Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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This thread is a break off from How significant is the Peroneus longus as a plantarflexor of the 1st ray thread.
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.
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
Could we count the calf? Going on tiptoes creates a pretty huge 1st met plantarflexion moment.
I'm loving this thread. Thanks guys! -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
Let me rephrase my question, what other muscle can directly, not indirectly, cause a first ray plantarflexion moment?? -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
When is the EHL tendon ever inferior to the horizontal axis of the first MPJ? -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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? -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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Re: How significant is the Peroneus longus as a Plantarflexor of the 1st 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. -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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. -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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. -
It will be important to define how many `degrees of separation`for an Indirect moment as well.
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Thanks for the change in thread title, Michael.
Here are what I would call direct and indirect muscle actions and moments for the extensor hallucis longus which we discussed somewhat already.
Extensor hallucis longus:
Direct actions:
1. Dorsiflexion moment at ankle joint.
2. Dorsiflexion moment at horizontal axis of midtarsal joint.
3. Dorsiflexion moment at 1st metatarsophalangeal joint.
4. Dorsiflexion moment at hallux interphalangeal joint.
Indirect actions:
1. Plantarflexion moment at horizontal axis of midtarsal joint with hallux dorsiflexion.
2. Plantarflexion moment at first ray with hallux dorsiflexion.
3. Dorsiflexion moment at first ray with stabilization of 1st metatarsophalangeal joint motion. -
Your welcome Kevin
So now we have internal moments of direct and indirect coming from muscle , how would we work out how effective the indirect moment is?
If for every force there is an equal and opposite force, is the direct and indirect moment equal and opposite. Or can they be of different magnitude and the total force acting on the joint be equal and opposite.
Ie EHL direct moment = dorsiflexion moment at 1st MTP joint and indirect moment = plantarflexion moment at the 1st ray with hallux dorsiflexion. Must these two moments be equal and opposite ?
Hope that makes sense -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
Abductor hallucis, flexor hallucis brevis, can create plantar flexion moment on the first ray when the MPJ is prevented from plantar flexing (fusion, ground reaction force). P. longus is a pennate muscle and can produce more force. Abductor hallucis and flexor hallucis brevis have a longer lever arm on the first ray. So, I can't say for sure that they create more moment than peroneus longus. You've got to use what you've got.
Eric -
EHL and plantar flexion of the ray. I think you all got it, but I'll add my two cents. When the toe dorsiflexes it will increase tension in the plantar fascia. The tendon will create a dorsiflexion moment at the ray and mpj. The tension in the fascia will create a greater plantar flexion moment the dorsiflexion moment from the tendon.
Eric -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
EricLast edited: Jan 20, 2011 -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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6 Nm of supination moment from tendon and 5 Nm of pronation moment from the ground. There is a net supination moment and the STJ will supinate. As the STJ supinates the center of pressure will shift laterally increasing the pronation moment from the ground. So, when the pronation moment from the ground exceeds the supination from the tendon there will be an acceleration back toward pronation the STJ will stop supinating and with a couple of oscilations equilibrium will be achieved in the more supinated position. Until the subject gets tired and relaxes the muscle.
The equal and opposite reaction thing often confuses people because they don't label the source of the force. For example the supination moment in the floor of the sinus tarsi in the above example can be easily confused. There is a an equal and opposite reaction between the talus and calcaneus. There is a force applied by the talus to the floor of the sinus tarsi of the calcaneus and there is a separate and distinct force from the calcaneus applied to the lateral process of the talus. To figure out which one of those forces you want to look at you have to choose which side of the joint you want to do the free body diagram on. Since we care about ground reaction force, we should choose the distal part of the joint. Now we can draw a free body diagram and calculate the moments about the STJ axis.
So, to answer your last question: the forces may be equal or one may be greater than the other.
Eric -
Re: How significant is the Peroneus longus as a Plantarflexor of the 1st Ray?
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In thinking further about these terms "direct" and "indirect" muscle action and/or moments, maybe they aren't the best terms to use. Muscle action/muscle moment production obviously depends on foot position, adjacent joint motion and/or ground reaction force change so that possibly the terms "direct" and "indirect" aren't the best terms. Does anyone else have any better suggestions for terms by which to classify these muscle action/muscle moment types??
Defining these muscle actions in such a fashion has never been done before within the medical literature, to my knowledge. It would probably require a small book to explain it fully especially in attempting to explain how the ever-changing STJ axis spatial location affects never every extrinsic muscle action/moment acting on the foot during weightbearing activities.
The foot is a complex machine, now isn't it?!:drinks -
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Can this be done without making it more complicated than it already is? Maybe not.:confused: -
Maybe I haven't followed this completely, but could the moments be sorted into 3 categories?
1. Moments that occur only in closed kinetic chain (weightbearing)
2. Moments that occur only in open kinetic chain
3. Moments that occur in both open and closed chain
...perhaps those categories are too out of context...
- Conrad
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