Trunk-pelvis motion, joint loads, and muscle forces during walking with a transtibial amputation.

People with unilateral, transtibial amputation (TTA) have an increased prevalence of chronic low back pain (LBP) relative to able-bodied people. However, a definitive cause of increased LBP susceptibility has not been determined. The purpose of this work was to compare dynamic trunk-pelvis biomechanics between people with (n=6) and without (n=6) unilateral TTA during walking using a computational modeling approach. A generic, muscle-actuated whole body model was scaled to each participant, and experimental walking data were used in a static optimization framework to calculate trunk-pelvis motion, L4L5 joint contact forces, and muscle forces within the trunk-pelvis region. Results included several significant between-group differences in trunk-pelvis biomechanics during different phases of the gait cycle. Most significant was greater lateral bending toward the residual side during residual single-limb stance (p<0.01), concurrent with an elevated L4L5 joint contact force (p=0.02) and greater muscle force from the intact-side obliques (p<0.01) in people with TTA relative to able-bodied people. During both double-limb support phases, people with TTA also had a greater range of axial trunk rotation away from the leading limb, concurrent with greater ranges of muscle forces in the erector spinae and obliques. In addition, a greater range of force (p=0.03) in residual-side psoas was found during early residual limb swing in people with TTA. Repeated exposure to atypical motion and joint/muscle loading in people with TTA may contribute to the development of secondary musculoskeletal disorders, including chronic, mechanical LBP.

Yoder AJ ，Petrella AJ ，Silverman AK 《-》

Persons with unilateral transfemoral amputation experience larger spinal loads during level-ground walking compared to able-bodied individuals.

Persons with lower limb amputation walk with increased and asymmetric trunk motion; a characteristic that is likely to impose distinct demands on trunk muscles to maintain equilibrium and stability of the spine. However, trunk muscle responses to such changes in net mechanical demands, and the resultant effects on spinal loads, have yet to be determined in this population. Building on a prior study, trunk and pelvic kinematics collected during level-ground walking from 40 males (20 with unilateral transfemoral amputation and 20 matched controls) were used as inputs to a kinematics-driven, nonlinear finite element model of the lower back to estimate forces in 10 global (attached to thorax) and 46 local (attached to lumbar vertebrae) trunk muscles, as well as compression, lateral, and antero-posterior shear forces at all spinal levels. Trunk muscle force and spinal load maxima corresponded with heel strike and toe off events, and among persons with amputation, were respectively 10-40% and 17-95% larger during intact vs. prosthetic stance, as well as 6-80% and 26-60% larger during intact stance relative to controls. During gait, larger spinal loads with transfemoral amputation appear to be the result of a complex pattern of trunk muscle recruitment, particularly involving co-activation of antagonistic muscles during intact limb stance; a period when these individuals are confident and likely to use the trunk to assist with forward progression. Given the repetitive nature of walking, repeated exposure to such elevated loading likely increases the risk for low back pain in this population.

Shojaei I ，Hendershot BD ，Wolf EJ ，Bazrgari B ... -  《-》

Three-dimensional knee joint contact forces during walking in unilateral transtibial amputees.

Individuals with unilateral transtibial amputations have greater prevalence of osteoarthritis in the intact knee joint relative to the residual leg and non-amputees, but the cause of this greater prevalence is unclear. The purpose of this study was to compare knee joint contact forces and the muscles contributing to these forces between amputees and non-amputees during walking using forward dynamics simulations. We predicted that the intact knee contact forces would be higher than those of the residual leg and non-amputees. In the axial and mediolateral directions, the intact and non-amputee legs had greater peak tibio-femoral contact forces and impulses relative to the residual leg. The peak axial contact force was greater in the intact leg relative to the non-amputee leg, but the stance phase impulse was greater in the non-amputee leg. The vasti and hamstrings muscles in early stance and gastrocnemius in late stance were the largest contributors to the joint contact forces in the non-amputee and intact legs. Through dynamic coupling, the soleus and gluteus medius also had large contributions, even though they do not span the knee joint. In the residual leg, the prosthesis had large contributions to the joint forces, similar to the soleus in the intact and non-amputee legs. These results identify the muscles that contribute to knee joint contact forces during transtibial amputee walking and suggest that the peak knee contact forces may be more important than the knee contact impulses in explaining the high prevalence of intact leg osteoarthritis.

Silverman AK ，Neptune RR 《-》

Lumbar loads and trunk kinematics in people with a transtibial amputation during sit-to-stand.

People with a transtibial amputation have numerous secondary health conditions, including an increased prevalence of low back pain. This increased prevalence may be partially explained by altered low back biomechanics during movement. The purpose of this study was to compare trunk kinematics and L4-L5 lumbar loads in people with and without a transtibial amputation during sit-to-stand. Motion capture, ground reaction force and electromyographic data were collected from eight people with a unilateral transtibial amputation and eight people without an amputation during five self-paced sit-to-stand motions. A musculoskeletal model of the torso, lumbar spine, pelvis, lower limbs, and 294 muscles was used in a static optimization framework to quantify L4-L5 loads, low back muscle forces, and trunk kinematics. Participants with an amputation had greater peak and average L4-L5 loading in compression compared to control participants, with peak loading occurring shortly after liftoff from the chair. At the instant of peak loading, participants with an amputation had significantly greater segmental trunk lateral bending and trunk-pelvis axial rotation toward the intact side, and significantly greater segmental trunk axial rotation toward the prosthetic side compared to control participants. Participants with an amputation also had greater peak frontal plane and transverse plane segmental trunk angular velocity. The postural differences observed in people with a transtibial amputation were consistent with their ground reaction force asymmetry. The cumulative effects of the altered movement strategy used by people with an amputation may result in an increased risk for low back pain development over time.

Actis JA ，Nolasco LA ，Gates DH ，Silverman AK ... -  《-》

Three-dimensional joint reaction forces and moments at the low back during over-ground walking in persons with unilateral lower-extremity amputation.

Abnormal mechanics of locomotion following lower-extremity amputation are associated with increases in trunk motion, which in turn may alter loads at the low back due to changes in inertial and gravitational demands on the spine and surrounding trunk musculature. Over-ground gait data were retrospectively compiled from two groups walking at similar self-selected speeds (~1.35m/s): 40 males with unilateral lower-extremity amputation (20 transtibial, 20 transfemoral) and 20 able-bodied male controls. Three-dimensional joint reaction forces and moments at the low back (L5/S1 spinal level) were calculated using top-down and bottom-up approaches. Peak values and the timings of these were determined and compared between and within (bilaterally) groups, and secondarily between approaches. Peak laterally-directed joint reaction forces and lateral bend moments increased with increasing level of amputation, and were respectively 83% and 41% larger in prosthetic vs. intact stance among persons with transfemoral amputation. Peak anteriorly-directed reaction forces and extension moments were 31% and 55% larger, respectively, among persons with transtibial amputation compared to controls. Peak vertical reaction forces and axial twist moments were similar between and within groups. Peak joint reaction forces and moments were larger (3-14%), and the respective timing of these sooner (11-62ms), from the bottom-up vs. top-down approach. Increased and asymmetric peak reaction forces and moments at the low back among persons with unilateral lower-extremity amputation, particularly in the frontal plane, suggest potential mechanistic pathways through which repeated exposure to altered trunk motion and spinal loading may contribute to low-back injury risk among persons with lower-extremity amputation.

Hendershot BD ，Wolf EJ 《-》