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\begin{document}

\title{Compensatory gait mechanics in person with multiple toe amputation: a
single case report}



\author[1]{Hirotaka Iijima}%
\author[2]{Ryo Eguchi}%
\author[2]{Aya Yamamoto-Kon}%
\author[3]{Yuta Terabe}%
\author[2]{Masaki Takahashi}%
\affil[1]{Nagoya University}%
\affil[2]{Keio University}%
\affil[3]{Kasukabe Chuo General Hospital Limb Salvage Center}%


\vspace{-1em}



  
  \date{May 15, 2024}


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\textbf{Compensatory gait mechanics in person with multiple toe
amputation:}

\textbf{a single case report}

\textbf{Key Clinical Message}

This case highlights the biomechanical influence of toe amputation on
contralateral limb force elevation, possibly through reduced ipsilateral
plantar flexor torque production.

\textbf{Keywords:} Care report, Diabetic neuropathy, Toe amputation,
Biomechanical analysis

\textbf{INTRODUCTION}

Diabetic neuropathy and the resulting partial foot amputation cause gait
alterations, including slower gait velocity, greater step variability,
greater inter-limb asymmetry, and altered ground reaction force
(GRF)\textsuperscript{1}. These biomechanical alterations with impaired
walking capacity increase the risk of falls as well as musculoskeletal
comorbidities, including osteoarthritis in the contralateral
limb\textsuperscript{2}, leading to loss of functional independence.

As partial foot amputation-induced gait alterations are prominent in
proximal amputation due, at least in part, to loss of moment
arm\textsuperscript{3}, surgical techniques have been proposed to save
the foot and prolong the bipedal ambulatory function. However, the
currently available data regarding partial toe amputation patients are
limited. For example, patients who have undergone first ray amputation
display slower gait velocity, reduced step length, greater step
variability, and decreased hip extension\textsuperscript{4}. To date, no
study has investigated the influence of non-first ray toe amputation on
gait alterations in patients with diabetic neuropathy.

Herein, we report the case of a patient who had undergone non-first ray
but multiple toe amputation, in who integrated gait analysis was
performed to assess spatiotemporal parameters, kinetics, and kinematics.
We demonstrated that multiple toe amputation caused a lack of push-off
with decreased hip extension in the ipsilateral limb accompanied by
elevated contralateral GRF. This single case study provides insight into
toe amputation-related biomechanical alterations and serves as a
framework for future studies to establish an effective rehabilitative
strategy and prevent musculoskeletal comorbidities following amputation.
The patient was informed that data concerning the case would be
submitted for publication, and he consented to it.

\textbf{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
system\textsuperscript{5} (\textbf{Fig. 1A} ). This new technology-based
gait assessment has been applied to characterize ambulation in patients
with neurodegenerative and musculoskeletal
diseases\textsuperscript{6-8}. As this analysis system evaluates gait
parameters in the right and left limbs separately (\textbf{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
amputation\textsuperscript{4, 9, 10}, as evidenced by slower gait
velocity, shorter stride length, and shorter step length, especially the
ipsilateral step length (\textbf{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
GRF\textsuperscript{1}, we determined whether toe amputation influences
these kinematic changes. We used a validated custom-made sensor-mounted
insole to assess the COP and GRF (\textbf{Fig. 2A}
)\textsuperscript{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 (\textbf{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 (\textbf{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
(\textbf{Fig. 2C} ). On comparison with healthy adults, our patient
displayed lower first and second peak values of GRF in the ipsilateral
limb (\textbf{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
system\textsuperscript{12}. 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 limb\textsuperscript{3}. \textbf{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\selectlanguage{ngerman}° vs. 27.7°, as
measured by Image J software).

\textbf{DISCUSSION}

This single case study identified alterations in spatiotemporal gait
parameters and biomechanics associated with multiple toe amputation
during level walking. Most notably, the patient displayed a lack of
push-off movement with reduced hip extension during the terminal stance
phase in the ipsilateral limb, which was accompanied by an elevated
first peak GRF in the contralateral limb.

\emph{Interpretation of the observed biomechanical alterations}

Comprehensive gait analysis is a fundamental step in identifying gait
disorders associated with amputation. However, to date, there is limited
evidence regarding biomechanical alterations in patients who have
undergone toe amputation. One study showed that patients who had
undergone first ray amputation displayed poor walking capacity with
kinematic alterations in hip extension\textsuperscript{4}. The current
study expands on this previous knowledge by showing that patients with a
history of multiple non-first ray amputations displayed biomechanical
alterations characterized by a lack of push-off accompanied by kinematic
changes in lower hip extension. These biomechanical alterations would be
attributed, at least in part, to the loss of function in the second to
fourth toes. Toe amputation reduces leverage, which is required to
produce plantar flexor torque during the terminal stance. It should be
noted that the patient included in this study had undergone amputation
of the third toe in the contralateral limb, suggesting that the poor
walking capacity and biomechanical alterations might be a consequence of
bilateral toe amputation.

Notably, the biomechanical alterations in the ipsilateral limb were
accompanied by an increased vertical first peak GRF in the contralateral
limb. The identification of biomechanical alterations in the
contralateral limb is valuable, as this may provide insight into
musculoskeletal comorbidities after amputation. Increased axial lower
limb loading at heel contact may lead to faster progression of existing
osteoarthritis\textsuperscript{13}. Knee osteoarthritis is a major
comorbidity associated with amputation\textsuperscript{14}. Although no
data are available on the prevalence of these comorbidities after
partial toe amputation, our findings serve as a foundation for future
cohort studies on musculoskeletal comorbidities after partial toe
amputation.

