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Gait deviations are nominally referred to as any variation of standard human gait, typically manifesting as a coping mechanism in response to an anatomical impairment. 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. However, amputees still display quantifiable differences in many measures of ambulation when compared to able-bodied individuals. Several common observations are whole-body movements, slower and wider steps, shorter strides, and increased sway.


Presentation and causes


Lower-limb amputations

Over 185,000 amputations occur annually, with approximately 86% of incidents being lower-limb amputations. The majority of cases are reportedly caused by
vascular disease Vascular disease is a class of diseases of the blood vessels – the arteries and veins of the circulatory system of the body. Vascular disease is a subgroup of cardiovascular disease. Disorders in this vast network of blood vessels can cause ...
(54%) and
trauma Trauma most often refers to: * Major trauma, in physical medicine, severe physical injury caused by an external source * Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic i ...
(45%). Lower-limb amputees are further categorized by where the amputation occurs with respect to the knee joint. However, 34.5% of individuals with an initial foot or ankle amputation experience a progression of symptoms leading to subsequent amputations at higher levels of limb loss. Out of these reamputation cases, diabetic patients had a higher likelihood of requiring further amputations, regardless of initial amputation location. The rate of amputation has decreased significantly with the introduction and optimization of
revascularization In medical and surgical therapy, revascularization is the restoration of perfusion to a body part or organ that has had ischemia. It is typically accomplished by surgical means. Vascular bypass and angioplasty are the two primary means of rev ...
to combat
vascular disease Vascular disease is a class of diseases of the blood vessels – the arteries and veins of the circulatory system of the body. Vascular disease is a subgroup of cardiovascular disease. Disorders in this vast network of blood vessels can cause ...
. An increasingly studied trend in amputation rates is the
gender disparity Sex differences in humans have been studied in a variety of fields. Sex determination occurs by the presence or absence of a Y in the 23rd pair of chromosomes in the human genome. Phenotypic sex refers to an individual's sex as determined by the ...
of women receiving more surgical revascularization treatments and less amputations than male counterparts.


Transtibial

An amputation between the knee and ankle joints transecting the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
, or shinbone, is referred to as a transtibial amputation. In this situation, the patient may retain volitional control over the knee joint. The cause of amputation may dictate the length of the residual limb and the corresponding level of control of the prosthesis. The main impairment for transtibial amputees is the lack of adjustment of the foot and ankle. The foot acts as a
lever arm In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of ...
directly attached to the
calf muscle The triceps surae consists of two muscles located at the calf – the two-headed gastrocnemius and the soleus. These muscles both insert into the calcaneus, the bone of the heel of the human foot, and form the major part of the muscle of the ...
, but more than that, it absorbs the
impulse Impulse or Impulsive may refer to: Science * Impulse (physics), in mechanics, the change of momentum of an object; the integral of a force with respect to time * Impulse noise (disambiguation) * Specific impulse, the change in momentum per uni ...
from the ground and adapts dynamically to changes in the ground's surface. Transtibial amputees lose the muscle activation pathways necessary for the physical ability to generate work about the ankle joint, as well as the
somatosensory In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It i ...
and
proprioceptive Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...
pathways of the lower leg.


Transfemoral

Unlike transtibial amputations, transfemoral amputations occur between the hip and the knee joints, along the length the
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...
. Therefore, the patient's residual limb is controlled solely by the hip joint. Implementing a prosthetic leg requires the user to mechanically control the behaviors of the prosthetic knee and ankle joints through gross adjustments of the hip, rather than the finer and more precise movements of the missing joints. Simple tasks such as walking on level ground, sit-to-stand transfers, and climbing stairs require complex alternative muscle activation patterns because the amputee cannot generate a moment about the prosthetic knee. This poses a problem when knee flexion is required, especially during the transition from the stance phase to the swing phase. Transfemoral amputees, on average, have more variability in stride length and walking speed, more asymmetry in temporal measures between limbs, and have an overall slower walking speed than transtibial amputees.


