Gait deviations
Lower-limb amputees are unable to maintain the characteristic walking patterns of an able-bodied individual due to the removal of some portion of the impaired leg.
Without the anatomical structure and neuromechanical control of the removed leg segment, amputees must use alternative compensatory strategies to walk efficiently.
Prosthetic limbs provide support to the user and more advanced models attempt to mimic the function of the missing anatomy, including biomechanically controlled ankle and knee joints.
Several common observations are whole-body movements, slower and wider steps, shorter strides, and increased sway.
[1] Orthopedic corrective treatments may also manifest into gait abnormality, such as lower extremity amputation, healed fractures, and arthroplasty (joint replacement).
[11] Simple tasks such as walking on level ground, sit-to-stand transfers, and climbing stairs[12] require complex alternative muscle activation patterns[13] because the amputee cannot generate a moment about the prosthetic knee.
[19][21][20][22] Stride length refers to the distance in the direction of forward motion that is between heel strikes of successive footfalls or steps.
[23][24][25] Stride length is arguably the most visible of the changes in amputee gait because it creates such an asymmetry between the intact and impaired limbs.
Increased step width is commonly accepted as an indicator of gait instability because it is a coping mechanism to deal with external or environmental balance perturbations.
[26][27] A similar widening of step width and concordant slowing of gait speed[28] has been observed between populations of elderly,[29][30] obese,[31][32] pregnant women,[33][34] and amputees.
[36] External lateral support mechanisms have been used to isolate the variable of balance in able-bodied subjects and succeeded in reducing both metabolic cost and step width.
Human metabolic rates are usually recorded via measuring the maximal oxygen consumption (VO2 max) during controlled incremental exercise under observation.
[39][40] The values from a theoretical model[41] and experimental analyses[38][42][43][44][45] are listed below: Another source[46] compiled a list of average metabolic cost increases categorized by amputation location and by cause of amputation: Although heavily related to the metabolic cost and overall optimization of the gait, the self-selected walking speed of amputees is significantly lower than able-bodied individuals.
[49][54] Even with the advanced computerized knee joint of Otto Bock's C-Leg transfemoral prosthesis,[55] the subjects experienced increased braking and propulsive impulses than that of the standard double inverted pendulum model of normal human gait.
[40] Similar to decreased stride length and increased step width, lateral sway is generally postulated to be an indication of gait instability.
The variability in length and width of steps can be attributed to a level of responsiveness to external factors and perturbations, or an indication of inherent instability and lack of control.
The following list shows examples of factors that are believed to influence the gait characteristics of lower-limb amputees: A common trend in modern technology is the push to create lightweight devices.
A 1981 collection of studies on amputees showed a 30% increase in metabolic cost of walking for an able-bodied subject with 2-kg weights fixed to each foot.
The length of the residual limb is related to the amount of asymmetry in the walking pattern, with longer stumps on average having greater control.
[21] Misalignment of joints could result in postures similar to those seen in congenital malformations such as bow-leggedness, knock-knee, pigeon toe, and club foot.
[65] The sole reliance on the hip joint to control the entire prosthetic limb makes fine-tuning foot placement difficult.
