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Lower Limb Amputation (LLA)
Lower extremity muscles generate propulsion, support and balance of the body during walking 7. However in lower limb amputees, the number of lower limb muscles required for locomotion are missing. Also, the amputated limb is affected by the loss of sensorimotor function leading to significant neural reorganization within the central nervous system 1,11. The level of amputation in the lower limb is characterized by the specific muscles and bones removed. Lower limb amputation is clinically categorized into two groups: above-the-knee amputation and below-the-knee amputation. Above-the-knee amputation involves the removal of the thigh tissue and femoral bone6. Below-the-knee amputation or transtibial amputation involves the removal of the foot, ankle joint, distal tibia, fibula, and corresponding soft tissue structures5. Trauma, infection, tumors and decreased vascular function of the lower limb are all possible causes for these type of amputations.

Gait Symmetry
Human gait has been thoroughly investigated by many scientific researchers and clinicians over the years. The gait cycle is initiated when one-foot contacts the ground and ends when the same foot contacts the ground again3. The gait cycle is divided into two phases: stance and swing phases. During the stance phase or the initial contact phase, the entire foot is on the ground4. During the swing phase, the foot is lifted from the floor (toe-off) and swung in the air for limb advancement4.

When walking, asymmetrical gait patterns are often exhibited in unilateral transfemoral and transtibial amputees. Lower limb amputees tend to add more weight to their intact limb than their prosthetic limb during natural cadence walking resulting in an asymmetrical gait pattern8. Specifically, the prosthetic limb characteristically has a smaller push-off force, longer step length, longer swing time and a shorter stance time when compared with the intact limb9. Also during gait, increased asymmetric trunk motion following lower limb amputation has previously been recorded to inflict higher net mechanical demands on the lower back2. The mechanical demands on the body have been reported to cause lower back pain and aggravation at the knee and hip joints.

Adaptation Strategies For Walking
For amputees, the amputated limb is affected by the loss of sensorimotor function while the muscles and joint(s) are removed1. As lower limb amputees begin to walk, the muscle activity at the hip and ankle as well as adjustments to the posture are needed to initiate gait1. In clinical rehabilitation settings, one goal is to help lower limb amputees develop compensatory strategies in both the intact leg and the remaining stump for over-ground locomotion10.

In previous studies over the years, researchers have analyzed lower limb amputees' gait patterns and compensatory strategies for walking. In 2020, Harandi et al. analyzed lower limb joint kinematics including the muscle and prosthesis contributions to the body center of mass (COM) acceleration in transfemoral amputees. Their findings suggested that the intact limb hip musculature plays a major role in compensating for reduced or absent muscles and joint function in the residual limb during over ground walking7. In a systematic review, Prinsen et. al. describes adaptation strategies in terms of joint power in both the amputated and intact leg of transtibial and transfemoral amputees10. Results demonstrated similar adaptations at the hip to compensate for the loss of plantar flexion power in both transtibial and transfemoral amputees10. However at the knee level, adaptations including decreased joint work during stance phase in transtibial amputees differed from transfemoral amputees. The intact leg of transtibial patients exhibits compensatory strategies for the reduced involvement of the amputated leg by increasing the performed work at the knee10.

Balance and stability of the trunk to decrease the mechanical demands of the lower back of lower limb amputees when walking has also been investigated. In 2008, results from the study conducted by Vrieling et. al. showed that increased limb-loading on the non-affected limb supported the stability of the trunk1. Also, the lower limb amputees used their prosthetic limb to lead gait initiation suggesting another adjustment strategy.

Future Directions
Further research is needed to investigate additional adaptative strategies in lower limb amputees. With more information reviewed from the literature regarding gait symmetry and adaptive strategies, scientist and clinicians can further develop rehabilitation training programs to help lower limb amputees develop gait patterns that will require less net mechanical demand and energy expenditure during walking.