Considering that, nearly one-third of the individuals require
re-amputation within 1 year following an initial toe
amputation\textsuperscript{15}, an enhanced understanding of the disease
trajectory after initial amputation is needed. Elevated plantar pressure
is a major risk factor of diabetic ulcers especially at
metatarsal\textsuperscript{16}, a precursor for
amputation\textsuperscript{17}. Our patient displayed reduced step
length in the ipsilateral limb, which reduces peak plantar pressure
during level walking\textsuperscript{18}. On the other hand, the COP
during the terminal stance in the ipsilateral foot was localized at the
first metatarsal, which may cause excessive plantar pressure in this
region, the common location for foot ulcers\textsuperscript{19}. These
altered biomechanics in the ipsilateral foot highlight the importance of
careful observation following the initial amputation to prevent
secondary amputation.

\emph{Practical and research implications}

This case report has the following implications: (1) the lack of
push-off after toe amputation should be carefully observed, as this may
cause increased contralateral limb loading and subsequent
musculoskeletal comorbidities. (2) Understanding the musculoskeletal
comorbidities in the contralateral limb after toe amputation is an
interesting future direction to determine the relationship between the
former and increased contralateral limb loading. In the future studies,
careful consideration for confounders, including preexisting arthritis
in multiple joints and cardiovascular status is warranted. Since we
cannot rule out that biomechanical changes in ipsilateral limb are
consequence of those in contralateral limb, determining the causal
relationship is also needed. Once the causal relationship of the lacked
push-off in ipsilateral limb and mechanical overloading with subsequent
comorbidities in contralateral limb is verified, rehabilitation and gait
retraining are of interest to improve the production capacity of plantar
flexor torque during the ipsilateral terminal
stance\textsuperscript{20}.

\textbf{Reference}

1. Dillon MP, Fatone S, Hodge MC. Biomechanics of ambulation after
partial foot amputation: a systematic literature review. JPO: Journal of
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2. Briem K, Snyder\selectlanguage{english}-Mackler L. Proximal gait adaptations in medial knee
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3. Hansen AH, Meier MR, Sessoms PH, Childress DS. The effects of
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4. Aprile I, Galli M, Pitocco D, Di Sipio E, Simbolotti C, Germanotta M,
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7. Fujita K, Iijima H, Eguchi R, Kuroiwa T, Sasaki T, Yokoyama Y, et al.
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8. Iijima H, Yorozu A, Suzuki Y, Eguchi R, Aoyama T, Takahashi M. Hip
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9. Menz HB, Lord SR, St George R, Fitzpatrick RC. Walking stability and
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10. Sawacha Z, Spolaor F, Guarneri G, Contessa P, Carraro E, Venturin A,
et al. Abnormal muscle activation during gait in diabetes patients with
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11. Eguchi R, Yorozu A, Fukumoto T, Takahashi M. Estimation of vertical
ground reaction force using low-cost insole with force plate-free
learning from single leg stance and walking. IEEE journal of biomedical
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12. Cao Z, Hidalgo G, Simon T, Wei S-E, Sheikh Y. OpenPose: realtime
multi-person 2D pose estimation using Part Affinity Fields. arXiv
preprint arXiv:1812.08008 2018.

13. Mundermann A, Dyrby CO, Andriacchi TP. Secondary gait changes in
patients with medial compartment knee osteoarthritis: increased load at
the ankle, knee, and hip during walking. Arthritis Rheum 2005; 52:
2835-2844.

14. Welke B, Jakubowitz E, Seehaus F, Daniilidis K, Timpner M, Tremer N,
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amputation?-A database analysis with 1,569 amputees and matched
controls. PLoS One 2019; 14: e0210868.

15. Littman AJ, Tseng CL, Timmons A, Moore K, Landry G, Czerniecki JM,
et al. Risk of Ipsilateral Reamputation Following an Incident Toe
Amputation Among U.S. Military Veterans With Diabetes, 2005-2016.
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16. Ledoux WR, Shofer JB, Cowley MS, Ahroni JH, Cohen V, Boyko EJ.
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\textbf{Figure legends}

\textbf{Figure 1. Laser range sensor-based leg tracking system reveals
poor walking capacity in the patient who have undergone toe amputation}

The patient's gait being assessed in a comfortable walking style/at a
comfortable walking pace using a laser range sensor (\textbf{A} ).
Calculation of spatiotemporal gait parameters (\textbf{B} ). Results of
the laser range sensor-based gait analysis (\textbf{C} ). Data of
spatiotemporal parameters in diabetic patients (DP) without amputation
are provided as a reference\textsuperscript{4, 9, 10}.

\textbf{Figure 2. Insole-based biomechanical analysis revealed a lack of
push-off in the ipsilateral limb and subsequent increased first ground
reaction force in the contralateral limb}

The sensor-mounted insole system estimates the center of pressure (COP)
and vertical ground reaction force (GRF) during level walking
(\textbf{A} ). The COP analysis in the patient revealed reduced
excursion in the left (ipsilateral) limb, which was derived from a lack
of push-off motion by the forefoot (\textbf{B} ). The COP in healthy
adults is provided as a reference. The patient displayed reduced first
and second peak GRF in the ipsilateral limb and increased first peak GRF
compared to healthy adults (\textbf{C} ).

\textbf{Figure 3. Video-based kinematic analysis revealed reduce hip
extension in the ipsilateral limb}

The whole-body skeleton was visualized during level walking using the
OpenPose system. Graphic illustrations represent the terminal stance
phase of the ipsilateral (left panel) and contralateral (right panel)
limbs. Terminal stance in the ipsilateral limb is characterized by
reduced hip extension, indicated by a lower hip extension angle (angle
between the femur and the vertical line) manually measured by Image J
software. The values of the hip joint angle are provided based on a
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