CASE REPORT
The patient was a 65-year-old
Japanese man with diabetic neuropathy, who had undergone multiple toe
amputation (second, third, and fourth phalanxes and at least part of the
metatarsal) in left limb in May 2013 (when he was 60-year-old) and
single toe amputation (third proximal phalanx) three year later, May
2016. The patient had
comorbidities of critical limb ischemia and received hemodialysis.
Although diabetic-related foot
deformity, including Charcot foot, was not confirmed, left foot
displayed clow toe after the surgery.
Joint mobility in both forefoot
and hindfoot was limited based on physical assessment by experienced
medical doctor. He could walk independently on flat surfaces without
using an ambulatory assistive device. Given the multiple toe amputations
in the left foot, henceforth we have used the term “ipsilateral” for
the left limb and “contralateral” for the right limb.
First, to determine whether the patient displayed a decline in walking
capacity, we evaluated spatiotemporal gait parameters during level
walking using a laser range sensor-based leg tracking
system5 (Fig. 1A ). This new technology-based
gait assessment has been applied to characterize ambulation in patients
with neurodegenerative and musculoskeletal
diseases6-8. As this analysis system evaluates gait
parameters in the right and left limbs separately (Fig. 1B ), it
provides insight into amputation-related gait alterations. As expected,
this patient displayed poor walking capacity compared to the reference
value derived from patients with diabetic neuropathy without
amputation4, 9, 10, as evidenced by slower gait
velocity, shorter stride length, and shorter step length, especially the
ipsilateral step length (Fig. 1C ). These data indicate that
patients who have undergone multiple toe amputation display gait
disorders with inter-limb asymmetry in step length.
As partial foot amputation influences the center of pressure (COP) and
GRF1, we determined whether toe amputation influences
these kinematic changes. We used a validated custom-made sensor-mounted
insole to assess the COP and GRF (Fig. 2A )11.
This system can measure a force similar to the vertical GRF by summing
the forces of 15 sensors attached to the insole. The system can also
estimate the COP positions in the anteroposterior and mediolateral
directions by calculating the weighted average of the sensor positions
and forces. We found that the ipsilateral foot displayed reduced COP
excursion, which was derived from a lack of push-off motion by the
forefoot (Fig. 2B ). In addition, the COP during the terminal
stance in the ipsilateral foot was localized at the first metatarsal,
which was not observed in the COP of the contralateral foot and in
healthy adults (Fig. 2B ). Of note, contralateral foot also
displayed reduced COP excursion compared to healthy adult,
suggesting that foot function in
contralateral limb is not necessarily normal. The confirmed inter-limb
difference in the COP was consistent with the GRF data showing
inter-limb asymmetry (Fig. 2C ). On comparison with healthy
adults, our patient displayed lower first and second peak values of GRF
in the ipsilateral limb (Fig. 2C ). Notably, the first peak GRF
in the contralateral limb was higher than that in healthy adults. These
findings indicate that the lack of push-off in the ipsilateral limb is
related to increased first peak GRF in the contralateral limb.
To further support the biomechanical inter-limb asymmetry, we recorded
level walking using a 60-fps stationary camera (HDR-CX550V; Sony Corp,
Sony Marketing Inc, Tokyo, Japan) and performed kinematic analysis based
on the whole-body skeleton visualized using the OpenPose
system12. We focused on the gait cycle from the
ipsilateral terminal stance (i.e., contralateral heel contact), which
corresponds to the observed alterations in the COP and GRF. This
decision was made based on previous biomechanical evidence that the
drop-off effect during the terminal stance in one limb leads to
increased GRF in the contralateral limb3. Fig.
3 shows the results of the gait movie analysis in the sagittal plane.
The hip extension angle during the terminal stance in the ipsilateral
limb was lower than that in the contralateral limb (12.7° vs. 27.7°, as
measured by Image J software).