If it was a true stress fracture, I’d say yes. Stress fractures are overuse injuries where the bone is stressed faster than it can repair.

John,
You make a great point regarding the distribution of forces in the foot in the shod vs. unshod state and I agree with your comments above.  I agree that the pattern of distribution of those forces change in one state vs. the other. My use of the cast analogy was an extreme example to show demineralization, as I have seen several stress fractures occur in patients who are coming back from injuries who have been recently casted.  I do however, believe that shoewear may have some impact on bone density, I just don’t have the scientific backing to prove it.  That impact may be like you said, in the pattern of distribution.  For instance, traditional bulky shoes are less flexible which would distribute the forces along the foot differently so your bones will adapt to those forces and if you change to minimalist/more flexible, shoewear the force distribution will be different.  It becomes quite complicated when you think about it, and designing a study to determine this with current technology would be frought with uncontrolled variable.  None the less, your thoughts are well recieved.

As for the Morton’s toe, I agree with Pete’s reply.  The length of the second toe will see increased forces on that metatarsal during the midstance phase over a longer duration of time.  It would thus be logical to expect more injuries with these runners. 

A bone densitometer study would be very interesting, and you’re right on about the sample opportunity. Hmm….

I agree with most of what you are saying here – absolute force will be the same, but how and where specifically it is applied will change. One of the big differences when barefoot is that it’s quite possible that force under the second met head will be magnified since there is no shoe sole underneath to spread force application out. If you have force application focused on a smaller area, stress in this area will increase, and thus bending of the second met could increase as a result.

I do suspect Morton’s toe might raise the risk for the reasons that you suggest.

In particular I wonder about the way that big toe is bent inwards by years of poorly designed and fitting shoes, if the big toes isn’t in good alignment with the 1st metatarsal then the amount of force we can apply through the big toe and the 1st metatarsal. 

I recall a post of Mark Cucuzella about use of Correct Toes spaces, and the importance of the alignment of the big toe for running barefoot.  This made sense to me at the time, but I didn’t then ponder on the role of distribution of load across the toes and metatarsals.

Is this plausible?  Could we get feedback from those with 2nd and 3rd metatarsal injuries as to whether their big toes is well aligned to their 1st metatarsal or not.  Any X-rays taken of the feet would be ideal for doing such a review.

If this little theory does have some merit then Correct Toes or similar tool for bringing the toes back into alignment might well be a good way to develop foot structure that is better able to deliver the loads we demand of them.  If one had a metarsal injury already perhaps looking at solving this part of the problem will help, or if new runners (or new to barefoot/minimalist) would be to look at solving the big toes alignment prior to introducing too much barefoot/minimalist running.

As a wee note, my own big toes still are not perfectly aligned despite being barefoot for most of the last year.  Sitting at desk barefoot probably doesn’t count too much though!

I’ll refer you to this study:

Skeletal Radiol. 2001 Feb;30(2):61-6.MRI abnormalities of foot and ankle in asymptomatic, physically active individuals.Lohman M, Kivisaari A, Vehmas T, Kallio P, Malmivaara A, Kivisaari L.They looked at 19 marathon runners post race with MRI and found areas of signal abnormality that are usually referred to as stress response and yet the athletes were asymptomatic.  This leads to the conclusion that MRI findings  do not always match clinical symptoms.  The answer still lies out there somewhere.As an aside, I saw at least 3 brave souls (or soles) on my trail run today (some areas of gravel) running barefoot.  I am not as brave and have resurrected my Kinvaras for now as my adidas adizero I feel are too narrow for my forefoot, despite my narrow width foot as it is.  There were giving me metatarsal pain which I found humorous since it was the subject of this topic.  

Thank you for sharing this article with us. 

I think you will discover lots of interesting things in foot thickness, muscle, and bone strength.

Mark Cucuzzella

I do think that shod runners will have different PATTERNS of bone mineralization, because the way they stress their metatarsals is different than how an unshod runner (especially a forefoot striker) would stress them.   Abruptly changing the stresses on the foot (by switching to barefoot running, for example) would stress the bone in a way it is not used to, causing a stress fracture.  Of course under this philosophy, an unshod runner would be at a similar risk if jumping into wearing shoes!

On a completely unrelated note, I’d be interested to know if Morton’s toe (having a longer second toe than big toe) is at all a factor in making second metatarsal stress fractures more common than 3rd, 4th, or 5th.  A runner with morton’s toe would have the second metatarsal head on the ground slightly longer (since the metatarsal is longer) than any of the other metatarsal heads, and that might cause more force to be directed into that metatarsal vs. the other four.  Thoughts?