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.