Prior1pod wrote:
> 
> In a message dated 22/03/98 22:38:39 GMT, Dorsalis wrote:
> 
> >>Then, I have to ask the same question of you.  Have you really had any
> experience with properly done Blake Devices?  I only know of a very few
> labs even here in the states, that know how to do them correctly.  A
> true Blake device intrinsically imparts a proportional amount of
> eversion to the forefoot as it inverts the rearfoot.  For that reason,
> it comes closer to actually holding the rearfoot in neutral, on a fully
> loaded forefoot, than any other device I have seen.  It truly brings the
> ground up to the foot.  For that reason the rearfoot "rests" inverted as
> the forefoot is loaded against it.  One of the fundamental reasons the
> old "Post em to perpendicular" devices resulted in the excessively
> pronated rearfeet pronating off the device is that a forefoot
> intrinsically posted against a perpendicular rearfoot which in CKC may
> be quite everted from its neutral position is simply a "looser" forefoot
> then the one which was casted.  >>
> 
> I think what you are saying here is that by inverting the rearfoot, the
> forefoot must evert to maintain ground contact. 

Close, Trev, but instead of "ground contact", what I am saying is that
as the RF inverts, the FF must Evert in order to maintain Loading (or
Locking) forces on the forefoot.  

>The amount of eversion that
> can occur will depend on MTJ motion plus 1st ray plantarflexion and 5th ray
> dorsiflexion, and perhas some dorsiflexion of the forefoot. 

Yes, that is exactly right!  What I see the Blake device doing (when it
is done well) is to drop the 1st ray on an exagerated intrinsic post,
while at the same time loading the lateral column.

>Thus there will be a maximum point beyond which further reafoot supination will cause the medial
> forefoot to lift from the ground. 

Except that in the Blake model, the medial side of the plate becomes
something of an extension of the 1st ray, sort of like making a longer
hypoteneuse.

>Do you assess this amount when deciding on
> the amount of control to prescribe ? I still agree with Ray that this device
> works by jacking up the rearfoot, whatever the secondary effect on the
> forefoot.

Well, the Kirby medial skive jacks up the rearfoot (into inversion), but
because it does nothing to counter the forefoot beyond a certain point,
its usefulness is limited in very inverted forefeet.  
> 
> Much cut
> 
> << Won't happen if the cuboid is so elevated that the peroneal tendon has
>  no mechanical advantage. Will happen if the rearfoot is maintained close
>  to neutral with a fully loaded forefoot. >>
> 
> Why will the cuboid be so elevated. If you can allow the first ray to
> plantarflex in latter stance, this will be stabilised by P.Longus. As the
> cuboid is the fulcrum point, the cuboid will be pronated and the cc joint will
> close pack = stability.

Yes, but at issue here was an extremely inverted forefoot deformity (16
degrees off the ground when the rearfoot is in NCSP).  As that forefoot
rolls down to the ground, the cuboid bends up to the point in which it
has less and less mechanical advantage. The first ray never gets a
chance to plantarflex UNLESS, intrinsic or extrinsic posting provide it
with a fulcrum from which to do so.
> 
> The problem with some of the theory quoted is the concept of control seen in
> static stance when patients stand on orthoses.
> 
> If I were to throw a controlled slow punch at a critic of biomechanics
> (hypothetically speaking), they would need to use a lot of force to deflect my
> punch (similar to standing on an orthotic - a lot of control, or as Kevin
> would describe this, a large supinatory moment). However, if I throw a more
> wild fast punch, much less force is required for deflecting the punch (in fact
> only a small amount). Thus during walking, smaller degrees of control are
> required as they deflect the motion more easily due to the speed of motion
> (moments, momentum blah blah).
> 
> To add my twopeneth to the science debate, I have begun to try and analyse
> general stability and the speed of gait with orthoses as, when my analysis
> suggests that the devices are correct, I observe that my patients walk quicker
> and report less effort. Over to you Keith regarding the index you described at
> the last summer school meeting.

Yes, I certainly concur with those observations.  That is a very worthy
twopeneth (or tuppence? what is where you are)?
> 
>To "coin" the old phrase, thanks for your two cents worth.

Collegially

Chip S.

************************************************************************
> ************************************************************************
> Charles C. Southerland Jr. D.P.M., FACFAS, FACFAOM
> Professor of Podiatric Orthopedics & Biomechanics
> Barry University School of Graduate Medical Sciences-Podiatric Medicine
> 
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