, and be aware of, is that this is what happens when you wear a shoe that has too soft a rear foot. At heel strike, instead of progressing forward into the mid and forefoot, the rear foot of the shoe deforms and forces you into more HEEL rocker, sustained heel rocker. If you stay in heel rocker too long, you won’t progress forward into ANKLE rocker (ankle dorsiflexion). This often causes knee hyperextension. If you have a good trained eye, you will see both of these things, prolonged heel rocker and never any ankle rocker/ankle dorsiflexion. IT is like the ankle in this video is frozen at 90 degrees the entire time, train your eye to see this absense of ankle rocker. This will cause premature heel rise and premature posterior compartment contraction which can cause premature forefoot loading. This is what happens when the heel of the shoe is too soft. A perfect example of “more cushion” is not always better. IT can be a liability as well. Remember the angry revolution over the MBT shoe and its mushy rear foot?. Same principle, same risks and concerns. Welcome to round two of the same old problems ????? Maybe. you decide. To be clear, this is a comment on the shoes being used, the technique is , well, perhaps interesting. That is all we are willing to comment on at this point until we look into it more. Look at the heel and ankle mechanics during the slow mo clips.
Sorry Ben Greenfield. We are not impressed, as of yet. We like your podcast Ben, you are doing us all a great service, but this one is promoting some potential problems that people need to know about.
Start with our “Shuffle Walk”. Google search it under the Gait Guys. That is a good start.

- Dr. Allen

Podcast 96: Minimalism Shoes, Toe Trauma, Meniscal Impingement.

The Minimalist Shoe Index, Pincer toe nails, toe problems, anteromeniscofemoral impingement syndrome and much more on today’s show !

A. Link to our server: http://traffic.libsyn.com/thegaitguys/pod_96f.mp3

Direct Download:  http://thegaitguys.libsyn.com/podcast-96

Other Gait Guys stuff

B. iTunes link:
https://itunes.apple.com/us/podcast/the-gait-guys-podcast/id559864138
C. Gait Guys online /download store (National Shoe Fit Certification & more !)
http://store.payloadz.com/results/results.aspx?m=80204
D. other web based Gait Guys lectures:
Monthly lectures at : www.onlinece.com type in Dr. Waerlop or Dr. Allen, ”Biomechanics”

-Our Book: Pedographs and Gait Analysis and Clinical Case Studies
Electronic copies available here:

-Amazon/Kindle:
http://www.amazon.com/Pedographs-Gait-Analysis-Clinical-Studies-ebook/dp/B00AC18M3E

-Barnes and Noble / Nook Reader:
http://www.barnesandnoble.com/w/pedographs-and-gait-analysis-ivo-waerlop-and-shawn-allen/1112754833?ean=9781466953895

https://itunes.apple.com/us/book/pedographs-and-gait-analysis/id554516085?mt=11

-Hardcopy available from our publisher:
http://bookstore.trafford.com/Products/SKU-000155825/Pedographs-and-Gait-Analysis.aspx

Show notes:

1. New Cameras In Japan Can Detect Drunks At Train Stations
http://www.popsci.com/cameras-japan-detect-drunks-train-stations

2. It takes a lot of nerve: Scientists make cells to aid peripheral nerve repair
http://www.medicalnewstoday.com/releases/297854.php
-Scientists at the University of Newcastle, UK, have used a combination of small molecules to turn cells isolated from human skin into Schwann cells

3. The Minimalist Shoe Definition study

http://www.jfootankleres.com/content/8/1/42

A consensus definition and rating scale for minimalist shoes
Jean-Francois Esculier123, Blaise Dubois13, Clermont E. Dionne14, Jean Leblond2 andJean-Sébastien Roy12* http://www.jfootankleres.com/content/8/1/42

modified Delphi study, 42 experts from 11 countries

http://www.jfootankleres.com/content/supplementary/s13047-015-0094-5-s1.pdf

-Results

The following definition of minimalist shoes was agreed upon by 95 % of participants: “Footwear providing minimal interference with the natural movement of the foot due to its high flexibility, low heel to toe drop, weight and stack height, and the absence of motion control and stability devices”. Characteristics to be included in MI were weight, flexibility, heel to toe drop, stack height and motion control/stability devices, each subscale carrying equal weighing (20 %) on final score.

