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Has anyone come across any articles/texts/emotive discussions relating to the particular changes in foot mechanics for individuals using in-line or roller skates?

I have recently managed a case of a fifteen year-old in-line hockey player with insertional tibialis posterior pain, and found my thoughts being provoked as rarely before.

Any input for future reference would be graciously received.

Jair

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Not exactly in-line, but this is as close as what we have to a related thread:
Anyone treating ice skaters? ?Peroneal nerve irritation in figure skaters?

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Jair,

The mechanics of in line skating are not that much different than walking. A medially deviated STJ axis will cause PT muscle high loads in both. This is another great advantage of using the tissue stress approach as opposed to some other approach of biomechanics (e.g. STJ neutral). You don't have to know what normal in line skating mechanics are. You only have to analyze the mechanics of the PT tendon.

When the center of pressure under the foot is lateral to the STJ axis there will be a pronation moment on the STJ. The farther lateral the CoP is to the axis the higher the pronation moment. The higher the pronation moment from the ground, the more tension is needed in the PT tendon to create a more supinated position. The angle of the bottom of the boot to the ground is critical in skating, so position of the STJ is critical as well. So, you have to change the location of the center of pressure under the foot. You could use varus wedging in the boot, or you could shift the wheels, or blade, of the skate more medially.

I believe Daryl Phillips had an article in JAPMA about this several years ago.

Regards,

Eric Fuller

Hi Jair, and Eric,
I would beg to differ and say that the mechanics of in line skating are actually quite different to walking.....it's more similar to skiing than it is to roller skates or walking. Roller skates are not the same as in line. The in line action is not heel to toe gait function at all and the need for specific STJ control via tib post to get on and off the medial edge of your control surface is far more like skiing than anything else. If you want me to elaborate I'm happy to, but I don't have time now.
regards Phill Carter

Hi Phil,

I was not clear at all about what I meant. What I meant was that as you analyze the activity you have to examine the stresses on anatomical structures and then modify the environment to reduce those stresses. In that sense there is no difference between walking and skating. In the above case you still have to reduce the stress on the posterior tibial tendon, because that is what hurts. You reduce stress on the tendon by reducing the pronation moment at the STJ.

Sorry, for the confusion in my original post,

Eric

Jair:

In-line skating is probably more like ice-skating than any other sport. Instead of a heel to toe gait pattern where the foot is planted firmly on the supporting surface, as is common to both walking and slower running, both in-line and ice skaters rely on producing their forward directed motion by the individual applying a laterally directed force to the supporting surface that is then resolved into a forward acceleration of the center of mass (CoM) of the body.

This type of "forward motion caused by laterally directed force application" type of sport is also common to windsurfing (i.e. sailboarding) and sailing where the laterally directed force from the wind on a sail is resisted by an oppositely directed force on the keel, centerboard or skeg of the vessel. The combination of these two strong laterally directed forces can create forward acceleration of the vessel as long as the vectors of force application to the sail and keel (or skeg or centerboard) are precisely aligned to allow a net forward force on the vessel.

A basic demonstration of this mechanical phenomenon can be seen by "squirting" a watermelon seed between your fingers to shoot the seed a significant distance with no throwing motion necessary to produce forward acceleration of the seed. In much the same way, in-line skaters don't necessarily need to push their feet and skates backward against the ground to propel themselves forwards.

Hope this helps.

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Sincerely,

Kevin

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Kevin A. Kirby, DPM
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