Purpose: Clinicians are often faced with prescribing a prosthetic foot for those persons
balanced compromised beyond unilateral lower limb amputation. This is particularly true
in the case of the older diabetic transtibial amputee with peripheral neuropathy.
A systematic, comprehensive and multi-domain study of the impact of four foot-ankle
combination prostheses was performed, that included the assessement of postural sway.
Foot-ankle prostheses were selected based on the need to characterize the effects of both
compliance (motion under loading) and energy storage features. The intent was to isolate
those componentry characteristics that effect amputee ground reaction forces (GRF) and
Center of Pressure. An ultimate objective of the study was to further ascertain any biomechanical measures
of balance or gait, relational to amputee’s prosthetic foot preference.
Methods: Methods: This descriptive study utilized a within subject, repeated measures design.
Twenty diabetic unilateral transition amputees were recruited ranging in age from 50 to
74 years (mean 57.6; Std. 1.4) and with at least one year permanent prosthesis usage. All were K2-K3 ambulators. All were
tested to determine their level of neuropathy. Four different
foot-ankle prostheses were fit, in random order, to each patient’s existing prosthesis: the
SACH foot (S), SACH with Earth Walk Ankle (SA), Carbon Copy II foot (CCII), and a
CCII with Earth Walk Ankle (CCIIA). Following each change in foot-ankle prosthesis, a
four week acclimatization period was allowed prior to evaluation. Postural sway was a
component of this evaluation. Participants performed three thirty second trials of a
randomly ordered Romberg test utilizing a single force plate for the feet together stance
and two force plates for the feet apart stance. In this manner, data was captured that
separated measures of the intact and prosthetic limbs.. Four stance conditions were
performed: Eyes Open, Feet Apart (EOFA); Eyes Closed, Feet Apart (ECFA); Eyes open,
feet together (EOFT) and; eyes closed, feet together (ECFT).
Area of sway, anterior-posterior (AP) and medial –lateral (ML) sway; trajectory
pathlength (TP) and velocity of sway were measured.
Results: There was no significant difference between the four foot/ankle combinations for any of
the measures of Postural sway and stance conditions.
While the participants stood ECFA, they bore a greater proportion of their weight on the
intact limb. Although this pattern was not statistically significant and less evident under
the EOFA stance, it was consistent across all four foot/ankle combinations.
Amputees demonstrated a greater area of sway, anterior-posterior and medial-lateral
sway distance under the ECFA stance compared to EOFA, but such differences, though
consistent, were not statistically signgnificant between foot-ankle combinations. The ECFT stance demonstrated similar phenomena and included increased sway path
length and velocity of sway when compared to EOFT, but again, was not statistically
significant between foot-ankle combinations.
In general, the SACH foot promoted the least amount sways measurement for all
conditions while the SACH with ankle promoted greater sway under the feet apart
condition and the cc2 under the feet together condition.
Finally, neuropathy scores correlated significantly (p-value < 0.05) with each of the
Romberg test stance area of sway, anterior-posterior and medial-lateral sway distances,
regardless of foot/ankle combination. However, there was no significant correlation with
the respective Romberg Quotients (EC/EO). Conversely, participant foot preference was significantly correlated (p-value < 0.05) with all sway measures corresponding to the eyes opened versus eyes closed conditions.
Conclusions: The results of this study indicate that postural sway during upright standing
is not significantly impacted by differences in prosthetic foot design.
As might be expected, the SACH foot typically incurred the least amount of sway, but
only one of the eighteen participants that completed the study pronounced the SACH as
their foot of choice. It seems unlikely that for such a population, standing balance
performance is a deciding factor in terms of foot preference.
It is not clear if the measures of postural sway utilized were sensitive enough to note
changes due to prosthetic foot design, or if the foot design simply had minimal impact on
standing balance. The relative literature suggests that other measures of postural stability
may be more sensitive to sway changes, and/or a larger sample population size is
necessary to overcome inherent variability.
Finally the level of neuropathy significantly increases the likelihood of grater sway
parameters, a consequence of lost proprioception as a component of the balance system.
Under the more challenging ‘eyes closed’ conditions, a possible compensatory
mechanism may have been for the amputee to shift a greater proportion of their body
weight on to their intact limb, enabling them to use their prosthetic limb as more of a
stabilizing device.
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