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An AFO supports the forefoot and prevents plantar flexion or "foot drop" during swing. But don't forget, an AFO additionally substitutes for the lack of a plantarflexion moment during stance phase of gait. You see, the plantar flexors must be active during midstance and terminal stance to counter the dorsiflexor moment that is produced by the ground reaction force about the ankle jt. In the presence of weak plantarflexors, the ankle dorsiflexes too rapidly and, because the lower extremity is positioned in a closed chain, the knee flexes.
Midstance knee flexion affects the person's stability. Someone with weak plantar flexors must compensate proximally at the hip, (High-stepping, abducting, circumducting, excessive quad firing, compensatory genurecurvatum, etc.) or must wear an external device (an AFO) that substitutes the force that the plantar flexors ordinarily provide. An AFO with a dorsiflexion stop can be used to stabilize the knee in extension using GRF control in stance and would also allow knee flexion in swing phase. The degree of correct plantarflexion moment can be dialed in by building the brace in 5-10deg of plantarflexion and adjusting heel height accordingly. I suppose you could also restrict knee flexion through the use of a KAFO with a locked knee. But the 3PP system which prevents knee flexion in stance phase would also prevent knee flexion in swing phase producing an inefficient walking pattern. The KAFO is a very safe orthosis for sure but, dang, that is one bulky beast of a brace! And Dude still has his Quads, right? Just a 3/5 mmt on the hammy's. The GRF control device (AFO) is more energy efficient but not as safe when compared to the 3PP control orthosis (KAFO) which creates a less energy efficient but safer gait pattern. A patient might do well with solid ankle AFOs (or a heel-less, anterior cuff style. Then you could include a pressure reducing FO!!) and bilateral rocker sole modifications. If you go this route, the rocker sole mods are the key to controlling the tibia's advancement over the toes through the correct placement of the rocker axis. It will also reduce the plantar pressures that can get pretty high in the FF found with a co-poly full-length footplate.
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The world of professional cycling is divided not into racers and non-racers but rather by varying degrees of users. Among the cyclists I make orthotics and wedges for are persons who consider themselves racers but may only accumulate 60 miles in a week or less during certain parts of the year. Hardly a professional training schedule you might say, but consider that they often come to me in an off season or on a down-training schedule and their mileage reflects their current load. My recommendation and fabrication technique is based on their current needs which may include less aggressive FF wedging, more flexible materials, and greater pedal float to actually allow for less influence over the STJ, greater medial midfoot excursion at full peak knee extension moment, and knee valgus during peak power stroke angles. (I also move the pedal axis proximal by 5mm)
WHY? Because at reduced loads and distances, (and in the absence of pathology) it's just plain comfortable! As their distances and workloads increase, I switch them to firmer orthotic materials (carbon fiber), fully corrected wedge angles, stiffer soled shoes (again, CF), tighter degree of float, etc...until they are locked-in to their full training/raceday LE posture. http://www.podiatry-arena.com/
Just an opinion, and at podiatry-arena, everyone has them. It is dominated by persons with lots of experience and seemingly lots of time on their hands to write responses. These men and women are devoted to the theories and techniques of foot and ankle biomechanics and, although the discussions are highly technical, you'll find an answer to virtually any podiatric question you may have. Go and Play! Thank you to my most recent customers. I'd like to thank RL from New Orleans, TB from Chicago, SP from Cherry Hill, CP from Potomac, GG from Cambridge, and JD from Washington. Your support is helping to fund my research to find the best combination of long-lasting, pressure-reducing materials in a performance enhanced foot orthotic. By now you all have discovered what I have known for many years; you are only as comfortable as your feet. Enjoy!
Peace and Props, Chris |
Chris Gracey MPT, Cped
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