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During a Bmech assessment I came across this unusual STJ action and wondered if someone might have an explanation.
Right foot has Medially rotated STJ axis position in open chain. (see diagram) Push near 1st Nav-cuneiform = pronation of STJ, but pus on 1st MPJ = supination of STJ??
The forefoot is valgus with reference to the rearfoot
Also, sometimes when walking she fully supinates the right foot at late swing and has a lateral forefoot strike which pronates the foot as the heel comes to the ground. She feels this is her normal walking but sometimes she has a more usual initial heel strike to toe off style.
Cheers Dave
Oops I just noticed I drew a left foot from a plantar view but you get the gist eh!
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Last edited by David Smith : 25th May 2010 at 05:13 AM.
Reason: Mistake
Alrighty I´ll stick my head out and see if it gets cut off or not.
Could it be that in your non weightbearing exam when you push in the 1st you increase the tension in the medial band of the plantarfascia and flexor Hallux´s longus which due to their position of effect on the Subtalat joint ,the Joint supinates. During weightbearing the Supinatory Ground reaction force is much greater froce than what I discribed above therefore STJ pronation .
During a Bmech assessment I came across this unusual STJ action and wondered if someone might have an explanation.
Right foot has Medially rotated STJ axis position in open chain. (see diagram) Push near 1st Nav-cuneiform = pronation of STJ, but pus on 1st MPJ = supination of STJ??
The forefoot is valgus with reference to the rearfoot
Also, sometimes when walking she fully supinates the right foot at late swing and has a lateral forefoot strike which pronates the foot as the heel comes to the ground. She feels this is her normal walking but sometimes she has a more usual initial heel strike to toe off style.
Cheers Dave
Oops I just noticed I drew a left foot from a plantar view but you get the gist eh!
Dave:
I have never felt that I had good reproducibility of STJ axis location by using the palpation method when going as far distally as the medial metatarsal heads due to the concomitant MTJ/midfoot dorsiflexion that occurs with the pushing force from my thumb. I generally recommend stopping the STJ axis location palpations distally at the midshaft level of the metatarsals in most feet for this reason.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Alrighty I´ll stick my head out and see if it gets cut off or not.
Could it be that in your non weightbearing exam when you push in the 1st you increase the tension in the medial band of the plantarfascia and flexor Hallux´s longus which due to their position of effect on the Subtalat joint ,the Joint supinates. During weightbearing the Supinatory Ground reaction force is much greater froce than what I discribed above therefore STJ pronation .
That sounds reasonable Mike, this is the first time I have noticed this so why wouldn't it happen more often. Maybe it does but I haven't noticed or tested for this. If it does then what does this imply about 1st MPJ c/out that is a common feature of my orthotic design. Are there some cases where a 1st ray/mpj c/o will reduce supination moments about the STJ for the reason you propose above?
Do we need to consider the effect of extending the medial arch in terms of supination via the mechanism you propose V's the supination displacement gained by enabling the hallux to dorsiflex and enable the windlass to cause displacement in terms of supination.
Cheers Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
That sounds reasonable Mike, this is the first time I have noticed this so why wouldn't it happen more often. Maybe it does but I haven't noticed or tested for this. If it does then what does this imply about 1st MPJ c/out that is a common feature of my orthotic design. Are there some cases where a 1st ray/mpj c/o will reduce supination moments about the STJ for the reason you propose above?
Do we need to consider the effect of extending the medial arch in terms of supination via the mechanism you propose V's the supination displacement gained by enabling the hallux to dorsiflex and enable the windlass to cause displacement in terms of supination.
Alrighty I´ll stick my head out and see if it gets cut off or not.
Could it be that in your non weightbearing exam when you push in the 1st you increase the tension in the medial band of the plantarfascia and flexor Hallux´s longus which due to their position of effect on the Subtalat joint ,the Joint supinates. During weightbearing the Supinatory Ground reaction force is much greater froce than what I discribed above therefore STJ pronation .
