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 Patients with musculoskeletal pain, weakness or limited range of motion often present conditions such as Trendelenburg's sign, limping, myopathic gait and antalgic gait. Patients who have peripheral neuropathy also experience numbness and tingling in their hands and feet. This can cause ambulation impairment, such as trouble climbing stairs or maintaining balance. Gait abnormality is also common in persons with nervous system problems such as cauda equina syndrome, multiple sclerosis, Parkinson's disease (with characteristic Parkinsonian gait), Alzheimer's disease, vitamin B12 deficiency, myasthenia gravis, normal pressure hydrocephalus, and Charcot–Marie–Tooth disease. Research has shown that neurological gait abnormalities are associated with an increased risk of falls in older adults. Orthopedic corrective treatments may also manifest into gait abnormality, such as lower extremity amputation, healed fractures, and arthroplasty (joint replacement). Difficulty in ambulation that results from chemotherapy is generally temporary in nature, though recovery times of six months to a year are common. Likewise, difficulty in walking due to arthritis or joint pains (antalgic gait) sometimes resolves spontaneously once the pain is gone. Hemiplegic persons have circumduction gait, where the affected limb moves through an arc away from the body, and those with cerebral palsy often have scissoring gait.
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 (54%) and trauma (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 to combat vascular disease. An increasingly studied trend in amputation rates is the gender disparity 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, 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 directly attached to the calf muscle, but more than that, it absorbs the impulse 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 and proprioceptive pathways of the lower leg.
Transfemoral Unlike transtibial amputations, transfemoral amputations occur between the hip and the knee joints, along the length the femur. 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 is characterized by its symmetry about the sagittal plane. In impaired individuals such as amputees, gait abnormalities are visible to the naked eye. 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 [body] and [torso] movement and increased variability of strides. The variability can manifest as a combination of differences in the length and width of the strides in comparison to the intact limb.
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