Technical Note: Thermoplastic
Klenzak AFO
Eugene Banziger, CPO(c)
Introduction
Traditional metal Klenzak ankle-foot orthoses (AFOs) offer the biomechanical advantages of good ankle control in the coronal
plane while allowing orthotists to easily vary
sagittal plane control from free motion to
spring-assisted dorsiflexion or a variable
plantarflexion stop. This technical note describes a method to obtain similar functions
in a thermoplastic AFO (see Figure 1
).
Technique
Although casting is performed in the conventional manner, model modification is
slightly different. Plaster is added to the
Achilles tendon region, creating a flat area
so the piston and spring can act in a straight
line without binding.
Ankle joints are placed per manufacturer's instructions. A piece of 3/8-inch (1 cm)
polypropylene is cut into a 1 inch by 4 3/4-inch
(2.5 by 12 cm) section and beveled on one
side into a hemi-cylinder. After being heated
with the polypropylene sheet that will form
the AFO, the hemi-cylinder is placed on the
mold, flat side down, where the buildup has
been added to the Achilles tendon area (see
Figure 2
).
Drape molding with vacuum assist is then
completed promptly to ensure good thermal
bonding between the two pieces (see Figure
3
). Once the plastic has cooled, it should be
trimmed and removed from the mold. The
foot and calf sections are carefully separated
using a band saw (see Figure 4
).
A 17/64-inch drill bit is used then to bore a
hole within 5/8-inch (1 cm) of the top of the
hemi-cylinder reinforcement's center. This
will form the channel that will later accept a
spring, plantarflexion stop pin and plastic
rod that acts as a piston (see Figure 5
).
After transferring the alignment of the
hole in the top reinforcement to the foot
piece, a corresponding 17/64-inch hole 5/8-inch
deep should be drilled in the foot piece reinforcement. This hole will receive the plastic
piston rod.
A Klenzak spring and proper length piston
rod should be inserted; the orthosis assembled and fitted in the standard manner. The
goal is to achieve smooth dynamic action
throughout the stance and swing phases. The
posterior reinforcements should be trimmed
to allow the desired range of motion. Spring
tension can be varied by using longer or
shorter plastic piston rods or by changing
spring length. If desired, the proximal end of
the cylinder can be threaded to accept a machine screw for easier adjustments. Figure 1
illustrates this modification.
When a plantarflexion limit is needed, a
pin can be inserted in the spring or the reinforcements can be left full length to function
as fixed plantarflexion stops. Dorsiflexion
can be limited by rivetting a webbing strip
onto each side of the cylinder (see Figure 6
).
Conclusion
Based on 140 pediatric and 20 adult fittings
during the past 15 months, the thermoplastic
Klenzak AFO has been a reliable and effective orthotic variation. To date, no failures
or repairs have been reported. This AFO has
proven useful for both ambulatory and nocturnal use.
The design combines the versatile control
usually associated with the metal Klenzak
design with the light weight and pleasing appearance of modern thermoplastics (see Figure 7
).
Acknowledgements
The author thanks Dr. Beauchamp at the
B.C. Children's Hospital and Ford Laboratories
for their support in the development of this
project.
Eugene Banziger, CPO(c), is director of the prosthetics and orthotics department at Kelowna General Hospital, 2268 Pandosy St., Kelowna, B.C. V1Y 1T2, Canada.
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