How To Achieve Improved Results With The Chopart Amputation
The major flaws of the below ankle design is that it lacks: an effective lever arm that would help to lift the partial foot; all the components used in the fabrication of the below ankle device itself; and the shoe during the swing phase of the gait cycle for level 1 to level 2 ambulators. The lack of an effective lever arm on the below ankle prosthosis, especially the slipper socket with toe filler type, compromises any benefit an energy restoring, carbon fiber foot plate would provide at toe off stance phase. It places an additional burden on the higher activity, level 2 ambulator and the result is usually additional gait deviations.
A Closer Look At The Chopart AFO ‘Prosthosis’
The prosthetic department of the Miami Veterans Affairs Medical Center has designed a Chopart AFO prosthosis that combines the most functional aspects of above and below ankle Chopart devices. It is indicated for level 1 and level 2 ambulators. Research is planned to determine its suitability for level 3 ambulators who have the ability to vary their cadence during the gait cycle. Its chief distinction with other models is that it combines a posterior leaf spring AFO, an energy restoring carbon fiber footplate, which is utilized during the toe off segment of stance phase, and a custom fabricated, total contact, flexible (pelite) liner for the partial foot. The liner is contained within a partial contact carbon fiber socket. It weighs 16 oz.
This “prosthosis” offers a few key features. Between heel strike and mid-stance of the gait cycle, the ground reaction force permits a plantarflexion moment between the anatomic (partial) foot and ankle. That reaction force carries over to the posterior leaf spring, the total contact flexible (pelite) interface and the partial contact, carbon fiber socket of the prosthosis. All three components work in concert to allow a plantarflexion moment that smoothes the transition between heel strike and mid-stance.
The Miami VAMC Chopart-AFO prosthosis does not work against a viable, total weightbearing partial foot and ankle, and all its functions. A small amount of inversion and eversion is contained within the total contact flexible interface but that movement is mitigated with the use of a silicone, partial foot sock or similar accessory. Additionally, its design allows for axial rotation of the lower limb. However, the rigid, solid, above ankle Chopart model does not permit the patient’s use of the ankle during any phase of the gait cycle, stance or swing.
The posterior leaf spring of the Miami VAMC Chopart-AFO also provides the wearer with dorsiflexion assist from toe off at the end of stance phase through the swing phase of the gait cycle. The longer lever of the PLS is a great help in lifting and keeping the partial foot, the shoe and all the components of the 16-oz. prosthosis on the patient’s limb through swing phase. The attributes of the energy storing, carbon fiber foot of the prosthosis are much more effective when one combines them with the longer lever arm of the PLS during the toe off phase of the stance cycle as well. The below ankle Chopart variants do not have such capabilities.
The success of the Chopart amputation will vary widely. Orthotists and prosthetists are frequently challenged to provide an effective, functional and comfortable device to accommodate the patient’s need and activity level. That need is often determined by degrees (i.e. range of motion, weightbearing tolerance, the absence of complications such as equinovarus, plantarflexion contracture, ability to walk short distances on the residual limb, etc.).
A variety of orthotic, prosthetic and hybrid “prosthoses” have been designed, modified and improvised to meet that need. With so many options available and the number of partial foot amputations/ preservations rising, those in physical medicine, rehabilitation and podiatry continue their work to exploit any and every physical advantage the patient may present during the process.
Mr. Zernich is a certified prosthetist (CP) working at the Veterans Affairs Medical Center in Miami. He frequently writes on orthotic, prosthetic and rehabilitative medicine subjects.
Mr. Dowell is a certified, licensed orthotist-prosthetist (CPO/LPO) and laboratory supervisor at the Veterans Affairs Medical Center in Miami.