Firstly, there is a pause between 'More' and 'on' so we are not here to rag on bad braces. But then again, why not? OK. Say it either
way. There are so many kinds of ankle-foot orthoses (orthosis = brace) that it is easy to get mired in extraneous detail. Let's look at examples just to ground ourselves in tactile realities. First the bad:
This is what we call a landfill orthosis. Depending on the child's need, braces can do various things. It is hard to
imagine just what this brace can do well. It is formless, lacking fit detail. Most likely, it is one of those one size fits many (off-the-shelf) items. A minimum requirement would be
to hold at least 90 degrees (allowing for an appreciable shoe heel height). If a flat sneaker were worn, then this brace lacks sufficient forward tilt for even standing (which requires 10
degrees forward tilt - in the shoe - for balance). It does not cover the ankle bones, and therefore is very unlikely to control left-right ankle sway. It will not correct nor prevent
flat foot or varus (club-like) posture. The foot side portions protrude too far forward. That extra extension of inadequate sides simply prevents flexibility
at the metatarsal heads (ball of the foot, just behind the toes). Forward roll is killed. The forefoot "trapping" caused by this defect will cause the foot to spin on the stuck toe area
into excess inward or outward leg rotation, whichever is easiest. This brace causes malrotation in late stance phase as the leg tries to swing impeded by the stuck toe area.
The backward lean of this brace will cause the child to flex at the hips to balance the body
weight over the feet. This "jack knife" hip posture is often blamed on torso or hip weakness.
Here are two kinds of AFO that do meet all the requirements. These are commercial products, ordered from afar, but fit based on a local vendor
heeding the important details. Beware, although we are showing them as optimum examples, poor ordering and fitting skills can mess them enough to be useless. On the left, are front and side views of solid ankle AFOs. On the right, the side view of a hinged AFO.
The SOLID AFO:
Well shaped to the foot, flexible fit with full contact padding at key pressure points. Ball of foot toe-plate area is flexible and not bounded by sides that would impede toe roll over. The
vertical 10 degree forward pitch is perfect, especially for sneaker wearing. There is sufficient strapping and forward ankle envelopment to keep the foot shaped and positioned
where intended. Remember, there are two main objectives. 1) Walking and 2) Shaping the foot against deformity. If the latter is important, then the enveloping fit, as seen here, is ideal
. The main problem with this orthosis, is that there are certain kids with postures that simply cannot attain this ideal configuration. They need totally custom fit orthoses that, by
application of filler material (applied outside the brace), the brace attains an outer contour that looks like this even though the ankle and foot, inside, do not. Thus we satisfy an inner
anatomy shaping-holding need as well as the outer walking geometry. We marry the concepts of orthosis making with prosthesis making.
The HINGED AFO:
Some children have mostly foot shaping needs. Hinges are fine, in that case. However, some have control only so far and not with every step. Rather than allow any degree of free forward movement, a back strap is used (see image) which lets the brace go so far and no further. This is a "control arc" concept. Allow some range which has demonstrated control
(strength equal to the task and reaction speed), but no more. Range without control is, well, you know.
The SPIRAL AFO:
Another way to allow "control arc" (limited arc)
motion in ALL directions (not just forward) and even nudge in one particular direction, is the spiral AFO. Certain children almost demand these. Regardless of the medical biomechanical logic or
physical needs, the athetoid patients, ataxic patients, and some dystonic patients fall apart when held stiffly. In these sensory dependent conditions, DAMPENING motion beyond an allowed
minimum is better than complete limitation. The spiral fit allows flexibility, the carbon component, limits or encourages motion in one direction over another. Because these cases are so sensory needy, leaving the ball of the
foot and toes uncovered is best (tactile reasons, not brace reasons). In fact, the strategy is to see how little covering can hold all the anatomical requirements and also to see how thin (for
sensory reasons) the brace bottom can be without the brace falling apart. These orthoses work when others fail. Down side? They are beasts to make and worse to adjust. Those
few brace makers who can make this brace, groan when they are asked to do so.
the Flimsy Brace:
The flimsy brace is actually one of our favorite braces. It isn't the most used, but rather the most appreciated working so well when other stuff fails. So why not use them all the time?