Compensatory Behaviors

Unimpaired
human gait A gait is a pattern of limb movements made during locomotion. Human gaits are the various ways in which humans can move, either naturally or as a result of specialized training. Human gait is defined as bipedal, biphasic forward propulsion of ...
is characterized by its symmetry about the
sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and div ...
. In impaired individuals such as amputees, gait abnormalities are visible to the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
. Amputees often employ strategies known as protective gait behaviors to compensate for their impaired balance and control. These behaviors are most commonly categorized into increased general odyand orsomovement and increased variability of strides. The variability can manifest as a combination of differences in the length and
width Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Intern ...
of the strides in comparison to the intact limb.


Bodily involvement

Before microprocessor-controlled prosthetic joints, the major findings were that the most noticeable movements could be seen in the
shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...
s, not the hips, and all subjects had uneven
pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The p ...
rotations, with more rotation on the prosthetic side. On average, the pelvic
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...
is highest in transfemoral amputees in
static Static may refer to: Places *Static Nunatak, a nunatak in Antarctica United States * Static, Kentucky and Tennessee *Static Peak, a mountain in Wyoming **Static Peak Divide, a mountain pass near the peak Science and technology Physics *Static el ...
non-walking studies. The integration of motion capture technology has been beneficial to more recent dynamic walking studies. Rotation of the pelvis is especially essential in transfemoral amputees for lifting the prosthesis and providing foot clearance. This behavior is colloquially known as 'hip-hiking'. As such, rotation and
obliquity In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbi ...
of the pelvis have been determined to be instrumental in producing more symmetric gait, even when the rotation itself is asymmetric between intact and impaired limbs.
Torso The torso or trunk is an anatomical term for the central part, or the core, of the body of many animals (including humans), from which the head, neck, limbs, tail and other appendages extend. The tetrapod torso — including that of a huma ...
or trunk motion is also linked to amputee gait, specifically increasing upper-body ranges of motion with decreasing walking velocity. Another study observed a coupling of torso and pelvis rotations. They noted that the 'hip-hiking' behavior made the rotations of the upper and lower body 'in' or 'out' of phase depending on the severity of the walking impairment, with the amputee subjects having a near-fully coupled bodily rotation. Torso involvement is not as readily apparent in able-bodied individuals. It is hypothesized that this gait deviation could lead to
lower back pain Low back pain (LBP) or lumbago is a common disorder involving the muscles, nerves, and bones of the back, in between the lower edge of the ribs and the lower fold of the buttocks. Pain can vary from a dull constant ache to a sudden sharp feel ...
.


Stride length

Stride length refers to the
distance Distance is a numerical or occasionally qualitative measurement of how far apart objects or points are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two counties over"). ...
in the direction of forward motion that is between heel strikes of successive footfalls or steps. During the gait cycle, amputees have characteristically shorter time spent in the stance phase on the prosthetic limb compared to the intact limb. 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. However, the shorter stance time may help the amputee compensate for the greater
margin of error The margin of error is a statistic expressing the amount of random sampling error in the results of a survey. The larger the margin of error, the less confidence one should have that a poll result would reflect the result of a census of the e ...
of the prosthetic limb, and several sources suggest the shorter strides are beneficial towards maintaining a straight walking path.


Step width

Step
width Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Intern ...
refers to the distance between the feet. A connection exists between step width and gait
instability In numerous fields of study, the component of instability within a system is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be mar ...
, though it is difficult to discern the difference between correlation and causation. 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. A similar widening of step width and concordant slowing of gait speed has been observed between populations of elderly, obese, pregnant women, and amputees. Physically widening the distance between feet in a standing posture increases the structural stability of the body by widening the base of support or foundation. External
lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...
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. A similar experimental setup was used on transtibial and transfemoral amputees: transtibial amputees had reduced energy cost and step width, but transfemoral subjects had increased cost and a more marginal reduction in step width, possibly due to the harness interfering with necessary pelvic movements.


Gait Deviations

The compensatory behaviors listed above describe the observable differences in ambulation between amputees and able-bodied individuals. The following gait deviation measurements quantify differences using
gait analysis Gait analysis is the systematic study of animal locomotion, more specifically the study of human motion, using the eye and the brain of observers, augmented by instrumentation for measuring body movements, body mechanics, and the activity of the ...
and other tests that typically necessitate specialized
instrumentation Instrumentation a collective term for measuring instruments that are used for indicating, measuring and recording physical quantities. The term has its origins in the art and science of scientific instrument-making. Instrumentation can refer to ...
or clinical environments.


