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How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Robertisaacs, Jan 18, 2011.

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  2. One of eric's pet subjects. Let's see what he has to say...
  3. Yeah.

    I just got to thinking about it in terms of lever arms and, yes Mike, vectors. Made me wonder what we think, and more importantly, why.

    Look forward to Eric's answer!

    What a fabulous resource this arena is. To be one post and (hopefully);) mere hours away from the most up to date opinion of the worlds finest on any given subject. How lucky we are.
  4. bob

    bob Active Member

    Can I vote for it being a rather rubbish plantarflexor of the 1st ray given its direction of pull and insertion at the base of the metatarsal and plantar surface of the medial cuneiform? Having said that, I assume it aids in resisting dorsiflexion of the ray by exerting a proximal, lateral and plantar pull on the first tarsometatarsal joint during gait. I presume this stabilises the medial tarsometatarsal joints through midstance and into propulsion, aiding in resistance of dorsiflexion of the 1st metatarsal head against ground reaction force.

    I have done very few (2-3) resections of os peroneum and none have gone on to develop dorsiflexed 1st rays in my experience (although I conceed a short NHS follow up).
  5. efuller

    efuller MVP

    Since you all asked so nicely.

    I've really got to finish this paper. It's 7/8ths written.

    Contrary to what you see in Normal and Abnormal function of the foot pernoneus longus does not pull the base of the first ray downward. It does pull it backward creating a force couple with compression of the met cuneiform joint creates a plantar flexion moment on the first metatarsal. You can treat the met and the cuneiform as a single unit and this will create a unit that will have a force couple of the force from peroneus longus and compression at the cun-navicular joint. And same continues back to talo navic joint. So, non weight bearing it creates a plantar flexion moment at the first ray. The lever arm of the peroneus longus tendon is equal to the distance from the tendon to the center of pressure of the joint surface at the met cun joint. (view all of above in sagittal plane.) This lever arm is much smaller than the lever arm that a rearward force applied to the first met head from the proximal phalanx. See drawings from my windlass paper.

    Weight bearing things get more interesting. Looking in the frontal plane, peroneous longus curves around the cuboid and lifts it upward when there is a contraction of the muscle and this creates a pronation moment about the STJ. So, when the STJ pronates there is eversion and increased load under the first met. This first met load increases the dorsiflexion moment from the ground on the first met. So, does STJ eversion create a greater dorsiflexion moment than the tendon directly creates a plantar flexion moment?

    I made a model with three positions of the STJ axis. (I presented a video of this at PFOLA some years back.) STJ position does matter as the longer the lever arm peroneus longus has to cause pronation the greater the eversion moment. In the model I left the lever arm at the first ray constant. With the most lateral position of the STJ (smallest pronation moment) the first ray plantar flexed and the STJ supinated. With the middle axis position the STJ pronated and the first ray did not change position (eversion pivoted around first met head). With the most medial position of the STJ the STJ everted and the first ray dorsiflexed (eversion pivots around "2nd metatarsal") So, the tendon created a plantar flexion moment in each situation but the amount of ground reaction force at the first met head changed because of the differing moments at the STJ.

  6. efuller

    efuller MVP

    The string is the tendon. It pivots around the cuboid (dowel) and attaches to the base of the first ray. Orientation: looking at the toes of a right foot.

    Attached Files:

    Last edited: Jan 18, 2011
  7. Eric, you are the wind beneath my wings. Thankyou. At the risk of being horribly cheeky, is there any chance you might dig out a phot or two of that model for us.

    What you say makes perfect sense to me. Here we have a muscle which is essentially its own antagonist. Which is very cool and answers my thinking.

    I was approaching this, like Bob, from the aspect of the angle of its pull. As I view a skeleton foot on the ground I see the cuboid notch not greatly lower than the base of the 1st met, and with only a little pronation, they are level. Re the lever arm I was wondering what we consider the lever arm to be. How much 1st ray movement happens met cuni and how much cuni Nav? Could we have a situation with two pivots here? Either way, it is a stumpy little lever arm compared to pivot - 1st met head.

    One, perhaps, for Bob. Do you feel that the peroneus longus exerts a rotational force on the 1st met down its long axis?
  8. efuller

    efuller MVP

    Here's the video of a lateral axis. It's a JPEG video, and apparently it doesn't move. If someone has the software to convert to something that is viewable send me a message and I'll send you the file to post


    Attached Files:

    Last edited: Jan 18, 2011
  9. Thanks Eric. Cross post, you'd put the picture before I'd even asked for it.
  10. bob

    bob Active Member

    Eric's model is very helpful and highlights that the direction of the pull of the tendon will be effected by the relative position of the cuboid (and all the other bones of the rearfoot to an extent). I would presume that there is some motion at the 1st TMTJ and the NCJ (otherwise there probably would not be a joint at these points) but I do not suspect that there is a huge amount of motion. Eric has more fully explained the idea of a compression or 'packing' of this area that I have long thought was the case. I presume you started the thread as, like me, you think that if you were going to create a tendon insertion to plantarflex the 1st metatarsal, then you would have probably put it nearer the head than the base (or away from the pivot point for the benefit of this thread)?

