Partial Foot Device for High-Level Ambulators
Jason Wening MS, CP AbstractA prosthosis was designed to maximize function for a young, healthy Lisfranc amputee. The device included an anterior shell, free plantarflexion, and dorsiflexion stop with dorsiassist joints. The patient successfully returned to work and demonstrated improved gait parameters with the prosthosis. The design presented here is believed to be beneficial for enabling partial-foot amputees to return to an active lifestyle. BackgroundAlthough a broad spectrum of solutions exist for partial-foot amputees, including everything from a simple toe filler to a laminated clamshell prosthesis, the evidence is not always clear as to what type of device will best serve an individual patient's needs and goals. The recently published State-of-the-Science Conference (SSC) on Biomechanics of Partial Foot Amputation indicated that a partial foot device may not have a significant impact on gait parameters; however, if it crosses the ankle, the device may significantly increase anterior translation of the center of pressure (COP).1 Case StudyThe patient, a 30-year-old male who underwent a left Lisfranc partial foot amputation secondary to trauma while working in highway construction (figure 1), demonstrated full range of motion with normal strength at the left foot and ankle. The patient was healthy, motivated, and capable of full end bearing. His primary goal was to return to work as a truck driver responsible for loading, delivering, and unloading materials to highway construction sites. His job required him to be able to get in and out of a truck cabin, control the truck's clutch with the amputated limb, walk long distances, and manipulate heavy loads. A custom-fabricated anterior shell prosthosis with free plantarflexion and dorsiflexion stop and dorsiflexion assist was designed to assist the patient in achieving his goal. The authors also quantified the changes in the patient's gait related to the prosthosis.
MethodsThe patient's residual limb and leg were cast in fiberglass up to the fibular head. Immediately after application, a plastic bag was placed over the distal cast and the patient's shoe was donned. The patient stood with full weight bearing while alignment lines were drawn on the lateral and posterior aspects of the cast. A positive plaster model was created. Minimal modifications were applied to smooth the model and build up bony prominences. An extension was created to simulate the shape and length of the sound side foot. Dorsiflexion Assist Tamarack Flexure Joints™ were placed on the cast at the location of the ankle joint and ¼-inch copolymer was formed over the model. The plastic was trimmed, plaster removed, and the anterior ankle slotted to allow for free plantarflexion. Most of the dorsal portion of the foot section was trimmed, and a soft foam mold was fabricated to form the foot and distal end pad (figures 2 and 3). The device was thinned to minimize distortion of the shoe. A Velcro® strap and D-ring were added to the proximal portion at mid calf (figure 4). The counter of the shoe provided sufficient suspension of the calcaneus (figure 5). At the time of fitting, adjustments were made to the anterior stop to provide for smooth rollover. Rollover can also be adjusted by thinning the plastic forefoot. Gait parameters and COP data were collected with the patient barefoot and wearing the prosthosis at a self-selected speed with the GAITRite Portable Electronic Walkway®2 (MAP/CIR Inc. Havertown, Pennsylvania).
ResultsThe result was a lightweight device that allowed the return to nearly full function with some distortion of the shoe. The patient successfully returned to work. Qualitatively, the patient stated, "I don't realize I have it on." On most days, he wears it from 5 a.m. to 10 p.m. Quantitatively, in barefoot walking, the patient increased walking velocity, cadence, and bilateral step length with the prosthosis (table 1). The step length symmetry also increased slightly. The prosthosis also allowed the patient to dramatically increase the anterior translation of the COP (figure 6) before sound-side initial contact. The 7.5cm increase in anterior translation may be responsible for more than half of the 13cm increase in sound-side step length.
DiscussionSubjective and objective results of this case show that the prosthosis improved this patient's functional ability. Since the patient was not fit with other devices, it is not possible to comment on the functional differences between the prosthosis and other devices. Data did show that the patient's walking ability improved and that there was a substantial increase in anterior translation of the COP prior to contralateral initial contact relative to the barefoot condition. These results are in agreement with the Biomechanics of Partial Foot Amputation SSC conclusion that the device must cross the ankle to allow significant improvement in anterior translation of the COP.1 This device seems to be most appropriate for healthy amputees interested in achieving a high functional level. Other experiences with this device indicate that it may not be appropriate for low-level ambulators who are taking short steps or for patients with loss of sensation due to diabetes. In other patients, uncomfortable neuromas and bone spurs have been accommodated; however, not to the degree needed to allow a return to normal function. It is hoped that continued improvements in design and materials will enable reduction of the size of the prosthosis and the expansion of the population able to benefit from it.
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