4. CASE:
Ivo: broken toe, prioprioception
this: http://www.ncbi.nlm.nih.gov/pubmed/2245598
and this http://www.ncbi.nlm.nih.gov/pubmed/19955289

5. CASE: anterior meniscofemoral impingment syndrome
http://tmblr.co/ZrRYjx1d8503W

http://thegaitguys.tumblr.com/post/17713779565/anterior-knee-pain-in-a-young-marathon-hopeful

6. Pincer Toe nails:

http://thegaitguys.tumblr.com/post/127638788139/pincher-nails-who-knew-note-there-are-two–  

Singer Songwriter Jewel and her knee hyperextension.

One of our favorite television shows is “Alaska: The Last Frontier”.  What some of you might not know is that the show is about Singer Songwriter Jewel’s family, the Kilchers. Yes, Her name is Jewel Kilcher.  The theme to the show is written and sung by Jewel and her father Atz Kilcher.  The Kilcher’s are tough folk who live off the grid (mostly) and maintain a subsistence living off the land in Alaska.  

Use the photo above to help you clearly understand what we are talking about in this video here (link)  where we see Jewel and her dad getting ready to sing the show’s theme. In this video, Jewel is in some insanely high heeled shoes and being the gait geeks that we are we could not help but notice the degree of knee hyperextension she was displaying.  

What can we extrapolate from this genu recurvatum / hyper extension knee posturing  ?:

We are going to keep it to things from pelvis down or we will be here all day.

1. Anterior pelvis tilt. She appears to be sitting back into her pelvis so to speak, doing so we can see an increased lumbar lordosis pressing the pelvis anterior.  In many cases combine this with suspect weak lower abdominals and the pelvis drops in the front. This position is often met with isometric contraction of the gluteals helping to maintain the forward/anterior shifted pelvis.
2. The above, will create an abnormal (possibly increased) tensile load on the hamstrings since the ischeal tuberosities are being drawn cephalad (up). This can create a net posterior shift of the knee joint since she is in relative hip extension, the pelvis is often also translated forward into the sagittal plane pushing the head of the femur into anterior glide into the front of the acetabulum.
3. The knees are often locked into hyperextension. This will create meniscal tensions and certainly cause increased patellofemoral pressures.  This can also create the rarely diagnosed, but often present, anteriormeniscofemoral impingement syndrome. In this type of presentation the anterior compressive forces are so great compared to what should be balanced forces around the entire joint that the superior leading edge of the anterior mensicus (can affect medial or lateral menisci) begins to become impinged and irritated as the femur rolls and translates too far anterior. You have to know it exists to make the diagnosis.
4. She will be in ankle plantarflexion because of the footwear instead of balancing the tibia neutrally over the talus.  The tibia will rest on the posterior talus. If constant, the plantarflexion means shorter posterior compartment (gastroc-soleus) and usually weak anterior compartment (tibialis anterior and long extensors of toes).  If she is a runner we bet shin splints were on her holiday list of things to resolve. 

These are just the sagittal plane flaws we can assume. There are more but this is plenty to think about right now. 

Remember, these are just assumptions. Like in video analysis, anything you pic up on film is just a compensation. It does not tell you what you have wrong until you can test them for neuromuscular integrity and motor pattern assessments.  Do not hang your hat on photos or video analysis. Do the extra work that is required.  After all, you know where ASSUMPTIONS get us.

The Gait Guys.

Shawn and Ivo

Lombard’s Paradox

 In searching our personal archives for neat stuff we came across an oldie but a goodie. One to certainly make your head spin. We do not even know where this came from and how much was our original material and how much was someone  else’s.  If you can find the reference we would love to give it credit.  We do now that we added some stuff to this but we don’t even know what parts were ours !  Regardless, there is a brain twister here worth juggling in your heads.  Lets start with this thought……..