    As far as rotation about the long axis of the first metatarsal goes - this would likely be resisted by tibialis anterior and the strong ligamentous constraints of the 1st TMTJ and surrounding joints including Lisfrancs ligament etc...
  11. Broadly what I had in mind Bob yes. I was considering the action of the P.longus as a plantarflexor and the mechanical advantage of it just struck me as unlikely given the direction of pull. Kevin and Simons recent paper really got me thinking in vectors.


  12. Good, that was the idea. But please add Dave's name to the list, he helped significantly with that paper too!
  13. As are many muscles acting upon the foot when we think in terms of the internal and external moments that their contractions generate... it's all about balance, me thinks.
  14. Sorry Dave.

    Always something new to learn!
  15. efuller

    efuller MVP

    The relative vertical position of the cuboid to the base of the met does not influence the leverage of the muscle. This idea that the relative heigth matters is some erroneus mechanics that is found in Normal and Abnormal Function of the foot by Root, Orien and Weed.

    The lever arm of peroneus longus at the base of the met is similar to the lever arm of FHL at the first MPJ or IPJ. The muscle belly is bi-pennate, so its physiological cross sectional area is quite large for its mass. So, the muscle can produce a lot of force. One way to calculate lever arm is to examine how far the tendon slides when the joint is moved through a certain angle of motion. For example the Achilles tendon will slide over an inch with 30-40 degrees of ankle motion. When I did some dissections the peroneus longus tendon moved 3-4 mm over the entire range of motion of the first ray. I don't remember if I figured out the number of degrees that came out to, but I think the travel of the met head was around a CM. The hard part is figuring out where the joint axis should be to be able to do the math at calculating the number of degrees of motion that comes oukt to. Looking at the radius of curvature of the anterior aspect of the first cuneiform, this would probably put the axis in or behind the talus. I don't feel like doing the calculations right now, but one could use several plausible distances of distance from the axis of motion to the met head and then figure the number of degrees of motion. Then figure the lever arm of the tendon once the degrees of motion is compared to the distance of slide of the tendon.

    If you look at the path of tendon in the tranverse plane I remember it being more ant post than medial to lateral. The ant post component would be parallel with the long axis of the met and a force parallel with the axis of motion will not create a moment. So, there is still a medial to lateral component that has to be thought about. Here's the hard part. You have to figure out where the counter force is to figure out the force couple that will cause the rotation. (For plantar flexion the force couple is assumed to be a forward force from the center of the joint and the rearward pull of the tendon at the plantar base of the metatarsal. Draw them in the sagittal view)

    Back to thinkig about long axis rotation. If the counter force is above the tendon attachment then there will be eversion and if the counter force is below the tendon then there will be inversion. If the counter force is right at the tendon then there will be no rotation about the long axis of the met. My guess, and it is a guess, is that the force will be the tendon and there will be little rotation.

    There is often a valgus rotation of the met in HAV. However, I think a more likely candidate for the cause of this rotation is the transverse intermetatarsal ligament. As the first MPJ "buckles" one of the structures that will prevent motion of the first met away from the second met is the transverse met ligament. The transverse met ligament is only plantar so it will create an eccentric force that will cause a valgus rotation.

  16. cpoc103

    cpoc103 Active Member

    Hi Bob and Robert, would putting the insertion point closer to the head, not create more of a dorsiflexion moment at the base of the 1st met. My brain is working slightly weird at the moment, the way im seeing it, is if you cause a P.flexion moment distal here and the head gets blocked for what ever reason against GRF this will dorsiflex the 1st met proximal to this position?? just a thought

  17. efuller

    efuller MVP

    The moment is determined by the line of action of the force. So, if the tendon ran just underneath and parallel to the metatarsal, the line of action of the force would not be any more plantar, even though the insertion was more distal.

    Line of action of force, is a line extentending in the direction of the force from the point of application of the force.

