How To Achieve Improved Results With The Chopart Amputation

By Gordon Zernich, CP, Tomas Dowell, CPO/LPO, Gary M. Rothenberg, DPM, FACFAS, and Michael M. Cohen, DPM, FACFAS

What You Should Know About Above Ankle Prostheses

The most important characteristics of the clinical evaluation are the activity, compliance and motivational level of the patient. It may or may not be related to the surgical outcome but the choice of the prosthetic device depends upon the patient’s ability to bear weight, ambulate and perhaps even to vary cadence. However, there are two basic types of Chopart prostheses: above ankle and below ankle.    Some of the above ankle designs will encase the affected limb and support the body’s weight through the patella tendon and the medial flare of the tibia. Another variation of that design includes the patella tendon bearing ankle-foot orthosis (PTB-AFO), which uses a patent bottom to substitute for the foot. The former Chopart prosthesis, weighing 5 pounds or more but rarely less, uses a very rigid footplate. Both may require a shoe lift on the contralateral side to keep the limbs equal in length, and both are indicated for level 0 to 1 ambulators who cannot bear weight on the affected foot.    Also keep in mind that normal gait may be compromised with either selection. Additional hip and knee flexion is not uncommon during the swing phase of the gait cycle to compensate for a partial foot restricted from total, if not partial, weightbearing and an ankle restricted or bypassed from its function in any and all spatial planes.    Some practitioners have used a solid ankle orthotic in the form of a Charcot Restraint Orthotic Walker (CROW) for the Chopart amputation level. It allows for a variable amount of partial foot weightbearing since one may fabricate this device to capture the load at the patella tendon or fabricate it to bear weight within the walls of the orthotic and throughout the affected limb by using a total contact socket compression technique or a combination of the two. A rocker bottom sole allows the device to further reduce pressure to the distal, anterior aspect of the foot. However, the ankle is restricted from its function in all spatial planes.    Another variation of the above ankle Chopart device is the use of a semi-rigid ankle AFO with a toe filler. The ability to bear weight completely and ambulate, as one may do with a semi-rigid AFO and toe filler, is a critical factor in selecting it over the Chopart prosthesis. One research study has shown there is an extra irregularity of weight progression during the gait cycle with the fixed ankle of the Chopart prosthesis over that of the AFO.4    Other research has shown that the Chopart clamshell prostheses with a rigid toe lever is able to restore the effective foot length and comfortably support the generation of substantial external moments during the terminal stance phase of the gait cycle to a greater degree than the below ankle, Chopart prosthetic device utilizing toe fillers and slipper sockets.5 The distinction between each study contrasts the rigid ankle, toe and foot of the Chopart clamshell prostheses with that of a semi-rigid AFO with toe filler and that of a below the ankle Chopart slipper socket with a toe filler.

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