When you are sitting the rectus femoris (a quad muscle) is “theoretically” shortened because the hip is in flexion. It crosses the bent knee in the front at it blends with the patellar tendon, thus it is “theoretically” lengthened at the knee.  When we stand up, the hip extends and the knee extends, making the R. Femoris “theoretically” lengthen at the hip and shorten at the knee.  This, it bodes the question…….did the R. Femoris even change length at all ? And the hamstrings kind of go through the same phenomenon. It is part of the  uniqueness of “two joint” muscles.   Now, onto Lombard’s paradox with more in depth thought on this topic.

Warren Plimpton Lombard (1855-1939) sought to explain why the quadriceps and hamstring muscles contracted simultaneously during the sit-to-stand motion.  He noted that the rectus femoris and the hamstrings are antagonistic, and this coactivation is known as Lombard’s paradox.

The paradox is classically explained by noting the relative moment arms of the hamstrings and rectus femoris at either the hip or the knee, and their effects on the magnitude of the moments produced by either muscle group at each of the two joints.

By virtue of the fact that muscles cannot develop different amounts of force in their different parts, the paradox develops.  The hamstrings cannot selectively extend the hip without imparting an equal force at the knee. Thus, the only way for hip extension and knee extension to occur simultaneously in the act of standing (or eccentrically in the act of sitting) is for the net moment to be an extensor moment at both the hip and knee joints. Lombard suggested three necessary conditions for such paradoxical co-contraction:

• the lever arm of the muscle must be greater at its extensor end
• a two-joint muscle must exist with opposite function
• the muscle must have sufficient leverage so as to use the passive tendon properties of the other muscle

In 1989, Felix Zajac & co-workers pointed out that the role of muscles, particularly two-joint muscles, was much more complex than has traditionally been assumed. For example, in certain situations, the gastrocnemius could act as a knee extensor. It is clear now that the direction in which a joint is accelerated depends on the dynamic state of all body segments, making it difficult to predict the effect of an individual muscle contraction without extensive and accurate biomechanical models (Zajac et al, 2003).

 In fact, back to the gastrocnemius another 2+ joint muscle (crosses knee, mortise and subtalar joints), we all typically think of it as a “push off” muscle.  It causes the heel to rise and accelerates push off in gait and running. But, when the foot is fixed on the ground the insertion is more stable and thus the contraction, because the origin is above the posterior joint line, can pull the femoral condyles into a posterior shear vector. It thus, like the hamstrings, needs to be adequately trained in a ACL or post-operative ACL, deficient knee to help reduce the anterior shear of normal joint loading. It is vital to note, that when ankle rocker is less than 90  degrees (less than 90 degrees of ankle dorsiflexion is available), knee hyperextension is a viable strategy to progress forward in the sagittal plane.  But in this scenarios, the posterior shear capabilites of the gastrocnemius are brought to the front of the line as a frequent strategy.  And not a good one for the menisci we should mention.

Andrews J G (1982)  On the relationship between resultant joint torques and muscular activity  Med Sci Sports Exerc  14: 361-367.

Andrews J G (1985)  A general method for determining the functional role of a muscle  J Biomech Eng  107: 348-353.

Bobbert MF, van Soest AJ (2000) Two-joint muscles offer the solution - but what was the problem? Motor Control 4: 48-52 & 97-116.

Gregor, R.J., Cavanagh, P.R., & LaFortune, M. (1985). Knee flexor moments during propulsion in cycling–a creative solution to Lombard’s Paradox. Journal of Biomechanics, 18, 307-16 .

Ingen-Schenau GJv (1989) From rotation to translation: constraints on multi-joint movement and the unique action of bi-articular muscles. Hum. Mov. Sci. 8:301-37.

Lombard, W.P., & Abbott, F.M. (1907). The mechanical effects produced by the contraction of individual muscles of the thigh of the frog. American Journal of Physiology, 20, 1-60.

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