In one study, the center of pressure (CoP) remained proximal to the end of the residuum in persons with transmetatarsal (TMT) and Lisfranc amputation using toe fillers, insoles, and slipper sockets [9-10].
Results from this investigation suggest that if below-ankle devices are being used in persons with TMT or Lisfranc amputation, the forefoot stiffness of these devices need not be a design consideration.
To ensure these insights are not taken out of context, we wish to make explicit that the following discussion applies only to the gait of persons with TMT and Lisfranc amputations. These insights should not, for example, be extended to the gait of persons with a metatarsophalangeal amputation.
This investigation provides insights into the effect of device design on the gait of persons with TMT and Lisfranc amputations. While we recognize that clinicians are often forced to consider competing goals, such as the need to reduce the likelihood of subsequent ulceration and skin breakdown or cosmetic restoration, we hope these insights provide some additional information about the function that can be expected from both below- and above-ankle interventions.
Notwithstanding the limitations of this investigation, we suggest that clinicians prescribe prostheses that incorporate a stiff forefoot, restrict/resist ankle dorsiflexion, and provide a means to comfortably manage the external moments caused by loading the prosthetic forefoot (e.g., an anterior tibial shell) if they wish to restore the effective foot length in persons with TMT and Lisfranc amputations. Incorporating all these design features into the prosthesis is also necessary to control the tibia as it rotates over the stance foot, reduce exaggerated loading of the sound limb during initial contact, and provide a means to control the external moments at the ankle and knee in lieu of the normal power generation by the ankle plantar flexors during late stance.
The limited power of this investigation should be kept in mind when generalizing these results to others with TMT and Lisfranc amputations.
The vertical GRF patterns observed on the sound limbs were quite variable during loading (Figure 2(a)), with the magnitude of the vertical GRF increased in the subjects with Lisfranc amputation beyond the 95% CI of the control cohort.
In the subjects with TMT and Lisfranc amputation, the GRF remained at a relatively fixed position (40%-50% of shoe length) until about contralateral heel contact, which occurred at 50 percent GC (Figure 3(b)).
Peak ankle dorsiflexion was delayed and exaggerated compared with the control group on the affected limbs of the subjects with TMT and Lisfranc amputation, and peak plantar flexion was reduced compared with the control group as well (Figure 6(b)).
On the affected limbs of the subjects with TMT and Lisfranc amputation, a normal knee moment pattern was observed until just after foot flat (Figure 8(b)), after which an extension moment was maintained until about 40 percent GC, when the magnitude of the moment was close to zero.
The subjects with TMT and Lisfranc amputation exhibited a peak plantar flexion moment of between one-third and two-thirds that of the control group (Figure 9(b)).
The power generated by the subjects with TMT and Lisfranc amputation was virtually negligible and comparable to that exhibited on the affected limbs of the subjects with Chopart amputation (Figure 12(b)-(c)).