Sorry, can't agree with this analysis guys. If you push on the first metatarsal head in the proper manner, and, can somehow, keep the first metatarsal head in the same position without it dorsiflexing and the forefoot inverting to a new position, and your pushing force on the first metatarsal head is still lateral to the STJ axis, then it will tend to pronate the foot, not supinate it.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
That sounds reasonable Mike, this is the first time I have noticed this so why wouldn't it happen more often. Maybe it does but I haven't noticed or tested for this. If it does then what does this imply about 1st MPJ c/out that is a common feature of my orthotic design. Are there some cases where a 1st ray/mpj c/o will reduce supination moments about the STJ for the reason you propose above?
Cheers Dave
Dave,
In your diagram you are only looking at the stj axis relative to the plane of the floor. But what about the pitch (inclination angle) of the stj axis. If you are dealing with an extremely low inclination angle of the stj, then it can be almost impossible to keep the foot in neutral. If you move slightly off of the stj axis, the stj either supinates or pronates. When you move the stj through an open chain rom, you will notice far greater inversion and eversion and far less adduction and abduction of the foot as compared to the average foot.
Any chance you are dealing with this type of unstable stj? I'm not sure how this might explain your result, but I'm curious if this is the foot type.
Dave,
In your diagram you are only looking at the stj axis relative to the plane of the floor. But what about the pitch (inclination angle) of the stj axis. If you are dealing with an extremely low inclination angle of the stj, then it can be almost impossible to keep the foot in neutral. If you move slightly off of the stj axis, the stj either supinates or pronates. When you move the stj through an open chain rom, you will notice far greater inversion and eversion and far less adduction and abduction of the foot as compared to the average foot.
Any chance you are dealing with this type of unstable stj? I'm not sure how this might explain your result, but I'm curious if this is the foot type.
No it's a slightly cavus foot with a normal calc inclination, below is a snap shot of that forefoot strike action and you get an idea of the foot shape.
She has an 8dg f/foot valgus with reference to the rearfoot and I think this may be a compensation to avoid inversion sprains if the stj is supinated by 1st met GRF and inverts due to the valgus f/f.
Cheers Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
During a Bmech assessment I came across this unusual STJ action and wondered if someone might have an explanation.
Right foot has Medially rotated STJ axis position in open chain. (see diagram) Push near 1st Nav-cuneiform = pronation of STJ, but pus on 1st MPJ = supination of STJ??
The forefoot is valgus with reference to the rearfoot
Also, sometimes when walking she fully supinates the right foot at late swing and has a lateral forefoot strike which pronates the foot as the heel comes to the ground. She feels this is her normal walking but sometimes she has a more usual initial heel strike to toe off style.
Cheers Dave
Oops I just noticed I drew a left foot from a plantar view but you get the gist eh!
Sorry, Dave, it is likely examiner error. In the thousands of feet I have done this exam on, I have never seen anything but a straight line of "points of no rotation" that I have marked on the plantar foot. If you change your drawing to being a metatarsus adductus foot, your patient's first metatarsal head may become medial to the subtalar axis. Please provide us with a photo of her plantar foot with the "point of no rotation marks" on it so we can try to help out more.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
No it's a slightly cavus foot with a normal calc inclination, below is a snap shot of that forefoot strike action and you get an idea of the foot shape.
She has an 8dg f/foot valgus with reference to the rearfoot and I think this may be a compensation to avoid inversion sprains if the stj is supinated by 1st met GRF and inverts due to the valgus f/f.
Cheers Dave
Dave,
A low inclination angle of the STJ axis can occur in a high or low arched foot. I'm not talking about the inclination angle of the calcaneus or the rearfoot. In fact, I believe I have seen this condition more often in higher arched feet.
Try this. Place the patient supine with her tibia parallel to the floor and put the stj in the neutral position. While applying a dorsiflexion force to her lateral forefoot, begin to slightly supinate and pronate the foot out of the neutral position. I would not be at all surprised if she immediately "falls off" the neutral position in both directions as you supinate and pronate the foot. Dr. Root described this as a knife edge stj. These feet don't want to stay in stj neutral. If you apply any appreciable dorsiflexion force to the plantar aspect of the forefoot, either the foot moves at the stj or the leg rotates in relationship to the foot. This condition can create a tendency for inversion ankle sprains.
A high stj axis creates just the opposite condition. The forefoot describes a much flatter arc in space as you move the stj because there is much more add/abduction and less inversion/eversion at the stj. There is far less tendency for the stj to move out of neutral when you apply a dorsiflexion force to the forefoot of a foot with a high stj axis.