Because out of their element they fail when ordinary braces are OK. Huh? A flimsy brace does not do correction well or even at all. They are - flimsy. They are great for feet already
corrected and just needing a bit of coaxing toward center - the sweet spot. There is very little skin covered so as not to shield sensation. They deform in a way that can be felt and
add to the sensory cue. It is a brace type for those kids who have sensory side impairments - the ones who do so BADLY in just about every other kind of brace. The spiral above is
also a very good choice for the sensory impaired as it can be made to behave in a similar way (minus most of the carbon). Oh! Good point! Don't confuse skinny with flimsy.
Carbon, great stuff, but rigid. Carbon allows some very trim shapes but those can be quite stiff. There is more on this topic under sensory impairment.
Some children have foot needs met by their AFOs, but that alone
does not control a remaining problem, leg rotation. A twister cable (metal cable) or a side metal bar extending down from a metal or plastic pelvic piece can satisfy that. But a simple elastic strap, as
shown on the right, attached by Velcro to a neoprene pelvic belt also does fine. Structurally, elastic control straps are like garters with an attitude. Parents can easily adjust the latter and use them
intermittently as need requires. The elastics are soft, cheap, and easily modified. Strung as shown, they let go (pull wise) in sitting. If the straps are run deep to the underpants, then the kids can toilet
without somebody helping. They hide well. Elastics work best attached high, that is, at the top of an AFO. Hooked to a shoe, without some kind of ankle area hold, , they MIGHT just twist the foot more so than the leg.
When knee protection is required, a thigh cuff is added (left). If the
hinge at the knee is unlocked, the thigh cuff does virtually nothing to walking. It is merely good protection of the knee against side to side forces. This is especially important in children with spina bifida. They
can actually destroy the knee joint before their teen years if the knee lacks such protection (as they have unique muscle instability problems at the knee).
Also at the left, we see another control arc solution at the ankle. The hinge has two set pins within it (occasionally with springs). They can
be set to allow so much foot pointing up and also set so much foot pointing down. Although such hinges are classically attached directly to the shoe, modern construction also allows a
molded plastic foot orthosis to be inside the shoe as the attachment, as shown here. This image also shows the use of leather (stiffened by shaped metal stays) as an alternative to
plastic. Why? Better pressure properties for insensitive skin and better breathing for circumstances of excessive sweating. Some of the most "impossible" to brace kids who suffer skin breakdown will thrive in these.
Bracing primarily for deformity means getting out of the way of
functional motion and both holding enough body to have sufficient push and to have enough square inches to dissipate those forces. Skin breaks down if focal pressure exceeds 7 pounds per square
inches. If you need, say, 20 pounds of push to reshape a limb contour over time, you had better have more than 3 square inches of contact at the push area. Do the math. Add to that, impulse loading (kids jump a lot).
So, for Blount's disease, for example, we do not need to worry
about control arcs, as the kids are totally normal in skills. We need to change shape, the leg angles AND twists. Twisting is easier when the joints are bent (eg: knee flexed). Alignment angles of the
long bones are most efficiently steered when the limbs are straight (extended). Such braces allow full ranges to get at both postures (as the child moves). The same brace corrects
different parts of the problem as the child moves into different positions.
Add to that, that there is no way to just push the leg totally straight in one oomph. It will
break the leg to "correct" it all at once. The brace must be made, initially, in the shape of the deformity then gradually recontoured every so many weeks to allow the anatomy to
biologically reshape by way of its growth. Unless the child has unusually slow growth milestones, this gets to be quite difficult by age three. That means we have to be about
DONE by age three. That, in turn, means that we have to identify the ones who should be braced EARLY and just get on with it. You CAN think this to death.
There are two ways to identify the brace needy group. 1) The lazy way, let all those who will get better (physiologic bowing) get better and whoever is left must be the ones. Or, 2) actually look closely. Physiologic bow is usually minimal with actual bow shape minimal to
zero, most being twist (torsion). The physiologic ones are improving with time. Blount's disease has major high tibial angulation with a few other oddities, and twist as well. The big
thing is that Blount's kids are WORSENING (even at 18 months old, worsening is NOT
physiologic). An x-ray taken with the knee pointed straight ahead (foot looks wrong when doing it correctly) will show that a line (weight bearing line) drawn on the x-ray from hip to ankle passes outside the knee - unsupported by bone. That lack of support may very well be
what pinches and damages the inner growth plate at the knee to create Blount's disease (or at least what makes it become a permanent growth defect, rather than a passing phase).
What does this have to do with AFOs? Well, the AFO may actually get in the way. These
braces need special metallurgy for the reshaping and AFO components may overly stiffen the construct creating too high a focal pressure at the knee. See?