  18. Eric and I have been around this stump a few times before. In fact, this is one of the few topics of where we disagree about something!:drinks

    I disagree with Eric in that I believe the position of the plantar aspect of the cuboid relative to the position of the insertion of the peroneus longus (PL) tendon onto the base of the first metatarsal and first cuneiform does make a difference in how much first ray plantarflexion moment that the peroneus longus can generate. Feet with higher medial arches will have greater first ray plantarflexion moment arm from the PL tendon than will feet with lower medial arches. If the first ray is modelled as having the horizontal axis at either the talo-navicular joint or the first cuneiform-navicular joint, then the greater the vertical distance between the plantar cuboid pulley to the PL tendon insertion point, then all other factors being equal, the greater will be the first ray plantarflexion moment. Eric is correct, that since the PL is pulling from lateral and not from directly posterior to the first met-cuneiform joint, then it will not have very good mechanical advantage to cause first ray plantarflexion. However, since the PL is the only stance phase muscle that passes plantar to the first ray and inserts onto the first ray, then it will exert significant plantarflexion moment, as long as the medial longitudinal arch is of normal to higher arched configuration.

    Is there any other muscle that has more ability to create a first ray plantarflexion moment than the peroneus longus? No.
  19. What about or what strength of Plantarflexor of the 1st ray is the extensor Hallucis Longus- If the extensor Hallucis longus causes a Dorsiflexion moment at the 1st MTP joint then there must be a Plantarflexion moment at the head of the 1st ray -right ?
  20. How does the extensor hallucis longus plantarflex the first ray if there is an arthrodesis of the first metatarso-phalangeal joint or a hallux rigidus deformity?
  21. Could we count the calf? Going on tiptoes creates a pretty huge 1st met plantarflexion moment.

    I'm loving this thread. Thanks guys!
  22. Where did the arthrodesis come from ? I agree it would reduce the effect to O, but in a 1st mtp joint with no limitus must have some effect. In saying that add the arthrodesis to the equation and the plantarflexion of the 1st ray by the PL become quite limited due to GRF moving distially due the increase in length of the 1st ray as we have now added the hallux. Which should by my tired brain cause a dorsiflexion moment of greater effect on the 1st ray.
  23. Ground reaction force combined with an increase in passive plantar fascial tension causes this 1st ray plantarflexion moment in hallux dorsiflexion while raising up onto the "tiptoe" position. Any first MPJ dorsiflexion should be considered as an indirect muscle action, not a direct muscle action, causing first ray plantarflexion moment.

    Let me rephrase my question, what other muscle can directly, not indirectly, cause a first ray plantarflexion moment??
  24. Via distal to proximal compression on the metatarsal head. The head of the metatarsal being inferior to the base and as long as the insertion of extensor hallucis is inferior to the axis, this should still produce a plantarflexor moment assuming an axis orientated at 90 degrees to the sagittal plane.
  25. The reason I brought up arthrodesis and hallux rigidus is that in those conditions, the extensor hallucis longus (EHL) now becomes a dorsiflexor of the first ray, the exact opposite action of what you said the PL muscle performed. Also when the anterior tibial is active in swing, the EHL is also a first ray dorsiflexor. How do you explain, now, that due to direct action of the EHL that the EHL is a plantarflexor of the first ray. When is the EHL active during the stance phase of gait? Is it active during late midstance when peroneus longus activity is at its greatest magnitude?

  26. When is the EHL tendon ever inferior to the horizontal axis of the first MPJ?
  27. I didn't mean the 1st MTPJ axis, I meant the axis at 1st metatarsal-cuneiform joint. In an arthrodesis, the 1st MTP, doesn't have an axis.
  28. The EHL tendon, or it's insertion, is not inferior to any joint axis of the foot.
  29. MR NAKE

    MR NAKE Active Member

    Now we can truly see who was dosing off in a physics lecture ha ha ha!:rolleyes:
  30. You sound very sure Kevin. If we look at the insertional point of the EHL, is it not closer to the foot's supporting surface, viz. the ground (i.e. inferior) than, for example, an anterior projection of the STJ axis?

    If we assume a rectus foot type in static stance and a sagittal plane view, the insertion of EHL is inferior to the 1st met-cuneiform joint due to the declination of the metatarsal to the ground. If we assume an instant centre of rotation to be within the 1st met-cuneiform joint and passing 90 degrees to the sagittal plane, then the EHL tendon insertion is inferior to this axis, i.e the 1st metatarsal-cuneiform joint axis is further from the ground than the insertion of the EHL tendon in the sagittal plane. When the EHL contracts, compression will occur between the proximal phalanx of the hallux and the 1st metatarsal head- agreed? So long as the centre of pressure produced by this compression between the proximal phalanx and the head of the first metatarsal and, moreover, the line of action of the force vector is inferior to the axis of rotation between the articulation at the base of the 1st metatarsal and the medial cuneiform, a plantarflexion moment of the first metatarsal will be produced- right? In other words, for your conjecture to withstand, the base of the first metatarsal should be lower to the ground than it's head. - right? Or, at least the force vector produced by inter-osseous compression at the first MTPJ has to pass superiorly to the axis at the first metatarsal-cuneiform joint- does it?

