How To Achieve Improved Results With The Chopart Amputation
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.
Below Ankle Prostheses: Can They Have An Impact?
The second type of Chopart prostheses, orthoses or “prosthoses” involve the below ankle types. Some are characterized by a total contact, below ankle partial foot socket and a soft interface capable of providing total weightbearing. Other designs use silicone or urethane elastomer materials to combine both the socket and interface for the same purpose. Both are fabricated over a modified, positive plaster or CAD-CAM mold of the partial foot. The mold modification process accommodates pressure sensitive and loading areas of the foot. The “prosthosis” will usually include a toe filler and may include a footplate extending from heel to toe. While the effectiveness of the below ankle socket and its full length footplate is questionable at the more proximal, Chopart amputation level, they are of great benefit at more distal amputation levels (i.e. transmetatarsal).6
The below ankle prosthosis (with some variants known as slipper sockets with a toe filler) is more effective when one couples it with a running shoe or a modified shoe with a rocker bottom sole to allow easier rollover and shorter steps to effectively decrease pressures on the plantar and distal plantar surface of the foot when indicated.7 A high top shoe becomes a practical necessity for the more proximal, Chopart amputation level since it can provide very limited suspension when one solely uses it to keep the prosthosis on the partial foot of the higher activity level amputee.