Metabolic cost

Energy expenditure is commonly used as a measure of gait quality and efficiency. Human metabolic rates are usually recorded via measuring the maximal oxygen consumption ( VO2 max) during controlled incremental exercise under observation.
Treadmill A treadmill is a device generally used for walking, running, or climbing while staying in the same place. Treadmills were introduced before the development of powered machines to harness the power of animals or humans to do work, often a type o ...
s are used for
gait analysis Gait analysis is the systematic study of animal locomotion, more specifically the study of human motion, using the eye and the brain of observers, augmented by instrumentation for measuring body movements, body mechanics, and the activity of the ...
and standard walking tests. Able-bodied and athletic individuals on average have smaller metabolic costs than impaired individuals performing identical tasks. The values from a theoretical model and experimental analyses are listed below: *Transtibial amputees experience 9-33% increase *Transfemoral amputees experience 66-100% increase Another source compiled a list of average metabolic cost increases categorized by amputation location and by cause of amputation: *Transtibial (traumatic) amputees experience 25% increase *Transtibial (vascular) amputees experience 40% increase *Transfemoral (traumatic) amputees experience 68% increase *Transfemoral (vascular) amputees experience 100% increase


Comfortable walking speed

Although heavily related to the metabolic cost and overall
optimization Mathematical optimization (alternatively spelled ''optimisation'') or mathematical programming is the selection of a best element, with regard to some criterion, from some set of available alternatives. It is generally divided into two subfi ...
of the gait, the self-selected walking speed of amputees is significantly lower than able-bodied individuals. Average values for comfortable walking speeds drastically vary between subjects because it is a personal measure. The speeds can be lower than 0.60 m/s or as high as 1.35 m/s. In comparison, self-selected elderly walking speeds are commonly below 1.25 m/s, and the reported comfortable walking speed of the able-bodied subjects is approximately 1.50 m/s.


Mechanical work

To compensate for the amputated segment of the limb, the residual joints are used for behaviors such as foot placement and general balance on the prosthetic limb. This increases the
mechanical work In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, for a constant force aligned with the direction of motion, the work equals the product of the force stre ...
generated by the residual joints on the amputated side. The intact limb is typically more adept at maintaining
balance Balance or balancing may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Balance as in equality or equilibrium Arts and entertainment Film * ''Balance'' (1983 film), a Bulgaria ...
and is therefore relied upon more drastically, such as the behavior in a limping gait. Accordingly, the joint
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
s and general
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
of the intact side must increase as compared to an able-bodied individual. Even with the advanced computerized knee joint of
Otto Bock Ottobock SE & Co. KGaA, formerly Otto Bock, is a company based in Duderstadt Germany, that operates in the field of orthopedic technology. It is considered the world market leader in the field of prosthetics and one of the leading suppliers i ...
's C-Leg transfemoral prosthesis, the subjects experienced increased
braking A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Backgroun ...
and propulsive impulses than that of the standard double
inverted pendulum An inverted pendulum is a pendulum that has its center of mass above its pivot point. It is unstable and without additional help will fall over. It can be suspended stably in this inverted position by using a control system to monitor the angle ...
model of normal
human gait A gait is a pattern of limb movements made during locomotion. Human gaits are the various ways in which humans can move, either naturally or as a result of specialized training. Human gait is defined as bipedal, biphasic forward propulsion of ...
.


Other deviations

*Lateral sway *Step variability *Internal rotation Similar to decreased stride length and increased step width, lateral sway is generally postulated to be an indication of gait instability. The gait naturally widens to account for a greater instability or external perturbations to balance. Step variability is also related to balance and lateral stability. 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. This has been a common discussion in analysis of elderly gait as well. Internal rotation is a culmination of measures of the hip and knee joints as well as the pelvic rotation and obliquity during gait. Typically, this has to be measured through motion capture and
ground reaction force In physics, and in particular in biomechanics, the ground reaction force (GRF) is the force exerted by the ground on a body in contact with it. For example, a person standing motionless on the ground exerts a contact force on it (equal to the perso ...
. Individual parameters can be calculated with inverse kinematics.