    But in a fusion can we have a centre of pressure between the proximal phalanx and the met head? This all comes down to the vectoring influence of the extensor hood/ sling.

    In which case, doesn't it depend on the angle of fusion between the hallux and it's metatarsal?
  31. MR NAKE

    MR NAKE Active Member

    clue! the slides simillar to those of the CT scan, equidistant and parallell?
  32. Come back when you can construct a sentence, Mr. Nake.
  33. OK. If we look at the projections of joint axes, and not the axes that exist within the joint themselves, then you would be correct.

    It is not the insertion point of the EHL tendon that is important but where the tendon path is in relation to the joint axis of the 1st MC joint, which is always superior to the horizontal axis of the 1st MC and the always superior to the horizontal axis of the first ray.

    I do agree that the EHL has the capacity to indirectly generate a first ray plantarflexion moment if it acts to dorsiflex the hallux, causing, in turn, increased tensile force in the plantar fascia, causing in turn, increased 1st MPJ compression force, which, in turn, causes a plantarflexion moment at the first ray. However, this analysis falls apart when the hallux doesn't dorsiflex (e.g. hallux rigidus, 1st MPJ arthrodesis, functional hallux limitus, co-contraction with anterior tibial muscle) since the slightly superiorly directed tensile vector of the EHL tendon on the hallux would cause a mild first ray dorsiflexion moment, not a first ray plantarflexion moment.

    Therefore, I would agree that, in some circumstances, the EHL has the capacity to indirectly cause a first ray plantarflexion moment. However, it also, in some circumstances, has the capacity to indirectly cause a first ray dorsiflexion moment.

    It is my contention there is no muscle in the body that has the ability to cause a direct first ray plantarflexion moment other than the peroneus longus muscle. I would define an indirect first ray plantarflexion moment as being caused by the muscle increasing the posteriorly directed joint compression forces at the first metatarsal head due to increased 1st MPJ compression force.
  34. Kevin, I'll come back more to you last post tomorrow, if I may. For tonight, what is the difference between an "indirectly" and therefore "directly" generated moment in terms of the joint kinetics and the ultimate influence of such moment upon the restraining tissues of said joint? In other words, why do we need to segregate "direct" from "indirect" internal joint moments?

    It might be helpful if you could define "indirect moment" and "direct moment".

    P.S are we talking about a foot with an arthrodesis of the 1st MTPJ or not? In the case of a fixed first MTPJ, then the hallux flexors should all create "direct" plantarflexion moment of the first metatarsal.
  35. I know that I may have opened a can of worms here and that this is something of a grey area due to the complexity of the moments acting on the human foot from muscle action and ground reaction force and joint compression forces. Maybe this direct vs indirect muscle action should be discussed in another thread.

    However, for the purposes of this discussion, I would initially define a direct muscle action (moment) as being that action/moment caused solely by the increase in tensile force of the muscle/tendon unit across a joint axis that is separate and distinct from the external forces or internal forces caused by ground reaction force or by movements of other adjacent joints that may also affect the kinetic and kinematic action/moment of the original muscle/tendon tensile force.

    For example, the direct muscular action of the gastrocnemius muscle in open kinetic chain is an increase in STJ supination moment. However, in the medially deviated STJ axis foot during weightbearing activities, the indirect muscular action of the gastrocnemius may be an increase in STJ pronation moment due to the increase in ground reaction force (GRF) on the forefoot (which is also, in turn, due to gastrocnemius activity) and that GRF being being far lateral to the STJ axis.

    I may need your help with this one Simon, Eric and others to make sure this all makes sense and is coherent and unambiguous. We should separate this discussion as a separate thread from peroneus longus function.
  36. efuller

    efuller MVP

    I'd agree with Kevin's answer to this, but I would like to add a little more.

    To calculate a moment about a joint axis you have to know the location of the axis, the point of application of the force, and the line of action of the force. The lever arm of the force is perpendicular distance from the line of action of the force to the axis of rotation. So, the line of action of the EHL tendon will always be dorsal to the first ray. The hood/sling may lower the point of application of force to some extent, but the line of action of the force will still be dorsal to the joint.

    Getting back to peroneus longus.. Even though the insertion is at the base fo the first met, in terms of what the STJ sees, the insertion is essentially where the tendon curls around the cuboid.


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