One source of error I've seen with the palpation of the axis technique is the patient contracting their muscles. Often in feet with high arches and laterally positioned axes you will push medial to the STJ axis and you will get a very small amount of supination and then the foot will pronate. If you are not paying attention to muscular contraction you would think that you are on the pronation side of the axis.
From the picture it looks like the patient is likely to have a more lateral positioned STJ axis. Perhaps when you pushed under the navicular you got a peroneal reflex. Some of these patients have a very dificult time allowing their foot to "relax" so that you don't see this unusual motion.
More data points might be needed. How many points did you use to determine the location of the STJ axis?
Ok I can see the error that might be occurring here as explained by Kevin and Eric and I understand what your saying Geoff. I did check and double check what was happening since it was unusual but she will be back in soon for a full assessment to make bespoke orthoses. So (with the patients permission) I'll video the process of examining the STJ axis position and post it for you to examine. Until the error probability is established further speculation about the describing the biomechanics and how to handle it may be pointless.
Regards Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Ok I can see the error that might be occurring here as explained by Kevin and Eric and I understand what your saying Geoff. I did check and double check what was happening since it was unusual but she will be back in soon for a full assessment to make bespoke orthoses. So (with the patients permission) I'll video the process of examining the STJ axis position and post it for you to examine. Until the error probability is established further speculation about the describing the biomechanics and how to handle it may be pointless.
Regards Dave
It would be great if you could get a video of the "reflex" peroneal firing in response to a supination moment applied to the plantar foot. Can you get a mirror so that you could show the plantar and lateral view simultaneously? It looks like she might be lean enough to see the tendons contract.
It would be great if you could get a video of the "reflex" peroneal firing in response to a supination moment applied to the plantar foot. Can you get a mirror so that you could show the plantar and lateral view simultaneously? It looks like she might be lean enough to see the tendons contract.
cheers,
Eric
Would you prefer a Woody Allen (ironic comedy) or Quentin Taretino (Slice off your face) esque styleee
Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Would you prefer a Woody Allen (ironic comedy) or Quentin Taretino (Slice off your face) esque styleee
Dave
Dave:
You aren't the first person to have technical difficulties in performing the subtalar joint axis palpation technique in this type of foot. When the medial column of a foot that has a low dorsiflexion stiffness and large range of motion from the unloaded to loaded position (i.e. loading force from the pushing thumb of the examiner) then, many times, there will be a large dorsiflexion excursion that the medial column must undergo before the plantar pushing force from the examiner's thumb may transmit sufficient force back to the rearfoot to cause sufficient subtalar joint (STJ) pronation or supination moment for the examiner to detect STJ pronation or supination.
During this large dorsiflexion excursion of the medial column, the forefoot will invert relative to the rearfoot thus changing the spatial position of the examiner's thumb pushing force relative to the starting position of the forefoot when it was unloaded. Unless the examiner notes this movement, and makes sure that the forefoot inversion that is seen is not mistaken for STJ supination, then it is easy for the examiner to assume that their pushing force is medial to the STJ axis, when, in fact, it may be directly underneath or lateral to the STJ axis. My solution for this has been to recommend examiners to stop their thumb pushing force during the STJ palpation technique at the mid-metatarsal shaft level since only two points of plantar location of the STJ axis are necessary to determine plantar representation of the STJ axis.
Hope this helps.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
You aren't the first person to have technical difficulties in performing the subtalar joint axis palpation technique in this type of foot. When the medial column of a foot that has a low dorsiflexion stiffness and large range of motion from the unloaded to loaded position (i.e. loading force from the pushing thumb of the examiner) then, many times, there will be a large dorsiflexion excursion that the medial column must undergo before the plantar pushing force from the examiner's thumb may transmit sufficient force back to the rearfoot to cause sufficient subtalar joint (STJ) pronation or supination moment for the examiner to detect STJ pronation or supination.
During this large dorsiflexion excursion of the medial column, the forefoot will invert relative to the rearfoot thus changing the spatial position of the examiner's thumb pushing force relative to the starting position of the forefoot when it was unloaded.
Kevin, not only might the forefoot dorsiflex, it might simultaneously adduct at the mtj. This could really increase supination moments at the stj when apply the force anterior to the mtj.
Unusual STJ action
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