Influential Factors

Across the field of research, many studies are focused on assessing how different factors can influence the overall gait of amputee subjects. The following list shows examples of factors that are believed to influence the gait characteristics of lower-limb amputees: *Weight of prosthesis *Distribution of weight *Alignment of components *Overall fit of prosthesis


Prosthetic weight and distribution

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. Correspondingly, transfemoral prostheses are on average only about one third of the weight of the limb they are replacing. However, the effect of added mass appears to be less significant for amputees. Small increases in mass (4-oz and 8-oz) of a prosthetic foot had no significant effect and, similarly, adding 0.68-kg and 1.34-kg masses to the center of the shank of transfemoral prostheses did not alter metabolic cost at any of the tested walking speeds (0.6, 1.0, and 1.5 m/s). In another study, muscular efforts were significantly increased with added mass, yet there was no significant impact on walking speeds and over half of the subjects preferred a prosthetic that was loaded to match 75% weight of the sound leg. In fact, it has been reported in several articles that test subjects actually prefer heavier prostheses, even when the load is completely superficial.


Alignment and fit

Initial alignment of a prosthetic leg is conducted by a
prosthetist A Prosthetist and Orthotist, as defined by The World Health Organization, is a healthcare professional with overall responsibly of Prosthetics & Orthotics treatment, who can supervise and mentor the practice of other personnel. They are clinicians ...
or
physician A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...
to ensure proper use of the limb. 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. Misalignment of joints could result in postures similar to those seen in congenital malformations such as
bow-leggedness Genu varum (also called bow-leggedness, bandiness, bandy-leg, and tibia vara) is a varus deformity marked by (outward) bowing at the knee, which means that the lower leg is angled inward ( medially) in relation to the thigh's axis, giving the ...
, knock-knee,
pigeon toe Columbidae () is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with short necks and short slender bills that in some species feature fleshy ceres. They primaril ...
, and
club foot Clubfoot is a birth defect where one or both feet are rotated inward and downward. Congenital clubfoot is the most common congenital malformation of the foot with an incidence of 1 per 1000 births. In approximately 50% of cases, clubfoot aff ...
. Misaligned sockets can simulate excessive hip and knee flexion and extension. As individuals get more experience on the limb, it is expected that they will optimize the alignment for their own preference. Transtibial In transtibial amputees, the adjustment of the foot is highly influential to gait changes. Proper alignment of the prosthetic foot about the ankle joint causes metabolic cost and gait symmetry at the anatomical hip and knee joints to improve, with hip flexion-extension motion being the most sensitive to alignment. Excessive rotational misalignment of the foot is compensated by internal rotation of the residual hip joint. Proper alignment of the transtibial prosthesis socket significantly reduced the loading on the intact limb during an 11-meter walk test, indicating that a misaligned limb could have drastic long-term consequences on the sound side of the body. Transfemoral Systematic changes to transfemoral prosthetic alignment altered the flexion-extension behavior of the hip, changing fore-aft ground reaction forces and the antero-posterior moments at the knee and ankle joints. The sole reliance on the hip joint to control the entire prosthetic limb makes fine-tuning foot placement difficult. Lowering the knee joint height was found to effectively increase the hip joint's
lever arm In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of ...
, thereby increasing precision control of the hip joint to improve gait symmetry and increase running velocity by 26% on average.


See also

* Gait training *
Rehabilitation engineering Rehabilitation engineering is the systematic application of engineering sciences to design, develop, adapt, test, evaluate, apply, and distribute technological solutions to problems confronted by individuals with disabilities. These individuals ...
*
Biomedical engineering Biomedical engineering (BME) or medical engineering is the application of engineering principles and design concepts to medicine and biology for healthcare purposes (e.g., diagnostic or therapeutic). BME is also traditionally logical sciences ...


References


External links

*Limb Loss Task Force, Amputee Coalition
Roadmap for Preventing Limb Loss in America.pdf
Knoxville, TN; 2012 *Advanced Prosthetics Center
Prosthetic Rehabilitation Manual: Transtibial (Below Knee) Amputation
Omaha, NE; 2013

{{Pathology Terrestrial locomotion Walking